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Ultralight - useful load

On the class of the high performance UL’s with a 915 Rotax engine in the 600kg class, as they have in Germany, I note that the usefull load is seriously impacted. We’re talking here about usefull load of 230 up to 250 kg. With 140 liter fuel tanks, it results in some +/- 130 to 150 kg usefull load remaining for the crew and the luggage all together if you go for a longer flight as the ads are promoting. That is really not a lot. These planes are designed for long distance flights at high speeds. But it makes little sense unless you prefer to travel by yourself.

Also, the high performance UL with the powerfull 915 engines use way more fuel than there predecessors with the 912 engine. Especially in the range of 185 kts, where we re hearing ( depending the modell) about fuel consumptions ranging from 26 to 32 liters an hour,

It of course depends the profile of the pilot, but in many cases, it might be better to opt for the version with the 912, which still allows to fly at very decent speeds of 150kts cruise, have a fuel consumtion of some 16 liters and a usefull load of some 300 kg ( German registered). When fuel tanks are fully topped up, you still have some 200 kg for pilots, crew and some luggage. That seems way more realistic, if you like to play it on the legal side. What do you think ?

Solex
ELLX EBZW LFMF EBAR, Luxembourg

Yes, but these kinds of thoughts are just way too rational for reality. Most private buyers want to fulfill their dream of a „hot“ machine that enables them to play with the big boys, flying at 170 knots FL85/FL95, often semi-IFR. Because you now can. For many of these buyers, whether it is 200k or 300k does not make a big difference if that‘s the one-off lifelong dream come true. Whether it is 20 or 30 litres of mogas per hour does not make a big difference. There is still enough money floating around. Regarding weight, it is normal that as soon as new limits are set, aircraft are designed to the very limit of these limits, which of course leads to them being flown overweight sometimes. Most of these people did not care for 30 years, why should they now?

But of course, that is just some small submarket of the this small overall market. The other one is mostly UL clubs and flying schools that just finally want to get out of the illegality zone. They will tend to buy the 100hp versions. Things like A22s and FK9s seem to be selling ok.

What limits the market is that with the new restrictions in Switzerland and France, even the UL crowd has now realized that ULs are actually just nationally approved machines, with just a few countries letting them in by goodwill rather than by regulation. This limits these attractiveness of the hi-speed travelling machines like VL3s a bit.

Last Edited by boscomantico at 26 Jul 06:02
Mainz (EDFZ) & Egelsbach (EDFE), Germany

What new restrictions in France?

France

He meant opt out from 600kg? yes it’s not a restriction if you fly ULM in France and happy with…if you are visiting with some “600kg ULM” it’s a restriction as you can’t cut some weight

Last Edited by Ibra at 26 Jul 06:59
Paris/Essex, France/UK, United Kingdom

The rotax 915 is powerful but 18kg heavier than the simple 912, and consume way more, for plane designed to work with a 100hp engine… It’s just nor the correct target.
The 912S is roughly giving 100hp for 20l/h, the injection can descend to 16l for the same in cruise, while the 915 is 22l at best eco and can go up to 32l/h at 75%.
For planes where usefull load is a great factor (usefull load ~= 1/2 MTOW), these consumptions plays a role in the mission.
Here are some figures in terms of engine weight and typical consumption:
915is: 90.kg / 26l/h (turbo/EFI/135hp MCT/141 hp max)
914:78.3kg / 22l/h (turbo/carbs/100hp MCT/115 hp max)
912is: 76.2kg / 18l/h (NA/EFI/90hp mct/100 hp max)
912s:72.5kg / 20l/h (NA/carbs/90hp mct/ 100 hp max).

With regards to light plane design, the simple 912s is still good, and whils 912is advertised weight of 76kg, it is usually greater (as plane designer add backup fuel pump + backup battery or alternator).

LFMD, France

boscomantico wrote:

Regarding weight, it is normal that as soon as new limits are set, aircraft are designed to the very limit of these limits, which of course leads to them being flown overweight sometimes. Most of these people did not care for 30 years, why should they now?

This is not unique to the UL world. It has been the situation for C150s used in training over the years, and also C172s and PA28-140s with 4 people on board

Darley Moor, Gamston (UK)
6 Posts
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