C-150 Unconventional Stall Characteristics

C-150 Unconventional Stall Characteristics

I own a 1972 C-150 and had a question regarding the stall characteristics.  My son is using the plane for flight training, and reported that if they stalled the plane in a level, full flaps, power off attitude, the plane immediately drops the left wing and enters a spin.  Only using full right rudder upon entering the stall will avoid the spin.  Is this a problem with the rigging, or is this some other problem?  The left wing leading edge was repairs several years ago after a bird strike, but the repaired wing looks to be the mirror image of the right wing, and all flight characteristics are normal except in the stall.  The right wing is usually a little "heavier" than the left due to fuel cross-feeding to that tank when it sits on the ramp.  Also, they did not try this with different flap settings, which would have provided more information, but after this experience the flight instructor was reluctant to attempt any more stalls.  I would be interested in hearing from anyone that has experienced this problem and getting some advice.

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Re: C-150 Unconventional Stall Characteristics

If the leading was replaced, the lower skin would have been removed during the process. The wing should have been placed in a fixture during repair to maintain the proper washout. The 150 wing has 1.5 degrees twist from the rib at the strut attach point, to the tip rib. This causes the inboard portion of the wing to stall first, still allowing some aileron effectiveness before full stall. If the wing was rebuilt with less or no twist, then it will stall all at once, while the other wing is still flying.

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Re: C-150 Unconventional Stall Characteristics

Thank you for the quick reply.  Is there a way for my A&P to verify this by inspection?  It sounds like a fairly expensive repair, requiring the wing to be removed, placed in a jig, and reriveted with the proper amount of twist.  I would want to be certain this is the cause before spending the money.

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Re: C-150 Unconventional Stall Characteristics

Yes, you can check it on the airplane. Info is in the service manual. Figure 18-2 Measuring wing twist. I was wrong above; twist for your model is 1 degree.
Del

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Re: C-150 Unconventional Stall Characteristics

I have an appointment with a mechanic to check this out.  However, I was flying the plane last night in very calm stable air, and notice when I had the plane trimmed for level flight, that the right wing would drop a little, and the ball was off center to the right.  The plane was holding a heading but the right wing was low.  I had to use a little left aileron to hold the plane level, and a little right rudder to center the ball.  Would this "heavy" wing condition also affect the stall characteristics?  Logic would lead me to think that if the left wing is generating more lift (counteracted by rudder deflection), then in level flight the left wing would also stall first.  I would appreciate any comments or advice.

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Re: C-150 Unconventional Stall Characteristics

Jon,
No, the left will not necessarily stall first. If your left wing has no washout or less than the right, it will generate more lift in cruise attitude, thus right wing heavy. However as you approach stall, your left wing will stall more suddenly because its angle of attack is more constant the full length of the wing. The right wing, on the other hand, will stall first on the inboard portion, then the stall will work its way on outboard more gradually because of the built in twist.

You can see this twist without aid of any special equipment. Stand with your back against the cabin door and look toward the tip. You'll see that the twist starts at the rib where the lift strut attaches. From that rib station the wing twist trailing edge up the further outboard you go. This decreased angle of attack allows more lift and drag to be generated by the inboard portions of the wings during cruise attitude, but also allows the stall to start inboard and work outboard. The outboard section will stall last to help maintain aileron control at speeds near stall, such as landing.

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Re: C-150 Unconventional Stall Characteristics

Oops.
When I stated above that the left wing will not necessarily stall first, then went on to explain that it will stall more suddenly, I forgot to mention wing adjustment.

Let's say your left wing does have less twist than the right; it will stall more suddenly. But, not necessarily first. The wings are adjustable, and it is possible to adjust the wings trailing edge up or down to find a happy medium where the stall is more manageable, but that would cause your right wing heavy condition in cruise, if you indeed have less washout in the left wing.

There are numerous factors involved in airframe rigging. You really need to find a mechanic who is familiar with your aircraft and has the patience to produce a result that your happy with.

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Re: C-150 Unconventional Stall Characteristics

Thank you Del.

I appreciate you taking the time to answer my questions.  I did locate a mechanic listed on the Cessna Pilot's Association web site in my area that has gone through their Cessna rigging training program, so I hope he can help me with this.  If you don't mind I would like to give him a copy of our forum dialog.

Thanks Again

Jon Plaxton

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Re: C-150 Unconventional Stall Characteristics

Jon, I took the Cessna Pilot's Association rigging course recently and I can recommend to any one looking for a mechanic that is qualified in Cessna rigging to select from this list. The instructors doing the class are very knowledgeable in this field.

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