Robbe Concorde

[Frank Day]

Hi,

 

I bothered members with Robbe Concorde questions before and am planning to fit edf's and now  have everything in place. Its no shelf queen so the conversion is the right way to go in my opinion.

The twin pushers are angled down at quite an angle. I've taken a few measurements etc and found that the thrust line of the motors runs up through the point of CG and to a point above the nose!. it also has the elevons set with some reflex/up elevator, almost a upside down helicopter.

 

My plan was to mount the motors at a more conventional angle. i'm absolutely certain that there are members out there with better knowledge of these things than me and thank you in advance.

 

 

[Paul De Tourtoulon]

I had one, twin speed 400's and the small white ( 5 x 3  ? ) multiplex props, I ran mine on a 3s 1.300 mah battery that was more then enough

why are you trying ducted fans, they will be small and inefficient,,,

[Frank Day]

Hi Paul,

 

The original owner ignored the instructions, ditched the standard servos  with separate ail & elev and went  with elevons with 9g servos they also fitted brushless motors of unknown parentage and a 2200 3s with 6x4 counter props. It sounds terrible. It currently puts out 800g static thrust, as I understand this is considerably more than standard. It also weighs about 30% less than standard

 

I have a pair of fms 11 blade 50mm fans putting out about 800g each when tested, an ebay member has produced some really nice custom thrust tubes, we've played with the eflux to get the right performance so I'm hoping even with a horrific 50% loss I'll hopefully still have an improvement on standard and it sounds good.

 

Also I cant leave anything alone.

[Trevor Crook]

Sounds interesting. Can't help with the thrustline query I'm afraid. Probably simplest to keep the nacelle parallel to the bottom of the wing and see what happens, then program in some throttle-elevator mixing if required. Please show and tell when it's finished.

[Simon Chaddock]

Frank

I doubt you will have to worry about the EDF thrust line being anything but along the fuselage datum unless you have an exceptional thrust to weight ratio.

The degree of elevator reflex will depend on the wing section used. If it is basically a flat plate some reflex will be required to give an adequate longitudinal stability for a model.

 

I am afraid I rather 'showed off' when I built my Depron Concorde and used a true scale wing section and included as many of the complex twists of the full size wing as I could.

It needed no significant reflex and its four small EDFs were parallel to the fuselage.

it used inboard elevators and outboard ailerons.  

      

[Frank Day]

Hi Trevor, Simon,

 

Parallel to wing/datum and some mixing sounds good. the wing although Concorde "shaped- ish" in plan view is completely flat underneath and like the Millennium Dome on top. 

 

The manual  suggested some reflex but that had to be dialed out as it just wanted to climb on throttle or bob about nose up.

 

Simon,  I looked at your Concorde before when I was bothering people with this, looks great, wish I had the time and patience. Any dis/advantage of separate ail/ele over elevon on her. The Robbe was designed as separate but must most seem to have ended up as elevons.

 

I would have liked to use 4x 30/35mm edf but not enough go and 4 x40mm just no. The 50s seem to have more than enough and a guy has printed me a series of thrust and inlet tubes to play with Im keen on the pair that been  flattened at the outlet, sorry cant think of the actual term.

 

With the removal of  the standard servos etc I may even be able to get some functional retracts on her, I've knocked up a nose wheel for testing (Freewing Lippisch unit with a pivot at the rear to retract forward) and it tucks away nicely,  mains im still looking at CG and fan placement