Damage by flap airspeed limit exceedance

[Hardy Heinlin]

Good morning,

- flaps fully extended
- flap load relief doesn't work
- flap limit speed heavily exceeded

What kind of damage might result from this?

Broken surfaces?
Hydraulic leaks?
Fuel leaks?
Pneumatic leaks?

What would break first?


Cheers,

|-|ardy

[Will]

Probably nothing.  But if something did break, I'd guess that the first thing would be bends in the mechanism that extends/retracts the flaps, meaning that they'd get stuck in the extended position and wouldn't retract.  Or they'd retract only partially.  I await word from the experts.

[Hardy Heinlin]

While we're at it, same question for gear airspeed limit exceedance. What might fail if the gear is down at high airspeeds?

[Mundyas]

Hi |-|
You do raise some interesting questions. PSX will be great!

In respect to gear down I would think it would be very very unpleasant indeed! How do Boeing test for things like this, in a wind tunnel?

Not something to do on your check flight, instant fail.  

The "book - Handling the Big Jets" unusually doesn't offer an answer!  But you know this as you got this book out from your basement.

Am I hallucinating (I did have 2 pints at lunchtime but ..) has your picture very recently appeared with your postings?

Andrew

[Hardy Heinlin]

Check your pints :-)

[Mundyas]

Whoops |-|

Good thing I didn't have any more to drink today or ...

EICAS
 "FUEL QTY SYSTEM" - Less than 2 pints remaining or input/output interface inoperative due to pilot lunch time refreshment. or perhaps even  "FUEL QTY LOW!!"

After 4 pints I might have forgotten to lower the gear or if lowered would have raised it!

Andrew

[dutch57]

Hardy, nice ideas,

Flaps, with the boundries you five, following might happen, you lose the aft flaps, moveble flap track fairings, fore  flaps than you loose the complete flaps including its tracks and shear the torque tubes,

Hardy it depends on the weakest link if you have a worn attachment of fore of aft flaps or a bad carrage assi this will go first. On a perfect new system the flap tracks will shear as the are hung on the forward side with fuse pins they brake off if the load becomes to high.

These pins we inspect when an overdpeed or hard/overweight landing occurs.

structual damage to the wing can occur , the aft attachments are with bolts 2 each. hydraulic fail yes if a torque tube shears at the wrong place , fuel leak i doubt that.

[dutch57]

Hardy for the gears , following , if you extend the gear at to high speed , you will loose a few gear doors.

Nose gear can go aswell, still depending on the speed.
Body gears might end up in the aft cargo hold , the trunions will hold but the drag brace not.

Wing gear same story,

If you loose a gear, yes structual damage and loss of hydraulics and fuel leaks will occur.

Bob

[Avi]

Three was a flight of a B747-SP (Chinese?) that went into a spin and the pilot lower the gear in an attempt to get out of it.
It worked but some gear doors broke and hit the elevator.
The pilots struggled to land (in San Francisco) but did it.

I don't remember more than this but I'm sure others will remember now .



Cheers,

P.S.
Here is a link to a photo and the description of the accident

[delcom]

Hi Hardy,
here's my opinion:

During test flights I have observed that the OUTBD fore flaps seem to take quite a beat near flap limit speeds. Air loads are enormous on the T/E flap surfaces at this point, engines screaming around 95 N1, flaps 30 units...the entire a/c is shaking and vibrating violently. Just outboard of track 1 and 8 the fore flaps are going up and down like crazy as they were made out of rubber.
 
Nothing spectacular on the mid and aft flaps other than you feel the vibe in your bones, scanning the flaps with your eye and waiting for something to fail.  Loads will be transferred from the flap tracks to the rear and mid spar ( landing gear support beam on track 4 & 5) twisting the wing. It's the forward flap track fitting that's under tremendous stress. The aft two bolts ( four for track 4 &5) don't play role in our case...since they only support the weight of the flaps on ground and during touchdown. They get pressed up against the rear spar, end of story.

I don't think the aft flap crank and rods would bend or break. I don't think the fore flaps would break or separate from the toggle assy's.

It's the main carriage assy spindle and the forward track fitting fuse bolt that more likely will fail. The good news is, that both of these have additional safety hardware installed. The forward track fuse bolt has a fail-safe bracket, the main carriage assy spindle has a fail-safe link. I've seen broken main carriage assembly spindles. Hard to believe that a giant solid (dia of my arm) piece can shear. But it can. The fail-safe link saved the day, held the separated mid flap onto the bird. Aft bogie remains a fixed point, mid flap (+aft flap) can move up due to the fail-safe link i'd say by 100mm. This will cause serious flight characteristics change, acting like an aileron.

If the fuse bolt fails to shear on the FWD track fitting...this is the worse case scenario...the entire fitting might get ripped out. That might cause fuel leakage through eight little holes. Four of them diameter of my index finger, the other four dia of my pinky. At this point I wouldn't bother with this insignificant fuel leakage, because the departing fore mid and aft flap messed up the tail of the bird beyond recognition.

I cannot imagine a scenario where torque tubes fail due to excessive airspeeds. Remember...there's ballscrews and transmissions in the drivetrain.

I cannot imagine hydraulic leakage doe to excessive airspeeds, other than separated components messing up the tail.

I see no problem with the L/E flaps and drivetrain. Again...huge gear (down) ratio, not much additional torque reaching the torque tubes. I'll give it a thought what the weakest link would be on the L/E panels. (But it's insignificant).

regards,
delcom

[dutch57]

Delcom,

I've seen broken main carriage assembly spindles. Hard to believe that a giant solid (dia of my arm) piece can shear. But it can.

The spindle is hollow and they do tend to crack, i experienced a few cracked assy`s last one also the failsafe link was sheared.

The fail safe strap on the track assy will not prefent a track from comming loose, it is a u-strap around the fwd attach point put the track can move aft if fuse pin is sheared off.

We in maintenance find all sorts of worn parts in the flap drive system, from broken bearings  cracked fittings missing fairings.
The maintenance programm is quite intense, because of the load on the flaps during normal operation.

But a prediction of what will happen i think cannot be made, just a educated quess to much variables to take into concern.
Bob

[delcom]

So I'd implement something like this (just a thought, other ideas are welcome)

The anxious end user seriously exceeds flap limit speeds:

One main carriage assy would fail, causing less lift and less drag on the affected side. Autopilot still can cope with it...of course with some lateral input. T/E flaps can be retracted in flight and on ground as normally. This failure might go "undetected", other than the unusual aileron wheel position...can be trimmed. Pitch is a bit off, manageable.

The mad end user keeps accelerating:

More then one main carriage assy fails on one wing. Full counter aileron input is just enough to prevent slow roll. Pitch is waaay off but still manageable with serious inputs. Flaps can no longer be fully retracted in air. I'd put a jammed situation on 10 units.

Very mad end user trying out how Hardy really programmed the inop flap relief scenario:

Mayhem...flap separation, severe tail damage (read tail gone) so no elevator, no rudder, no stab trim, all 4 hydraulic systems gone (let's assume the hydraulic fuses went with it). Fuel leakage if she had HST. If our hero landed the big mamma somehow, no APU (it's swimming with the fish).

No logo light

regards,
delcom

[Hardy Heinlin]

Thank you, all.

I think I can implement some of your suggestions :-)

Re aileron: Whether left or right aileron is required probably depends on how far the flaps are extended. If we lose more lift than drag, we can lift that wing with the aileron. But if we lose more drag than lift, that wing will travel faster, generating some yaw which in return will increase the lift (Dutch roll). Hard to apply the correct aileron at the right time ...

Should the mayhem brake out only at flaps settings greater than 20? In that case I'd say we will lose more drag than lift (jammed at 20 units instead of 10).


Cheers,

|-|ardy

[delcom]

The spindle is hollow.

The wall thickness of the neck of the MCA is enormous, I wouldn't call it hollow. Indeed there is a hole inside the neck, but I'd say it's insignificant considering the diameter of the neck. If I roll up the release form really tight it fits in this hole. There is a lot of meat around it. In my opinion the AMM illustrations are exaggerated for both INBD and OUTBD MCA's.

Last time we ended up with a spindle in two pieces...one can imagine the forces involved capable of splitting it in two right at the forward thrust collar.

regards,
delcom

[Jeroen Hoppenbrouwers]

Interesting topic ID, this.

[delcom]

We in maintenance find all sorts of worn parts in the flap drive system, from broken bearings  cracked fittings missing fairings.
The maintenance programm is quite intense, because of the load on the flaps during normal operation.

Bob

We are in the same shoes then
Ironically I'll be crawling in M3 today in order to install a FWD flap track fitting we removed last Thursday. I'd rather be chilling on the beach having a cold one instead...but hey, the job has to be done.

cheers,
delcom

[delcom]

Interesting topic ID, this.

T/E flap load rel...Hey Jeroen, can I buy you a beer one of these days? It's finally sunny here. Piet Weerbericht keeps lying that it stays like this for the whole week. What do you say? I know some nice pubs near Wijk ann Zee...ck to 25 and 30 units.

proost,
delcom

[Jeroen Hoppenbrouwers]

I'm not regularly near Amsterdam but there are a few opportunities coming up so I'll try to remember!


Jeroen

[Hardy Heinlin]

On the big sims one can set asymmetric TE flap malfunctions. Has anybody tried this?

I wonder how great the asymmetry can get before all other controls -- aileron, rudder, thrust --  cannot compensate the error anymore. Full flaps on one side, no flaps on the other, certainly won't be flyable.


|-|

[delcom]

The fail safe strap on the track assy will not prefent a track from comming loose, it is a u-strap around the fwd attach point put the track can move aft if fuse pin is sheared off.

Hi Bob,
I'm not sure what you mean.

If a fuse bolt shears at one location only on a track, the fail safe strap will prevent the broken bolt falling out. If it shears at two locations, the nose of the track will drop down (with airloads on the flaps) onto the strap. It's the aft attachment bolts that will not let the forward end of the track to slide out of the fail-safe strap. If the drag vector is great enough to shear off the two aft bolts (or four for #4 and #5) the track can slide out of the strap leaving you with no flaps.

cheers,
delcom