Horse Power help!

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Ar2hur

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Oct 10, 2012
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Good idea Dana, I would like to build an airplane with a 20 hp, 4 stroke, 3600rpm , aircooled gasoline engine, that weighs 25 kg.
 

autoreply

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Good idea Dana, I would like to build an airplane with a 20 hp, 4 stroke, 3600rpm , aircooled gasoline engine, that weighs 25 kg.
Ok, that's a good start.

Some random comments. Any 20 HP aircraft will have severe limitations on it's practicalities. Study existing designs to get an idea.

Study and study hard. Some great books were suggested, read one or more of those, they'll give you a better grasp of the how's and what's. Note that none of the suggested books are by any means complex or hard to understand at all.


Get a few flight hours. Essential IMHO before you are capable of deciding what you want.

Decide what you want. Do you want to own an aircraft? Then buy one, homebuilt or not. Wanna build? Build an established design.

You want to design? Prepare for an absolutely massive (and fun) task.

I can wholeheartedly encourage this as a good starter:
http://www.amazon.com/Simple-Science-Flight-Insects-Jumbo/dp/0262513137
 

Head in the clouds

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Before deciding on any particular configuration to build, or kit to buy, for inspiration I suggest having a look at the hundreds (thousands) of different types that exist (or have existed). There used to be an annual publication called something like 'compendium of homebuilt aircraft' (not a Jane's publication) but I can't find any reference to it now.

A very good book worth buying is Berger-Burr's Ultralight and Microlight Aircraft of the World. There are two editions, the second has more in it but the first has a fair bit that isn't in the second. If you only bought one I would buy 2nd edition. It was published in 1986 but not much has changed since then. You can get them used on Amazon for just a couple of bucks each - Amazon.com: ultralight and microlight aircraft of the world, berger burr

Edit - you can also get it used in UK from about GBP4 - http://www.abebooks.com/servlet/SearchResults?isbn=9780854294817&n=100121503
 
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Battson

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Jan 30, 2012
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New Zealand
I think he means "To fly"
with 20hp...:ponder:

PS:Sarcastic are we becoming , young padawans...?
You said it. The tone is so condescending in some cases I'm sureprised our Irish friend came back .... it was post no.4 after all!


For my uneducated additions.... from what you describe, it sounds like you're thinking of building an open-air ultralight trike sort of dealy-o, rather than an enclosed "aeroplane" in the ususal sense?
Unless you're thinking of something very small for "short hops" around a farm paddock, rather than a high-flying all-signing all-dancing recreational aircraft?

What do you want to do in your aircraft? :)
 

wsimpso1

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A couple enthusiastic flight geeks got 12 hp fabic covered canard biplane to lift off, fly higher than the lauch point, and land again using the benifit of a significant headwind. Look it up and you will have a pretty good idea of one end of the spectrum. Well, the engine made 12 hp when it was fresh. Who's airplane? Well, they did invent the controllable airplane as we know it... Grin.
 

Jan Carlsson

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Good idea Dana, I would like to build an airplane with a 20 hp, 4 stroke, 3600rpm , aircooled gasoline engine, that weighs 25 kg.
A glider with motor for take off can, if a lighter one take off safely with 20 hp, Also a light plane like SD-1 SPACEK s.r.o. 23-50 hp
A flying Hammoch will be limited with 20 hp due to high drag.
So it is very much a question about wing span load, and airframe efficiency.

The way you asked in your first posts, is like asking, how high is up?! It is not easy to know how to answer aquestion like that. Be more specific, enjoy this forum and the know how, and not least the humor online here.
 

Erudite Celt

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Oct 14, 2012
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Ulster
Does anyone know how much weight ( of an aircraft, in this case) can a 20 hp engine lift? Approximately how much hp is required to lift up to 200kg. Will be very gratefull. thanks
Hi Ar2hur, you need to factor in the lift coefficient of the wings then multiply that by the wing surface area. If the coefficient/surface area were high enough and the runway long enough a 20hp engine could theoretically lift 6000lbs!
 

proppastie

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Great Zombie thread.....found it as I thought about how 550 ft/lb-sec, for one hp seems like a lot of force.
 

lr27

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As I recall, the recommended power for a Sky Pup was 20 hp. I think it had a two stroke with a redrive. I think that the original probably flew at only 170 or 180 kg. I think a longer wing, a somewhat cleaner design. and a lower geared motor swinging a bigger prop might work ok if you didn't mind flying slowly.
 

Dan Thomas

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There is that picture of a ULF-1 being towed into the air by one actual horse.
Yup, but the enormous losses when one horsepower is put into a propeller it costs so much that no one-HP engine is going to fly a man-carrying airplane. We once did a bunch of calculations to see what HP was required to accelerate a 172 at gross weight to takeoff speed under standard conditions and book distances. 26 HP was the answer, from a 150-HP engine turning at 2450 or so and producing maybe 125 HP. Huge losses to propeller and airframe drag, wheel bearing and tire friction, and so on. Propeller especially, at those low forward speeds. Constant-speed prop would change that.

I once watched an old fellow cruise up the river in an airboat he'd created himself. It was a 12-foot aluminum fishing boat with a stock VW bug engine mounted over the back end with a prop on it. It would have been at least 35 HP, maybe as much as 50, and that boat was hardly moving, barely on plane. If that 35-50 HP had been an outboard driving a water propeller, on the same boat, it would have shot across the water like crazy.

Similary, if the 172's 150 HP engine had been mounted in a 2300-pound car, at full throttle that car would accelerate to 60 MPH a lot faster than the 172. 2300 pounds would be a very light car. We used to have a little 2001 Chev Cavalier, and it weighed 2750 empty, had an engine that developed 150 HP at 5600 RPM (seldom got that much RPM) and it would outrun a 172 like mad even with a couple of people in it and fuel, making it weigh a lot more than 3000 pounds.
 

wsimpso1

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It would be a pretty sickly horse that can only make one horsepower. Folks were interested in telling folks how many horses on a windlass their steam engine would replace, and horses saunter in that kind of work.

As to the losses, a prop wastes no more than about a fifth of the energy available, whether moving air or water. Sounds to me like the airboat had prop way wrong for the job.

The key to flight on low power is low wing loading and low span loading. Yeah, that means slower, but that is it. Once it will fly, the power remaining is available for climb or to go faster...
 
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proppastie

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550 ft-lb is a lever 550 ft long with one lb on the end,...or 1 ft long with 550 lb force on the end. It is hard to wrap my head around that it takes at least 15-20 of that to fly the most minimal of aircraft or PPG. Apparently flying is very inefficient compared to walking or riding a bicycle.
 

wsimpso1

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Actually one horsepower is doing 550 lb-ft of work in a second, such as lifting a 200 lb weight 2.75 feet every second. Last I checked, I could take my 200 pound self up a stairway faster than that.

Ground vehicles with wheels support their own weight mechanically and roll with little drag compared to their weight for low speed operation. Horses or oxen can easily move substantial vehicles on the flat.

Try to make it fly, and the act of holding it aloft consumes power. Somehow you have to drag a foil through the air fast enough that its projected area and speed squared make as much lift as the vehicle weighs. With fixed wings, that also sets the min speed the thing can move. With rotating wings, that sets the min speed the rotors can turn and still fly. That is the price for being airborne. Once you have paid the cover charge, you can add some more power and climb or go faster or both and get some benefit for the cost of running the thing.

Billski
 
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