Next to electric 4 strokes have a very consistent stunt run for very little effort. I was wondering if we could get a ranking of the different 4 stroke engines available based on size, power and weight? Which ones give that solid stunt run that holds rpm when pushed by the wind and which ones are not for real good for stunt.

4 strokes have fallen out of VOGUE with the stunt community since we do the pull test based on weight not engine size. Electric is all the rage with big tuned pipes still in solid standing. But 4 strokes work right out of the box with little changes (ok you could change the carb to a venturi) needed to get a solid running stunt engine. I think with a little prop work they could be a strong setup for anyone that is short on build time, doesn't want to spend a lot of money on fuel (4 strokes use half the fuel) and doesn't want a lot of noise. What is the ranking?

Best,    DennisT

I don't know what the ranking is (is there one?) but I've been using (and still use) the SAITO 72 for 11 years with Bob Reeves's carb modification in F2B competition and I'm as happy as one can be.

It's a very powerfull engine, it consumes 4 oz of fuel for a 6:30 minute flight (10% nitro), you can use a five dollar wood prop, you get a
perfect stunt run 10 out of 10 flights and it weighs the same as a  PA 61+header+pipe.
 
I must say that I fly also with a PA 61 since 2003 and I just LOVE it too!!!

Later,
Claudio.

I had a Saito 72 and still have OS 70 Ultimate. In my opinion, the OS 70 ultimate is the best 4s for c/l

Same weight as Saito 72, but it is built with much higher quality.

No oil leaking whatsoever; not one molecule comes out of mine.
Burn less fuel than Saito 72, only 90ml of 20/20

I remove the pump and adapt a custom made venturi

Martin

Martin,
Very nice job. Is it just a venturi or can you adjust the throat size?

I have an idea that I want to try. I have an old YAK 9 that my uncle built way, way back that has been siting around waiting for a new lease on flying. The YAK has a lot of open fuse to work with. Since flying electric I got very comfortable with being able to put the ship in the Stooge and walk to the handle without it being at full power. I like that, but electric needs more planning then IC, you need to allow time to charge batteries and can't just pick-up and go fly when the urge hits you.

4 stroke gives very similar power control as electric. Many 4 strokes have been flown with just using the stock carb set wide open and have done very well. So....maybe one could set up a 4 stroke with a spring loaded throttle arm so that you could have the engine at idle ish, have a cable back to the Stooge with tail hook. When the Stooge was released it would release the throttle cable to go to full power and the airplane. Seems simple enough, I want to try it on the test stand. I have an OS FS 26 Surpass that is waiting to be flown again and it seems like a good match for the YAK 9 ship. Only question is with the movable throttle barrel how to make sure it is sealed from air leaks?

Any thoughts?

Best,    DennisT

   You are dreaming the impossible dream here, I think. If you have a throttle with moving parts, you will have a throttle barrel that will rattle and leak air around it. They need to have the clearance they have so that they do not foul or jam up with dust, dirt or oil. That is why if I am using an R/C 4 stroke with a throttle on it, I close the throttle some times up to 1/2 to counter any air leaking with more fuel draw. Some carbs you can lock down the barrel in the spot with an idle adjustment screw and limit it's movement but air can still leak around it. Bob Reeves came up with the carb mods to eliminate all of that but it also eliminates the throttle function. Not necessary for stunt.  I see no real need to have an engine at idle while you walk out to the center. If you are ready to fly, just get to it. If you need to do something else, don't start the engine until you are ready to fly. Any other function you add to the mix will just be something else that can cause a problem or fail. The stooge is all you need. There is nothing to be gained or that hurts an engine for it to be running at your desired needle setting while you walk to the handle. In fact, I think it's good for the engine to warm up and settle down a bit in that amount of time.
   Type at you later,
  Dan McEntee

Martin,
Very nice job. Is it just a venturi or can you adjust the throat size?

I have an idea that I want to try. I have an old YAK 9 that my uncle built way, way back that has been siting around waiting for a new lease on flying. The YAK has a lot of open fuse to work with. Since flying electric I got very comfortable with being able to put the ship in the Stooge and walk to the handle without it being at full power. I like that, but electric needs more planning then IC, you need to allow time to charge batteries and can't just pick-up and go fly when the urge hits you.

4 stroke gives very similar power control as electric. Many 4 strokes have been flown with just using the stock carb set wide open and have done very well. So....maybe one could set up a 4 stroke with a spring loaded throttle arm so that you could have the engine at idle ish, have a cable back to the Stooge with tail hook. When the Stooge was released it would release the throttle cable to go to full power and the airplane. Seems simple enough, I want to try it on the test stand. I have an OS FS 26 Surpass that is waiting to be flown again and it seems like a good match for the YAK 9 ship. Only question is with the movable throttle barrel how to make sure it is sealed from air leaks?

Any thoughts?

Best,    DennisT

Hi Dennis,

Thank you for the compliments! I designed the venturi and a good friend made it for me. It is a fix diameter venturi. One of the things I love about this engine is that it seems not to bother with significant changes in climate and density altitude, which boggles my Engineer Mind!  The only thing I change to adjust for climate conditions is the props.

I guess your idea of linking the throttle to the stooge will work and it is a cool idea.

Good luck and make videos!

Martin

Martin