Friend gives me Multiplex Twister crashed model

[solentlife]

Starting a repair thread for a smashed Multiplex Twister ...

The model will likely come with knackered EDF ... shot motor .... so now I'm looking for economic suggestions ... Hobby King based as I live in Latvia and don't have access to USA suppliers ....... for good DF unit and motor.
I rebuilt his F16 and found the 70mm really needed a 5S ... with the 2800 - 3000kv units. I am considering similar for this Twister.... Turnigy 2836 3200kv and 5S ... on a standard 6 blade DF unit.

Once I get the bits - I'll start the review of rebuild.

Any info / notes / on Twister ... very interested ... (I know there's a huge thread on RCG ... but read 4000 posts ?) ...

Nigel

[solentlife]

Ok ... delivered !









First ... canopy missing ... EDF unit and hatch missing ... tail unit is not securely glued in ... TV unit is from the F16 he gave me before !

She still has all servos working and fitted ... but ailerons have shot foam hinge lines - all cracked.

First to gloue up and sort before real repairs ...





Tail now is stiff as should be.



Crack in wing filled - to be smoothed later





Ailerons cut away and rehinged with mylar strips and epoxy.

The model is now reasonably straight and what is there is serviceable.

I shall now order a 6 blade 70mm and 3200kv EDF set-up capable of 5S ... plus look at ways to sort the canopy. I can buy a new canopy via Germany from Multiplex ... but reckon I can do it with foam block or formers .. The hatch will be my usual 6mm sheeet depron work.

The TV unit will be disabled .... until all is sorted then I will decide whether to activate or remove.

Overall the model is not so bad that a bit of warm air to straighten some, bit of glue and foam here and there will sort rest.

Colour scheme ? The Twister reminds me of the Folland Gnat, the plane used by Red Arrows before the Hawk ... so that may be the scheme ... Red is good anyway in the air.

Nigel

[solentlife]

Power plant ...

as I said in previous post ...

3200kv 5S capable 2836 Outrunner

6 blade 70mm standard HK fan unit

60A Opto ESC

Ubec

5S 3000 LiPo

Above should give it a really good thrust ratio as factory is 3600kv on 4S and most reports are moderate to good performance but nothing spectacular.
I've watched a Twister on 4S set-up correctly and she flew ... just needed a touch more IMHO ...

Nigel

[solentlife]

Test run on red ... see what ..



Looks not so bad ...

Now canopy ... this will be framed foam job ...





She's actually starting to look ok ...

Nigel

[solentlife]

Folland Gnat (Red Arrows) :



Nigel

[solentlife]

Canopy ... this is an awkward shape .. with double curvature ...

I tried planking :



Works but not happy ...

So out with block ...



This is now painted white base ... to lock the sanded foam ... then will be painted final ... it's more square, but to be honest given rest of models general condition - will fair in well enough.

Nigel

[max2112]

I don't have any experience with the Twister, Nigel so I can't offer any suggestions there. Nice job on the repairs.

I do love flying my foam Habu. I'm looking forward to reading about the re-maiden.

[solentlife]

Repairs now wait my return home and also the new EDF set-up ... Once I have those - I can then fashion a new hatch over the EDF ... and she'll be ready to install radio and maiden.

Colours will be recoated and brought to reasonable finish.

Nigel

[solentlife]

2836 3200kv and EDF unit at home ready to go in ... with 5S LiPo ...

Itching to get home and put her in the air ...

Nigel

[solentlife]

Over on RCG ... seems many have luck flying this on 3S ... but later then found out they have different kv motor as stock to the one supplied in the German kit to my mate. Plus many of the 3S boys appear to change up to higher count blade fan.
Seems the factory spec'd stock 3600kv motor is swapped out by shop to a 2800 unit. No wonder it didn't fly well ... even on 4S.

Well my 3200 on 5S will put pay to that ... may even give it a whirl on 4S if weather's calm enough.

2800 x 14.8 = 41,440

3600 x 11.1 = 39,960 ..... mmmm VERY marginal to my thinking !!

but my 3200 x 14.8 = 47,360 ... much better and probably not too high an amps draw.

3200 x 18.5 = 59,200 Wey Hey ! - that's getting it on ! but no doubt amps draw will be high.

Can't wait to get home .... !!

Nigel

[solentlife]

Well I started installation of new EDF ... ran up against problem of remaking a hatch ...

THEN received call - Ticket at airport !! I'm away again on assignment ... so apologies - rebuild will be delayed !

Nigel

[solentlife]

Having test flown the 2836 3200kv with 5S in the F16 ... it burnt out and ESC popped with the motor ... I am now reverting to a 4S in this.

Hatch made ... just canopy is a real pig as the shape is a compound ...

But anyway - tested the 70mm 6 blader, 2836 3200kv, 4S 2700 LiPo ...

Total weight incl battery 1180gr

Thrust static measured : 840gr

this gives a thrust to weight of 0.7 : 1 .... so flyable.

This is with Thrust Vector system as well ....

4S allows all the gear originally fitted to be used.

Now it's finish that canopy and get the painting done.


Nigel

[mclarkson]

Originally Posted by solentlife

Having test flown the 2836 3200kv with 5S in the F16 ... it burnt out and ESC popped with the motor

I think that might indicate some sort of over-volt situation.

[solentlife]

Originally Posted by mclarkson

I think that might indicate some sort of over-volt situation.

Which is b***** annoying as I was told it would take a 5S !!

Nigel

[solentlife]

Nearly there ..... revised motor combo as said is 3200kv 2836 on 4S ... downgraded from my wished for 5S ... but still will be flyable.

I have bashed away at the canopy but having bad time with it .. its such a daft shape ...

But anyway here's the colour scheme applied so far ... just need to do white Z stripes along sides now ...



Nigel

[mattman0182]

Congrats man! You have talent for sure.
That thing reminds me of a Mirage F1.
http://www.google.com/imgres?q=mirag...,r:9,s:0,i:123

[solentlife]

Originally Posted by mattman0182

Congrats man! You have talent for sure.
That thing reminds me of a Mirage F1...............

Have to say that sprang to mind as well ... Great Minds !!

Talent ? No way ... just able top picture things in my mind ... put a busted up model etc. in front of me and I start hatching ways to put it back together ... a lot of my ways are unconventional !! and liable to change while in process ...

A good point is the canopy. It's now on version 3 !! But now I have a secure canopy that a) has a good air scoop front end to cool ESC / LiPo ... b) secure front and pegged rear to avoid those fly-away canopy moments .... c) light and with framing.

Here she is ... finished :



Here you can see the air scoop and front band hold down ..



General (I'll add white side stripe later after proving flight)



Rear end with Thrust vector unit





Underside - nice contrast for my bad eyes !!



The rockets have been touched up since to an overal grey ... they are only held by Cocktail sticks through into wing tips .. no glue.

Have run up the motor combo .... Turnigy 2836 3200KV with 4S pack, Haoye 6 blade 70mm unit..... 40A 488W steady after an initial 45A start .... Thrust 840gr

Lipo was not happy even though it's a 35C 1800 .. which should carry a 63A max ... A better C rating is called for.

Initial balance checks with 1600 4S and 2700 4S ... (using too extremes to see range). Measurements are from wing root at fuselage joint.

Factory CoG dimple is 105mm

1600 gave 70mm - pack weight 149gr
2700 gave 55mm - pack weith 259gr

All up weight with 2700gr pack is 1180gr.

Just added 30gr to tail (I use car wheel balance weights - the self-adhesive ones for alloy wheels ... they are made in specific weights !)... original owner fitted the steel balls .. ! but still needs the extra.

This brings balance point to 98mm with 1600 and 85mm with the 2700 ... which is still forward but I think is safe for maiden ... and AUW now 1210gr ... a heavyweight !!

The factory spec quotes about 880gr ... How ?? Thats a big difference ...and they are quoting with a 2200 3S pack in her (weighs similar to my 1800 4S pack).


Anyway ... on we go ! maiden will wait a bit as weather for next days is strong wind ...

Nigel

[solentlife]

I have an intriguing idea to solve the CoG problem ... I measured up and checked to create a battery box in the underside of fuselage. I can thern move it back significantly, with Rx / ESC / BEC still where they are - over-top of new battery area. This then brings all weight rearwards. I reckon to cut into the fuselage ... line it with balsa to put back strength and stiffness, make a hatch in balsa / foam sandwich ... I may have to create a false floor in the cockpit area to get the depth, but that will be good for organising the RX, ESC, BEC ...

I can even carry a 5S there without too much move of CoG ... once I get the 5S motyor fitted of course !

Banded on to find right position ...





Marked round ..



CoG points ... blue dot is factory dimple, yellow pen is 4S, white pen is 5S



Here's the LiPo's with weights marked on ..



I dunno about others - but each LiPo I receive gets weighed once connectors are fitted etc. - so I have correct in-use weight.

Nigel

[solentlife]

Something's wrong .... today was test maiden..

Previous owner gave it the hand launch ... she immediately stood on her tail and stalled out ....

Before launch - we checked movement and neutrals .... my only thought is the Vector unit may not have been dead straight thrust .... Difficult to eye-ball.

Cracked wing, cracked nose ... but simple fixes. Aileron servo lead was severed but is now rejoined.

Will set-up a bungee hook and alter my ramp to suit her ... needs to be wider. Give her a bungee launch next time ...

Nigel

[solentlife]

Here's the video of the failure ....

Twister 17-03-2013 failed maiden

Initially it appears that launch was too nose up .. but slow down the video and you see her RISE up in pitch on launch ... then stand on her tail.

This says to me - bad thrust line ... allied to launchers slight up launch.

Having no original Twister to compare nozzle angle to - I'm going by what I consider needed. I shall now dial in some downthrust to the nozzle. Cannot be elevator as model is not at speed for it to act enough.

Just laid a straight edge along fuselage and found a couple degrees up and couple left on the nozzle ... both now adjusted out. Doesn't seem enough to create the launch we see above ... but then I have a theory of EDF's and Pushers ....

A conventional tractor prop PULLS a model along, so any thrust line error basically is able to be countered by control ... at low speed the prop PULLS her through.
A thrust from the rear as with EDF or Pusher - that creates a moment to push tail down, up, left or right as thrust error determines. The model not being at speed, the model inertia fighting the thrust fwd ... creates a Tail overtaking the nose situation ...

I think this is why so many hand launch EDF's / Pushers appear to sit on tail a bit at initial part. A catapult launcher on the other hand gets model to flight speed literally at exit of ramp ... so the characteristic is not observed.

Put it this way. Put a stick in a bowl of water. Now pull front end ... stick follows ok. Now push the rear end and it turns one way or another depending on how offset your push is.

My theory anyway.

Nigel

[mclarkson]

Could she be too tail-heavy?

[solentlife]

Originally Posted by mclarkson

Could she be too tail-heavy?

Checking with other Twister flyers - they all reckon to set CoG slightly ahead of the factory dimples ... which I did. So she should be ok.

I rechecked with original owner about the thrust line - he reckoned he had trouble till he dialled in a couple degrees down on the vector unit.

She has a hook for catapult now - so next maiden will be by bungee - so g'tee for a straight launch and no pitched up throw.

Nigel