Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cluttonfred, Jul 13, 2010.
The kt100 is still being made. 15hp 21lb, $750.
Depends upon what you mean by "get by". The early ultralights like the VJ-24 had absolutely minimal performance, especially in terms of climb. I recall seeing advertised climb rates for some of these early birds at 50-100 fpm. A Cessna 150 is F-15 Eagle-like by comparison.
The entire point of the early ultralights was simply to "become airborne." They could do that, mostly, if it was a very calm day and the pilot skimped on breakfast. Expecting any better performance in a conventional-looking ultralight with 15hp or so is unrealistic. If you want any better than that, the English Electric Wren points the way: Span, absolutely minimal weight, and aggressive aerodynamic clean-up.
"Skimped on breakfast"... Well that explains a lot of my running across fields like the introduction to "Those Magnificent men...." and all those laugh at the early idiots videos.
I've said it before, There's nothing quite like flying in ground effect towards the forest rising above you. At less than one wingspan altitude.
The 10hp Mac engines run at 10,000rpm with a 2 foot prop converted fuel & oil into noise very efficiently. Thrust? Not so much. Reduction drives and bigger props helped enormously, but 14hp is marginal for the best machines. Pterodactyl, Easy Riser, CGS Hawk. All much prefer More.
Any excess power equals climb rate. No excess power....no climb rate.
I have asked for recommended decarb and overhaul times of the Raket and will get them on the Thor also. The cost is more meaningful when you have an idea of the implied quality.
The KT100 is still the standard engine for one particular karting class. If I'm not mistaken, that $750 doesn't include an exhaust or a starter (not even a pull cord; the karts start by pushing them), and no redrive. By the time you add those things, the price of, say, the similar HP Solo 210 (Hirth F36) begins to sound more attractive. The KT100 needs a tuned exhaust to make its 15HP; the Solo does it with a simple box muffler.
During a brief moment of madness 10 years ago I owned and flew an old KT100 powered weightshift Quicksilver...
We already know that a relatively dirty aircraft with only moderate span and a relatively small prop isn't going to do well on low power.
Do we have an example of a clean ultralight with 35 feet or more of span that's low powered but swings a nice large prop at, say, 2,000 rpm? (And the prop must be a good one!) I think a lot of the problem is inefficiency in the propeller.
I ran into this video awhile ago and it reminded me somewhat of a self launching untetherd kite that I've been playing with. It's kind of a cleaned up multiwing,simi ridged paraglider. Anyway I thought of this thread because the engine's mainly for getting you up when there is no wind and back home when there's a little to much. 14 hp would probably do nicely. I hope you enjoy the video... https://youtu.be/rEm8l2PoWbg
F-36 with Recoil Start $2027.00
F-36 with Recoil Start & Re-Drive $2581.00
F-36 with Electric start & Re-Drive $2882.00
Yes, a redrive is going to be handy, but what happened to hand propping?!
Hand propping a single cylinder engine with a redrive isn't easy.
I've done my share of hand propping, I could still do it but prefer just about any alternative because of the other things associated with it like untying the rope(s) solo, not having the throttle "cracked" just right, bottom line it is just a clumsy way to do things unless you have a helper.
I think about larger diameter props for ultralights (and most any other plane) and especially in the case of ultralights it is either the weight associated with mounting the engine and re-drive for propeller clearance of aircraft structure and/or the ground, or c.g. concerns when you hang it so far to either end to make clearance that way. Basically a long propeller is going to have to be mounted way up or way fore (or aft) or some combination of both, another idea is to mitigate the mounting distance with longer landing gear and larger diameter wheels and tires. Everything associated has an additional weight penalty from a larger diameter re-drive pulley or gear, the propeller ad infinitum. Any effort to hang more weight on a lever farther from c.g. is obviously going to effect the weight and balance as well which is usually narrow to begin with. In addition you are also changing the thrust line and need to be sure you have enough control authority to manage the change.
Macready (Aerovironment) Solar Challenger might be a good place to start. Its size and very low wing loading were driven by the large area required by the inefficient solar cells of the time (1980) and the low power they produced. Something less extreme but along similar lines might be downright sporty on 14 hp. Well, maybe not sporty, but viable. ;-) It certainly seems like an efficient way to package a low-powered ultralight and still have clearance for a big prop.
Length: 29 ft 0 in (8.8 m)
Wingspan: 47 ft 0 in (14.3 m)
Empty weight: 205 lb (90 kg)
Gross weight: 350 lb (159 kg)
Powerplant: 2 × solar-powered electric motors, 3 hp (2.2 kW) each each
Maximum speed: 40 mph (64 km/h)
Range: 400 (projected) miles (645 projected km)
Endurance: 11 (projected) hours
Service ceiling: demonstrated 14,300, calculated at summer solstice 35,000 feet ft (4,360 m)
G limits: +6, -3
Rate of climb: 150 ft/min (0.765 m/s)
The significance of such a design would be to go some distance. With a 40mph maximum speed you are going to be lucky to cruise in the low 30mph area. Wind speeds can often exceed the speed available for cruise especially going up in altitude (so you would fly backwards relative to ground speed), and even if they are say only around half of your cruising speed ... well going somewhere at less than 20mph ground speed ..., there doesn't appear to be any room for so much as a Johnny bottle ... I hope the people below don't mind!
Building structure to cruise closer to the allowed speed limit for ultralight in at least some wind (gust and shear activity) and still be streamlined and have enough wing to do it on 14hp (and room for a Johnny bottle). This is the kind of challenge that needs a financial sponsor to put up a significant prize.
I like it, don't get me wrong but it ain't easy, all I'm saying.
Wasn't the main point of the original post basically just to fly? BTW, I've seen video of the VJ-24W flying. There is one where it's just barely in the air, but you can hear the pilot throttle back shortly after he gets off the ground, so I think in that video he's just goofing around. I've seen other video where it climbs out at a reasonably steep angle and appears to be several hundred feet in the air by the time it gets to the end of the grass runway. I imagine the details of pilot weight, type of prop, redrive, etc. make a big difference. No doubt if I sat in a VJ-24W and tried to take off, it would climb considerably slower than normal.
What is the span of the ultralights you are comparing it to? If they're not close to 36 feet, you're comparing apples and oranges, though I admit neither of those would make a decent aircraft. ;-)
More apples vs oranges.
Pterodactyl 33 foot span canard. Canards aren't so great for maximum lift, plus it still has significantly less span than a VJ-24. Or maybe you meant some other version?
Easy Riser 30 foot span swept flying wing biplane
CGS Hawk 29 foot span and heavier (310 lbs empty)
Dewoitine D.7 is pretty close. Gross weight only 550, and I'm guessing the whole aircraft would be lighter when using the Raket or something like it, with maybe some modern materials here and there. Plus you get to have a replica!
Matthew suggested the McCready plane as a STARTING POINT. Once you get rid of the solar panels, change to a conventional airfoil*, shrink the absurd tail, and use 15 hp through a large, slow prop, the performance should pick up significantly. The horsepower change alone ought to get the speed up to 54 mph, if the prop is kept efficient. If we can believe Wikipedia, the aircraft was stressed to +6/-3 g's, so structural changes probably aren't necessary unless using a thinner wing. The aircraft was designed as a one-off, so I'm guessing if you could obtain drawings, the rest would be relatively easy.
If I remember correctly, the original idea was just to fly, not to go fast, though I can see the utility, on breezy days, of a bit more speed.
*Solar Challenger airfoils were flat where the solar panels were.
I was just yesterday looking closely at Paul McCready's Solar Challenger for ideas about optimal structure. The black carbon main spar is visible in the photo. I am wonduring if the tube spar at the 1/4 chord is more optimal than a D -Cell?
=22 HP (VW 1100), 120 kg...
I see the spar shadow through the fabric. Is it a tube? What does it weigh?
edit: found it was 120 kg.
The designer is very small!
I love that plane in the link, awesome! I also would never fit in it unfortunately.
Yes, just getting airborne was the point, just like the early hang gliders where the rule was "don't fly higher than you're willing to fall." It was pretty cool when nobody had done anything like that before, at least at that price. But people eventually got bored with short hops, frustrated with the limitations (can't fly if there's any significant wind, which is why the FAA made the exception allowing ultralights to fly a half hour before sunrise and a half hour after sunset), and got tired of repairing the fragile structures.
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