As some of you may know, I'm a pilot. I'm also building a light sport aircraft. That said, I'm looking for a motor to power it. I went to some experimental aircraft forums and I keep running into people that want to throw cash to the wind. I get advice to buy a Lycoming for $30k or a Rotax for $5k. What I need is a 50 hp engine that has a thrust to weight ratio around 1:2. For example I need a 50hp engine that weights about 100 lbs. A Rotax weighs about 140lbs after the gearbox is on it. Most car engines have a thrust to weight ratio of 1:4 (100hp:400lbs). It's been suggested to me to look at a motorcycle engine. I've been eyeing a BMW R75/5 or R80GS which are both 50hp engines, boxer engines (won't have to try to look around it when I fly), and air cooled. But, I don't know what they weigh. I saw a R80GS on Ebay for around $900. I have a lot of time to shop around as I won't be done with the airframe until spring 2012. I wanted to put a Harley engine in it for their sound but they shake too much. Any advise from the motorcycle crowd would be appreciated.
Motorcycle engine for LSA question
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iparks81
Well-Known Member
your going to need an engine that has high torque at low rpm (you already know this)...you dont want to be spining your prop at over 3000 RPM depending on the pitch/Diameter
I cant name any motors strait off, but look at V-twins (yam SV-650) V4's (Honda VFR) you get most of your power pretty low in the band.
i dont think a sport bike engine (inline 4) would be a good choice at all being that they make their power way up at 10K+...unless you have a big ol gear reduction and that would be a ton of weight.
what sort of HP you looking for ...I know the LSA's are limited to 100hp, are you looking to get every bit of that or a little less?
I went through MMI here in Phx and now im an A&P working at the scottsdale airport ..kinda the best of both worlds
I cant name any motors strait off, but look at V-twins (yam SV-650) V4's (Honda VFR) you get most of your power pretty low in the band.
i dont think a sport bike engine (inline 4) would be a good choice at all being that they make their power way up at 10K+...unless you have a big ol gear reduction and that would be a ton of weight.
what sort of HP you looking for ...I know the LSA's are limited to 100hp, are you looking to get every bit of that or a little less?
I went through MMI here in Phx and now im an A&P working at the scottsdale airport ..kinda the best of both worlds
A while back, I was on a Yamaha forum and a guy came in asking a similar question about snowmobile engines. Could this possibly work? I know you can get a two stroke air cooled engine that might meet your requirements. A centrifugal clutch is a whole lot less weight than a transmission. And I'm sure you could find one pretty cheap, too. You could get a liquid cooled one with more horsepower and torque, but that would cost you a little more weight for a cooling system.
Just a thought.
Just a thought.
motobrewer
I'm no atheist scientist, but...
i wouldn't buy a sportbike engine, as parks said they don't make power until at least 10k.
sv650 motor is a good suggestion.
don't buy a ducati motor, for a variety of reasons.
sv650 motor is a good suggestion.
don't buy a ducati motor, for a variety of reasons.
What I need to do is use a prop speed reduction unit at a 2:1 ratio. I'll have the engine turn at 5000rpm and the prop will turn at 2500 rpm. I need an engine at 50hp at 5000 rpm. The nice thing about a boxer engine is it will be out of my view. The prop will rotate at my center line which will be about mid sternum when I sit. Also, it's a taildragger meaning it sits nose high when taxiing. So, an inline engine will put the cylinders right in front of my face when I taxi. As for using a snowmobile engine, a Rotax 503 is the same engine for the SkiDoo snowmobile. My problem is, Phoenix, AZ doesn't stock a lot of snowmobiles. ;-) But they run about $3-5k. And they're inline and a 2-stroke engine. Two strikes against IMHO. I saw on Wikipedia that the "toaster" (R75/5) weighs about 500lbs. But, that's with weight of the whole bike I need to know how much just the engine weighs. I also am looking for a used engine as it will give me an excuse to get more tools. :-D
Here's something I looking for:
But, I think this is a R100GS at 70hp and direct drive. Meaning that at 2500 rpm, they getting about 50hp. But, you lose the rest of the power curve and pay for it in extra weight that you aren't using. A PSRU solves this by using a smaller engine running at a higher RPM.
But, I think this is a R100GS at 70hp and direct drive. Meaning that at 2500 rpm, they getting about 50hp. But, you lose the rest of the power curve and pay for it in extra weight that you aren't using. A PSRU solves this by using a smaller engine running at a higher RPM.
motobrewer
I'm no atheist scientist, but...
get a yamaha tz250 motor. two stroke, but makes 90hp (at 12k...)
entire bike weights 230lb dry, so i bet the motor is pretty small.
entire bike weights 230lb dry, so i bet the motor is pretty small.
brewingkitty
Well-Known Member
an honda '85 - '87 crx si 1488 cc WITH 5 speed weighs 212 pounds and puts out 100 hp to the wheels.
a honda 450cc twin is around 45 hp and weighs maybe 65 pounds.
a honda 450cc twin is around 45 hp and weighs maybe 65 pounds.
If I remember correctly, BMW engines are setup like boxer engines. I don't know if all of them are, but I do know that a lot of them are. And after a brief search, it looks like there are a lot more inline engines that are horizontal. Maybe one of the smaller displacement engines? I couldn't tell you much about weight, but I would like to think that they are rather reliable engines, which I would think translates well in the aircraft field.
