# Flying on 14 hp

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#### cluttonfred

##### Well-Known Member
HBA Supporter
Lately I have become enamored of the idea of a simple little aircraft designed around the 14hp Radne Raket 120 Aero RD-ES engine. This engine is quite popular with paramators, toecutter powered hang gliders and nanolight trikes. See the manufacturers web page or download a brochure with performance curves and dimensions (2.3MB .pdf file) for more info and specs. The good news is that the engine complete with starter, redrive and basic exhaust is available from the factory for less than $1,100. Even with a prop, battery and optional tuned exhaust, the total powerplant runs less that$2,000.

I already have some clear ideas on how I might tackle this, but I'd like to hear ideas and suggestions from the members here. A few basic criteria:

1. Payload (pilot & fuel) of 250 lb
2. Performance within European microlight limits (40 mph stall, 660 lb gross weight) and preferably closer to U.S. Part 103 ultralight limits (27 mph stall, 254 empty weight). Full compliance with Part 103 is not required.
3. Fixed wing design (not Rogallo wing trike or powered hang glider)
4. Two- or three-axis controls
5. Not foot-launched and with some crash protection for the pilot
6. Suitable for building in a small workshop (single car garage or less)
7. Easily assembled/disassembled (less that 30 minutes) for transportation on or in a small trailer
8. As the Raket is already set up as fan-cooled pusher, the engine should remain in that orientation
I have deliberately not specified any configuration, construction method, etc. as I want this to be a brainstorming session. Like I said, I have some ideas that I will share later, but I want to hear yours first. Word concepts are great, sketches are better and pics and references of actual aircraft to use as inspiration are best.

Thoughts?

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#### Dana

##### Super Moderator
Staff member
This has been discussed here before; search the archives.

While it's certainly possible to build an airplane that will fly on 14HP, it will be an extremely marginal aircraft. It would have to be very light (forget 660# gross). What you'll have is a very slow aircraft limited to the very calmest conditions and/or very lightweight pilots... and/or very marginal performance. PPGs and PHGs can get away with it because the structural weight is so low (but PPGs, in particular, are also very limited in the weather conditions they can handle). Even for PPG, 14HP is considered marginal these days. While the Radne is still used on some foot launch powered hang gliders, the light "soaring trikes" now use engines of at least 28HP, which is a realistic minimum for any kind of rigid aircraft.

As for quick folding wings, there have also been many threads on the subject. There aren't many fixed wing folders, especially at the light end.

If your requirements are low power and portability, ruling out flexwing trikes and parawing aircraft makes it a lot more difficult.

-Dana

Campaigns to bearproof all garbage containers in some national parka have been difficult, because as one biologist put it, "There is a considerable overlap between the intelligence levels of the smartest bears and the dumbest tourists."

#### Rienk

##### Well-Known Member
Check out the Demoiselle thread, those extruded fuselage fittings are excellent and aluminum tube/wire bracing is probably the lightest type of construction. These fittings could also be used for a fabric covered square section fuselage.

The Shuttleworth Collection also has some interesting aircraft like the English Electric Wren that flies on 3.5 hp.

http://www.homebuiltairplanes.com/forums/light-stuff-area/5286-demoiselle-construction-details.html
I have collected info on the Wren for a while; it is one of my inspirations for an ultralight glider. We're working on a low cost "rolling launch" concept right now, but it will be almost impossible to meet the 155 lb weight limit. Thus, we are considering engines such as these, so that we can have true self launch. Strojnik has shown that it doesn't take much power to have an adequate powered sailplane.

I've been toying around with the idea of having a retractable prop like the Stemme, and injection molding the half blades. The only thing that would extend or retract on the central shaft would be the large nose cone (not a spinner, because it won't spin), so that all the systems are fairly simple. Of course, to do this right, the plane should probably be a more complete kit or ready to fly (which then might as well be all composite).

As I told the guys at the HSA, if someone will help design/engineer it, I will build it.

(each of my four kids would like their own)

#### cluttonfred

##### Well-Known Member
HBA Supporter
To start the creative juices flowing, here are a few possible inspirations, all of which flew on less than 10 hp. Google will turn up more info in addition to the links below. All of these are, admittedly, best suited to light pilots, but then again, I don't weigh 50% more than those guys, so I should have power to spare. ;-)

Francois Butterfly (9 HP)
http://www.flyingflea.org/docs/butterfly.html

Croses Pouplume (8 HP) (this one's in French)
http://www.croses.fr/articles.php?lng=fr&pg=62

Debreyer Pelican (9 HP in the original prototype, the more angular model in the lower right photo)
http://www.nurflugel.com/Nurflugel/Fauvel/e_pelican.htm

Sandlin PIG (unpowered, but easily adapted to a paramotor engine)
http://m-sandlin.info/pig/pig.htm

##### Well-Known Member
There's also the original Rutan Quickie (18 hp), which I think is a more interesting starting point. Of course, climb sucked.

#### cluttonfred

##### Well-Known Member
HBA Supporter
I have collected info on the Wren for a while; it is one of my inspirations for an ultralight glider...
If you like the Wren and similar designs I hope you have the book ULTRALIGHTS: THE EARLY BRITISH CLASSICS by Richard Riding. Nice little chapter on the Wren and many other inspirational designs....

#### PTAirco

##### Well-Known Member
If you like the Wren and similar designs I hope you have the book ULTRALIGHTS: THE EARLY BRITISH CLASSICS by Richard Riding. Nice little chapter on the Wren and many other inspirational designs....

I have that book. It's overdue at a Brisbane library since August 1991....

Great information on many not so well known vintage utralights. Incidentally, in Britain the term ultralight had no legal significance then, it was simply applied to anything less than 1200lbs or so gross weight.

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#### Denis

##### Well-Known Member
A realistic single seat motorglider can be surely built on 14HP. If the takeoff weight is limited to 500lb, which is again realistic, and the sunk rate at best L/D speed is about 200fpm (again quite achievable), this motorglider will have 400fpm climb rate, what is already quite enough. Bearing in mind that the climb airspeed of such lightly loaded plane will be something like 40mph, this rate translates into a very satisfactory climb gradient of more than 1 to10. The TO distance will be also spectacularly short, thanks to the low liftoff and climb airspeeds.
Such performance can be obtained with a wingspan of 36-38feet. This is not too much from the viewpoint of structural weigt, for instance, while using a strut-braced high-wing layout and tube and fabric technology.
The only dark side here is the use of a two-stroke engine. The fuel burn is actually twice that of a small four stroke.
I think the better idea is top use asmall industrial four stroke V-twin, for instance, Briggs & Stratton.
Their smallest Vanguard V-twins begin from 472cc and make 14 or 16HP at 3600RPM. The dry weight is already acceptable 72lb. This weight will be further reduced by removal of unnecessary parts. Even larger such V-twins fit the weight budget of FAR-103 designs.

#### cluttonfred

##### Well-Known Member
HBA Supporter
That's an interesting thought, Denis, especially about the B&S Vanguard or similar engines. It seems though, that a lot of people are talking about using such engines, but only a few very experienced builders are having any success with them. For someone like me, who is not an engine expert, I would be first in line if someone offered a simple, reliable aero conversion of that type of engine with all the bugs worked out. Unfortunately, no one seems to be doing that. The nice thing about the Radne, despite two-stroke noise and fuel consumption, is that it is a complete package, ready to mount and proven in paramotors and powered hang gliders.

#### Denis

##### Well-Known Member
A bright example B&S aero conversion is Colomban MC30 Luciole.

Aircraft Summary

##### Well-Known Member
For a single aircraft, probably the best starting point would be a modern glider, with seriously reduced span and increased wing area which gives you about everything you want (crash protection, low drag fuselage. Most gliders can maintain flight (@ 50 kts) with roughly 3-4 hp. Many gliders use engines of 20 hp or so to "turbo" home, even the big (1800 lbs) ones.

How about a "motorized" wooden glider (Ka-6) or early plastic (Cirrus, LS1). Fuselages can be bought for low money and the wing is pretty straightforward to build.

#### Yogi

##### Well-Known Member
How would you calculate how much power/thrust needed for a climb rate of 500 ft/min ?

#### Autodidact

##### Well-Known Member
Roughly and simplistically, calculate the drag at a straight and level speed slightly less than cruise. What slope (rise over run) will result in a 500 fpm climb at that speed? That amount of drag plus the weight of the aircraft times the sine of the angle of that slope (which will be relatively small) is the thrust required to maintain equilibrium in the climb.

I.e., velocity (in FPM) * sin(the angle) = 500 FPM OR

the angle = arcsin(500 FPM/velocity)

double

##### Well-Known Member
And power:

How would you calculate how much power/thrust needed for a climb rate of 500 ft/min ?
500 ft/min is 2.5 m/s

speed times force is power.

2.5m/s * weight*gravity acceleration = power

So for 500 lbs (230 kg):

That's excluding drag and prop efficiency.

If you have a 200 fpm descent power-off, you need an extra 2300 W to stay in level flight, thus 8050 Watt for that climb. Figure in a 75% efficient prop and you'll need 10.7 HP

#### Autodidact

##### Well-Known Member
And power:

500 ft/min is 2.5 m/s

speed times force is power.

2.5m/s * weight*gravity acceleration = power

So for 500 lbs (230 kg):

That's excluding drag and prop efficiency.

If you have a 200 fpm descent power-off, you need an extra 2300 W to stay in level flight, thus 8050 Watt for that climb. Figure in a 75% efficient prop and you'll need 10.7 HP
That's cool, I need to start thinking like an engineer rather than a geometry student.

#### Topaz

##### Super Moderator
Staff member
Log Member
Some additional photos of the English Electic Wren, taken at the Shuttleworth Trust in 2002.

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##### Well-Known Member
That's cool, I need to start thinking like an engineer rather than a geometry student.
Simplify (as few formulas as possible) and add lightness (beer) :gig:

Bearing in mind that the climb airspeed of such lightly loaded plane will be something like 40mph, this rate translates into a very satisfactory climb gradient of more than 1 to10.
The more I think about it, the more enthusiastic I get about it, especially if you consider the climb angle.

While my preferences are different from the Luciole (plastic fantastic and much better looks), something with similar performance and configuration (low wing, conventional layout) seems interesting, achievable and affordable.

Given the small size CNC-cutting of the molds would be feasible (only one mold for elevators+fin is needed) and the fuselage mold could be built by hand. Once the skins are made it shouldn't be too much work (compared to much bigger aircraft) to construct it further.

As a note to the TS, one of the major problems I foresee is getting the machine rolling. Static thrust of such low HP is minimal. To overcome the initial drag to roll might (on grass) might require more force than your prop can deliver.

#### Dana

##### Super Moderator
Staff member
The more I think about it, the more enthusiastic I get about it, especially if you consider the climb angle.
Yes, watch a 14HP PPG climb... the actual climb rate may not be impressive, but at only 20mph the angle is quite respectable. A PPG with 25HP and a bit of breeze can go skyward at a spectacular angle.

As a note to the TS, one of the major problems I foresee is getting the machine rolling. Static thrust of such low HP is minimal. To overcome the initial drag to roll might (on grass) might require more force than your prop can deliver.
It's not a problem with PPG trikes, which weigh less but have a huge amount of aerodynamic drag as the wing inflates. We're talking about such a slow aircraft anyway that static thrust probably isn't much worse than climb speed thrust.

-Dana

I don't trust a government I can't shoot back at.