OS 35 FP economy expectations.

[Dane Martin]

is it theoretically plausible to assume a four ounce tank would be enough to complete the pattern on a magician with an OS 35FP ?

[Steve Helmick]

Depends! Not a repeat of the adult diaper humor attempt, it really depends on the engine setup as a whole. I'd expect an ABN to get better mpg than an iron/steel version, if for no other reason than ABN will  need less oil in the fuel. A 'tuned' engine probably would burn more fuel, and one of the SSW reworks with the blocked boost port more yet. More prop load or bigger venturi, more fuel. Smaller venturi, smaller prop, less fuel. Smaller muffler outlet, much less fuel, because it'll probably want to runaway and cruise at about 75 mph. More fuel consumption is sometimes a very good thing.

Assuming it's stock, with a decent muffler, maybe a .156" spraybar, I'd expect 4oz would at least be worth a try if you can run 5% and will maybe even work with 10%. Sometimes that Coleman Lantern Fuel trick is worth keeping in the back of the mind. Also remember that most plastic tanks seem to hold a bit over nominal.  Steve 

[Dane Martin]

aha! forgot there were different versions. its the most modern ABN version. all stock with the stock 762 muffler. i don't know the venturi our spray bar sizes. and i plan on a dubro s-4 tank.

[Dave_Trible]

I would think if it were a stock engine it should have no problem.  On the family profile fleet which always used the FP .40,  the tanks I built were about 4 ounces and when full could do about a pattern and a half.  Now we didn't fiddle with a 'Fox' run.  All set for a solid two cycle with an 11-4 prop.  I'd use a 10-4 APC on the .35.  If you can actually burn more fuel then that's great- if you aren't burning fuel then you aren't making power.  High mileage is no virtue in stunt motors.

Dave

[Dane Martin]

I would think if it were a stock engine it should have no problem.  On the family profile fleet which always used the FP .40,  the tanks I built were about 4 ounces and when full could do about a pattern and a half.  Now we didn't fiddle with a 'Fox' run.  All set for a solid two cycle with an 11-4 prop.  I'd use a 10-4 APC on the .35.  If you can actually burn more fuel then that's great- if you aren't burning fuel then you aren't making power.  High mileage is no virtue in stunt motors.

Dave

10-4. i definitely want to burn up as much as possible. just making sure i don't need more. a 4oz fits great, so that would be sweet.

[Steve Helmick]

I think that #762 muffler is the small & restrictive unit that pretty much assures a 'runaway', so watch for that. I'd suggest a Randy Aero CNC Tube muffler.  Steve

[Paul Smith]

I have that engine/airplane combination.  Four ounces is a lot more fuel than I need.

[Dane Martin]

I think that #762 muffler is the small & restrictive unit that pretty much assures a 'runaway', so watch for that. I'd suggest a Randy Aero CNC Tube muffler.  Steve

you know, speaking of the muffler, i was wondering about a lighter one. i have 1.5oz lead in the tail to compensate for that. no muffler, no lead. but of course, i don't want to run muffler-less...  i was thinking of a tongue muffler.

[Dane Martin]

I have that engine/airplane combination.  Four ounces is a lot more fuel than I need.

thanks Paul. that helps to ease my mind

[rich gorrill]

Dane, I was using an fp35 newer model on my Fran Twister til the P&L went bad. I used a tongue muffler to cut down on weight and it worked o.k. 10-4 prop cured the runaway I encountered but the plane still flew faster than I liked. If you have a Brodak Magician it is a lot lighter than the twister, the 35 may be a little too much engine unless you like to fly fast. I am using an LA25 on my Brodak Magician and it is just right for that plane. No speed issues or runaway. I tried adding an extra head gasket to the 35, speed was about the same but fuel consumption went way up. I used the os needle valve and 8mm venturi. Maybe the 7mm venturi would have helped but I never got a chance to find out. Good luck

Rich

[Steve Helmick]

I'm not a fan of tongue mufflers, which is why I suggested the Randy Smith CNC Tube muffler. I add a 'rubber ducky' and a pressure tap, and sometimes open up the outlet a bit. Put the pressure tap to the engine side of the seam...a 4-40 or 6-32 tap is fine.  Steve

[RknRusty]

On my old beater 37.5 ounce Skyray I have a stock steel .35FP with an OS#8 plug and a #762 muffler on which I cut off the stinger and widened the exhaust outlet. I use a Dubro 4 ounce clunk tank on muffler pressure. Under 90*F, at my field's altitude of about 470' I use exactly 3 ounces of fuel for a full pattern and get about 7 laps after a full pattern. I launch at about 11,100 RPM with a TF 10-4 prop running around 5.1 second laps on 60' of .015 line. In higher temperatures I use more fuel but 4 ounces of Powermaster 10/22 or Sig 10/20(+2% castor) is always enough.
Hope this helps.
Rusty

[Dennis Moritz]

Which Magician. The Midwest or the Brodak. Fuel consumption with these engines is largely a function of venturi size. My Midwest sized Magician used near 4 ounces with a .272 venturi, powered by a Tower 40, a comparable engine. Excellent run. Wet 2, harder 2 break. I used a 4.5 ounce tank and pulled out some fuel, depending upon the conditions at the field. In cold weather more fuel tends to be consumed. I'd use a tank that size to provide wiggle room. A friend flew a Vector with an FP35 for many years. It had a custom 4 ounce tank. Getting ready for the competition season, flying in cold weather, meant he had to abort before the full pattern. As weather warmed, fuel tank capacity proved adequate.

[RknRusty]

Dennis's statement makes me question what I said in my last post about fuel usage in hot weather.
Hot air is less dense, so reduced air and no other change would richen the mixture. Meaning you close the needle to balance the F/A mix back to where the engine is happy. So you should use less fuel in hot air. Am I misunderstanding something?

Maybe something else was going with my engine when I last flew on that hot day in July. In any case my 35FP economy over the past year of use is consistent at 3oz for the pattern.

Rusty

[Dennis Moritz]

What size venturi? What size/weight/amount of drag is your plane? How rich/lean is the mixture that you prefer? The cold air/hot air effect on my friend's plane is the way I described. I always install at least 4.5 ounces with FP40s/FP35s. Come to think of it my last profile, a flea marked purchased Prowler ($10) needed nearly 5 ounces for the pattern. A thick airfoil porker weighing 44 ounces, powered by a Tower 40, underwent a very interesting tuning process. I wound up going to a large venturi .283, a very free flowing tongue muffler (holes on both sides of the tongue), taking all the head gaskets out of the engine. This in order to get a break. After some stubborn resistance on my part (taking out all the head gaskets was Mike Palko's and Dan Banjok's recommendation) that was a tune that worked. Nice even run with break on 10% 50/50 Powermaster. I just realized that I forgot to mention taking into consideration the amount of nitro in the fuel, when predicting engine run. On 10% fuel, mileage for pattern was inadequate with a  4.5 ounce tank. On 5% there was no problem. But on %5 engine was not happy. Danny suggested mixing fuel, half 5% and half 10%. That worked. I really liked that plane. Best profile I every flew. Tracked. Cornered. At our contest, plane went in. A hinge near the flap horn (far as I could figure) pulled out enough to give me no down (which meant up) when doing the inverted laps. Kaboom. Broke fues along old break. Not bad.

The Magician weighed 33 ounces. Magician airfoil much thinner. No problem with the 4.5 ounce tank. I'd pull out a little under 1/2 ounce when flying an official. That engine (same engine) was tuned with two extra head gaskets and a .272 (mid size) venturi when flying the Magician. On the Prowler, running %10, with engine tuned very differently, 4.5 ounce tank was too small.

[Dane Martin]

alright, good questions. I'll answer all that i can. i don't know what manufacture it is. i had to add lead to the tail to balance it. afterwards, its barely over 32oz. it appears to be an ARF, but i didn't buy/build it, so not positive. when i got it, the wing had a pretty nasty warp, but that's fixed now. the pattern maneuvers look pretty nice with this plane. i have a tongue muffler now, so I'll be reducing the weight by a nice amount. under 30 may be possible.
ummm.. the venturi is the larger one, so right now it likes to run a little fast. that will be changed soon. i like an engine run a little rich. slower break, i guess. I'm running a 12.5% 11%-11% blend. still trying props. bouncing between 10x4 and 10x5

[Dennis Moritz]

I like to start with .272 venturi and 10.5x4.5 apc sport prop. Light plane. Tongue muffler takes weight off the nose. Should be able to remove tail weight. Fly the plane with the setup you have. If run is 6 and half minutes or longer. You probably are carrying enough fuel for the pattern. Fly the pattern. If you're running that long. Leave off the overhead eight and clover. Count laps left. Add maneuvers, if you have sufficient run time. Chicken hoppers work well, if you need more fuel in a limited space. Don't be afraid to run the FP in 2-stroke. It needs to run that way. If you are running away, open up the tongue muffler. Run the engine at a faster setting. Engine should stabilize. You can go down to a smaller venturi to reduce power, if your light plane is flying too fast. .265 is the small FP40/35 venturi.

[Dane Martin]

the engine run is solid. real consistent, great shut off, everything a guy would want. that tank was an experiment. it went well, but too small. a dubro 4oz clunk tank fits there, but if that's not enough, ill look for a 4.5 - 5oz. tank.
 someone said a 10x4 prop, but that's what i run on my .25LA. would an 11x4 be reasonable? or is the 10x4 the bees knees?
and, this plane is pretty fast! not terrible, but I'll bet it would do well with slower lap times. what would be the lines to start with? I'm using 60' .018 now.
sorry for all questions, but this plane can do a nice pattern. I'm still inexperienced in the tuning of a plane. thanks guys!

[Dennis Moritz]

See if you can fit a chicken hopper that is 4.5 ounces. A .265 venturi will increase run time, if you are using a larger one. Retunning this and that might be necessary. Very good that you have a consistent run. 10 1/2 x 4.5 apc is where I start. Keep everything the way it is, if you can fit a larger tank and you have enough power. With an FP35 on a plane weighting 30 ounces, that would be no issue.