Long Fuselage problems
 

Ok I am looking for some advice.

I am building a Dorneir Do 335 with an 81' wingspan, this is bigger than anything I have ever built before and I am finding out that my fuelage is longer than any premade control linkage. I am a little out of my comfort zone when it comes to creating one off control linkages considering the stress these linkages might face. I do not want to move my servos closer to the tail, this plane already has issues with tail weight and the amount of compenstation required to keep the CB where it should be.

So does anyone have some experience with a problem like this? I do not want to put something together here and have a 10 cent failure that destroys the plane on its' maiden flight.

http://image.rcuniverse.com/forum/up...02/Iz36739.jpg

RE: Long Fuselage problems
 

Hi Mel,

I'll ask my buddies this afternoon about it. In the meantime, can you show some photos of where your servos are to be mounted and give us some measurements back to the control surfaces?

Pending that, my only knowlege of this stuff (I'm way behinfd you in building endeavors) would be to custom fit, cut and make your own control rods from carbon tubes or similar and add support brakets from the servos back at a couple of places to keep the control rods from flexing if at all possible.
Terribly sorry if you have already thought of this.

That is a very cool looking plane, can't wait to see it finished.
Best regards,
Greg

RE: Long Fuselage problems
 

Is this a glow powered or an electric powered model?

Consider that a truly satisfactory set of pushrods for this model is going to be heavy and mostly behind the balance point (CG) of the model. I would be tempted to explore the possibility of installing a seperate receiver and set of servos in the tail of the model. Place the battery for the rearward flight pack as far forward as possible. This would minimize flexing issues with long pushrods and finding uncommonly sized pushrod materials. Just a thought.

This is not offered as a final "should employ" solution. It is just something to consider.

The balance point of the model is a critical issue, but so is the mechanical integrity of the linkages, as you have pointed out previously.


Ed Cregger

RE: Long Fuselage problems
 

Use a pull-pull system. This minimizes tail weight and give a no slop, no friction control. Works well on both rudder and elevator.

RE: Long Fuselage problems
 

How about carbon fiber pushrods?

RE: Long Fuselage problems
 

Hi!
Yes! Pull-pull wire system is much better than anything else.
I use thinnest possible fishing wire. Plastic coated steel wire.

RE: Long Fuselage problems
 

I built a Ziroli Zero last year for a friend. Same problem, model needs lots of weight on the front to balance, so a lot off work went into not adding weight in the rear. I mounted the servos at the firewall and used Dave Brown composite pushrods. They needed to be extended, so I joined them with pieces of 1/4" aluminium tubing. Worked perfect. Bear in mind, if you do elect to use long pushrods over a pull-pull system, the pushrods will need some support along their length.
Central Hobbies, (I think it is), has a good carbon pushrod system, that I used a couple years ago, and it works well also.

RE: Long Fuselage problems
 

Ok I am at work at the moment and I do not have the measurements but here is another photo showing the front engine, directly behind the firewall is the bay where the servos are to be mounted per the plans. I can tell you off the top of my head the distace from this bay and the tail of the plane is greater than 54', I can get the exact distance later tonight after I get off work.

Push pull is a very interesting thought, I would still have to use guide tubes to avoid air lines and electronics but tubes are a need no matter what the final design is.

http://image.rcuniverse.com/forum/up...02/Nl30818.jpg

There are additional photos of my build in the link below but the above photo provided the best view of servo bay.

http://www.rcuniverse.com/forum/m_5326051/tm.htm

RE: Long Fuselage problems
 

Found some pics of the Zero push rods:

RE: Long Fuselage problems
 

You have several choices:

1. Pull-Pull on the elevator and rudder.

2. Custom made carbon fiber rods such as Dave Brown

3. Use Nyrod, well supported (such as Sullivan ). You can join the inner rods by using a piece of the all threaded rod (provided ) and you can join the outer sheath by cutting a piece of the outer sheath about 2" - 3" long and splitting it lengthwise. Slide an outer sheath in from each end and butt them against each other then use thin CA to adhere the cut piece to the 2 sheaths. I suggest staying about 1/8" away from the seam where the 2 outer sheaths butt together. As long as this is well supported you will have no problems.

Pull-Pull will be the lightest, then the Nyrod followed by the Carbon Fiber rods.