RE: Thrust Required For 2M Pattern?
 

I don't see how the 123 cells can fit into pattern, packs are way to heavy compared to lipo.

RE: Thrust Required For 2M Pattern?
 

Thanks to Chad and Dick for weighing in here, they are very knowledgable wrt electrics and gas engines and I appreciate their input here.

Chad - If I assume the 12" pitch goes with the 6500rpm end of the range and the 15" with the 5800rpm end, that gives a pitch speed range of 78-87mph. My example of a 10" pitch at 7500rpm or so should be OK then, considering the unloading that will take place in the air with the gas engine. Good to know it sounds like a decent starting point.

Dick - I will keep the part throttle performance in mind when setting up the pipe and I will start on the long side and sneak up on it. I will start with the 20x10 and also try a 20x12 after the engine is run in a bit. My prop calculator predicts around 6900rpm with a Menz-S 20x12 and that just might be the best all around combination. Both combinations show predicted static thrusts in excess of 23lb, which should be lots for a 2M pattern plane. Do you have any comments on the hard mounting vs. soft mounting issue? Any testing on current draw to the servos for one or the other?

Thanks to all for the help and information,
Mark

RE: Thrust Required For 2M Pattern?
 

The radio and the 123 cells are a whole other story
first the 123 cells - are they heavier?
yes
BUT
they will do what no LiPos or other LiIons will do -- they will put out far greater amperage and with out dropping dead doing it -
they also recharge on the spot using very high charging rates
they don't explode and cost is much lower
That's for openers - new lighter ones are bound to pop up in near future
If you have not used em or really studied them -it is easy to believe that the LIPos are "better ".
At the moment - the Li Pos weigh less
end of their advantage
Now the radio -and servos
I know some will really not go for this
BUT
the new DX7 tx and rx will make even inexpensive non digital servos work beautifully
also, as the rx can stand 9 volts and 30 amps to the buss - no regs are needed
next part ---
the 123 cells (2) provide 2000 usable amperhrs without recharge
recharge takes LESS time than it does to refill your gas tank .
so no regs - no expensive battery paks
just 4.5 ounces of 123's
and
the output of the two cells is far far greater than any combinations of servos can pull - add dual feed to the receiver and you will have a very constant power (not just unloaded voltage reading) throughout the flight(s) tho there is no regulator - th servos can suck all they want - th cells will put out up to 60 C (way over what a servo can pull with out smokin
so - let's say you have to recharge every flight or every other flight
whatever - who cares - you simply plug in th charg lead and if you are usingthe CELLPRO charger - th charger looks at the two cells balances (really not that necessary ) and loads up th cells again as you crank or let th fuel pump refill the tank.
Whatabout letting the pack cool ? not necessary
what about charging in the plane? Why not no danger
how fast can you charge it ?
if you have ANY 123 charger properly designed - you can cram in the charge as fast as the charger supply will allow -10 amps charge rate is just fine.

RE: Thrust Required For 2M Pattern?
 

Hi Mark

It can be pretty much any combination of pitch and rpm, a 20x15 with the right setup can spin into the mid 6000's. I think around 90 mph and change is about as high a pitch speed as you can get with the current 20-22" electric setups.

RE: Thrust Required For 2M Pattern?
 

Thanks, Chad.

It looks like the 46cc gasser will get me into the neighborhood at least and I will have to fine tune from there. Nothing new in that...


Mark

RE: Thrust Required For 2M Pattern?
 

I am almost certain it is impossible to take those RPMs using current cas engines with mentioned 20 and 22 inch propellers and pass noise/sound test in FAI F3A. I do not know how national classes like AMA rules do.

Maximum F3A noise is 94dB(A) on hard surface and 92dB(A) on short grass. Were those limits used already last four years?

Sure some sound reduction is achieved designing current soft mounts for gas. Some reduction using three or four blade propellers. Intake noise should be muffled. Best result obviously can and should be done reducing exhaust gas "bite". The temperature of burning gas is higher than methanol and exhausting gas expands faster and by nature is louder. Using better muffling ingreases weight and reduces power.

It seems like voltage in FAI will be 56V for 2008...2011 as proposed by F3A Subcommittee. After a month, Mars 24th we know new regulations.

You are doing great work experimenting and I really hope you could get successful results.

Esa

RE: Thrust Required For 2M Pattern?
 

Hey Esa,

You make a very good point about the sound limits. I am not competing at even a local level, just sport flying, but for those that are it is a very real issue. I plan to use an ES Composites carbon pipe, so the exhaust noise should be very minimal, but intake noise may not be and it will harder to muffle with the side intake engine than the rear intake of the ZDZ. We shall see about the hard vs. soft mounting as well, once I get there. I will try to get some sound readings when I am ready to fly, but it will be quite a while before that happens at my current pace of building...

Mark