Do I dare touch it?
Thread Starter
Joined: Jul 2001
Posts: 504
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From: South Yorkshire
Do I dare touch it?
The mixture control in the aircraft I have a share in looks absolutely ancient. To my knowldge no-one has every attempted to lean the engine using it. I have only ever seen it in the Full Rich and Idle Cut-off positons. It is not operated via a vernier control, and the action is not smooth. The aircraft does not have an electric starter, and so if the mixture is leaned too aggressively and the engine cuts out, the result would be somewhat unpredictable. 
So do I attempt to use it, and if so, is there some technique I can use to minimise the risk of reaching a point where the engine stops? Or do I just accept that this aircraft is always going to be thirsty?
So do I attempt to use it, and if so, is there some technique I can use to minimise the risk of reaching a point where the engine stops? Or do I just accept that this aircraft is always going to be thirsty?
Joined: Aug 2002
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From: Surrey, UK.
If, as it sounds, you are concerned that this mixture control is either "on" or "off", why not try leaning the engine whilst still safely on the ground?
If it works normally, great - lean as required
If it works "digitally", then you know not to use it in the air.
Or did I miss something?
If it works normally, great - lean as required
If it works "digitally", then you know not to use it in the air.
Or did I miss something?
Joined: Oct 2000
Posts: 510
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From: England
You didn't say what the aircraft / engine are, but in my experience a fixed-pitch prop won't stop in flight even if you switch off the mags, or pull the mixture to ICO.
My disclaimer is that there may be some engine / prop combinations where you can easily stop the prop in flight. However, in my experience you have to slow the aircraft to just above the stall to stop the prop in flight after switching off the mags.
Further disclaimer.... (Don't try this at home). Although you have difficulty in stopping the prop in flight, if it does stop you will also have difficulty restarting it, i.e. to get over the first compression stroke. It may require a steep dive up to VNE, and even then it may remain stationary, and you will probably have used up 2000 feet of altitude.
If you ever have to do this for real there are two tricks left: pull at max g out of the dive, or roll the aircraft opposite to the prop rotation direction. Remember, however, that you will be way over design manoeuvring speed.
My disclaimer is that there may be some engine / prop combinations where you can easily stop the prop in flight. However, in my experience you have to slow the aircraft to just above the stall to stop the prop in flight after switching off the mags.
Further disclaimer.... (Don't try this at home). Although you have difficulty in stopping the prop in flight, if it does stop you will also have difficulty restarting it, i.e. to get over the first compression stroke. It may require a steep dive up to VNE, and even then it may remain stationary, and you will probably have used up 2000 feet of altitude.
If you ever have to do this for real there are two tricks left: pull at max g out of the dive, or roll the aircraft opposite to the prop rotation direction. Remember, however, that you will be way over design manoeuvring speed.
Joined: Mar 2003
Posts: 71
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From: Chessington, UK
I'm with QNH 1013 on this. The prop almost certainly won't stop, so if you pull the mixture to ICO in flight the engine is still turning, and the mags are still sparking the plugs. All that's missing is the correct mixture - so if you calmly return the mixture to fully rich the engine WILL burst back into life. There should be no need to crank it - and you probably shouldn't even need to switch the fuel pump on. If it doesn't come back to life there's something wrong with the engine.
Surely the mixture control must be usable on your aircraft? You don't mention whether it's on a C-of-A or not, but I'd be amazed if any aircraft would get through an annual with an u/s mixture control.
Surely the mixture control must be usable on your aircraft? You don't mention whether it's on a C-of-A or not, but I'd be amazed if any aircraft would get through an annual with an u/s mixture control.
Joined: Apr 2004
Posts: 130
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From: Mostly hotels
i havent flown the props for almost 15 yrs now so please excuse if am wrong.
you have a few options
1.you could get an engineer to take a look at it.
2.you could try to lean it on ground.
3.depending on your comfort level,your experience etc . give it a try at a safe altitude from which you could glide to the runway incase the engine quits on you and doesnt start again.
the best solution is to ask somebody very qualified on the type to answer your question and to be with you when you do try the above in air.
the props that i have flown we did have to lean the mixture at high altitudes else we had too rich a mix.
ALL THE SAME FLYING IS SERIOUS BUSINESS so take care and happy landings
you have a few options
1.you could get an engineer to take a look at it.
2.you could try to lean it on ground.
3.depending on your comfort level,your experience etc . give it a try at a safe altitude from which you could glide to the runway incase the engine quits on you and doesnt start again.
the best solution is to ask somebody very qualified on the type to answer your question and to be with you when you do try the above in air.
the props that i have flown we did have to lean the mixture at high altitudes else we had too rich a mix.
ALL THE SAME FLYING IS SERIOUS BUSINESS so take care and happy landings
Thread Starter
Joined: Jul 2001
Posts: 504
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From: South Yorkshire
Thanks for the suggestions.
The aircraft is a Aeronca Chief with a Continental C90 Engine and MA3-SPA carburetor. It is on a PFA Permit to Fly.
As far as I know the mixture control does work progessively, but never having tried it in the air or on the ground I don't know how linear it's operation is. I'll definitely try it on the ground first.
I'm keen to use it correctly as this should extend the safe range of the aircraft which is not generous when two up.
If it works on the ground, I'll try it in the air when within gliding distance of an airfield, and when in practice with PFLs. I am taking comfort in the fact that at least two people reckon the engine is unlikely to stop in the air even with the mixture down to ICO.
Thanks again
The aircraft is a Aeronca Chief with a Continental C90 Engine and MA3-SPA carburetor. It is on a PFA Permit to Fly.
As far as I know the mixture control does work progessively, but never having tried it in the air or on the ground I don't know how linear it's operation is. I'll definitely try it on the ground first.
I'm keen to use it correctly as this should extend the safe range of the aircraft which is not generous when two up.
If it works on the ground, I'll try it in the air when within gliding distance of an airfield, and when in practice with PFLs. I am taking comfort in the fact that at least two people reckon the engine is unlikely to stop in the air even with the mixture down to ICO.
Thanks again
Joined: Aug 2000
Posts: 1,966
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From: Norfolk
HAL26 leaning
Tacpot,
If I relay my experiences with leaning my HAL26, I believe that it may help you.
In the cruise above 2500', I always leaned it.
I'd set the power to 2350 or somewhere around there, then very very slowly I would pull the mixture knob towards me until I could hear the revs rise. I'd then continue pulling it until the engine revs began to reduce.
Then I'd push the mixture towards the dash - and basically by judgement guesstimate halfway between increasing revs and decaying revs.
As you descend don't forget to enrichen it!
I have occasionally pulled the mixture out too far and the engine has begun to die, the prop is still whizzing raround ut it has gone seriously quiet up front...
but by pushing the mixture back, the little C90 always burst back into life. And after a moment of two, I would attempt to lean it with less vigour!
Stik
If I relay my experiences with leaning my HAL26, I believe that it may help you.
In the cruise above 2500', I always leaned it.
I'd set the power to 2350 or somewhere around there, then very very slowly I would pull the mixture knob towards me until I could hear the revs rise. I'd then continue pulling it until the engine revs began to reduce.
Then I'd push the mixture towards the dash - and basically by judgement guesstimate halfway between increasing revs and decaying revs.
As you descend don't forget to enrichen it!
I have occasionally pulled the mixture out too far and the engine has begun to die, the prop is still whizzing raround ut it has gone seriously quiet up front...
but by pushing the mixture back, the little C90 always burst back into life. And after a moment of two, I would attempt to lean it with less vigour!
Stik
Thread Starter
Joined: Jul 2001
Posts: 504
Likes: 0
From: South Yorkshire
Cheers Stik
It does indeed help. Its very useful to see your cruise settings and leaning technique. Exactly what I needed to know.
Thanks for the confirmation that even if the mixture is pulled too far back, a C90 can still be pursuaded back into life.
Good point about remembering to enrichen the mixture on the descent. Hours spent polling around the circuit at Full Rich means that this check is somewhat unfamiliar...
Cheers.
It does indeed help. Its very useful to see your cruise settings and leaning technique. Exactly what I needed to know.
Thanks for the confirmation that even if the mixture is pulled too far back, a C90 can still be pursuaded back into life.
Good point about remembering to enrichen the mixture on the descent. Hours spent polling around the circuit at Full Rich means that this check is somewhat unfamiliar...
Cheers.
Jet Blast Rat
Joined: Jan 2001
Posts: 2,081
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From: Sarfend-on-Sea
Try doing a 4-point hesitation roll in a Chipmunk, or any carburettor-engined aircraft. Cuts off fuel to the engine when inverted, no power produced but continues turning. When back in positive g the engine springs back into life. Perfectly normal practice, and in any piston engine that is working correctly you can cut the fuel supply, the prop will windmill, and as soon as fuel is restored the engine will produce power again.
