Airflow at ground level versus airflow at 30000ft

[mickjoebill]

Please excuse any incorrect terminology!

I'm filming the effects of an explosive decompression, by blowing a hole in a parked pressurised aircraft, a similar stunt to what the USA TV show The Mythbusters did.

I have been pondering trying to simulate (partially at least) the effects that airflow over the fuselage would have on the debris from the explosion.

Th idea is to illustrate that debris from an explosion can be blown/travel down the fuselage and could make contact with control surfaces or engines.

This aspect of the test is not scientific (!) but it would help the viewer understand that debris from an otherwise non catastrophic explosion could damage rudder or engines.

To put you in the picture we have available a 300hp special effects wind machine with 2 x 3ft feet long blades and Im wondering if this was positioned 15 feet form the blast how this would compare to wind forces of a commercial jet in flight.

My question; is it true that the volume and force of air across a fuselage at say 600 knots at 30000ft is similar to the forces at lower speeds and lower altitudes?
If the wind machine can generate say 120 knots at ground level what is this pressure or force (?) equivalent too at 20,000ft or 30,000 ft?
I realise that the wind speed will decrease with distance from the wind machine, thats about the only law of thermodynamics I think I know.


thanks!

Mickjoebill

[Adrian Cronauer]

Mate. 30000 feet? Typically you'd only be traveling at about 250 - 280 knots. The ground speed and "true" airspeed would be greater, but the speed the aircraft feels (IAS) would only be as mentioned.

[mickjoebill]

Thank you!

Mickjoebill

[Basil]

Me ol' RAF Computer Dead Reckoning Mk. 4A. and I think the following could be ball park figures:

35000' M0.82 TAS 470 IAS 275
30000' M0.79 TAS 460 IAS 295
20000' M0.66 TAS 405 IAS 310

At about 170kn I've known a chunk of rubber from a B747 tyre burst go forward, bounce off the wing and damage the fan of an engine well forward of the tyre. Or perhaps the bit which left the mark on the wing wasn't the same piece which entered the engine which, I may say, continued to run perfectly (RR RB211).

Since, in real circumstances you'd be doing about 460kn, I think it may be a bit difficult to depict accurately. I'm sure you will be able to edit the speed up a bit :ok:

[mickjoebill]

Thanks Basil,

Mickjoebill

[sb_sfo]

You might also want to look into the UA811 accident in 1989. Various items from inside the fuselage were found in #3 and #4 engines. On a lump, #4 is better than 50 feet from the side of the fuselage, I believe.

United Airlines Flight 811 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/United_Airlines_Flight_811) will get you some basic info.

[Basil]

Re the UA811 accident, if you intend to have a hole in the side of the aircraft and both engines on that side out and want to impress professional jet transport pilots remember the following:
1. In level flight the aircraft will require almost full rudder and aileron to maintain direction. This is because, in addition to having the engines out, there is additional drag from damage on that side.
2. As speed is reduced and flap is extended for landing, drag will increase and more power will be required. More power equals more control input. No more control is available so aircraft will roll toward dead engines - bye, bye.
3. Solution: Commence descent and flap extension from 30 miles and 10,000ft so that live engines remain well below full power. You cannot fly level and are committed to land with no possibility of a go-around.