[BK1]

Thanks for posting the pics- I am going with the same setup.

[stegl]

Better reread... The numbers I gave are for your Scorpion 4020-14 motor. A APC 15x7 or 15x8 incher should work just fine. got the numbers from a program.

BK1... If you need more pictures let me know will try and help.

[BK1]

Thanks again- cant wait to get this in the air.

[davidmc36]

Originally Posted by stegl

Better reread... The numbers I gave are for your Scorpion 4020-14 motor. A APC 15x7 or 15x8 incher should work just fine. got the numbers from a program.

Aaaaah, gotcha. Looks good.

[stegl]

Originally Posted by BK1

Thanks for posting the pics- I am going with the same setup.

Don't forget to do a lateral balamce, Had to add 1 oz in the right wingtip.

[davidmc36]

So I got some run-up tests done.

With the 15X8 two blader: 53 amps and 7800 RPM 9lb 2oz thrust.

With the 15X7 three blader: 53 amps and 7800 RPM 9lb 6oz thrust.

It was holding at 19.7 volts during the tests. Looks like just over 1000 watts. 815 absorbed at the prop for the 15X8 according to Prop Calc.If it dresses out at about 13 lbs with Rx battery thats about 80 watts per pound into the power system, 62 watts per pound at the prop. Should fly fine the way it looks from here.

So it just goes to show, the thrust is just a bit of a gravy number. It would appear that the 7 inch pitch prop would be the better one based on thrust but the 8 inch pitch prop should make it go a bit faster. With a tad extra thrust I suppose it may get 'out of the hole' a bit quicker but will have a slower top speed.

[stegl]

Originally Posted by davidmc36

So I got some run-up tests done.

With the 15X8 two blader: 53 amps and 7800 RPM 9lb 2oz thrust.

With the 15X7 three blader: 53 amps and 7800 RPM 9lb 6oz thrust.

It was holding at 19.7 volts during the tests. Looks like just over 1000 watts. 815 absorbed at the prop for the 15X8 according to Prop Calc.If it dresses out at about 13 lbs with Rx battery thats about 80 watts per pound into the power system, 62 watts per pound at the prop. Should fly fine the way it looks from here.

So it just goes to show, the thrust is just a bit of a gravy number. It would appear that the 7 inch pitch prop would be the better one based on thrust but the 8 inch pitch prop should make it go a bit faster. With a tad extra thrust I suppose it may get 'out of the hole' a bit quicker but will have a slower top speed.

Interesting numbers... way to go ! I think you are on the right track now. Again that thrust is just secondary ( difference of only 4 oz is minimal) if you want to call it that. I would have thought that the 15x7 3 blade would draw more power than the 2 blade. I would go with the APC 15x8 for that little extra speed; that way you can throttle back and the amps draw will drop substantially.... more at half throttle (+ or -) for level throttle. Question ? what ESC are you using ? If you have one that supplies 5A to the receiver/servo system then you can dump the receiver battery..... put some balance weight way up front like I did in one of my previous pictures and probably drop some weight. ???? Also I think that at 52-54 full power amp draww should give you lots of flying time on a 5000 pack. Your views ?

My way of thinking that if using the on board BEC ; you always have a good supply of power as each time time you fly, you start with charged batteries and a source of 5v for the system with no chance of voltage sag like NiMh or NiCad batteries. I understand that this is more criticle with Spektrum systems.

Have quit using extra battery supply for Rcver/servo applications 4 years ago and wouldn't go back. I use Castle Creations Ice and Ice Lite ESC's in all my applications as it is one of the few that supplies 5A to the receiver/servos and have used up to 8 digital servos (medium to mini ) with no problems. Of course, in most cases only 5 servos maximum or less, at one time are being used.

[davidmc36]

Originally Posted by stegl

Interesting numbers... way to go ! I think you are on the right track now. Again that thrust is just secondary ( difference of only 4 oz is minimal) if you want to call it that. I would have thought that the 15x7 3 blade would draw more power than the 2 blade. I would go with the APC 15x8 for that little extra speed; that way you can throttle back and the amps draw will drop substantially.... more at half throttle (+ or -) for level throttle. Question ? what ESC are you using ? If you have one that supplies 5A to the receiver/servo system then you can dump the receiver battery..... put some balance weight way up front like I did in one of my previous pictures and probably drop some weight. ???? Also I think that at 52-54 full power amp draww should give you lots of flying time on a 5000 pack. Your views ?

My way of thinking that if using the on board BEC ; you always have a good supply of power as each time time you fly, you start with charged batteries and a source of 5v for the system with no chance of voltage sag like NiMh or NiCad batteries. I understand that this is more criticle with Spektrum systems.

Have quit using extra battery supply for Rcver/servo applications 4 years ago and wouldn't go back. I use Castle Creations Ice and Ice Lite ESC's in all my applications as it is one of the few that supplies 5A to the receiver/servos and have used up to 8 digital servos (medium to mini ) with no problems. Of course, in most cases only 5 servos maximum or less, at one time are being used.

I found the numbers raised my eyebrows a bit too. The current was virtually identical (I rounded off the decimal points for conversation purposes). And that thrust thing: only like 2.7% difference. Previous run-up tests on other planes showed me about 10-15% increase in static thrust when going from two bladed to three bladed props of equal pitch. I still want to hunt down a three blade 15X8. Gives it a better scale look and will still not max out the 85A constant/100A burst ESC. And I wont sacrifice the top speed compared to the 7 inch pitch.

ESC is a Hobby King and after taking a second look I see it specs out at 5.5V/5A SBEC. I thought from memory it was only 3A. I just may go with the BEC in that case. I must say that most of my planes I have set up that way and have had zero problems. I would be ready to go with no extra ballast needed. With only 6 analog servos total, it should be dandy.

One pack at 54 amps would give 5.5 minutes full throttle and save 1.4 lbs. Would be a decent flight time actually. Have to think about that one.

The Spek Rx's 'Specs' say 3.5 to 9 volts. So far my experience has been it has to get way down there on voltage to show any issues. I had the Rx pack in the TO go one bad cell (three year old pack that came with my DX7 and got tons of use) and at 3.7 volts or so it would still bind and power up but moving the sticks around pulled the voltage down under 3 volts and things of course got totally wazzooed then.

[stegl]

Originally Posted by davidmc36

I found the numbers raised my eyebrows a bit too. The current was virtually identical (I rounded off the decimal points for conversation purposes). And that thrust thing: only like 2.7% difference. Previous run-up tests on other planes showed me about 10-15% increase in static thrust when going from two bladed to three bladed props of equal pitch. I still want to hunt down a three blade 15X8. Gives it a better scale look and will still not max out the 85A constant/100A burst ESC. And I wont sacrifice the top speed compared to the 7 inch pitch.

ESC is a Hobby King and after taking a second look I see it specs out at 5.5V/5A SBEC. I thought from memory it was only 3A. I just may go with the BEC in that case. I must say that most of my planes I have set up that way and have had zero problems. I would be ready to go with no extra ballast needed. With only 6 analog servos total, it should be dandy.

One pack at 54 amps would give 5.5 minutes full throttle and save 1.4 lbs. Would be a decent flight time actually. Have to think about that one.

The Spek Rx's 'Specs' say 3.5 to 9 volts. So far my experience has been it has to get way down there on voltage to show any issues. I had the Rx pack in the TO go one bad cell (three year old pack that came with my DX7 and got tons of use) and at 3.7 volts or so it would still bind and power up but moving the sticks around pulled the voltage down under 3 volts and things of course got totally wazzooed then.

Re the spektrum receiver low voltages and not operating... I was just going with what I have seen at out club and what I have read and low voltage to the receiver creates H E L L and unbinding results. By running a BEC that problem should never exist ; at least on paper. I also thought I read somewere that Horizon had sent a notice to use 5 nicad or nimh cells instead of the 4 cells. But then what do I know. I don't use Specktrum

Tried to find out on the Hobby King website if their 5a was actual continous running or a peak BEC current. You should be ok anyways.

So the motor run numbers you gave ... they are actual running right ?

If you have flown the H9 Twin Otter ; you will find that this one is much more of a handfull over the TO until after several flights, to get comfortable with it.

Thanks

[davidmc36]

Originally Posted by stegl

Re the spektrum receiver low voltages and not operating... I was just going with what I have seen at out club and what I have read and low voltage to the receiver creates H E L L and unbinding results. By running a BEC that problem should never exist ; at least on paper. I also thought I read somewere that Horizon had sent a notice to use 5 nicad or nimh cells instead of the 4 cells. But then what do I know. I don't use Specktrum

Tried to find out on the Hobby King website if their 5a was actual continous running or a peak BEC current. You should be ok anyways.

So the motor run numbers you gave ... they are actual running right ?

If you have flown the H9 Twin Otter ; you will find that this one is much more of a handfull over the TO until after several flights, to get comfortable with it.

Thanks

Yes, that was in the driveway all hooked up and running for the motor tests.

I had an idea this will be a much different animal to fly. Just waiting for a nice weather day now.