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Jan 14, 2009, 11:22 AM
Registered User

Stock Banana SR71 Attributes?

Just got the stock arf sr71 from banana hobbies and am wondring about the cg, realistic control throws, and potentital for hand lauchnching of the stock setup. The only thread Ive been able to find is and excellent one, but related to 3rd party motors and esc's rather than stock.
would apprecate any input on these items of the out of the box SR71.
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Jan 14, 2009, 06:33 PM
Registered User
cool plane, my buddy just bought one but has not built it yet. how about trying to contact pete at banana and ask him your questions? might be a good place to start. good luck with your new jet!
Jan 15, 2009, 10:17 AM
Registered User
thanks, appreciate it.
May 28, 2009, 01:45 PM
Registered User

Just bought one!

Hey guys, old thread I know, but I am waiting for ine to arrive here in the UK. Right now it's some where over the US in a much larger plane, getting ever closer.

Come on Pete, give us some advice on this...
What sort of wind conditions can it handle, what should we look out for?
May 28, 2009, 02:04 PM
Registered User
The manual states the cg,this guy needs speed for stabitlity. Wind is really not a prob.
May 28, 2009, 02:43 PM
On the Edge of Space
dLdV's Avatar

LX SR-71 Equipment

I'm starting my build today. Going light/slow due to small field, 200X400 M, ringed with tall evil trees and cursed with roiling turbulence. Parts on hand - 2 each ELE brand 64mm 3600 Kv fan motors spec.ed at 14 oz thrust drawing 13 amps on 3S; 3S 2200 30C battery; 5V/5A BEC; 2 each 18A ESC's. 5 each 9 gram servos. Anyone care to speculate if I'm heading for the sky or disaster?
May 28, 2009, 05:41 PM
Dark Angel's Avatar
Originally Posted by dLdV
I'm starting my build today. Going light/slow due to small field, 200X400 M, ringed with tall evil trees and cursed with roiling turbulence. Parts on hand - 2 each ELE brand 64mm 3600 Kv fan motors spec.ed at 14 oz thrust drawing 13 amps on 3S; 3S 2200 30C battery; 5V/5A BEC; 2 each 18A ESC's. 5 each 9 gram servos. Anyone care to speculate if I'm heading for the sky or disaster?
Not sure about the sr but I recently built a GWS 15 and used 3400 kv motors the plane would fly but barely above stall speed very slow with scary turns I would not consider hand launching even though now it has hyperion 4400kvs in it. Also not sure but everything you mentioned tall trees and turbulence more power would help
May 28, 2009, 06:19 PM
Registered User
Hook those ELE motors up to a meter and see what the produce. I had a pair of the 3900 kv, 210 watt motors in the 64mm fans. They did not come close to producing 210 watts.....more like 160 each. They did not see the light of day in my EPO GWS -15. Returned them to BP and replaced them with some hot Ammo 4875kv inrunners from Tower.
May 29, 2009, 07:17 AM
On the Edge of Space
dLdV's Avatar
OK, that's two votes for disaster. Yeah, testing is probably in order. I'll borrow a meter and see what they really eat, separate and in tandem. On prop planes 100W/lb is OK but it seems like the fan guys want 200W/lb or more. Is that approximately correct? All components and frame weighed 28 oz, and BP claims 14 oz thrust per motor, total 28 oz, and 144W/motor, total 288W. Would that be considered drastically underpowered for a fanjet? BTW, what was the all up weight on those F-15's?
Last edited by dLdV; May 29, 2009 at 07:39 AM.
May 29, 2009, 11:30 AM
Dark Angel's Avatar
Mine came out out HEAVY 42.55 ozs. The best of any of my set ups is 1to1 thrust ratio. So nothing insane I had a AT SU 27 and ran those 3400 kvs in and it would do about 65 so it is not impossible to get it flying. You can always build it up weigh the AUW and then measure thrust 2/3 to 3/4 to 1 and it will fly. Sooo I know for a fact because my SU weighs 28ozs. right now and has 20 ozs. of thrust and flys not a barn burner but it flies.
May 29, 2009, 07:48 PM
On the Edge of Space
dLdV's Avatar
Yeah DA, that's what I'm hoping for, thrust to weight 1 to 1 or a little less. This field is crazy to land at with a heavy, low drag plane. You have to swoop down after clearing the trees and while you try to bleed off speed this ground layer wind lifts the plane back up and it wants to sail into the neighbors yard. If your plane is too fast you end up just constantly turning during the flight and it gets kind of boring/nerve wracking. Thanks for the comparison with the SU 27.
Jun 29, 2009, 06:45 AM
On the Edge of Space
dLdV's Avatar
TIK, finally tested these motors. I tested both running at the same time. 300W on 3S 2200mAH 30C (fresh charge). This seems to support the vendors spec of 144W / motor. That's about 150W/lb. so it should at least fly in theory. Just need to hook up main gear and elevons and let 'er rip.
Jul 03, 2009, 08:05 PM
On the Edge of Space
dLdV's Avatar
Finally flew it, used gyros for roll and pitch axis, so it was very stable. Hand launch was no problem. It was slow, maybe 40 or 50 mph I think. It needs more elevon throw because it wouldn't make a turn to fit our little field and got treed. Easy fix, it's only in 3 pieces. Soo... removing landing gear, kicking up roll throw, and rolling straight thrust tubes, then it should suit the field. Try again Sunday. True statement Dark Angel, you don't need 1 to 1 power to weight.
Last edited by dLdV; Aug 11, 2009 at 10:05 PM. Reason: Emphasize "used gyros"
Jul 08, 2009, 08:13 AM
Registered User

Finally flew mine...

Ok so I was going to do a whole thread but just haven't the time!
When mine arrived here in the UK, I built it up. After charging the battery and hooking everything up, I spooled up the motors and the right ESC when pop and smoked!

Not too worry, I got onto live support and they said they would send through a replacement ESC for the burn't out one. Shortly after, a package arrived with two ESCs fully wired up and ready to go! Nice one Pete!

Now I couldn't see a way into the bird without breaking out the knife. To be sure, I used the Live Support again and they confirmed I would have to make cuts.

I have several points to make here. Firstly, the motor hatches are bonded as well as screwed on. It's best to use a razor blade to break the bonding (be careful not to cut through the servo wires or ESCs). I managed to snap both of my hatches but a little 5 minute epoxy puts them back together. Now to cut.

I cut across directly where the ESCs are and up along a natural line about 5 inches, back across and down to the ESCs.

I have decided to use some magnets i have hanging around from a broken outrunner to hold the flap on so if i need to repair in future i can get in there no hassles! Pete at Banana Hobby, if you're reading this - perhaps you should include this as a revision on the production plane....? I have pictures if you want.

Anyways, got it all together. Almost time for test flight. I just bought myself a DX6i TX and RX so I thought i'd take out the Blitz Gear and pop that in. The Blitz radio gear probably works fine but I wanted to make doubly sure that there were going to be no technical problems at all.

After fiddling for what seemed an eternity to figure out how to Mix the servos properly, it was time for the test flight.

Unfortunately, the combination of grass + low lipo power made take off hard. It needed the best part of 100 yards to get off the deck and I only got a few circuits out of it before the motor started to slow up so I landed it. One thing that does strike me is that this beast floats really well. It is my first EDF and my first take off and landing from tera firma and all was fine. The next flight is going to be speed testing to see what it's like at full charge.

It was definately quick, even with a low battery. That day, I was just happy to have got it set up, flown a few circuits and got it back down in one piece.

Although it was a slight inconvenience having to wait for replacement parts and cutting into the bird. I would say that it has been a good experience. I now have a better understanding of the layout of the plane and can swap out bits and pieces without hassle. I would also add that Banana hobby gave me excellent customer service. I had to pay a lot and wait along time for USPS to get their butts in gear to get it shipped over but it was very much worth the hassle. I just wish that I lived in the States now so I could get some of the other goodies on Pete's website!
Last edited by TheD; Jul 08, 2009 at 08:20 AM.
Jul 08, 2009, 11:34 AM
On the Edge of Space
dLdV's Avatar

Way to go D.

Hey D, glad to hear you finally got it in the air. Fried a speed control but they replaced it, yeah. Thats 1 in the minus column and 1 in the plus, so I guess its a wash for BH's rep. Do you know what the setup is for that version; Kv, fan type, battery, total watts? I put mine in a tree, insufficient roll throw (gyros both axiseseses), fixed it and flew again. It has 3600Kv six blade 64mm fans, 3S 2200 30C battery, and 20A ESC's, about 280 total watts. It's too slow, 30-35 mph (revised down from earlier estimate of 40-50), so just bought 4300Kv motors and 40A ESC's capable of 4S battery if needed, for a retrofit. Should be much better next time out. BTW, have any idea the weight of your craft?
Last edited by dLdV; Aug 11, 2009 at 10:08 PM. Reason: Point out gyros were used - do not try this at home