O-290D2 in a PA-11?

Hi all, I'm in the process of attempting a field approval (unless someone knows of an STC- couldn't find one) of a O-290D2 in a PA-11 that already has the -18 tail, flaps, fuel system, etc. Does anyone have experience with this or would you be willing to share a copy of a 337? It should be fairly straightforward; installed in accordance with Piper drawing 12447, as listed on the PA-18 type certificate, calculated various weight and balance scenarios, fuel system flow is adequate, etc., etc. But we all know how "should be fairly straightforward" goes... Thanks in advance.

Don't know about a 0-290 in a PA-11 but in general for ease of getting the approval limit the power to the maximum which you can show is approved. Limit your engine RPM with a red line on the tach at the rpm which your engine will produce the same power which the other approval is. In usage you use the honor system not to exceed the approved power. What you do when no one is looking is your business.8)

The following is from the TC A-691
Engines and Engine Accessories - Fuel and Oil System
311 D PA-11
(6) Lycoming O-235-C Use actual weight and arm Eligible on landplane only and when installed in accordance with Piper Dwg. No 12447. Engine Limits: All operations, 2600 r.p.m. (100 hp) Fuel: 80 minimum octane aviation gasoline. Oil Capacity: 6 qts. (-31) Propeller Limits: (with propeller, Item 10 or 11 only) Static r.p.m. at maximum permissible throttle setting: Not over 2450, not under 2250. No additional tolerance permitted. C. G. Range: (+12.9) to (+17.3) Aircraft weight and balance should be checked to determine need for 11¼ lb. ballast at (+179) or limitation to solo from rear seat only. Placard required in full view of pilot: "All acrobatics, including spins, prohibited."

Notice that the 0-235 is limited to 100 hp by restricting the rpm to 2600. You do the same with your 0290 at whatever rpm produces 100 hp. IF you attempt to get your approval at the full horsepower rating of the 0-290 you could run into a can of worms requiring way more testing, engineering and $$$ than you wish to become involved.So in other words you are just going to substitute a 0-290 for the 0-235 installed in accordance with Piper Dwg. 12447. Think about the words which you use when talking to the FAA.

Before you go through a lot of paper excersize, have you done an HONEST W/B to see what the actual empty weight is going to be? I suspect that modified as you describe, your empty weight will be so high that the pilot will have to weigh < 90 lbs, and limit gas to one hour......

With a legal GW of 1220, there's not a lot of wiggle room.

MTV

Skywagon- thanks, that has been suggested by someone else and definitely is worth looking into. Any ideas on how to determine actual hp at rpm? On second thought, I think the operating manual has charts for that. Mike, the airplane weighs 966 empty with the 290 and all accessories except starter. So with a 170 lb. pilot, you could have close to two hours of fuel by the time you added some oil.

Bear in mind that there are two primary things to determine hp, rpm and manifold pressure. RPM alone isn't enough since the prop pitch will make a difference. You may need to install a manifold press gauge and yes the engine manual has the charts.

Please report back when you get it done. Someone on here years ago talked about flying one set up just like you're talking. Said it was a real performer.

Will do- it's not my plane, but I agreed to help the owner with the field approval. I'm excited to see how it does- that's an honest weight on certified scales, so it should be lots of fun. The power to weight ratio comes out very similar to a 1150# 160hp Cub, but with the same wing, flaps, tail, etc., it'll be pretty cool if we can get the Feds to buy off on it.

One other item of interest, you may be able to use full 0-290D2 power if you limit the engine to full rated power for one minute for take off only followed by 100 hp for maximum continuous power. This will limit all your testing to the 100 hp rating.

My -11 was set up will all the -18 mods including flaps and -18 tanks just like you. Was porky at around 900# or so but even with the C90 it was fine at sea level.