X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao103.cox.net ([68.230.241.43] verified) by logan.com (CommuniGate Pro SMTP 5.2.13) with ESMTP id 3577888 for flyrotary@lancaironline.net; Sat, 11 Apr 2009 22:22:58 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.43; envelope-from=rv-4mike@cox.net Received: from fed1rmimpo03.cox.net ([70.169.32.75]) by fed1rmmtao103.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20090412022210.NHPV4363.fed1rmmtao103.cox.net@fed1rmimpo03.cox.net> for ; Sat, 11 Apr 2009 22:22:10 -0400 Received: from wills ([68.105.85.56]) by fed1rmimpo03.cox.net with bizsmtp id eSN81b0021CvZmk04SNA7m; Sat, 11 Apr 2009 22:22:11 -0400 X-Authority-Analysis: v=1.0 c=1 a=_P0x7ggvB_YA:10 a=8_Iqg-Ze0kQA:10 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=kviXuzpPAAAA:8 a=UretUmmEAAAA:8 a=Ia-xEzejAAAA:8 a=nUuTZ29dAAAA:8 a=rHNAy4Kcz---bsDYPooA:9 a=F-ipKvmoJnWmejPjkW8A:7 a=Dsie47idhZx2UngTzdD8pfAQih0A:4 a=XF7b4UCPwd8A:10 a=EzXvWhQp4_cA:10 a=Pp7q0i4j7ojnDFIY:21 a=21qQ7C60e-R8S3wN:21 a=SSmOFEACAAAA:8 a=AqRLKeAxJGEI_-sV0OkA:9 a=WteUX0R_6c1_V0_vQA4A:7 a=JfYiYeMOM_zv7xitLTzrK48NVJoA:4 a=AfD3MYMu9mQA:10 X-CM-Score: 0.00 Message-ID: From: "Mike Wills" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Gary Casey was [FlyRotary] Re: Rotary Engines Date: Sat, 11 Apr 2009 19:22:07 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0046_01C9BADA.CDC4E680" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_0046_01C9BADA.CDC4E680 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable This has been an interesting thread. In the end, it doesnt really matter = how many "major" parts you have - even a minor failure can bring you = down. While I believe the basic rotary engine itself is more fault = tolerant than a recip, the peripherals used in the typical rotary = install are a lot more complex than a typical recip install. Since we = rotary fliers dont have the benefit of 70 years worth of experience = flying behind the typical LyCon farm implement I think overall our odds = are considerably worse. Comes down to how well an individual engineer's = his installation and there is a tremendous amount of variation here. The dependence on electronics in the typical rotary install is a good = example. I may be a little sensitive to this issue since I've been = trying to find an intermittent glitch (2 times in 22 hours of engine = testing). Mike Wills RV-4 N144MW =20 ----- Original Message -----=20 From: Ed Anderson=20 To: Rotary motors in aircraft=20 Sent: Saturday, April 11, 2009 7:31 AM Subject: [FlyRotary] Gary Casey was [FlyRotary] Re: Rotary Engines Good analysis and logic, Gary. =20 You'd make a good addition to the "rotary community". I have noticed = over the 10 years I have been flying my rotary powered RV-6A that the = problems have decreased considerably, the success rate and completion = rate has gone up and first flights are now occurring without significant = problems - even cooling is OK {:>). I believe most of this improvement = can be attributed to folks sharing their knowledge, problems and = solutions with others - such as on this list. =20 =20 I know that fewer parts count is often touted as one of the rotary = benefit - and while it is true that the part count is lower, the most = significant thing (in my opinion) is not only does the lower part count = help reliability (if it is not there - it can not break), but if you = look a the design of the eccentric shaft (for example) you notice the = absence of the jogs in a typical crankshaft and their stress points. = The thing is over 3" in diameter at some points and does not have the = same inertia loads born by a piston crankshaft. The parts that are = there are of very robust design. Finally, the rotary is (I believe) = more tolerant of damage and tends to fail "gradually and gracefully", it = can take a licking and keep on ticking as the old saying goes. Only = extended time and numbers will provide the true MTBF for the rotary, but = I believe it looks very promising. =20 Failure of rotary engines are extremely rare, but unfortunately, as = with many alternative engine installations, auxiliary subsystems such as = fuel and ignition frequently being one-off designs have been the cause = of most failures - with probably fuel the prime culprit. The good news = is that for some platforms (such as the RVs) we have pretty much = established what will make an installation successful. The Canard crowd = is fast approaching that status with their somewhat more challenging = cooling requirements being over come. =20 Having lost a rotor during flight due to putting in high compression = rotors with worn apex seal slots worn beyond specs (found this out later = - my fault for not being aware of this spec limit and checking it) which = led to apex seal failure and consequence lost of most of the power from = one rotor, I was still able to maintain 6500 MSL at WOT and fuel mixture = knob to full rich - flowing 14.5 GPH - a lot of it undoubtedly being = blown through the disabled rotor. Flew it back 60 miles to a suitable = runway and made a non-eventful landing. There was a small increase in = vibration due to the power strokes no longer being balanced, but nothing = bad and you could still read the needles on the gauges. Other folks = have had FOD damage to a rotor and also make it to a safe landing. Two = folks lost cooling (one loss of coolant fluid , one lost of water pump) = and while they did cook the engines, both made it back to a safe = landing. So all things considered, I think the rotary continues to show = that if the installation is designed properly, it makes a very viable = and reliable aircraft power plant. =20 Failure of rotary engines in aircraft are extremely rare, but = unfortunately, as with many alternative engine installations, auxiliary = subsystems such as fuel and ignition frequently being one-off designs - = have been the cause of most failures. The good news is that for some = platforms (such as the RVs) we have pretty much established what will = make an installation successful. The Canard crowd is fast approaching = that status with their somewhat more challenging cooling requirements = being over come. =20 My rotary installation cost me $6500 back in 1996, the primary cost = being a rebuilt engine $2000 and the PSRU $2900. I have since purchased = a 1991 turbo block engine from Japan for $900 and rebuilt it myself for = another $2200. My radiators (GM evaporator cores) cost $5.00 from the = junk yard and another $50.00 each for having the bungs welded on. So = depending on how much you buy and how much you build the price can vary = considerably. Today, I would say it would take a minimum of around = $8000 and more nominally around $10000 for a complete rotary = installation in an RV - some folks could do it for less, some for more. =20 But, regardless of the technical merit (or not) in someone's mind, the = crucial thing (in my opinion) is you need to address two personal = factors: =20 1. What is your risk tolerance? It doesn't really matter how sexy = some "exotic" engine installation may seem - if you are not comfortable = flying behind (or in front) of it, then it certainly does not makes = sense to go that route. After all, this is supposed to have an element = of fun and enjoyment to it. =20 2. What is your knowledge, experience and background (and you don't = have to be an engineer) and do you feel comfortable with the level of = involvement needed. =20 So hope you continue to contribute to expanding our knowledge and = understanding of the rotary in its application to power plant for = aircraft. =20 =20 Best Regards =20 Ed =20 =20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm -------------------------------------------------------------------------= ----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] = On Behalf Of Gary Casey Sent: Saturday, April 11, 2009 8:36 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Rotary Engines =20 Just to add a few more comments and answers to the several excellent = comments posted: =20 How many parts does it take to make a rotary rotate? Well, "parts = aren't parts" in this case. Mark was right in that there are maybe 4 = "major" components, but you have to define major. A piston engine = certainly has far more major parts. Is a valve a "major" part? I think = so. Is a rotor corner button a major part? Not sure, but probably not. = Is each planet gear in the PSRU a major part? I say yes, and the PSRU = is an integral part of the rotary engine. As someone correctly pointed = out, it's not how many parts, but the reliability of the total system = that counts. Just looking at the history of the rotary (which, from the = implication of another post) it's not that good, but I don't think it = has anything to do with reliability of the concept. It's more to do = with the experimental nature of the builds and installations. My = original point, perhaps not well expressed is that to say there are just = 4 parts is an oversimplification. But let's face it, to put in an = engine that has had many thousands of identical predecessors is less = "experimental" than one that hasn't.. =20 Are we ES drivers more conservative? Probably so, since the ES is = probably one of the experimentals most similar to production aircraft, = and not just because the Columbia (can't force myself to say Cezzna :-) = was a derivative. Therefore, it tends to attract conservative builders = and owners. Not surprising then that almost all ES's have traditional = powerplants, with the most excellent exception of Mark. While there may = be more, I know of only two off-airport landings caused by engine = failures in the ES in almost 20 years of experience. One was caused by = fuel starvation right after takeoff (fatal) and one was caused by a PSRU = failure in an auto engine conversion. So our old-fashioned conservative = nature has served us pretty well. =20 Yes, I was assuming that the rotary had electronic fuel injection and = ignition, but that by itself doesn't change the inherent fuel efficiency = of the engine. Direct injection does have a potential to improve BSFC = because the fuel charge can be stratified. It will probably decrease = available power, though. I think the best rotary will be 5% less = efficient than the "best" piston engine(same refinements added to each). = But I stated that as a simple disadvantage - as Mark pointed out, it = isn't that simple. The rotary already comes configured to run on auto = gas. The piston engine can also be so configured, but the compression = ratio reduction would reduce its BSFC and maybe durability advantage. = The total operating cost is certainly significantly less if auto gas can = always be used to refuel. I assumed in my assessment that it will only = be available 50% of the time. The real disadvantage, which I failed to = state, is that the extra fuel required for a given mission might be 5 or = 10% higher and that negated the weight advantage, if only for long-range = flights. =20 Is the engine less expensive? I did a thorough analysis of a = direct-drive recip auto engine installation and my conclusion was that = if the auto engine were equivalent in reliability to the aircraft engine = it would likely cost just as much. Is the same true of the rotary? I'm = not sure, but you have to consider the total cost, including engineering = of all the parts in the system, not just the core engine. I would love = to do a rotary installation, but I don't think I could justify it by = cost reduction. =20 It wasn't mentioned in the posts, but some have claimed the rotary is = "smoother" than a recip. I at first resisted that notion. Sure, any = rotary given sufficient counterbalancing, is perfectly balanced. A = 4-cylinder opposed recip is not - there is a significant secondary = couple. The 6-cylinder opposed engine is perfectly balanced, but only = for PRIMARY and SECONDARY forces and couples - higher order forces have = never really been analyzed, although they would be very small. And then = consider the forces within the engine that have to be resisted by that = long, heavy, but flexible crankshaft. So it isn't the mechanical = balance that gives the rotary an advantage. Let's take a look at the = the torsional pulsations, comparing the 3-rotor against the 6-cylinder: = A 6-cylinder engine has 3 power impulses per rotation, as does the = 3-rotor, so they are the same, right? Wrong. They both incorporate 4 = "stroke" cycles, meaning that there separate and sequential intake, = compression, power and exhaust events so that is the same for both. The = power event, which is the source of the torque impulse, takes 1/2 of a = crank rotation for the recip. In the rotary the power event requires = 1/4 of a ROTOR rotation, but the rotor rotates at 1/3 crank rotation - = the result is that the power impulse lasts 3/4 of a CRANK rotation, 50% = longer than in a recip. Therefore, the torsional excitation delivered = to the propeller, PSRU and to the airframe is significantly less than = for a recip. And if you analyze the actual forces imparted, they go = down by the square of the rpm. The torsional vibration amplitude goes = down by a factor of 4 just because the rpm of the rotary turns about = twice as fast. If you've skipped to the bottom of the paragraph, as you = probably should have :-), yes the rotary is "smoother" - a LOT = smoother.. (my apologies to rotary purists, for simplicity I used the = word "crankshaft" for both engines) =20 But just because you can burn auto gas should you? The biggest = problems with auto gas in recip aircraft have nothing to do with the = engine, but with the high vapor pressure of the fuel - it is more prone = to vapor lock. The fuel systems of certified aircraft are not = particularly well designed with regard to vapor lock. "Fortunately", = rotary engines typically have no mechanical fuel pump and are forced to = rely on electric pumps. Fortunately because the pumps can be located at = the very bottom of the aircraft and close to the fuel tanks, making = vapor lock much less likely. I would caution any builders to consider = vapor lock possibilities very seriously, much more so if you intend to = run auto gas. when I was going to do this I planned to put one electric = pump in the wing root of each wing, feeding the engine directly(the = check valve in the non-running pump prevents back-feeding). Redundancy = was by a "crossfeed" line that could connect the tanks together. =20 And thanks, Mark for - probably incorrectly - referring to me as a = "good engineer". I'll have to put that in my resume! =20 Have a good day, Gary (do you allow us outsiders in your events? I'll park well away :-) =20 __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ------=_NextPart_000_0046_01C9BADA.CDC4E680 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
This has been an interesting thread. In = the end, it=20 doesnt really matter how many "major" parts you have - even a minor = failure can=20 bring you down. While I believe the basic rotary engine itself is more = fault=20 tolerant than a recip, the peripherals used in the typical rotary = install are a=20 lot more complex than a typical recip install. Since we rotary fliers = dont have=20 the benefit of 70 years worth of experience flying behind the typical = LyCon farm=20 implement I think overall our odds are considerably worse. Comes down to = how=20 well an individual engineer's his installation and there is a tremendous = amount=20 of variation here.
 
The dependence on electronics in the = typical rotary=20 install  is a good example. I may be a little sensitive to = this issue=20 since I've been trying to find an intermittent glitch (2 times in 22 = hours of=20 engine testing).
 
Mike Wills
RV-4 N144MW  
----- Original Message -----
From:=20 Ed=20 Anderson
Sent: Saturday, April 11, 2009 = 7:31=20 AM
Subject: [FlyRotary] Gary Casey = was=20 [FlyRotary] Re: Rotary Engines

Good = analysis and=20 logic, Gary.

 

You=92d = make a good=20 addition to the =93rotary community=94.  I have noticed over the = 10 years I=20 have been flying my rotary powered RV-6A that the problems have = decreased=20 considerably, the success rate and completion rate has gone up and = first=20 flights are now occurring without significant problems =96 even = cooling is OK=20 {:>).  I believe most of this improvement can be attributed to = folks=20 sharing their knowledge, problems and solutions with others - such as = on this=20 list. 

 

I know that = fewer=20 parts count is often touted as one of the rotary benefit =96 and while = it is=20 true that the part count is lower, the most significant thing (in my = opinion)=20 is not only does the lower part count help reliability (if it is not = there =96=20 it can not break), but if you look a the design of the eccentric shaft = (for=20 example) you notice the absence of the jogs in a typical crankshaft = and their=20 stress points.  The thing is over 3=94 in diameter at some points = and does=20 not have the same inertia loads born by a piston crankshaft.  The = parts=20 that are there are of very robust design.  Finally, the rotary is = (I=20 believe) more tolerant of damage and tends to fail =93gradually and = gracefully=94,=20 it can take a licking and keep on ticking as the old saying = goes.  Only=20 extended time and numbers will provide the true MTBF for the rotary, = but I=20 believe it looks very promising.

 

Failure of = rotary=20 engines are extremely rare, but unfortunately, as with many = alternative engine=20 installations, auxiliary subsystems such as fuel and ignition = frequently being=20 one-off designs have been the cause of most failures =96 with probably = fuel the=20 prime culprit.  The good news is that for some platforms (such as = the=20 RVs) we have pretty much established what will make an installation=20 successful.  The Canard crowd is fast approaching that status = with their=20 somewhat more challenging cooling requirements being over=20 come.

 

  = Having lost a=20 rotor during flight due to putting in high compression rotors with = worn apex=20 seal slots worn beyond specs (found this out later =96 my fault for = not being=20 aware of this spec limit and checking it) which led to apex seal = failure and=20 consequence lost of most of the power from one rotor, I was still able = to=20 maintain 6500 MSL at WOT and fuel mixture knob to full rich =96 = flowing 14.5 GPH=20 =96 a lot of it undoubtedly  being blown through the disabled = rotor. =20 Flew it back 60 miles to a suitable runway and made a non-eventful=20 landing.   There was a small increase in vibration due to = the power=20 strokes no longer being balanced, but nothing bad and you could still = read the=20 needles on the gauges.  Other folks have had FOD damage to a = rotor and=20 also make it to a safe landing.  Two folks lost cooling (one loss = of=20 coolant fluid , one lost of water pump) and while they did cook the = engines,=20 both made it back to a safe landing.  So all things considered, I = think=20 the rotary continues to show that if the installation is designed = properly, it=20 makes a very viable and reliable aircraft power=20 plant.

 

Failure of = rotary=20 engines in aircraft are extremely rare, but unfortunately, as with = many=20 alternative engine installations, auxiliary subsystems such as fuel = and=20 ignition frequently being one-off designs - have been the cause of = most=20 failures.  The good news is that for some platforms (such as the = RVs) we=20 have pretty much established what will make an installation = successful. =20 The Canard crowd is fast approaching that status with their somewhat = more=20 challenging cooling requirements being over = come.

 

My rotary=20 installation cost me $6500 back in 1996, the primary cost being a = rebuilt=20 engine $2000 and the PSRU $2900.  I have since purchased a 1991 = turbo=20 block engine from Japan for $900 and = rebuilt it=20 myself for another $2200.  My radiators (GM evaporator cores) = cost $5.00=20 from the junk yard and another $50.00 each for having the bungs welded = on.  So depending on how much you buy and how much you build the = price=20 can vary considerably.  Today, I would say it would take a = minimum of=20 around $8000 and more nominally around $10000 for a complete rotary=20 installation in an RV =96 some folks could do it for less, some for=20 more.

 

But, = regardless of=20 the technical merit (or not) in someone=92s mind, the crucial thing = (in my=20 opinion) is you need to address two personal=20 factors:

 

1.  = What is your=20 risk tolerance?  It doesn=92t really matter how sexy some = =93exotic=94 engine=20 installation may seem =96 if you are not comfortable flying behind (or = in front)=20 of it, then it certainly does not  makes sense to go that = route. =20 After all, this is supposed to have an element of fun and enjoyment to = it.

 

2.  = What is your=20 knowledge, experience and background (and you don=92t have to be an = engineer)=20 and do you feel comfortable with the level of involvement=20 needed.

 

So hope you = continue=20 to contribute to expanding our knowledge and understanding of the = rotary in=20 its application to power plant for = aircraft.

 

 

Best=20 Regards

 

Ed

 

 

Ed=20 Anderson

Rv-6A = N494BW Rotary=20 Powered

Matthews,=20 NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.r= otaryaviation.com/Rotorhead%20Truth.htm

From:=20 Rotary motors in aircraft = [mailto:flyrotary@lancaironline.net] On=20 Behalf Of Gary Casey
Sent: Saturday, April 11, 2009 = 8:36=20 AM
To: = Rotary motors in aircraft
Subject: [FlyRotary] Re: Rotary = Engines

 

Just to add a few more comments and answers = to the=20 several excellent comments posted:

 

How many parts does it take to make a rotary = rotate?=20  Well, "parts aren't parts" in this case.  Mark was right in = that=20 there are maybe 4 "major" components, but you have to define major. =  A=20 piston engine certainly has far more major parts.  Is a valve a = "major"=20 part?  I think so.  Is a rotor corner button a major part? =  Not=20 sure, but probably not.  Is each planet gear in the PSRU a major = part?=20  I say yes, and the PSRU is an integral part of the rotary = engine.=20  As someone correctly pointed out, it's not how many parts, but = the=20 reliability of the total system that counts.  Just looking at the = history=20 of the rotary (which, from the implication of another post) it's not = that=20 good, but I don't think it has anything to do with reliability of the = concept.=20  It's more to do with the experimental nature of the builds and=20 installations.  My original point, perhaps not well expressed is = that to=20 say there are just 4 parts is an oversimplification.  But let's = face it,=20 to put in an engine that has had many thousands of identical = predecessors is=20 less "experimental" than one that = hasn't..

 

Are we ES drivers more conservative? =  Probably=20 so, since the ES is probably one of the experimentals most similar to=20 production aircraft, and not just because the Columbia (can't force myself to say = Cezzna=20 :-) was a derivative.  Therefore, it tends to attract = conservative=20 builders and owners.  Not surprising then that almost all ES's = have=20 traditional powerplants, with the most excellent exception of Mark.=20  While there may be more, I know of only two off-airport landings = caused=20 by engine failures in the ES in almost 20 years of experience. =  One was=20 caused by fuel starvation right after takeoff (fatal) and one was = caused by a=20 PSRU failure in an auto engine conversion.  So our old-fashioned=20 conservative nature has served us pretty=20 well.

 

Yes, I was assuming that the rotary had = electronic=20 fuel injection and ignition, but that by itself doesn't change the = inherent=20 fuel efficiency of the engine.  Direct injection does have a = potential to=20 improve BSFC because the fuel charge can be stratified.  It will = probably=20 decrease available power, though.  I think the best rotary will = be 5%=20 less efficient than the "best" piston engine(same refinements added to = each).=20  But I stated that as a simple disadvantage - as Mark pointed = out, it=20 isn't that simple.  The rotary already comes configured to run on = auto=20 gas.  The piston engine can also be so configured, but the = compression=20 ratio reduction would reduce its BSFC and maybe durability advantage.=20  The total operating cost is certainly significantly less if auto = gas can=20 always be used to refuel.  I assumed in my assessment that it = will only=20 be available 50% of the time.  The real disadvantage, which I = failed to=20 state, is that the extra fuel required for a given mission might be 5 = or 10%=20 higher and that negated the weight advantage, if only for long-range=20 flights.

 

Is the engine less expensive?  I did a = thorough=20 analysis of a direct-drive recip auto engine installation and my = conclusion=20 was that if the auto engine were equivalent in reliability to the = aircraft=20 engine it would likely cost just as much.  Is the same true of = the=20 rotary?  I'm not sure, but you have to consider the total cost, = including=20 engineering of all the parts in the system, not just the core engine. =  I=20 would love to do a rotary installation, but I don't think I could = justify it=20 by cost reduction.

 

It wasn't mentioned in the posts, but some = have=20 claimed the rotary is "smoother" than a recip.  I at first = resisted that=20 notion.  Sure, any rotary given sufficient counterbalancing, is = perfectly=20 balanced.  A 4-cylinder opposed recip is not - there is a = significant=20 secondary couple.  The 6-cylinder opposed engine is perfectly = balanced,=20 but only for PRIMARY and SECONDARY forces and couples - higher order = forces=20 have never really been analyzed, although they would be very small. =  And=20 then consider the forces within the engine that have to be resisted by = that=20 long, heavy, but flexible crankshaft.  So it isn't the mechanical = balance=20 that gives the rotary an advantage.  Let's take a look at the the = torsional pulsations, comparing the 3-rotor against the 6-cylinder: =  A=20 6-cylinder engine has 3 power impulses per rotation, as does the = 3-rotor, so=20 they are the same, right?  Wrong.  They both incorporate 4 = "stroke"=20 cycles, meaning that there separate and sequential intake, = compression, power=20 and exhaust events so that is the same for both.  The power = event, which=20 is the source of the torque impulse, takes 1/2 of a crank = rotation for=20 the recip.  In the rotary the power event requires 1/4 of a ROTOR = rotation, but the rotor rotates at 1/3 crank rotation - the result is = that the=20 power impulse lasts 3/4 of a CRANK rotation, 50% longer than in a = recip.=20  Therefore, the torsional excitation delivered to the propeller, = PSRU and=20 to the airframe is significantly less than for a recip.  And if = you=20 analyze the actual forces imparted, they go down by the square of the = rpm.=20  The torsional vibration amplitude goes down by a factor of 4 = just=20 because the rpm of the rotary turns about twice as fast.  If = you've=20 skipped to the bottom of the paragraph, as you probably should have = :-), yes=20 the rotary is "smoother" - a LOT smoother.. (my apologies to rotary = purists,=20 for simplicity I used the word "crankshaft" for both=20 engines)

 

But just because you can burn auto gas = should you?=20  The biggest problems with auto gas in recip aircraft have = nothing to do=20 with the engine, but with the high vapor pressure of the fuel - it is = more=20 prone to vapor lock.  The fuel systems of certified aircraft are = not=20 particularly well designed with regard to vapor lock. =  "Fortunately",=20 rotary engines typically have no mechanical fuel pump and are forced = to rely=20 on electric pumps.  Fortunately because the pumps can be located = at the=20 very bottom of the aircraft and close to the fuel tanks, making vapor = lock=20 much less likely.  I would caution any builders to consider vapor = lock=20 possibilities very seriously, much more so if you intend to run auto = gas.=20  when I was going to do this I planned to put one electric pump = in the=20 wing root of each wing, feeding the engine directly(the check valve in = the=20 non-running pump prevents back-feeding).  Redundancy was by a = "crossfeed"=20 line that could connect the tanks = together.

 

And thanks, Mark for - probably incorrectly = -=20 referring to me as a "good engineer".  I'll have to put that in = my=20 resume!

 

Have a good = day,

Gary

(do you allow us outsiders in your events? =  I'll=20 park well away :-)

 




__________ Information from ESET = NOD32=20 Antivirus, version of virus signature database 3267 (20080714)=20 __________

The message was checked by ESET NOD32 = Antivirus.

http://www.eset.com

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