I have acquired a stunt model from a club member which is a very nice looking Hawker Typhoon, and is powered by a OS.70 Surpass. It was built by Walt Brownell, about the time that Windy had his Z-tron equipped Typhoon, and it was 4 stroke powered I believe, but this model isn't a copy of Windy's airplane My question is about the OS.70 Surpass that powers the airplane.
   My experience with 4 strokes has been limited to a Saito .56 installed in a Top Flite Score. I have flown this combination for quite some time, using the Bob Reeves set up with a screw into the venturi side to adjust choke area, and 13-6 and 13-7 props, and muffler pressure on a standard plumbed plastic tank. This combination has worked very satisfactorily for me. When I got the Typhoon, I remembered that I think I had seen Walt fly the model back then, but in talking with him, all he could remember about it was that he could not get consistent engine runs. I don't think he tried to fly it a lot, and don't know what he used for fuel. The engine was a bit stuck and gummy, but I got it freed up and running fine on a test stand.
    Walt had the engine mounted in the model with a bell crank and push rod attached to the R/C carb to hold the throttle position open. The tank was a 4.5 ounce uniflow, and the muffler pressure line ran to the uniflow vent. I figured this was most of his problem. After checking other things out, I plumbed the engine to run on muffler pressure with the tank set up as a standard suction, and the throttle closed to about 3/4 throttle and locked in place. I am thinking this would sort of replicate a Bob Reeves set up since I had no C/L venturi for it. I test ran the engine like this mounted in the airplane and all seemed well. The Surpass puts out amazing power, and with the needle set at 8,300 RPM, the model was difficult to hold!. I finally got a good, calm day to try flying it. Lines are set at almost a full 70 feet from handle to model center line. Ground RPM was set at 8300 RPM and released. The take off was smooth, but I could tell instantly that it was too fast. The prop Walt chose was a 14-5 Zinger, and initially I was worried about that being not enough pitch, but it was pulling the model at close to a 4.5 second lap time! Way too fast for me to fly any , maneuvers. The engine shut off earlier than expected also. The tank is only 4.5 ounces. I was hoping for this to be big enough, as there really is no room for a bigger tank. For a second flight, I slowed the engine down to about 7600 RPM and this was much more sane! Better take off, nice vertical pull for the wing over, inverted flight was the same as upright, and things were looking good. About 4 minutes into the flight I could tell it was starving for fuel a bit and at 5 minutes it shut off. I parked the model for the day to evaluate what to do next so we could fly this model some more and enjoy it. I needed to slow the model down to the preferred lap time of 5.2 to 5.4 lap time and still get the pattern in on 4.5 ounces of fuel.
    I have done a search of the four stroke forum and there really isn't any information on the .70 Surpass engine. It's no light weight, 22 ounces I think for the engine, spinner and prop, but I figured some had used it a time or two. I want to try and keep it in the airplane as Walt built it. My next attempt will be with the carb set at about 1/2 throttle, and have a 13-5, and 13-6 prop ready to try . If the 14-5 is still too fast, I'm hoping a smaller prop turning the 8000 RPM or so will get me the lap time I want and the fuel mileage I need. I don't think power will be an issue, given what I have seen out of this so far, but will take things one step at a time.  I have been starting to think of replacing the engine with a Saito .56 or .62 if I can't tune the Surpass .70 to what I need to have from it.
     Who has any experience with the OS.70 Surpass? Any C/L venturi's available for it out there? Any idea of an optimum venturi size?  The model without the engine weighs only 56 ounces or so, and is quite light. It was designed with the .70  Surpass in mind I think, because of the short nose and such. Walt has just a bit of solder wrapped wound the tail wheel strut to balance the airplane. Any kind of engine swap won't drop the weight too much because I will have to add nose weight to get the balance point back where it needs to be. I know this isn't a world beater stunt model, but it is a very nice looking airplane, but I think with a few small changes it can perform well enough for Walt to enjoy seeing it fly while he still can. Thanks in advance for any help and advice.
    Type at you later,
      Dan McEntee

Dan,
Any updates on this setup? I am working on a new 4 stroke ship and would like to use the existing R/C carb to allow starting and going to idol (while walking to the handle with the ship on a stooge) then when released go to full power. I have two engines to choose from the Saito 56 and an OS 52 Surpass. They both weigh in at around 14oz and will turn the 13" prop so carb performance is what will make the difference. Want to get a solid steady run at full power up and down.

Best,    DennisT

     I eventually gave up on it and donated the model to a local museum. I managed to get about three flights with the needle setting it needed. The the lap time was just a tenth or two fast or slow, the model flew completely different and was just too hard to handle. The model was fairly large, and weighed 80 ounces, with almost 22 ounces of that being the engine and spinner. I tried everything I could with the carb but it still would leak air. No one made any kind of after market venturi for it because no one was using it for stunt because of it's weight. I tried closing down the throttle to reduce the choke area of the carb to help with fuel draw and was only mildly successful. So, rather than mess up a really nice looking model, it now resides with a small museum at a local airport. Given what I experienced with the .70, I think you will find that full throttle with an R/C card will vary on you and won't be too consistent You will have to experiment with limiting the full throttle setting to actually about 3/4 throttle or less to help with fuel draw. I did that on a profile scale model that came from the same estate with a Surpass .52 in it. Other wise it was a bit over powered, and would go through 4 ounces of fuel in the drop of a hat, and no room for a larger tank.
    Type at you later,
     Dan McEntee

Dan,
Interesting information. I think a lot of the issues with FS fuel draw can be addressed by using a larger ID fuel pickup tube, like K&S 5/32" OD or even going to 3/16" (drill out the click also) and using large fuel line, might need to wire it onto the carb fuel nipple. This was one of the little known tricks to keep Dyna-Jets starting and running, those that used 1/8" would have a devil of a time to get them going.

Second thing would be to repitch the prop to control the lap time. I have had very good success with heat repitching the wood props. To do this you need to do a heat soak as you warm the wood. This means heat say top then flip over, heat bottom repeat several times (like you do for APC IC props) then with the pitch gauge locked to the new pitch twist the blade to the new pitch and check, tweek a little then cool by blowing on it. After a few tries you get a feel for it and can repitch as fast ad a CF prop. I have had the repitched props sit in a hot car for hour and in the sun and never lost the pitch.

The guys in Europe were doing what they called a "variable load pitch" on their FS's. I am trying to get some info this but don't have a direct contact over there. I am searching. I also what to try some low-pressure bladder system (pipette bulbs) to see if the FS's will benefit from more constant pressure, this will be after the holidays.

For your Saito 56, what fuel/prop/rpm did you find reliable? Planning on using one in a OTS Victory (60" span ship) that was designed around an Atwood 60 and I think the Saito will be more than enough to pull this ship.

Best,   DennisT

        I wouldn't use a Saito .56 in that airplane. In the construction article and plans kit shows a, ST.46. If built to the plans with that short tail moment, I would maybe consider a Saito 40 if you must use a 4 stroke. Other wise I would go with the St.46 as shown, or LA.46, or maybe an ST.51 if I thought i was going to need the power. The Victory has a big wing but there is next to nothing for the rest of the air frame so it shouldn't be terribly difficult to build to a reasonable weigh. I have my Saito .56 in a Top Flite Score with an all up weight of 72 ounces, with a 13-6/7 prop, with take off RPM in the 7800 to 8000 range on Powermaster YS-20/20 fuel.  That Victory would come in around the 50 to 55 ounce range with no trouble, I think, and I would try to figure out what the longer tail moments that he used were and build a longer fuselage to help with balance.
  Type at you later,
  Dan McEntee