Reduction in Piston Engine Horsepower due to High Temperature
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From: 26000 to 28,000 lightyears from the galatic centre
Reduction in Piston Engine Horsepower due to High Temperature
Hi Chaps
Can you please direct to a source of data relating to the Engine performance of Lycoming 0235/0320/0360 or other light aircraft engines at very high surface temperature say above 25 deg c?(My 0320 manual has no info on this topic)
Over the last few days at these high temperature its like taking off with the Carb Ht selected to hot.
I have managed to Search PPrune and come up with a WW2 dated paper but that’s all.
Are there any more relevant up to date papers on the subject?
While Aircraft Manuals and AIC 67/2002 do give performance corrections for temperature they do not quantify the horsepower reduction at high temperatures.
Thanks Orion
Can you please direct to a source of data relating to the Engine performance of Lycoming 0235/0320/0360 or other light aircraft engines at very high surface temperature say above 25 deg c?(My 0320 manual has no info on this topic)
Over the last few days at these high temperature its like taking off with the Carb Ht selected to hot.
I have managed to Search PPrune and come up with a WW2 dated paper but that’s all.
Are there any more relevant up to date papers on the subject?
While Aircraft Manuals and AIC 67/2002 do give performance corrections for temperature they do not quantify the horsepower reduction at high temperatures.
Thanks Orion
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From: UK
As a first approximation, it's all down to air density.
A quick back of envelope calc tells me that in going from 15°C (ISA Sea-level temperature), to 25°C (ISA+10°C), at the same pressure equates to a drop in air density of about 4%, or equivalent to being about 1200ft higher airfield elevation.
I had a hand in producing a ready-reckoner for GASCo a little while ago which helps you work out the effects of elevated temperature on a light aircraft. You can download it in a handy kneeboard format here, or there's an article about it here. As you'll see from there, that increase in temperature from 15°C to 25°C should give you about a 20% increase in TODR.
As you say, not unlike taking off with Carb Heat on - since basically the same is happening, air density is dropping with the increased temperature.
G
A quick back of envelope calc tells me that in going from 15°C (ISA Sea-level temperature), to 25°C (ISA+10°C), at the same pressure equates to a drop in air density of about 4%, or equivalent to being about 1200ft higher airfield elevation.
I had a hand in producing a ready-reckoner for GASCo a little while ago which helps you work out the effects of elevated temperature on a light aircraft. You can download it in a handy kneeboard format here, or there's an article about it here. As you'll see from there, that increase in temperature from 15°C to 25°C should give you about a 20% increase in TODR.
As you say, not unlike taking off with Carb Heat on - since basically the same is happening, air density is dropping with the increased temperature.
G
Last edited by Genghis the Engineer; 23rd June 2005 at 12:26.
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From: Euroland
If you want accurate engine performance fighures, you need to get hold of the engine manual produced by the engine manufacturer and consult the appropriate graphs.
Your friendly maintenance organisation will probably have one since they get a new one with each new/ manufacturer overhauled engine or contact Lycoming direct.
Note that Lycoming will only deal with engine output, it will not make any allowances for the actual aircraft instalation or the propeller used.
Regards,
DFC
Your friendly maintenance organisation will probably have one since they get a new one with each new/ manufacturer overhauled engine or contact Lycoming direct.
Note that Lycoming will only deal with engine output, it will not make any allowances for the actual aircraft instalation or the propeller used.
Regards,
DFC
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From: Sydney NSW
Joined: Jun 2000
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From: Australia
The detrimental effect on engine power due to increasing cylinder head temperatures caused by unnecessarily extended engine run up's, should be taken into account.
For example, the Convair 440 Metropolitan (Pratt & Whitney R2800 engines) had BMEP gauges which in effect measured engine horse power.
During the take off run and initial full power climb, the BMEP would show a gradual decrease as the CHT's increased. If the CHT was already high due perhaps to extended running at high power to clear fouled spark plugs, the drop of BMEP from standard take off reading , was quite noticeable. Typically one would expect 235 BMEP (left engine) as the throttles reached the take off limit manifold pressure at standard OAT, but by the time the aircraft had reached 200 feet the BMEP had dropped to 225 or thereabouts. Obviously this gradual decay in power could make single engine rate of climb reduce from optimum for the conditions.
From that it was clear that run-up's for engine testing on the ground should be as brief as practicable in order to obtain the best BMEP for the conditions. Ths same principle I presume would apply to CHT increases on light twins such as the Chieftain, Baron etc. The habit of "burning out the plugs" at high power if the mag drop check is outside limits, is a two edged sword. High power on the ground causes increased CHT's. The spark plugs get cleared eventually, at the cost of reduced engine power on take off.
For example, the Convair 440 Metropolitan (Pratt & Whitney R2800 engines) had BMEP gauges which in effect measured engine horse power.
During the take off run and initial full power climb, the BMEP would show a gradual decrease as the CHT's increased. If the CHT was already high due perhaps to extended running at high power to clear fouled spark plugs, the drop of BMEP from standard take off reading , was quite noticeable. Typically one would expect 235 BMEP (left engine) as the throttles reached the take off limit manifold pressure at standard OAT, but by the time the aircraft had reached 200 feet the BMEP had dropped to 225 or thereabouts. Obviously this gradual decay in power could make single engine rate of climb reduce from optimum for the conditions.
From that it was clear that run-up's for engine testing on the ground should be as brief as practicable in order to obtain the best BMEP for the conditions. Ths same principle I presume would apply to CHT increases on light twins such as the Chieftain, Baron etc. The habit of "burning out the plugs" at high power if the mag drop check is outside limits, is a two edged sword. High power on the ground causes increased CHT's. The spark plugs get cleared eventually, at the cost of reduced engine power on take off.
Joined: Oct 2003
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From: Ireland
Silly question, but what about incorporating some form of air cooler to increase the MP (due to increased air density) any time in any aircraft engine?
Isn't that what happens on a cold morning - MP increases due to the cold, but the cold ambient temp increases outside air density for a corresponding drag rise?
Told you it was silly!
Confab
Isn't that what happens on a cold morning - MP increases due to the cold, but the cold ambient temp increases outside air density for a corresponding drag rise?
Told you it was silly!
Confab
Joined: Feb 2005
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From: flyover country USA
Not so silly, Confabulous!
That's part of the reason for water injection. It does two things for you:
o Evaporative cooling, plus
o More mass flow
Now all you have to worry about is corrosion, water pump failure, freezing, ...
That's part of the reason for water injection. It does two things for you:
o Evaporative cooling, plus
o More mass flow
Now all you have to worry about is corrosion, water pump failure, freezing, ...
Joined: Oct 2003
Posts: 338
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From: Ireland
I know this is nitpicking, but let's say we have a Lycmning TSIO-540 or similar, and want to add an air cooling system based on water.
1. If it's a turbocharged engine, what about using bleed air (or excess wastegate pressure) to pressurise the water tank, and use a valve linked to MP indications and/or throttle position to control flow? No pump needed!
2. Alternatively, what about using a venturi arrangement in the engine air intake - the faster the airflow, the more water gets sucked into the venturi.
3. With regard to water freezing - how about antifreeze?
4. Corrosion - use aluminium?
Apologies, I'm sure these ideas have been thought of before, you'd probably need a lot of water to make this really work!
Confab
1. If it's a turbocharged engine, what about using bleed air (or excess wastegate pressure) to pressurise the water tank, and use a valve linked to MP indications and/or throttle position to control flow? No pump needed!
2. Alternatively, what about using a venturi arrangement in the engine air intake - the faster the airflow, the more water gets sucked into the venturi.
3. With regard to water freezing - how about antifreeze?
4. Corrosion - use aluminium?
Apologies, I'm sure these ideas have been thought of before, you'd probably need a lot of water to make this really work!
Confab
Joined: Feb 2005
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From: flyover country USA
You know, I don't recall all the details of water injection on recips - but I think you've correctly addressed some of the concerns.
Re corrosion - I was thinking mostly of hot end corrosion (Cylinder heads, valves & seats & bushings...) and I think demineralized water usually solved that issue. Methanol was mixed with the water for antifreeze.
Re corrosion - I was thinking mostly of hot end corrosion (Cylinder heads, valves & seats & bushings...) and I think demineralized water usually solved that issue. Methanol was mixed with the water for antifreeze.
