DH86 Refurbishment

[John Rickett 102]

Thanks for the history, all good stuff.

Well at least we agree they are Lasers! I have always thought they were 62s. The 50s have 50 stamped on them but not the other two, only the letter K on each, plus my initials followed by 1 or 2,  which is what Neil liked to do at the time. As far as I'm aware Neil did not put together any specials, they were current production models at the time. Perhaps they are even older that we thought, time unfortunately dims the memory, though I'd vouch that all the engines have only been installed in this one model. When you get them on your bench you may be able to determine what capacity they are and when they were made.  

[Jon H]

K is a 1992 engine so that could be a very late 62 or early 70. I will have a measure up when the time comes ? 

[EarlyBird]

This is all very intriguing, a cross between 'a touch of frost' and 'time team'. I am following along avidly.

[John Rickett 102]

The undercarriage has now been removed and the bad covering stripped off fortunately it came away without causing further damage. I must have used Balsaloc or similar on some parts as the Solartex had a tenacious grip, especially around the windows, on other parts it came away easily. An inspection of the tail showed that there's no visual damage though I may cause some trying  to remove the covering. The hinges are Robart type (glued in) so I'll leave the tail section as is and worry about how to paint that area later.

 

 

The flaps were driven by trusty Futaba S148 servos, one per wing stub. I remember needing to reverse one of the servos so had to disassemble it and swap over the motor and feedback pot wiring - this is a good example of the use of programmable servos which will make setting up so much easier.

The 1/16 sheeting has started to lift but will have to come off anyway to replace the wing joiners, these were brass tubes using piano wire as the joiner. The stresses on a biplane wing attachment are not as high as a cantilever wing so were adequate for the purpose.........provided all landings were perfect! They will be replaced with thicker aluminium rods running in phenolic tubes     

The elevator and rudder servos were mounted high in the fuselage, immediately behind the cockpit, this gave a direct run to the surfaces. I don't think I'll alter anything here, just change the servos for something modern. A bit of useful work will be to dispense with a hatch-latch when recovering and use neodym magnets. I'd not heard of them until a few years ago but are now my preferred method of retaining hatches.   

   

[John Rickett 102]

A slight distraction today from cutting into wood.

Having removed the undercarriage I was a bit embarrassed by the corrosion that had built up, so not wanting to keep looking at the sorry state while continuing with the airframe, I though I ought to make the oleos clean and serviceable.   

A before and after picture of a cleaned up oleo, fresh grease applied inside the sliders.

The oleos were supplied by Tony Goodger when he was running Unitracts. They are simply two legs separated by a square plate. The screws were tapped into the legs 6BA however there is very little metal for the bottom screws and they had pulled out. I bodged a repair by fitting self-tapping screws, hardly an elegant engineering solution so I decided to do the job properly - thanks Boris for giving us all the time in the world.

Raiding my do-not-throw-these-away stash I found 4BA taps and suitable screws, though the screws needed filing down until they would go in tight but not bind on the springs beneath.

One leg down and one to go.

 

Plenty of metal at the top for a tapped hole, but very little on the oleo tube, hopefully 4BA will last longer than 6BA

 

The centre hole in the oleo plate had made a convenient place to mount a home made silencer. On the inners the Laser exhausts came just on the front curve of the wheel fairings which would have meant an enormous hole in a visible place, so the solution was to use bendy extensions and route the exhaust to the bottom rear of the fairings. This has worked well so will be retained on the refurbished model.    

       

[Martin Harris - Moderator]

3mm thread insert kits are available from Chronos (and other suppliers no doubt) - very handy for retract restorations and soon pays for itself...

 

I've also used them for new threads in aluminium that are likely to be undone on a regular basis to add durability.

[John Rickett 102]

Thanks for the information Martin, I'll make a note of it. We'll see how the larger tapped hole stands up to my landings before changing things again.

 

A couple of the rigging supports which pulled out are in the outer engine nacelles. This one is the outside of the right outer, it was attached to the nearest rib to the outer, sandwiched using epoxy, between the rib and a ply riblet, clearly not strong enough. 

  

 

To gain access to the same fixing position would have meant cutting away quite a bit of wing, so have opted for bending a new support which fits to the 1/8" ply engine bearer support plate.

The tell tale cut out in the sheeting shows that I've attempted a repair in the past, obviously with only temporary success.

 

 

The support is 2mm mild steel strip from B&Q, which at 10mm wide is conveniently the right size for the dual fork-ends (from Mick Reeves). Unfortunately the fork-ends have a 1.6mm gap and as I don't have any milling equipment, I've had to reduce the section by hand filing, not particularly neat but it will work.

 

 

 

The new rigging support fixed into position with 3mm screws. The next job will be to replace the removed planking and then it on to the other side.  

[Jon H]

I have received the engines from John and (following a blur of flailing allen keys) each has been stripped to see what we have to work with. 

 

Basically, all 4 engines have the same issues. Rust, castor goo, more rust, and more castor goo. Nothing out of the ordinary really although one of the 50's is pretty nasty in the crankcase with heavy rusting on all ferrous parts. I have seen plenty worse, so it should be fine. The two 62's have their piston rings seized into their pistons but i hope i can save them. On the plus side, none of the valves are worn and the liners all look good. 

 

If you see this John we are looking at new bearings x3 and valve springs for all 4. New PTFE gudegon pin pads would be a goo idea as well particularly on the 50's as they have melted. Clearly both 50's are running hot, the 62's seem ok. 

 

If anyone is interested i can post some photos of the rebuilds? 

[EarlyBird]

2 minutes ago, Jon - Laser Engines said:

If anyone is interested i can post some photos of the rebuilds? 

 

Yes please. Thanks. ?

[John Rickett 102]

Jon, Thanks for quickly turning your attention to the engines. If any defence of the state of the engines is needed, originally the standard recommendation was to run the engines with fuel containing some castor. I went off that idea as soon as non-castor fuel was available but I'm sure some damage will have occurred by then.

If we can get away with just bearings, springs, gudgeon pin pads and a good internal clean, then I'll consider that the winged gods of Laser are smiling sweetly on this project.

Please post the pictures of the engine rebuilds, for me it will help maintain enthusiasm during the more mundane aspects of the airframe repairs.   

     

[Graham Davies 3]

16 hours ago, Jon - Laser Engines said:

If anyone is interested i can post some photos of the rebuilds? 

 

Plus one here Jon; I'd be fascinated to watch master craftsmanship!

[Jon H]

These are photos of one of the 62's. It was the first engine i laid my hand on and its representative of all 4 so i wont detail all of them as its likely to be an insomnia cure. 

 

So here it is all in bits

 

 

 

 

 

Pretty grotty mix of castor and rust

 

 

Rust on the gudgeon pin. Easy to ignore but it would wear the little end of the rod

 

 

Grab it in a drill chuck and hit it with oiled 400grit wet n dry. As you can see the rust has caused some minor pitting. These could eventually cause the pin to crack, but its 10cc and not likely for quite some time if at all. If it was a 360v i might be a little more concerned. 

 

 

Nasty mix of castor oil and rust particles. 

 

 

If anyone still thinks flooding an engine with acetone or whatever will restore it let this image be a lesson. You aint washing that lot out. Take it apart, bin the bearing, buy a new one. 

 

 

 

This is pretty standard stuff, i would say 70% of engines that come back to me are in this sort of state so dont worry John, i am not making an example! 

Edited March 10, 2021 by Jon - Laser Engines

[GrumpyGnome]

Lurking, and reading with interest! Great project, will be fab to see it serviceable again.....

GG

[John Rickett 102]

With the rigging supports completed on either side it seemed, seeing as I was cutting into the nacelles, that improvements could be made to the interplane strut fixings at the same time. With the model being only to 1/6th scale the struts were made as one piece units and were a push fit into ply recesses in the nacelles, then held in compression by the rigging. This wasn't a particularly good arrangement as the upper and lower wings were quite floppy during model assembly and didn't become rigid until the rigging was fully tightened.

I decided it would be better if the struts were fixed with 3mm screws in 4 places, two at the bottom and two at the top. The problem was how to install fixings that were no wider than the 1/8" ply recesses that the struts fitted into. The solution opted for was to install a captive screw thread into each strut. Not having any heavy wall brass tubing that could be tapped, I found some tubes which were a sliding fit and if soldered one inside the other, could then be tapped.

       

The tubes were then cut and epoxied into slots in the struts. They will not be under a lot of strain as they only have to hold the upper and lower wings in their respective positions until the rigging is tightened.

  

Access to the screws is through the tank hatch in the bottom of each nacelle.

 

 

The wood removed in the planking to allow for the rigging support and strut work is now replaced and blended in with filler. A couple of layers of fibreglass cloth will be applied to the nacelles to provide strength and a smooth finish.

Now to sort out the upper wing strut fixing and to repeat for the other wing.....     

[Chris Walby]

John and Jon, great stuff and a real pleasure watching you guys progressing through the various elements of the rebuild. 

 

Keep the text and photos coming

[John Rickett 102]

Thanks Chris for the kind words, it's appreciated and helps to maintain enthusiasm. 

The upper ends of the interplane strut have had threaded brass tube glued in, in a similar manner to the lower ends.   

 

With the sheeting cutaway the hole (this one at the front) is visible. A small piece of 1/4 ply acts as a cap and with a careful bit of measurement, the hole in the cap lines up with the brass tube below. This took a bit of trial and error, but got there in the end.   

 

 

The picture above shows the rear fixing and the strut poking out of the wing below. Once covered it should be just down to the cap screws showing. Unfortunately though once the covering is applied there will be 4 screws visible and they will probably be where the registration lettering is going to be! If I was starting from scratch I would have tried to devise a better method of retaining the struts. On a similar larger model the supports extended below the wing and had the fixing bolt more or less hidden, a much better idea. but too late for this model. Oh well, it's not for Sunday best, I must remind myself that the object of the exercise is to get an unused aeroplane back into the air.

 

The new rigging support has been added by the outer strut and the redundant hole where the upper aileron pushrod went up inside the strut, filled in.  

 

Lightweight filler is wonderful stuff for hiding all the imperfections.  

[RottenRow]

Hi John,

 

This is really interesting, thanks for sharing it all with us.

 

I am in the process of building a DH Rapide based on the Martin Tuck plan, also 1/6th scale. Much of your model, with the covering removed, looks very similar to my Rapide. The plan, from the late 1980s, leaves a lot to be desired in a lot of places and had I known that from the start I would probably have used the Jerry Bates plan instead. Anyway that's off the topic somewhat.

 

Interestingly I have fixed my interplane struts is a similar method to yours, only as I was making the struts from scratch I had a bit more flexibility in what I did. I used 3mm brass tubing and soldered square M3 nuts on one end (the nuts looked like those that used to come with 'proper' Meccano). I happened to have these to hand, rescued from old electronic equipment, but normal hexagonal nuts could have been used instead. This produced long Tee nuts, which were epoxied into T-shaped slots in the ends of the 1/8" ply struts. Each side of the struts was then clad with balsa and shaped. Unfortunately I didn't take any photos during their construction.

 

The wings had 3mm clearance brass tubes in holes through which M3 cap-headed screws are passed and screwed into the struts. I have used stainless steel countersunk M3 screws, I think they were 60mm long and I cut them down to the length required (put a nut on first, file the cut end to a smooth chamfer and wind the nut off). These screws are easily available from a UK supplier on eBay.

 

I installed some square 1/8" ply plates into the wings for the screw heads to bed down into. These are countersunk. I then mixed some epoxy and microballoons, and put a small amount in the countersink. I put a smear of vaseline on the screw, including the countersunk head, and wound the screws in, with the wings in position on the rest of the model. When the heads were flush with the surface, any excess epoxy was removed and everything left to set. Afterwards, the screws were undone and this left perfect smooth countersunk holes at exactly the right angle.

 

I can take some photos if you are interested and post them later.

 

This is the Rapide, there has been some progress since these photos were taken.

 

Brian.

[John Rickett 102]

The Rapide is looking good Brian, well done. I like your idea for finishing off the interplane strut bolts, I'll see if I can incorporate a similar method without having to retrace my steps too much. 

I built the same Martin Tuck model in the late 80s when it was first published and made the same discovery with regard to some of the drawn parts being incorrect, the fuselage formers especially, I recall. Nevertheless it was a good flyer, and does not needs much power. At around 13lbs mine was more than adequate on OS 48 4-strokes.

Shortly after building the Rapide, I read an article in the now defunct Wingspan magazine, about the DH86 and decided there was no reason why it should should not fly just as well and it turned out to be the case. There was a centre page 3-view included with the article and that formed the basis for the design.

Good luck with the model, there aren't nearly enough de Havilland transports around in my opinion!   

[RottenRow]

Thanks John,

 

I'll take a few pictures and post them later. I forgot to mention that the M3 CSK screws I used were hex drive (ie for an Allen key). A 2mm Allen key fits them.

 

Yes the fuselage formers on the Martin Tuck plan weren't symmetrical, the wing rib outlines not only had to be trimmed by different amounts to allow for sheeting and cap strips but a couple of them were the wrong size anyway. It also turned out that although the wing is undercambered on the model, it isn't on the full-size Rapide. If it helps it fly better though that's fine. Also the outboard (single) interplane strut was one inch too short!!

 

I suspect that the errors crept in at the draughting stage at MAP. I remember Martin flying the original model at one of the Old Warden Scale Days in the 1980s. He used to work for De Havilland / British Aerospace at Hatfield so had access to drawings etc.

 

Mine is going to be powered by two ASP / SC 52s. It will have the BEA livery of the full-size that currently lives at Old Warden but belongs to Philip Meeson.

 

I like your idea on the undercarriage with the square plates. Mine are made from HobbyKing oleos fitted into pianowire stubs with an aluminium spreader bar. I retained the spring coil but only put in one turn. I think the square plate idea might be better, to prevent one leg bending back more than the other, although the axle should help with that. I'll look at modifying mine, it will be more of a rectangle rather than a square otherwise the wheel would hit it on full oleo compression.

 

Is your DH86 going to be military again or in a civilian scheme this time?

 

Brian.

[John Rickett 102]

The square plates on the DH86 undercarriage were thoughtfully included by Tony Goodger (Unitracts) to prevent sideways movement of the legs damaging the close fitting trousers. The plates are just over 1mm thick so will not do much to prevent one leg from bending backward more than another. Having said that, I've not experienced any problems in that regard and the legs are probably quite a bit longer than yours at 8 1/2" so I doubt you will have any problems.

 

The finish will be a British civilian scheme and not predominately silver as most were. I no longer have the sharp vision of youth and do not have to fly far away before an all-silver model blends into the cloud. In their relatively short lives these aircraft changed ownership frequently so there are some interesting schemes to choose from. With just about all the pictures being in black and white, the hard part is knowing what shade of a colour was used, two pictures of the same aircraft livery can be quite deceptive in what shade they were - perhaps it doesn't matter, the longest surviving example was broken up after suffering irreparable damage in Spain in 1958, so even the most ardent rivet counter would be hard pressed to prove a colour was wrong!    

[John Rickett 102]

A slight distraction occurred yesterday when a packet arrived, 20 lenses for use as landing light glasses - I only need one but those clever little marketing people in China had a minimum order quantity of 20. They are called cabochons and produced for jewellery making. I found I could buy one for about £40 from America or 20 for about £8 from China so a decision wasn't too long in the making.

 

I had previously used a circle of perspex, which promptly melted under the power of the 50w halogen lamp, this was substituted for a piece of flat glass from an old torch but being flat didn't look the part, however this one, at 35mm diameter, curves pretty much perfectly with the curve of the front fuselage.

 

The grey matter now needs to be employed in how to produce a convincing rim to retain both lens and lamp yet still be able to remove the lamp if necessary 

        

[Danny Fenton]

Cabochons also work well for the top lens on WW2 gun sights, used them on a Nijhuis Spit sight and one on a Taylor Hurricane.

[John Rickett 102]

Ok Danny, I'm sure, as you've discovered, they have a few applications in modelling, deception is partly the joy of the hobby. It must have been my lack of education and sheltered life thereafter but I had not come across the word cabochon before, I was simply calling them glass domes.  

[Danny Fenton]

I stumbled on them as well, yours look a bit better formed than the ones I found (UK)

 

 

Enjoying your restoration John ?

 

Cheers

Danny

[John Rickett 102]

That looks very neat Danny, did you make the rest of the gunsight?