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

From: Mike Wills

To: Rotary motors in aircraft

Sent: Wednesday, March 04, 2009 10:14 PM

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

Dave,

 

 I remember looking at this when you posted about it previously. Not sure a race is quite what I had in mind, but better than nothing. I think documented performance numbers at typical cruise configurations would be more useful. Cant argue with your bang for the buck numbers - one of the primary reasons I went rotary as well. I still dont think it's fair to claim an economy victory based on the price/use of Mogas because you CHOOSE to burn it and your Lyc powered RV buddies CHOOSE not to.

 

 I dont know about you guys but the typical questions/comments are:

 

1) It will weigh more than a Lyc powered RV (in my case true).

2) It will be slower and climb slower than a Lyc powered RV (the jury is out in my case).

3) Those rotaries burn more gas than an aircraft engine.

4) You're crazy to fly behind a car engine.

 

My responses to 1 and 2 are maybe, to 3 is it varies depending on how its operated. My response to 4 depends on my mood and how the comment is made.

 

Anyway, it would sure be nice if a number of guys flying did as good a job of documenting and advertising their performance as they do documenting their build process. There are enough flying now to have some statistical relevance. I'd like to be able to point to a website when someone quizzes me on performance.

 

Mike

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

From: David Leonard

To: Rotary motors in aircraft

Sent: Tuesday, March 03, 2009 9:12 PM

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

Hey Mike,

I have done such a real world direct comparison. 

We did a race where where were filled tanks before and after to compare fuel burn as well as speed.  Scroll down here to see the results:
http://www.rvproject.com/race.html

Bear in mind:
1) the fastest 2 planes were tandem, and had an advantage.
2) the slowest 2 planes were trying to win the efficiency contest rather than the speed contest.

Of the 5 remaining planes, mine was right in the middle in terms of speed and fuel burn.  All other planes were 180 or 200 hp lycs with c/s props.  I had the only f.p. prop and my installation cost at least $15k less than any of the others.  Because I was the only one able to use MOGAS, my fuel cost were the cheapest (of the non-economy flight profile group).

Bottom line: the rotary proved to be very comparable in terms of power and fuel burn. (as others have noted).
---------
I now have 370 hours and almost never remove the cowl anymore.  I fly it hard and put it away wet.  I have not had an engine or engine systems issue in nearly 200 hrs. 

Compare that the the first 100 hrs where I was putting in almost 10 hrs of maintenance for each our of flying and she has really come a long way.

Way worth it!

--
David Leonard

Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net

On Tue, Mar 3, 2009 at 7:55 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