freakingfast

My Feedback: (3)

I needed an engine for warbird racing and I wanted to run a two stroke and the largest I can run with 585 square inches of wing area is a .70 size and there aren’t many currently made two strokes except the heli engines Thunder Tiger, OS and the Webra prop engine.
Well I couldn’t locate the Webra and the TT’s carb looked a bit hookie so I settled on the OS Max-70SZ-H. The OS has a three needle carb for idle, mid and high speed. All the engines are rated at 2.5hp at 16000 which look like that just might swing an APC 10X10 at that speed.

The prop drive hub and woodruff key were easy, they are even listed in the engine manual #2770810. The prop will need to be reamed out to .312 thru with a .375 x .125 deep counter bore (engine side). A prop hand ream tool made this easy in one op.

***Update*** I just realized that the spinner's back plate hole is .375 and that makes it unnecessary to counter boar the engine side of the prop, however a short shaft adaptor should be used, I will post the adaptor part numbers and prop I.D. later.***

I used a Macs standard header (#2860) muffled pipe 10 cc. (#1260) and a 90* thin wall pressure fitting (#9051) mounted just to the rear of the pipes apex.

An APC 10X9 prop for break in with 40 oz. 15/18 Power Master. Before starting, I cut off a few inches of header knowing it was way long. After break in and changing to the 10X10, the engine ended up peaking with the header cut to 4” over all length. The engine runs beautifully, VERY low idle, whip fast rev-up to peak and no hint of loading up at any speed in-between.

After a ¾ gallon of fuel, here are the results;
APC 10X10 prop. Air temp 100*
30* Wildcat Youngblood Heli fuel 16050 rpm peaked
15/18 Powermaster 15450 rpm peaked
FAI Powermaster 14700 rpm peaked (used to flush out engine)

I did a post run inspection, looking into the exhaust port and removing the head without disturbing the cylinder location.
The hone marks in the cylinder looked untouched and the piston ring was about 90% shiny polished. It may take a while but I don’t think it’s totally broke in yet.

I may switch back to the 10X9 if the engine lugs down as the prop hooks up at speed, but I don’t think I will need to.
This thing may be quick but the guys running the YS 110s may still take me….one way to find out.

combatpigg

My Feedback: (3)

Nice find, FF! Keep us posted about how it makes your plane move out and compare it to those YS monsters. Don't forget to hit the black oil spray button when you pass them [8D]

Kmot

My Feedback: (24)

Nice test stand! Where is that sourced from?

freakingfast

My Feedback: (3)

Heck, I'll be happy if I don't mid-air. [:@] It's quite common at these races.

freakingfast

My Feedback: (3)

I don't think they are made any more, I'll ask the guy next time I see him.

freakingfast

My Feedback: (3)

They no longer make the engine test stands. Sorry.

airraptor

My Feedback: (66)

A 110 spinning a 13x13N at 12,000 is a bit hard to beat with these motors

Kmot

My Feedback: (24)

Okay, thank you for checking into it.

[email protected]

PSP Manufacturing makes a beautiful fully adjustable test stand also.

I have one & love it.

www.pspmfg.com

Mike

Kmot

My Feedback: (24)

Thanks Mike. I already have the PSP stand but I would not mind adding this ETS stand to my stable! [8D]

bob27s

My Feedback: (19)

The OS70H is a pretty well kept secret.... something to keep an eye out for at swap meets.

YS80 engine is also a good treasure.

freakingfast

My Feedback: (3)

Well it's quick, but I think the YS 110-S will pass me. It will be competitive in bronze and silver class thou. The 10X10 proved to be a bit too much prop in the air so I dropped down to a 10X9 at 16,600 on the ground, this unloaded well in the air. I think there's more power to be found and I have a new cowling and header to invert the engine, but I'm out of time to mess with it because there's a race next weekend so it flies as is. Sure flies sweet.......but lands like a warbird.

combatpigg

My Feedback: (3)

She looks awesome Man! Good luck and have fun with her.

SpeedBoy

Yes she looks cool !!

freakingfast with what fuel did you run it ??? I suppose with Wildcat Youngblood but could you confirm it please , after see your results I'm motivated to buy this engine to my new project .

mk1spitfire

cool bird

freakingfast

My Feedback: (3)

Thanks guys.

Speed boy, I'd hold off getting one of these just yet. Keep in mind I went with it to squeak into a race class. It has a heli carb and it may have issues when turning a prop. When I went to count the turns out on the screws for reference and found the low speed screw is turned full lean (180*) and the mid range screw is completely closed and it's still a tad rich at idle through mid range. It will idle fine for at least 30 seconds and if you don't let it load up too long, it revs up like there's no prop on it.
I'm going to have a look at the carb after next weekend to see if that’s the way it is or if something’s wrong or missing. It seemed better on the test stand but I did have the carb apart to shorten it's throttle shaft. The carb has very powerful fuel draw or the pipe develops a lot of tank pressure and thats with carb location near the top of the tank. The fuel is 30* Wildcat "Youngblood", heli air temp 103*. I have tried OS # 8 , K&B hp and now the K&B 1-L, all run the same.

airraptor

My Feedback: (66)

Hey freak I still think you have to much pitch and not enough thrust to pull it in the air. the Four's need the higher pitch because of the lower rpm. I would try an 11.5x7 bolly or an apc 12x7 and cut about 3/16 of the tip.

The nine pitch is to much for the drag of this plane if those props are not enough in the air the increase the dia. by one inch. the extra trhust will help in the corners and then unload more in level to get your top end. have some one with a radar gun to verify speed. This is what I would do and it is your plane, these are just suggestions.

SpeedBoy

Mmmm........... what about if we fit other carb there I mean from a airplane engine ??? that would facilitate the things don't you think ??? some guys at the field had made this on other heli engines with good results.

Anyway I'll follow your progress and see how the engine works with its own carb ( with a prop ).

Just another thing ...... why you dont try to modify a 10x10 APC just reducing the airfoil , that will help you to gain some RPM and better transition than using the normal prop , if the load of the stock 10x10 is " just a bit " too much prop this must work for the engine IMO.

bob27s

My Feedback: (19)

I agree here......

The engine is running well. You may want to prop it to turn a bit lower than 16,000 rpm on the ground. Closer to 15,500 would probably be better. If need be lengthen the pipe 1/4" or so.

Try an 11x7, 11x8, 11x9 ..... get some blade area out there....... that is a draggy airframe. Lots of frontal area. It will probably not be slower, and as noted it will get off the line quicker and corner exit speeds will be better.

Of course, get the carb situation taken care of. If the carb does not seem responsive to needle settings (no needle range), you may have the pipe set a bit too critical (too short). Set it back to the default needle settings (mid and low range)... get the top end set first, then work back on the transition.

Expect it to load up a bit in transition - a short pipe like that will tend to do that as it tries to stage. The high end mixture is set to run when on the pipe, and while in flight. That requires "X" amount of fuel. When on the ground, you open the throttle to full, and the engine takes a bit of time getting up on the pipe and to rpm. It will be rich at that point since its receiving the "flight" fuel while at or below ground peak rpm. Its just the nature of a high timed/higher rpm setup. Also, if the midrange is set lean enough to transition up smoothly, throttling down off of the pipe into midrange can create a very lean condition you cut off the fuel with the throttle, but the pipe/engine remain at rpm for a moment.... this is actaully where most people blow glow plugs.

freakingfast

My Feedback: (3)

I will be trying a 11X7 apc, but I'm thinking I'll lose some top speed with that prop. Right now it's hardly loosing any speed after a clean hard pylon turn. The engine has a rated practical range of 2000 to 18000 so I'd like to keep the RPM up where it's making ponies 16 – 17 K.


Prop choices, static RPM, Thust lb., Pitch speed mph.
APC 10X9...........16600 ......11.5.......141.5
APC 11X7..........16100*......12.8.......106.7
MA 11X8 (S-2)...16500*......12.4.......125.0 (This may be the one.)
*projected RPM

The high speed needle is easy to set and definite at 1 5/8 turns out for flight. I couldn’t ask for better transition, I just can’t close down the mid and idle adjustments any more so it loads up if you let it run a while from idle to 1/3 throttle without clearing it out. I’ll figure it out latter I’ve seen a lot worse.

combatpigg

My Feedback: (3)

Unless you're doing 3D, who cares if the carb works? I agree with doing more prop testing and verifying lap times. Set up some poles and glue a stop watch to your radio, it's a tough job, but someone's got to do it.

airraptor

My Feedback: (66)

What does it spin an 12x6 and 12x7 at.

remember with the lower pitch it should unload in the air where as the 9" pitch might be loading up some and slowing it down.

Tommy_Gun

The carb has to work for him to use it in the warbird racing at SAMs.
They have an idle speed check before the first race of the day.
"All engines must have an operational carburetor and demonstrate the ability to maintain an engine speed of 4000 RPM or less for a period of 10 seconds prior to takeoff. During this “idle down” period and prior to takeoff, no contact will be made between the pilot or holder and the engine or fuel system. “No needle adjustments, fuel line pinching, etc.)"

combatpigg

My Feedback: (3)

The idle rule restricts having large venturis, then. I think that bringing up the system's pressure will help give the carb more to play with.

freakingfast

My Feedback: (3)

Well the idle problem is solved, there was a bad O ring from the factory, purrs like a kitten now. The new problem is that I mounted the engine wrong (vertical) and should have been mounted horizontally. The carb is too high over the fuel tank for racing and the G forces pull the fuel back out of the carb in the turns. It's fine for the first 4 laps with hard pylon turns but than it lean sags or wants to quit in the turns, I land richen, and it's good for another few more laps. It's fast enough to win in bronze as is if I keep the turns wide. I was timed and was told that if I could maintain the hard turns the plane is fast silver. I have the new cowling but not the time to do it right. This race today is a bust, out of time and I lent my spinner to another racer, the local HS was out. He was trying to use a WM spinner and it was so out of balance that it shook the plane so hard that the motor mount screws at the fire wall were loose at the first run up. See my old post # 11. http://www.rcuniverse.com/forum/fb.asp?m=7147382