Author Topic: What am I doing wrong??? (Read 2398 times)

Wynn Robins · « **on:** February 20, 2012, 06:39:53 PM »

Why is everybody else getting more efficiency from their system and thus being able to use smaller packs than me??

two scenarios

legacy - weighs 66ox ready to fly.
Motor - Scorpion 3026-890 running at 9100(circa) rpm
Castle ICE lite 50 in control line governor mode
Hubin FM9-V timer - Castle New High Governor mode
13x 5.5 APC pusher.
Pack - 4000mAh 4s - using 2600-3-2800mAh per flight

yatsenko classic
61.5oz ready to fly
Plettneberg Orbit 20-18 motor
Schulze F2b ESC
Hubin FM-9 timer - in schulze mode
APC 13 x 5.5 running abour 9300rp,s
Pack - 5s 3000mAh - using 2200mAh average.

Loren Nell turns up with his thundergazer - 68oz - Renecle timer/governor, Turnigy ESC, Emax 2826/06 motor - 4s 3000mAh pack and using 2200mAh slightly less RPM and APC 12x6 APC pusher..

plus looking at otehr setups here I am using far more capacity than most people and I dont know why - I'd love to drop the pack size and cells down to save a lot of weight - especially in the Yatsenko

Any ideas folks?

Bob Hudak · « **Reply #1 on:** February 20, 2012, 07:10:48 PM »

Wynn,
What line lengths are you using? And what are the lap times you're getting?
Bob

Wynn Robins · « **Reply #2 on:** February 20, 2012, 07:21:03 PM »

Bob- 63ft lines - lap times are 5.2- 5.3

Bob Hudak · « **Reply #3 on:** February 20, 2012, 07:47:24 PM »

Loren Nells setup looks like it may have the answer to your question. He uses a smaller diameter higher pitch prop spinning at a lower rpm. Your bigger blade with lower pitch needs more rpm to get the same result? I noticed the same increase in mah use when I tried the 11x4.5ep on my Vector. Ended up going back to the 11x5.5ep at lower rpm's and wound up using 150 mah less battery.
Bob

Wynn Robins · « **Reply #4 on:** February 20, 2012, 08:17:55 PM »

I thought that might be the case - I have some 12 x 6.5 pushers coming from Dennis A to try - so will see if I can get that to sort it out....

Dennis Adamisin · « **Reply #5 on:** February 20, 2012, 09:13:47 PM »

Bob made good suggestions. In addition:

Motor up-size: In my Mythbuster I cut battery usage by 100-150 mah by switching from a 35-36 motor to a 35-42. The slightly longer/stronger motor apparently draws less power to turn the same prop. Your birds (especially the Pletty) may like the 12x6.5 Wide better than the 13x5.5. You might experiment by taking one of your 13" props and clipping it to 12". It will have to spin a little faster but it will also un-load the motor.

Line Rake: Maybe Bob Branch can check in here. He was messign around with a LOT of line rake on his T-Rex and discovered that when he reduced the rake (lead-outs forward) his lap times went faster and he throttled back a couple hundred RPM which cut his battery usage by a fair amount (I think it was 200 MAH)

Flight Duration: You did not say how long you are flying - you of course do not want to cut yourself short, but cut down anything that is excess to what you need to fly.

Keep us posted, I agree your power usage sounds higher than I would expect...

Russell Bond · « **Reply #6 on:** February 20, 2012, 10:57:00 PM »

My 70oz (fueled) plane has a 930 kv motor and uses a 3300mah 4s battery.
65' eye to eye lines and 5.5 secs/lap at 9400 using the old original (best) 13x4.5 thin pusher.
It uses 2300mah on a bit windy day and 2450 on a calm day.

Mark Scarborough · « **Reply #7 on:** February 20, 2012, 11:03:10 PM »

It would be extremly helpfull if people could list their lap times and total flight time with these figures. It would help to relate greatly ,,perhaps even what motor you are using,,
thanks

Russell Bond · « **Reply #8 on:** February 20, 2012, 11:21:48 PM »

Ha!!!
That's the one thing I forgot.
Motor run is 5.5 minutes. Combine that with the 24 seconds before spool up and that makes about 6 minutes total.
The motor is an Orbit 25-10.

Derek Barry · « **Reply #9 on:** February 21, 2012, 05:02:54 AM »

Also, Yatsenko planes are designed to be very "draggy" if you know what I mean. I have heard Orestes and the Yatsenko brothers say that it is the drag that makes the corner better. Thats is why they have all those cheak cowls and the newer models have a thicker rudder to add more drag. All this plus the big prop can add up fast I would imagine.

Derek

Igor Burger · « **Reply #10 on:** February 21, 2012, 07:49:28 AM »

Draggy? compared to what? if they compare it to old "CCCP" models by Kolesnikov, Listopad Petrov, etc, then yes, because they had thin airfoils, wings with low load (and thus low induced drag) able to fly with weak engines, but they does not differ from actual 18% airfoils we use with 10cc piped motors. Most of the model drag comes from wing and that is similar to actual models. thick rudder cannot change too much.

Igor Burger · « **Reply #11 on:** February 21, 2012, 07:58:17 AM »

The trick is not "draggy" plane, but simply better airfoil. Many guys try to use thinner airfoils for electric, but it does not work, because thinner airfoil has less drag in level flight, but when it comes to high G loads, with heavy battery, it reachs end of its ability to make enough lift at low drag, and all works just opposite, it brakes in corner. So they have low drag in straigh flight and high drag in corners, just opposite we want. The proper way is airfoil wich works well in corners, not in straight flight. Higher drag in level is not bad, and low drag in corner is goal. Some guys does it with thick airfoils and some with good configuration :- )))))

Allan Perret · « **Reply #12 on:** February 21, 2012, 09:16:29 AM »

Quote from: Igor Burger on February 21, 2012, 07:58:17 AM

Some guys does it with thick airfoils and some with good configuration :- )))))

What do you mean by "good configuration"

Wynn Robins · « **Reply #13 on:** February 21, 2012, 12:47:58 PM »

Quote from: Mark Scarborough on February 20, 2012, 11:03:10 PM

It would be extremly helpfull if people could list their lap times and total flight time with these figures. It would help to relate greatly ,,perhaps even what motor you are using,,
thanks

sorry - lap time 5.3 - flight time 5:30 - have a 25 second delay from time I push button to when the motor spools up - I think I covered my motor but the Plett ins 20-16 not 20-18 as I said before.

hey russ - if you need any more of the 13 x 4.5 let me know - I have a few i need to get rid of

William DeMauro · « **Reply #14 on:** February 21, 2012, 03:43:27 PM »

Wynn,
Your numbers are very close to what I get with my SV22 with almost the same setup. My SV 11 with the scorpion was almost the same too but with the Plett 15-18 was about 100-200ma more efficient but that could even be a slightly different setting or the way the Shulze works in comparison to the Castle. I have also noticed that different brand chargers seem to come up with different numbers. I am pretty sure that has to do with the way they balance the batteries. When I was using the budget chargers my numbers were always about 5% higher than I am getting with the I-Chargers.

Will Moore · « **Reply #15 on:** February 21, 2012, 08:00:04 PM »

Wynn;

If you are using a Plettenberg 20-16, it has a KV rating of 720, vs 640 for the 20-18.

To get the same lap speed, with the 20-16, will require a slightly lower throttle setting because of the

higher KV. The lower throttle might translate into slightly lower efficiency , as it is a usually more

efficient motor run to stay about 80% or slightly higher in throttle levels. A Plettenberg 20-18 might be a better

choice with a 5 cell battery. I'm running a Yatsenko Shark, with the 20-18, and 13/6.5 pusher APC prop and

5min 30 sec flights, 5.1 to 5.2 sec lap speeds on 64 foot lines and drawing 1800 to 1950 mAh depending on wind conditions

Bob Hudak · « **Reply #16 on:** February 21, 2012, 08:05:09 PM »

Wynn,
I would also try to fly with the shortest line length the plane feels comfortable on. Even if you lose 6 inches you will use less battery to make a full circle. You might have to slow the plane down a bit to get the lap time you like when you do this and there comes the power savings again, double bonus on the mah use.

Bob

Igor Burger · « **Reply #17 on:** February 22, 2012, 12:44:00 AM »

Quote from: Allan Perret on February 21, 2012, 09:16:29 AM

What do you mean by "good configuration"

Every airfoil has some properties, designer must be able use them properly, means not to push it to its weak conditions anywhere during flight. I mean you not need only good airfoil, you must have also proper flaps size, proper tail, proper flap to elevator ratio, proper CG to keep airfoil in proper conditions for flying. Average airfoil can be used "properly" with much better result than "best" airfoil killed by improper flaps size or wrong elevator deflection etc.

Dean Pappas · « **Reply #18 on:** February 26, 2012, 02:16:31 PM »

Hi Wynn,
The rule of thumb I use to estimate battery usage is between 0.6 and 0.7 Watt-Hours per ounce of all-up weight.
The Legacy figures at 0.65, right in the middle of the range.
The other is even lower.
Don't sweat it, I'd say.
Dean P.

Steve Helmick · « **Reply #19 on:** February 26, 2012, 03:12:29 PM »

Forgetting about the electric power for now, remember that the flying style (how hard you hit the corners) also has a lot to do with energy consumption. Easy to see with an underpowered IC powered plane, especially when the wind is up a bit.

Steve

Bob Hudak · « **Reply #20 on:** February 26, 2012, 06:16:03 PM »

The rule of thumb I use to estimate battery usage is between 0.6 and 0.7 Watt-Hours per ounce of all-up weight.

Dean,
Is this calculation used without a battery added to the plane ?
Bob

Dean Pappas · « **Reply #21 on:** February 28, 2012, 06:41:17 PM »

Hi Bob,
All-up weight or in other words ready for takeoff with the battery.

Dean

Bob Hudak · « **Reply #22 on:** February 28, 2012, 07:53:08 PM »

Dean,
I can't get the formula to work. Here's my dilemma. I have a 52 oz. plane with a 2700 mah battery. So 52x.6=31.2. It looks like I need a bigger battery. So I try a 3300mah battery. It weighs 3.6 oz. more bringing the planes weight up to 55.6 oz. So 55.6x.6=33.36. Now my 3300 mah battery is falling short of requirements. I stopped calculating because I started to see as the weight went up so did the battery needed. What am I missing or doing wrong here ?
Thanks, Bob

Wynn Robins · « **Reply #23 on:** February 28, 2012, 08:35:08 PM »

Bob,

heres another quick and relatively accurate way to work out your required capacity

Total Watts = weight /16 *112
Average current = total watts/battery voltage
mAh Used - flying time/3600x (average current x1000)
Recommended capacity = mAh used/7.5*10

Dean Pappas · « **Reply #24 on:** February 29, 2012, 05:56:45 PM »

Quote from: Bob Hudak on February 28, 2012, 07:53:08 PM

Dean,
I can't get the formula to work. Here's my dilemma. I have a 52 oz. plane with a 2700 mah battery. So 52x.6=31.2. It looks like I need a bigger battery. So I try a 3300mah battery. It weighs 3.6 oz. more bringing the planes weight up to 55.6 oz. So 55.6x.6=33.36. Now my 3300 mah battery is falling short of requirements. I stopped calculating because I started to see as the weight went up so did the battery needed. What am I missing or doing wrong here ?
Thanks, Bob

Hi Bob,
The trick is in paying attention to the units: the formula I gave was for Watt-Hours not milliAmp-Hours.
The 0.6 to 0.7 figure is for Energy needed per ounce.

So, 52 oz * 0.65 w-H/oz = 33.8 watt-hours.
divide by volts and you get amp-hours so 33.8 / 14.4 (I assumed 4S) gives 2.35 Amp-Hours. Your 3300 or 3.3 Amp-Hour battery is plenty.
Yes, there is a domino effect! Add a few silly ounces and then add a bigger motor to carry them and then you'll need a bigger battery to feed it and then you just might have a pig.
What can I say, light is good!

hope that helps,
Dean

Bob Hudak · « **Reply #25 on:** March 01, 2012, 06:27:56 PM »

Dean,
Thanks! The missing part of the formula of dividing by 14.4 volts gave the results I was looking for. I used the formula(weight in oz. x .6 / 14.4 volts) on my already flying Vector 40. The results were only 100 mah higher than what I actually use in 5-1/2 minutes of flying.

Bob