DH88 - I can rebuild her!

[Chris Bott - Moderator]

Morning. Just been and checked, and it did really happen. My Ripmax DH88 Comet is in lots of bits.

Flew 3rd and 4th flights with Danny and his Fury yesterday morning. I was getting used to, and really enjoying the DH88 when disaster struck. Theres a video below of the last 90 seconds. I have at least three theories as to what happened.

Listen to the engine note just before the first flick/tipstall.

[Tim Mackey]

Too slow and she stalled...and obviously a rather tricky model to recover from stalling? Those extremely tapered wings would suggest a tendancy to tip stall ? I honestly cant say with authority, as I have not flown one. It did behave a little oddly a little before the main incident too, and although the speed seemed reasonable, it looked for all the world like it just "stopped flying" in the rather sharp manouveres.

Great shame mate, and hope you decide to rebuild her as it looked very nice .

[David Ashby - Moderator]

As Tim says - a stall by the looks.....sorry to see Chris

[Chris Bott - Moderator]

I beleive that it flicked on opening the throttle just beforehand. The thought was going through my head that I'd lost a motor. It recovered with power off. So the most likely scenario is that while I was deciding what to do about that, and looking round for a deadstick landing, it got too slow. I did decide to try throttling up again to see if it flicked again. I even think I did start to throttle up again, but I guess by then it was too late. A dab of down elevator instead and all might be in one piece.

Testing at home:- I'd used 770mAh of 2300. Eagle tree, from the motor that may not have started when it flicked, shows good volts, lowest during takeoff and the loop and higher again round the last circuit and at the end.  Both batteries are OK but battered. Both motors run fine, both ESC's work. (Could one have overheated? not at the currents I was pulling I doubt).

I'll have some damage photos later. I wish I'd taken some on the ground straight after.

[Chris Bott - Moderator]

Heres some pics

This last one is after the split repairs

[Chris Bott - Moderator]

Right on to the rebuild decision.

Damage report:-

• Plasic over ply & carbon skeleton fuselage crushed, splintered and split back past wing LE. Internal skeleton ply formers in pieces, carbon tubes in splinters. Wing seat ply broken and broken out. Ply former for wing dowels broken and out. Ply cross piece for wing bolts broken out and bent. Servo tray, broken out. Canopy, Cockpit, and whole tail end - fine.
• Fibreglass Nacelles, both crushed at front, both firewalles broken, motor mounts bent and in bits. Cowls OK except mounting holes torn. Motors, ESC's, batteries & undercarriage fine. (1 battery needs a rebuild but all cells are OK)
• Wings. Cenre section crushed where nacelle mounts on dowells. Nacelle mount screw has pulled through wing. One Wing tip piece has root rib mising and some of bottom skin ripped out.
  

I have done a few repair tests on the plstic of the fus. Where I could pull the splits together, I've taped over with sellotape outside, getting the join spot on. Then applied thin skinning cloth with thin Zap on the inside. This technique has already nearly restored the fus skin, right up to the front of the wing. I will carry on and see how far forward I can get with it still looking OK.

[Chris Bott - Moderator]

Repairing splits in the thin plastic

Nasty tear....

Sellotape over..

Skinning cloth pieces

Cyano inside with pink Zap

Hey presto - bggr some paint came off. of course earlier ones were much better when I didnt take piccys.

So, is it worth continuing with this? Its not costing much..

[David Ashby - Moderator]

Tricky one Chris, some would say no, can't be bothered and others would say yes definately! I often just cant bring myself to repair a badly damaged model but you may be different. 

I'd almost be tempted to do it just to get some more airtime from the model and see how she flies. If she's a corker than perhaps get a new model..? 

[Chris Bott - Moderator]

She looks a real corker in the air and on the ground. But those pointy wingtips bite! First flight was a nightmare. So I got a heat gun and my hob nail boots on the wing tip sections and added lots of washout.  Of course that meant thrustlines and trim were out. Flight 2 proved very stable at low speeds, but it went well nose up at full power. So thrustlines were changed. Flight 3 on Sunday was nerve wracking but I enjoyed it. Flight 4 I was getting confident. (Often my downfall).

I see it as a challenge now. As long as I don't spend (waste) much money and then fail.

Repairs could go in fits and spurts, do a bit then leave it a while..

Fus is firming up nicely. Looks like theres a big bit missing though, I thought we'd retreived everything.
Some part of the nose will have to be new...

Anyone know the best way to ask Ripmax if they can do a new Fus as a spare?  I really dont have good experiences of local model shops ordering me stuff.

[David Ashby - Moderator]

I've just sent an email to Ripmax about something else so I've asked them for you

[Chris Bott - Moderator]

Wow - many thanks

[Chris Bott - Moderator]

Its getting longer! (ooer missus) But it seems that some kind soul took some pieces to throw away for me.

[Danny Fenton]

Having seen the size of some of the bits, (they were tiny tosay the least) to see that much of the fus in one piece is pretty amazing. I bet you spent all of your childhood doing 3D puzzles

Hope its ready for our leccy fun fly in August

[David Ashby - Moderator]

Chris, Ripmax say they will have to order up a fus' as they don't have any and it'll be about £85. Not sure about timescales though.....

[Chris Bott - Moderator]

Many thanks David. Its a difficult one at that price.  Probably worth going for. I can restore the rest of the plane into almost good as new. But the fus will always look battered and mended.  Especially as I have a big piece missing !

[Chris Bott - Moderator]

Well I seem to have a habit of putting crashed models up one corner of the garage and just leaving them. I had got on well with the fus on this one, up to the front of the wing, but there were plenty of other issues that I could see going wrong trying to rebuild. So it stayed in the corner. This week I decided I sould either get over those issues or throw it out to make some space.

 

Here's the result. Still tons to do, but it has retained it's storage space, (for the time being)

 

Ripped out fixings for the nacelles have been restored. Nacelles have been straightened pending glassing inside. And the wing leading edge has been rebuilt and the nacelle dowell locations restored.

 

 

Edited By Chris Bott on 04/04/2010 12:24:07

[Tim Mackey]

PSS mate!

[A.A. Barry]

Stall......... nup,  the first, issue was that sudden "dip", the flying speed,  looked OK. even in the loop it appears to not to have a stalling problem. The next few seconds tells the story, it was flying level, and it then rolls in...........my opinoin is/was a faulty alerion servo...out of charracter, for it to once flying speed is "set", for it just to roll in, I see you have flown it before, obvilious this was not an issue before, even on landing, where "stalling" is most  vunerable ...

A.A.Barry 

[A.A. Barry]

Sorry I didn't answer the Q.............................yep rebuild it

A.A. Barry

[Biggles' Elder Brother - Moderator]

The Comet is a lovely looking airplane, and its certainly impressive in the air. The problem is of course that they were specifically designed as "point-to-point" racers - so agile they certainly are not! For us modellers that always going to be a problem cos of course we have to fly in circles - the one thing it does badly!

 

I'd love to see you rebuild it Chris - but without wishing to be a prophet of doom, I can't help but think that the DH88 is a constant tip-stall waiting to happen. Its probably OK if you stick to flying up and down the field with big wide gentle turns at each end - but anything else and you take your life in hands as it were  

 

BEB

[A.A. Barry]

BEB, shurly, racers have to turn in the air, particuly around pylons, or was designed to go in a straight line..........uumm , I feel not

A>A.Barry

[Chris Bott - Moderator]

PSS - now there's a thought!  To be honest I think it's a little delicate for that. 

Thanks for the thought though Timbo.

 

AA Barry, oddly enough one aileron servo is now loose inside the wing. I have assumed that happened in the crash.

I think I did fly it too slow. Both times a wing dropped I had just slammed on full power. You can hera that on the first dip. But it doesn't drop in the direction that would be caused by torque. I guess I just applied power too late?? 

 

It will be rebuilt. Not sure how many time gaps there will be though lol. I'll post updates here as and when.

 

Cheers

Chris 

Edited By Chris Bott on 04/04/2010 13:20:05

[A.A. Barry]

Chris, welcome to Twin engines, stick with it , there is satifaction...trust me

B

I.C  ???????

Edited By A.A. Barry on 04/04/2010 13:22:54

[Chris Bott - Moderator]

AA I think I/C would just give me two more things to worry about

 

[Bob Cotsford]

Posted by Chris Bott on 04/04/2010 13:18:51:I think I did fly it too slow. Both times a wing dropped I had just slammed on full power. You can hera that on the first dip. But it doesn't drop in the direction that would be caused by torque. I guess I just applied power too late?? 

 

Could it have been the application of power that tipped it over the edge?  You said you had to add downthrust after earlier flights, I wonder if the change in airflow over the tail could have caused a slight increase in attitude taking the model past the point of stalling, and it still needs more downthrust to hold the nose down under power?  Maybe setting both ailerons a shade up at neutral would help as well?  I'd be tempted to stick a big block of foam in the nose, carve to roughly the right shape and skin with class cloth and resin or Poly-C, just to get some more airtime with the model.