I know we do not use 4 cycle engines in our helis but could we use them ?
I just fly scale and i'm really bored to use Thunder tiger engines...
Too much problems with that brand.

Thx for respondig.

First of all, have you tried other brands of engines other than Thunder tiger? O.S Engines are really reliable and tuning is as easy as can be. YS makes some fantastic engines as well.

There are alot of issues when you try to run a 4 stroke engine in a helicopter. The 4 strokes do not run as many RPM's as a two stroke so the gearing needs to be modified. The entire power difference between the two engine designs requires a complete rethinking of the helicopter design.

I tried to run a 4 stroke in a Century Hawk several years ago. They made a conversion kit so you could run a OS FS-52 engine where a OS 32 was at. I never really could get the 4 stroke to run we enough to make it fly correclty. I live at 6500 ft and it just couldn't get enought air to produce power and when leaned out to produce power, there just wasn't enought ambient air to keep it cool enough to prevent overheating. I might not have had these issues if I lived at a lower altitude but that is not an option at this time.

Excellent response sir!
Thx so much!
I will try OS engines then.
I bought a .50 Thunder Tiger last month and after 2 mins or more the barrel in carburetor alway jam and i must disconnect the hose comming in carb to stop the engine.
I have 2 .39 Thunder Tiger too and after same time they seems to loose power!
One has no more than one hour of runnuing time and the other a few hours.

Great thx!
Steff.

i tried a 4stroke heli about 4 years ago as i fancied a change from all my 2 strokers.

i brought a good condition vario sky fox cub which already had the conversion kit in it and the os 91 4 stroke which also was good condition and lots of compression.

i was though very disappointed with the power as it only just was able to hover and gradually i could creep foreword and back but that was about it..
i tried a couple of other things like changing the blade length but though it improved a bit it didn't make it very flyable as it still was barely just able to hover. that blade length had to be reduced though to a more or less unacceptable amount as the heli is mostly flown with 68cm blades with a 2 stroke but it wouldn't lift off the ground unless i used 62 cms or less..

if you do a search on this forum though there is a heli flyer that had good experiences with 4 strokes on helis but sadly for me by the time i read his advice i had already put the 2 stroke engine and kit in the heli.
i think he mostly advised about 30% nitro fuel and the type of exhaust might be very important as well.

hope this helps

Ok.
I will stay in 2 cycles but will change my Thunder Tigers for OS engines.

Thx very much for your help guys!

This forum is very helpful!

Steff.

guy out at my field has a magnum 52 in a raptor 30 frame. I talked to him about it yesterday and he said fitment wasn't bad. Cut about 5mm off the crank and it went in relatively easy. The thing seems to hover real well and the bit of tail kicking I witnessed was probably more due to a crappy analog servo running off a 401. I doubt it would make a 3d bird by any means but it would definitely be a good hover trainer. Flies forever on a tank of fuel thats for sure.

The other issue I ran into when I had my Hawk conversion wasn that the carb was lower than the fuel tank and fuel would
siphon down to the carb and flood the engine while sitting still. It also made tuning during idle almost impossible. That problem
could have been eliminated if Century had moved the fuel tank lower on the conversion kit.

I had a YS 91-FZ 4 stroke sitting here for a little while that needed a project. I thought about adapting it into my Ergo 60 but I
think the gearing would have been wrong with the stock gear ratios. I had been told that if I had run the gas set-up that it might
be Ok but i ended up using the engine in a plane instead.

I would like to give it another try and maybe work on a few things that gave me problems before. I wish I had access to a maching
shop so that I could make custom gears so that I make my own gear ratios and place the fuel tank where ever I want to. In
addition, I would also like to work on the cooling shroud so the engine get the full benefit. The YS 91-FZ is a super charged
engine and puts out the power of a 120 4 stroke. Those engines are almost the perfect engine for that type of project.

Hey man, easy on my cheap Hitec servo. Actually 5% more gain had it right. The 4 stroke Rappy flies fairly well and has no running issues. I dont know why but it does not siphon fuel, may be the header tank. Running is flawless, will Idle all day with good transition and has clean top end. It is a stock 49bb .30 with .50 gearing. has a top head speed of 1630 which computes to 14200+ engine rpm. I have been told by a long time fourstroker that these .52 engines are purposely underated by the manufacturers and indeed they are capable of 14000+ rpms. It has run two 20min timed sessions on one tank and had a full header a a little left in the main. It aint no home sick angel but has reasonable climb authority. All in all I am very pleased with my experiment it has worked very well from the first flight.

Here are some pics.

Cant get the pics to load!

lol...not really knocking your cheapy hitec! i've used hitecs in a lot of places and always happy with their performance but when it comes to the tail on the heli I'll throw a dig on it just for that added piece of mind. You aren't kidding though, I thought it flew great for what it was and to hear you talk about it I didn't think it was going to have enough power to get out of its own way but it definitely looked like a stable rock up there. I would have suggested seeing if messing with the gain toned that down but looks like it did. Definitely two thumbs up for ingenuity and making it work, that engine sounded pretty happy in that raptor imo and with the cost of fuel way it is, thats a great way to get some relaxing flying in.


I'd love to see it inverted though

edit - you know, come to think of it, after the lovely performance of that hien I might ought to see about stuffing that saito into a 30 along the same lines of your conversion

Im just kiddin, saving a little$ on the unkown, looks like I may lavish a 9254 on it after all. What happened with the Hein?