Derating an Engine

J

JustinPinnix

Pre-Flight
Joined
Oct 28, 2006
Messages
85
Location
Raleigh, NC
Display Name
Display name:
Justin
So here's a question I've wondered about for years. I have been told that the Lycoming O-360 in my plane is derated to 180hp. There are some other planes that have a 200hp version of the O-360.

How is that accomplished? What is different about the 200hp version? When I dial in the power setting that my POH says is 75% power, is that really 75% or is it actually 75*180/200? Can I expect my derated engine to last longer than the 200hp version since it has the same parts and isn't working as hard?
 
JustinPinnix said:
So here's a question I've wondered about for years. I have been told that the Lycoming O-360 in my plane is derated to 180hp. There are some other planes that have a 200hp version of the O-360.

How is that accomplished? What is different about the 200hp version? When I dial in the power setting that my POH says is 75% power, is that really 75% or is it actually 75*180/200? Can I expect my derated engine to last longer than the 200hp version since it has the same parts and isn't working as hard?
Click to expand...

First, AFaIK all 200 hp Lyc 360's are IO-360s (fuel injected). Second, your engine has a "rated" power and that is likely 180HP. A 75% power setting in such an engine should produce 75% of 180 HP.

Finally, engines are sometimes "derated" for various reasons. One would be because the airframe isn't designed to handle the full HP, another reason would be to reduce the noise footprint. Usually the derating is accomplished by limiting RPM since an engine's power output is generally proportional to RPM at wide open throttle.
 
I may very well be wrong (which will be proven very soon if so), but I think the O-360 is the 180hp version and you have to go to the IO-360 (fuel injected) to get the 200hp.

From my experience with non-aviation equipment - namely Ag-Chem TerraGators running John Deere 8.1L Diesel Engines - the biggest difference with de-rating an engine is the amount of fuel you can get to burn effectively in the cylinders. I run a 2004 6103 TerraGator with 8.1L engine that is rated for 250hp. In my newest 2006 6103 TerraGator running the same 8.1L 'block' as the '04 model, I'm able to get 300hp b/c they put a bigger fuel pump and intercooler to make it possible to squeeze more fuel into the cylinders.

I know that aviation turbine engines are routinely derated for their intended purpose.

** I sit and wait to be corrected. **

-Chris
 
CJones said:
I may very well be wrong (which will be proven very soon if so), but I think the O-360 is the 180hp version and you have to go to the IO-360 (fuel injected) to get the 200hp.

From my experience with non-aviation equipment - namely Ag-Chem TerraGators running John Deere 8.1L Diesel Engines - the biggest difference with de-rating an engine is the amount of fuel you can get to burn effectively in the cylinders. I run a 2004 6103 TerraGator with 8.1L engine that is rated for 250hp. In my newest 2006 6103 TerraGator running the same 8.1L 'block' as the '04 model, I'm able to get 300hp b/c they put a bigger fuel pump and intercooler to make it possible to squeeze more fuel into the cylinders.

I know that aviation turbine engines are routinely derated for their intended purpose.

** I sit and wait to be corrected. **

-Chris
Click to expand...

It's not the amount of fuel that limits horsepower, it's the amount of air. You can add all the fuel you want to a gasoline engine and it will simply run richer (and produce less power once you go past about 100F ROP EGT). The amount of air an engine ingests is a function of the manifold pressure, the engine's volumetric efficiency, and RPM (for all intents and purposes its the product of those three). There are tricks that can be done with fuel to extract more power, mainly more accurate mixture control to each cylinder, but simply adding fuel won't help unless the mixture is already lean. And of course, once you get more air into the cylinders you need more fuel to keep the mixture correct. On a diesel power iscontrolled by the amount of fuel, but that's because they almost always run lean by design. Even then, adding more fuel than the engine can burn at full power for a given RPM will just increase the soot level not the HP. Chances are the difference in power between the two engines you mentioned is due to a higher manifold pressure (if supercharged) or higher RPM limits.
 
Last edited:
Lance, re: your comment about "noise footprint", don't you mean detuning the engine to match a specific propeller?

BTW, I love it when you talk stochiometric equalivencies. Ooo, baby.
 
lancefisher said:
It's not the amount of fuel that limits horsepower, it's the amount of air. You can add all the fuel you want to a gasoline engine and it will simply run richer (and produce less power once you go past about 100F ROP EGT). The amount of air an engine ingests is a function of the manifold pressure, the engine's volumetric efficiency, and RPM (for all intents and purposes its the product of those three). There are tricks that can be done with fuel to extract more power, mainly more accurate mixture control to each cylinder, but simply adding fuel won't help unless the mixture is already lean. And of course, once you get more air into the cylinders you need more fuel to keep the mixture correct. On a diesel power iscontrolled by the amount of fuel, but that's because they almost always run lean by design. Even then, adding more fuel than the engine can burn at full power for a given RPM will just increase the soot level not the HP. Chances are the difference in power between the two engines you mentioned is due to a higher manifold pressure (if supercharged) or higher RPM limits.
Click to expand...


That's why I qualified my statement with "amount of fuel you can get to burn EFFECTIVELY in the cylinders". ;)

-Chris
 
The 200HP IO-360 also has a higher compression ratio than the 180HP O-360, which is one reason you can't run it on less than 100 octane fuel, while the 180 HP O-360 may be run on the old 91/96 avgas and the new 92 unleaded avgas (available in Europe but not in the USA -- yet). Higher compression ratio will always give you more power when all other parameters remain the same.

In any event, "derating" involves some sort of limitation to prevent the engine from developing more than the derated rated power. An example is the STC to put higher compression pistons in the 150 HP O-320-E2G, originally rated at 2700 RPM. The modfied engine would produce 160 HP at 2700 RPM, but in order to keep it rated at 150 HP (for reasons involving certification of the installation of the engine in the Cheetah and Traveler), the modified engine is rated at 2650 RPM rather than 2700 RPM, thus moving the redline down 50 RPM, and stays rated at 150 HP. The result is an engine rated at 150 HP that acts like a 160 HP engine during takeoff/climb (when RPM is well below redline even at full throttle).
 
Last edited:
The 180 HP O and IO-360 Lycoming engines are NOT derated 200 HP engines. The 200 HP known in the trade is an "angle valve" engine as opposed to the 180 HP series being a "parallel valve" engine. The angle valve engines have a higher compression ratio, tuned induction and more efficient cylinders in order to be rated at 200 HP. Charlie Melot Zephyr Aircraft Engines
 
Robinson helicopters have derated engines. The Raven II, for example, has an IO-540 which is derated to 205 hp continuous, and 245 hp for 5 minute takeoff power. The derating is accomplished by placing artificial MP limits. The IO-540 is perfectly capable of producing 300 hp if the limits are ignored. The reasons for derating are 1) provide extra performance at high DA, 2) to extend TBO to 2200 hours.
 
RotaryWingBob said:
Robinson helicopters have derated engines. The Raven II, for example, has an IO-540 which is derated to 205 hp continuous, and 245 hp for 5 minute takeoff power. The derating is accomplished by placing artificial MP limits. The IO-540 is perfectly capable of producing 300 hp if the limits are ignored. The reasons for derating are 1) provide extra performance at high DA, 2) to extend TBO to 2200 hours.
Click to expand...

Bob:

I don't know about your specific helo, but in general on rotary wing stuff, there is always some limiting part that holds up power transfer to the rotors (and in the past the rotors themselves have been an issue). There are times the engine is the weak point. More often, what the transmission can handle, etc. I'd be surprised, in addition to what you mention, if there isn't some component in the power chain that can't take the higher power.

Best,

Dave
 
now that we've had some valid responses, it's time to hijack this thread ...

"Stupid Engine! You'll never amount to anything!"
"You're a lazy, no good, waste of 100LL, pile of iron!"
"I always thought you were no good!"

Sorry, since I first saw the title, I thought it said "Berating an engine" :D
 
CJones said:
That's why I qualified my statement with "amount of fuel you can get to burn EFFECTIVELY in the cylinders". ;)

-Chris
Click to expand...

Ah yes, I thought I read "amount of fuel you can get into the cylinder". Your statement was indeed correct.
 
Dave Siciliano said:
Bob:

I don't know about your specific helo, but in general on rotary wing stuff, there is always some limiting part that holds up power transfer to the rotors (and in the past the rotors themselves have been an issue). There are times the engine is the weak point. More often, what the transmission can handle, etc. I'd be surprised, in addition to what you mention, if there isn't some component in the power chain that can't take the higher power.

Best,

Dave
Click to expand...

Very true. It's the rotor system, spindles, transmission, etc. that you have to worry about.
 
You must log in or register to reply here.
Back
Top