Jodel Robin DR400

[Roy Hill 3]

In order to avoid going 'stir crazy' during the recent lock-down, I bought the plans for a 100-odd inch Jodel Robin DR400 from Nexus designed by CJ Murfitt via Sarik. I am not a novice builder and I found the plans very clear and concise. I estimate that the project will take me at least a year to complete. There are a few areas where I need the expertise of the contributors of Model Flying.

a.Has anyone any experience of building from Sarik?

b. The old chestnut raises it's head concerning engine off-set! I have acquired a MVVS 35cc, The plan gives off-sets as 3 degrees down and to the right. What are the readers views on off-sets?

c. The aircraft has a very big wing cord, giving a low wing loading and will fly slowly and sedately - a bit like me - therefore what would be the suggestions for servos?

Any further information and advise will be appreciated.

Stay safe and happy landings. Roy

[Gary Binnie]

I have several hundred hours of flying DR400s and DR300s, a very clever design. The key to its performance is the marked washout of the outer wing panels, when it's at low angles of attack (cruise) it's flying on the inner wing only, less drag, more speed.

Handling at the stall is benign but can flick if pulled hard in a turn.

Hopefully the plan has guidance on engine thrust line? The full size appears to be mounted straight.

Servo wise the flaps are fairly narrow chord strips and the ailerons are not particularly big, good standard size servos might be ok. The Flair Tiger Moth (1/4 scale) uses standard servos throughout, the rudder through a geared linkage and it is a slower flyer.

The DR400 has an all moving tailplane so something bigger needed there depending on where it is hinged relative to the aerodynamic centre.

It wouldn't hurt to get some advice from the LMA, they have a building inspection scheme which I believe is necessary for the paperwork.

For info the DR400 Regent has wing fillet fuel tanks and a cockpit roof (the better looking version IMO), the photo I can see on the plan page is the lighter glider tug version with no wing tanks and a greenhouse (hot!) canopy.

The wheel spats often filled up with grass cuttings/mud and are left off many tugs, also makes strut, wheel and brake inspection easier

Cheers

Gary

[Roy Hill 3]

Thanks for that, Gary. I've almost completed the wing build. It has taken 131 hours to date! I have used 'snakes' for flaps and ailerons and incorporated full lighting. The wing wash-out is more noticeable on the model than on the full-size! I have machined the oleos for main and nose myself. I will try to post some photos in the very near future. As I said in the original post, the plans give 3 degrees off -set. I was interested in seeing others views on the subject. Cheers Roy

[Gary Binnie]

Look forward to the photos.

I've just finished an Xtra Wot using an OS 120AX, the kit comes with a side thrust wedge which I used, the angle of it is not stated, there is no up or down thrust.

[Roy Hill 3]

 

As promised, I've started to produce a build log. As most builders do, I began with the wings and after 130+ hours of balsa bashing this is the result. The drawings give a double slide-in tongue system for wing-tip retention, which I found very effective. I have used the plug-in type electrical connectors for power to the wing-tip lights. It's the first time that I have used this system and I must say that it is a bit fiddley to get them to line up. I found them to be a very tight fit and I would think twice about using them again! I cut out part of the leading edge and used the bit as a plug to produce the landing light. I spent a great deal of time wondering what to use as a reflector and stumbled across the idea of using the inside of a beer can, which works perfectly. Emptying the can was also quite enjoyable!

As I said in my original posting, I've used snakes for the flap and aileron function. The bell-crank for the flaps was a bit time consuming to set up. I made the oleos from ali pipe sourced from B&Q. A thin piece of card, liberally soaked in 3 in 1 gave a good fit and ample lubrication between the inner and outer tubes. The oleo spring came from a model car suspension.

In order to operate the landing lights, I used a micro-switch, coupled up to the flap servo which only connects on full flaps for landing. The screw on the servo arm operates the micro-switch. The remaining mechanics and electrics are, from top to bottom, 8 channel receiver and satellite and some old servos used throughout just to get things working. The next bay houses the control unit for the lighting and the battery packs for receiver and lighting. At the bottom is the flap servo set-up.

There is always much debate on using wheel spats particularly on less than smooth runways. The ones on the Robin are very stylish and I think that not using them will lessen the effect of the model. Our club field, Barton Point in Kent is grass and is very well maintained but might cause me grief because of the small amount of wheel exposed. Don't panic, the wheels are not fitted in the photos! I made these spats from several pieces of balsa and I'm still not sure whether to use them as they are or to use them as 'plugs' and produce glass-fibre items.

With the wing production as far as it can go at present, I turned my attention to the fuselage. The formers were cut and dry assembly began. The process for getting the MVVS 35cc in the correct position is always time-consuming for me. The drawings give the firewall set at 3 degrees right and down, therefore it would be pointless to change things. The supplied exhaust system had to be discarded because it 'fouled' the firewall. I thought that a custom- built unit would have to be sourced but then I stumbled upon a silencer from a strimmer and a light-bulb moment happened. I machined a spacer to keep the silencer from 'fouling' the engine cooling fins and 'Hey Press-stud'......success. All that is now required is a flexible tube to get the fumes to exit in the right place and we're in business.

So work continues in a very crowded workshop. (See above!) I may soon have to thin out my fleet to make room for the Robin. I will continue the build blog in a few weeks when more progress has been made and there is photographic evidence of my labours. I look forward to any comments and suggestions, that fellow modellers have, be they good, bad, constructive or what-ever. Stay safe and happy landings. Roy.

Edited By Roy Hill 3 on 25/08/2020 09:39:46