"Discovery Wings" channel showcases a test pilot....

[frank wight]

And one of the "tests" is to fly high and level
and throw the after-burner switch, then go to idle,
and then back on after-burner.

Trouble is, they didn't actually film the event
and I'm curious about what such a procedure feels like.

Anybody know?

[Peter Stickney]

In article >,
(frank wight) writes:
> And one of the "tests" is to fly high and level
> and throw the after-burner switch, then go to idle,
> and then back on after-burner.

Sure. It's a pretty good way to induce a compressor stall. You also
stand a pretty good chance, if the engine is an an afterburning
turbofan, to get a pressure pulse up the fan duct, when the afterburner
relights, that can casue all sorts of inlet/engine airflow havoc.


>
> Trouble is, they didn't actually film the event
> and I'm curious about what such a procedure feels like.

A pretty good jolt of acceleration when the AB lights. Then a pretty
fair deceleration when the engine come out of burner and down to
idle. Then a pretty good jolt as things spool back up.
If all goes well, that is. Worst case, a pretty fair jolt when the AB
lights off, then a bunch of deceleration, as before, then no
accelration and a lot of racket as the engine tries to deal with the
disturbed off-design airflow. If it doean't sort itself out, then a
shutdown shutdown & airstart. If it doesn't restart, you may, (best
case) be putting your single engine landing drill to use, or, (worst
case) looking at an ejection seat ride and a mountain of paperwork.

It's the sort of thing that you can't really predict ahead of time,
computationally, and wind tunnel testing isn't representative enough.

It's an important set of test points.
Like most test flying, it's pretty straightforward - you hit your
conditions, and take your data, and all goes well. Most of the time.
But reality isn't always what the predictions indicate. Then things
get very exciting.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

[Air Force Jayhawk]

On Mon, 13 Sep 2004 16:39:28 -0400, (Peter
Stickney) wrote:

>In article >,
> (frank wight) writes:
>> And one of the "tests" is to fly high and level
>> and throw the after-burner switch, then go to idle,
>> and then back on after-burner.
>
>Sure. It's a pretty good way to induce a compressor stall. You also
>stand a pretty good chance, if the engine is an an afterburning
>turbofan, to get a pressure pulse up the fan duct, when the afterburner
>relights, that can casue all sorts of inlet/engine airflow havoc.
>
>
>>
>> Trouble is, they didn't actually film the event
>> and I'm curious about what such a procedure feels like.
>
>A pretty good jolt of acceleration when the AB lights. Then a pretty
>fair deceleration when the engine come out of burner and down to
>idle. Then a pretty good jolt as things spool back up.
>If all goes well, that is. Worst case, a pretty fair jolt when the AB
>lights off, then a bunch of deceleration, as before, then no
>accelration and a lot of racket as the engine tries to deal with the
>disturbed off-design airflow. If it doean't sort itself out, then a
>shutdown shutdown & airstart. If it doesn't restart, you may, (best
>case) be putting your single engine landing drill to use, or, (worst
>case) looking at an ejection seat ride and a mountain of paperwork.
>
>It's the sort of thing that you can't really predict ahead of time,
>computationally, and wind tunnel testing isn't representative enough.
>
>It's an important set of test points.
>Like most test flying, it's pretty straightforward - you hit your
>conditions, and take your data, and all goes well. Most of the time.
>But reality isn't always what the predictions indicate. Then things
>get very exciting.
>

And as we say in the test business, that is why we don't want pilots
with a history degree being the one to do it for the first time...
---
Ross "Roscoe" Dillon
USAF Flight Tester
(B-2, F-16, F-15, F-5, T-37, T-38, C-5, QF-106)