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ryanjames170

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so i was talking to my cousin the other day about the airplane idea.. and we came up with the idea of what if you ditched trying to find a 30HP V twin and went for a 2 engines of lower HP to power it..

could something like this work? i know there would be more support for getting HP out of smaller engines but most non 2 stroker engines are splash lube.
 

pictsidhe

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twin engines worked for the lazair. I was planning on twins for my flying wing.
Splash lube has its pros and cons, do you dislike the lack of cooler?
 

blane.c

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I love the multi engine concept! Big fan!

Lets expand on that? Why only 2 engines? Why not 3 or more?
 

Dana

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As mentioned above the Lazair had two engines, as did the Kolb Flyer which had two 15HP Solo engines. Homer Kolb also built a 4 engined ultralight, with I think 9HP engines. All were 2-strokes.
 

lr27

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I think the OP was talking about 4 strokes. I don't know much about it, but the Home Depot Plane had two 4 strokes. The V-twins do seem to be heavy. A further advantage is that most of the smaller engines run at the same 3600 rpm, so you can get more prop disk area with the same tip speeds.
 

cluttonfred

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Keep in mind that, at least in the USA, the multi-engine approach leads to all sorts of complications once you get beyond a Part 103 ultralight. I don't know that there are any four-stroke engines with the power you'd need (at least 2 x 10 hp) that would come in light enough for ultralight use.
 

pictsidhe

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10hp is not unreasonable for the 200cc industrial engines. Karters tune them to over 20, but I wouldn't want to try that. 15 might work. Harbor freight sells quite reasonable ones for $99, so they are very affordable to experiment with.
 

lr27

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I think a 1/2 VW weighs 90 lbs, and people use that. The "Big Twin" is supposed to weigh 120 lbs! I imagine two 10 hp 4 strokes could be less than that. Maybe a lot less if you use some kind of souped up go-kart or lawn mower tractor pull engine. However, it's hard to find the real weight, and even harder to find what the weight is when stripped for aircraft use. For our use, we usually want more torque rather than more rpm, so the mods may be slightly different.
 

Wanttaja

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so i was talking to my cousin the other day about the airplane idea.. and we came up with the idea of what if you ditched trying to find a 30HP V twin and went for a 2 engines of lower HP to power it..
The downside here is that the probability of engine failure just doubled.

Production multiengined aircraft are required to exhibit a certain minimum performance after an engine failure. That's why modern twin jets climb so steeply; with both engines running, they've got scads of excess power.

A Part 103 aircraft doesn't have that requirement, of course. But if you're using two 15 HP engines because you need 30 HP, all that second engine will do is carry the plane to the site of the accident. And, again, since you have two engines, it's twice as likely one will fail.

Ron Wanttaja
 

pictsidhe

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If you are flying at 50', losing an engine could easily br a big deal. With a bit of spare height, well, 15hp is enough for level flight for many ultralights.
 

ryanjames170

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for what its worth guys i do have a 6.5HP HFT engine that i can pull down and look at the weight of.. i know you can maybe ditch 1 or 2 lbs of them threw a aly flywheel..

and pictsidhe is right they do push those 212 predator engines over 20HP alot.. infact its pretty well documented on how to get them to various HP levels becuase of this.. i could weight it with a few parts removed and see what it weighs in at..
 

blane.c

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The downside here is that the probability of engine failure just doubled.

Production multiengined aircraft are required to exhibit a certain minimum performance after an engine failure. That's why modern twin jets climb so steeply; with both engines running, they've got scads of excess power.

A Part 103 aircraft doesn't have that requirement, of course. But if you're using two 15 HP engines because you need 30 HP, all that second engine will do is carry the plane to the site of the accident. And, again, since you have two engines, it's twice as likely one will fail.

Ron Wanttaja
Prove by mathematical probability that it is twice as likely that one will fail. I triple dog dare you. No self respecting man can turn down a triple dog dare!
 

lr27

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Seems like there are some cases, I don't know how many, where having two engines won't increase the chance of failure. For instance, really bad fuel, carb icing, etc. Anyway, if you have a 500 lb ultralight going along at 50 feet per second, and only getting an L/D of 6:1, and 15 shaft horsepower, you'll climb if your prop is more than 50 percent efficient. Not necessarily very fast! I think I calculated around 80 fpm for 60 percent. OTOH, if you get 12:1, then, even with the crappy prop, you could climb around 250 fpm. A hot day would make things worse. I could have messed up some of these numbers, but they seem reasonable.
 

blane.c

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If you are flying at 50', losing an engine could easily br a big deal. With a bit of spare height, well, 15hp is enough for level flight for many ultralights.
I have lost engines on the takeoff roll, continued take off, I am here without further incident.
 

poormansairforce

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I think a 1/2 VW weighs 90 lbs, and people use that. The "Big Twin" is supposed to weigh 120 lbs! I imagine two 10 hp 4 strokes could be less than that. Maybe a lot less if you use some kind of souped up go-kart or lawn mower tractor pull engine. However, it's hard to find the real weight, and even harder to find what the weight is when stripped for aircraft use. For our use, we usually want more torque rather than more rpm, so the mods may be slightly different.
For reference, the Predator 212cc engine can be stripped to be less than 30 lbs direct drive. Maybe less than 25 lbs if needed. My son put one on his go kart so I was "examining" it;) Runs great.
 

blane.c

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for what its worth guys i do have a 6.5HP HFT engine that i can pull down and look at the weight of.. i know you can maybe ditch 1 or 2 lbs of them threw a aly flywheel..

and pictsidhe is right they do push those 212 predator engines over 20HP alot.. infact its pretty well documented on how to get them to various HP levels becuase of this.. i could weight it with a few parts removed and see what it weighs in at..
Weigh it! Hp to weight is all that matters. Hp to cc or ci doesn't mean a thing it is hp to weight that matters everything else is BS.
 
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