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Jul 23, 2012, 11:47 AM
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Build Log

B2 Stealth Kfm2 53 inch span B-2 Bomber


B2 Stealth Scaled from 10 inch plastic model B-2


This is a new design and has not been test flown yet.
You might want to wait until after the maiden flight before building.

This is not a “new flyer plane” but is for an experienced pilot.
Now that we have that out of the way here are the details.

Wing Span 53 inches
Length 20 inches
AUW 29 ounces

I wanted a simple B2 with drag rudders.
That in itself puts a new slant on “simple build”.
The design ended up with 8 servos but they are small and light
and makes linkage setup a cinch.

If you are looking for a simple build and easy to fly plane try my Wing1 thread.
The Wing1 was designed from the same plastic model as this B2
and it has been test flown several times. It is a very nice flying plane and reasonably fast.
It is simplified with only 2 servos and one simple set of elevons.

The back side of the Wing1 does not look like a B2 and it is without drag rudders.
So that one is really simple. Wing1 served as a proof of concept for my
new B2 with drag rudders.
Last edited by jjr2001; Jul 23, 2012 at 02:23 PM.
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Jul 23, 2012, 11:48 AM
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jjr2001's Avatar
B2 with drag rudders Parts List

Blue Core Fan Fold Foam or 6mm Depron
3/4 ounce fiberglass cloth and a can of WBPU
Turnigy 2836-3200 motor
Castle T-Bird 54 ESC
2200 to 2600mah 3S Lipo (as much C as you can get)
4.1x4.1 prop to start (pulls about 35 amps full charge)
4.7x4.7 prop for later testing and speed runs
6 - HXT 500 servos (two for each drag rudder, one for each of the small elevons
2 - HXT 900 servos (one for each of the large elevons)
2 - 1” wheels (mains)
2 - 1/2 or 5/8 wheels (nose)
4mm carbon fiber tube (light duty is fine)
5/64 piano wire for Landing Gear
3/64 piano wire for push rods
1/16 plywood

The pdf files contain the drawings with dimensions.
I did break out the KFm2 top blue core pattern so you can see it more clearly.

The complete pdf is quite busy but you can build the entire plane from it.
Print the pdf at Office Max in black and white.
Transfer that to a piece of poster board.
I then fit the poster board on top of the blue core and punch large t-pins in every line intersection.

After the entire side is punched I draw lines on the blue core using t-pins in the holes
and a ruler to put the lines on the blue core.

Make another piece using the same template but face down
on your other blue core blank, punch the holes, and draw the lines.

You now have a left and right side. Use Gorilla glue to glue them at the center to make the main wing.
Careful with the GG. Use just enough but not too much.
I will “rake” the joint after it starts to foam and pull off the excess,
then at about 30 minutes do it once more.
Use the same process to make the KFm2 sheets but don't glue them together.

Cut in the channels for the carbon fiber spars. Install the CF spars, GG or epoxy.

You are now ready to gorilla glue the two KFm2 pieces to the base or main piece.
Use a lot of small weights after you apply the GG. I spread it fairly thin
on the KFm2 piece and then dampen with a cloth the main wing.
Place them together and weight them down.
I like to do one KFm2 at a time, let it cure and then do the other side.
Now that you have the main wing together you can rout in the channel for the servo wires.

Add the plywood pieces for reinforcement.
Use light weight spakle to fill any dings or voids in the foam surface.
Form the control surfaces (I used Balsa Aileron Stock).
Form the tapered leading edge and the wing tips, sanding block with 60 and 100 grit.

If desired cover the entire wing with 3/4 ounce fiberglass and wbpu.
Four coats of thinned wbpu. (40% water)
If you are not going to use the glass then give it at least 4 coats of wbpu
to seal the foam if you are going to use oil based Rustoleum paint.

Mount the control surfaces with either pin hinges or CA hinges. (I use epoxy with CA hinges on foam).
Control horns should be the same length as the servo control arms, I made mine from 1/16 ply.

Both Drag rudder servos on each side are wired together by
soldering the servo leads and burying that in the channel.

When placing your drag rudder servos you need to test the servos on each side.
I tape them together and attach the control arms to make sure they are moving
in the right direction to open the drag rudders.

Remember that with drag rudders only one side will open at a time.
That is:
Right rudder opens the right drag rudder and does not affect the left.
Left rudder opens the left drag rudder and does not affect the right.

The push rods are made with a “jog” for adjusting.
Simple Z-bend on each end of the pushrods. I make the pushrods up and
fit them to the control horn and servo arm and THEN mount the servos with epoxy.

I always punch holes in the blue core under the part I am epoxying in so epoxy enters the foam.

You will need to do some TX programming.
The large elevon and small elevon are wired together by soldering also.
I am using 5 channels from the receiver.

Left elevon
Left drag rudder
Right elevon
Right drag rudder
Throttle

For the Futaba T8FG I have set up the following:
Function Menu
_______Ctrl_____Trim
1 Ail ____J1______T4
2 RUD2_ --_______T1
3 THR__J3_______T2
4 RUD__J4_______T1
V1 ELE_J2________T3
Note that I use Reverse Trims.

For normal trims:
My trim____Normal Trim
T4_________T1
T3_________T2
T2_________T3
T1_________T4

Model Type_____Airplane
Wing__________Flying Wing
2 Ail
Rudder________Winglet

TX channels
1 and 6 Ailerons (Elevons)
2 and 4 Rudder
3 Throttle

Under Model Menu
Winglet
Rudder ____+0_____+120
Rudder2____+120___+0


Maiden Flight to follow.......Hopefully soon.


Initial setup:
Elevons are set with a bit of reflex. About 3 or 4 degrees up on all elevon surfaces.
Drag Rudders are set about 5% open. With luck she should fly.
Last edited by jjr2001; Jul 24, 2012 at 08:01 AM.
Jul 23, 2012, 11:18 PM
skumgummi dave
Good looking drawings. Looking forward to flight results.

Dave-
Jul 23, 2012, 11:31 PM
Zen in the art of foam
djacob7's Avatar
Looks like a very nice design and a thorough job too! Good luck on the maiden!
Jul 24, 2012, 05:28 AM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
I think you’ll find by opening both drag rudders simultaneously , that alone will stabilize the wing in yaw... With opening either one or the other , it will induce a wig wagging sorta’ yaw... needing constant correction ... JMHO...
Latest blog entry: Lost plans
Jul 24, 2012, 09:47 AM
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jjr2001's Avatar

B2 Maiden Video


Thanks for all the nice comments guys.
I added the initial setup control throws at the end of the first post.
Here is the Maiden video:

B2 Stealth Bomber RC Model KFm2 53 inch wingspan Crash Landing Limited Damage (3 min 49 sec)
Jul 24, 2012, 10:07 AM
Registered User
Dickeroo's Avatar
Congratulations. That is a beautiful aircraft that flies extremely well. You did a tremendous job with this build.

~ Dick
Jul 24, 2012, 08:10 PM
Zen in the art of foam
djacob7's Avatar
Excellent job and thanks for sharing!
Jul 25, 2012, 01:51 AM
Registered Plan-a-holic
Hepdog's Avatar
Nicely done! They do tend to be a bit of a bugger to land.....
Jul 25, 2012, 06:25 AM
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jjr2001's Avatar

Improvements to the B2


Thanks again guys for all the nice comments.

While being a challenge to land so far, I think it is well worth it.

In the single flight so far I did not see any large value to the drag rudders except for stabilization.
They seem to roll the plane as much as the elevons without inducing yaw.

I could save about an ounce of weight by removing the 4 servos for the drag rudders and
just fixing them open 5 or 10 percent. I will know more after today's flight.

On the first "landing" or should I say "crashing" the nose gear bent and I took out one of the bottom drag rudder servos.
The nose gear has been improved and I added a piece of CF near the lower control horns on the drag rudders to prevent servo damage.

The next landing should be better.

Cheers, JR
Jul 25, 2012, 02:23 PM
12th Pursuit Squadron
TheAeronut's Avatar
Landing might be easier if you were to open both drag rudders simultaneously as airbrakes. This would allow a steeper descent that could be controlled with a bit of power and might be a bit more stable too. Just a guess on this project, but I have had planes that respond well to adding a bit of drag for landing.

J.P.
Jul 25, 2012, 02:35 PM
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jjr2001's Avatar
Quote:
Originally Posted by TheAeronut
Landing might be easier if you were to open both drag rudders simultaneously as airbrakes. This would allow a steeper descent that could be controlled with a bit of power and might be a bit more stable too. Just a guess on this project, but I have had planes that respond well to adding a bit of drag for landing.

J.P.

Thanks JP. It is surely worth a try. I can put in a mix to one of my sliders and give that a try. Great Idea.

Cheers, JR
Aug 04, 2012, 04:57 PM
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jjr2001's Avatar
Quote:
Originally Posted by TheAeronut
Landing might be easier if you were to open both drag rudders simultaneously as airbrakes. This would allow a steeper descent that could be controlled with a bit of power and might be a bit more stable too. Just a guess on this project, but I have had planes that respond well to adding a bit of drag for landing.

J.P.
I did add a mix for using the drag rudders as air brakes and it does make landing easier. I will try to get a fresh video up.
Aug 14, 2012, 12:49 PM
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jjr2001's Avatar

B2 Stealth Bomber KFm2 53" span Landing Gear included


http://www.youtube.com/watch?v=l2LUZjmS5-E

Landings are better with the drag rudders full open as they were in this little
Hat Cam video.

Cheers, JR
Aug 14, 2012, 01:50 PM
Registered User
Nice job, that thing is sweet!


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