The pic below shows an older (~12 years old) pattern plane which I built and just recently started flying again. The WS is 50.5" and with an OS 25 SF, weighs ~3-3.5 lbs. The problem is the engine. The OS is also old (bought in 1989) and doesn't seem to have enough power to really pull this plane around. The main problem is on takeoff. I fly off a grass runway and with 2" wheels the plane barely gets off the ground in ~100-150ft. In the air, the plane could also use a little more umph. I was thinking of replacing the .25 with something bigger, but wasn't sure which engine would be best. Here are the choices I was considering:

1) OS .32 SX (new)- should be more than enough power, but a little pricey.

2) Thunder Tiger .36 (new)- maybe too much power?

3) an older (~12 years old) ASP .40, which is currently in my trainer plane. I like this engine, mainly because I already have it and don't have to spend any $$$, but am worried the plane may be overpowered. I suppose I could just fly it at 1/2 throttle. Since I needed a lot of lead (~3 ounces) with the .25 engine, the ASP, which weighs more might be perfect as far as balancing the plane w/o the need for more lead weight.

What are your thoughts on my above choices? Are there other engines I should consider?

I would install an O.S 46LA , it costs $60 and produces a reliable 1.2bhp. Also, it will not make your plane nose heavy.
To take off from grass you will need 2-1/2" or 2-3/4" wheels, preferably non-threaded type.

Really? So this wouldn't be overpowering it with a .46? Maybe I'll go ahead with my ASP .40 then. If I don't have to spend the $$ on another engine, I'd rather not.

The only problem you might have is a short landing gear. I would use the ASP .40. As you said, you can always throttle back.

Make sure you aren't using tiny little servos and get the balance correct. You might try an 11-4 prop to start with. More climb, but less speed.

Install what you feel is "comfortable" for your plane. I think that you do not "really" need more than 1.0bhp=>OS 40LA

Do not forget about the 2-1/2" non-threaded tires though!

I think your old ASP will work fine, especially if the plane is tail heavy with the .25. If you need 3oz of lead in the tail with the .25, you may still be a little tail heavy with the .40. The .40 is probably 5 or 6oz heaver than the .25, but the lead in the tail is likely much farther away from the CG than the engine.

Like you said, you can always throttle back if the .40 has more power than is needed.

Eric

Use the ASP and enjoy as Fife and Ed suggested if you are comfortable with that engine. High speed will be slightly faster Take off and climb will be much better landing approach will be slightly more difficult to slow down. Like they said be careful of the CG and use a long flat prop.

John

Why non-threaded tires?

I can't figure out why that would make a difference on grass...

Actually I added up all the little 1/4oz squares last nite and I had 24 of them (6 oz!!!) in the nose. The 40 ASP will help a lot with the balance, although I still might need an ounce or so of lead.
I was planning on using my 10x6 or 10x7 prop.

KINGX -- The .46 LA produces a reliable 0.8 hp vs an advertised 1.2 HP, similar to the .40 LA producing 0.65 HP vs an advertised 1.0 HP.

JZINCKGRA -- No plane short of a park flyer will be overpowered by a .46 LA -- go for it.

Use your 40 ASP because you already have it. It will help balance that tail weight and give you additional power if needed.

Use the largest diameter prop that will fit and still clear the ground. An 11 X 4 will help the plane slow down more when landing, while also making your take off runs shorter.
Dennis-

I'm not sure about the non-treaded tires either. Here is a link to a recent discussion about treaded vs. non-treaded tires.

http://www.rcuniverse.com/forum/m_16...tm.htm#1613106

Some of my planes have treaded tires and some have non-treaded tires. I can't tell a difference.

Eric