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Swappable B25 Twin-Engine Mitchell Bomber

Mid7night

Jetman
Mentor
#21
View attachment 86694

Got her maidened today at Flitefest. No video yet but it flew pretty nicely. Looped and rolled without any difficulty. No video yet, but maybe tomorrow.
Hey, I think I threw that for you! I really wish I put faces/names/forum-names together better, I had no idea that was your plane when I met you. >_< :p

It flew like a champ, beautiful in the air!
 

SlingShot

Maneuvering With Purpose
#22
Hey, I think I threw that for you! I really wish I put faces/names/forum-names together better, I had no idea that was your plane when I met you. >_< :p

It flew like a champ, beautiful in the air!
Thank you and thanks again. Yes you chucked the maiden I think. Then I threw one and scared myself. Then Tim threw one. After that I got good tosses on my own. :cool:

Edited: I think I have that backward. Tim threw first.
 
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SlingShot

Maneuvering With Purpose
#23
Summary &amp; Review

Firstly I would like to thank Ultramicrobe for doing the plans. It's a nice plane. I will build another.

Summary: This was my first experimental/beta build and only my second scratch build. First bomber, first multi-engine, and the biggest power plane I had ever built or flown. I thought it flew very well and looked majestic in the air. The beefed up wing was strong and handled the stress of aerobatics well. Some complained of tail heaviness. Mine was actually flown a little too nose heavy.

Build: just a couple of minor issues with the plans that were easily dealt with as earlier descibed. With the benefit of hindsight, the asymmetric elevator should have been handled differently. I should have copied the big half. That would have looked better as well as given more elevator area.

The tail is a little flimsy and I'll do something about that next time. Upon unpacking for final assembly, I noted that one side of the horizontal stab was a little droopy. I glued a medium sized craft stick to the top to splint it, and that remedy brought it back square.

For the wing, I cut down a heavy duty 5 gal. paint stirrer to match the foam spar and glued it the leading edge side of the foam spar. A regular sized paint stirrer with the handle part cut off was also glued to the spar. This was for landing gear as well as for additional strength and support. The wingtips were each reinforced with BBQ skewers at the leading edge score cut.

When it came time to join the wings, I pumped in a lot of hot glue and split another craft stick to use as a joiner at the spar. I then closed up the center section of the wing using several small pieces of fitted foam. I guestimated 50% dihedral. Tape as usual.

I eliminated the rudder and I moved the elevator servo forward. This helped with managing the CG as many had complained of tail heaviness.

It was supposed to have differential thrust but I couldn't get it configured so I grabbed a Y-harness in order to fly it.

It flew well. Loops, rolls and Cuban Eights looked pretty good. I did a sloppy 4 point roll that added negative g with no problem.
(2) 2200 3s's provided plenty of juice and ballast. My motors provided about 15% more power than a C pack.

We took no video :( I hope some shows up.
 
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SlingShot

Maneuvering With Purpose
#24
Great video of Josh Bixler enjoying Mid7night's A-4. It's also cool for another reason :cool:

With permission Ben. The B-25 has a prominent supporting role in this video:p



At:
0:45 you see the big white bird rolling onto her back ready to pull through;
1:17 an appearance (of several);
1:39 initial attack run on the A-4;
1:45 high, top of screen pulling hard while still maintaining energy advantage;
1:55 you can clearly see the B-25 SS pulling lead on the A-4.

Edited: If you don't pause it and go frame by frame at the time marks, you'll probably miss most of it.
 
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SlingShot

Maneuvering With Purpose
#26
motor.jpg

I final word about the power plant used. When I got home and checked my motors I realized that I had been flying the B-25 with stock C-Pack motors. This contradicts what I told many people. I am sorry. I had some larger 80 gram motors that I had originally planned to use and I somehow forgot that I had scaled back :eek:

Also they were 9" props. 9050 three bladers that were pretty soft. I forgot to pack the ESC's so I bought some from the FT store. Next generation.....very small 30a.

All in all, the thrust, weight and drag combination was very fun to fly. If it cruised along at 45-50 mph it felt like it pulled hard straight up at about the same speed. Delicious torquey goodness.
 
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#27
I finally build my b-25! It is almost done, material is 6mm depron.

IMG_20170708_180223 (Large).jpg

Maiden flight was little bit scary because of heavy tail :D but now it is ok, and fly very well.
Motors is 1060kv D2808, 30A ESC and 9x7 props, 9 gram servos, and I use 2200mAh 3s battery
Wing dihedral is just a bit.

IMG_20170708_010720 (Large).jpg

IMG_20170708_134546 (Large).jpg
 

SlingShot

Maneuvering With Purpose
#31
View attachment 100641

Ready to maiden. Time to find out if I can get the same good flight characteristics that I attained with my first one.
Haha. Over a year later, and I finally got around to flying this thing. The verdict is in: having flown 2 of them, I can safely say that it is a great airplane. It as an absolute delight to fly, and with a 60" wingspan it has good size, stability and presence in the air.

Like the first one, I doubled up the wing spar with a cut down 5 gallon paint stirer. This one is slightly heavier, and in the future I will try the techniques to remove the hard to remove paper. It still has good power with the C pack motors carrying two 2200 mah 3s batteries. I plan to try twin 1500's and 1800's to fly it a little lighter.
 
#32
Wow, its cool to see so many version of this plane and so many nice upgrades. I have to admit when I set up this thread not much happened at first and I sort of stopped looking at it - for years! Nice work all around and I am glad to hear the outcome is generally pretty good. I thought the plane was a delight to fly - pretty easy to control for a big twin. I agree with the idea of skipping the rudder and doing differential thrust. The rudder is a bit of a technical nightmare, probably a better way to do it but I wanted to avoid 2 servos.

I actually went the route of doing differential thrust and no rudder on a different design I posted later. Sorry, this is off topic, but if you like the B25 you might also want to look at this one, it is a mini-Lancaster and I thought it was even more fun to fly and its also way easier to build, which is pretty surprising for a quad motor bomber. Anyway, if anyone is interested it is hard to find by searching because it is pretty old but it is here:

https://www.flitetest.com/articles/swappable-lancaster-bomber-with-fpv-bombsight

Happy flying.