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-   -   CAF Dakota crash, Burnet, TX 21-7-18 (https://www.pprune.org/rumours-news/611358-caf-dakota-crash-burnet-tx-21-7-18-a.html)

sablatnic 23rd Jul 2018 05:53

Could look like a gust lock at :30 sec. A square plate at the root of the elevator.
https://www.youtube.com/watch?time_continue=1&v=BUtxp4V-jPw

http://i889.photobucket.com/albums/a...psq9g7zhkv.jpg

oxenos 23rd Jul 2018 08:34

No discernable elevator movement during the take-off attempt, but one of the post crash photos clearly shows the elevator hanging down . Given that the control gust locks are external this cannot be a result of cables shearing and releasing the elevator to drop under its own weight. Possible that the lock got knocked off during impact, but that area of the plane does not appear to have impacted anything, so unlikely.

Chris Scott 23rd Jul 2018 09:41


Originally Posted by bcmpqn (Post 10203588)
If elevator control locks were installed, would the be visible in the video. Not sure what they look like on a DC-3, as installed externally.


They are large wooden blocks, normally painted red and with a long red banner attached. But the banners tend to get frayed and shortened with time, so that's up to the operator. It would be astonishing if the pilot had not checked full-and-free control movement before starting the take-off. Hurried, multi-sector operations can lead to a degree of complacency. So failure to remove locks and pins, followed by failure to perform the pre-take-off check properly, has been done before. But that regime hardly applies to an historic-flight operation.

[Start watching at 11:00]

The key to this accident may lie in that pronounced swing to the left early in the take-off run. That could have been caused by a crosswind gust, but not by a locked elevator.

KiloB 23rd Jul 2018 09:44

I remember DC3 elevator gust locks as being long and relatively narrow (so that they don’t bear on the unsupported fabric portion of the elevator. They were retained by a bungee cord to the LE. Not likely to come off without significant damage having been caused to the stabiliser/ elevator. Rudder lock was shorter and just pushed on.
But I admit this was long ago and far away!

Centaurus 23rd Jul 2018 13:27


FWIW, however, here's the single paragraph describing the stall characteristics of the C-47, taken from the UK Air Ministry's Pilot's Notes for the Dakota 4, published in 1946 (my emphasis):
"There is little warning of the approach of the stall except for a slight tail buffeting which may be felt some 5 m.p.h. (kts) before the stall itself. At the stall the nose drops gently. In all cases recovery is straight-forward and easy."
And that is certainly true because the test flight to determine the stall characteristics would have been in level flight and speed gradually reducing at one knot per second until the stall occurs. A similar discussion arose several years ago on Pprune about DC3 stalls. My experience on type confirmed that a wing drop would occur with startling rapidity if the power was on and in level flight. Test pilot John Farley replied on Pprune that a sharp wing drop would occur if the stall was approached at a faster rate than one second per knot reduction. That may explain why reports of a vicious wing drops during practice stall recoveries were quite common in DC3 days.
That was because pilots would tend to raise the nose to around ten degrees above the horizon to accelerate speed reduction towards stall IAS, rather than gently maintain level flight while reducing IAS at approx. one knot per second which I think is a certification parameter.

Chris Scott 23rd Jul 2018 14:16


Originally Posted by Centaurus (Post 10203942)
And that is certainly true because the test flight to determine the stall characteristics would have been in level flight and speed gradually reducing at one knot per second until the stall occurs. A similar discussion arose several years ago on Pprune about DC3 stalls. My experience on type confirmed that a wing drop would occur with startling rapidity if the power was on and in level flight. Test pilot John Farley replied on Pprune that a sharp wing drop would occur if the stall was approached at a faster rate than one second per knot reduction. That may explain why reports of a vicious wing drops during practice stall recoveries were quite common in DC3 days.

One assumes there must have been problems in the very early days for NACA to do that test programme with United Airlines as early as September 1937. Without running the video for a second time, I think the speed decay in each demonstration run is fairly modest. But they do investigate power-on and banked stalls. I also infer that they considered the retrofitting of the sharp leading-edge inboard of the engines solved the problem, so it's interesting to read the comments of you and others.

That was because pilots would tend to raise the nose to around ten degrees above the horizon to accelerate speed reduction towards stall IAS, rather than gently maintain level flight while reducing IAS at approx. one knot per second which I think is a certification parameter.
Yes, I'm sure that 1 kt/s deceleration is used for certification. I guess that covers the approach case quite well, but not the sudden pull-up to avoid an obstruction.

Vzlet 23rd Jul 2018 15:01

One type of lock:
https://cimg7.ibsrv.net/gimg/www.gmf...7366945904.jpg

Three Lima Charlie 23rd Jul 2018 15:02

In this photo you can clearly see the elevators down, no control lock. Later in the fire, the elevators sag to the ground and move upward to a more neutral position.

https://static-16.sinclairstoryline....?1532222524452

oxenos 23rd Jul 2018 15:41

https://static-16.sinclairstoryline....?1532222524452
Yes, that was the photo I was refering to in post no. 42.

Tailspin Turtle 23rd Jul 2018 20:57


Originally Posted by Three Lima Charlie (Post 10204039)
In this photo you can clearly see the elevators down, no control lock. Later in the fire, the elevators sag to the ground and move upward to a more neutral position.

https://static-16.sinclairstoryline....?1532222524452

In later pictures, the aft fuselage has canted to the right with the right hand stabilizer and elevator tips resting on the ground. That's why the elevators look to be streamlined with the stabilizer in those pictures.

Eric Janson 23rd Jul 2018 22:04

One other thing that will affect the severity of a stall in a DC-3 is the control rigging. If the ailerons are not rigged correctly you can get an abrupt wing drop.

I know of one case of buffet followed by the aircraft rolling almost inverted - told to me me by the Captain doing the training.

Chris Scott 23rd Jul 2018 22:14

To re-state the obvious, none of these discussions of DC-3/C-47 stall characteristics, interesting as they are, helps to explain why the tail-wheel remained more or less on the ground until the a/c became airborne.

Mach E Avelli 24th Jul 2018 01:03

It is fairly apparent that it became airborne before it was meant to. Think about an aircraft doing, say 40 knots. Stall speed is about, say 60. Encounters a rapid increase in headwind of say, 25 knots. It will fly until that headwind component drops back to say, 15. Then we see the behaviour that others have discussed. What happened appears obvious - it stalled just after lift-off. Until the pilots are interviewed, why it happened is the mystery.
As an anecdote, I have heard of a DC3 becoming airborne with the elevator gust lock still attached. The crew flew it to a successful landing using trim. Don't know whether fact or fiction, but believe it could be done in the right conditions.

cncpc 24th Jul 2018 01:50


Originally Posted by Three Lima Charlie (Post 10204039)
In this photo you can clearly see the elevators down, no control lock. Later in the fire, the elevators sag to the ground and move upward to a more neutral position.

https://static-16.sinclairstoryline....?1532222524452

The left stab/elevator hit the ground partway through the sequence. It appeared to be quite a whack and there was a distinct dust cloud generated.

Pilot DAR 24th Jul 2018 01:56


Think about an aircraft doing, say 40 knots. Stall speed is about, say 60. Encounters a rapid increase in headwind of say, 25 knots. It will fly until that headwind component drops back to say, 15.
If the pilot lifts the tail of a taildragger, it'll stay on the runway. It is possible to run a taildragger down the runway at a speed much greater than the normal liftoff speed for that weight, just by lowering the nose enough. The same principle applies in landing taildraggers, once the main wheels are on the runway during a wheel landing, lifting the tail a bit will prevent a bounce.

I can imagine a wind gust from 15 to 25 knots in some circumstances, zero to 25 knots is much less common - that would be quite a ride for most types! A 15 to 25 knots gust is easily managed in any certified airplane, with a little piloting skill. A 25 to 15 knot lull next is the reason to lift the tail of a taildragger, and hold it on the runway a little longer, so the margin of speed over the gusts is what you want to maintain control nicely.

Airbubba 24th Jul 2018 02:30


Originally Posted by Mach E Avelli (Post 10204369)
As an anecdote, I have heard of a DC3 becoming airborne with the elevator gust lock still attached. The crew flew it to a successful landing using trim. Don't know whether fact or fiction, but believe it could be done in the right conditions.

I believe one case of a DC-3 taking off with the gust locks on and landing successfully occurred on December 27, 1984, perhaps out of Naples, Florida, with PBA (Provincetown-Boston Airline). The feds had given PBA their operating certificate back earlier in the month after an emergency revocation for shady practices like pencil whipping DC-3 type ratings and flying a YS-11 without a type rating.

Tragically, a PBA EMB-110 crashed in Jacksonville, Florida three weeks earlier with the loss of all 13 people on board so the gust lock incident received little notice outside the local area. The DC-3 gust lock takeoff is mentioned in this 1985 Inc. magazine article about the rise and fall of PBA which at one time was the largest commuter airline:

https://www.inc.com/magazine/19850301/1288.html

Mach E Avelli 24th Jul 2018 05:06

I currently run training in two quite different simulators. In the more primitive when windshear is selected it produces fluctuations of IAS about 20 knots, with sink rate about 1000fpm. So this is a very crude simulation of just one type of windshear.
The more advanced simulator has preprogrammed models of generic and actual historical events, including increasing head and tailwinds on the runway and airborne. Several produce a rapid change of 25 knots in IAS, so I do think big and instantaneous changes would accompany a down burst over the runway, or occur in the surrounds of a dust devil. If the tail was already up it could be possible to ‘pin’ a taildragger to the runway and not go flying unintentionally, but if the tail was still down it would be airborne - like it or not - if the gust was strong enough. If the gust was sideways, even with the tail up the chances of a runway excursion would be high, no matter how skilled the pilot.
Sailing in the sub tropics, I once got too close to a water spout. Not much you can do to avoid them when you are doing 5 knots. I can assure you that the wind went from a few knots to about 40 in a trice. We got flattened, yet a minute or so later all was calm again. Scary stuff on water, potentially deadly in the air.

cappt 24th Jul 2018 05:30

That was really ugly, looked like it went off the left side of the runway before they pulled it up and rolled it right. It will be interesting to find out who was on the controls.

Mach E Avelli 24th Jul 2018 06:51

It would be interesting to know what it was that had the guy taking the video invoking religion and excrement so early in the take-off run. He appears to have seen something unfolding before it actually did. Let's hope he is a reliable witness.

LeadSled 24th Jul 2018 07:51

Long time ago, now, an RAAF C-47 was lost practicing "short field" takeoffs, prior to being used as part of the Australian antarctic flight.
They used a "tail down" takeoff run, got airborne more or less in the "three point" attitude.
What happened was described to me by the only survivor, who worked for Qantas for many years after the RAAF.
At very low speed, just lifting off, one wingtip was hit by a williewillie (dust devil/small whirlwind), a common and completely unpredictable event, and the aeroplane dropped a wing and cartwheeled.
A possible explanation??
Tootle pip!!
PS: Low speed characteristics of the DC-3/C-47, in the real world, were such that we always conducted stalling exercises at a minimum of 10,000 AGL, daylight CAVU only, not just VMC. The wing drop in the stall was quite sudden, with as near as made no difference nil warning, incipient spins were common, developed spins happened on occasions and were, apparently, quite scary, with a height loss of around 5000' being the norm.


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