Vintage Twinjet Refurbishment Project

[Edgeflyer]

Acquired in a pretty much written off state but I like the Multiplex Twinjet and a challenge. This one like many seems to have suffered attempts to overpower it so lots of holes, breaks... Still "In for a penny in for a pound", which is what I paid. I am going to use matched 480 contrary running brushed motors and single ESC, but a 2 or 3 cell small lipo.

[Edgeflyer]

First stage, remove old decals and fill holes using pu foaming glue covered with paper tape to allow curing without over foaming. Next the nacelles had been badly glassed and need sanding and filling. I've glued the nose back on and am working on removing the old balsa stiffener that was in several parts anyway, as I need access to the hollow motor wires bay. I removed the old plastic " inner tube" as it too was cracked . I will need to think around that.

[Geoff S]

I have a TwinJet stuffed at the back of the loft over my workshop.  I'll be watching with interest.

[J D 8]

       I like a good fix up. Or with this one a raise the dead job.😁

[Outrunner]

I had a Twinjet back in the day, it went great on its supplied twin brushed motors and Gunther props and a bunch of nicads, should never had sold it.

I hope your project goes well 

[Guest]

Yep hoping to replicate that but the lipo will reduce weight over nicds

[Edgeflyer]

Slow progress.

Balsa keel removed and motor wires installed for motor installation.

[Edgeflyer]

Servos rewired and glued in.

[Geoff S]

Are you intending to retain the brushed motors?  One of the reasons I didn't persist with updating my Twinjet was the difficulty of fitting reasonably priced brushless motors was because of the rotating outer case fouling the mounting recess.  New servos isn't so much of a problem.

[Guest]

Yes that's pretty much my thinking. Also much thinner motor wire to fit the grooves in the wing. Plus I just wanted to fly like the original. It must have been ok with brushed to stay so popular. That said filling the fuse with nicds is not for me! Lipo system should be lighter and brushed maybe enough thrust. Plus I'm just cheap!

[Guest]

You could go inrunners though as the tiny props need high kv.

[Frank Skilbeck]

Loved my Twinjet, I upgraded to 3s lipo, extra power made the.motors run hot and the hot glue I'd used to fix the motors give up, one motor came loose and chopped away at the back end of the wing, didn't end well 😚

[Geoff S]

You could run the original 40 (as mine is) or the 480s (on yours?) on 2 S LiPOs but it would be a different set of batteries and I have loads of 2200 3S packs already.

 

When I looked into it inrunners were very expensive. Perhaps they're cheaper now?

[Edgeflyer]

Yes I baulked at £40 for 2 inrunners as I only paid £1 for the airframe! If the 2 cell lipo lacks thrust from the 480s, I am going to try out an intelligent lion battery which is a 4 cell pack of Samsung 25R 18650 2500mAh High drain cells (rated 20amp continuous) but with a built in charger/input/ output electronic device that can output 9 volts. On a 2 s lipo at 7.4v the current draw is 26amps at WOT on 5.5x4.5 props. I will also try 6x4 props when they arrive.

it looks like with lithium cells there will be room for a weighty pack to balance the model.

[MaxG]

What I did when I wanted to replace the 480 with an outrunner in my Zagi was to take the guts of the 480 out just leaving the metal can/shell. I mounted the new outrunner to the front of the 480 can and then stuck the can back in place as originally mounted and it has worked very well. If I remember correctly I used a bit of 3mm ply as an adaptor plate to match the holes on the front of the 480 can and the X mount of the outrunner. Thinking of doing the same when I "outrunner" my Twinjet. Solves the mounting issue, allows cheaper outrunners and prevents motor heat loosening the mounting glue. HTH

[Edgeflyer]

Good thinking! Any pics? How did you deal with running thick wires through the fuse and wings?

[MaxG]

This is of my Zagi. You can see the old empty can of the original motor, part held by the ziptie. You can also see the 3mm ply adaptor plate .

 

When I come to do it on the twinjet I will mount each ESC in the wing like the servos and run the wires in a slot cut in the foam. If the slot needs to be quite wide I will glue a piece of stripwood on top of the wires to fill the slot.

[Edgeflyer]

Finally made some progress. Got the fins on after some reshaping and carved a rear " canopy". Worked out that the original builder had the fins reversed.

[flying pastor]

I think that the fins are reversed now. Thinking back many years to mine the fins should be closer at the top than they are at the base. Hope this makes sense. A quick Google for twinjet images should show what I mean.

 

All the best...Chris

[leccyflyer]

That's right - the fins should lean inwards, not outwards.

[Edgeflyer]

Well I like to be different! F22 and F15 both have twin fins leaning outwards. Mine have assymetric profiles and didn't fit the wing cutouts the other way.

[leccyflyer]

5 minutes ago, Edgeflyer said:

Well I like to be different! F22 and F15 both have twin fins leaning outwards. Mine have assymetric profiles and didn't fit the wing cutouts the other way.

F-15 fins are vertical. Perhaps you are thinking of the F/A 18?

[Edgeflyer]

Outwards canted twin stabilizers have their tips outside the disturbed airflow from the frame, they get much cleaner air and can function better. F-35 and F-18 do not have thrust vectoring, but they can still fly very controllably at very high alpha angles because of their canted twin tails.

[Edgeflyer]

Sorry yes f35 not F15. Anyway if my old twinjet manages to fly I'm happy. I like the look of outward canted fins. 

[GrumpyGnome]

I suspect it's purely aesthetics at our scale...