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Leeham News and Analysis
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Irkut MC-21 missing ultimate load test
By Bjorn Fehrm
April 05, 2017, ©. Leeham Co: United Aircraft’s IRKUT MC-21 passed 90% of the static Ultimate load test end February at the TsAGI test institute in Moscow, reports ATO.RU. But the aircraft failed the 100% test.
The test simulates a load which is 150% higher than the highest load that the aircraft should be subject to in its operational life. The test failure does not stop the aircraft from beginning flight testing, for that the aircraft needs to pass the limit load test (highest load during flight), which it has.
Missing the Ultimate load test for new airliners is nothing unusual. The designers tries to pass this test with the smallest possible margin. Any excess margin will make the aircraft unnecessary heavy. Other aircraft to have missed the test are Mitsubishi Aircraft’s MRJ, Airbus’ A380 and Boeing’s 787.
According to ATO.RU, who quotes IRKUT, the reinforcements in the wingbox necessitated by the failure will weigh 25kg. It’s not clear if the changes will affect the start of test flights. These should have started during April.
Another YAK that is unable to handle 150% load? No worries there will be time to get the issues addressed before commercial operation, somewhere around 2020.
This is the new contender for MOM. No wonder other manufacturers arent rushing to jump in for what could be a limited order book. ( 400-800 orders)
The only problem is that it is made in the wrong country, fix that and it would be a better contender.
The only company that would be suitable for license production and could provide western levels of operational support would seem to be Embraer. This wouldnt cut into their current offering and would push them into being a major player alongside Boeing and Airbus.
Embraer isnt exactly flush with capital for a venture of this sort. There are rivers of money going into anything called a startup based in loft warehouses in SanFrancisco, but not so much for a real product.
Of course aviation was the hot thing of the future back in the late 20s when most of the big names got started.
It is sad but on a positive note a little startup was recently given some backing by Boeing and Jet Blue Zunum Aero
You seem to know very little about Embraer to suggest such a partnership. Embraer does not have much taste for adventures and I must remember that the UAC company competes directly with Embraer with the Sukhoi Superjet.
It would be more plausible if Embraer joined Boeing for a joint development of a new aircraft (? NMA).
Boeing could build the Irkut MC-21 under licence as a B737 replacement.
I checked for the 3rd of the new airliners with carbon fibre wings the Cseries, which did get to 100%.
So thats 2 out of 3 that didnt make the design extreme load. Its not really a design failure as either way the numbers from the strain gauges will lead to smallish changes.
Next big wing is the 777X, Boeing should do fine on this as they have learnt from the 787 wing design and uses the same autoclave methods.
the MC-21 wing , is of course more advanced with ‘out of autoclave’ production, which is likely to be the future way ahead.
http://www.compositesworld.com/articles/resin-infused-ms-21-wings-and-wingbox
The Mc-21 is 10cm wider than the A320 and 30 cm wider than the 737.
As for the empty weight advantages of carbon fibre:
“According to Rubtsov, Irkut has designed the MC-21 with an empty weight that is 3,600kg (8,000lb) lighter than the A320, despite carrying 30 more seats in a longer and
wider fuselage. ”
http://eng.irkut.com/upload/FlightInternational-16.pdf
Interestingly Irkut has a tentative max production rate of 7 per month.
Its simply not going to sell as no one is going to want to get tangled up with the Soviet Union.
They also have no support and all their world wide stuff fails miserably.
Its a system, not just a product.
Geez, @TW, how old are you? The Soviet Union collapsed in 1991…. 🙂
I think we should seperte this out.
1. The 787 did not fail at the wing, it failed at the wing joint.
I know that sounds “picky” but I think its important that they did get the wing right.
Also it was one of the parts they lightened form original to save weight, they had it right to start with.
I think it had a lot to do with the disjointed understanding between those scattered segments.
Also keep in mind, the 787 WING never did reach failure, they stopped it at 155% or so (maybe a bit more) They did not want shrapnel blowing all over the place damaging test equipment . No one knows how much further it would go.
A380 simply failed. However it failed where they said it would, just sooner. Based on that, they beefed it up and never ran the test again, allowed to make a paper justification. I am ok with that in that case.
I think it was less than 200 pounds for each wing.
I am not seeing the same out of the MC-21 but it looks much the same with beef up in a known area.
It was worse than that TW
http://www.seattletimes.com/business/boeing-aerospace/boeing-787-wing-flaw-extends-inside-plane/
It wasnt just the wing- wing box join but with the end points of the wing stringers.
I forgot the other new carbon fibre wing in service which passed the ultimate load test, the A350.
Although this story seem to suggest the ‘1.5x the maximum load’ calculation isnt used any more
http://theflyingengineer.com/2014/01/14/understanding-the-ultimate-load-wing-test-a350/
“The ultimate load is calculated as 2.5 times the maximum expected G load that the aircraft would ever encounter in its service life. For the Airbus A350, which is limited in the G loads that it may experience, by the Fly By Wire system to +2.5G, or with the FBW system deactivated, as is the case with a reversion to direct law, approximately between 3-3.5G with the aerodynamic limitations of the flight control surfaces. The ultimate load is then possibly between 7.5 – 8.75G.”
The deflection under this force is calculated and the wing is loaded to achieve it.
For the A350, the deflection calculated was ‘over 5m’, the 787 went to 7.6m ( their more flexible wing design ?)
The C Series also passed the 150% ultimate load test
http://www.bombardier.com/en/media/newsList/details.788-bombardier-completes-ultimate-load-test-on-cseries-aircraft-demonstrator-wing.bombardiercom.html
There seems to be confusion over various ‘loads’
From the FAA part 25 standards [25.303]
‘Unless otherwise specified, a factor of safety of
1.5 must be applied to the prescribed limit load
which are considered external loads on the structure.’
and then there is the aerodynamic loads testing ( Ultimate) [25.337 ]which indicates between 2.5 and 3.8 SF (depending on weight) x the maximum G from the flight control systems.
I hope I got that right and not mixed up some parts?
“The test simulates a load which is 150% higher than the highest load that the aircraft should be subject to in its operational life.”
Actually it should read “….is 50% higher…”
There are 2 ways tout reach the objective. Firstly, design the wing to make sûre it does not exceed the 150 % target which is the mc-21 ans 787 solutions, secondly design the wing to mâke sure it does exceed the 150 % target which thé cseries solution.
The first solution yelds minimal weight, the second exceeds minimal weight unnecessarily.