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Ultralight testing and compromises

some ultralights may not have been properly tested for flutter, but instead had the test data forged. I know this is not a popular topic, because it smells of a “certified” aircraft owner being “anti” the ultralight option (which I am not – so long as people appreciate that 450kg is going to result in an awful lot more compromises than say 1200kg) but there have been too many scandals in this area.

I thought this interesting enough for a separate thread.

As regards testing: this must be dependent on country. Some countries take testing of ultralights very serious, the UK not the least. There are movies on Youtube of microlights being spun by UK testers (example for the Eurofox:

, whereas many countries totally forbid spinning an ultralight. This makes it only stranger that many countries mutually accept each others’ type validations. Your allegiation about forged data might perhaps apply to certain southern countries, perhaps even not as far south as Africa , and could also explain how we see a constant stream of very high performance ultralight designs from CZ.

About the compromises: no matter what gross weight chosen, designers (and salespeople!) will always try to get the ultimate compromise out of a given design. The average two-seater microlight being overweight with two average adults and a bit of fuel seems no worse than the PA-28 not being considered a real four-seater except with the most powerful engine options. The microlight will at least keep its centre of gravity within bounds.

EBZH Kiewit, Belgium

and could also explain how we see a constant stream of very high performance ultralight designs from CZ.

You may well think that but I couldn’t possibly comment

Administrator
Shoreham EGKA, United Kingdom

my experience (and insight as I used to be part of that business sometimes end of the last century). There are companies making their reputation on proper design and testing. To give you an example – before we sell the first ever aircraft to UK we had done 400+ spins – according to AC applicable for part 23 aircraft. We used to have unsuable fuel 3 litres and just because of UK certification we made the test. The result was 0.6 litres. So we increased the number to be on a safe side.

Look at the flight manual – if the flight manual is high standard and similar as you might expect for part 23 aircraft – this might be a good indication they know what is is about.
Flatter – as far as I know each and every UL produced out of CZ must have an analyses for flutter. And the analyses is done by solo party, so not just anyone who read the book the week before.

LKKU, LKTB

could also explain how we see a constant stream of very high performance ultralight designs from CZ.

To a large extent it’s a product of long-standing aviation traditions. Few Eastern European countries had so much aircraft design and manufacturing capacity per capita as Czech Republic in the past.

LKBU (near Prague), Czech Republic

The average two-seater microlight being overweight with two average adults and a bit of fuel seems no worse than the PA-28 not being considered a real four-seater except with the most powerful engine options.

Most newer types ultralights are designed for MTOW 600 kg. This makes them overweight on paper only. A PA-28 is constrained by low power to weight ratio, a ultralight (with a 912 ULS) has a power to weight ratio like a rocket in comparison. The only constraint is an artificial and arbitrary number.

The UK does indeed have many strange rules, but to spin test an aircraft makes all the sense in the world, especially if spin is forbidden for that aircraft. You can enter a spin by accident, and if you cannot exit, you are dead. What makes no sense is that the UK seems to treat even homebuilts as if they were all build equal.

some ultralights may not have been properly tested for flutter, but instead had the test data forged.

I have never heard of any such incident. The point is really also irrelevant. (European) ultralights are not designed according to any common and accepted standard, and they are not built according to any such standard, and no QA system exist for them.

This makes it only stranger that many countries mutually accept each others’ type validations.

To be honest, to me the concept of type validation for ultralights is stranger. Ultralights are not built according to any standard, except whatever “industry standard” that is “in” at any given moment. Ultralights do not have “types” or “models” in the way certified aircraft have. Pretending one individual is equal the next, does not make it true. The overall basic aerodynamics and dynamic behavior (like spin and stall) will not differ much between individuals, but delicate issues like flutter and fatigue properties may change due to minute differences caused by slightly different methods of production. The main thing is, what is the problem? The answer is, there are no problems.

Lots of processes, certifications, methods etc for certified light aircraft are solution to problems that never existed in the first place, not for real. And this is a real problem, it is THE problem for light GA.

Last Edited by LeSving at 27 Jul 21:48
The elephant is the circulation
ENVA ENOP ENMO, Norway

re: LeSving and Flutter – unfortunately- there were accidents on flutter. Link. and I know personally guy who happened to have flutter just last weekend.
but overall there is a point in your comment, some of technology/equipment/etc is absolutely OK to fly even when the extensive certification by CAA/EASA is not done. But one needs to be carefully here, don´t just ignore all the “proper” aircraft requirements.

LKKU, LKTB

The microlight will at least keep its centre of gravity within bounds.

this is a most dangerous thinking, because especially most microlights don’t. For the FK14, Eurostar, Dynamic I know that for a fact. Just do some w6b calculations and see how fast it gets out of the rear limit. If flown way over gross, many typed tend to run out of dynamic stability margins. There have been many accidents attributed to this (well… some people may say a stall spin would be independend from a too far aft cog, but I tend not to agree).

Most newer types ultralights are designed for MTOW 600 kg. This makes them overweight on paper only.

Which ones?

Last Edited by mh at 28 Jul 13:23
mh
Aufwind GmbH
EKPB, Germany

Most newer types ultralights are designed for MTOW 600 kg. This makes them overweight on paper only.

Which ones?

mh
Aufwind GmbH
EKPB, Germany

most microlights don’t. For the FK14, Eurostar, Dynamic I know that for a fact.

That is quite surprising and alarming to me, and contrary to everything I was told; though one can hear a lot said, of course, if willing to listen. I have some difficulty imagining the “why”, because on this type of craft most optional weight (2nd person on board, fuel, luggage) is at or very near to the centre of gravity. Care to elaborate?

But I must admit I was mostly thinking of my own Apollo Fox and its category: tricycle, braced high-wing, 912-powered.

As to the 600 kg actual design limit, it sounds reasonable to me: many designs want to cover as broad a market as possible, so they first aim to be eligible for a US’an LSA approval (1200 lbs?), then artificially limit MTOW to 450/472,5 kg for European countries.

EBZH Kiewit, Belgium

Which ones?

Almost everyone that also are sold as LSA. The FK9, the Shark, The Pioneers (mtow 550 or something), Pipistrel Virus SW and many others I’m sure, even the Sonex (which also is aerobatic).

The elephant is the circulation
ENVA ENOP ENMO, Norway
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