# Low powered aircraft design

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### Piloot

##### Active Member
Hello! Recently I have been interested in reading about aircraft with incredibly low power requirements. From light wing loading, to huge wing spans, or human power and engine power! I think, because of how much engines cost, affordable flight would be a single seat, low horsepower flying machine. I am thinking of something with less than 8 hp, practical flight is hard, but just getting off the group may be possible.

I had a few ideas with this topic for a few design choices.

An English Electric Wren was able to sustain flight on 3 hp, but needed an assisted launch, but could attain flight on it's own with a 7.5 hp motor. It had a big fuselage shaped like an airfoil, and the wings thinned out as they went, but the wingspan was around 37-40 feet. This aircraft is ultralight.
I was thinking if there would be a low power design based on the Wren, it would use insulation foam for fuselage or wing ribs.(Like Skypup)

The next design is a Skycraft Scout lookalike. A monoplane with thin aluminum ribs(what is the specific name for these?) covered in sailcloth, but a simple A Frame like pilot cage with a beam or tube serving as the connection point for the A Frame, Wings, Tail Surfaces, and tail skid/wheel. The original Skycraft Scout used exactly 8 HP aswell.

Finally, this one was sort of tried, but with 12 Horsepower. A biplane low wing loading boxkite pusher akin to the Whing Ding. I was thinking of a wood and foam fuselage with foam ribs and a ladder-like spar structure.

Give any inputs, for a better design choice, or how marginal marginal performance will be with such little power, or maybe considering a blimp type machine, or how rolling the airplane down a steep hill would work.

Have fun!

#### Victor Bravo

##### Well-Known Member
HBA Supporter
Look into the Debreyer Pelican, an incredible airplane which Nestofdragons has so kindly provided a tremendous amount of information for on his fabulous website.

The original wooden version flew successfully with 9HP. But that is not the important part... Debreyer's triumph was to achieve this with a compact, completely usable aircraft instead of a 60 foot span ultra-light kite that would not be a usable airplane. Debreyer's Pelican is an aircraft that can be operated "normally" from a "normal" airfield, while flying on low power and low fuel consumption. THAT is a tremendously noteworthy achievement.

So although it is possible to create an ultralight motorglider that can maintain level flight on 3 or 5HP, the Pelican would allow you to fly in this realm every week, under realistic conditions, and go for the fabled $100 hamburger. Pursuing flight on 2 or 3 HP, using$500K in exotic materials and requiring an entire university for support.... that has been done already. Being able to do it yourself, on any given Saturday, is the last worthwhile frontier.

#### Jon Ferguson

##### Well-Known Member
Look into the Debreyer Pelican, an incredible airplane which Nestofdragons has so kindly provided a tremendous amount of information for on his fabulous website.

The original wooden version flew successfully with 9HP. But that is not the important part... Debreyer's triumph was to achieve this with a compact, completely usable aircraft instead of a 60 foot span ultra-light kite that would not be a usable airplane. Debreyer's Pelican is an aircraft that can be operated "normally" from a "normal" airfield, while flying on low power and low fuel consumption. THAT is a tremendously noteworthy achievement.

So although it is possible to create an ultralight motorglider that can maintain level flight on 3 or 5HP, the Pelican would allow you to fly in this realm every week, under realistic conditions, and go for the fabled $100 hamburger. Pursuing flight on 2 or 3 HP, using$500K in exotic materials and requiring an entire university for support.... that has been done already. Being able to do it yourself, on any given Saturday, is the last worthwhile frontier.
The Debreyer Pelican is a very intriguing little plane. I would like to learn more about it.

#### Riggerrob

##### Well-Known Member
Have you read any of Alex Strojnik's 3 books on low-powered, Laminar airplanes?
Strojnik's various designs were mostly single or 2-seater tandem motor gliders that climbed with tiny engines. He also suggests numerous ways to simplify construction while retaining smooth flying surfaces.

#### Victor Bravo

##### Well-Known Member
HBA Supporter
The Debreyer Pelican is a very intriguing little plane. I would like to learn more about it.
Koen's website has a large amount of information on this aircraft. Also, the Pelican has been built as a wooden prototype, a composite second prototype, and there have been additional variants built or planned ("Vampyr") by someone named Michel Mangenot.

Again, Koen will know far more about these later developments than most of us. But I believe it is safe to say that the majority of the Fauvel derivative aircraft, which includes the Pelican, are shown to be safe and sane aircraft with good basic flight characteristics. In other words, if you built a Pelican you would have a good, safe, and usable aircraft... your time and money will not have been wasted.

For whatever its worth, the Pelican is also a potentially good candiate for sheet metal construction if you wish to take advantage of what sheet metal offers. This obviously also holds true for using the modern carbon fiber pulltrusion strips to lighten or strengthen the composite or wooden versions.

A reasonably light Pelican using one of today's better 20-25HP paramotor engines would be a very capable efficiency/economy flyer. Four or more of these aircraft could share one medium size hangar. You could buzz around all afternoon on five or six gallons of gas.

#### larr

##### Well-Known Member
Hmmm ... going in another direction, what about something like the Klemm KL 20? 2 seater, 20 H.P.
this is the one that crossed the Alps.

#### Jon Ferguson

##### Well-Known Member
I checked out the page on Koen's site VB. I emailed him regarding plans. I would like to study them.

#### Riggerrob

##### Well-Known Member
Piuma motor gliders

#### Piloot

##### Active Member
Thanks for all the stuff! These are really helpful resources!

In stead of those expensive, easily crash able, human powered designs that are really impractical, but low horsepower, I was thinking of something that is a small airplane, most likely an Ultralight, that uses a low amount of force to get aloft.

A lot of pioneer era aircraft exemplify this kind of philosophy.

The Percy Pilcher Flying Machine was never built, but a recreation of this triplane aircraft was made, and it managed to make flights out of just four horsepower!
There is a whole documentary on the machine, and the man behind it.

Next, is the Matthew Bacon Sellers II airplane. A crazy looking Quadruplane that managed to attain flight with just 6 Horsepower! Really a strange design, and if the top wing would stall or something, there would be some nasty surprises for the pilot!

Matthew B Sellers matthewbsellers.com

Thanks again for all the stuff, but these airplanes are sort of the vane of aircraft I think are low power. I mean, these guys did not have foreign materials, or huge overinflated budgets, they were just guys who wanted to fly! That is what I like about pioneer aviation, I love all of those crazy looking airplanes. The people who built all these planes were homebuilders, from Walden, A dentist in New York, or two Bicycle Salesmen in Dayton, Ohio. The name of the game of the time was to test and try to fly, and because of no set example on what is the most efficient design, all these innovators were just making planes based on a few principles, which led to all those crazy looking Flying Machines.

##### Well-Known Member
Hello! Recently I have been interested in reading about aircraft with incredibly low power requirements. From light wing loading, to huge wing spans, or human power and engine power! I think, because of how much engines cost, affordable flight would be a single seat, low horsepower flying machine. I am thinking of something with less than 8 hp, practical flight is hard, but just getting off the group may be possible.

I had a few ideas with this topic for a few design choices.

An English Electric Wren was able to sustain flight on 3 hp, but needed an assisted launch, but could attain flight on it's own with a 7.5 hp motor. It had a big fuselage shaped like an airfoil, and the wings thinned out as they went, but the wingspan was around 37-40 feet. This aircraft is ultralight.
I was thinking if there would be a low power design based on the Wren, it would use insulation foam for fuselage or wing ribs.(Like Skypup)

The next design is a Skycraft Scout lookalike. A monoplane with thin aluminum ribs(what is the specific name for these?) covered in sailcloth, but a simple A Frame like pilot cage with a beam or tube serving as the connection point for the A Frame, Wings, Tail Surfaces, and tail skid/wheel. The original Skycraft Scout used exactly 8 HP aswell.

Finally, this one was sort of tried, but with 12 Horsepower. A biplane low wing loading boxkite pusher akin to the Whing Ding. I was thinking of a wood and foam fuselage with foam ribs and a ladder-like spar structure.

Give any inputs, for a better design choice, or how marginal marginal performance will be with such little power, or maybe considering a blimp type machine, or how rolling the airplane down a steep hill would work.

Have fun!
Wrong premise. Light engines, still powerful enough to fly a plane are expensive. It also requires complex (many hours of build time) structures.

The Archeopterix or the Swift are good examples of this. Both have excellent performance on 10 hp, but are very expensive due to all the labor.

IMHO you'd be better off with more power and a simpler airframe, because that's a cheaper way to get into the air. Think Hummelbird or CX4, that kind of thing.

Personally, I'd still love a hybrid Sparrow Hawk. Have like a 10 hp 4-stroke engine in it, driving a tiny generator (or direct) while cruising 125 mph, while a small battery back provides the extra power for quick climbs and in case the engine quits.

#### Victor Bravo

##### Well-Known Member
HBA Supporter
The DeBreyer Pelican seems interesting, and possibly even useful for everyday use. Why so few?
Ask Koen, because he actually had correspondence with the designer (Debreyer) and the current rights holder (Mangenot).

For whatever my half-a**ed guess is worth, I believe the designer sold or turned over the design rights to a promoter type person, and assumed that the promoter would promote the product, and the promoter is not 100% committed to it. The promoter (Mangenot) is envisioning full composite kits and new complete airplanes and what not.

Combined with this, the average Cesna/Piper/Beech pilot is very leery of flying wings.

I strongly believe that there is no legitimate, justifiable reason for why the Pelican is not being built in larger numbers.

#### Aesquire

##### Well-Known Member
Early 1980's hang gliders needed about the same horsepower as the Wright Flyer. 12...more or less. Less meant you skimmed the ground and ran into the trees at the end of the field you just ran halfway across in slowly increasing bounds.

We were somewhat limited by the early FAA decision to let us get away with aviation.... if we could pick up our airplanes and take off carrying it at a dead run.

Took a few years to let us use the Wheel. Then the limit was a jerry can full of fuel, not allowed to kill passengers too, and a weight limit that just happened to match the most popular ultralight on the market. ( yes this is cynical... but reasonably accurate )

The original Quicksilver hang glider with about 120 sq. ft. of wing & a "please let this keep running long enough to turn around and make the field I took off from" 10 ( We WISHED ) hp engine. ( @ 10,000 rpm ) was pretty marginal. Going to 20 hp & 156 sq. ft. on the production Ultralight made a reasonable airplane... in the tradition of the early 1910's. ( when we went from "a heavier than air machine can fly!" to long range heavy bombers in one decade )

The man powered aircraft that depend on 1/3 hp to struggle off the ground require pretty much zero wind and still air. The turbulence that a hang glider pilot looks for to sustain flight will turn almost all the Human powered machines into scrap.

If you don't care about the arbitrary weight limits of Pt. 103, and actually want to fly on any day a leaf might blow across your lawn, I'd say 18-20 hp is plenty. Going much less costs so much in either performance or cost that it's a marginal proposition.

A Sparrowhawk is a great example of a high performance craft that could fly nicely on less than 20 hp. Quite the contrast to a powered hang glider.

#### jarnicoton

##### Active Member
I met Jean-Claude Debreyer and his first 56 kg and 7 meter span Pélican at Romorantin airfield, central France, in 1986. Span and aspect ratio are low : L/D is not very high, but since weight is very low, minimum necessary power is low if you accept a modest cruising speed.
If I well remember his paper published in the eightees in les cahiers du RSA, his problem was : how can I have a 10% climb angle with minimum power ?
His answer : with quite a low AR, accepting a moderate L/D ; because higher AR would increase climb power and decrease angle because of increased structure weight, even if you consider the better L/D. 7 meter span was calculated as the best compromise.

A first and fast method for estimating the possible L/D for any aircraft (except perhaps tandem wings) : use following formula giving induced drag ID :

ID = 66 kilograms-force x W² x S² x 1/V²

Where:
W = weight in metric tons
S = span in decameters
V = speed in (km/h x 100)

Sorry if you don't see aspect ratio in the formula : span only is necessary. Sorry if most people refuse tu admit.

Well ; after that, minimum drag at best L/D is exactly ID x 2
You juste have to estimate stall speed with the known wing loading and suppose best L/D speed at about 1,4-1,5 stall speed. Then power for flying at best L/D speed is : 2 x ID x 1,5 x stall speed, before propeller efficiency. Minimum power is a bit less.

#### Piloot

##### Active Member
Thanks everyone, but I have a quick question.

Larr, where did you find the Klemm KL 20 picture and information? I have been searching and all I can find is just the Klemm KL 25.
I read about the Klemm KL 15, which was designed on the principle of using 7.5 hp, which is really the main focus of the thread. If you can get some information or leave a link that would be appreciated.

#### plncraze

##### Well-Known Member
HBA Supporter
Thanks for sharing this! Span loading is what you are talking about. Low weight means you dont need a lot of span

#### Swampyankee

##### Well-Known Member
Maybe we should start a "design a low-powered aircraft" thread. I've seen some interesting design threads here, and I'm quite sure that there are some people here who could come up with a great preliminary design for a practical low-powered aircraft, one in which a 95% male could fit with his wallet and a small duffle bag (enough for a change of underwear, toothpaste, razor, and laptop), fly a couple of hundred miles, tie down, and buy a hamburger that doesn't quite cost \$100 dollars, and fly back home and do it on no more than 20 (real) horsepower.

Suggested requirements:
1) No more that 20 hp
2) Range 200 nautical miles + 45 minute reserve
3) Accommodate one 95% male (US; let's not make this too hard. We could pick the Dutch ) plus a 12 in by 12 in by 24 in duffle (20 lb)
4) Stable, certifiable flight characteristics
5) Stressed to +4.5/-2.0 g, with 50% safety margin

I'll go hide now.

#### Jon Ferguson

##### Well-Known Member
I'm no designer but I think it's a good idea Yankee. Not sure I would travel 200 miles in 20 hp plane though.

#### plncraze

##### Well-Known Member
HBA Supporter
I think you are one of the potential designers Swampyyankee!!