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Oct 25, 2008, 04:43 PM
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Rittinger B-25 for twin Speed 400

Sharing a few shots of this nice little Navy variant B-25 solid nose transport originally constructed by Jim Emery from plans by Mark Rittinger. Yes, thatís all balsa and flat paint you're looking at. Iím now its trustee and after installing a new elevator servo, fixing one stripped aileron servo, getting the motor electronics installed and doing a bit of paint work, itís ready to take to the air once again.

Span is 42Ē and all up weight is 32 ounces. Motivation is provided by a pair of Speed 400 7.2V brushed motors turning APC 6x4 E props on direct drive. Energy is via a 2S (7.4V) 2100 mAh ThunderPower Lipo, feeding a Kontronik Sun speed controller (a sweet deal from the NSP $10 grab box at the recent NEAT Fair!). 7.4V is a significant voltage drop from the 8.4V (or pushed to 9.6V) this bird might have flown with back in the days of round 1.2V NiCad cells, so a really firm throw on launch is planned to get it quickly up on step. Eventually I'll paint out the props in black with yellow tips and do more detailing.

I am tempted to convert this beauty to brushless motors using inexpensive inrunners and ESCís sourced from United Hobbies, but I love the simplicity of a dual brushed set-up and have to go that way first. I am cautiously optimistic that the brushed performance is up to my modest expectations. I'm not looking to tear-up the sky.

Here are a few shots. Will maiden on a nice calm day. Soon, I hope.

10/28 Update: Thanks to some good feedback from Mark Rittinger (see comments section), this will be taking flight on 3S LiPo power and 5x5 props. Mark is correct, available thrust and throttle management is better than underpowered.

01/10 Update: Added current photograph

01/28/09 Update: Made conversion to brushless power.
Last edited by SPasierb; Dec 28, 2009 at 12:05 PM.
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Oct 25, 2008, 05:02 PM
Der Flieger kommt schnell
WWIFlyin'Ace's Avatar
really nice.
good luck on your maiden
Oct 25, 2008, 08:22 PM
Gravity sucks.
mrittinger's Avatar
Nice work. I suggest 5/5 APC props and 3s 2100 Lipo. The 6/4 2s won't cut it. I have tried several setups since the lipos came on strong, and the 3s with 5/5 or 5.5/4.5 works best. You need about 25 to 26 amps static. The props will unload about 10 to 15% in the air, so you will be OK.
Good luck!
Oct 25, 2008, 09:52 PM
What the Pfotenhauer?
B Rocka's Avatar
Very Cool!
Oct 25, 2008, 10:31 PM
Team PowerBox Systems
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Thanks for the information! I didn't want to cook the motors, so I'm glad to hear I was way too conservative. I have both the 5x5 and 5.5x4.5 in the shop -- what ones were your favorite???? Plenty of 3S packs, so that's an advantage too.
Last edited by SPasierb; Oct 25, 2008 at 10:39 PM.
Oct 27, 2008, 11:23 AM
Gravity sucks.
mrittinger's Avatar
5/5 seems best all around, but it depends on your style. Either will work OK, but the 5/5 pulls a little less amps.

Nov 02, 2008, 02:54 PM
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It's a winner!

First flight was this morning. Fantastic all around. Big thanks to Mark for the power recommendations.

Left my hand level and fast, actually suprisingly fast on the 3S + 5x5 combo. Most of the flight was at 1/2 throttle and it grooved nicely. Without the ability to feed in rudder coordinated with aileron, it fights the turns a small bit -- those twins want to keep moving forward. Overall I was very happy.

Tame stall. Actually glides pretty well with power off. My landing was a bit too hot -- now I know I can slow it even more in the future and flare a bit before touching down. Very happy to have a fun flight and bring it home in one perfect piece!

I used a ThunderPower eVolution battery @ 2200 mAh -- as a 25C with burst to 50C, it came out of the plane barely warm. I'll be mindful of pushing the 7.2V brushed motors too hard. Looking foward to more flights.

- Steve
Last edited by SPasierb; Nov 02, 2008 at 03:02 PM.
Nov 03, 2008, 06:25 PM
Gravity sucks.
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Good to hear, I knew that setup was the buggers behind
If you want to slow it down a tiny bit, swap to 5.5 x 4.5 APC, but be mindful of the amps. Figure about a 10-15% unload in the air. I've used 25 amp ESC's without problem so......
THe 7.2's a about $4.00 now, so don't worry TOO much about them.
I still get good performance from them by simply adding a drop of oil to the bearings, and blowing the motors out after each flight with a Com oil the car guys use. The Quadzilla is still yanking 460 watts from 4 7.2 motors. Just require a bit of care , that's all.

Now, gotta see a nice flight shot!
Dec 28, 2009, 12:02 PM
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Well Mark you were right. I got a good season out the Speed 400 motors. One finally gave up the ghost.

I had a pair of Mega 16/15/5 motors without a home, scrounged up two Thunderbird 18 ESCs from the parts box and married those to APC 6x4 props. It was a whole lotta fun fishing the ESC receiver leads through the wing back into the fuselage!! According to the Medusa meter, full throttle draw for the pair is 29 Amps. Man, does it have more thrust! Full throttle will not be necessary.

While I was at it, I changed the radio to an AR6200 receiver to have the redundancy of the extra remote receiver.

Still loving this bird.

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