Legalities of derating engines

LAMPSguy · #1 06-05-2012, 05:41 AM

Should rules be changed to limit max HP to 180, what "requirements" are there to officially limit an engine to that max HP?

Lets say you have a 200 HP engine installed, FAA changes some rules, you now want a "180 HP" engine. 180= 90% of 200. .9*2700=2430 RPM. Is it as easy as limiting that 200 HP@2700RPM engine to 2430 RPM and now calling it a 180 HP engine?

Just curious. Builders who have not selected an engine have more options, but some already have an engine installed.

RV10inOz · #2 06-05-2012, 05:51 AM

works for the C182 with IO540.............Why not!

Silly things really, the 182 at 2400 is the same as the RV10 at 2400, except ............well you know

airguy · #3 06-05-2012, 07:32 AM

If you have the restriction of 180hp, that would change with altitude - at some critical altitude (maximimum available manifold pressure) wide open throttle and 2700 rpm would produce 180hp. A straight RPM restriction in that case would not make sense, maybe a restriction for less than 2450 RPM below a certain altitude? Or just ops limits calling out a maximum power percentage and leave it up to the pilot to implement?

Kahuna · #4 06-05-2012, 07:59 AM

What requires EAB to have a placard on the engine? Why would it even have to be accurate? Why would we bother with placards at all?

mannanj · #5 06-05-2012, 08:11 AM

Carbon Cub, et al derate their O-360 engines to stay within LSA guidelines. A friend, with support from Sonex derated a Jabiru 120 hp. engine to keep it LSA.

JonJay · #6 06-05-2012, 08:23 AM

Cub Crafters builds their own version of ECI's Stroker 340 and calls it the CC340. It is fully rated to 180hp for 5 minutes, or something like that, and then you follow the chart(placard) to limit RPM at specific altitudes.
I am told that engine will run all day long at full power, but the restrictions are put in so they can meet the LSA requirments for the Super Sport Cub.

They do some other trick stuff to that engine, like build their own sump, dual EI, and I am sure more to keep weight down.

I am not sure what paper work gymnastics where done with the fed's. Maybe RL will chime in.

SHIPCHIEF · #7 06-06-2012, 09:01 AM

How handy.
I have a 'homebuilt' Lycoming engine, an O-290G conversion in a T-18.
The builder of the engine entered in the log that it is converted to an O-290-D2. But it's not, as a D2 has a hydraulic cam, and this conversion has a solid cam. Also, the sump, carb and accessory case are from an O-320E.
Who could know what the HP is?
Also, I have a Mazda Rotary in my RV-8 project. I registered it @ 170 HP just to keep it below 180. Who could know how much it will produce before it's first flight?
The days of bragging up the HP are over.
Besides, wouldn't it be cool to top out @ 200 MPH on 160 HP instead of 200 HP?
Keep it light.