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Inverted 717...not a Sim

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Inverted 717...not a Sim

Old 21st Jul 2019, 19:16
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Inverted 717...not a Sim

Am not allowed to post links yet. But, if you go to YouTube and search for 'Stall 717-200' there is cockpit test flight footage that is eye-watering.

A search indicates that this particular footage has not been discussed before on PPRuNe. So, question from a non-pilot: The snap left hand wing drop in approx 1.5 seconds and roll into fully inverted: is this a characteristic of most T tail aircraft...or are others more benign? And there was me thinking T tail aircraft were prone to super stalls...only to see this!



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Old 21st Jul 2019, 19:22
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Old 21st Jul 2019, 19:35
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That's the one ORAC. Thanks for the link. Love the comment at the end from the chap on the Jump Seat "I'll see how they're doing down the back..." !!
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Old 21st Jul 2019, 21:05
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That clearly wasn’t what they expected; any idea what they were trying to do?
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Old 21st Jul 2019, 21:26
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Originally Posted by ShotOne View Post
That clearly wasn’t what they expected; any idea what they were trying to do?
Go to the avgeek link below the video - it discusses it (a power-on stall) - and yes the result was obviously unexpected.
When I was on stall related flight testing, everyone was strapped in so it's unlikely anything bad happened in the back (maybe some dirty underwear or used vomit bags).
All the experimental flight test pilots I dealt with were first class stick and rudder types (a few were also rather arrogant - but most were really good, friendly people).
Probably the most nervous I ever got on a flight test was on the 747-8 - we were testing some new engine venting hardware and the condition was to fly at a 20 degree yaw (!) to make sure the vent worked properly. We were somewhere over central California at 10k, but perhaps only 6k or 7k AGL. I was observing in the flight deck and it was clear how much the aircraft didn't like flying with that much yaw. I kept thinking, if we suddenly departed controlled flight, we didn't have much altitude available to recover , but the pilot nailed it. The condition was to hold the yaw one direction for 30 seconds, take a break, then do it the yaw other direction for 30 seconds. The first condition the pilot struggled a bit to hold a consistent 20 degree yaw, but he was a quick study and the second condition was rock steady.
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Old 22nd Jul 2019, 01:13
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It wasn't your regular straight ahead stall. They were doing some test or another regarding side slip limits, you can see from the control wheel the amount of right aileron being applied prior to the break. Unexpected result? I bet not. You don't cross control like that to the point of stall without expecting an exciting ride, simple aerodynamics will tell you why.
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Old 22nd Jul 2019, 02:09
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Megan, I'm pretty sure they're doing a 'wind up turn' - you can't do a power on stall straight and level since to stall straight and level, you need to slow down and you can't slow down with 'power on'. In a 'wind up turn', you keep the thrust high, then keep pulling the turn tighter until it stalls (usually when it stall, you just fall out of the turn). We did a lot of wind up turn flight testing to test the inlet at high power/high angles of attack.

As for the apparent cross control going on, that's a good question as to what they were attempting. But I've never, ever heard of a flight test condition where the plan was to 'depart controlled flight'...
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Old 22nd Jul 2019, 02:51
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Of course, any self-respecting aerobatic pilot would expect a smart crack on the back of the helmet from the IP if he rolled 30 degrees past inverted and then recovered by rolling back 210 degrees rather than just rolling through and recovering wings level...
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Old 22nd Jul 2019, 06:33
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Not a wind up turn td, heading remains constant. Example of a wind up turn at 4:30, no cross controlling.


From
Keith Freitas - B717 (MD95) flight test was done out over the Pacific in the VFR Area called W-291 which start south of Catalina down to Mexico. This is Fuse T-1 and had a nasty stall behavior and these flight were done to figure out why. Eventually the fuse got chopped up in LGB.Capt Gary "Bear" Smith, and in the right seat is Capt Tim Dineen, if memory serves me right, that day as I was one of the Dispatchers on duty. There were several of these tests done and other MDC pilots may have flown other flights with Capt Smith. There was always a minimum crew of the 2 pilots and 1 or 2 engineers on these flight. MDC employeed alot of Navy and Air Force pilots.
Side note:
Capt Smith was a Blue Angel and was still active in the Naval Reserves, and was a McD test pilot. He died in 2005 in his Super Decathalon while giving advanced flight instruction to an instrument-rated private pilot near Oroville; apparently the student was at the controls.
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Old 22nd Jul 2019, 07:18
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Originally Posted by tdracer;10524613,
you can't do a power on stall straight and level since to stall straight and level, you need to slow down and you can't slow down with 'power on'.
That would depend on your current altitude, weight, configuration and which side of the drag curve you're flying at the time, surely...

PDR
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Old 22nd Jul 2019, 18:43
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Originally Posted by PDR1 View Post
That would depend on your current altitude, weight, configuration and which side of the drag curve you're flying at the time, surely...

PDR
Fair enough - if you're at 39k and heavy it might be possible to stall going straight and level with the throttles full forward. But at sub cruise altitudes you need to do wind up turns - specifically when we were testing for inlet compatibility in the takeoff envelope which only extends to 17k (it was also rather unpleasant for the body - the only time I've ever had motion sickness in an aircraft was after about 4 hours of wind up turns ). OTOH, when I was onboard for 'normal' stall testing we'd just fly straight and level and gradually slow down until the wing stalled (it was rather humid and the engineer geek in me got a kick out of watching the condensation show the flow separation develop over the wing)

Megan, are you sure they're not turning? With the resolution of the video I can't really tell (and for some reason my browser won't let me go to full screen on embedded videos).
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Old 23rd Jul 2019, 00:20
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are you sure they're not turning
Not turning td. Below the attitude indicator in the box top centre of screen you can see the top of the HSI (compass) is locked onto a constant heading while maintaining a fixed angle of bank, I estimate about 20 - 30°. I'd assume because of the large side slip angle a lot of drag is being produced which may explain the high power.
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Old 23rd Jul 2019, 01:26
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Originally Posted by tdracer View Post
...(and for some reason my browser won't let me go to full screen on embedded videos).
[fyi]
Not playing embedded vids full screen is a quirk of some message boards.

Once you have the embedded video playing, click on 'Youtube' at the lower right.
That will take you to the video on the Youtube site, where it will play full screen.
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Old 23rd Jul 2019, 06:43
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Originally Posted by tdracer View Post
and for some reason my browser won't let me go to full screen on embedded videos
Start the video running, then click on the YouTube logo in the bottom RH corner. That will open a regular YouTube page in a new tab, with the video running, and then you can go to full-screen.
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Old 23rd Jul 2019, 11:38
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As to whether the pilots were expecting this, and whether it was normal:

The linked article clearly states that this was a follow-up test of previously-reported "unusual stall characteristics" with this airframe - first off the line.

So yes, this crew was intentionally pushing the envelope hard to find out what was going on, and likely expected quite a ride.

And this particular airframe was in fact never sold, but later scrapped.

The particular 717 was the first off the line. The aircraft had previously experienced some unusual stall characteristics. This test was an attempt to determine why so that engineers could solve the issue.
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Old 23rd Jul 2019, 22:35
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Originally Posted by megan View Post
Not turning td. Below the attitude indicator in the box top centre of screen you can see the top of the HSI (compass) is locked onto a constant heading while maintaining a fixed angle of bank, I estimate about 20 - 30°. I'd assume because of the large side slip angle a lot of drag is being produced which may explain the high power.
Thanks - I see it now - I was so focused on the PFD that I completely missed that the HSI was visible right below it.

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Old 23rd Jul 2019, 22:49
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Originally Posted by pattern_is_full View Post
As to whether the pilots were expecting this, and whether it was normal:

The linked article clearly states that this was a follow-up test of previously-reported "unusual stall characteristics" with this airframe - first off the line.

So yes, this crew was intentionally pushing the envelope hard to find out what was going on, and likely expected quite a ride.

And this particular airframe was in fact never sold, but later scrapped.
Did they ever find or infer why this particular airframe had these "unusual stall characteristics"?
What was different about it?

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Old 23rd Jul 2019, 23:14
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WingNut, over the years I've tried researching the event but unable to find info. Someone else may have better luck. Track down one of the crew?
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Old 24th Jul 2019, 00:23
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WingNut, no information on this particular case, but interesting 'errors' are not uncommon during the assembly of the very first aircraft off the line. A couple of examples that I do have knowledge of:
The first 767 - VA001 - the wing wasn't straight. No idea how it happened, but apparently the wing on one side of the aircraft had 2.5 degrees more sweep than on the opposite side.
The first 777 - WA001 - somehow they managed to swap the front and rear main wing spars during build. It didn't affect the ultimate strength of the wing, but it did mess up the fatigue life. At the time, it was assumed that because of the wing error, we'd never be able to deliver it for commercial service. But it turned out that someone did the fatigue life calculations - it wasn't that bad - and they sold it to Cathay with a specific reduced fatigue life (it was one of the first 777s to be retired from service and scrapped).
When I was on assignment in Indonesia working on the N250 (~25 years ago - when it was called IPTN) - the IPTN test pilots told us that every single CN-235 off the line flew differently due to the unpredictable build tolerances. I didn't like flying on the CN-235 to begin with, hearing that was pretty much the last straw. Since the CN-235 was what they then used between Bandung and Jakarta, I took the train after that - it took 4 hours instead of 45 minutes, but it wasn't scary.
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Old 24th Jul 2019, 01:15
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megan / td - Thanks for response
It's hard to imagine how some of those would have slipped through. Very interesting nevertheless.

Never flew on a CN-235 - one of Habibie's pet projects, as I recall.
Seldom seen out east.

Have covered many miles in the old C-212 including Tanjung Bara - Pontianak - Seletar during evacuations following civil disturbances associated with Tim-Tim independence.
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