X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail-ew0-f167.google.com ([209.85.219.167] verified) by logan.com (CommuniGate Pro SMTP 5.2.13) with ESMTP id 3578055 for flyrotary@lancaironline.net; Sun, 12 Apr 2009 07:46:01 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.85.219.167; envelope-from=msteitle@gmail.com Received: by ewy11 with SMTP id 11so2558480ewy.19 for ; Sun, 12 Apr 2009 04:45:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=aqCp4qHpzWif8BpAxneNhq0wzazkGhzCPv8JxokQitM=; b=Sb7um0CjDsgu/Ftw39GbG/+idELkT5lmfs7MzIZ6IrtfRV68OCfKs+MxENl0FNmgyf tTAKLvg2v7Z5QJeZaMIV8pz+ucA7mUHho9LBmTQaF4hu11dpKkcGciRu7rsveEjsOhGX Ql3DzkZR+f4+qbXqJIrRSoYTLkJPycokaaFoo= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=qr8GryIAzIezeK8YYc3jaf09hgM7CXCoYwAyfBOJi6R2sqBNGkl05/uxei5EIZd8ut 4736koJA9v0aCxHJRIS6DY9uE0jDtYnyO1fPzN/wniPpuYP5/s1Wns0d/9lKS+E1DmpB xO57GvlD6Or7vKfjpCP5KBe0lFow6H6u2/K4A= MIME-Version: 1.0 Received: by 10.210.111.17 with SMTP id j17mr4457857ebc.22.1239536724281; Sun, 12 Apr 2009 04:45:24 -0700 (PDT) In-Reply-To: References: Date: Sun, 12 Apr 2009 06:45:24 -0500 Message-ID: <5cf132c0904120445q1a3998c9w678e34421b85cf6@mail.gmail.com> Subject: Re: [FlyRotary] Re: Gary Casey was [FlyRotary] Re: Rotary Engines From: Mark Steitle To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=0015174c3fc2230ca304675a22a1 --0015174c3fc2230ca304675a22a1 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Mike, Has anyone ever tried to document the rotary incidents resulting in a force= d landing? Here's what I recall from memory, so it likely is missing a few; 3 forced landings due to ruptured oil coolers 1 forced landing due to apex seal coming out of its slot (rotor out of spec) 1 forced landing due to improper assembly of engine (seal wedged betwee= n rotor & side housing) 1 forced landing on highway due to catastrophic overheating of engine 2 forced landings (one fatal) due to probable fuel system design flaw 1 forced landing on highway due to ingestion of FOD. There were a few others, such as turbo failures which allowed for continued operation at reduced power, so we may or may not wish to include those here. While a number of these incidents date back quite a few years, and we have made excellent progress, it says to me that we still have room for improvement in the peripheral department. The good news is that out of all of the incidents listed above, none of them were caused by a true engine failure. That's where the rotary has really earned my respect as a viable a/c engine. Pay attention to the details! Mark S. On Sat, Apr 11, 2009 at 9:22 PM, Mike Wills wrote: > 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 tha= n 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 th= e > benefit of 70 years worth of experience flying behind the typical LyCon f= arm > 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 > > ----- Original Message ----- > *From:* Ed Anderson > *To:* Rotary motors in aircraft > *Sent:* Saturday, April 11, 2009 7:31 AM > *Subject:* [FlyRotary] Gary Casey was [FlyRotary] Re: Rotary Engines > > Good analysis and logic, Gary. > > > > You=92d make a good addition to the =93rotary community=94. I have notic= ed 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 gon= e > up and first flights are now occurring without significant problems =96 e= ven > 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. > > > > I know that fewer parts count is often touted as one of the rotary benefi= t > =96 and while it is true that the part count is lower, the most significa= nt > thing (in my opinion) is not only does the lower part count help reliabil= ity > (if it is not there =96 it can not break), but if you look a the design o= f 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=94 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 f= ail > =93gradually and gracefully=94, it can take a licking and keep on ticking= as the > old saying goes. Only extended time and numbers will provide the true MT= BF > for the rotary, but I believe it looks very promising. > > > > 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 =96 with probably fuel the prime culprit. The good news is that= for > some platforms (such as the RVs) we have pretty much established what wil= l > make an installation successful. The Canard crowd is fast approaching th= at > status with their somewhat more challenging cooling requirements being ov= er > come. > > > > 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 = =96 > my fault for not being aware of this spec limit and checking it) which le= d > 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 =96 flowing 14.5 GPH =96 a lot of it undoubtedly being blown t= hrough > 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 th= e > power strokes no longer being balanced, but nothing bad and you could sti= ll > read the needles on the gauges. Other folks have had FOD damage to a rot= or > 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 engin= es, > both made it back to a safe landing. So all things considered, I think t= he > rotary continues to show that if the installation is designed properly, i= t > makes a very viable and reliable aircraft power plant. > > > > 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 - h= ave > been the cause of most failures. The good news is that for some platform= s > (such as the RVs) we have pretty much established what will make an > installation successful. The Canard crowd is fast approaching that statu= s > with their somewhat more challenging cooling requirements being over come= . > > > > 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. Tod= ay, > I would say it would take a minimum of around $8000 and more nominally > around $10000 for a complete rotary installation in an RV =96 some folks = could > do it for less, some for more. > > > > But, regardless of the technical merit (or not) in someone=92s mind, the > crucial thing (in my opinion) is you need to address two personal factors= : > > > > 1. What is your risk tolerance? It doesn=92t really matter how sexy som= e > =93exotic=94 engine installation may seem =96 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. > > > > 2. What is your knowledge, experience and background (and you don=92t ha= ve > to be an engineer) and do you feel comfortable with the level of involvem= ent > needed. > > > > So hope you continue to contribute to expanding our knowledge and > understanding of the rotary in its application to power plant for aircraf= t. > > > > > > Best Regards > > > > Ed > > > > > > 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] *O= n > Behalf Of *Gary Casey > *Sent:* Saturday, April 11, 2009 8:36 AM > *To:* Rotary motors in aircraft > *Subject:* [FlyRotary] Re: Rotary Engines > > > > Just to add a few more comments and answers to the several excellent > comments posted: > > > > 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 pa= rt > of the rotary engine. As someone correctly pointed out, it's not how man= y > 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) i= t's > not that good, but I don't think it has anything to do with reliability o= f > 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 p= ut > in an engine that has had many thousands of identical predecessors is les= s > "experimental" than one that hasn't.. > > > > Are we ES drivers more conservative? Probably so, since the ES is probab= ly > one of the experimentals most similar to production aircraft, and not jus= t > because the Columbia (can't force myself to say Cezzna :-) was a derivati= ve. > Therefore, it tends to attract conservative builders and owners. Not > surprising then that almost all ES's have traditional powerplants, with t= he > most excellent exception of Mark. While there may be more, I know of onl= y > 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 takeo= ff > (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. > > > > 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 becau= se > the fuel charge can be stratified. It will probably decrease available > power, though. I think the best rotary will be 5% less efficient than th= e > "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 ca= n > also be so configured, but the compression ratio reduction would reduce i= ts > BSFC and maybe durability advantage. The total operating cost is certain= ly > significantly less if auto gas can always be used to refuel. I assumed i= n > 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 fo= r a > given mission might be 5 or 10% higher and that negated the weight > advantage, if only for long-range flights. > > > > Is the engine less expensive? I did a thorough analysis of a direct-driv= e > recip auto engine installation and my conclusion was that if the auto eng= ine > were equivalent in reliability to the aircraft engine it would likely cos= t > just as much. Is the same true of the rotary? I'm not sure, but you hav= e > 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 installati= on, > but I don't think I could justify it by cost reduction. > > > > 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 rot= ary > 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 force= s > within the engine that have to be resisted by that long, heavy, but flexi= ble > 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 s= ame > for both. The power event, which is the source of the torque impulse, ta= kes > 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 excitatio= n > delivered to the propeller, PSRU and to the airframe is significantly les= s > 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 do= wn > 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) > > > > 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 w= ith > the high vapor pressure of the fuel - it is more prone to vapor lock. Th= e > fuel systems of certified aircraft are not particularly well designed wit= h > regard to vapor lock. "Fortunately", rotary engines typically have no > mechanical fuel pump and are forced to rely on electric pumps. Fortunate= ly > 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 t= he > engine directly(the check valve in the non-running pump prevents > back-feeding). Redundancy was by a "crossfeed" line that could connect t= he > tanks together. > > > > And thanks, Mark for - probably incorrectly - referring to me as a "good > engineer". I'll have to put that in my resume! > > > > Have a good day, > > Gary > > (do you allow us outsiders in your events? I'll park well away :-) > > > > > > > __________ Information from ESET NOD32 Antivirus, version of virus > signature database 3267 (20080714) __________ > > The message was checked by ESET NOD32 Antivirus. > > http://www.eset.com > > --0015174c3fc2230ca304675a22a1 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Mike,

Has anyone ever tried to document the rotary incidents result= ing in a forced landing?

Here's what I recall from memory, so it= likely is missing a few;
=A0
=A0=A0=A0 3 forced landings due to rupt= ured oil coolers
=A0=A0=A0 1 forced landing due to apex seal coming out of its slot (rotor o= ut of spec)
=A0=A0=A0 1 forced landing due to improper assembly of engin= e (seal wedged between rotor & side housing)
=A0=A0=A0 1 forced land= ing on highway due to catastrophic overheating of engine
=A0=A0=A0 2 forced landings (one fatal) due to probable fuel system design = flaw=A0
=A0=A0=A0 1 forced landing on highway due to ingestion of FOD.= =A0

There were a few others, such as turbo failures which allowed f= or continued operation at reduced power, so we may or may not wish to inclu= de those here.=A0

While a number of these incidents date back quite a few years, and we h= ave made excellent progress, it says to me that we still have room for impr= ovement in the peripheral department.=A0 The good news is that out of all o= f the incidents listed above, none of them were caused by a true engine fai= lure.=A0 That's where the rotary has really earned my respect as a viab= le a/c engine.

Pay attention to the details!

Mark S.


On Sat, Apr 11, 2009 at 9:22 PM, Mike Wills <rv-4mike@cox.net> wr= ote:
This has been an interesting thread. I= n the end, it=20 doesnt really matter how many "major" parts you have - even a min= or failure can=20 bring you down. While I believe the basic rotary engine itself is more faul= t=20 tolerant than a recip, the peripherals used in the typical rotary install a= re 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 ho= w=20 well an individual engineer's his installation and there is a tremendou= s amount=20 of variation here.
=A0
The dependence on electronics in the t= ypical rotary=20 install=A0 is a good example. I may be a little=A0sensitive to this issue= =20 since I've been trying to find an intermittent glitch (2 times in 22 ho= urs of=20 engine testing).
=A0
Mike Wills
RV-4 N144MW=A0=A0
----- Original Message -----
From:=20 Ed=20 Anderson
Sent: Saturday, April 11, 2009 7:31=20 AM
Subject: [FlyRotary] Gary Casey wa= s=20 [FlyRotary] Re: Rotary Engines

Good analysis and=20 logic, Gary.

=A0

You=92d make a good=20 addition to the =93rotary community=94.=A0 I have noticed over the 10 yea= rs 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 i= s OK=20 {:>).=A0 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.=A0

=A0

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 opin= ion)=20 is not only does the lower part count help reliability (if it is not ther= e =96=20 it can not break), but if you look a the design of the eccentric shaft (f= or=20 example) you notice the absence of the jogs in a typical crankshaft and t= heir=20 stress points.=A0 The thing is over 3=94 in diameter at some points and d= oes=20 not have the same inertia loads born by a piston crankshaft.=A0 The parts= =20 that are there are of very robust design.=A0 Finally, the rotary is (I=20 believe) more tolerant of damage and tends to fail =93gradually and grace= fully=94,=20 it can take a licking and keep on ticking as the old saying goes.=A0 Only= =20 extended time and numbers will provide the true MTBF for the rotary, but = I=20 believe it looks very promising.

=A0

Failure of rotary=20 engines are extremely rare, but unfortunately, as with many alternative e= ngine=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 fu= el the=20 prime culprit.=A0 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.=A0 The Canard crowd is fast approaching that status with thei= r=20 somewhat more challenging cooling requirements being over=20 come.

=A0

=A0 Having lost a=20 rotor during flight due to putting in high compression rotors with worn a= pex=20 seal slots worn beyond specs (found this out later =96 my fault for not b= eing=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 1= 4.5 GPH=20 =96 a lot of it undoubtedly =A0being blown through the disabled rotor.=A0= =20 Flew it back 60 miles to a suitable runway and made a non-eventful=20 landing.=A0=A0 There was a small increase in vibration due to the power= =20 strokes no longer being balanced, but nothing bad and you could still rea= d the=20 needles on the gauges.=A0 Other folks have had FOD damage to a rotor and= =20 also make it to a safe landing.=A0 Two folks lost cooling (one loss of=20 coolant fluid , one lost of water pump) and while they did cook the engin= es,=20 both made it back to a safe landing.=A0 So all things considered, I think= =20 the rotary continues to show that if the installation is designed properl= y, it=20 makes a very viable and reliable aircraft power=20 plant.

=A0

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.=A0 The good news is that for some platforms (such as the RVs) w= e=20 have pretty much established what will make an installation successful.= =A0=20 The Canard crowd is fast approaching that status with their somewhat more= =20 challenging cooling requirements being over come.

=A0

My rotary=20 installation cost me $6500 back in 1996, the primary cost being a rebuilt= =20 engine $2000 and the PSRU $2900.=A0 I have since purchased a 1991 turbo= =20 block engine from Japan for $900 and rebuilt it=20 myself for another $2200. =A0My radiators (GM evaporator cores) cost $5.0= 0=20 from the junk yard and another $50.00 each for having the bungs welded=20 on.=A0 So depending on how much you buy and how much you build the price= =20 can vary considerably.=A0 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.

=A0

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

=A0

1.=A0 What is your=20 risk tolerance?=A0 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 =A0makes sense to go that route.=A0=20 After all, this is supposed to have an element of fun and enjoyment to=20 it.

=A0

2.=A0 What is your=20 knowledge, experience and background (and you don=92t have to be an engin= eer)=20 and do you feel comfortable with the level of involvement=20 needed.

=A0

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.

=A0

=A0

Best=20 Regards

=A0

Ed

=A0

=A0

From:= =20 Rotary motors in aircraft=20 [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: [F= lyRotary] Re: Rotary=20 Engines

=A0

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

=A0

How many parts does it take to make a rotary rotate?=20 =A0Well, "parts aren't parts" in this case. =A0Mark was rig= ht in that=20 there are maybe 4 "major" components, but you have to define ma= jor. =A0A=20 piston engine certainly has far more major parts. =A0Is a valve a "m= ajor"=20 part? =A0I think so. =A0Is a rotor corner button a major part? =A0Not=20 sure, but probably not. =A0Is each planet gear in the PSRU a major part?= =20 =A0I say yes, and the PSRU is an integral part of the rotary engine.=20 =A0As someone correctly pointed out, it's not how many parts, but the= =20 reliability of the total system that counts. =A0Just looking at the histo= ry=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 =A0It's more to do with the experimental nature of the builds and=20 installations. =A0My original point, perhaps not well expressed is that t= o=20 say there are just 4 parts is an oversimplification. =A0But let's fac= e it,=20 to put in an engine that has had many thousands of identical predecessors= is=20 less "experimental" than one that hasn't..

=A0

Are we ES drivers more conservative? =A0Probably=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 m= yself to say Cezzna=20 :-) was a derivative. =A0Therefore, it tends to attract conservative=20 builders and owners. =A0Not surprising then that almost all ES's have= =20 traditional powerplants, with the most excellent exception of Mark.=20 =A0While there may be more, I know of only two off-airport landings cause= d=20 by engine failures in the ES in almost 20 years of experience. =A0One was= =20 caused by fuel starvation right after takeoff (fatal) and one was caused = by a=20 PSRU failure in an auto engine conversion. =A0So our old-fashioned=20 conservative nature has served us pretty=20 well.

=A0

Yes, I was assuming that the rotary had electronic=20 fuel injection and ignition, but that by itself doesn't change the in= herent=20 fuel efficiency of the engine. =A0Direct injection does have a potential = to=20 improve BSFC because the fuel charge can be stratified. =A0It will probab= ly=20 decrease available power, though. =A0I think the best rotary will be 5%= =20 less efficient than the "best" piston engine(same refinements a= dded to each).=20 =A0But I stated that as a simple disadvantage - as Mark pointed out, it= =20 isn't that simple. =A0The rotary already comes configured to run on a= uto=20 gas. =A0The piston engine can also be so configured, but the compression= =20 ratio reduction would reduce its BSFC and maybe durability advantage.=20 =A0The total operating cost is certainly significantly less if auto gas c= an=20 always be used to refuel. =A0I assumed in my assessment that it will only= =20 be available 50% of the time. =A0The 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.

=A0

Is the engine less expensive? =A0I did a thorough=20 analysis of a direct-drive recip auto engine installation and my conclusi= on=20 was that if the auto engine were equivalent in reliability to the aircraf= t=20 engine it would likely cost just as much. =A0Is the same true of the=20 rotary? =A0I'm not sure, but you have to consider the total cost, inc= luding=20 engineering of all the parts in the system, not just the core engine. =A0= I=20 would love to do a rotary installation, but I don't think I could jus= tify it=20 by cost reduction.

=A0

It wasn't mentioned in the posts, but some have=20 claimed the rotary is "smoother" than a recip. =A0I at first re= sisted that=20 notion. =A0Sure, any rotary given sufficient counterbalancing, is perfect= ly=20 balanced. =A0A 4-cylinder opposed recip is not - there is a significant= =20 secondary couple. =A0The 6-cylinder opposed engine is perfectly balanced,= =20 but only for PRIMARY and SECONDARY forces and couples - higher order forc= es=20 have never really been analyzed, although they would be very small. =A0An= d=20 then consider the forces within the engine that have to be resisted by th= at=20 long, heavy, but flexible crankshaft. =A0So it isn't the mechanical b= alance=20 that gives the rotary an advantage. =A0Let's take a look at the the= =20 torsional pulsations, comparing the 3-rotor against the 6-cylinder: =A0A= =20 6-cylinder engine has 3 power impulses per rotation, as does the 3-rotor,= so=20 they are the same, right? =A0Wrong. =A0They both incorporate 4 "stro= ke"=20 cycles, meaning that there separate and sequential intake, compression, p= ower=20 and exhaust events so that is the same for both. =A0The power event, whic= h=20 is the source of the torque impulse,=A0takes 1/2 of a crank rotation for= =20 the recip. =A0In the rotary the power event requires 1/4 of a ROTOR=20 rotation, but the rotor rotates at 1/3 crank rotation - the result is tha= t the=20 power impulse lasts 3/4 of a CRANK rotation, 50% longer than in a recip.= =20 =A0Therefore, the torsional excitation delivered to the propeller, PSRU a= nd=20 to the airframe is significantly less than for a recip. =A0And if you=20 analyze the actual forces imparted, they go down by the square of the rpm= .=20 =A0The torsional vibration amplitude goes down by a factor of 4 just=20 because the rpm of the rotary turns about twice as fast. =A0If 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 ro= tary purists,=20 for simplicity I used the word "crankshaft" for both=20 engines)

=A0

But just because you can burn auto gas should you?=20 =A0The biggest problems with auto gas in recip aircraft have nothing to d= o=20 with the engine, but with the high vapor pressure of the fuel - it is mor= e=20 prone to vapor lock. =A0The fuel systems of certified aircraft are not=20 particularly well designed with regard to vapor lock. =A0"Fortunatel= y",=20 rotary engines typically have no mechanical fuel pump and are forced to r= ely=20 on electric pumps. =A0Fortunately because the pumps can be located at the= =20 very bottom of the aircraft and close to the fuel tanks, making vapor loc= k=20 much less likely. =A0I would caution any builders to consider vapor lock= =20 possibilities very seriously, much more so if you intend to run auto gas.= =20 =A0when 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 th= e=20 non-running pump prevents back-feeding). =A0Redundancy was by a "cro= ssfeed"=20 line that could connect the tanks together.

=A0

And thanks, Mark for - probably incorrectly -=20 referring to me as a "good engineer". =A0I'll have to put t= hat in my=20 resume!

=A0

Have a good day,

Gary

(do you allow us outsiders in your events? =A0I'll=20 park well away :-)

=A0




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