Light aircraft down Pretoria, ZS-UKU KR2

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Re: Light aircraft down Pretoria.

Unread post by Airwayfreak » Mon Nov 08, 2021 7:23 am

V5 - LEO wrote:
Mon Nov 01, 2021 6:11 pm
....was that really the "maiden" flight, what about the flights to proof she is airworthy for an ATF, or is that only after initial build and not rebuild / modifications?
Great question. I cannot believe that any test pilot would conduct a maiden test flight in such a manner. Its just not done like this.
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Re: Light aircraft down Pretoria.

Unread post by GeraldNagel » Mon Nov 08, 2021 11:32 am

More reading material.
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Re: Light aircraft down Pretoria.

Unread post by milegrin » Mon Nov 08, 2021 12:03 pm

Does anyone have a photo of the wing that was found separately from the incident site? Specifically the area suspected to have failed.

KRnet is an international KR-2(s) group; some of whom know the KR-2 backwards including the likes of Mark Langford, Larry Flesner and a few other guru's who have 1000's of hours flying the KR-2 and KR-2S. They are asking for photographs of the suspected failed spar and any relevant details please.
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Re: Light aircraft down Pretoria.

Unread post by Deanw » Mon Nov 08, 2021 12:13 pm

milegrin wrote:
Mon Nov 08, 2021 12:03 pm
Does anyone have a photo of the wing that was found separately from the incident site? Specifically the area suspected to have failed.
I suspect you may have to wait for the preliminary report which should be issued within 30 days from the date of the accident.
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Re: Light aircraft down Pretoria.

Unread post by StressMerchant » Mon Nov 08, 2021 1:45 pm

The pics of the KR2 spar test are interesting, and do point to a strong structure. I don't know how many KR2s (and variants) have suffered structural failure, but based on the absence of Google hits I'd suggest that failures are pretty rare. Given that the design has been around for 40+ years, there would be some high time airframes out there, I'm sure many hours more than the one involved here.

But, I would caution against reading too much into the spar test quoted. Firstly, the build quality will vary from aircraft to aircraft. Secondly, there appear to be variations in the design - removable wings, extended wings, tip tanks, etc. I think someone mentioned a join in the middle of the centre section - which is not shown in the drawing, or in the test pics.

Finally, the stresses in a wing structure are dependent on the amount of load, and the way in which it is distributed. A given quantity of load concentrated at the roots would have less effect than the same amount of load spread over the wing span. The one that most people forget is the effect of the applied torque on the wing, which causes the wing to twist (as opposed to bending). The torsion is particularly important in high speed cases. I've twice seen wings fail on the test rigs during certification tests. In one case it was a production error, in the other case it was a mid-G high speed load setting. And although pilots "feel" the g-loading on the aircraft, a high speed / low G case can cause major wing stresses without the pilot being aware.

How are the ribs attached to the spar (particularly the root ribs), and how are the wings attached to the fuselage?
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Re: Light aircraft down Pretoria.

Unread post by richard C » Mon Nov 08, 2021 1:50 pm

Neville (RIP) was never one to mince his words on Avcom.

If he were with us, I wonder what he would have had to say regarding this accident ?
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Re: Light aircraft down Pretoria.

Unread post by SandPiper » Tue Nov 09, 2021 10:18 am

richard C wrote:
Mon Nov 08, 2021 1:50 pm
Neville (RIP) was never one to mince his words on Avcom.

If he were with us, I wonder what he would have had to say regarding this accident ?
Maybe that aerobatics can be flown in any airplane provided that the pilot is properly trained and that it is ok to fly the crap out of a wooden/foam/fibre glass/Volla powered homebuilt. Who knows?

RIP Neville.
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Re: Light aircraft down Pretoria.

Unread post by mi'cmaq » Tue Nov 09, 2021 10:48 am

Interesting discourse on the integrity of wooden structures

Is it possible that wooden aircraft will make a comeback ?

There is a company that has come forward with a replacement for Balsa wood for the aerospace industry - It is a hemp derived alternative that is stronger, cheaper and more durable than the wooden alternative - The product would be intended for the fighter aerospace plane manufacturing industry

https://incarenewtech.com/
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Re: Light aircraft down Pretoria.

Unread post by Theuns v V » Tue Nov 09, 2021 7:58 pm

The problem with wood is to get good quality and that spruce is rare by now. You als need a mechanic that knows his stuff to be able to get the correct piece for the propper application, looking at grain, year ring spacing ,density and allignment of grain when joints are made.

Unlike allu or steel you can get different strength and weights in a single board.

I think wood is not the way to go for mass production, composites can do the same with better quality controll, but even this will have a fatique life unlike wood, if wood does not break you can flex it for ever
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Re: Light aircraft down Pretoria.

Unread post by Sands » Mon Nov 22, 2021 1:48 pm

I am open to correction, but the plane that was taken for its maiden flight is in Nelspruit.
Please can we all be sensitive towards Neville’s family. They need our support at this time.
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Re: Light aircraft down Pretoria, ZS-UKU KR2

Unread post by Ugly Duckling » Wed Nov 24, 2021 9:33 pm

Preliminary report
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Re: Light aircraft down Pretoria, ZS-UKU KR2

Unread post by StressMerchant » Thu Nov 25, 2021 12:28 am

I see that the report quotes some of the figures from the POH. Data for NTCA aircraft is sometimes difficult to acquire, since the original designer may not have shared information to the extent expected of a Type Certified aircraft. The problem isn't limited to homebuilts, I've seen ex-military types on the various experimental registers with a lot of varying info.

In this case the POH is quoted as saying:
The aircraft design stress loading is ±7g at 800 pounds (lbs) gross weight and the redline is [VNE (never exceed speed)] 200 miles per hour (mph). The aerobatic operation within the flight load factor on the aircraft type is limited to full aft stick manoeuvres at minimum controllable airspeed, lazy eights, chandelles, and steep turns
Where did the POH source it's data?
  • I've seen a few other KR2 POHs, usually written by the owner, and most seem to quote 4.4G and mention "utility category".
  • Plus and minus 7G?
  • I've seen an account of a wing spar "test" to around 7G - see some of the discussion in posts above. Aside from querying the extent to which the test was representative, the 7G would represent an ultimate load. For normal practice this would imply a limit load of 4.6G (at most).
  • How was Vne determined?
If there are some knowledgeable KR2 people on the list, there are some design details that intrigue me.
  • There seems to be a join between the outer and inner wings, with separate skin panels for outer and inner. How are the skin panels connected across the join?
  • Where is the root rib? Is part of the root rib shown in the shot of the wheel fairing?
  • Are all controls mass balanced?
  • Did this aircraft have standard wings and ailerons?
I'm sure that the accident investigators are already asking these questions, hopefully the final report will have the answers
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Re: Light aircraft down Pretoria, ZS-UKU KR2

Unread post by Airwayfreak » Thu Nov 25, 2021 1:21 am

How does a PPL hold a Grade II Instructor rating?
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Re: Light aircraft down Pretoria, ZS-UKU KR2

Unread post by savas » Thu Nov 25, 2021 7:39 am

Apart from PPL - Grd3 thing, report is pretty complete and comprehensive
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Re: Light aircraft down Pretoria, ZS-UKU KR2

Unread post by Frontiersman » Thu Nov 25, 2021 9:17 am

Airwayfreak wrote:
Thu Nov 25, 2021 1:21 am
How does a PPL hold a Grade II Instructor rating?
It could be that he once held a commercial licence and had it downgraded to a PPL? Maybe an instructor's rating is something that never expires once you have it, but can only be used in conjunction with a comm licence, so will be dormant if you downgrade to PPL until you maybe one day decide to go back to a comm licence?

Anyway, just throwing some suggestions out there, somebody more knowledgeable might be able to confirm it for us.

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