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Dirty Birdy went down

Old 08-31-2014, 01:18 PM
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WRM
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Default Dirty Birdy went down

Fellows
I was flying my GP Dirty Birdy ARF downwind in a 15-20 MPG wind. I pulled back some
on the throttle to slow my downwind travel . I began to set up for a 180 turn . Nearly completely
through the turn the plane suddenly nosed down . I had absolutely no control .The plane went
down and was totaled . Was this a high-speed stall or a down draft ,or what do you think?
Old 08-31-2014, 03:16 PM
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8178
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He who stallith fallith.
Old 08-31-2014, 05:16 PM
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WRM
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I you are not from Texas . We fly in this all the time.
Old 09-01-2014, 06:09 AM
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BeauMiller
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Sounds like a stall of the LOW speed variety. An accelerated stall, or a high speed as you say, would be the result of exceeding the critical AOA with either positive or negative G force. A recovery from this is easy, because you just need release pressure to exit the stall. The aircraft will be flying again and all control surfaces should react normally.

A low speed stall would result in the situation as you described, where you lose all control (at least elevator control).

Of course, this is all speculation based off your limited description. Did you check the model for the possibility of control surface failure or radio issues? Texas isn't the only place where people have to fly with wind you know.

EDIT TO ADD: Also, if it was a downdraft or wind issue, I would expect the aircraft to keep a similar pitch attitude, but either drop or rise vertically depending on the conditions. A dramatic wind shear to a tail wind could cause the situation you described. The changed from a strong headwind to a tailwind would cause the indicated airspeed to drop, which could result in a stall and the nose dropping. Unlikely though, if you were landing into a headwind.

Last edited by BeauMiller; 09-01-2014 at 09:51 PM.
Old 09-01-2014, 11:32 AM
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I agree with BeauMiller. Good post. Any crash hurts bad but at least you were flying an havin a kik azz time. What kik azz plane shall i fly next, and how soon can ya make that happen?
Old 09-02-2014, 03:32 PM
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Hi,
Did You try any throttle before it hit the ground? Or was it 100% out of Control?
How steep bank was it in the turn? More bank and turn the more lift is required and stall speed increase rather much as bank increase.

Was anyting left of the radio gear in the plane? If Yes, have You tried the radio again after the crash and did it work?
Is the radio rather new 2.4 GHz or is it an older radio?

/Bo
Old 09-03-2014, 11:01 AM
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Sorry for your loss! It sounds like a classic 'downwind turn stall'. It happens in full-scale as well.

Because you're flying using visual reference, with no airspeed indicator, the plane seems to be going plenty fast so you reduce power just a bit. If you had an airspeed indicator or telemetry, you probably would have seen you were very close to stall speed. Bank the wing, give a little up-elevator to hold altitude (because now it's quite a ways downwind and low), and you've run out of airspeed without realizing it.

How to prevent this? I teach people to fly a bit mechanically. When the wind is calm, fly the downwind leg with just enough throttle and elevator (trim if needed) to hold altitude. This throttle setting will remain constant in steady winds (add a couple clicks when gusty) as well as no-wind. Reduce power just a bit to start a descent, but don't pitch up unless needed. Throttle controls altitude, pitch controls airspeed.

When it's windy and the plane is getting blown downwind at that seemingly too-fast speed, keep the same throttle and pitch setting, but start the turn to base quite early. The crosswind on base leg will slow your progress, as will flying into the wind on final (the airplane will seem too slow). Leave the throttle alone, unless correcting for gusts. The plane is trimmed for an airspeed and it will seek it. Landing into a headwind seems much slower because the groundspeed is low, but the airspeed is enough to fly.
If you're bouncing your landings, that's another sign your airspeed is not correct - it's too fast.
Old 09-09-2014, 08:44 AM
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Did the same type of stall with and Ultra Sport. Didn't see it, thought I had negative attitude but must of had positive in the turn as I cut power to be slow into my set up for final and ended in a stall with the same results of an uncontrolled spin into the ground.
Old 09-09-2014, 11:58 AM
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Apparent wind speed is your forward speed less tailwind. You stalled.
Old 09-12-2014, 08:52 AM
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Originally Posted by WRM View Post
Fellows
I was flying my GP Dirty Birdy ARF downwind in a 15-20 MPG wind. I pulled back some
on the throttle to slow my downwind travel . I began to set up for a 180 turn . Nearly completely
through the turn the plane suddenly nosed down . I had absolutely no control .The plane went
down and was totaled . Was this a high-speed stall or a down draft ,or what do you think?
The DB wing had that weird character built in. The problem had always been a smallish wing for the load it carried. Back in the early 80's when I flew DB's I learned the hard way I had to keep in some speed to keep the wing flying. The 8# + weight of the crate didn't help. Way way overdesigned which made it much heavier than needed. Luckily mine wasn't totaled on it's first crash (between two cars as I recall, it crash landed on its wheels; lucky me)

EDIT- latter scratch built efforts removed more than a pound of dead weight which made the crate fly as it was intended.
Old 09-13-2014, 06:37 AM
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"It sounds like a classic 'downwind turn stall'. It happens in full-scale as well"
Just not so, not at all. If it were so, every time a boat is turned "down stream" it'll get swamped. Relative wind is relative wind, ground speed and airspeed (true, indicated, or calibrated) are not.
Sounds like your DB was too slow in the turn with an increasing load factor leading to a stall, a great classic pattern ship, hope you're able to put together another one.
hook

Last edited by hook57; 09-14-2014 at 04:47 PM.

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