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Author Topic: XB47-D  (Read 1167 times)

Offline skyshark58

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XB47-D
« on: June 03, 2007, 09:39:07 AM »
This is my Boeing XB47-D built from 1958 Model Airplane News plans. Power is from two OS15FPs with throttles. It has working nose wheel brakes and drag chute. It uses a Roberts control system. It took third place last week at the Northwest Regionals in Eugene Oregon. Flys fast and lands hot.    Mike
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Offline Bill Little

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Re: XB47-D
« Reply #1 on: June 03, 2007, 11:02:31 AM »
That is a great looking model! 

I have seen plans on the 'bay that look like that.  I wonder if they are the same......

I am interested in how you rigged the two throttle controls off the Robert's unit.  I have played around with the idea of three 90* cranks driven off the third line arm.  Am I way off in right field??  Pictures (heck, even sketches) would be great.

Thanks
Bill <><
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Offline skyshark58

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Re: XB47-D
« Reply #2 on: June 03, 2007, 11:41:45 AM »
Thanks.  I came off the Roberts bellcrank forward to two 90 degree bellcranks. One for the left engine and the othe to reverse direction and work the right engine. These 90 degree bellcranks were hooked to RC type flexi cable down to the engines. The front brake works off of a push rod tied to the down elv rod then to a 90 degree bellcrank with a rod running vert. down to the wheels pushing down stopping them.    Mike
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Offline Dennis Adamisin

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Re: XB47-D
« Reply #3 on: June 03, 2007, 11:41:59 AM »
skyshark:
CONGRADS on a great project!  CLP**  BW@

Sounds like the drag chute and wheel brakes came in handy too.  You said it flies fast - would you characterize it as easy/stable - or a handful - to fly?

Ditto Bills question too.  That sounds like a serious bit of pushrod routing.  ???
Denny Adamisin
Fort Wayne, IN

As I've grown older, I've learned that pleasing everyone is impossible, but pissing everyone off is a piece of cake!

Offline chuck snyder

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Re: XB47-D
« Reply #4 on: June 03, 2007, 04:48:20 PM »
A minor simplification to the twin engine control linkage is a method I used on a profile X-F-5-F several years ago. I drove the throttle bellcranks off the third line rather than the output arm of the main bellcrank. It is already moving spanwise.

Are there any photos on the web of the other models from the Northwest Regionals?

Chuck

Offline skyshark58

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Re: XB47-D
« Reply #5 on: June 03, 2007, 05:37:01 PM »
The throttles do work off of the third line, the brakes work off of down elevator and the drag chute off of a fourth line. What makes it hard is the engines are very low and the bellctank is on CG high in the fusalage.If I were to build another I would put the bellcrank much lower and run the leadouts under the wing. With this set up I think electric throttles would be the way to go. I tried to build it close to the plans as I could.     
I had to add two oz. of tip weight and three oz of nose weight for trim. It flys about 60 mph and lands at about 30 mph. Flys pretty stable but could use a better elevator control set up than was used per plans.   Mike
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Offline Paul Smith

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Re: XB47-D
« Reply #6 on: June 05, 2007, 06:14:53 AM »
skyshark:
CONGRADS on a great project!  CLP**  BW@

Ditto Bills question too.  That sounds like a serious bit of pushrod routing.  ???

I've talked to several successful two-engine scale flyers.  They all tell me that the method of choice is a big-diameter (maybe .5") rotating tube with three control horns soldered onto it.  One in the middle for input from the Roberts unit, and one at each engine. 

The same system could do four, assuming the engines are pretty close to "in a straight line", as in B-24 or B-29.
Paul Smith

Offline Trostle

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Re: XB47-D
« Reply #7 on: July 09, 2007, 12:05:53 AM »
I am not trying to hijack Mike's thread or to sidetrack any attention to his really neat version of his XB-47D.

I have finally figured out how to post pictures, so here are some photos of my 1/2A Profile Scale of the same airplane.  This was built several years ago for a contest in Southern California for 1/2 A profile scale models.  It has had some success here in the Southwest where there have been some profile scale events.  Sort of an afterthought, I took the airplane with me to the 2000 Nats where I competed in the Precision Scale event (with another airplane) and entered this 1/2A model in the Profile Scale event there.  (That is the year that Chuck Snyder won Profile Scale with his really neat DeHavilland Hornet, later published in Flying Models.  Chuck's Hornet, in my opinion, sets the standard for what profile scale can be.)  This XB-47 placed third which was a pleasant surprise. 

Some particulars on the model:  1/36 scale, (1" = 3'), works out to be about a 39" span and 36" length.  About 180 sq in and 28 ounces.  Power is by two Norvel .049 Big Migs with throttles.  It uses the Roberts control system with all of the controls inside the model structure, except, of course, the leadouts.   (Getting the bellcrank inside the swept wing of a relatively small 1/2A model was a bit of a challenge.)

The photograph shows the flying propellers and spinners.  For display, it has similar spinners, but has the 4-blade propellers.

A lot of ideas were taken from the Robert Parks article and plans in the May 1958 issue of Model Airplane News.

I need to apologize for the quality of the photos.  I will try to do better in the future.

Keith


Offline Balsa Butcher

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Re: XB47-D
« Reply #8 on: July 16, 2007, 11:35:23 PM »
For those who don't wish to design their own system Brodak sells a "Carrier Kit" (BH-400) which includes bellcranks and hardware to set up throttle control on a twin.  Although intended for the Roberts/Brodak Grumman Tigercat I'm sure it could be used on other designs. 
Pete Cunha
Sacramento CA.
AMA 57499


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