Some stall testing in a Grand Caravan

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PilotDAR
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Some stall testing in a Grand Caravan

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I flew about 40 stalls, and all configurations, in a modified Cessna 208B Grand Caravan yesterday. Here's a video made by the Engineer who was right seat to me. It was a really bright day, so some instrument face reflections. But, you can see on each of the instruments what's happening.

The requirement was to demonstrate the airplane with the modifications was "spin resistant" (equivalent level of safety). So (in accordance with an approved flight test plan and on a flight permit) I approached the stall configured with full flaps, 75% power, brought the plane to the stall, and as the nose dropped, applied full nose up control, and held it against the stop for at least three seconds. After that, I lowered the nose (Indeed, full nose down for a moment), and the bank angle had to be controllable within 60 degrees, which it was. The slowest speed I saw during this stall was 41 KIAS (Cessna's correction chart does not go that low, so KCAS not known). The airplane passed all of the stalls during the testing, though this was one of the more demanding.

As we were lighter weight, and a more aft C of G, a few of the stalls required full nose down control to be applied and held to initiate recovery. Other stalls I was required to demonstrate were with 30 bank, slipped one ball out, 75% power, which the plane handled similarly well.
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Re: Some stall testing in a Grand Caravan

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Other stalls I was required to demonstrate were with 30 bank, slipped one ball out, 75% power, which the plane handled similarly well.
What would an aeroplane have to do (or not do) to fail this test?
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Re: Some stall testing in a Grand Caravan

Post by Schooner69A »

PilotDAR: What was the reason for the 1500 fpm climb? Couldn't get it to satisfactorily stall otherwise?
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Re: Some stall testing in a Grand Caravan

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What was the reason for the 1500 fpm climb? Couldn't get it to satisfactorily stall otherwise?
It is required by the standard to approach the stall at one knot per second deceleration, and I was at 30 flap. Maintaining a particular altitude is not a requirement of that stall standard. With 75% power set, it was inclined to climb, and trying to decelerate at the specified rate meant it would continue to climb to the point of the stall. Other stalls are done at lesser power settings, and there is little or no climb with those. Being a turbine, I did not want to slow and add power going into the stall [to be at 75% at the onset of stall], both for care of the engine, and not to be changing the configuration of the plane as the stall neared.

So;
What would an aeroplane have to do (or not do) to fail this test?
The requirement is that the plane remain within certain roll and heading change limits (varies by type of stall entry) during the recovery (not spin). So how you get to the point of the stall, as long as it's not inertial, is less important than what the plane does when it stalls from the set condition. The one knot per second maximum deceleration rate is a part of assuring that the entry is not inertial. Other stalls I was required to enter were more intertial, where the decel rate must be entered at 3 - 5 knots per second, and pulling some G.

The "normal" power off stalls are done too, where there is little altitude change during the approach, so a "normal" stall from a training perspective. The requirement for 75% power is to show that the torque is not changing a decent stall into a spin. Though I resisted in the Caravan, I have been required to enter both stalls and spins at 75% power, and that can yield some startling entries!

I tested one brand new certified plane many years back (I won't be identifying it), which was later found to have a defect in rigging. It spun viciously no matter how precisely I approached even a power off stall. That was a fail, and reported to TC as such. The rigging defect, and manufacturing error which allowed it was corrected under TC supervision.

As I aid, I did about 40 stalls in the Caravan yesterday, of all different types, so just about every possible abusive entry was tested. The Caravan is an excellent plane to stall. That's not an invitation, nor a suggestion, just the results of the required testing! The stall in the video was in the last hour of 12.7 hours of flight testing for the mod. I think I'm flying it again with a TC crew in January, if they wish. In the mean time, there are dozens of pages of reports for them to review!
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Re: Some stall testing in a Grand Caravan

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Do you have a ballistic parachute to exit an unrecoverable spin? I'm just curious quite how far things can go wrong. After all, if you were certain about the results of the test, you wouldn't have to test.
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Re: Some stall testing in a Grand Caravan

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if you were certain about the results of the test, you wouldn't have to test.
I can't use the word "certain", but I'm comfortable with "very confident". The test is a demonstration of compliance. Approval of the modification requires that compliance with the design requirements be demonstrated and found [by the authority, TC, in this case]. TC may choose to make a finding based upon a report of a demonstration of compliance, or they may choose to see for themselves - come flying with me. I have not heard which yet, though I think they like to come flying, just 'cause it's fun! recent events with the 737MAX, have made TC more inclined to "see for themselves" and who could blame them!

No spin 'chute, though they are a safety feature, they also have their hazards. From my previous experience flying one turn spins in a Grand Caravan, and both C of G extremes, I was very confident that this testing would not require extra recovery aides. And, this test did not require that I actually enter a spin, much less hold it in for a turn. It was a demonstration of the airplane's natural resistance to spinning, which is excellent!

It is noteworthy, for those pilots who might wonder what one does with all of that range of control motion. Note that in seconds, I went from applying and holding the elevator against the nose up stop, to applying and momentarily holding against the nose down stop. It is possible to need all of the control available. I have flown a misrigged Cessna 206, to find that I did not have enough nose down elevator to break a stall with 20 flap. I returned it for a rigging correction. Seven flights after that, it flew right!

As a final note about the use of nose down control in the Caravan, the stall warning silences the moment the control wheel hits the forward stop. Perhaps because the stall is recovered, but certainly because there's a switch in there somewhere which silences the stall warning horn if the elevator is full nose down. This is simply to prevent nuisance stall warnings while taxiing in the wind. I found this while taxiing back after a flight, and I was holding the elevator a little off the nose down stop. The stall warning was bleating. I relaxed the elevator, and the bleating stopped. I'd have to agree that if you have reached full nose down elevator in flight, either the stall is recovered, or it's about to be, there's not much more you could do with the elevator to recover the situation!
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