X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [65.54.250.83] (HELO hotmail.com) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1054181 for flyrotary@lancaironline.net; Fri, 31 Mar 2006 11:23:32 -0500 Received-SPF: pass receiver=logan.com; client-ip=65.54.250.83; envelope-from=lors01@msn.com Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Fri, 31 Mar 2006 08:22:47 -0800 Message-ID: Received: from 4.171.147.180 by BAY115-DAV11.phx.gbl with DAV; Fri, 31 Mar 2006 16:22:45 +0000 X-Originating-IP: [4.171.147.180] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Very short intake manifold length Date: Fri, 31 Mar 2006 11:21:45 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0050_01C654B5.4B8EA090" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.20.0026.0800 Seal-Send-Time: Fri, 31 Mar 2006 11:21:46 -0500 X-OriginalArrivalTime: 31 Mar 2006 16:22:47.0487 (UTC) FILETIME=[590974F0:01C654DF] This is a multi-part message in MIME format. ------=_NextPart_000_0050_01C654B5.4B8EA090 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Great summary on aircraft vs Auto racing engine differences Lynn and an = interesting discussion on manifolds in general. =20 There is not enough appreciation of these differences. The original = comment that started this thread (about my short runner carburetor = manifold) has to be evaluated in this context. In a race car, that = manifold would be a disaster but it was an unqualified success in the = airplane. Compare it to the stock manifold. The entire short runner = intake system with carbs weighed 9 pounds vs about 45 for the stock = system. And, it was redundant. It could tolerate the complete failure = of any one of its three carburetors and keep flying. The engine (1988 = NA 13B) with short runners made 160 HP vs 146 in the car (granted, much = of the increase was from exhaust system changes) As installed, it was = the first auto engine conversion to equal or better the power to weight = ratio of the Lycoming engine that it replaced (as far as I know). Regarding the suitability of short runners on motorcycles, the short = runners do not preclude good performance at low rpm. The Yamaha XS 1100 = was legendary for it's low end torque. Ever ride a Harley Davidson? = Stump pulling torque. Ever see long runner intakes on one? Could = these engines make even more torque with a long intake runner manifold? = Of course they could, but the point is that good low rpm performance is = not impossible with short runners. (Also really funny that we are calling 6000 rpm "low" : ) There is another important factor that is frequently missed when = comparing rotary and piston engine manifolds but that is a discussion = for another day. Tracy (loading plane for S n' F) Subject: [FlyRotary] Re: Very short intake manifold length In a message dated 3/31/2006 6:31:49 A.M. Eastern Standard Time, = Hennie.vanRooyen@kumbaresources.com writes: "That 173.3 HP from the dyno sheet is from an engine with a very = short intake tract. It is tuned for best power at 9,400 RPM. That was = 244.9 HP. It is not tuned for 6,500 RPM. In use there is no reason to be = below 7,800 RPM and I watch the tape from each session to alert the = driver is he is dragging the Revs that low in some situations. We will = change final drive ratios or hold off an upshift to a different location = to avoid going below 7,800 RPM (229.4 HP)." Hi Lynn, I'm sure I'm going to be flamed for this question, but I'll reveal = my ignorance by asking anyway. (I'm still a baby at this, but growing = stronger every day) If the rotary engine can be tuned for higher output at higher RPM, = why are they operated in the lower RPM range for aircraft applications = even though we use PSRU's? Is it for fuel consumption, heat generation = and reliability only or should I ought to know something else? Hennie It sounds like you know those answers. Drag (friction) increases at the square of velocity. So, the higher = you rev any engine the more difficult the efficiency problem in BSFC. = Even if the engine is not loaded, some of that goes on. Loaded is worse = of course. So the race engine has the big HP numbers and is in use for 45 = minutes. But the duty cycle is actually pretty low. That is the amount = of time spent at WOT is always less than the owner wants it to be. I = heard a famous driver complain to the engine man about power after the = second engine change. The frustrated engine man asked the driver if he = was going around the corners flat out? Of course not said the driver. = Well then, talk to the chassis guys not me. Anyway, in the aircraft application, the duty cycle is close to 100% = Get in the plane. Open throttle to 100%. fly to Sun&Fun (Zephyr Hills is = better) reduce throttle, land, shut down. So almost 100% full throttle. = The rotary is not as efficient as the piston engine, so for each HP = produced it takes more fuel measured in pounds per HP hour. Brake = specific fuel consumption.=20 So the piston engines are about 28% efficient. Recovers only 28% of = the total heat from the fuel is converted to work. In the rotary about = 26% efficient. That means that there is one big bunch of heat to get rid of, when = that unused heat appears as coolant heat, oil heat, and the big one is = exhaust heat. For example, it is normal to end up with between 160 to 180 HP in the = airplane roll, and to the man, there is a temp watch on all flying, very = bad when local air temps are high. The heat load can be adjusted with = the throttle to reduce the total BTU load on the cool system, (But what = fun is that). So I can build you a 250 HP engine, but you cannot cool = it. But you could use it for takeoff and hope that the airspeed goes up = faster than the water temp.=20 I have the biggest radiator Griffin makes and on scalding hot days, = the water and oil is at 190 degrees. When 180 water and 150 to 160 oil = would be great. Tracy needs to make a three speed reduction unit, so the rotor heads = can leave Lakeland in the vertical. Another problem is the wear rates go up with speed and fuel = consumption, and since reliability is a selling point, rapid wear is = nothing to look for. The more popular higher reduction lets the swept volume go up, so the = engine gets to act like a bigger engine. Yes it does. Since it is = burning more fuel per each revolution of the prop, and the number of CCs = involved per revolution is higher.=20 Another factor is the short stroke, low mechanical advantage of the = short stroke is overcome by running at higher RPM than a piston engine = to produce a specific HP number.=20 So direct driving a prop at 2,750 would get you maybe 50 HP. Only 25 = or so is required to go 70 MPH with a slick car so for cars it isn't a = big deal. But not of any value for airplanes.=20 Lynn E. Hanover ------=_NextPart_000_0050_01C654B5.4B8EA090 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Great summary on aircraft vs Auto racing engine differences = Lynn and=20 an interesting discussion on manifolds in general. 
 
There is not enough appreciation of these = differences. =20 The original comment that started this thread (about my short runner=20 carburetor manifold) has to be evaluated in this context.  In = a race=20 car, that manifold would be a disaster but it was an unqualified success = in the=20 airplane.  Compare it to the stock manifold.  The entire = short=20 runner intake system with carbs weighed 9 pounds vs about 45 for the = stock=20 system.  And, it was redundant.  It could tolerate the = complete=20 failure of any one of its three carburetors and keep flying.  The = engine=20 (1988 NA 13B) with short runners made 160 HP vs 146 in the car (granted, = much of=20 the increase was from exhaust system changes)  As installed, it=20 was the first auto engine conversion to equal or better the power = to weight=20 ratio of the Lycoming engine that it replaced (as far as I know).
 
Regarding the suitability of short runners on motorcycles,  = the short=20 runners do not preclude good performance at low rpm.  The Yamaha XS = 1100=20 was legendary for it's low end torque.  Ever ride a Harley = Davidson? =20 Stump pulling torque.  Ever see long runner intakes on = one?  =20 Could these engines make even more torque with a long intake runner=20 manifold?  Of course they could, but the point is that good low rpm = performance  is not impossible with short runners.
 
(Also really funny that we are calling 6000 rpm  "low" : = )
 
There is another important factor that is frequently missed when = comparing=20 rotary and piston engine manifolds but that is a discussion for another=20 day.
 
Tracy (loading plane for S n' F)
 
Subject: [FlyRotary] Re: Very = short=20 intake manifold length

In a message dated 3/31/2006 6:31:49 A.M. Eastern Standard Time, = Hennie.vanRooyen@kumb= aresources.com=20 writes:
"That=20 173.3 HP from the dyno sheet is from an engine with a very short = intake=20 tract. It is tuned for best power at 9,400 RPM. That was 244.9 HP. = It is not=20 tuned for 6,500 RPM. In use there is no reason to be below 7,800 RPM = and I=20 watch the tape from each session to alert the driver is he is = dragging the=20 Revs that low in some situations.  We will change final drive = ratios or=20 hold off an upshift to a different location to avoid going below = 7,800 RPM=20 (229.4 HP)."

Hi Lynn,

I'm sure I'm going to be flamed = for this=20 question, but I'll reveal my ignorance by asking anyway. (I'm still = a baby=20 at this, but growing stronger every day)

If the rotary engine = can be=20 tuned for higher output at higher RPM, why are they operated in the = lower=20 RPM range for aircraft applications even though we use PSRU's? Is it = for=20 fuel consumption, heat generation and reliability only or should I = ought to=20 know something = else?

Hennie


It sounds like you know those answers.
 
Drag (friction) increases at the square of velocity. So, the = higher you=20 rev any engine the more difficult the efficiency problem in BSFC. Even = if the=20 engine is not loaded, some of that goes on. Loaded is worse of = course.
 
So the race engine has the big HP numbers and is in use for 45 = minutes.=20 But the duty cycle is actually pretty low. That is the amount of time = spent at=20 WOT is always less than the owner wants it to be. I heard a famous = driver=20 complain to the engine man about power after the second engine = change.=20 The frustrated engine man asked the driver if he was going around the = corners=20 flat out? Of course not said the driver. Well then, talk to the = chassis guys=20 not me.
 
Anyway, in the aircraft application, the duty cycle is close to = 100% Get=20 in the plane. Open throttle to 100%. fly to Sun&Fun (Zephyr Hills = is=20 better) reduce throttle, land, shut down. So almost 100% full = throttle.=20 The rotary is not as efficient as the piston engine, so for each HP = produced=20 it takes more fuel measured in pounds per HP hour. Brake specific fuel = consumption.
 
So the piston engines are about 28% efficient. Recovers only 28% = of the=20 total heat from the fuel is converted to work. In the rotary about 26% = efficient.
That means that there is one big bunch of heat to get rid of, = when that=20 unused heat appears as coolant heat, oil heat, and the big one is = exhaust=20 heat.
 
For example, it is normal to end up with between 160 to 180 HP in = the=20 airplane roll, and to the man, there is a temp watch on all flying, = very bad=20 when local air temps are high. The heat load can be adjusted with the = throttle=20 to reduce the total BTU load on the cool system, (But what fun is = that). So I=20 can build you a 250 HP engine, but you cannot cool it. But you could = use it=20 for takeoff and hope that the airspeed goes up faster than the water=20 temp. 
 
I have the biggest radiator Griffin makes and on scalding hot = days, the=20 water and oil is at 190 degrees. When 180 water and 150 to 160 = oil would=20 be great.
 
Tracy needs to make a three speed reduction unit, so the rotor = heads can=20 leave Lakeland in the vertical.
 
Another problem is the wear rates go up with speed and fuel = consumption,=20 and since reliability is a selling point, rapid wear is nothing to = look=20 for.
 
The more popular higher reduction lets the swept volume go up, so = the=20 engine gets to act like a bigger engine. Yes it does. Since it is = burning more=20 fuel per each revolution of the prop, and the number of CCs involved = per=20 revolution is higher.
 
Another factor is the short stroke, low mechanical advantage of = the short=20 stroke is overcome by running at higher RPM than a piston engine = to=20 produce a specific HP number.
 
So direct driving a prop at 2,750 would get you maybe 50 HP. Only = 25 or=20 so is required to go 70 MPH with a slick car so for cars it isn't a = big deal.=20 But not of any value for airplanes. 
 
 
Lynn E.=20 Hanover   
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