X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.123] verified) by logan.com (CommuniGate Pro SMTP 5.3.9) with ESMTP id 4509744 for flyrotary@lancaironline.net; Sun, 17 Oct 2010 15:45:49 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.123; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.1 cv=VmbICTAd0FXyA7HzV3SMmHTv6TrHSBm6jOcF5xZxrZ0= c=1 sm=0 a=lXzHJM8WJe0A:10 a=rPkcCx1H5rrOSfN0dPC7kw==:17 a=3oc9M9_CAAAA:8 a=Ia-xEzejAAAA:8 a=HZJGGiqLAAAA:8 a=7g1VtSJxAAAA:8 a=AgMqSna9lJzhELv6YZEA:9 a=FZ3LMlWjwbNOMCRWVhIA:7 a=_Woef5a40XqNmnxLtkqVvyQz1zYA:4 a=wPNLvfGTeEIA:10 a=Qa1je4BO31QA:10 a=U8Ie8EnqySEA:10 a=EzXvWhQp4_cA:10 a=HeoGohOdMD0A:10 a=OBlFpxp4WdtTNRAq:21 a=pmZDTScKfBngd70E:21 a=16nWFlIE5eWEkhZrDCsA:9 a=pbkvWdGILJXGYGb2OyMA:7 a=CNx4Y8LhIpC5uagEaRRbinzOxvMA:4 a=EuYzuBWi9C_J2d4D:21 a=GOZqx4_-akZ88HT_:21 a=rPkcCx1H5rrOSfN0dPC7kw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.167.5 Received: from [174.110.167.5] ([174.110.167.5:51103] helo=EdPC) by cdptpa-oedge03.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 37/C0-14739-8425BBC4; Sun, 17 Oct 2010 19:45:14 +0000 Message-ID: From: "Ed Anderson" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Re: The Case For Turbocharging Date: Sun, 17 Oct 2010 15:44:51 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0068_01CB6E12.3C8C1070" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_0068_01CB6E12.3C8C1070 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ah, I ditched MS office for the free "Open Office" - I guess that is why = I had no problem opening it. Ed From: Kelly Troyer=20 Sent: Sunday, October 17, 2010 1:59 PM To: Rotary motors in aircraft=20 Subject: [FlyRotary] Re: The Case For Turbocharging Sorry guys..........Did not think about my "Open Office" files not = opening for everyone !! Hope this is not too big for the forum !!................... Turbocharging Automotive Engines for Aircraft Applications April 27/98=20 With automotive engines finding increasing use powering homebuilt = aircraft, we find many people entertaining the idea of turbocharging to = boost the power to weight ratios and altitude performance of these = engines. We will examine the various facts and myths regarding = turbocharging as applied to light aircraft use. History Turbos in aircraft were first successfully applied in mass numbers = during WWII. The P-38 and P-47 were the best known turbocharged fighter = types and both had excellent high altitude performance. In general aviation use as applied to air cooled opposed engines, = turbocharging has a less revered reputation. Much of this has to do with = the air cooled engine itself and the fact that most of these engines = were never designed to be boosted to begin with. They may have been = modified a bit for the turbo but with power to weight ratios being a = major concern, many are structurally and thermally not up to the task. = Other concerns such as turbo cooling and lubrication by inferior = aviation type oils also led to premature turbo failures. What is a Turbocharger? A turbo consists of a centrifugal compressor connected to a turbine = wheel which is spun at high rpm by the energy of the engine exhaust = gasses. It is a very simple device, but the high temperatures and = stresses acting on it require exotic materials in the turbine section = which are somewhat expensive. A turbo will cost in the neighborhood of = $800 to $1300 with the wastegate assembly. Turbine wheels come in many shapes and sizes. Constructed of high = temperature alloys such as Inconel or Hastaloy. This is the hot end.=20 Turbine housings are cast from a high nickel/iron alloy.=20 The compressor pressurizes the intake manifold to achieve higher hp or = maintains sea level pressure as the aircraft climbs. This permits higher = climb rates at altitude and increased cruise speeds. Compressor wheels are cast from aluminum alloy and come in many sizes or = trims. This is the cold end.=20 Compressor housing is cast from aluminum alloy. Shape is designed to = slow the air, thus compressing it.=20 Cast iron center section or bearing housing contains floating sleeve = bearings or more recently ceramic ball bearings. High pressure oil from = engine feeds the bearing and is drained out the bottom of the housing = back into the engine. Some housings are water cooled to prevent coking = of oil deposits leading to bearing failure.=20 Elegant Simplicity Turbocharging is the most efficient method of boosting hp with the least = weight penalty known. A typical turbo installation on a light aircraft = including intercooler and exhaust is around 35-50 pounds. Such an = installation is capable of tripling hp at sea level or adding 50% to the = naturally aspirated output up to 15,000 feet. Sea level manifold = pressures can be maintained to 25,000 feet in some cases. An aircraft = capable of 200 knots at sea level would true out at nearly 300 knots = with a good turbo system at high altitude. Spinning the compressor with an exhaust driven turbine is a much better = way than by the mechanical means as in a supercharger. It is lighter, = more reliable and more efficient and has the added advantage of having = more drive energy available as the aircraft climbs due to lower = backpresure, which is exactly what is needed.=20 Fuel Flow vs. Power There is a common misconception that turbocharging increases fuel flows = because of the backpressure of the turbine. This may be true in air = cooled engines using a poorly matched turbo without intercooling because = the air cooled engine cannot maintain temperature stability without = adding fuel for cooling purposes. Reduced fuel flows at altitude in = naturally aspirated and turbine engines is not due to some magic = process, it is due to the fact that as altitude is increased, less power = is produced thus less fuel is required. Many people also don't seem to = realize that fuel flow is related to hp developed and that a turbo = engine will develop more power at altitude than a naturally aspirated = engine, obviously requiring more fuel and delivering higher speeds at = the same time.=20 Testing done back in the '40s and '50s on turbo engines actually confirm = that fuel flows were LOWER at the same BMEP with turbocharging than in a = naturally aspirated engine developing the same power. This suggests that = when properly applied, the turbo actually recovers more energy from the = exhaust to be applied to reduce pumping losses during the compression = stroke than is consumed during the exhaust stroke working against higher = backpressure. With approximately 50% of the energy in the fuel going out = the exhaust in the form of heat and pressure, turbocharging can recover = some of this waste and put it to good use. It was shown that turbos could achieve fuel flows 3-6% lower and = turbocompounding could achieve up to 15% lower fuel flows. Cylinder head = and piston cooling were shown to be the primary limitations to achieving = lower BMSFC figures. We can conclude from this that as applied to liquid = cooled engines with their superior thermal rejection rates, = turbocharging really has few disadvantages compared to the many = advantages it offers. It should be no surprise that the latest certified liquid cooled engines = from Toyota and Orenda are turbocharged. People also should remember the = awesome turbocompound radials of the '50s. These engines offered = extremely low BSFC and high power. It seems foolish not to turbocharge = most good aircraft engines used at any kind of altitude as you are = throwing away performance without it. Turbocharged Air Cooled Engines As mentioned earlier, turbocharged , conventional opposed air cooled = engines have a less than stellar track record and many lay people blame = the turbo. In fact, the fault lies with the engines it is applied to. = The average Lycoming or Continental has a lot of things not going for = them. Many of these engines suffer premature failure of crankcases, = cylinders, heads and valves in their turbocharged iterations. Let's = examine why. Probably the leading cause of case and barrel cracking is the lack of = rigidity these engines have in the cylinder/ case area. For ease of = barrel replacement I assume, the designers of these engines chose to = bolt the cylinders individually to the crankcase at the bottom of the = cylinder using a flange. This arrangement creates a very willowy = structure and with each firing impulse, combined with the sheer mass of = the huge reciprocating parts used in these engines, a definite high = amplitude, cyclic stress is put on these parts eventually leading to = cracking. The increased gas pressures associated with turbocharging = compound this problem. This design problem is actually the cause of a = major portion of the high vibration levels associated with conventional = aircraft engines. The flange method puts the barrel under a tension load with every firing = impulse too which is just plain stupid given the thickness of the = cylinders. Modern automotive racing practice would use through studs to = retain the barrels, thus putting the barrels under compression. Cylinder head cracking and exhaust valve burning and sticking are = primarily due to insufficient cooling in these areas which is = exaggerated by the extra heat introduced by turbocharging. Air cooling = is relatively inefficient at sinking heat off around the exhaust port = and valve seat area. This problem is compounded by the use of very low = compression ratios resulting in higher EGTs thus even higher heat flux = in the critical exhaust port area. Typical air cooled aircraft engines = run cylinder head temperatures in excess of 400 degrees on a regular = basis. With aluminum alloys losing roughly 50% of their strength at this = temperature it is easy to see why cracking is all too common here. The = high EGT's are also detrimental to the life of the turbo's turbine = section. Valve problems are due to the same cause, temperatures being too high = from inefficient heat transfer. Many factory turbo aircraft are forced = to either open cowl flaps or richen the mixture at high altitude to keep = temperatures within limits. With power being maintained at altitude and = air density falling off, there is often insufficient mass flow available = for cooling. This is rarely a problem on naturally aspirated engines as = power and cooling requirements are dropping off with increasing = altitude. Not a lot of design went into the induction system on many of these = engines hence fuel distribution is usually not the greatest. This = contributes to engine roughness and problems with leaning. Leaning is = limited by the mixture in the hottest cylinder with the others running = richer than desired. The oils used in aircraft engines are relatively crude by modern = synthetic automotive standards and consequently not the best for the = turbocharger. The use of these oils appears to be a result of the very = loose tolerances required in an air cooled engines because of the high = operating temperatures which also leads to the high oil consumption = characteristic of these engines. Finally, many certified installations never used intercooling which is = simply amazing. The advantages and necessity of it was clearly = understood in WWII. High charge temperatures at altitude required even = more fuel for cooling and yet more cowl flap opening to control head = temperatures. Turbocharged Liquid Cooled Engines Liquid cooled engines are a natural for turbocharging because of their = higher heat rejection capabilities. Water cooling also enables the turbo = center section to be water cooled which alleviates a primary cause of = turbo failure- coked bearing holes from high heat and fried oil. Water = cooled engines can use modern synthetic oils because of their tighter = clearances. Synthetic oils with their much higher temperature = capabilities are more suitable to lubricate the turbo than old = fashioned, aircraft oils derived from natural base stocks. The popular = Mobil 1 synthetic oil, common in the racing world, can withstand = temperatures of 350 degrees continuously and even 450 degrees = intermittently without significant degradation. With proper lubrication = and cooling, turbochargers will easily last the life of the engine. If we compare the Popular Subaru EJ22 and EJ25 horizontally opposed 4 = cylinder engines to their certified counterparts we find many advantages = especially in turbocharged trim. The Subaru has 5 main bearings instead = of 3 which means that the crank is better supported. The Subaru has a = higher compression ratio for higher thermal efficency. Its overhead cam, = 4 valve per cylinder arrangement provides lower friction and higher = volumetric efficiency than a 2 valve pushrod setup. Finally, the = integrated block and head design is many times stiffer and stronger than = the aircraft engine. As long as the radiator and ducting are properly designed, cooling = problems are not a concern on the liquid cooled engine. The induction system on the Subaru has proper runner lengths to boost = torque, relatively equal airflow to each cylinder and can easily use a = modern digital, electronic fuel injection system to precisely meter = fuel. All of these things aid in producing more power with less fuel. Power vs. Weight vs. Manifold Pressure vs. Life vs. Cost The EJ engines when turbocharged and equipped with a radiator, PSRU and = composite propeller are slightly heavier than the popular Lycoming and = Continental 360 cubic inch engines which are rated at 180- 200 hp for = takeoff and around 135- 150 hp for maximum cruise. The Subaru can easily = attain 200- 250 hp at 50 inches for takeoff and reliably deliver 140 to = 170hp at 35-38 inches for cruise. The 3.3L EG33 six cylinder is capable = of 300+ hp for takeoff and 200-250 hp in cruise making it a viable = alternative to the O-540 engines. These power levels can be maintained = during climb and cruise at altitude thanks to turbocharging and liquid = cooling. Projected TBO is in the 1000-1200 hour range at this time. Most people = flying the EJ engines are confident that no interim work will be = required during this period such as cylinder barrel replacement and = valve grinding operations which are quite common on aircraft engines = before reaching their stated TBO. In other words, if you change the oil = and check the water, that is about all that is required during those = 1000 hours. There are no magneto or even valve adjustments to worry = about. Expect spark plug replacement every 100- 250 hours or so at $3 = each. Overhaul costs will range from about $500 to $1500 for parts and = machine work depending on condition. Labor would be in the $500 to $1200 = range. We are all familiar with the costs to overhaul a certified = aircraft engine.=20 Matching a Turbocharger As applied to the popular Subaru EJ22 and EJ25 engines for general = purpose use below 15,000 feet we can narrow the choice of turbos down a = bit. Garrett T3 turbos are recommended as they are relatively cheap, = reliable and easy to fix with a vast array of combinations available. = The compressor side may be either a -50, -60 or super 60 wheel with a = stage 3 turbine wheel in a .82 A/R housing, depending on the exact use = and hp. These may be ordered with an integral wastegate and a water = cooled bearing housing which are both highly recommended. These turbos = are quite capable of producing enough boost to extract 250 hp at sea = level and still have 175+ hp available at 15,000 feet. The integral wastegates are generally more reliable than an external = type especially on an aircraft application in which it is almost = constantly bypassing exhaust. The wastegate is simply a valve used to = bypass exhaust gasses around the turbine to control turbine and = compressor speed and thus boost pressure. It is usually actuated = automatically by a diaphragm sensing manifold pressure. Many people have tried to use the OE turbo on auto aircraft conversions, = often with limited success. The turbos on cars were not matched to = operate at high altitude and continuous high power settings so they are = mismatched and inefficient when used on aircraft. High exhaust back = pressures and overspeeds with consequent catastrophic failure are not = uncommon. In extreme cases, compressor or turbine wheel bursts can cause = engine damage and failure due to part ingestion or oil loss. This is not = a good idea. Use a turbo which is professionally matched for your engine = and intended use by someone familiar with high altitude turbocharging.=20 Intercooling Intercoolers are heat exchangers placed between the compressor and = intake manifold. Their purpose is to reduce the temperature of the = compressed air before it enters the engine. Whenever air is compressed, = its temperature increases. In the case of a high boost turbo at high = altitude, the air exiting the compressor may reach 300-350 degrees F. = This lowers the mass flow of air into the engine and reduces power. It = also raises EGTs and lowers the detonation limits. All of these things = are detrimental to performance and engine longevity.=20 An effective intercooler will lower the charge temperature to within a = few degrees of the ambient temperature. Exhaust Systems The exhaust system on turbocharged engines is critically important. High = temperature materials such as stainless steel or Inconel should be used = for their construction to ensure longevity. Tubing thickness should be a = minimum of .060 inch to withstand the constant 1500 degree temperatures. = Careful attention to thermal expansion is necessary so that cracking = possibilities are minimized. Bellows or slip joints are often required = at junctions. The turbo itself should never be supported by the headers. = A strong, triangulated structure should support the weight of the turbo = on the engine. If possible, the primary header tubes should be equal length and mandrel = bent for low restriction and maximum pulse energy with equal pulse = spacing. The turbine discharge pipe should be 2.25 to 2.5 inches to = minimize backpressure. A muffler is often unnecessary to reduce exhaust = noise as the turbo usually does a good job of this. This helps to offset = the weight of the turbo installation to some degree. Future Developments Watch the Aircraft section for pictures and updates on turbo = installations as they become available. We are currently flying our = turbocharged EJ22 powered RV6A seen elsewhere on this site. R.F. Fuel Octane vs. HP 03/13/98 In turbocharged engines there is a fine balancing act when it comes to = making a lot of power on low octane fuel. In most cases, ignition timing = must be retarded as the boost pressure rises above a critical point and = finally there reaches a further point where the engine simply loses = power. If the timing was not retarded with increasing boost, destructive = preignition or detonation would occur. Normal combustion is = characterized by smooth, even burning of the fuel/air mixture. = Detonation is characterized by rapid, uncontrolled temperature and = pressure rises more closely akin to an explosion. It's effects are = similar to taking a hammer to the top of your pistons.=20 Most engines make maximum power when peak cylinder pressures are = obtained with the crankshaft around 15 degrees after TDC. = Experimentation with increasing boost and decreasing timing basically = alters where and how much force is produced on the crankshaft. Severely = retarded timing causes high exhaust gas temperatures which can lead to = preignition and exhaust valve and turbo damage. We have a hypothetical engine. It's a 2.0L, 4 valve per cylinder, 4 = cylinder type with a 9.0 to 1 compression ratio and it's turbocharged. = On the dyno, the motor puts out 200hp at 4psi boost with the timing at = the stock setting of 35 degrees on 92 octane pump gas with an air/fuel = ratio of 14 to 1. We retard the timing to 30 degrees and can now run = 7psi and make 225hp before detonation occurs. Now we richen the mixture = to 12 to 1 AFR and find we can get 8psi and 235 hp before detonation = occurs. The last thing we can consider is to lower the compression ratio = to 7 to1. Back on the dyno, we can now run 10psi with 33 degrees of = timing with an AFR of 12 to 1 and we get 270 hp on the best pull. We decide to do a test with our 9 to 1 compression ratio using some 118 = octane leaded race gas. The best pull is 490 hp with 35 degrees of = timing at 21 psi. On the 7 to 1 engine, we manage 560 hp with 35 degrees = of timing at 25psi. To get totally stupid, we fit some larger injectors = and remap the EFI system for126 octane methanol. At 30psi we get 700hp = with 35 degrees of timing! While all of these figures are hypothetical, they are very = representative of the gains to be had using high octane fuel. Simply by = changing fuel we took the 7 to 1 engine from 270 to 700 hp. From all of the changes made, we can deduce the effect certain changes = on hp; Retarding the ignition timing allows slightly more boost to be run and = gain of 12.5%. Richening the mixture allows slightly more boost to be run for a small = hp gain however, past about 11.5 to 1 AFR most engines will start to = lose power and even encounter rich misfire. Lowering the compression ratio allows more boost to be run with less = retard for a substantial hp gain. Increasing the octane rating of the fuel has a massive effect on maximum = obtainable hp. We have seen that there are limits on what can be done running pump gas = on an engine with a relatively high compression ratio. High compression = engines are therefore poor candidates for high boost pressures on pump = fuel. On high octane fuels, the compression ratio becomes relatively = unimportant. Ultimate hp levels on high octane fuel are mainly = determined by the physical strength of the engine. This was clearly = demonstrated in the turbo Formula 1 era of a decade ago where 1.5L = engines were producing up to 1100 hp at 60psi on a witches brew of = aromatics. Most fully prepared street engines of this displacement would = have trouble producing half of this power for a short time, even with = many racing parts fitted. Most factory turbocharged engines rely on a mix of relatively low = compression ratios, mild boost and a dose of ignition retard under boost = to avoid detonation. Power outputs on these engines are not stellar but = these motors can usually be seriously thrashed without damage. Trying to = exceed the factory outputs by any appreciable margins without higher = octane fuel usually results in some type of engine failure. Remember, = the factory spent many millions engineering a reasonable compromise in = power, emissions, fuel economy and reliability for the readily available = pump fuel. Despite what many people think, they probably don't know as = much about this topic as the engineers do. One last method of increasing power on turbo engines running on low = octane fuel is water injection. This method was evaluated scientifically = by H. Ricardo in the 1930s on a dyno and showed considerable promise. He = was able to double power output on the same fuel with the aid of water = injection.=20 First widespread use of water injection was in WW2 on supercharged and = turbocharged aircraft engines for takeoff and emergency power increases. = The water was usually mixed with 50% methanol and enough was on hand for = 10-20 minutes use. Water/methanol injection was widely used on the = mighty turbocompound engines of the '50s and '60s before the advent of = the jet engine. In the automotive world, it was used in the '70s and = '80s when turbos suddenly became cool again and where EFI and computer = controlled ignitions were still a bit crude. Some Formula 1 teams = experimented with water injection for qualifying with success until = banned.=20 My personal experience with water injection is considerable. I had = several turbo cars fitted with it. One 2.2 liter Celica with a Rajay = turbo, Weber carb and no intercooler or internal engine mods ran 13.3 at = 103 on street rubber on pump gas back in 1987. This was accomplished at = 15psi. With the water injection switched off, I could only run about 5 = psi before the engine started to ping. I think you might see water = injection controlled by microchips, catch on again in the coming years = on aftermarket street turbo installations. It works. =20 Kelly Troyer "DYKE DELTA JD2" (Eventually) "13B ROTARY"_ Engine "RWS"_RD1C/EC2/EM2 "MISTRAL"_Backplate/Oil Manifold "TURBONETICS"_TO4E50 Turbo -------------------------------------------------------------------------= ------- From: "shipchief@aol.com" To: Rotary motors in aircraft Sent: Sun, October 17, 2010 12:40:28 PM Subject: [FlyRotary] Re: The Case For Turbocharging Kelly: Maybe I'm a bonehead, but those zip files didn't include anything = readable for me.... On the other hand, I'm using a Turbo on my RV-8 prject, so I'm in as far = as selecting a turbo. I finally decided to use a turbo because of Tracy's muffler experiments. = I have a Turbo engine, with the open exhaust ports, so the sound = pressure is very high and would require an extra strong and tough = exhaust system (heavy). So I decided to use that weight in the form of a = Turbo to knock the most vicious element form the exhaust noise. I hope = for a higher rate of climb as a result of the increased power potential. = I realize that all engines have a sweet spot that would be best for = cruise and range, which would co-incide with the engine torque peak RPM = and an airspeed less than Vne, so sustained high turbo boost is not = practical or desired unless 25 gallons per hour fuel flow is expected! = That's a pretty short flight with 42 gallons total fuel aboard. I set my goals to a more attainable level, with a prop that should draw = about 200 HP at 6500 RPM. It's a left hand turning equivalent of the = prop for RV-8s with a 180 HP O-360 Lycoming. I have Tracy's RD-1 2.19:1 = 4 planet gear, so I don't plan to abuse it past the 200 HP limit he has = established. I simply calculated the prop power draw 180HP / 2700RPM =3D = 200HP / 3000 RPM. By the way, for you prop chord measuring guys, it's a CATTO 2 blade = 68x74 prop, with the greatest chord about 6-3/16" falling from 16" thru = 20" in from the tip, which is right in front of the cowl cheek edge. This last week I put the wings on and set the incidence, made the fuel = tank attach brackets and fit the flaps & fairings. Now the wings are = back off, getting the fairing platenuts etc.=20 I'm not that far from taking the whole caboodle to the airport!! -----Original Message----- From: Kelly Troyer To: Rotary motors in aircraft Sent: Sun, Oct 17, 2010 9:50 am Subject: [FlyRotary] The Case For Turbocharging Group, Perhaps of interest to those us interested in Turbocharging our = projects..........It is from the "SDS" website............. =20 Kelly Troyer "DYKE DELTA JD2" (Eventually) "13B ROTARY"_ Engine "RWS"_RD1C/EC2/EM2 "MISTRAL"_Backplate/Oil Manifold "TURBONETICS"_TO4E50 Turbo -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html ------=_NextPart_000_0068_01CB6E12.3C8C1070 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ah, I ditched MS office for the free "Open = Office" - I=20 guess that is why I had no problem opening it.
 
Ed

From: Kelly Troyer
Sent: Sunday, October 17, 2010 1:59 PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: The Case For=20 Turbocharging

Sorry guys..........Did not think about my "Open Office" files not = opening=20 for everyone !!
Hope this is not too big for the forum !!...................
 

Turbocharging Automotive Engines for Aircraft Applications

April 27/98=20

With automotive engines finding increasing use powering homebuilt = aircraft,=20 we find many people entertaining the idea of turbocharging to boost the = power to=20 weight ratios and altitude performance of these engines. We will examine = the=20 various facts and myths regarding turbocharging as applied to light = aircraft=20 use.

History

Turbos in aircraft were first successfully applied in mass numbers = during=20 WWII. The P-38 and P-47 were the best known turbocharged fighter types = and both=20 had excellent high altitude performance.

In general aviation use as applied to air cooled opposed engines,=20 turbocharging has a less revered reputation. Much of this has to do with = the air=20 cooled engine itself and the fact that most of these engines were never = designed=20 to be boosted to begin with. They may have been modified a bit for the = turbo but=20 with power to weight ratios being a major concern, many are structurally = and=20 thermally not up to the task. Other concerns such as turbo cooling and=20 lubrication by inferior aviation type oils also led to premature turbo=20 failures.

What is a Turbocharger?

A turbo consists of a centrifugal compressor connected to a turbine = wheel=20 which is spun at high rpm by the energy of the engine exhaust gasses. It = is a=20 very simple device, but the high temperatures and stresses acting on it = require=20 exotic materials in the turbine section which are somewhat expensive. A = turbo=20 will cost in the neighborhood of $800 to $1300 with the wastegate = assembly.


Turbine wheels come in many shapes and sizes. Constructed of high = temperature alloys such as Inconel or Hastaloy. This is the hot end.=20


Turbine housings are cast from a high nickel/iron alloy.=20

The compressor pressurizes the intake manifold to achieve higher hp = or=20 maintains sea level pressure as the aircraft climbs. This permits higher = climb=20 rates at altitude and increased cruise speeds.


Compressor wheels are cast from aluminum alloy and come in many = sizes or=20 trims. This is the cold end.=20


Compressor housing is cast from aluminum alloy. Shape is designed = to slow=20 the air, thus compressing it.=20


Cast iron center section or bearing housing contains floating = sleeve=20 bearings or more recently ceramic ball bearings. High pressure oil from = engine=20 feeds the bearing and is drained out the bottom of the housing back into = the=20 engine. Some housings are water cooled to prevent coking of oil deposits = leading=20 to bearing failure.=20

Elegant Simplicity

Turbocharging is the most efficient method of boosting hp with the = least=20 weight penalty known. A typical turbo installation on a light aircraft = including=20 intercooler and exhaust is around 35-50 pounds. Such an installation is = capable=20 of tripling hp at sea level or adding 50% to the naturally aspirated = output up=20 to 15,000 feet. Sea level manifold pressures can be maintained to 25,000 = feet in=20 some cases. An aircraft capable of 200 knots at sea level would true out = at=20 nearly 300 knots with a good turbo system at high altitude.

Spinning the compressor with an exhaust driven turbine is a much = better way=20 than by the mechanical means as in a supercharger. It is lighter, more = reliable=20 and more efficient and has the added advantage of having more drive = energy=20 available as the aircraft climbs due to lower backpresure, which is = exactly what=20 is needed.

Fuel Flow vs. Power

There is a common misconception that turbocharging increases fuel = flows=20 because of the backpressure of the turbine. This may be true in air = cooled=20 engines using a poorly matched turbo without intercooling because the = air cooled=20 engine cannot maintain temperature stability without adding fuel for = cooling=20 purposes. Reduced fuel flows at altitude in naturally aspirated and = turbine=20 engines is not due to some magic process, it is due to the fact that as = altitude=20 is increased, less power is produced thus less fuel is required. Many = people=20 also don't seem to realize that fuel flow is related to hp developed and = that a=20 turbo engine will develop more power at altitude than a naturally = aspirated=20 engine, obviously requiring more fuel and delivering higher speeds at = the same=20 time.

Testing done back in the '40s and '50s on turbo engines actually = confirm that=20 fuel flows were LOWER at the same BMEP with turbocharging than in a = naturally=20 aspirated engine developing the same power. This suggests that when = properly=20 applied, the turbo actually recovers more energy from the exhaust to be = applied=20 to reduce pumping losses during the compression stroke than is consumed = during=20 the exhaust stroke working against higher backpressure. With = approximately 50%=20 of the energy in the fuel going out the exhaust in the form of heat and=20 pressure, turbocharging can recover some of this waste and put it to = good=20 use.

It was shown that turbos could achieve fuel flows 3-6% lower and=20 turbocompounding could achieve up to 15% lower fuel flows. Cylinder head = and=20 piston cooling were shown to be the primary limitations to achieving = lower BMSFC=20 figures. We can conclude from this that as applied to liquid cooled = engines with=20 their superior thermal rejection rates, turbocharging really has few=20 disadvantages compared to the many advantages it offers.

It should be no surprise that the latest certified liquid cooled = engines from=20 Toyota and Orenda are turbocharged. People also should remember the = awesome=20 turbocompound radials of the '50s. These engines offered extremely low = BSFC and=20 high power. It seems foolish not to turbocharge most good aircraft = engines used=20 at any kind of altitude as you are throwing away performance without = it.

Turbocharged Air Cooled Engines

As mentioned earlier, turbocharged , conventional opposed air cooled = engines=20 have a less than stellar track record and many lay people blame the = turbo. In=20 fact, the fault lies with the engines it is applied to. The average = Lycoming or=20 Continental has a lot of things not going for them. Many of these = engines suffer=20 premature failure of crankcases, cylinders, heads and valves in their=20 turbocharged iterations. Let's examine why.

Probably the leading cause of case and barrel cracking is the lack of = rigidity these engines have in the cylinder/ case area. For ease of = barrel=20 replacement I assume, the designers of these engines chose to bolt the = cylinders=20 individually to the crankcase at the bottom of the cylinder using a = flange. This=20 arrangement creates a very willowy structure and with each firing = impulse,=20 combined with the sheer mass of the huge reciprocating parts used in = these=20 engines, a definite high amplitude, cyclic stress is put on these parts=20 eventually leading to cracking. The increased gas pressures associated = with=20 turbocharging compound this problem. This design problem is actually the = cause=20 of a major portion of the high vibration levels associated with = conventional=20 aircraft engines.

The flange method puts the barrel under a tension load with every = firing=20 impulse too which is just plain stupid given the thickness of the = cylinders.=20 Modern automotive racing practice would use through studs to retain the = barrels,=20 thus putting the barrels under compression.

Cylinder head cracking and exhaust valve burning and sticking are = primarily=20 due to insufficient cooling in these areas which is exaggerated by the = extra=20 heat introduced by turbocharging. Air cooling is relatively inefficient = at=20 sinking heat off around the exhaust port and valve seat area. This = problem is=20 compounded by the use of very low compression ratios resulting in higher = EGTs=20 thus even higher heat flux in the critical exhaust port area. Typical = air cooled=20 aircraft engines run cylinder head temperatures in excess of 400 degrees = on a=20 regular basis. With aluminum alloys losing roughly 50% of their strength = at this=20 temperature it is easy to see why cracking is all too common here. The = high=20 EGT's are also detrimental to the life of the turbo's turbine = section.

Valve problems are due to the same cause, temperatures being too high = from=20 inefficient heat transfer. Many factory turbo aircraft are forced to = either open=20 cowl flaps or richen the mixture at high altitude to keep temperatures = within=20 limits. With power being maintained at altitude and air density falling = off,=20 there is often insufficient mass flow available for cooling. This is = rarely a=20 problem on naturally aspirated engines as power and cooling requirements = are=20 dropping off with increasing altitude.

Not a lot of design went into the induction system on many of these = engines=20 hence fuel distribution is usually not the greatest. This contributes to = engine=20 roughness and problems with leaning. Leaning is limited by the mixture = in the=20 hottest cylinder with the others running richer than desired.

The oils used in aircraft engines are relatively crude by modern = synthetic=20 automotive standards and consequently not the best for the turbocharger. = The use=20 of these oils appears to be a result of the very loose tolerances = required in an=20 air cooled engines because of the high operating temperatures which also = leads=20 to the high oil consumption characteristic of these engines.

Finally, many certified installations never used intercooling which = is simply=20 amazing. The advantages and necessity of it was clearly understood in = WWII. High=20 charge temperatures at altitude required even more fuel for cooling and = yet more=20 cowl flap opening to control head temperatures.

Turbocharged Liquid Cooled Engines

Liquid cooled engines are a natural for turbocharging because of = their higher=20 heat rejection capabilities. Water cooling also enables the turbo center = section=20 to be water cooled which alleviates a primary cause of turbo failure- = coked=20 bearing holes from high heat and fried oil. Water cooled engines can use = modern=20 synthetic oils because of their tighter clearances. Synthetic oils with = their=20 much higher temperature capabilities are more suitable to lubricate the = turbo=20 than old fashioned, aircraft oils derived from natural base stocks. The = popular=20 Mobil 1 synthetic oil, common in the racing world, can withstand = temperatures of=20 350 degrees continuously and even 450 degrees intermittently without = significant=20 degradation. With proper lubrication and cooling, turbochargers will = easily last=20 the life of the engine.

If we compare the Popular Subaru EJ22 and EJ25 horizontally opposed 4 = cylinder engines to their certified counterparts we find many advantages = especially in turbocharged trim. The Subaru has 5 main bearings instead = of 3=20 which means that the crank is better supported. The Subaru has a higher=20 compression ratio for higher thermal efficency. Its overhead cam, 4 = valve per=20 cylinder arrangement provides lower friction and higher volumetric = efficiency=20 than a 2 valve pushrod setup. Finally, the integrated block and head = design is=20 many times stiffer and stronger than the aircraft engine.

As long as the radiator and ducting are properly designed, cooling = problems=20 are not a concern on the liquid cooled engine.

The induction system on the Subaru has proper runner lengths to boost = torque,=20 relatively equal airflow to each cylinder and can easily use a modern = digital,=20 electronic fuel injection system to precisely meter fuel. All of these = things=20 aid in producing more power with less fuel.

Power vs. Weight vs. Manifold Pressure vs. Life vs. = Cost

The EJ engines when turbocharged and equipped with a radiator, PSRU = and=20 composite propeller are slightly heavier than the popular Lycoming and=20 Continental 360 cubic inch engines which are rated at 180- 200 hp for = takeoff=20 and around 135- 150 hp for maximum cruise. The Subaru can easily attain = 200- 250=20 hp at 50 inches for takeoff and reliably deliver 140 to 170hp at 35-38 = inches=20 for cruise. The 3.3L EG33 six cylinder is capable of 300+ hp for takeoff = and=20 200-250 hp in cruise making it a viable alternative to the O-540 = engines. These=20 power levels can be maintained during climb and cruise at altitude = thanks to=20 turbocharging and liquid cooling.

Projected TBO is in the 1000-1200 hour range at this time. Most = people flying=20 the EJ engines are confident that no interim work will be required = during this=20 period such as cylinder barrel replacement and valve grinding operations = which=20 are quite common on aircraft engines before reaching their stated TBO. = In other=20 words, if you change the oil and check the water, that is about all that = is=20 required during those 1000 hours. There are no magneto or even valve = adjustments=20 to worry about. Expect spark plug replacement every 100- 250 hours or so = at $3=20 each. Overhaul costs will range from about $500 to $1500 for parts and = machine=20 work depending on condition. Labor would be in the $500 to $1200 range. = We are=20 all familiar with the costs to overhaul a certified aircraft engine.=20

Matching a Turbocharger

As applied to the popular Subaru EJ22 and EJ25 engines for general = purpose=20 use below 15,000 feet we can narrow the choice of turbos down a bit. = Garrett T3=20 turbos are recommended as they are relatively cheap, reliable and easy = to fix=20 with a vast array of combinations available. The compressor side may be = either a=20 -50, -60 or super 60 wheel with a stage 3 turbine wheel in a .82 A/R = housing,=20 depending on the exact use and hp. These may be ordered with an integral = wastegate and a water cooled bearing housing which are both highly = recommended.=20 These turbos are quite capable of producing enough boost to extract 250 = hp at=20 sea level and still have 175+ hp available at 15,000 feet.

The integral wastegates are generally more reliable than an external = type=20 especially on an aircraft application in which it is almost constantly = bypassing=20 exhaust. The wastegate is simply a valve used to bypass exhaust gasses = around=20 the turbine to control turbine and compressor speed and thus boost = pressure. It=20 is usually actuated automatically by a diaphragm sensing manifold = pressure.

Many people have tried to use the OE turbo on auto aircraft = conversions,=20 often with limited success. The turbos on cars were not matched to = operate at=20 high altitude and continuous high power settings so they are mismatched = and=20 inefficient when used on aircraft. High exhaust back pressures and = overspeeds=20 with consequent catastrophic failure are not uncommon. In extreme cases, = compressor or turbine wheel bursts can cause engine damage and failure = due to=20 part ingestion or oil loss. This is not a good idea. Use a turbo which = is=20 professionally matched for your engine and intended use by someone = familiar with=20 high altitude turbocharging.=20

Intercooling

Intercoolers are heat exchangers placed between the compressor and = intake=20 manifold. Their purpose is to reduce the temperature of the compressed = air=20 before it enters the engine. Whenever air is compressed, its temperature = increases. In the case of a high boost turbo at high altitude, the air = exiting=20 the compressor may reach 300-350 degrees F. This lowers the mass flow of = air=20 into the engine and reduces power. It also raises EGTs and lowers the = detonation=20 limits. All of these things are detrimental to performance and engine = longevity.=20

An effective intercooler will lower the charge temperature to within = a few=20 degrees of the ambient temperature.

Exhaust Systems

The exhaust system on turbocharged engines is critically important. = High=20 temperature materials such as stainless steel or Inconel should be used = for=20 their construction to ensure longevity. Tubing thickness should be a = minimum of=20 .060 inch to withstand the constant 1500 degree temperatures. Careful = attention=20 to thermal expansion is necessary so that cracking possibilities are = minimized.=20 Bellows or slip joints are often required at junctions. The turbo itself = should=20 never be supported by the headers. A strong, triangulated structure = should=20 support the weight of the turbo on the engine.

If possible, the primary header tubes should be equal length and = mandrel bent=20 for low restriction and maximum pulse energy with equal pulse spacing. = The=20 turbine discharge pipe should be 2.25 to 2.5 inches to minimize = backpressure. A=20 muffler is often unnecessary to reduce exhaust noise as the turbo = usually does a=20 good job of this. This helps to offset the weight of the turbo = installation to=20 some degree.

Future Developments

Watch the Aircraft section for pictures and updates on turbo = installations as=20 they become available. We are currently flying our turbocharged EJ22 = powered=20 RV6A seen elsewhere on this site.

R.F.

 

Fuel Octane vs. HP

03/13/98

In turbocharged engines there is a fine balancing act when it comes = to making=20 a lot of power on low octane fuel. In most cases, ignition timing must = be=20 retarded as the boost pressure rises above a critical point and finally = there=20 reaches a further point where the engine simply loses power. If the = timing was=20 not retarded with increasing boost, destructive preignition or = detonation would=20 occur. Normal combustion is characterized by smooth, even burning of the = fuel/air mixture. Detonation is characterized by rapid, uncontrolled = temperature=20 and pressure rises more closely akin to an explosion. It's effects are = similar=20 to taking a hammer to the top of your pistons.

Most engines make maximum power when peak cylinder pressures are = obtained=20 with the crankshaft around 15 degrees after TDC. Experimentation with = increasing=20 boost and decreasing timing basically alters where and how much force is = produced on the crankshaft. Severely retarded timing causes high exhaust = gas=20 temperatures which can lead to preignition and exhaust valve and turbo=20 damage.

We have a hypothetical engine. It's a 2.0L, 4 valve per cylinder, 4 = cylinder=20 type with a 9.0 to 1 compression ratio and it's turbocharged. On the = dyno, the=20 motor puts out 200hp at 4psi boost with the timing at the stock setting = of 35=20 degrees on 92 octane pump gas with an air/fuel ratio of 14 to 1. We = retard the=20 timing to 30 degrees and can now run 7psi and make 225hp before = detonation=20 occurs. Now we richen the mixture to 12 to 1 AFR and find we can get = 8psi and=20 235 hp before detonation occurs. The last thing we can consider is to = lower the=20 compression ratio to 7 to1. Back on the dyno, we can now run 10psi with = 33=20 degrees of timing with an AFR of 12 to 1 and we get 270 hp on the best = pull.

We decide to do a test with our 9 to 1 compression ratio using some = 118=20 octane leaded race gas. The best pull is 490 hp with 35 degrees of = timing at 21=20 psi. On the 7 to 1 engine, we manage 560 hp with 35 degrees of timing at = 25psi.=20 To get totally stupid, we fit some larger injectors and remap the EFI = system=20 for126 octane methanol. At 30psi we get 700hp with 35 degrees of = timing!

While all of these figures are hypothetical, they are very = representative of=20 the gains to be had using high octane fuel. Simply by changing fuel we = took the=20 7 to 1 engine from 270 to 700 hp.

From all of the changes made, we can deduce the effect certain = changes on=20 hp;

Retarding the ignition timing allows slightly more boost to be run = and gain=20 of 12.5%.

Richening the mixture allows slightly more boost to be run for a = small hp=20 gain however, past about 11.5 to 1 AFR most engines will start to lose = power and=20 even encounter rich misfire.

Lowering the compression ratio allows more boost to be run with less = retard=20 for a substantial hp gain.

Increasing the octane rating of the fuel has a massive effect on = maximum=20 obtainable hp.

We have seen that there are limits on what can be done running pump = gas on an=20 engine with a relatively high compression ratio. High compression = engines are=20 therefore poor candidates for high boost pressures on pump fuel. On high = octane=20 fuels, the compression ratio becomes relatively unimportant. Ultimate hp = levels=20 on high octane fuel are mainly determined by the physical strength of = the=20 engine. This was clearly demonstrated in the turbo Formula 1 era of a = decade ago=20 where 1.5L engines were producing up to 1100 hp at 60psi on a witches = brew of=20 aromatics. Most fully prepared street engines of this displacement would = have=20 trouble producing half of this power for a short time, even with many = racing=20 parts fitted.

Most factory turbocharged engines rely on a mix of relatively low = compression=20 ratios, mild boost and a dose of ignition retard under boost to avoid=20 detonation. Power outputs on these engines are not stellar but these = motors can=20 usually be seriously thrashed without damage. Trying to exceed the = factory=20 outputs by any appreciable margins without higher octane fuel usually = results in=20 some type of engine failure. Remember, the factory spent many millions=20 engineering a reasonable compromise in power, emissions, fuel economy = and=20 reliability for the readily available pump fuel. Despite what many = people think,=20 they probably don't know as much about this topic as the engineers = do.

One last method of increasing power on turbo engines running on low = octane=20 fuel is water injection. This method was evaluated scientifically by H. = Ricardo=20 in the 1930s on a dyno and showed considerable promise. He was able to = double=20 power output on the same fuel with the aid of water injection.

First widespread use of water injection was in WW2 on supercharged = and=20 turbocharged aircraft engines for takeoff and emergency power increases. = The=20 water was usually mixed with 50% methanol and enough was on hand for = 10-20=20 minutes use. Water/methanol injection was widely used on the mighty=20 turbocompound engines of the '50s and '60s before the advent of the jet = engine.=20 In the automotive world, it was used in the '70s and '80s when turbos = suddenly=20 became cool again and where EFI and computer controlled ignitions were = still a=20 bit crude. Some Formula 1 teams experimented with water injection for = qualifying=20 with success until banned.

My personal experience with water injection is considerable. I had = several=20 turbo cars fitted with it. One 2.2 liter Celica with a Rajay turbo, = Weber carb=20 and no intercooler or internal engine mods ran 13.3 at 103 on street = rubber on=20 pump gas back in 1987. This was accomplished at 15psi. With the water = injection=20 switched off, I could only run about 5 psi before the engine started to = ping. I=20 think you might see water injection controlled by microchips, catch on = again in=20 the coming years on aftermarket street turbo installations. It = works.


 

Kelly Troyer
"DYKE DELTA JD2" (Eventually)

"13B ROTARY"_ Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil = Manifold

"TURBONETICS"_TO4E50 Turbo



From: = "shipchief@aol.com"=20 <shipchief@aol.com>
To:=20 Rotary motors in aircraft = <flyrotary@lancaironline.net>
Sent: Sun, October 17, 2010 = 12:40:28=20 PM
Subject: = [FlyRotary] Re: The=20 Case For Turbocharging

Kelly:
Maybe I'm a bonehead, but those zip files didn't include anything = readable=20 for me....
On the other hand, I'm using a Turbo on my RV-8 prject, so I'm in = as far as=20 selecting a turbo.
I finally decided to use a turbo because of Tracy's muffler = experiments. I=20 have a Turbo engine, with the open exhaust ports, so the sound pressure = is very=20 high and would require an extra strong and tough exhaust system (heavy). = So I=20 decided to use that weight in the form of a Turbo to knock the most = vicious=20 element form the exhaust noise. I hope for a higher rate of = climb as a=20 result of the increased power potential.
I realize that all engines have a sweet spot that would be best for = cruise=20 and range, which would co-incide with the engine torque peak = RPM and an=20 airspeed less than Vne, so sustained high turbo boost is not practical = or=20 desired unless 25 gallons per hour fuel flow is expected! That's a = pretty short=20 flight with 42 gallons total fuel aboard.
I set my goals to a more attainable level, with a prop that = should=20 draw about 200 HP at 6500 RPM. It's a left hand turning equivalent = of the=20 prop for RV-8s with a 180 HP O-360 Lycoming. I have Tracy's RD-1 = 2.19:1 4=20 planet gear, so I don't plan to abuse it past the 200 HP limit he has=20 established. I simply calculated the prop power draw 180HP / = 2700RPM =3D=20 200HP / 3000 RPM.
By the way, for you prop chord measuring guys, it's a CATTO 2 = blade=20 68x74 prop, with the greatest chord about 6-3/16" falling from 16" thru = 20" in=20 from the tip, which is right in front of the cowl cheek edge.
This last week I put the wings on and set the incidence, made the = fuel tank=20 attach brackets and fit the flaps & fairings. Now the wings are = back=20 off, getting the fairing platenuts etc.
I'm not that far from taking the whole caboodle to the = airport!!
-----Original=20 Message-----
From: Kelly Troyer <keltro@att.net>
To: Rotary = motors=20 in aircraft <flyrotary@lancaironline.net>
Sent: Sun, Oct 17, = 2010 9:50=20 am
Subject: [FlyRotary] The Case For Turbocharging

Group,
    Perhaps of interest to those us interested = in=20 Turbocharging our projects..........It
is from the "SDS" website.............
 
Kelly Troyer
"DYKE DELTA JD2" = (Eventually)
"13B ROTARY"_ = Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil=20 Manifold
"TURBONETICS"_TO4E50 Turbo
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