Engine torque output

[AMCKen]

It seems all aeroengines have listed output in horsepower, but I have yet to see what their output is in foot-pounds of torque (or other applicable units). One can calculate the output from the rpm and horsepower, but that only applies to the torque at the same rpm as the horsepower (2100hp@2700 = 4085ftlbs@2700). As we know from automobile engines, the peak torque is usually higher than the torque at hp peak, and at a lower rpm. Anyone have info? Thanks.

 

[pbehn]

It seems all aeroengines have listed output in horsepower, but I have yet to see what their output is in foot-pounds of torque (or other applicable units). One can calculate the output from the rpm and horsepower, but that only applies to the torque at the same rpm as the horsepower (2100hp@2700 = 4085ftlbs@2700). As we know from automobile engines, the peak torque is usually higher than the torque at hp peak, and at a lower rpm. Anyone have info? Thanks.

I think the use of constant speed props and superchargers/ turbo chargers makes torque values pretty redundant in most discussions.

 

[AMCKen]

Part throttle settings always change things. I'm asking about the maximum available - test stand numbers, just like the maximum horsepower.

 

[pbehn]

Part throttle settings always change things. I'm asking about the maximum available - test stand numbers, just like the maximum horsepower.

What is the difference between a part throttle setting and a part boost setting? Torque curves (or lack of curve) are important on atmospheric car and motorcycle engines, the flatter the curve is the easier they are to drive or ride, the more they show a peak then the more you have to work the gear box. A two stroke motorcycle engine of the type I used to race has a torque and power curve that rises with RPM and then shuts off, they are impossible to ride in any way other than to race, out of the tuned power band they have close to no power at all. Supercharged engines are different especially those from WW2, you choose the MEP (torque) from the boost and the HP stems from that. The story of P-38s in the far east is an illustration of this, pilots had a choice of how lean or rich and what RPM they ran with, this had a massive effect on fuel consumption and therefore range.

 

[AMCKen]

No big difference between part throttle and part boost. And the torque curve is what I'm asking about. Where is the peak, what is the peak, how curvey is the curve?

 

[pbehn]

No big difference between part throttle and part boost. And the torque curve is what I'm asking about. Where is the peak, what is the peak, how curvey is the curve?

Are you really stating that there is no real difference between maximum and minimum boost on a late war Merlin engine, the boost level changes power output by over 1000BHP? I would imagine that the curves are fairly flat but you need a different curve for each level of boost and other settings which affect power output.

 

[AMCKen]

As I've said, I'm asking about _maximum_ torque, regardless of which boost setting is being used to get it. The engines have a listed maximum horsepower, why not a maximum torque?

 

[pbehn]

As I've said, I'm asking about _maximum_ torque, regardless of which boost setting is being used to get it. The engines have a listed maximum horsepower, why not a maximum torque?

Because it isn't important? For the reasons I stated. The max torque obviously depends on the boost and fuel being used, torque is a measure of pressure on the pistons, piston stroke etc, summed up as Mean Effective Pressure (MEP).

 

[AMCKen]

Horsepower is calculated from torque and rpm, which is what a dynamometer actually measures. Obviously it will take maximum boost and fuel.

 

[pbehn]

Horsepower is calculated from torque and rpm, which is what a dynamometer actually measures. Obviously it will take maximum boost and fuel.

And temperature, air pressure (altitude) forward speed (ram effect) etc etc.

 

[AMCKen]

Ram effect is not part of test stand measuring standards. Maximum HP is rated according to corrections for temperature, humidity, air pressure, etc at the engine test stand. All I'm asking for is maximum torque under the same circumstances.

 

[Rubenova]

This is actually a good question about peak torque. I think one would have to look into unlimited hydroplane racing or tractor pulling for the Allison V-12 for example. They have to tune those things somehow. Why not on some kind of Dynamometer? I'm not aware of any ground/water sport using any WW2 radials. I would be interested to see any torque @ rpm numbers to see if there was any relation to cruise, loiter and maximum flying time speeds.

 

[pbehn]

Ram effect is not part of test stand measuring standards. Maximum HP is rated according to corrections for temperature, humidity, air pressure, etc at the engine test stand. All I'm asking for is maximum torque under the same circumstances.

I would imagine that an aero engines economical cruise settings would be an indicator of peak torque, but its complicated, for some engines/settings the fuel flow was used not only for combustion but also for cooling of the inlet charge. Ram effect is part of the calculation of actual power and therefore torque at a given airspeed.

 

[AMCKen]

In (unsupercharged anyway)auto engines, peak torque, volumetric efficiency, and hp/unit of fuel/time (lbs/hphr) are usually pretty closer to each other in rpm.

 

[Rubenova]

Not much out there. Check out
Aircraft Engine Dynamometer Testing | Allison Competition Engines, Inc

 

[pbehn]

In (unsupercharged anyway)auto engines, peak torque, volumetric efficiency, and hp/unit of fuel/time (lbs/hphr) are usually pretty closer to each other in rpm.

That depends entirely on what unsupercharged auto engine you are discussing, in my youth I owned a 1 litre Austin Mini and a 1.7litre Holbay Hillman Hunter GLS, the Holbay had twin choke Weber carburettors struggled to do 100MPH and rarely did better than 10MPG. The Mini was better lol.

 

[AMCKen]

That depends entirely on what unsupercharged auto engine you are discussing, in my youth I owned a 1 litre Austin Mini and a 1.7litre Holbay Hillman Hunter GLS, the Holbay had twin choke Weber carburettors struggled to do 100MPH and rarely did better than 10MPG. The Mini was better lol.

Must have been something wrong there.
My 80 Spirit with 5.0 litre and 2 barrel carb averages over 19mpg. Weighs about 3200 pounds empty.

 

[swampyankee]

During the time I worked in the aircraft industry (Sikorsky and what was then called Hamilton Standard), torque rarely came up in conversation unless we were talking about gearboxes and shafting. Outside of sizing shafts and gears, torque has really very little importance to the people designing the main and tail rotors or propellers.

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Generally, for naturally aspirated engines, the best volumetric efficiency will set the best torque. With some modern engines, this gets messed up by things like variable valve timing and variable-length intake manifolds.

 

[pbehn]

Must have been something wrong there.
My 80 Spirit with 5.0 litre and 2 barrel carb averages over 19mpg. Weighs about 3200 pounds empty.

Nope, that's what they did, https://www.automobile-catalog.com/performance/1972/1027070/hillman_hunter_gls.html, economy figures were always measured with a warm engine, from cold it did 4 MPG for the first 5 miles, which is how far I had to drive to work.

 

[AMCKen]

Nope, that's what they did, https://www.automobile-catalog.com/performance/1972/1027070/hillman_hunter_gls.html, economy figures were always measured with a warm engine, from cold it did 4 MPG for the first 5 miles, which is how far I had to drive to work.

That page says "mpg (imp.): 23.5-28.3 / 17.3-20.8 / 18.2-21.9 / 22.7"