agentbishop

I just bought a Great Planes Big Stick with an older K&B 65 sportster on it. My question is, the H.P. on the K&B is only 1.1 HP wouldn't I be better off putting my 46FX that has 1.6 HP on the plane instead. I don't understand how a .65 can have such low HP.

Hobbsy

My Feedback: (102)

The K&B is a low rpm mildly tuned engine that will turn a larger prop than the OS, not owning either, if I were to make a guess, I'd say the K&B would fly it better. HP is a totally useless figure, about as useless as the number of turns on a needle from one engine to the next. Example, I have a Fox .50 that will turn a 10x6 at about 14,000 rpm and a Merco .50 that turns a 12x6 at 8,500, the Merco flies a TeleMaster much better.

agentbishop

Now the specs for the K&B say 11X7 prop at 12500 rpm and the 46fx says 11X7 at 17000 max rpm. If it actually turns out those numbers or not I don't know. Why do they have these specs if they're not accurate. I'm not trying to be argumentative I'm just trying to understand.

turbo-RCU

The Sportster 65 has an unusual power curve. It is more like a 4 cycle 65 in prop selection. I use a 13 x 6 on .40 planes. The engine needs extra oil. I use 22% lube.

The stock muffler is very quiet and robs considerable power. I have taken the insert out and gain several rpm's back, but now it sound loud like other 60's. I went to an aftermarket muffler to gain the rpm's back and keep it quiet. JFYI, it uses the same muffler as the HB 40-61, ST 45-60BB, K&B 61.

I have not been happy with my 65 as a 2 stroke 60. I know people that use them on BIG planes like telemasters and really like them. R/C Report suggested using them like a poor mans 4 stroke. I did and really like it in that role.

The Big Stick 60 is fairly large. I have flown them with strong piped 61's and 80's. The power with those set ups is a good fit. The 46Fx will fly it, but you will have limits. The 65 will pull it around a little better IMHO, but it will not be a speedster. It is going to fall down to your preferences in selecting the best powerplant.

I have had people not believe that my 65 sportster was a 2 cycle, K&B sportster. When I land, and they can see it, they say a few choice words and still really don't believe it. IT is not an application for everyone, but I like it. I do have some real powerhouse 61's. There is a place for both.

Good luck,
turbo

RaceCity

I'd stay with the K&B .65 and ditch the phony specs. Your OS cannot achieve 17,000 rpm on any sort of prop that would fly an airplane.


The other comments are correct. The .65 "thinks" it's a 4C. Use a 13-6 prop and you'll get nice results. Extra oil is a definite yes! Friends up north who have used these engines for years have said that a length of silicone tubing attached to the exhaust outlet actually raises the power output of the engine substantially. Sort of a weird tuning effect.

I haven't tried it myself, but I trust their reports....besides, some tubing is a cheap, non-commital thing you can experiment with.

Don't be fooled by numbers!

have fun!

'Race

agentbishop

Do you mean the tubing that diverts the excess fuel away from the fuse?

RaceCity

Yeah...the exhaust outlet on the muffler. Try a 6" piece of silicone tubing on there (hi-temp).

Measure the RPM before you install the tube, and after.

See what happens and let us know...I've been told by the boys back home that it works really well. Like I said before, I haven't tried it, but it's cheap and won't hurt anything if you decide it's not worth it...just take if off.

'Race

DarZeelon

Curt,

This same Hobbico exhaust deflector, when used on the end of an MVVS standard muffler, on an MVVS .49, "chewed away" 1,000 RPM and left the engine with nary a top end.

Yes it is a tuning effect, that can either have a bad influence, or a good one.

RaceCity

You're right Dar...adding anything to the exhaust outlet should NOT help, but....?????

Stranger things have happened. It's a cheap experiment and the folks up north have been running these things for eons. I suspect they aren't lying.

(I'm partial to the .20/.28's)

I think the bottom line is that the original poster should not be confused by "hazy" power output specs. The numbers quoted by the manufacturer are not wrong...they just aren't relevant.

I have the feeling that OS (and others) get their HP numbers with a 3" prop. All show and no go.

'Race