More car gas is polluted with alcohol nowadays because the distributors don't always want to maintain separate facilities for everything, even where alcohol is not required in fuel, it can be easier for them to just sell it anyway.  Of course if you have an airport selling mogas it won't have alcohol but if you self fuel from the local gas station you may find there is alcohol even if your state doesn't mandate it.  Would be good to double check.

Since the rotary runs perfectly fine in cars with alcohol, so long as your fuel tanks and plumbing can handle it without falling apart, you shouldn't have a problem.  Alcohol may have a bit less power but not enough to be unsafe.  Important thing for combustion properties is the octane of the fuel which alcohol does not reduce.

Rumors of alcohol causing frozen fuel are just FUD.  No one has ever seen it happen and the chemistry does not make it particularly likely.  Ethanol freezes at -114C!

On Wed, Mar 4, 2009 at 5:21 AM, Mark Steitle <msteitle@gmail.com> wrote:

Mike,

 

I agree with you that some of the Lycomings can burn mogas, but few actually do it.  I belong to the Lancair list and they are constantly debating how to (or not to) run their engines so as to not damage them.  Most are just plain scared to run their engines lean of peak where they are able to get close to the "advertised" bsfc.  They're willing to burn more fuel in order to sleep better at night.  But the rotary is designed to run on mogas.  So, why not do it?  Alcohol and possible vapor lock are the only issues I know of, and with a properly designed EFI fuel system, vapor lock isn't an issue.  As long as they don't start blending alcohol in the fuel in my neck of the woods, I'll keep burning mogas and pocketing the difference. 

 

You stated, "But really the biggest motivation was to do something a little different."  As for that statement... I couldn't agree more, but how do you quantify something like that?  And I believe that it isn't just different, but in a lot of ways the rotary is definitely better.   

Mark S.

On Tue, Mar 3, 2009 at 9:55 PM, Mike Wills <rv-4mike@cox.net> wrote:

Glad I woke you guys up! :-)

 

While it may appear from my post that I was trying to discourage this guy and am not happy with my rotary powered airplane that is not the case. I'm very happy with it. Will be even happier once I get all of the little glitches fixed so I can just fly it.

 

 I simply wanted to make sure William understands what he's getting into. What appears to be a fairly straight forward mod is a lot more complicated than it appears and there are potential pitfalls that are not necessarily obvious.

 

 My bad on the misread regarding fuel efficiency - he was talking about homebuilt aircraft versus factory built planes, not rotaries versus certified engines. I think he's still way off base here which was why I replied to his post.

 

 Al, I dont know anyone who actually KNOWS what BSFC they acheive with their Lyc/Cont. I know that low .40s is a published number that is stuck in my head. I know what kind of fuel consumption I got with my Lyc powered RV-6A at cruise and I know there are certainly enough flying Lyc powered RVs to pretty firmly establish a cruise performance baseline. Since there are more flying rotary powered RVs than other types, seems like we should be able to get at least an idea of how they compare. Lets challenge the rotary RV fliers here to post real cruise performance (altitude, TAS, fuel consumption) and answer the question. Or give me a year and 100 hours and I'll let you know how my RV-4 stacks up against the -6A for a data point.

 

 As for your performance against conventional powered Velocities, thats great news. I think thats one of the significant short comings of our little group here. Common perception is that rotaries are gas hogs and we dont do anything to accurately document and advertise our performance.

 

 Mark, I agree that burning Mogas definitely makes a big difference economy-wise. But that's a red herring. You could legally burn Mogas in a Lyc/Cont also - just that most guys who are too conservative to choose an auto conversion are also too conservative to burn Mogas. Burning Mogas isnt the exclusive territory of the rotary. I personally know a guy with a 200HP Lyc in an RV-8 who has burned Mogas exclusively for years. Really what it comes down to is convenience and comfort. Lets be fair, compare apples to apples, and while we're at it throw in the additional cost and hassle of having to pour in 2 stroke oil for your rotary (assuming you do that as most seem to do).

 

 I do totally agree with you on the price of parts. And that was one of my huge motivations for going this route. But really the biggest motivation was to do something a little different. When my RV-4 finally makes it's appearance at a fly-in (hopefully this year) it's not going to be lost in the sea of belly button RVs that show up.

 

Mike Wills

RV-4 N144MW

 

 

----- Original Message -----

From: Al Gietzen

To: Rotary motors in aircraft

Sent: Monday, March 02, 2009 9:51 PM

Subject: [FlyRotary] Re: Questions on buying a rotary plane

 I dont know where you got the idea that rotaries are more fuel efficient. Lycosaurs/Continentals typically have BSFCs in the low .40s. The commonly accepted number for a rotary is about .50. Some here seem to do better, others worse.

 

Mike;

 

I’m not disagreeing with the points in your message; but I am wondering if you know anybody actually flying a Lyc/Cont and achieving BSFC in the low 40’s.  I see numbers like .43 or .45 bandied about, but I guess no one leans enough when flying to get that for fear of burning out a valve – or worse.  I’ve yet to hear from anyone flying a Velocity like mine with a Lyc who can surpass the speed/fuel burn that I get with the 20B. I don’t know why – it surprised me; but there it is.

 

I think in the real world operation the BSFCs are comparable.  I may have a bit lower drag because of smaller cowl; or other factors.

 

Al