Exceeding Limitations - GA

[shdw]

There is a difference in no damage and not failing.

Thank you, I was trying to clarify that earlier in the thread. One last question though, you say "has to withstand 2G's," and tgray said, "the structure still must withstand a load factor of 2.0." To me, 2G's implies the same thing as a level 60 degree bank turn. When I read what tgray said, I assume a force 2 times greater on the controlling surface than that of typical level flight at Vfe. Do you see how confused I am from this? grr

Unless, structure implies aircraft and not flaps? If that is the case, then it all makes sense.

 

[tgrayson]

Unless, structure implies aircraft and not flaps? If that is the case, then it all makes sense.

Why not both?


§ 23.345 High lift devices.
(a) If flaps or similar high lift devices are to be used for takeoff, approach or landing, the airplane, with the flaps fully extended at VF, is assumed to be subjected to symmetrical maneuvers and gusts within the range determined by -
(1) Maneuvering, to a positive limit load factor of 2.0; and
(2) Positive and negative gust of 25 feet per second acting normal to the flight path in level flight.
(b) VF must be assumed to be not less than 1.4 VS or 1.8 VSF, whichever is greater, where -
(1) VS is the computed stalling speed with flaps retracted at the design weight; and
(2) VSF is the computed stalling speed with flaps fully extended at the design weight.
(3) If an automatic flap load limiting device is used, the airplane may be designed for the critical combinations of airspeed and flap position allowed by that device.
(c) In determining external loads on the airplane as a whole, thrust, slipstream, and pitching acceleration may be assumed to be zero.
(d) The flaps, their operating mechanism, and their supporting structures, must be designed to withstand the conditions prescribed in paragraph (a) of this section. In addition, with the flaps fully extended at VF, the following conditions, taken separately, must be accounted for:
(1) A head-on gust having a velocity of 25 feet per second (EAS), combined with propeller slipstream corresponding to 75 percent of maximum continuous power; and
(2) The effects of propeller slipstream corresponding to maximum takeoff power.

 

[shdw]

(1) Maneuvering, to a positive limit load factor of 2.0; and

This is the particular structural limitation you were defining, which now makes sense. Now I don't see how this means both the flap structure and the wing structure. Maybe my confusion is with basic physics.

What I mean is, if x force is placed on the flaps at 30 degrees at 70 knots, increasing to a 2g load would not yield a value of 2x on the flaps. It would increase the load on the flap by a factor of the ratio of lift that the flap device gives in comparison to the wing, I would think?

The flap doesn't produce all the lift and thus doesn't take all the load, is what I think I am trying to say. So am I botching basic physics here?

 

[tgrayson]

So am I botching basic physics here?

No, but maybe basic arithmetic. Let's say that the distribution of lift between the wing and flap was .7 and .3. If you double the quantity of lift across the wing, that would make the distributed lift 1.4 and .6.

This is assuming that the lift distribution is constant at the increased AoA, which is probably a false assumption.

 

[Douglas]

2) He forgot to retract the flaps during a takeoff and instrument approach (10 minutes of flying over Vfe with the flaps in T/O position - probably < 10 degrees).

Nothing personal about the guy but is it possible that he doesn't know that Vfe is for full flaps. Approach flaps are restricted to below 152 knots IIRC, which is can be difficult to reach with the flaps set to approach and the typical I'm-staying-in-the-local-and-cheap power settings.

 

[shdw]

No, but maybe basic arithmetic. Let's say that the distribution of lift between the wing and flap was .7 and .3. If you double the quantity of lift across the wing, that would make the distributed lift 1.4 and .6.

This is assuming that the lift distribution is constant at the increased AoA, which is probably a false assumption.

Wow...talk about a brain fart.

 

[Chief Captain]

I'll go ahead and say that I'd take it in for an inspection too. Can't be too careful.