Useful info on Pprune!

[stiknruda]

Recently a topic digressed into the merits of "fish-tailing" to restart an engine in flight.

Saturday last I was participating in an aerobatic competition. Underneath me is an 800 metre runway and despite the very strong cross wind I've landed on it from glide approaches twice in the past few hours.

During the first unknown sequence my engine stopped.......:eek:

Figure one was a downwind roll of the top to firure two a one turn erect spin to figure three a half Cuban.

I had entered the aerobatic box at 1600', 2600rpm/160mph. Because I was going downwind I was really steaming through the box, pulled up into a half loop, right rudder, full left aileron and rolled erect on the reciprocal heading at about 80mph and at a nose-bleeding 2300'.


Power to flight idle, keep pitching the nose up to arrest any tendency to descend until I can feel the buffet - quick ASI check shows 60mph, stick almost full back. Full left rudder and the stick fully back should have been the next thing to do BUT the aeroplane decided that it wanted to spin to the right - just as it began to depart I hoofed in bags load of left pedal and brought the stick fully back.

The aeroplane began to spin but I noticed that something wasn't right - somebody had turned the music off! :rolleyes: After half a turn I began to feed in forward stick to make the spin exit more vertical.

Then and only then did I realise that whoever had turned the music off had left a piece of wood strapped to the front of the aeroplane where the propeller disc should be.....£*** me that is the propeller:{

Confusion really began - what to do, what to do? At this stage I am lying in fifth place and a good unknown sequence should see me with a podium place.

Should I try and restart the engine with the key?
Should I complete the spin power off then pull to the horizontal then restart before the next figure and hope I had sufficient speed for a half Cuban?
Should I abandon the sequence and land and explain that a technical problem caused me to abort - the rules do allow for this.

By this stage the aeroplane is heading downhill, picking up speed and I realise that I've over-rotated by 180 degrees and will have scored zero for this maneouver.......preservation takes over and I stop the spin and concentrate on building the speed. At 1200' I am doing 110mph and the prop hasn't moved, milliseconds later I am through 1000' and nearer to 125mph and still nothing.

At 800' I decide that if nothing has happened by 500', I shall pull out of the dive and set up a circuit to land from. This does not overly faze me. What fazes me is my inability to move my left hand from the throttle and forward 13" to the starter key.

At 700' - like a bolt from the blue I realise that fishtailing might help. I press right rudder and then left and suddenly the dead stick starts to flick over, one blade, two blades and roars into life.

I pull to horizontal just under 600' and with almost 150mph on the ASI.

I performed three wing rocks to signify that I was breaking my sequence. I then re-positioned myself and after a further 3 wing rocks flew the rest of the sequence.

Unfortunately the stationary prop blunted my concentration and the rest of the sequence was not flown with the necessary accuracy to maintain my placing.

I landed after the sequence and gave a silent thanks to the good burghers of Pprune for mentioning FISHTAILING recently. It certainly saved me some embarrasment!

Stik

ps - I didn't come last!!

[Genghis the Engineer]

How many points did it lose you, and is it worth including in future "unknown sequences"?

Seriously, well done on some quick thinking, I'm not sure I'd have been quite so together in the circumstances.

G

[Aerobatic Flyer]

Well done for not coming last!;) And good thinking for over-rotating by 180 degrees. If the engine hadn't started you'd have been nicely set up on a downwind leg to land. They ought to give you a few points at least!

Regarding the fishtailing, perhaps the good burghers of Pprune should have said "try the starter first, and if that doesn't work, try fishtailing"!

Do you have any idea why the engine stopped?

[FNG]

An interesting tale well told, Stik. Well done.

[formationfoto]

Sounds like a good 'I learnt about flying from that' article. I quite like the idea of including it deliberately in the sequence :)

[rustle]

Agree with FNG - good story, thanks stik.

I hope I'm that cool when it happens to me... :eek:

[BRL]

Thats pretty neat flying mate.
I pull to horizontal just under 600' and with almost 150mph on the ASI.
Still a nutter though......... :cool:

[kabz]

Good lord man. I bow before your immense testicles.
:cool:

[TheKentishFledgling]

Yup, well done stik - glad you and the aeorplane are safe.

tKF

PS Why didn't you mention it earlier?!

[Hersham Boy]

Stik - the very fact that were even considering options (a) and (b) as well as the life-preserving (c) is giving you an instant placing in the "Krazee Mofo" category in my book. :D

This should make me want a Pitts less... but stragely it seems to be increasing the attraction! :}

Hersh

[Ludwig]

'kinhell old chap, is adrenalin really brown? Seriously good thinking on your part, at least breaks are unpenalised at standard:)

As an earlier poster asked, do you know why it stopped in the first place; do you want to sell it?;)

Well done you.

[stiknruda]

Why did it stop?

I honestly do not have a concrete answer for that! It has never stopped before and I have been through the fuel system checking filters, been through the throttle linkage for play and can confirm it still idles somewhere between 750 and 800rpm. I've checked the mixture at idle and it is a tad rich (safe). I actually checked the mixture was fully rich on Sat once it was stopped and I checked that the purge valve was closed, too.

I have convinced myself that as it wanted to depart to the right and I wanted it to go left - I turned it hard against the engine and gyroscopically stopped it.

Once I had it running again it was running very sweetly but figure 5 was a stall turn and I need to close the throttle again just as the rudder bites to stop torque overpowering aileron authority...you can bet that I pulled the power back very, very gently and gave a huge sigh of relief when it carried on running!

Funny old thing was that the sequence came with a recognised break point after figure two for Aerobats and Stampes - no penalty for breaking as Ludwig stated - I just zero'd the second 270 turn as my mind wandered back to the spin!

Ho hum.

Going to fly it again tomorrow (off for a meeting at Wellesbourne) then when I get home I'll run through the sequence a few times and do exactly what I did on Sat to see if I can recreate the problem.


Stik

[Genghis the Engineer]

I've seen this on flight test jobs once or twice.

Engine to idle, enter a steep turn - typically looking at g-stalling or mishandled spin-entries, and the engine goes shudder-shudder-shudder-stop.

They've always re-started first time once I'm back to level flight, although it can concentrate the mind slightly. I think probably that it's precession of the rotating prop putting a back-load onto the engine and stalling it.

You can probably investigate it by taking yourself up to safe height in gliding range of a friendly (and quiet) airfield, closing the throttle and flying increasingly steep turns (known in the FT trade as wind-up turns) and see what happens. Solution may be to tweak the idle up a little on the carbs?

G

[Chimaera]

...see if I can recreate the problem

stik

You want to do that AGAIN???

You really are NUTS:\

[Circuit Basher]

Stik - 'RESPECT, MON' :)

Well done - goes without saying that managing to avoid bending one of the oh too few flying machines made your existence on this earth worthwhile! ;)

I've had something akin (but under much more benign flight conditions) happen on a 160hp Lycoming. Doing stalls in the Fuji with a pax, progressively increasing the steepness of the pre-stall approach, had the donk stop when at high alpha (but no wing drop / rotational component). Again, slightly raised adrenalin levels, but stuffed the nose towards the deck and kept the prop rotating and it then recovered without further intervention.

Not too frightening except when the glide characteristics of the Fuji are considered - it's time for rapid (and CORRECT!) decisions when it all goes quiet in a Fuji!

[Tinstaafl]

When I did my aero training stopping the engine & restart via both dive & starter was required. When I didn my aero training approval the bloke asked if I'd done restarts before. When I said 'yes' he said 'that'll do."

[stiknruda]

For the sake of good order, I have felt bound to answer many of the questions that this topic prompted...

It has taken some time, because of other distractions , to actually be in a position to be able to respond: checking out aeroplane, new pup, PFA permit renewal, sufficient spinning to actually have a point of view, etc.

Q. So what happened?
A. Really I dunno :uhoh:


I have tried to replicate everything save from doing it over the same aerodrome but it has never happened again.

I checked the fuel filters/ injection screens initially, I have done loads of ground runs - I replaced the oil as part of my permit renewal and had yet another look at idle mixture/speed.

Tuesday this week I flicked the aeroplane into both left and right multi turn spins and had no adverse effect. Wednesday I did my permit renewal flight and did simple spins to validate - last evening I ran through the same sequence at sequence height 3 times - initially overhead just in case then elsewhere as confidence grew.

I've spoken to ONE other Pitts pilot (BA747 Captain) who years ago experienced a similar occurrence.


So the short answer is I don't know - that is a bit worrying!

Anyway this w/e will be practicing for next w/e's comp at Breighton


Stik & Reno (my pup)

[John Farley]

Stik

I have had several prop stops with a carb Lycoming doing spinning trials in a light GA aircraft. Never did find a reason. Could not repeat to order. I suspect that quite a few engines can quite easily stall at idle when thrown about at very low airspeeds and with funny prop gyro effects etc. I would not let it bother you as there is no reason it will not start again under normal conditions of flight. It will of course be an F’ing nuisance so far as your sequence goes but that is not a safety issue. If your height does not allow enough IAS for a dive restart there is no harm in using the key of course. In fact if it ever happens again why not go for the key at once and give yourself some confidence? The worst problem I ever had with this stopping business was with the Lycoming 540 in an Optica. Since it was driving a ducted fan the RPM always went to absolute zero if there was ANYTHING wrong with the idle and you had no option except to use the book ground hot restart as the donk got NO help from the fan. In said Optica this called for 7 actions in sequence using both hands. So if you had it out of trim and happened to be at low level it was time to use the knees. Best thing was not to throttle all the way back while you depended on the donk - as in the circuit.

[ShyTorque]

I recall the prop stopping on the Bulldog (Lycoming again) a few times whilst spinning. It was something we used to brief solo students to be aware of before they went off doing solo aeros.

It was almost as if the initial entry to the spin provided enough rolling motion for the aircraft to "catch up with the prop" slightly and it would fail to go over compression, especially if the idle speed was a little too low. Effectively you have "stalled" the engine, very similar to stalling a car engine when not using enough throttle when pulling away.

Two ways to start it. One, obviously on the starter motor. Two, the recovery from the spin usually gave enough ergs back into the prop to rotate the engine and it would simply fire up and run again. The important thing was not to get disracted from the recovery or the spin could easily go high rotational, quite alarming in a 'Dog. It is worth noting that it's not generally the increased airspeed in the dive that gets the prop over compression, but the change in airflow through it caused by the pitching moment when recovering from the dive. So, if "fishtailing" doesn't work, try pulling a little 'G'.

[John Farley]

From what ShyTorque and I have been saying it seems possible that the following applies:

We adjust the idle controls of mixture and throttle stop on the ground to give the desired RPM and smooth running as per the engine manuals.

We then go fly and change pressure, temperature, density and even vibration levels (poor old float wobbling about and so allowing different fuel levels in the carb) and g. The fact that the engine idles satisfactorily following such possible variations is perhaps due to the prop shoving it round and also providing a smoothing flywheel effect. If the prop for some reason is having its own airflow changes (big yaw or pitch effects like spinning) and is at very low airspeed anyhow then bingo the deficiencies of the current idle set up become apparent.

[B2N2]

..the engine stopped in a steep (well steeper than normal) stall in a tired lil' 150...:p
Didn't really bother me since we where very close to a 5000' grass strip.
As soon as I lowered the nose it sputtered back to life again probably thanks to it's low compression.
Tried to " windmill" start a C172 yesterday got it up to 140 mph but no turning prop yet.
Fishtailing made it flick once or twice, not really sure whether it would have worked in this scenario, just continued it and dead-sticked it in.:}
Like to do that every now and then to keep the practice up..

[sycamore]

To add a couple of points to JF and Shy`s, many years ago instructing the Navy on the `Dog we had a few instances of engines stopping during spins,and everyone was suitably briefed about the problem.Usual engineering fix was an adjustment to the idle/mixture which usual cured the problem; well, it always did on the Chimunk. One morning a QFI and student go off to do a low-level navex,and demo of bad -vis SOP`s. After closing the throttle and reducing speed, putting flaps down,etc, opening up on the power,nothing happens-- at about 250ft over the N.Yorks moors. They try to carry out a forced landing, but probably stall-in,and sadly both are killed.The subsequent investigation and full strip-down of the engine, revealed that a piece of swarf/debris in the injector manifold was possibly /probably the culprit. The engine had been "adjusted " to give a better idling during spinning, and eventually the swarf had migrated when the throttle was closed, giving a total rich-cut, with tragic consequences. So, beware of just tweaking the carbs/mixture if the idle is erratic.

I also used to teach to test-pilot students that you will get the true characteristics of the a/c if you stop the prop, by stalling the a/c first, and then going into the spin. This will show what effects the prop has on the spin, and also shows that you can start the prop with a bit of "g", or yaw, or the starter. It`s also a bit of an eye-opener for those who have only flown parafin-lamps

A couple of points further; if it`s a fixed-pitch prop, keep the throttle closed until you are recovered/climbing, and if its a c/s prop,then pull the rpm lever back to prevent the prop overspeeding, until you are climbing.

Syc



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