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View Full Version : Have you ever been caught in the limiting mach number


Harvard1964
21st Feb 2015, 21:51
of a sub sonic aircraft.


In about 1970 I was doing a maintenance test card on a Canadair Tutor (CT-114). One part of the test card was to ensure the upper limit marked on the mach meter was on the safe side of the actual air frame max of Mach 0.78. To do this, we would climb to 35,000 feet and then begin a gradual descent at full throttle. As the mach meter reached the red line we would retard the throttle and pop the boards.


Well, this one day with one particular aircraft, the nose tucked just as I popped the boards and the hydraulic pump cavitated (sp?). I was then stuck in the low drag point of the drag profile of the shock waves. Without the speed brakes, no matter what I did with the stick the aircraft just kept getting steeper and steeper. The nose tuck occurred at about 30,000 feet.


I played dumb, which comes natural, and just sat there waiting for something to give. Sure enough it popped out on its own at about 12,000 feet so I had plenty of room to pull out of the dive.


Well, it never ever happened to me again but I was wondering if anyone else had a similar experience in a sub sonic aircraft?

Loose rivets
21st Feb 2015, 23:01
Yeh, I did, but it wouldn't be fair for me to wade in until the other chaps have had a go. Chaps . . . ?

con-pilot
21st Feb 2015, 23:20
No, can't say I ever have. Also in every jet aircraft I have flown, which are a lot, I've made barber pole descents. Even in early 20 series Lears, which had a rather nasty habit of Mach tucking if allowed to go past max Mach (M-mo).

megan
22nd Feb 2015, 04:38
I've made barber pole descents. Even in early 20 series LearsYour Lears were not fitted with "THE SWITCH" con? :E

Takan Inchovit
22nd Feb 2015, 05:46
Didn't someone in the 70's put a 727 into that speed range after playing with the slat circuit breakers in cruise?

Loose rivets
22nd Feb 2015, 10:57
Yes they did, and the resultant high M-number pushed the starboard gear structure back, buckling the fabric of the wing.

Bet he didn't do that again.

Shaggy Sheep Driver
22nd Feb 2015, 11:07
I remember the report on that 727 said something like 'during recovery the pilot reports seeing parts of the attitude indicator he'd never seen before'. The maker's name on the back of the ball, perhaps? :)

parabellum
22nd Feb 2015, 12:22
I don't suppose me, exiting badly from my first ever solo barrel roll and seeing 173kts indicated, that also being the Vne for a Chipmunk and, by coincidence, the course number of our pilot's course, counts in the same league, but I will never forget it! :)

Rossian
22nd Feb 2015, 14:49
.......as I see you are "new here" I'll be gentle. Mention of "avi%$&(n" here in jetblast is regarded as very poor form and usually requires an apology in advance should it turn out to be unavoidable. I offer this in the spirit of kindness to a poor fellow mortal. Please don't be offended.

Were you to offer this subject for discussion in, say, R&N, you would be deluged with the vapid outpourings of MS fltsim fanatics and spotty spotters who wouldn't recognise a real aircraft if it bit them on the arse, but will have plenty of opinions as to you SHOULD have done. (Oh and they will have a handy METAR to post to explain that it was/was not weather related)

Can I take my tongue out of my cheek now please.

The Ancient Mariner

ONE GREEN AND HOPING
22nd Feb 2015, 15:21
Operating as co-pilot on a 707-320 series C of A test, did get into serious Mach Tuck that wasn't planed to be deep. Aircraft just out of heavy check after sitting on ground for long time. Instrumentation was the problem. Don't recall detail, but had plenty of altitude and recovery not a problem. Your mention of an incident just reminded me why I liked and trusted the 707, that's all...

Shaggy Sheep Driver
22nd Feb 2015, 16:59
parbellum, barrel rolls are easy to get wrong. Guess how I know! The real danger, especially if the speed gets as high as yours did, is applying a lot of rolling 'G'. The Chippy is a tough old bird (I don't think one has ever come apart in the air), but even she has her limits! Even more so these days as the airframes are usually considerably older than the pilots!

Capot
22nd Feb 2015, 17:56
I tried to spin a friend's Cherokee 140 in the Gulf, and had some difficulty recognising and recovering from the resulting spiral dive, which seemed nearly vertical but probably wasn't. I knew that it would be difficult to spin, and used the method of slowing to just above the stall, then applying full elevator and full rudder suddenly and holding that until a spin developed. Except it didn't.

I have no idea what the airspeed got to. I doubt that you can use the words "limiting Mach Number" and "Cherokee 140" in the same sentence. I was too scared to look, anyway. The manoeuvre started at 8,000 ft and finished at 1,200 ft, as I recall.

Does that count?

PS; I did some aerobatic training in a Chippy (G-APPM) at Biggin in the late 60's; it didn't come apart, exactly, but we did need to return to the field quite carefully when the fabric started peeling back from the port main spar.

Shaggy Sheep Driver
22nd Feb 2015, 18:54
but we did need to return to the field quite carefully when the fabric started peeling back from the port main spar.

Yes, that lovely aeroplane has fabric covering from the spar back, on the wings. Also the elevators and rudder are fabric covered. Never ever heard of it coming unstuck on a Chippy despite some pretty naughty excesses by some pilots. I suspect that Biggin one must have had a fault in the initial fitting of the fabric for that to happen. Or the fabric was in a poor state and well overdue for replacement.

That 'flick entry to the spin' capot describes was my introduction to spinning on the PPL course in the 70s; it was the only way to get the C150 to spin instead of spiral!

parabellum
22nd Feb 2015, 23:45
Rossian - I understand your kind explanation to the OP but don't you think it is nice that this thread is still in the hands of real pilots and hasn't degenerated in the manner you describe it would in R&N? ;)


(280/02 CAVOK +30/+03 1014 NoSig !!!).

Loose rivets
23rd Feb 2015, 00:14
You forgot to mention it was gusting 3kts.:=


A mate jumped into the back of the Chipppy and at some point asked if he could have a go. Since he'd taught me my first aerobatics, I let him. He'd been off flying for weeks doing the written, so was a bit out of practice, also, one could only just make out the ground from 6k.

After the first barrel roll we were well nose down. He then went for another one, a large part of which was vertical.

Oh, how we laughed as we patted the wing surface as flat as we could get it, and walked away, hands in pockets, whistling.

BOING
23rd Feb 2015, 01:06
Don't exceed the limit in a Vulcan or VC10 for sure.
B757/767 - never seen one near limiting mach.
B747 I suspect would enjoy it but don't chop the power to recover on the 100 series or you will have engine surging as well as limiting mach.
B727, I could never find anyone who knew how the aircraft flew after limiting mach (I researched this specifically after flying the V's above), anybody who did know probably did not want to talk about it. :)

ONE GREEN AND HOPING
23rd Feb 2015, 06:51
Poor Chipmunks had to put up with a lot, perhaps. In 1962, being cleared for briefed solo exercises, but not yet anything aerobatic, I thought barrel rolls sounded easy, so tried one anyway. I remember just hanging upside down with dust and stuff drifting past my face, and wondering what the next move should be......was more cautious after that. Someone on my course managed some kind of hammer stall, and shredded fabric off the elevator. Couldn't hide that one.....

Shaggy Sheep Driver
23rd Feb 2015, 10:31
I had a strange experience looping a Yak52 a bit like that. First couple went fine, but at the top of the third one the aeroplane decided to roll. To this day I don't know why - can't have been a stall as we were pretty much weighless over the top; engine torque maybe?

I remember the controls went feather-light and I decided just to 'go with it' rather than do anything to recover it to where I'd intended it to go. I got the distinct impression that if I did anything drastic it wouldn't forgive me. It felt as if balanced on a pin head. Once it was upright and pointed downwards normality returned, I stopped the roll and all was well. Odd.

Checkboard
23rd Feb 2015, 15:34
I used to do barber pole descents flying freight in a Westwind:

https://c1.staticflickr.com/3/2700/4165075673_b6857ed76d.jpg


Mmo into Vmo was 0.765 into 360 knots - and you could hold that for a 90 intercept on the ILS at 10nm and still cross the fence at Vref. :ok:

A hair over M0.765, though, and the nose would drop alarmingly quickly :ooh: