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  #1  
Old 01-25-2010, 03:33 PM
viper2fly viper2fly is offline
 
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Location: Willmington Island, GA
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Question Rotax in an RV-8?

Hey all,

This is probably a huge newbie question, but here goes...

Is it possible/practical to use a Rotax engine (unsure of model) in an RV8 that would give you similar (if not better) performance as comparible to the IO-360 that seems typical? Is it more cost effective? I am sure that as with most things there are many pros and cons from ethier side of the fence.

My curiosity was peaked when I saw an FPNA (Float Planes and Amphib"s) Cape Town (granted light sport catagory and all) that was getting some incredible performance with (usually cheaper) MoGas, and was informed that they have a 6 cyl. model that might be an attractive option.

I realize that I may be putting the cart way before the horse here as I am still trying to find a way to fund my entry into this amazing world of RV's.

Thanks you in advance for your time and replies!

Keith G.
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  #2  
Old 01-25-2010, 04:37 PM
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BikePilot BikePilot is offline
 
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Location: Cambridge MA
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Default

I'm also just an RV-wanna-be, but I don't believe there are any rotax aircraft engines suitable for the RV8. The most powerful I know of is the 914 that makes 115hp and weighs under 200lbs IIRC. You would need a very long engine mount to get the weight and balance correct.

The performance would be quite terrible I fear. Even with less weight, going from 200hp down to 115 isn't going to provide very satisfactory results.

If you want a rotax powered RV, the RV-12 is the plane for you

I've never seen a 6-cyl rotax production aircraft engine. I also didn't see one listed in the kitplanes directory. Perhaps you are thinking of the 6-cyl jabiru? If so, the same applies as its only 120hp. Jabiru did make an 8-cyl that has on rare occasion found its way into an RV, though I think there have been some issues with it and am not sure it is currently in production.

You can build a lyc to run on mogas without problems. The general rule of thumb is a compression ratio of 9:1 or less. With the new IO-390 from lyc you can run mogas and still make all the power the airframe was designed for.
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Last edited by BikePilot : 01-25-2010 at 04:41 PM.
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  #3  
Old 01-25-2010, 06:05 PM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Default low aspect ratio wing needs more power

The basic problem is that the low aspect ratio wing is not efficient enough to get by with such low power. You might look at the RV-9 as a possibility - I think it would be OK with 115 hp.

Otherwise, for the -8, you better find an engine with at least 160 hp.
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  #4  
Old 01-25-2010, 06:08 PM
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Geico266 Geico266 is offline
 
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Quote:
Originally Posted by scsmith View Post
The basic problem is that the low aspect ratio wing is not efficient enough to get by with such low power. You might look at the RV-9 as a possibility - I think it would be OK with 115 hp.

Otherwise, for the -8, you better find an engine with at least 160 hp.
Since we are brain storming here and you are an AE how about a -8 twin? Twin Rotax 912S 100HP? The wings are not really designed to handle that kind of weight. Obviously, this would require some serious mods.
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Last edited by Geico266 : 01-27-2010 at 10:44 AM.
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  #5  
Old 01-25-2010, 07:11 PM
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Lionclaw Lionclaw is offline
 
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If you're going to mention a twin engine rv-8 then we might as well go back to talking about an f-82 style mod
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  #6  
Old 01-25-2010, 07:52 PM
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MSFT-1 MSFT-1 is offline
 
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Default There is actually an airplane out there like this

It's called a Tecnam P2006T.

It uses two Rotax 912s (100hp each). Runs on Mogas and cruises at 145kts on 10gph.

Italian built, mostly composite and certified. $500k I think.

There is one at a local airport here in VA.
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  #7  
Old 01-25-2010, 07:59 PM
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N941WR N941WR is offline
 
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Besides the expected poor performance from that small HP number on a plane designed for between 150 to 200 hp, there is that CG thing you have to think about.

There is a thread on here about putting that engine on an RV-3 (designed for 108 to 160 hp) and the rough calculation was that the engine mount would have to be extended another 20".

Keep dreaming, that?s how new designs come about.

For comparison, look at the T51 Mustang. It is about the same size as the -8 but runs the Rotax engine.
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  #8  
Old 01-25-2010, 09:22 PM
viper2fly viper2fly is offline
 
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Location: Willmington Island, GA
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Default TWIN RV8...excellent idea!!!!!

Hey Y'all,

I am always amazed at the amount of knowledge that exisits in the RV community...I am humbled...

I am no where near an aeronautical engineer, and I have very limited experience in this area...so I intend to spend some time leaning on the kind folks in these forums. Thank you!

Keith G.
RV8 or maybe RV10 Wanna be builder!
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  #9  
Old 01-26-2010, 10:19 AM
aerhed aerhed is offline
 
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Location: Big Sandy, WY
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Default Comanchero!

I have a friend that started a twin 8 with twin comanche wings/gear. He ran some computer modeling that said it would work, so he bought wings & such and started cutting off the spars. And there it sits. Anyone need a pair of T-commie wings with short spars? He really did have some nice drawings though.
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  #10  
Old 01-27-2010, 10:40 AM
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osxuser osxuser is offline
 
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Default

Now that sounds cool.

I'd rather have the TwinCo, but if you just had stub wings, with a rocket or -8 fuse, and retractable gear...


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