turning prop backwards
Join Date: Apr 2002
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As well as everything said so far, my reasons for turning a prop by hand in past years have been:
- to clear the nosewheel tow bar (on the club Fuji, which has long prop / short nose leg) - the prop pretty well always stops in the vertical and requires turning horizontal (having checked I've got the keys in my pocket!)
- the PA28 which I had a share in at Bournemouth was parked outside. It also had a very small / slightly k*ackered battery. In cold weather, my standard procedure was to prime the engine, pull it through 4 blades, one more squirt of primer and then attempt to start. This worked most times and saved having to prop swing a live engine, which I try to avoid if possible.
- to clear the nosewheel tow bar (on the club Fuji, which has long prop / short nose leg) - the prop pretty well always stops in the vertical and requires turning horizontal (having checked I've got the keys in my pocket!)
- the PA28 which I had a share in at Bournemouth was parked outside. It also had a very small / slightly k*ackered battery. In cold weather, my standard procedure was to prime the engine, pull it through 4 blades, one more squirt of primer and then attempt to start. This worked most times and saved having to prop swing a live engine, which I try to avoid if possible.
Join Date: Jan 1999
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bluskis
I except what you say about turning the prop backwards damaging a vac pump but only if it is worn almost to the point at which it is about to fail.
The carbon vanes in the pump are so lightly loaded at the speeds that you can turn the prop by hand that I cannot see how any damage could take place except if the vane had excecive play in the rotor IE a high time pump. I can see how damage could be done if the pump was run at high speed backwards.
The latest pumps on the market have an inspection port to monitor vane condition this should put the end to the lie that " the pump failed because it was turned bacwards " when the engineers remove pumps with worn vanes before the pump fails.
I suspect the warning that came with your new pump is due to smart thinking on the part of the pump maker in using this bit of aviation folklore to keep the warranty clames down and to muddy the waters in case of leagal action after a pump failure , now that it is posable to see inside a pump and check the state of the vanes i see the truth coming out.
What I dont see is this disappering from the folklore quickly after all only last week I was told that the engine in a PA28 should not be leaned below 5000 ft ( this is a tiger moth limitation ) .........................it never fails to amuse me how these things become folklore !!!.
The carbon vanes in the pump are so lightly loaded at the speeds that you can turn the prop by hand that I cannot see how any damage could take place except if the vane had excecive play in the rotor IE a high time pump. I can see how damage could be done if the pump was run at high speed backwards.
The latest pumps on the market have an inspection port to monitor vane condition this should put the end to the lie that " the pump failed because it was turned bacwards " when the engineers remove pumps with worn vanes before the pump fails.
I suspect the warning that came with your new pump is due to smart thinking on the part of the pump maker in using this bit of aviation folklore to keep the warranty clames down and to muddy the waters in case of leagal action after a pump failure , now that it is posable to see inside a pump and check the state of the vanes i see the truth coming out.
What I dont see is this disappering from the folklore quickly after all only last week I was told that the engine in a PA28 should not be leaned below 5000 ft ( this is a tiger moth limitation ) .........................it never fails to amuse me how these things become folklore !!!.
Join Date: Jun 2001
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Circuit Basher, I use a similar technique for cold starting the Archer which I fly occasionally from Barton.
It has a rather lazy starter(engineers have looked at it & the battery many times but it always behaves the same), as well as being a bit temperamental on cold and warm starts.
I've found the almost guaranteed way to get a quick fire-up in the morning is -
prime six pumps
all switches OFF, handswing through 6 compressions with throttle cracked open a tad.
Jump in, flick the switch and she's away first turn.
Once she's warmed up it's a different story - great has to be taken not to flood her on warm starts.
Incidentally, I used to take a masochistic delight in helping people handswing props to start them (on wooden prop PFA jobs mostly). However I gave it up after I got bitten with a backfire by a Luton Minor. Nasty gash, but I was lucky, it fully healed. Others have not been so lucky.
It's a horrible feeling when your hand goes numb and you daren't look at it to see what the damage is.....
It has a rather lazy starter(engineers have looked at it & the battery many times but it always behaves the same), as well as being a bit temperamental on cold and warm starts.
I've found the almost guaranteed way to get a quick fire-up in the morning is -
prime six pumps
all switches OFF, handswing through 6 compressions with throttle cracked open a tad.
Jump in, flick the switch and she's away first turn.
Once she's warmed up it's a different story - great has to be taken not to flood her on warm starts.
Incidentally, I used to take a masochistic delight in helping people handswing props to start them (on wooden prop PFA jobs mostly). However I gave it up after I got bitten with a backfire by a Luton Minor. Nasty gash, but I was lucky, it fully healed. Others have not been so lucky.
It's a horrible feeling when your hand goes numb and you daren't look at it to see what the damage is.....
I'matightbastard
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Hard to follow that post
but here goes...
You might consider getting the prop remounted on the flange.
With a four cylinder engine for instance, the crank is likely to stop in one of four positions. So the prop will tend to stop in one of two positions - in your case, this sounds like vertcal or horizontal. But if the flange has 8 bolt holes, you can remove the prop and relocate it one hole over and it'll usually stop on the disgonal.
but here goes...
prop pretty well always stops in the vertical and requires turning horizontal
With a four cylinder engine for instance, the crank is likely to stop in one of four positions. So the prop will tend to stop in one of two positions - in your case, this sounds like vertcal or horizontal. But if the flange has 8 bolt holes, you can remove the prop and relocate it one hole over and it'll usually stop on the disgonal.
Join Date: Oct 1999
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Onan,
This may not be possible. On many aircraft the prop mass is included in the engine balance so can only be fitted in one position.
I'm surprised at the lack of knowledge of engines and systems shown here. Having been in engineering for many years and being a bit of an anorak a lot of this stuff seems to be pretty basic to me. I'd have thought, especially if you own an Aircraft learning how the systems work would be an essential thing to do.
With modern cars so reliable and complex people no longer tinker so don't learn how things work. Even with Motorcycles a lot of new riders these days can't even do simple things like adjust the drive chain.
This seems also to be the case with many pilots. They treat aircraft like cars, just jump in and go. I'm not saying that you should have to be a licensed engineer before you're let lose in an aircraft but some time spent with the manuals would be a good thing. (Something I must do myself shortly!)
At least people are asking questions here which is a good thing because It makes you think about what you're doing and that may just save your life. (Or an awful lot of money)
This may not be possible. On many aircraft the prop mass is included in the engine balance so can only be fitted in one position.
I'm surprised at the lack of knowledge of engines and systems shown here. Having been in engineering for many years and being a bit of an anorak a lot of this stuff seems to be pretty basic to me. I'd have thought, especially if you own an Aircraft learning how the systems work would be an essential thing to do.
With modern cars so reliable and complex people no longer tinker so don't learn how things work. Even with Motorcycles a lot of new riders these days can't even do simple things like adjust the drive chain.
This seems also to be the case with many pilots. They treat aircraft like cars, just jump in and go. I'm not saying that you should have to be a licensed engineer before you're let lose in an aircraft but some time spent with the manuals would be a good thing. (Something I must do myself shortly!)
At least people are asking questions here which is a good thing because It makes you think about what you're doing and that may just save your life. (Or an awful lot of money)
I'matightbastard
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WM, I don't know enough to respond, but if it's the case, It would be news to me as I always thought the prop balance was a separate issue. I'll look into it though. Thanks.
Your other comments are pretty much spot on though and I feel like it's time I stuck my nose back in the books too.
Jackie Cochrane in her biography said a similar thing. Her comments were that when she started off flying, it was pretty rare to make the journey in one hop and quite common to have to find a field, set down and clean the plugs. Not sure I'm ready for quite THAT level of education.
Cheers.
Your other comments are pretty much spot on though and I feel like it's time I stuck my nose back in the books too.
Jackie Cochrane in her biography said a similar thing. Her comments were that when she started off flying, it was pretty rare to make the journey in one hop and quite common to have to find a field, set down and clean the plugs. Not sure I'm ready for quite THAT level of education.
Cheers.
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OTC
It's something I'd not really thought about until we got rain erosion on the prop on the aircraft I have a share in. When we took the prop off it was doweled to the boss and the boss was indexed by a master spline to the crank output shaft. So it would only fit in one position. Thinking a bit more about it, this could be more to do with the fact that its not fitted with a starter motor. This would fix the firing position of the impulse mag with the prop so that the blade is in the right position for swinging perhaps.
See what I mean about making you think
It's something I'd not really thought about until we got rain erosion on the prop on the aircraft I have a share in. When we took the prop off it was doweled to the boss and the boss was indexed by a master spline to the crank output shaft. So it would only fit in one position. Thinking a bit more about it, this could be more to do with the fact that its not fitted with a starter motor. This would fix the firing position of the impulse mag with the prop so that the blade is in the right position for swinging perhaps.
See what I mean about making you think
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I don't think the "instant vac pump damage if turning brop backwards" is universal, or even common.
Recently when searching for a vac pump which is STCd for my plane (to keep around as a spare) I read some details of a fairly common pump which was rated for 50 hours of reversed operation at cruise RPM!
One may ask how on earth could that be achieved; apparently it can be achieved if fitting a pump to the "wrong" engine in a twin. Or, in a case of a vac pump failure (perhaps in a twin but not necessarily), one may have to fit the "wrong" kind of pump as an emergency measure.
Recently when searching for a vac pump which is STCd for my plane (to keep around as a spare) I read some details of a fairly common pump which was rated for 50 hours of reversed operation at cruise RPM!
One may ask how on earth could that be achieved; apparently it can be achieved if fitting a pump to the "wrong" engine in a twin. Or, in a case of a vac pump failure (perhaps in a twin but not necessarily), one may have to fit the "wrong" kind of pump as an emergency measure.
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After some rounds of emails with my vacuum pump manufacturer the conclusion is that the prop may be turned backwards without compromising pump life. However it should not be run backwards.
So that's it. The folklore had a grain of truth, but not the full story, for this particular pump.
So that's it. The folklore had a grain of truth, but not the full story, for this particular pump.
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From AvWeb:
In the early 1970s, general aviation switched to dry vacuum pumps manufactured principally by Airborne and relative newcomer Sigma-Tek. Although there are differences between the two, Airborne and Sigma-Tek pumps use self-lubricating graphite vanes which are both the solution (no engine oil required for lubrication) and the problem (the pumps tend to produce spec vacuum throughout their lives and then disintegrate internally in a cloud of carbon dust).
Compounding the sudden failure mode is a frangible coupling that is designed to shear abruptly in the event of overstress or sudden stoppage. In most cases, the aircraft operator will see no sign of any problem until the vacuum gage reading falls precipitously to zero.
Perhaps backwards pulling of the prop causes the vanes to dig in, and refer to the latter para ...
however a further search of AVWeb got me:
http://www.avweb.com/news/maint/182905-1.html
Backwards is Bad
The hub slots of Airborne pumps are canted in the direction of rotation. For this reason, Airborne offers different pump models for clockwise and counterclockwise applications. The most common model numbers are 211CC and 441CC (for counterclockwise rotation) and 212CW and 442CW (for clockwise rotation). It's not difficult to break the code.
Installing a wrong-direction pump is a sure prescription for premature failure. Most Continental engines require a clockwise pump, and most Lycomings require a counterclockwise pump. But not always. In fact, twins with counter- rotating props need one of each!
so it would appear that turning one backwards WILL cause problems depending on it's installation.
In the early 1970s, general aviation switched to dry vacuum pumps manufactured principally by Airborne and relative newcomer Sigma-Tek. Although there are differences between the two, Airborne and Sigma-Tek pumps use self-lubricating graphite vanes which are both the solution (no engine oil required for lubrication) and the problem (the pumps tend to produce spec vacuum throughout their lives and then disintegrate internally in a cloud of carbon dust).
Compounding the sudden failure mode is a frangible coupling that is designed to shear abruptly in the event of overstress or sudden stoppage. In most cases, the aircraft operator will see no sign of any problem until the vacuum gage reading falls precipitously to zero.
Perhaps backwards pulling of the prop causes the vanes to dig in, and refer to the latter para ...
however a further search of AVWeb got me:
http://www.avweb.com/news/maint/182905-1.html
Backwards is Bad
The hub slots of Airborne pumps are canted in the direction of rotation. For this reason, Airborne offers different pump models for clockwise and counterclockwise applications. The most common model numbers are 211CC and 441CC (for counterclockwise rotation) and 212CW and 442CW (for clockwise rotation). It's not difficult to break the code.
Installing a wrong-direction pump is a sure prescription for premature failure. Most Continental engines require a clockwise pump, and most Lycomings require a counterclockwise pump. But not always. In fact, twins with counter- rotating props need one of each!
so it would appear that turning one backwards WILL cause problems depending on it's installation.
