Metro falls out of the sky

[duknweev]

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?

[Near Miss]

I think you mean Vmo, not Vne.
Vmo 246 and Mmo 0.52

[Adamastor]

I think it was a Merlin not a Metro, and whatever those speeds are he exceeded them!!! And then some!!!

[Far Canard]

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).

[Speeds high]

OK i know im a little slow, but ive been through the manual backwards and cant find referance to Vd, are you implying that one can fly safely above the barbers pole?

please explain?

[Capt Claret]

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. :ugh:

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! :\

[Romeo Tango Alpha]

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.

[Metro man]

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 !

[Full Noise]

Does any one have any real answers as to what happend with this metro falling out of the sky!!!! Sounds Scary:eek:

[itchybum]

No Answers but here's my SPECULATION.

A demonstration of Vmca gone wrong. Just a guess folks.

[Far Canard]

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.

[FlexibleResponse]

...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!

[Duff Man]

Yes, Adamastor, the merlin must have had a strong tailwind to show groundspeed in excess of 400 kts. And what was that descent, around 10,000 ft in a minute? eeek

[gaunty]

Phaaaaaaaark if any of the above is true re this aircraft and its alleged departure, its time for a rigging check, before further flight.

[Speeds high]

Cheers for explaining :O

I was under the impression that the first thing to give way on the Metro above Vmo would be the center windscreen; Any truth to this?

SH

[OVER THE TOP]

Vmo in the metro is restricted by the engine/propeller combination not the airframe.

[Binoculars]

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.

:O

[tobzalp]

Well the wobbulation and the sub clutter visibility would all have contributed to the rpm aming a real 3 nm/5 nm vector east right heading the norm in such a descent.

[Binoculars]

Err, right. I think. :confused:

[TopTup]

Does anyone know who's metro / merlin it was?

[ITCZ]

I was under the impression that the first thing to give way on the Metro above Vmo would be the center windscreen; Any truth to this?

With a max pressure diff of 7.5psi trying to push 200-odd square inches of centre window OUT, maybe not!

Think you heard a metro "urban legend"

[Duff Man]

Binos. Correct - radar ground speed during descent was minimal (in a left orbit from memory). The high speed was seen after radar established valid mode C when the aircraft levelled off and recommenced climb. Don't think it's my place to mention the callsign. Anyway I'm sure the pilot called class E "VFR descent" to avoid paperwork ;)

[NAMPS]

Was the requirement for 250kts below 10,000 cancelled? :}

[turbinejunkie]

ITCZ,

Not meaning to be anal, but I think a small correction to your post is needed for the benefit of other readers (since the limitation is a major structural one for the aircraft):

With a max pressure diff of 7.5psi

Max diff in the Metro is 7.25Psi (at which point the safety dump valve will open). Max normal operating diff is 7.0 Psi.

Regards,

TJ:ok:

[Far Canard]

"Vmo in the metro is restricted by the engine/propeller combination not the airframe"


OVER THE TOP
Where did you get this from?

[ITCZ]

turbinejunkie, you are quite correct -- it has been a while!

[Mode SHHH]

Actually a sweeping right orbit, Duff Man but the rest was pretty accurate. Just over 400kts GS, and the radar couldn't keep up with the Mode C and gave an invalid reading for most of the descent (only other time I've seen that was when I asked a Hornet for best rate of climb off the deck to F130 and he levelled out two miles and thirty seconds later and asked if that was okay :O ). Our Merlin friend got from F160 to just over A050 in under a minute. Then back up to over A100 in the next minute! Scary to watch from the comfort of my chair so must have been positively heart-stopping in the cockpit. There were a whole lot of people in that room hoping that it was all going to end well.

[Speeds high]

With a max pressure diff of 7.5psi trying to push 200-odd square inches of centre window OUT, maybe not!

Ummmm, so at 5 miles, 1500 feet, with about 0.1 PSI diff and 246 knots there is how much pressure on that window?

Mabey the windows not the weakest link, but i dont think your reason is the one why (if that make's sense).

[The Messiah]

Yes Vmo/Mmo is an engine/prop speed limitation which is common amongst fixed shaft Garretts like the Metro, MU-2 etc.

I got my info from Garrett when flying the type.

[AIRCAB]

Were there passengers or was it just crew on board?

Was it a Bk based merlin or metro??

If it was a merlin pretty obvious who's it is.. I wonder if the old boy was the pilot?? :ok: