Bede BD5 no permit to fly

[saaby93]

these used in octopussy
http://www.bbc.co.uk/news/uk-england-devon-3760796...
Whats leading them to fall out the sky?

[Eric Mc]

Wasn't the Octopussy version jet powered?

[saaby93]

BD-5J
https://en.wikipedia.org/wiki/Bede_BD-5
Quite a high failure rate but cant see any common causes

[CanAm]

Eric Mc said:

Wasn't the Octopussy version jet powered?

Yes and the one referred to in the OP's post was also jet-powered though the library photo showed a piston-engined version.

Edited by CanAm on Tuesday 11th October 17:49

[DamienB]

Are we sure it was a jet powered one?

Piccy here:

http://www.pilotweb.aero/news/bede_bd_5_in_fatal_c...

...shows a prop.

And contains this quote:

Pilot said:

Its one significant failing is that it pitches up after engine failure. If you don’t catch the pitch-up within two seconds (the FAA’s assumed fit, professional pilot’s reaction time) you can’t prevent it stalling. Depending on span and aerofoil, stall recovery takes around 500 feet. After that it’s fine, if you’re still above ground.

Considering the lack of protecting structure ahead of its pilot, I did later calculate the BD-5’s impact energy to be more than five times that of a glider of similar weight and cockpit structure, merely on the basis of its higher stalling speed.

[CanAm]

The original BBC news article on the crash from 2015 here refers to this particular plane being jet-powered. However your link looks to be a lot more reliable and accurate!

[Simpo Two]

It looks too short to be very stable to me. There's some Me163 in its lines!

[MartG]

Guessing the pitch-up issue is due to the high location of the engine/propeller - the aircraft would need to be trimmed nose-up to counter the nose-down effect of the high thrust line

[saaby93]

DamienB said:

Piccy here:

http://www.pilotweb.aero/news/bede_bd_5_in_fatal_c...

...shows a prop.

Would the jet be able to have a lower thrust line?

[Simpo Two]

MartG said:

Guessing the pitch-up issue is due to the high location of the engine/propeller - the aircraft would need to be trimmed nose-up to counter the nose-down effect of the high thrust line

That makes sense. Basic design error that could have been seen on the drawing board.

[davepoth]

Simpo Two said:

That makes sense. Basic design error that could have been seen on the drawing board.

Not really. Look at one on the ground:



You'd have ground clearance problems quite quickly if you lowered the prop centre.

[saaby93]

davepoth said:

Not really. Look at one on the ground:



You'd have ground clearance problems quite quickly if you lowered the prop centre.

What about lifting the wings to be on top fuselage?

[MartG]

saaby93 said:

davepoth said:

Not really. Look at one on the ground:



You'd have ground clearance problems quite quickly if you lowered the prop centre.

What about lifting the wings to be on top fuselage?

Would need a complete redesign e.g. the cockpit would need to be moved forward to make room for the wing spars to pass through - at which point you have a new aircraft design

[Simpo Two]

davepoth said:

You'd have ground clearance problems quite quickly if you lowered the prop centre.

Agreed; the problem of a pusher prop. But it has very short legs...

Essentially light a/c have evolved the way they have for good reasons. Try to be funky and you get something less good.

[saaby93]

Simpo Two said:

Agreed; the problem of a pusher prop. But it has very short legs...

Essentially light a/c have evolved the way they have for good reasons. Try to be funky and you get something less good.

It cant be good for tail strikes either
or CofG?

[Eric Mc]

Simpo Two said:

It looks too short to be very stable to me. There's some Me163 in its lines!

The 163 was actually a very stable and easy aeroplane to fly, according to Eric Brown. Its problem was the engine, not the airframe.

It evolved out of series of tailless gliders.

[Simpo Two]

Eric Mc said:

Simpo Two said:

It looks too short to be very stable to me. There's some Me163 in its lines!

The 163 was actually a very stable and easy aeroplane to fly, according to Eric Brown. Its problem was the engine, not the airframe.

My two points are really unconnected - the analogy was with the profile. The Me163 wing is swept and deep (as it would have to be with no tail).

[Eric Mc]

What is interesting is that the DH108 Swallow, which bore a passing resemblance to the 163, was very unstable and difficult to fly.

[Simpo Two]

Eric Mc said:

What is interesting is that the DH108 Swallow, which bore a passing resemblance to the 163, was very unstable and difficult to fly.

I'd say 'wings too long/too far back' - though I'm in no way qualified to make that statement (other than the fact I made lots of gliders as a teenager!).

[Eric Mc]

I think there were Centre of Gravity issues with the Swallow which was the main reason for its problems. Unlike the 163, which was pure design in that it was designed from scratch, the 108 was more "cobbled together", effectively a Vampire fuselage with new wings and the tail booms etc removed.

Three 108s were made, all a bit different in order to explore different flight regimes. And all of them crashed.