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Flexwing Pitch Stability


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As many posts read.. majority of pilots fly Airborne machines and a few fly the European brands. The reasons are common and usually simple... price, parts and that's how its'bin for many years.



 

 

 

In contrast, the price of European microlight aircraft is higher than our Australian products due to exchange rates and manufacturing cost for NAA Certification - the German DULV Flexwing Aerodynamic Pitch Stability Requirements are expensive and tough on stability... Just wondering if any pilots out there have evr thought about this subject or if the product you fly is pitch stable by NAA Certification Compliance... Can anyone confirm if Airborne wings are pitch certificated..? Interesting subject actually..!

 

 

 

 

 

 

 

Smooth flights..



 

 

 

Chris keen.gif.9802fd8e381488e125cd8e26767cabb8.gif

 

 

 

 

 

 

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Hi Chris,

 

I've never really heard of the issue of pitch stability on trikes being discussed much before other than a quick observation that the pitch stability comes from the centre of mass being so far away from the wing.

 

I assume you are referring to a trike wings resistance to entering an end over end tumble in turbulence, or a stall?

 

I'm not familiar with NAA Certification and not even that familiar with BCAR-S Primary Category certification which the Airborne Trike I fly is certified to.

 

Rgds,

 

Glen

 

 

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Guest Crezzi

NAA is National Airworthiness Authority Ie CASA here, CAA in UK, FAA in USA etc. Overseas trikes are accepted here on the basis that they have been tested to the standards mandated by the NAA in the country of manufacture Eg BCAR Section-S for the Uk. So if I understand correctly Chris, part of your question is what pitch stability testing is specified in these standards ? Section-S is online at http://www.caa.co.uk/docs/33/CAP482.PDF

 

Yes, I have thought about this after a fatal accident in the uK (10 or more years ago). The investigators report wasn't conclusive but discussed the possibility of vertical downdraft causing sufficient rotation that the trike tumbled. The velocity mentioned was well within would could occur naturally but would have exceeded the response of the pilot to prevent it. Unfortunately I can't find the report on the AAIB website - I'll check at home later & see if I still have a paper copy. I do remember that that there was mandatory, before-next-flight, inspection of all trikes of that type to confirm the length of the luff-lines was within spec.

 

AFAIK the XT wasn't tested to BCAR Section-S but to a CASA mandated level which exceeded it (hence certifed in primary category & acceptance in the UK without undergoing Section-S testing). I don't have any specific details of any pitch stability testing however.

 

Cheers

 

John

 

 

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Thanks guys.. nice to see some wisdom about flexwing pitch stability emerg... on ya Crezzi for a clear picture..! We flew 2gether in the Hunter Valley...sure you remember.! Pegasus Quantums & Quasars...them good English machines.

 

The real question is since about 1990 - manufacturers of hang gliders are to satisfy either USAHGMA or DULVQRH pitch testing..! Just wondered if any trikers out there really see the reason why our machines cost so much today..!

 

The pitch test rig in Germany is an amzng expensive piece of equipment. This vehicle is fitted out with several computors and has a massive steel support arm above which a wing is mounted... and can be hydraulically moved in the pitching axis whilst driven at nominated speeds - forward & in backward flight attitude positions!

 

This method of flexwing aerodynamic pitch testing allows the crew to position the wing beyond normal flight pitch attitudes. Confirmation of the wings lift characteristics is substantiated by video footage & lift coefficient tags which confirm the correct CG position, operation of the reflex trailing edge bridles and the leading edge round/twist performance of the airframe. The computor software is able to replicate by mathimatical algorithm the aerodynamic performance of the wing under test and by digital printout the wing either passes or fails the acceptable NAA Design Requirements for flexwings.

 

Therefore...the cost is enormous to have a wing tested & certificated under the DULV rig.. the manufacturers of Europe build great flexwings and they are expensive.. But the security and safety is more important to me, when you fly a wing that is pitch approved ..especially if the air is big, rough and unpredictable!! A DULV pitch tested wing has a defined accurate sense in all flight attitudes.

 

I witnessed the first tumble in Australia.. Ian Hodgenson, the RAA honour this gentle man with the best trike trophy each year at Natfly...bless his soul! We have lost several other pilots/passengers over the years... and my opinion about pitch stability and 70knot flexwings is that we can never really talk enough about how to handle your aircraft in all aspects within the flight envelope..!

 

Therefore my question is...are our Aussie trike wings pitch tested on either the DULV or HGMA test vehicle or another test vehicle I am not aware maybe...I know the Moyes & Airborne hang gliders are... but is your Wizard..Streak 1,II or III or B..not sure how many there are now!??

 

There is no price limits on safety ..and its gotta be fun.!

 

It's not always what happens in the air that's dangerous..

 

...rather - how you decide to handle it that matters!

 

Have fun..clear skies.

 

Chris :yin_yan:

 

 

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Guest Crezzi
We flew 2gether in the Hunter Valley...sure you remember.!

I certainly do - I learnt a lot & thoroughly enjoyed it :)

 

I've seen photos of the BHPA test-rig in the UK which I think is similar to the DULV one - I don't know if its routinely used for testing trike wings or just HG. The only paperwork I could find last night on the UK accident I mentioned was the diagram for check the lufflines dimensions. It might be handy for any Flash 2 Alpha owners in Aus. None of which answers your question on Airborne wings unfortunately.

 

we can never really talk enough about how to handle your aircraft in all aspects within the flight envelope..!

Absolutely agree. With more high performance trikes in Aus, its inevitably going to change how they are used. Rather than just local flights at first light they will be increasingly flown during the day & on bigger trips. I've already noticed this at YCAB (& I'm probably partially responsible for encouraging it). Its not a bad thing but it does expose pilots to a bigger weather envelope and more potential for scenarios they haven't trained for.

Cheers

 

John

 

 

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Folks,

 

Yet another interesting thread. The Aircreation Wing looks very similar to my DTA 450 Wing in shape and dimension.

 

When purchasing the DTA we were also assured and presented with the results of the testing undertaken on the wing for pitch stability.

 

It is interesting to note that DTA recommend that -ve g should be avoided for any sustained period and only give you certification for upto -2g in the envelope for flight in turbulence.

 

Having been alarmed from recent ATSB investigation reports I made a point of having a comparative look at the construction of outer wing sections of Pegasus, Airborne and DTA and found some real differences. I have deduced that this section is perhaps key to your long term survival and therefore should be carefully checked for signs of early failure. I did notice that the European Wings have a number of telescopic sleeves along the outer section in comparison to the Australian Wings that only have a single sleeve. Whilst I am not a structural engineer, I can only deduce that the reason for multiple sleeves is to enable appropriate flex of the section whilst spreading the point stresses on the leading edge section during flexing that occurs in turbulence - I have noticed that my outer wing actually endures significant upward and downward flex during turbulent sorties.

 

I also believe that the likelihood of a breakup in turbulence does not depend on the nationality of your trike. Due to the terminal consequences resulting from a likely outer-wing failure (my thinking is that this can be stress induced without significant input), my wife an I have bit the bullet and are investing in a ballistic chute. This is a last option for the advent of a tradgedy such as sycamoring into the ground.

 

I would appreciate more advice on the stresses experienced on the outer wing sections and whether there are some real (unbiased) learnings that could warn would-be cross country trikers of the necessary considerations during such flight?

 

Regards

 

Perry

 

 

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Folks,It is interesting to note that DTA recommend that -ve g should be avoided for any sustained period and only give you certification for upto -2g in the envelope for flight in turbulence.

Perhaps Im missing the point, I would have thought that all trike manufacturers andinstructors will want -ve G avoided for "sustained periods". Lets face it, there called weight shift for a reason, and that reason requires +ve G. any sustained -ve G places you in an uncontrollable (wrt pilot input) aircraft. Thats why the loop thing is a major no no. There are very few pilots that can "go over the top" and still be +ve G (relative to the trike base). Those that cant maintain +ve G become darwin award candidates and the basis of ATSB reports.

 

I suspect though that the -ve G your talking about is the transient type associated with turbulent opperations. That being true sustained probably isnt the right description for something that I suspect you meant associated with constant cycles of -ve then +ve G?

 

While also being unqualified to discuss the aeronautical engineering aspects, I'd question as to how many events have occured that lead you to be concerned over any wings flying in australia WRT -ve G loading?

 

WRT stress, I dont recall if the manufacturers put a life, in hrs, on the wing, I seem to recall my instructor saying that 1000hrs on a trike wing is a lifetime and the wing needs to be completely retired after that, but dont recall on what engineering or manufacturers basis that statement was made.

 

Andy

 

 

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  • 9 months later...

I remember reading some time ago about the possibility of exposing parts of a microlight wing to sustained -ve G loadings under reasonably normal flying conditions. From memory, here's the scenario:

 

As we all know, a microlight flexwing has washout built in to the wingtips. The purpose of washout is to ensure the nose tips forward as you approach a stall. Let's say you're flying straight and level and begin to push the bar out. The AoA of the wing root (main centre section) increases above 16 degrees and in begins to stall, however the wingtips have washout (lower AoA) therefore they keep on flying. Because the wingtips are behind the CofG, as the root of the wing stalls, the wing will naturally pitch forward, increase speed and begin to fly again - all good.

 

Now consider the opposite situation. You are flying straight and level, apply engine power and begin to pull the bar in to speed up. The AoA on the root of the wing decreases and your speed increases. If you have a powerful 912 on the back you can pull the bar right in to your gut and really speed things up. You might even decide to do this in a shallow dive to give you that bit of extra speed. In this situation the AoA of the root will be very small but the built in washout of the wingtips may have put the wingtips into continuous -ve G as they are now pushing down!

 

Now consider the scenario where you fly into turbulance. A natural reaction might be to pull the bar in to speed up so you can 'punch through' the turbulance and reduce your exposure to it. This may place the wingtips close to (or maybe into) sustained -ve G's with turbulance added on top. Suddently we might end up with wingtip failure due to -ve Gs without ever attempting loops.

 

Anyway, I remember reading that explanation somewhere and it sounds like it might be possible. I'm no expert so I'll open it up for comment ...

 

 

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Guest rprewett

Thanks Jayay for your clearly understandable explanation, which fully tells me of MY lack of knowledge where AoA is concerned. Hopefully my only experience of -ve G will have been in trying to get vertical descent from a stream which had taken over my need for height before I realized my straight and level was a +300 fpm altitude change. Worried that turning wasn't an option and pulling back was only giving me a bellyache! I've often wondered about that.

 

 

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