TowerHobbies.com


LXVJ18 Master Airscrew 9x7 3-Blade G/F Nylon Propeller 1 $6.99
LXGYM7 Master Airscrew 9x7 3-Blade Pusher G/F Nylon Propeller 1 $6.99

Originally Posted by Kurt

TowerHobbies.com


LXVJ18 Master Airscrew 9x7 3-Blade G/F Nylon Propeller 1 $6.99
LXGYM7 Master Airscrew 9x7 3-Blade Pusher G/F Nylon Propeller 1 $6.99

Thanks Kurt, I plan on replacing both propellers with the Master Airscrew 9X7 3-Blades....for balance and pitch match....I can't see replacing one motor pusher to a Master Airscrew and leaving the other side with the stock prop.

Best regards,
TwistedGrin

Originally Posted by Kurt

oh believe me I know!
http://www.rcgroups.com/forums/showp...postcount=5070

Hi Kurt, that's right. I had seen your posts before, just forgot.

You can't really see it in my pictures, but due to a few scrapes at the beginning (once after a perfect landing and being filmed, of course, I taxied back to where we were standing and wanted to shut the engines off, got a brain freeze and fliped the under carriage switch -scrraaaaape) my props are looking like they shouldn't fly any more. The tips are all scraped and bits broken off. One blade is even a few mm shorter than the others. I just sort of filed the shreds away or smoothed out the jaged broken plastic on the tips, and away she goes. Not a hint of anything amiss in the air. I'll replace all the blades soon, but have to wait for a rainy dain - too much fun flying now. She'll probably even go faster with brand new blades

Originally Posted by gadorey

She'll probably even go faster with brand new blades

That's one nice thing about the P-38, worst that can happen retracting the gear on the ground is a couple busted props.
On my FMS Mustang, instead of flaps I flipped the gear switch after landing. Doh! One of the retracts jammed and wouldn't reliably work after that, so took the opportunity to upgrade to 514s..

The plan is to put these on my V2 JPower:
http://www.hobbyking.com/hobbyking/s...in_Trike_.html
They're really incredibly nice and except for slightly small wheels are nicely sized for the 1400mm Lightning, and very well made especially for ~$15.

Originally Posted by Kurt

That's one nice thing about the P-38, worst that can happen retracting the gear on the ground is a couple busted props.
On my FMS Mustang, instead of flaps I flipped the gear switch after landing. Doh! One of the retracts jammed and wouldn't reliably work after that, so took the opportunity to upgrade to 514s..

The plan is to put these on my V2 JPower:
http://www.hobbyking.com/hobbyking/s...in_Trike_.html
They're really incredibly nice and except for slightly small wheels are nicely sized for the 1400mm Lightning, and very well made especially for ~$15.

Kurt, Saw your notes on Z8's blog....I trust his reviews and yours too. Thanks for posting up here. Regarding those landing gear...they look really heavy. When you get them ...anyway you could provide the weight of the original and new landing gear??

Best Regards,
TwistedGrin

Twisted - thanks!
I've had the aluminum gear for a while, they're about 10g more each so not bad at all

http://www.rcgroups.com/forums/showt...0#post22220246

Gents,

Are you flying the V2 JPower P-38 on 4S? If so or not....what size batteries 3s/4s are you operating with? This question has probably been fielded several times on the thread....but I am coming up short finding a post regarding 3/4s battery operations....

Thanks in advance,
TwistedGrin

I have a couple of flights on my V2 with 4S packs. I am using blue lipo 2200 4s 30C packs. I had to move the packs back about 1.5 inches to maintain CG. Suprisingly, it is not much faster. I think the stock props are flexing with 4s. I still prefer 3S for most of my flights as it seems to fly lighter on 3S.

The pitch of the prop determines the speed. After achieving the optimum speed, any extra rpm only adds very little in resulting speed. To get the most of your 4s, you'd need to get higher pitch and lower diameter. 2 blades would help too.

Originally Posted by dude_109

The pitch of the prop determines the speed.

Pitch speed is defined as pitch X rpm, and is the airspeed at which thrust drops to zero.

So all else being equal, more pitch and higher RPM are interchangable. (getting both is, of course, better than either one alone)

If the prop tips approach the speed of sound, or the prop blades flex so their pitch is reduced, then all else is not equal, but AFAIK that's about it.

Drag increases with speed squared, thrust does not increase with pitch speed squared. I suspect you're just finding the point of diminishing returns or bumping up against motor torque limits

Originally Posted by rdeis

Pitch speed is defined as pitch X rpm, and is the airspeed at which thrust drops to zero.

So all else being equal, more pitch and higher RPM are interchangable. (getting both is, of course, better than either one alone)

If the prop tips approach the speed of sound, or the prop blades flex so their pitch is reduced, then all else is not equal, but AFAIK that's about it.

Drag increases with speed squared, thrust does not increase with pitch speed squared. I suspect you're just finding the point of diminishing returns or bumping up against motor torque limits

Good time to insert a chart...see attached:
TwistedGrin

Originally Posted by TwistedGrin

Good time to insert a chart...see attached:
TwistedGrin

I always have a hard time discerning what our electric motor sizes are!!

TwistedGrin

Originally Posted by TwistedGrin

I always have a hard time discerning what our electric motor sizes are!!

TwistedGrin

Can't vouch for accuracy, but a good start might be to look at watts (per chart at link), then back-calculate how you are gonna get an e-power combo (motor that pulls that wattage, given amps, volts, prop sizing....) to do the equivalent work.

http://www.hobbyking.com/hobbycity/f...o_electric.jpg

One of my electric foamie planes provided a Max load usage of: 462Watts peak on a bench test....the Watts load overall was around 430w as the battery starts to lose energy...so on average somewhere between 430 and 460Watts load......

So that 430Watt motor could be rated somewhere around a .30 size gas engine if we can trust this information.....regarding propellers, plane sizing, plane gross weight, engine thrust and battery power....matching a propeller is nearly a black art.......

Glow Engines vs. Electric Motors
♠ .20-size glow engine / 300w electric motor
♠ (OS Max 0.20 engine develops 0.4 hp = 300w electric motor (AXI 2820) )
♠ .35-size glow engine / 500w electric motor
♠ (Fox 0.35 stunt engine develops 0.7 hp = 522w electric motor)(AXI 2826)
♠ .40-size glow engine develops 1.0 hp = 750w electric motor (AXI 2826 or 4120)
♠ .60-size glow engine develops 1.3 hp = 975w electric motor (AXI 4120 or 4130)
♠ .90-size glow engine develops 1.6 hp = 1200w electric motor (AXI 5320 or 4130)
♠ 1.20-size glow engine develops 3.0 hp = 2250w electric motor (AXI 5330)
♠ DA-50 develops 5.0 hp = 3750w electric motor (AXI 5330)
♠ DA-100 develops 9.8 hp = 7311w electric motor (Double AXI 5330)

Great, so now we have motor ratings in KV....no charts for this....so back to the starting point!!

Best Regards,
TwistedGrin

Hold on! If you have the prop chart, then you can figure what prop for the I.C equiv motor, and you now have the 'frame-size' of elec motor you need so you just need to figure an RPM (KV = RPMs per volt) that you can sustain, with that prop, that does not exceed the ampere rating of the motor (which are usually pretty loosy-goosy anyway). Right? Don't like a parameter a bit, i.e. cant find exact KV you want, then tweak the prop parameters slightly until it matches what is actually available at LHS or mail order or in your flight box...

I haven't actually done much of this, so I could be all wet, but it does seem that as long as you don't get lost in the variety of options to chose from, you can make some assumptions, then test them, then if it fails, make another pass with an adjustment in the right direction.