damage

[MachFly]

my mates dad had to restart his vulcan in the early 70s after they accidentally switched over to empty tanks somewhere over the north sea. cost them ~5,000' and new underwear all round. iirc they kept quiet about it

You mean the Avro Vulcan?
I can't imagine what it would be like to loose all your four engines at the same time.

[RTHolmes]

yup he flew canberras for years then moved into vulcans. the conversation was almost 20yr ago after dinner and tbh I'd had a coupla beers and he'd had a bottle or 2 of claret and a few cognacs

I assume it was all 4 engines because he said they lost the engines and power one at a time in about 30s. they assumed it was an electrical system problem and after running through the procedures noticed the fuel settings, rerouted the tanks and restarted. he said it felt like 15mins til they had the engines back up but was probably more like 60s due to the effects of adrenaline and so much training you can blast through a checklist even though you cant even remember your own name ... iirc he said the vulcan had a very complex fuel system with a bunch of tanks that you can reroute to any of the engines.


edit: the weird thing is my mates dad was the first officer on that flight. a few years later my dad discovered that one of his new bosses knew my mates dad, from his RAF days as it happened. it turned out my dads boss was the pilot!

[hitech]

So since you guys disagree with my idea of stopping the prop, what's the point of designing a governor that will not feather the blades when you loose oil pressure?

It has nothing do to with governor design.  But rather the internals workings of the prop, the max degree of rotation of the blades is limited by the distance the piston can travel. Looking at most Hartells they work similar to a piston and crank shaft setup where the movement of the piston is attached to  a push rod attached to the outside of the prop. Oil and spring, or oil and counter weight turn the blades. Making these work to the degree needed for feather is more complex and heaver. Hence only put on multi engine planes.

On a multi where you loose and engine it is very desirable to minimize drag since you can maintain flight with the lost engine. With single engine the trade off is not worth it.

There are also other trade offs. For instance most single engine constant speed props use oil presure to increase blade angle and a spring to decrees the angle. This has the effect of loss of oil pressure flattens the prop I.E. High rpm.  For normal planes the only time you loose pressure , the odds are your engine is also not running. Or you can just pull power back. I.E it is only in an emergency situation.

When flying aerobatics with and inverted oil systems, there are conditions where when flying in the vertical at zero g the valve can get stuck temporally between inverted and normal flight, hence starving the engine of oil. When at full power loss of oil pressure would cause prop to go flat, and almost instantly over rev the engine. Hence aero props work with counter weights to increase pitch and oil pressure to decrease pitch. So in the case loss of oil pressure, loads down the engine which is the much more desirable case.

Ive heard the engine load down  in my rv a few times in the vertical zoom part of a hammer head.

So to answer your question why not make all. It is just like any part of aircraft design. There is not any one best design. It always has to do with tradeoffs , and what is most important in any particular usage.

HiTech

[MachFly]

See I always knew that the internal components of the prop that on a multi engine are heavier, but is it significant? The only extra parts that you have are the counterweights, those weigh around 1-2lb.

Ive heard the engine load down  in my rv a few times in the vertical zoom part of a hammer head.

So when you zoom up the prop is not capable of compensating and the RPMs decrease?

[MachFly]

yup he flew canberras for years then moved into vulcans. the conversation was almost 20yr ago after dinner and tbh I'd had a coupla beers and he'd had a bottle or 2 of claret and a few cognacs

I assume it was all 4 engines because he said they lost the engines and power one at a time in about 30s. they assumed it was an electrical system problem and after running through the procedures noticed the fuel settings, rerouted the tanks and restarted. he said it felt like 15mins til they had the engines back up but was probably more like 60s due to the effects of adrenaline and so much training you can blast through a checklist even though you cant even remember your own name ... iirc he said the vulcan had a very complex fuel system with a bunch of tanks that you can reroute to any of the engines.


edit: the weird thing is my mates dad was the first officer on that flight. a few years later my dad discovered that one of his new bosses knew my mates dad, from his RAF days as it happened. it turned out my dads boss was the pilot!

I see.

[colmbo]

See I always knew that the internal components of the prop that on a multi engine are heavier, but is it significant? The only extra parts that you have are the counterweights, those weigh around 1-2lb.

Not all props have counter-weights.  Some of the added weight will be an accumulator, or other system, that can be used to un-feather the engine.  On the B-17 and B-24 the props were feathered by using of a "feathering pump".  Simply an electric pump used to pump oil into the hub to drive the blades into the feather positiion. It was also used to unfeather.  The oil reservoir was set up with a sump below the oil line to preserve enough oil to feather if an oil line to the engine was cut/broken/leaking.   

[MachFly]

Not all props have counter-weights.  Some of the added weight will be an accumulator, or other system, that can be used to un-feather the engine.  On the B-17 and B-24 the props were feathered by using of a "feathering pump".  Simply an electric pump used to pump oil into the hub to drive the blades into the feather positiion. It was also used to unfeather.  The oil reservoir was set up with a sump below the oil line to preserve enough oil to feather if an oil line to the engine was cut/broken/leaking.  

Right, I forgot about the accumulator.

How can you have a prop with no counter-weights that will feather due to lack of oil pressure?

[hitech]

See I always knew that the internal components of the prop that on a multi engine are heavier, but is it significant? The only extra parts that you have are the counterweights, those weigh around 1-2lb.

So when you zoom up the prop is not capable of compensating and the RPMs decrease?

Yes , the prop gets starved of oil for a brief period of time. And hence goes full course pitch. As mentioned above the other way to solve the issue is with a pressure accumulator, most I have seen have a nitrogen bladder that oil is pumped into compressing the air, then when the valve gets stuck in the middle there is enough reservoir feeding the prop. I have only seen these on planes that have a non areo prop. But not sure if they are used in others.

HiTech

[colmbo]

Right, I forgot about the accumulator.

How can you have a prop with no counter-weights that will feather due to lack of oil pressure?

I don't know of any prop that will feather without oil pressure unless it's an electric hub.  McCauley's use a spring that drives the blades to low pitch in the event of no oil pressure.  Hitech stated his prop is driven to the high pitch stop with no oil pressure.  Counter-weights just produce a force to drive the blade in one direction, the oil pressure is used to work against the counter-weights (or springs).

[Motherland]

On the subject of damage, what has happened to the plans to work the more detailed World War I model into World War II?

[MachFly]

I don't know of any prop that will feather without oil pressure unless it's an electric hub.  McCauley's use a spring that drives the blades to low pitch in the event of no oil pressure.  Hitech stated his prop is driven to the high pitch stop with no oil pressure.  Counter-weights just produce a force to drive the blade in one direction, the oil pressure is used to work against the counter-weights (or springs).

Right, that what I thought.

[MachFly]

Yes , the prop gets starved of oil for a brief period of time. And hence goes full course pitch. As mentioned above the other way to solve the issue is with a pressure accumulator, most I have seen have a nitrogen bladder that oil is pumped into compressing the air, then when the valve gets stuck in the middle there is enough reservoir feeding the prop. I have only seen these on planes that have a non areo prop. But not sure if they are used in others.

HiTech

Hmm, I see.

[MachFly]

The first time you lose an engine and attempt to stop the prop you're policy will be quickly revised.  In something like a J-3, Champ, maybe a 150 or 152 you might be able to get the prop stopped...anything with much higher performance engine or higher stall speed it's not going to happen.  Like I said about the 182 and 206...I was on the ground before the prop stopped...at speeds to low to maintain flight.  

You should go try your idea before having an actual engine loss.  Try it under controlled conditions instead of when it really matters.

BTW about a year ago I did this test in AH and the results showed that stopping the prop would be a good idea. Granted the type of aircraft is a little different, but what do you think about this?

I made a series of tests today to figure out Spit14's best glide speed. I took a Spit14 with 50% fuel and used the SW spawn at A22 in the training arena. Prop RPMs were set to minimum.

TEST 1: Used 175mph for the first test (HTC's programed autoclimb speed for Spit14). After landing, I asked someone to serve as a reference point for my further tests. Had him put his airplane right where my is in order to measure distance for further tests.

TEST 2: 200mph, landed 5K before the reference point.
TEST 3: 165mph, landed 3.1K after the reference point.
TEST 4: 140mph, landed 3.3K after the reference point.
TEST 5: 130mph, landed 3.3K after the reference point.
TEST 6: 135mph, landed 3.8K after the reference point.

135 mph is the best glide speed for Spitfire mk XIV is this configuration.  


I know in reality the plane will glide further with prop stopped than feathered. So I decided to test if HTC implemented this in AH.

TEST 7: Used the same 135mph as before. With the engine ignition off I had pitch up and reduce my airspeed beyond stall to 20mph which caused the airplane to climb another 2000ft, then since the airplane was already in the stall I had to dive down to initial altitude to recover from the stall. Then I continued the glide. I landed beyond 6K from the reference point so I do not know the exact distance. Since in test 6 I landed 3.8K from the reference point I this test proves that the plane glides better with the prop stopped. Additionally in test 6 I overflew the reference point at 2000ft MSL, in test 7 I overflew the reference point at 4000ft MSL, which additional proves that gliding with prop stopped results in a longer & more efficient climb.


This demonstrates that the energy lost due to maneuvering to get the prop to stop can pay of assuming that the glide is from a relatively high altitude.

Note: It will not necessarily pay off if the glide is from a low altitude.

WARNING: DO NOT DO THIS AT LOW ALTITUDE AS YOU MAY NOT RECOVER FROM THE STALL.




Special thanks to Electric for dedicating his time acting as a reference point.

[colmbo]

Granted the type of aircraft is a little different, but what do you think about this?

I agree that there is less drag with a stopped prop.  No doubt.   

[icepac]

Springs and gears......many props use them instead of rods and levers.