Author Topic: Flight model problem? (Read 123 times)

Fidd · « **on:** June 04, 2002, 10:10:41 AM »

I've noticed that pushing negative G at slow air-speeds causes the stall-warner to operate. Makes me wonder if somthing isnt a bit porked in the flight-model?

Fidd

Mister Fork · « **Reply #1 on:** June 04, 2002, 10:20:34 AM »

Heck I thought it was just my eyeball veins popping...

I'm so smart... s m r t...

CptTrips · « **Reply #2 on:** June 04, 2002, 10:20:49 AM »

Why would you think that?

A stall occurs when the angle between the airfoil and the relative wind exceeds a critical value. That "critical angle" is +- degrees to the relative wind (although the critical angle might be different between the two depending on the airfoil shape).

I'm sure there might be problems in the FM somewhere, but this doesn't sound like one of them.

Regards,
Wab

Fidd · « **Reply #3 on:** June 04, 2002, 12:02:18 PM »

Your statement is correct, the value typically being 14 degrees (ish). My point was that when pushing negative g, the AoA is reducing, and therefore if not stalled previously, the stall warner should assuredly NOT commence at that point, ergo it is porked.

Evidently if you were to push massive negative g, you could incurr a negative AoA in excess of the critical angle - and the aerofoil would stall, but this state of affairs would only last as long as the wings remained attached!

I'd be interested to hear if anyone else gets this?

Fidd

Quote

Originally posted by AKWabbit
Why would you think that?

A stall occurs when the angle between the airfoil and the relative wind exceeds a critical value. That "critical angle" is +- degrees to the relative wind (although the critical angle might be different between the two depending on the airfoil shape).

I'm sure there might be problems in the FM somewhere, but this doesn't sound like one of them.

Regards,
Wab

CptTrips · « **Reply #4 on:** June 04, 2002, 12:35:34 PM »

I've just been trying it offline and have not been able to reproduce the effect you describe.

Heres what I did (tried both p51 and spit):

1. Take off and climb to 5k
2. Level off cut engine wait until just above stall
3. Neg G push over with maximum stick deflection

I was unable to generate sufficient neg AoA to activate the stall warning. In fact I never stalled at all until I had complete 3/4 of the outside loop and was climbing again.

Can you give us more information about how you are able to reproduce this effect? Can you go offline, reproduce it and give us a step by step procedure? Plane type? Fuel load? Speed? Alt? etc?

Theres no point in discussing whether its "porked" or not until someone else can reproduce it.

Regards,
Wab

CptTrips · « **Reply #5 on:** June 04, 2002, 02:00:59 PM »

Fidd?

Yippee38 · « **Reply #6 on:** June 04, 2002, 03:01:05 PM »

Try to produce an accelerated negative G stall, or try rolling inverted before pushing the nose over.

CptTrips · « **Reply #7 on:** June 04, 2002, 03:12:31 PM »

Neither of those is the behavior he described.

He said he was flying along at low speed but not yet stalled (I assume he wasn't inverted). He pushed over neg G and the stall horn immediately sounded. "Ergo" its porked.

That is the behavior he described. That is the behavior I have been trying to reproduce. I can't do it as he described.

Can you?

Wab

Yippee38 · « **Reply #8 on:** June 04, 2002, 09:46:08 PM »

I haven't tried (no time to fly tonight), but I was just trying to provide other possible scenarios that might produce the effect in question.

The reason I said inverted was if you're flying on the edge of a stall and push negative Gs, you're decreasing the angle of attack (unless you really shove it over hard, in which case you could force it to a negative angle which should cause a stall) .

Dunno. Just trying to help. I'll shut up now.