well then a ten inch diameter will do, however the pitch can go as high as you want, I believe the OS 40 will swing a 9X10 or a 10X10.... Just in case you don't know, quick study, the pitch number is the second number and represents the distance traveled in one revolution... in reality this doesn't wash sense air is not perfect.. Imagine a block of soft butter ( for a wierd way of explaining it) In one revolution the 9X6 will travel 6 inches through it, the 9X10 will travel 10 inches through it in one revolution...... if there was one, a 2X10 would travel ten inches as well, however now we factor in air.... Hmmm a slopy medium for the application for sure.... now then a 9X10 technically will not go as far in air as a 10X10 since there is one extra inch of prop to bite air........ now factor in the engine, will your OS40 swing the 10 inch prop or the 9 inch prop at full power to full potential RPM, or will the extra energy needed to swing that extra inch of prop reduce the rpm and thustly reduce the efficiency of your 10 pitch prop....... gee there is a lot of stuff to think about isn't there???????? Hmmmmmm hope this all helps....and when you are done with the block of butter, you can go get toast.................... Captain Crash...

My 40 la would not run on anything less than 15 percent and a os #8 glow plug, and the air bleed screw I took it out... ran better w/o it

I had this problem with my LA and I needed to replace the fuel lines. Try that, sometimes they get pin-holes and leak air into the lines. Don't forget the one from the needle valve to the carb.

Steve

Mine runs a little choppy with 10%. But I just bought another gallon of 10% so I guess I'm stuck with it. Also, I use the OS A3 plug. My airbleed screw is almost out as well.

captain crash,
will a 10x7-8-9 prop kill the engine or overrev it or something? I shot a brushless motor by over-proping it.
[:@]

Hmmmmmmm I dont know what to tell you there, but go check out this thread, there is a wealth of information there about propellers and maby you could apply it to your needs............. Under the Beginners section ( where we are right now) from your origional post drop down I think ten to twelve posts and look for the thread............(( Still a little confused on prop selections))............ a lot of information rests within that thread....... hopefully you can find out what you are asking there........ I have never done electrics and wouldn't have a clue......... Captain Crash.......

I am using an 11 X 5 (good low end torque) and a 10 X 7 (for speeed) with my LA 40. Maybe a 3 blade would be better for your "air truck", or at least let you lower the CG? Also, it seems to like at least 15%, and the air bleed is right in the middle. Also the # 8 plug is hotter, and likes that better than the A3. Your burned oil problem happened to me too, from being run too lean, it's hard to get off, but also have heard the crock pot & antifreeze thing will clean it. I haven't tried it.

k thanks! [8D]

The APC 11 by 5 works great with it. I have a 10 by 7 i am going to try this weekend and a 10 by 6.

Not in your wildest dreams!

You guys are wildly overpropping these things & costing yourselves a bunch of performance.

At sea level the 40 LA has its power peak at 13,400 rpm & the torque peak at 12,700 rpm, developing 0.78 HP & 63 oz-in of torque, as measured by real-world dyno testing. At sea level it swings a 10-6 at 12,100 rpm --already 600 rpm short of its torque peak & 1300 rpm short of its power peak. It would swing a 10-9 at ~10,000 & a 10-10 at ~ 9800 rpm -- about a light year away from either its power or torque peaks.

The 40 LA also swings a 10-7 and an 11-5 at ~10,900 rpm -- a long way off its peak performance band. You may think that it is pulling well with the 10-7 or 11-5, but it isn't even close to its best performance.

Very much better choices would be 9-6, 9-7, 10-5, 10-6 & 11-4, depending upon the airframe specifics and density altitude.

Brit..... sounds like you have your specs down pat...... technically you are correct, however by application, this is a land based vehicle, I suppose he uses it 20 to 30 yards at a time roughly,, in an airplane, the higher torque and rpm, would build to perfection, on shortie runs like i can only suppose he makes, I do wonder if full air biting takes place either way????? Getting into the "Power Band" (rpmxpitch=distance traveled) may never happen on his application...... I am truely interested in your oppinion, what do you think??? Captain Crash...

Colour me pink -- I just noticed the land-based application thing.

That still doesn't change the need to operate the engine within its optimal performance range. It should be propped so that unloaded at speed, its rpm reaches but doesn't exceed the power peak. I haven't seriously played with a prop driven car for years, although I still mess around with snow buggies made from the fuselages of crashed planes (someone else's crashed planes of course).

If acceleration is not a big issue & peak speeds can develop, I think that the prop diameter should be fairly small, so that the pitch could be maximized for high ground speed. Drag is still an issue, so some testing will be necessary, but speeds near 100 mph should be possible. The stock 40 LA can turn a 9-6 at 13,400 RPM (static) -- right on the peak -- but it will unload at speed, so a bit more pitch could be tolerated. It will also spin an 8-8 at about the same RPM -- and that will really get a ground vehicle moving. If the engine can be tweaked (piped, for example) to both increase power & RPM, the 8-8 should also still work well. If an 8-9 can be found, & if the vehicle drag is low, it should also work.

If the vehicle is used in very short bursts, as you surmise, then a much flatter pitch prop will be needed, since the coarse pitch prop will be at or near stall at low speeds & will provide very poor acceleration. In that case the bigger the diameter the better, but since he is limited to ~ 10", typical aircraft props are probably more suitable. A 10-4 would turn at ~13,400 static and would obviously be very good for rapid fire bursts of speed & still not seriously over-rev the engine.

Are you sure - on the os website they say the #8 is medium hot and the #A3 is hot.

[link=http://osengines.com/accys/glowplugs.html]OS Glowplug Chart[/link]

Brit...... now that makes perfect sence to have it working at full rpm...... Hmmmm we used to use aluminum sno disks (sledding) with KB40's on em up north in the winter time..... ND is not Canada, but TX is not ND either hahahahahah we havent seen real snow down here for some time now......... thanks for the correct configuration on rpm and power........... you been listening ( I Brake ....????) later all...... Capain Crash...

Thanks. Yes it does appear that way. I was told that the #8 is a hotter plug though. It (LA 40) does seem to prefer the #8,
but that may have been caused due to the degraded condition of the A8 plug it replaced.
If the #8 is a cooler plug, then that makes sense. Higher cost=thicker element, although if an A8 is a hotter plug,
it would likely be shorter life, contrary to the description given at their site, describing it as a long life plug.


As far as the props, my Duraplane DT 40 will barely get off the ground with a 10X6. It is overweight due to some mods.
Before I moved up to the 11X5 there was hardly any throttle response, tons of lag, etc....

could be ur piston ore liner is wearing a lot not sore doe but it sounds 2 me like its 2 leanhope this helps m8..........how long u ad the engine 4....

Sorry for not replying...I've been in the car forums as you can tell by my avatar. britbrat, I can swing a prop 10" in diameter or less, if I swing like a 9x6, I can actually cut the engine mount shorter, lowering the CG. I drag raced a brushless RC18T down a empty parking lot the other day, running a 10x6 prop and 10% fuel. I accelerated faster than the 18T, but I topped out just a hair faster. Then, this 30MPH gust blew from behind, and being a air powered car, it swerved into the RC18T, then went head-over-heels, catching an edge on the 18T's body, but it meraciosly flipped over on all fours, and I continued driving. Then, our radios went out of range and the RC18T took off at Wide Open Throttle into a curb, scratching the bumper, and my engine shut off because the failsafe took over. Thanks goodness I had a failsafe!

So ya, theres my day, and I live at ~600 feet above sea level, so I think I'll try swinging a 9x6 later on.

thanks for the replies!

Oh and for noise:
RC18T= Silent
OS .40 = loud, 2 stroke exauhst blowing everywhere.

I'd just like to add that now I am paranoid of flying, kinda...I bought a new engine (OS .46 AX) and everytime I fly, I dead stick and am forced to land...the 5 flights I had with that engine all resulted in dead sticks...usually the airplane is going too fast when I bring her in and I crash into the embankment...better ask my instructor if the mixture is right (he set it).

Ibrake..... Howdy, I assume that you have properly broken in that engine????? Some questions, are you throtteling a lot from high to low or are you pretty much in high gear when you fly?? Does it allways seem to die at or near the same time frame in your flights???? Do you do a lot of acrobatics,inverts,climbs,dives or do you slo fly???
As far as dead sticks... if you are real low when it dies then ya gotta just horse her in... If you have good altitude, trimming is important, I dead stick a lot, well allways actually, when I have elevation, I go into the soaring mode, which is slooooow gentle turns, I actually trim it to just before stall speed and "Knowing" which way I am gonna land, I take slow circles above 1/2 of the runway in the direction from which I expect to land this way the landing "legs" arent too long and with practice, you can tell if you need to float around one more time or dive and flair at the end of the runway...... It takes a lot of judgment calls on how you are loosing altitude and if I am just a little too high, I stretch the last circle out a little just before I bring her in, well actually before gravity and drag brings her in...... Hope some of this helps , just remember, What goes up, WILL come down! ....... Captain Crash... the name says it all...

1. The engine is not broken in all the way yet
2. I fly in high gear.
3. Yes
4. well, I wanted to do aerobatics but lately, with that new engine, I've been flying the pattern right side up.

Ibrake....... Hmmmmm you got problems...... but simple problems.... Since the engine is not actually all the way broke in, that may cause problems, but not in a distinctive way.... the third question you answered yes to tells a lot, if it Allways seems to die out at a certain part or time in flight, ( in a usual pattern style fly) then its probably a setting problem, probably coupled by a pressure , or tank location problem.
Some more questions......
Is your plane a kit or a arf ........?
Have you made any custom modifications to make things fit, engine, fuel tank ect.....?
Is your engine side mounted or inverted or straight up......?
Are you running a stock muffler with a pressure fitting.....?
You are just running two lines from the tank arent you...?
Is there about the same amount of fuel in your tank when you deadstick in..?
How much fuel do you have in your tank when it dies...?
Have you tried filling the tank 1/4 full and starting and running it...?
Do you have excessive vibration or seem to...?
Is this one too many questions..?????? Captain Crash...

1. Its the RTF Avistar, with a glued wing and glued stabs
2. Well, I've put new hardware in the stock fuel tank
3. Mounted straight up.
4. Yes, I have the P-BOX muffler that came with the engine
5. Yes, fuel and pressure
6. about, yes
7. Almost full
8. No
9. Not really, kinda choppy at times
10. As long as I give enough info and get the problem fixed, I'd answer as many questions as needed.

Ibrake....
Some possibilitys.....
1. you changed out the hardware in the stock fuel tank.......
6. same amount of fuel when it dies.......
7. allmost full.......
Some thoughts......
since it doesnt seem to run very long, ( allmost full tank) when it dies, and you changed out some hardwear in the stock tank, there is a possibility that the tank and lines are at fault..
Have you ever tried filling it up and running a tank through it at the pits?
will it start and run with 1/4 tank of fuel?
Are you sure you didn't accidentaly scar one of the lines on the tubing hardwear( possibly creating a small pinhole leak) when you installed them?
Are you sure the clunk is not doubling back on itself, pinching the line?
How is your clunk line set up, does it in order have theclunk,short tubing,long pipe,short tubing then the go between line at the tank throat??
Do you do a tip test pre flight? ( holding running plane nose straight up) ...
While the engine is running if you pinch the fuel line with your fingers behind the needle valve, does it lean out instantly and increase rpm?
Is the tank mountd below the level of the carburator? this would be agrivated by loss of pressure....
Just some things to think about and check out...... hope it all helps somehow... Captain Crash...

I'm pretty sure its not a tank problem...more likely a fuel line problem/mixture problem...

It's just heavy. Flies great with the 11X5
I have 2 of them, (OS 40LA) they act the same, on the DURAPLANE TRAINER 40, just don't seem to have enough low band tourque with a 10X6 to take off very well,
even if the 11X5 is too much prop for it. Maybe i'll try an 11X4.5