Hello. I have a CMP hellcat that I was originally going to power with a 120 or 125 four stroke engine. However, I would rather go with a converted gas engine. I am wondering what gas engine to convert. Will the 25cc poulan/homelite engine be good? 32cc mcculloch? Ryobi 31cc? Also, should i use a CH ignition if i do the conversion? Relevant Specs for this plane are here:

Wingspan: 70"
Length: 53.5"
Weight: 9.9lbs to 10.23 lbs
Engine .90-120 4 stroke

Thank You.

All these will have good power for your plane.

The Ryobi is longer and narrow compared with the others because of the rear carb and exhaust.

The CH ignition will not substantially give you more power. Just ease of starting.

wont the ch save a lot of weight? Also, what is the most powerful out of the 3?

The Homlite 30 has more potential than the others.

The C-H saves weight but weight is not always bad.

The 33cc Chain saws from Poulan and Homlite are the current trend. They run better as they come out of the saw than the whackers

I was really looking at the ryobi 31cc because it is really easy to do. I think I may go this way but i dont know if this is too much engine for this plane.

Power wise it is not too much but the overall length of the engine and mount may get you in trouble?

Varad, there is a HUGE thread on the cmp hellcat, and its clones on the warbird forum, I can tell you a few things I have found on it as I just finished doing similar to what you are doing...First of all, I think ther were three guys at least that had installed g-23's...which compares probably to a unmodified 25 cc closely. One guy was running a g-26..he said his plane was 15 pounds and flew well. I am using a 25cc mcculloch, it came out at 12 and a half pounds. I haven't flown it yet..it will probably be spring before I do. I think the 31 cc would hinge on how much heavier it is than a 25 cc. If its close it should work. I mounted my elevator servo's 12 inchs from the back of the plane to help balance things. Some of the guys on the warbird thread were even removing 3 inchs on each wing panel at the root, because they thought it was too floaty. That is why the plane is able to support the heavier motor with an unmodified wing. Obviously if you are going gas you need to reinforce and think through the different weight issues on the airframe, I decided to glass the center wing section to be safe. Mechanical retracts are pretty much unuseable with a gas motor I think.. so you will need fixed gear or air retracts .. There is MUCHO info on the warbird thread.. Most of my information here is from what I remember reading on the 57 pages of that thread....

http://www.rcuniverse.com/forum/m_2530290/tm.htm

prepare to be swamped with cmp hellcat talk !

Thanks a lot for the help w8ye and foodstick. A couple of days ago I was reading that exact thread but probably made it to about page 15. There is a lot of helpful info there and I will continue that "book" to find info for gasoline. I was concerned with the 31 cc being too long. Im thinking that a poulan 25 cc with CH ignition will be the best option. I have heard this engine weighs in at 40 oz. with that ignition.

There's no such thing as "too much power". That's an oxymoron like "military intelligence".

I tell my students, that left side lever on the radio moves up AND down, and is a control; not an on/off switch. You can always pull that throttle back, but when you want more power and the throttle is at max, you are stuck with what you've got!

Happy New Years,
AV8TOR

I totally agree with Av8tor. I fly a lot of indoor and I see more people with low powered models crash than those with a lot of power available. I design my models so they fly at no more than 3/4 for most of the flight. Just make sure you don't use the extra power in horisontal flight as you could induce flutter if the airspeed becomes too high (looks spectacular though!)

Michael

No I agree with both of you (I have a 1/4 scale extra with a 45cc gas engine) and I like the extra power. I guess I didnt say what I meant. The extra power of the ryobi (31cc) comes with more weight which is 62 oz. The poulan (25cc) with CH ignition that I am looking at comes in at 40 oz. So its a tradeoff either way. I am just wondering what would be the best out of these two engines for flying this hellcat? I think I have it narrowed it down to these two engines anyhow.

Personally I would recommend the Homelite 33cc from the Bandit chainsaw.

AV8TOR

You know, I've been lurking about, reading with much interest, all the info I can about conversions and homebrew fuel so that I can be more prepared when it comes time to put my Hawk together. The Ryobi's seem to be such a great choice, so I go out to my shed the other day to look at my trimmer. Lo and behold, it's a Ryobi 31cc. Now I don't know about you all, but this trimmer is the biggest piece of crap I've ever had, so I can't imagine putting it into a plane that could potentially fall from the sky.
I'll have an OS 1.20 four-stroke soon, but I'd like to save on fuel cost...so the conversions have interested me. Seems to me like the biggest concern is not necessarily the size of the engine, but the carb/muffler configuration. I'm not sure I can fit one into my plane without hacking it up. I know it's been done because of other threads, but I'm just not sure.
So what was the decision maker for you all??

Scott

for most its the price of a gas engine, with a little work and ingenuety they work pretty darn good I have a homelite 45 and a couple ryobi's .they are adequate. and operate way cheeper than glow. It is also a chalenge anda lot of fun.