WW II BOMBER ->XB-42 Mixmaster-WITH CONTRA ROTATING MOTORS-1,72 M. WINGSPAN

[CESARNOGUEIRA]

Pusher contra rotating-> how to do it?
I´m in the meddle step of a XB-42 Mixmaster bomber full depron construction.

It will be motorised, as the rela one, with 2 contra rotating motors.

My calculations shows thata it will have a AUW of 2,5 Kilos.

My questions, if somebody could kindly help me :

1)A contra rotating motor set wit 1.320 grams will make it take off from a grass
runway?

2)The Xb-42 is a PUSHER bomber, how should the contra rotating electric motors AND PROPELLERS BE POSITIONED AND ADJUSTED?

YHANKS A LOT FOR THE HELP, WATTFLYER IS A PLACE FULL OF VERY KIND FLYING PEOPLE !

[gramps2161]

I can't help with the contra rotating props, but that is a sharp plane I haven't seen this one.
Someone will post up a answer to your question. Hope you continue to post your progress on this unique looking plane, and welcome to WattFlyer.

[pmullen503]

The front of the propellers should be facing the front, whether pusher or tractor. The labels (if they have any) on the props should face the front of the airplane.

At just over 50% thrust to weight you may have difficulties on the grass. You motor choice is a little small for a 1.7m plane.

[Wildflyer]

HobbyKing has (or at least had, I haven't looked at them lately) contra rotating motor units. Some of them are quite powerful.
I believe they are one motor with a hollow shaft driving one prop, and the other motor drives through the inside to power the other prop
Good luck, hope this helps

[CESARNOGUEIRA]

At just over 50% thrust to weight you may have difficulties on the grass. You motor choice is a little small for a 1.7m plane.[/QUOTE]


Do you guys know any other contra rotating motor with more power,please ?

[pmullen503]

Originally Posted by CESARNOGUEIRA

At just over 50% thrust to weight you may have difficulties on the grass. You motor choice is a little small for a 1.7m plane.

Do you guys know any other contra rotating motor with more power,please ?[/QUOTE]

http://www.hobbyking.com/hobbyking/s...dProduct=16618 560 watts. That would get you close to 100w/lb.

[CESARNOGUEIRA]

Continuing building:

All fuselage and wings ribs already glued.

In order to have a stronger vertical & horizontal fin, it´s built with 3 layers of depron, and depron ribs.

A fuselage panel test was glued with another glue (´till now was glued with hot glue, applied with a gun) and it seens pretty strong.

Fuselage will be reinforced with 2 wood or fiberglass stick, both sides.

A BIG problem seens to be the L.Gear, cause original plane had a very complicated LG system.

I´m thinking about try the HK L.Gear designed to the F4u Corsair (wheels turns 90 degrees togheter with the 90 degrees of the whole L.G.)

Any ideas?

[pmullen503]

Not sure that 90 rotation is needed. Your retract unit will need to mount at an unusual angle. You should build a mock up of that section and see if you can find an angle that works. It may not be possible to exactly get scale function with a 90 degree retract unit - rotating or not.

If I had to guess you'll need to mount the units at say, 45 degrees to the vertical plane near the center so the retraction is backwards and in toward the center line. Make the gear doors and openings to fit. You may have to add rotation too but I'd see if you can make it work without. Tough to figure out without a 3d cad model.

Look at how folks have done F-16 landing gear. It has a similar motion.

[CESARNOGUEIRA]

Originally Posted by pmullen503

If I had to guess you'll need to mount the units at say, 45 degrees to the vertical plane near the center so the retraction is backwards and in toward the center line. Look at how folks have done F-16 landing gear. It has a similar motion.

I made my first attempt to draw something in Google Sketch and (SORRY for the low qualqity...) got this rough drawing.
Do you mean something lie this?

[pmullen503]

Can't really tell what I'm looking at from your drawing. Here are some I did in Sketchup from different angles. Shows extended and retracted positions. Note that there is no rotation of the strut, just a simple 90 degree retract.

[CESARNOGUEIRA]

pmullen503, THIS WAS FAR, FAR better than I could expect from Wattflyer friends, THANKS A LOT, FRIEND!

Yes you are correct!

The secret is place the LG right in the middle of the fuselage, at 45 degrees,
as your draw shows clearly.

This way when retracted, it will be completely enclosed by the fuselage!
So simple and so close to the real plane!

Thanks a lot!!!!

[CESARNOGUEIRA]

Originally Posted by pmullen503

Do you guys know any other contra rotating motor with more power,please ?

http://www.hobbyking.com/hobbyking/s...dProduct=16618 560 watts. That would get you close to 100w/lb.[/QUOTE]



pmullen503, what would be your choice, this one with 560 watts (close to 100w/lb) or this one -> The Himaxx CR3516, with 10 oz weight,
3 cells, 1030 Kv, 800 W ?

Thanks again

[pmullen503]

The HK CR motor is only $30. I'd be tempted to try that before I drop $199.

560 watts should be adequate, better than 375 watts in any case.

[CESARNOGUEIRA]

Originally Posted by pmullen503

The HK CR motor is only $30. I'd be tempted to try that before I drop $199.

560 watts should be adequate, better than 375 watts in any case.

Do you think it will be able to take off from grass field with 560 Watts ?

[CESARNOGUEIRA]

First test of wing in the base.

As told before, still needs some refinement (sanding).

One thing became clear to me-> if you cut a REAL CLARK Y, the bottom of the profile isn´t flat, is curved.

But in this size, the depron simple make it become completely flat.

So, with a 1,72 m wingspan depron wing, follow the KISS philosofy (Keep it simple, stupid!) and simply make your profile with a flat botttom...

In order to distribute forces in a grass field landing, the losangle reiforcements have been done.

My Dremel will arrive, after this I´ll cut the reinforcement glued in a wrong place (it must have a reiforcement in the CENTRAL depron piece, but the asshole who writes this info right now glued it in other psition...

One more Dremel mission: cut some holes in the wood structure.

[CESARNOGUEIRA]

METAL FINISHING:

For some time I´ve been studying Carl Bachhube´s Rc models, in my humble opinion, a genius of designing and assemblyng Giant Scale RC planes.

I just think he is not a fan of electric planes , using exclusively internal combustion engines, and this makes their models more cumbersome and difficult to fly if compared to electrics planes.

It is clear that they need to fly faster than scale and that there are often imbalances in power between the various engines, pulling the plane from one side to the other in flight.

If electrics they would be much more reliable in what concerns to breakdowns and symmetry of thrust and even could make use of sound synthesizers with the real sound of the Pratt & Whitney radials ...

But, back to-finish.

Carl Bachhube opens the game-> uses CHROME POLYESTER ADHESIVE FILM, like those sold by certain visual solutions companies .

Can be found in the internet and are very cheap.

I think I'll test it in the XB-42, but surely will not have the quality of work of Carl´s planes, because depron sufaces will never be as smooth as the balsa wood sanded and filled with magic filler.

But I think it will be more or less satisfactory.

See what a wounderfull work Carl did here and in the picture also:

[CESARNOGUEIRA]

After a LONG PAUSE I´m back.
Now I´m working on the nose, using depron slices glued and sanded.
Almost get the right shape, but need yet some trim.

[xmech2k]

Glad to see you're back at it. I love the rare birds! Maybe one day I'll get my act together enough to start building my own. Can't wait to see your model progress and fly.

[pmullen503]

Good! I was hoping to see more progress.

[CHELLIE]

Originally Posted by CESARNOGUEIRA

After a LONG PAUSE I´m back.
Now I´m working on the nose, using depron slices glued and sanded.
Almost get the right shape, but need yet some trim.

Glad to see you back the $30.00 contra motor as recomended by Pmullen, with a 4 cell lipo will make your plane leap off the grass, you can always throttle down after take off, but for take off, you will have more than enough power with a 4 cell lipo, and i think you will need the weight of a 4 cell in the nose to help balance the planes CG because the motors is in the back of the plane, just my 2 cents worth Take care and have fun, Chellie

[CHELLIE]

Also, make the motor mount adjustable so you can adjust some down thrust into the motor if needed to load the wing if the plane wants to porpoise in the Air.

http://www.wattflyer.com/forums/showthread.php?t=39483

http://www.wattflyer.com/forums/showthread.php?t=39733

maybe some of my Scratch built planes might give you some ideas that you can use in your build.
http://www.wattflyer.com/forums/show...652#post715652