PT-6A Holding the prop on start up?

[CitationJet]

I have often read that it is possible to hold the propeller of a PT-6A during start up. Has anyone actually witnessed this????

I understand why it is theoretically possible, however can it actually be done for more than a couple of seconds after air starts flowing over the power turbine?

Wouldn't it cause enormous damage to the power turbine if you were trying to prevent it turning by holding the propeller when fuel is introduced?

Is this just an OWT??

[waren9]

Can be done, after all other types eg ATR's and Saabs, have prop brakes as options which not only will hold a prop but stop it with the engine running.

The obvious danger aside, whether or not its possible with your own hand is debatable. Saabs will break a prop strap on start if still attached and I doubt anyone would be strong enough. If it started to move, there'd be no stopping it.

May be better asked in the Tech Log forum?

[Metro man]

Some free turbines have a prop brake so that the engine may run without the propellor turning. This efffectively give an APU without the additional expense and weight. The ATR 72 is an example of this, having a prop brake on the right engine enabling power and air to be supplied without the danger of a spinning propellor.

[Ejector]

Thanks for the input, but with respect, a Saab Donk is hardly a PT6A which is a tiny turbine. I have seen PT6A-20, 27 and 34's all held during start and at idle. They were bear hugged buy a normal size man, seen done many times, hundred of times actually, the management only wanted to hear the engineers who told them what they wanted to hear, although, the better engineers in my opinion, were disgusted with the practice and all insisted it would cost them massively in the long run. I quit that gong show and so did my other friends, so I don t really know if it lead to PT issues later, sorry.

[VFRSTAR]

How funny would it be if the bear huggers started rotating with the props :eek: ...be a helluva ride though!!

[waren9]

Ejector

With respect, the OP didn't mention which PT-6A. The -67F is more than a match for a Saab 340A at about 1700SHP, I believe. I dont doubt what you say about the smaller ones, you definitively answer the OP's question, but you won't catch me trying to hold on to one that size.

[Ejector]

Yeah, OK, I will leave the Saab comment out of it. No offense intended.

On the smaller ones I have seen, when the person let go, they were in feather still and they had plenty of time to let go with out issue.

I really do wonder what damage was being done with hot spots and particularly on light up, my gut feeling is a lot of damage was being done but I am no expert of course.

Also, a dash 20, 27 or 34 on start up, if the prop tie was on, it would rip it off. Although I never saw it happen, I have seen several planes where the metal clip dented the fuse skin. I am guessing, but may be bear hugging the end of the prop gives you enough leverage?

[tinpis]

WHY? :hmm:

[Ricky Bobby]

In strong winds if the prop is spinning the other way, nothing wrong with someone holding it steady with one hand till its ready to turn itself.

[SeldomFixit]

Better you than me fella :eek:

[rigpiggy]

used quite regularly in the arctic to avoid blowing the prop seals, by getting low pressure warm oil to the gearbox/prophub. I used to sit under the PC6 when the Boss would do starts and hold it with one hand, always good for fireworks:)

[FGD135]

... my gut feeling is a lot of damage was being done ...


I very much doubt that any damage was being done. If damage was possible, then P&WC would have advised against the practice.


... used quite regularly in the arctic to avoid blowing the prop seals, by getting low pressure warm oil to the gearbox/prophub.

Yes, holding the prop until the oil has warmed (and become sufficiently viscous) means that the gearbox won't be damaged by what would otherwise be inadequate lubrication.

[Arm out the window]

Not the same engine of course, but it was common practice to hold the
UH-1H rotor blade for as long as possible on start (up to about 20-30%-ish N1I think) to avoid the blade sailing too much at low rpm, and no harm was ever done by doing it as far as I know.

[tinpis]

Wokka pilots, respect.
How they managed pullin' all them levers and switches AND holdin' on to the rotorary blades I'll never know...:hmm:
No wonder they was feared guardin' the BBQ area at Vungers. :ooh:

[MakeItHappenCaptain]

In strong winds if the prop is spinning the other way, nothing wrong with someone holding it steady with one hand till its ready to turn itself.

In strong wind with the prop spinning the other way you should have turned the aircraft into the wind to reduce the chance of a hot start.
Basic stuff for PT-6A endos.:cool:

[Doodlebug]

It was a much-overused prank in my PT6 days. Somebody would hide under the starboard engine where the pilot couldn't see him (co-pilot usually still closing the door or heaving bags around) and hang on to the prop-tip while the guy was starting, the idea being to flummox him when he heard the bangers going and the turbine spooling, but saw no prop-movement. Obviously it would be a short time only until the prop would overpower the hand and would go from 0 to serious revolutions in seconds, whilst the hand would go scurrying backwards to safety, banging his head on the flaps on the way for his trouble. :)

[Delta_Foxtrot]

Arm, holding the blade might have been OK for those little two-stroke helos you used to fly, but you wouldn't want to do it with a Chook...

[Arm out the window]

Steady on there, DF, dodging the other blade as it came round like an intermeshing egg-beater would have been too hard for me anyway!

Tinnie, it was a bit tricky to try and do it yourself - loady normally took the role - but I know of a few people who have tried to eliminate the middleman by starting with the blade still tied to the tail boom, that always causes something of a kerfuffle. :) (not me by the way).

[j3pipercub]

Quote:
In strong winds if the prop is spinning the other way, nothing wrong with someone holding it steady with one hand till its ready to turn itself.

In strong wind with the prop spinning the other way you should have turned the aircraft into the wind to reduce the chance of a hot start.
Basic stuff for PT-6A endos.

Yeh, cos the wind never swings over night...

Besides, PT6 drivers have no concept of hot starts, come to Garret land and see the real thing.

[tinpis]

One fella I knew had a go at starting a Nomad with the engine bungs in.
"Right, sodding #2 wont start lets try the other one..."

[The Green Goblin]

Besides, PT6 drivers have no concept of hot starts, come to Garret land and see the real thing.

The problem is somewhat alleviated with the removal of the NiCad batteries and addition of Lead Acid or some of the other alternatives that I have seen :cool:

[tinpis]

Why is it littlely turbine engines start hot? :hmm:

[Super Cecil]

Why is it littlely turbine engines start hot?
Maybe your holding your tongue wrong?:8 Are you giving it too much choke? Is the ring gear worn and slipping? Maybe your throttle bashing? Sounds like it's your fault anyway Tinny. :E

[criticalmass]

I've seen it done on a Twin Otter, bloke only managed to hold it for several seconds before it broke free from his grasp.

[Joker 10]

Why is it littlely turbine engines start hot? No APU and littley batteries to spin them up.

[tinpis]

Hullo boss? Yeh I'm in Oodnapuckimwoopwoop and the battery is below voltage limits.Some blackfellas here reckon for a carton they can spin the prop fast enough to start, shall I try that?"

God ya miss GA doncha?

[MakeItHappenCaptain]

Yeh, cos the wind never swings over night...

Do flight manuals prohibit pushing the aircraft around?

[Jober.as.a.Sudge]

Do flight manuals prohibit pushing the aircraft around?

A rather simplistic point-of-view there MIHC.

Getting to the airport at oh-dark-thirty of a morning to find your aircraft pointing the wrong way given the prevailing conditions for an "approved" engine-start... "pushing" the (let's say minimum 3 tonne) aircraft around (by hand, in the absence of an approved tug) on your own, unassisted, may be a bit of a big ask... don'cha think???

I can think of any number of similar scenarios that my result in less-than-ideal engine-start conditions -but probably best we just pause there and really think about what we're typing...

don'cha think???

[j3pipercub]

Wow Captain, who do you instruct for?

[MakeItHappenCaptain]

pushing" the (let's say minimum 3 tonne) aircraft around (by hand, in the absence of an approved tug) on your own, unassisted,

So who's gonna hold the prop then?

Fair enough to say I've never had to start a Caravan with a tailwind. Two of us were always enough to move it if required (and not on a sealed surface either).

Know of one company that even advises getting the pax to give a shove if so required. (All adds to the experience I suppose.) Never heard of holding the prop as a technique though. Any engineers want to comment on this?

Yup, Jober. I'm sure everyone can come up with a scenario to justify themselves. (Not saying I'm innocent either.:cool:)
What do you mean "we", Kemhosahbe?

[j3pipercub]

Two pilots in a caravan, hmmmm, that explains a lot....

Yep, real professional getting the pax to pull the aircraft around, kinda fits with the unsealed strip stereotype though.

Even in a 15 knot tailwind, a caravan peak temp might be 20-30 degrees hotter. Big FCUKING DEAL! Especially when it peaks at 800 and the company limit is 900. IF you're running around with a battery on the way out this may change things however...

j3

[MakeItHappenCaptain]

Didn't say it was my company, dude.

How about using common sense rather than cowboy stunts to get around a situation?

Don't see why it's so f:mad:cking hard if you have got someone who can hold a prop, both of you can't at least turn the a/c side on to the wind.
Wouldn't want to see the pilot/princess doing any physical work now, would we?

[j3pipercub]

Cowboy stunts? What, a cowboy stunt is to load the pax and accept the downwind vs get them to push your aircraft around? Yeh, way to instill confidence... I'll fly with you anyday Mav, once I've helped clutch start your aircraft...cos that's what they're thinking...

How about using common sense rather than cowboy stunts to get around a situation?
I don't get anyone to hold props, never been in a harsh enough environment like the arctic. Your original statement was to the effect that you should face it into wind as it is 'basic PT6'A' stuff. I have had it several times where overnight the wind has swung and I have been by myself. What then genius? Then you start it with a tailwind, and if you have never been in this situation, you musn't be a very experienced 'big flashy turbine driva'. You must be one of those second career guys judging by your age.

Wouldn't want to see the pilot/princess doing any physical work now, would we?

Actually, lets see the pilot push/pull the 3 tonne machine around, damage his back and have to spend the night in the middle of nowhere. Been there, tried that. But I forgot, you fly those realy complicated 2 crew caravans... so you'd have a spare pilot. Do you have a pretend gear lever so the 'F/O' can raise it once you get positive rate? How do your transition checks read? How do you two handle the speed of joining the circuit at that Vne of 175kts? Does the 'Captain' get to wear 4 bars and braid around the shoulder?

j3

[morno]

HappenCaptain,
With around 1,500hrs of PT6 time (both large and mid sized PT6's), I've never noticed much of a difference in temperature during the start, when starting with a tail wind. Sure, avoid it where possible, but as j3 has alluded to, it's not always possible.

Pushing my 5 tonne King Air around just to face into wind, is asking a bit much, when it'll make bugger all difference in the start. Let alone if you can even budge it!

morno

[John Eacott]

Our PT6 powered Bell 212's needed a hefty engineer to hold the blades on start up when we had strong/gusty winds in the North Sea. Otherwise, blade sailing could happen before Nr increased such that we had some control of the main rotor and avoid hitting the tail boom with an errant blade.

The chunkiest engineer usually managed 20-30% torque before he had to let go :ooh:

[MakeItHappenCaptain]

J3, Deaf, dumb or both?
Again, didn't say it was my company, dude.

My point was if you have someone who can hold a prop, you should be able to push the aircraft. Obviously if you are by yourself, and yes, as morno points out, with 5 tonne, different story, but this isn't the scenario. If you've already done your back in by 27, maybe you should spend some more time in the gym?

Also didn't say it was a two pilot operation, but you probably won't hear that either. I was never shy about helping other pilots get underway.

Amusing to see how the insults come out when you run out of logical arguments. Got any idea how many hours go with that age, junior?:E

[Roger Greendeck]

Not sure about the wisdom or otherwise of holding the prop by hand (have seen the Huey start and the rotor spins up a bit slower than a prop!) but given that PT6's are used in a few different helos with rotor brakes I see no reason why the engine is not capable of being safely run with the prop stopped.

[j3pipercub]

MIHC,

I assumed from these words...

Fair enough to say I've never had to start a Caravan with a tailwind. Two of us were always enough to move it if required (and not on a sealed surface either).

...that it was a two crew operation, cos I have never had a flight attendant or a gate agent that would help me pull an aircraft.

Amusing to see how the insults come out when you run out of logical arguments. Got any idea how many hours go with that age, junior?

Well with comments like...

Do flight manuals prohibit pushing the aircraft around?

and others to the effect that you should never start a PT6 in a tailwind show that however many hours you do have, you either haven't learnt much from them or don't have much turbine time there old man.

If you've already done your back in by 27, maybe you should spend some more time in the gym?

You wouldn't know mate, you've never pulled the aircraft around by yourself have you...

j3

[havick]

MakeItHappenCaptain..

I've gotta agree with J3 on this one.. I currently fly B412's (PT6 donks in the ol girl), and it's not possible to turn the aircraft around into wind when the aircraft is on skids (no wheels, and the ground handling wheels live in the hangar).. It's actually quite common to be starting with a tailwind, obviously you would avoid it if you could.

The start is a little warmer, but just a matter of keeping your eye on it (as you would with any normal start anyway).

[MakeItHappenCaptain]

Ceasefire, J3.

I can understand how easy it is to make assumptions based on the limited info that is posted here sometimes, I've been guilty myself. The way some people snipe at genuine suggestions makes it easy to fly off the handle and again, been there done that.

My statement was not that it's prohibited to start with a tailwind, just preferable that it's done into wind and with two people around, a caravan isn't that hard to push. Yes, I have done it on many occasions so I'm not being hypocritical. I never had the inclination to see if the instructor who endorsed me was wrong.

Don't think a Kingair or PC12 would have as much drama (smaller exhaust area and yes, a bit harder to move) but (disclaimer) this could just be my assumption.

[Ejector]

I am not sure if P&W have said anything about the practice, but I do not recall ever seeing it as a approved starting procedure in any of the approved manuals. Someone who knows much more than me will have to answer that.

[tinpis]

Indeed, if anyone is in possession of a manual/document extolling the virtues of hanging on to any engine/prop combination during start (not wokkas) please tell us.

[boofhead]

Has anyone had to "milk" the start with the condition lever to keep the temps below limit on start? Was a common procedure on Darts.

[tinpis]

Was a common procedure on Darts


As long as there are Darts it shall be thus.

[Brian Abraham]

if anyone is in possession of a manual/document extolling the virtues of hanging on to any engine/prop combination during start (not wokkas) please tell us
Bristol Britannia http://www.pprune.org/aviation-history-nostalgia/353683-bristol-britannia-details.html
Crews only requested the prop to be held, during it's engine start-if there was a wind present that caused the prop to rotate in the opposite direction. The prop (if unrestrained and the wind was strong enough), could pick up a considerable rotation speed in the wrong direction and then cause considerable bearing load and adverse effects of gas temps over the turbine-before rotating in the intended direction. The procedure was to hold a blade between finger and thumb until the turbine began to drive the prop shaft. The blade then moved ever so gently out of the holder's finger/thumb.

[tinpis]

The Proteus has a free turbine and as such the prop has a parking brake. The brake was released prior to starting the engine. In order to stop the prop spinning the wrong way during engine start, the ground crew could hold it. You knew when to let go when you felt the prop moving with the engine when it started.

Temps. :hmm:

A Pommy electrical nightmare that required a good FE. One that knew which part of the cabin floor to stamp on to unstick recalcitrant relays etc. :ooh: