Metro falls out of the sky
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Metro falls out of the sky
Anybody got any info about the swearingen that pulled out of an unintentional dive north of Richmond a couple of days ago? What is Vne for this type?
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Turboprops have their Vmo set at what is effectively the top of the green range. You can exceed the Vmo and still have structural margin at speeds up to Vd. The major problem is the loading on the airframe during recovery (bent wings).
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Speeds high
I think VD is part of the type certification process and a percentage over Vmo. I don't think the implication is that one can exceed Vmo, but it's be pretty sad if the machine fell to bits if one did.
I've never seen it published in an AFM but recall the Bombardier DH8 test pilot telling a story years ago of performing a VD test on the DH8-300 during certification when the gear decided to extend at some 100 odd KIAS above Vlg, without any bits leaving the airframe!
I think VD is part of the type certification process and a percentage over Vmo. I don't think the implication is that one can exceed Vmo, but it's be pretty sad if the machine fell to bits if one did.
I've never seen it published in an AFM but recall the Bombardier DH8 test pilot telling a story years ago of performing a VD test on the DH8-300 during certification when the gear decided to extend at some 100 odd KIAS above Vlg, without any bits leaving the airframe!
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Yeah, but that's typical DeHavilland, even if now owned by Bombardier / Boeing!
The Tiger Moth is an interesting aircraft - Vne is NOT structural, it is an aerodynamic speed - the aeroplane CANNOT go any faster because of all the parasite drag! It's 139 kias. You can SAFELY and easily recover the aircraft from Vne, without fear of breaking ANYTHING.
Always had confidence in any DH aeroplane I have ever flown. ALWAYS. Same applies to Douglas aircraft.
Boeing, well....they're Boeing.
The Tiger Moth is an interesting aircraft - Vne is NOT structural, it is an aerodynamic speed - the aeroplane CANNOT go any faster because of all the parasite drag! It's 139 kias. You can SAFELY and easily recover the aircraft from Vne, without fear of breaking ANYTHING.
Always had confidence in any DH aeroplane I have ever flown. ALWAYS. Same applies to Douglas aircraft.
Boeing, well....they're Boeing.
Two terms come to mind when describing load on an airframe ,Ultimate and Proof.
Below proof the structure will deform but return to it's original shape ,think wings flexing.
If loaded to proof the structure will deform and stay deformed but will not break.
If loaded to ultimate the structure wil break.
From memory, manufacturers test dive an aircraft during certification at high speed ,in excess of Vne. It is worth knowing this value for your aircraft just in case, ie jet upset.
I don't know any manufacturer who test dives their aircraft to ultimate !
Below proof the structure will deform but return to it's original shape ,think wings flexing.
If loaded to proof the structure will deform and stay deformed but will not break.
If loaded to ultimate the structure wil break.
From memory, manufacturers test dive an aircraft during certification at high speed ,in excess of Vne. It is worth knowing this value for your aircraft just in case, ie jet upset.
I don't know any manufacturer who test dives their aircraft to ultimate !
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Vd - Design Diving Speed
Vd = Vc x 1.25
Vc = 33 x square root of the wing loading
Metro Vd = 311 knots
The structure can withstand +/- 25 fps gust at Vd. At Vc it can withstand +/- 50 fps gust.
Vmo is set so it is less than Vc. It is also set with respect to an inflight upset (i.e Vd will be unlikely to be exceeded).
The structure must also handle the positve load factor at Vd. For the Metro this is +3.02G at 311 knots.
The structure also has a 1.5 safety factor. Below the ultimate load factors the structure will not fail but may permanently deform.
You can see there is plenty of margin if you stay below Vmo. The system has worked, as the inflight upset of this Metro did not lead to structural failure. It would be interesting to know if the upper skins on the wings are wrinkled.
Vd = Vc x 1.25
Vc = 33 x square root of the wing loading
Metro Vd = 311 knots
The structure can withstand +/- 25 fps gust at Vd. At Vc it can withstand +/- 50 fps gust.
Vmo is set so it is less than Vc. It is also set with respect to an inflight upset (i.e Vd will be unlikely to be exceeded).
The structure must also handle the positve load factor at Vd. For the Metro this is +3.02G at 311 knots.
The structure also has a 1.5 safety factor. Below the ultimate load factors the structure will not fail but may permanently deform.
You can see there is plenty of margin if you stay below Vmo. The system has worked, as the inflight upset of this Metro did not lead to structural failure. It would be interesting to know if the upper skins on the wings are wrinkled.
...and that is just for starters. There are other structural loads to be considered and of course the biggy, catestrophic failure from aerodynamic flutter.
For a long and happy career, the Flight Manual limits seem to work just fine!
For a long and happy career, the Flight Manual limits seem to work just fine!
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I'm reading between lines here, and perhaps have it all wrong, but Adamastor and Duff Man appear to be speaking from knowledge of radar readouts.
I have no real knowledge of radar control, having been in towers all my career, but I would have assumed that an aircraft in a vertical dive doing 400ktsTAS would show on a secondary radar screen as doing zero kts for the duration of the dive, since it was achieving no forward speed.
I am at pains here to say that this is a genuine question, and I am happy to confess to utter ignorance of the subject. Advice from radar experts greatly appreciated, and to pilots, sorry for the slight hijack.
I have no real knowledge of radar control, having been in towers all my career, but I would have assumed that an aircraft in a vertical dive doing 400ktsTAS would show on a secondary radar screen as doing zero kts for the duration of the dive, since it was achieving no forward speed.
I am at pains here to say that this is a genuine question, and I am happy to confess to utter ignorance of the subject. Advice from radar experts greatly appreciated, and to pilots, sorry for the slight hijack.
