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Top Flite P51 - 65" span

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Peter Jenkins01/04/2020 18:21:18
1529 forum posts
256 photos
Posted by Darrin Pretorius 1 on 01/04/2020 11:40:47:

I noticed your mention of the size difference between the 3/32 and the 3/16 Robart hinges. I wonder if the 1/8 might not have been a little better?

You make a good point Darrin. Do you have any in stock? I'll PM you my email address.

Peter

Peter Jenkins01/04/2020 18:36:29
1529 forum posts
256 photos

Hi Chris

Nice looking model. Hope mine comes out as good as that. Thanks for the warning not to over complicate things but I will take care not to add too much weight. I know that the fuselage structure looks pretty solid and I wonder if there might not be some opportunity to save weight there. However, with an OS 120 FS up front I suspect that model could do with a little extra weight that a retracting tail wheel will add. I don't think doors will add a lot of weight but will complicate things. The sequencer for the main door operation I already have and it works really well with the Robart electric retracts so the only issue is building and hingeing the doors. Not looking forward to that!

Are there any poo traps I should watch out for in the build? I've read the construction manual through several times to try and get a picture of the build in my brain and I cannot see any issues at the moment. That, of course, will change when I hit them!

Peter

Peter Jenkins01/04/2020 18:43:16
1529 forum posts
256 photos

This morning, the postman brought me a book I'd seen on Mustangs flown by the Polish pilots in 303 Sqn. There are some lovely photographs of the Mustang IV or P51D model giving a host of detail that is tempting but I will pass up! Here's the front cover and as I'm sure you will agree the finish will be a lot easier than going for the camouflage that was used by the RAF up until Mar/Apr 1945. The aircraft I intend to depict was flown by the last 303 Sqn Cdr who was also one of the original group of pilots who formed 303 in Aug 1940 and flew in the B of B. He got 3 kills in the Battle and a total of 8 kills and 3 probables. He was also the last CO of 303 Sqn and was there at the end of 1946 when the squadron was disestablished at RAF Hethel. Must have been a very sad day for the Poles given that their homeland had become a no go area for them after the war.

mustang 08.jpg

Peter Jenkins01/04/2020 18:46:45
1529 forum posts
256 photos

As I'm using aliphatic glue, my progress is not as blazingly fast as the manual would have you believe! What I have done today is to make up the four sets of skins to cover the tailplane top and bottom and left and right. They are drying off in the shed and I hope to get the top skins on tomorrow. The photo shows just 2 of the skins together with a drill jig I made up from some scrap ply (resting on the pliers) in order to drill the hinge point hole in the centre of the tail plane and elevator. Given Darrin's input, I'm probably going to move up to the 1/8" Robart hinges.

mustang 09.jpg

DaveyP02/04/2020 09:45:03
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226 forum posts
47 photos

Hi Peter, steady progress and I do like your drill jig idea thumbs up

Dave P

Peter Jenkins02/04/2020 23:48:15
1529 forum posts
256 photos

I finally found a use for my LiPos which are all at storage charge!

mustang 10.jpg

Underneath that pile of LiPos is the tailplane with the top sheeting glued in place and the LiPos making it stick! I shall steam a curve into the bottom skins so that there is less of a drama in trying to get the skin to adhere to the ribs and spars! Funny how much you forget if you don't build something for some time!

Chris Freeman 303/04/2020 07:53:37
353 forum posts
525 photos

Hi Peter

I found that the manual was very informative and that the kit is very well thought out. A mustang is one of the few war birds that does not need nose weight so the retracting tail wheel is not a bad idea. I made fibre glass parts in the plastic kit parts, I just used PVA release and then made my parts in the plastic. They are a little smaller then but came out quite well and will not be as brittle as the plastic.

The main goal that I set myself with this build was to see what sort of finish I could get using plastic film and not going the glass and paint route which can add quite a bit of weight. By using the manual directions I got what I thought was a good finish and a great flying aircraft. The cowl was sprayed white and the black covering was ironed onto the paint and has stayed in position. A mustang really is a treat to fly if it is done right, even the retracts and flaps do not need mixing when used.

mu1.jpg img_2621.jpg

Tim Flyer03/04/2020 10:19:01
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1275 forum posts
234 photos

Very impressive indeed Chris.! I must say I also used the plastic film route on my recent Chipmunk build and it certainly was easier for me and I think was probably turned out better than my efforts at painting. By the way does anyone know if this Top Flite Mustang kit is still available. I have a spare OS95v and a Laser 80 so maybe I should have a go too ?  

Edited By Tim Flyer on 03/04/2020 10:21:00

Peter Jenkins03/04/2020 20:41:01
1529 forum posts
256 photos

Oooh, that does look nice Chris. I see you went for the second u/c door. Any tips you'd like to share on doing the job once?

With an OS120 FS up front, a retractable tail wheel and doors should help with getting the CG in the right place. What engine are you using and did you have a custom silencer made?

Peter Jenkins03/04/2020 20:46:29
1529 forum posts
256 photos

Tim, I've not been able to find any sign of TopFlite kits. I bought mine when it was offered on the BMFA Classifieds site. As it happens, I was offered the chance of buying a second one and did so. That's my insurance policy or my 2and airframe with a different identity.

Peter Jenkins03/04/2020 21:13:22
1529 forum posts
256 photos

Today, progress was limited to fixing the bond between skins and some ribs as well as the skin to LE join. Needed my entire stock of spring clamps, so just ordered a load more. Used a razor plane to plane off the excess sheet to level with the LE.

3 ribs were clearly too low on the underside after taking off the tabs and sanding the ribs and TE and LE flush. So, some remedial action was required. Back to the left over balsa sheets to cut some soft balsa as packing. Next job will be to send the ribs to shape, cut out the sheet covering the balance tabs before gluing the 2 bottom skins in place. Hope to show some pictures after tomorrow's session.

Tim Flyer03/04/2020 21:57:58
avatar
1275 forum posts
234 photos

Good idea to buy two Peter. I must admit to having done that before too

Peter Jenkins04/04/2020 23:44:11
1529 forum posts
256 photos

Well, I finally managed to get some time in the shed today.

First of all, I was surprised to see that most of the ribs on the underside of the tailplane seemed to have very little camber. After consulting the plan it was clear that the tailplane was symmetrical so I grabbed a sheet of balsa out of which I'd popped the tailplane ribs and cut some 1/8" strip. I then cut these to size and glued them to the top of the ribs that seemed to have a flat undersurface profile as you can see below.

mustang 11.jpg

I sanded these to the required section and then cut out the sheet that covered the structure into which the balance tab would fit. I then glued on the previously glued together sheeting. It was only after the glue had set that I remembered I wanted to fit some balsa blocks to drill into for fixing the Robart hinges!!!!!

So, after carefully marking where I needed to cut our the sheet, I bit the bullet and cut! The 1/8" Robart pin hinges had arrived just after lunch and proved to be exactly the right size. So, I decided that 3 hinges per elevator would be fine and made up 4 blocks from 1/2" sheet to fit the space. The third hinge block will be the block I glued in to the inboard end of the balance tab cutout. Having got the blocks glued in it now looks like this.

mustang 12.jpg

Once the glue had dried, I added the last bit of sheeting and clamped it up to dry. While it was drying, I took the time to put the 3 sizes of hinge pin side by side and it quite surprised me how big the difference in size was! The grey one on the left is 3/16", the black one in the middle is the 1/8" one, and the black one on the right is the 3/32" one.

mustang 13.jpg

Once the glue had dried, I used a razor plane to cut back the LE sheet so that it came level with the LE spar. It now looks like this, although since I've taken the picture, I've put a bit of light weight filler over the 2 cut outs I had to make to get the hinge blocks in! It now looks more like a stabiliser!

mustang 14.jpg

Tomorrow, I'll glue on the tip blocks, sand the LE to the required shape and figure out how best to sand the rear stab structure so that it has a concave structure as well as shaping the elevator leading edges.

Peter Jenkins06/04/2020 18:50:54
1529 forum posts
256 photos

Just to clarify on the hinging of the control surfaces, this is what I am trying to achieve.  The black + marks the hinge point for the control surface.

mustang 15.jpg

As it happens, the 1/16" square stringers are not really needed so I will not be using them when hinging the rudder and ailerons. Using a bit of scrap, I mocked up what this might look like and checked that it worked OK and that 's the next photo.

mustang 16.jpg

It all works fine provided that you have properly radiused the control surface LE. As I was to find later, it is best done by trial and error! Isn't it always?

So, I then drilled the elevators using my home make centre drilling jig and then shaped the leading edge. The photo below shows one elevator LE shaped and one about to be. Using the long Permagrit sanding block makes the job very easy to achieve.

mustang 17.jpg

mustang 18.jpg

As you will see on the right most hole in the lower elevator, I have cut a clearance slot either side of the hinge pin head. That allows the hinge to operate without fouling the balsa.

The next job was to form the tailplane trialing edge to create a hemspherical socket for the elevator to fit into. This proved to be a real pain and that decided me on altering the construction for future control surfaces as I mentioned earlier. So, here's the first elevator in place with the pin hinges dry engaged. They won't get stuck in place till I've covered the Mustang.

mustang 19.jpg

As you can see, the hinge is pretty close to the full size and a lot closer to scale than the normal V hinge. Finally, here are both the elevators dry connected, the tips sanded to shape (final sanding still required) and the balance tab slots in the tailplane cut out. I will be gluing the balance tabs on in my next session and also sorting out the elevator saddle/horn and dry fit that. That needs to move aft by 1/8" so that it sits on the new hinge line.

mustang 20.jpg

Edited By Peter Jenkins on 06/04/2020 18:51:46

Edited By Peter Jenkins on 06/04/2020 18:52:41

Ron Gray06/04/2020 20:03:59
1931 forum posts
803 photos

Nice attention to detail Peter

Peter Jenkins06/04/2020 20:23:44
1529 forum posts
256 photos

Thanks Ron.

Bruce Collinson06/04/2020 20:37:07
515 forum posts

Watching with interest Peter.

Those long reach spring clamps are not ones I have tripped over before but look useful. Where from please?

BTC

Peter Jenkins06/04/2020 23:12:48
1529 forum posts
256 photos
Posted by Bruce Collinson on 06/04/2020 20:37:07:

Watching with interest Peter.

Those long reach spring clamps are not ones I have tripped over before but look useful. Where from please?

BTC

Sorry Bruce, I've had them for so long that I can't remember where I got them. They are prone to falling apart! That is the yellow pad tends to detach just as you are about to clamp something up! I prefer the ordinary spring clamp that you can see in some of the photos and will no doubt see when I start on the wing!

Peter Jenkins09/04/2020 23:14:58
1529 forum posts
256 photos

There has been a slight delay while I ponder two issues. The first is the placement of the main retracts and the second is the issue of using Oracover Chrome. On the issue of the retracts, as I'm going to be using two doors, I need to make sure I have a workable solution before starting the wing build. This is what I'm going to have to accommodate:

mustang 21.jpg

The blue board, in between the 2 wheels, is the Turnigy retract and door timing controller while the red coloured box connected to the retract is the Robart control box for their electric retracts. After pondering how I might combine these two contollers, a light went on in my brain - yes, I know! The blue control box will control the door servos and provide the timing while the Robart control box will control the retracts and both will be on a Y lead originating from the Gear Channel of the Rx. The door servo will move much more quickly than the retract servo and there is a slight delay in the retract beginning to operate once the command has been issued.

To be absolutely sure this will all work in practice, I've decided to build a mockup of the part of the wing from the centre line to the end of the retract. This will allow me to check how deeply to position the retract so that the door attached to the leg lies flush with the wing and secondly to construct the inner gear door and test out the geometry for the servo linkage to open and close the door. My gut feel is that I might need a fairly powerful digital servo as the inner doors are quite large and may require a bit of force to operate in flight as well as to hold the commanded position against any blow back. That indicates a digital rather than an analogue servo to avoid any chance of blow back.

There is no clear statement as to whether Oracover Chrome will block the radio signal so I will build a small box, cover it with Chrome, install the Rx and aerials inside it and then see is the Rx range is still the same as the original range in range check mode. If this fails, then the option will be to hide the Rx aerials on the external skin of the fuselage using some of the markings to hide the aerial. My first thoughts are to put some black trim to simulate the canopy track behind the canopy and the black squadron numbers to provide the orthogonal requirement for aerial mounting. The only problem will be the secondary Rx which on my 11 Ch JR DMSS set up has no external aerials. The secondary Rx also provides the telemetry transmission so that will let me know if the Rx transmission is working as well during the test.

Edited By Peter Jenkins on 09/04/2020 23:17:00

Peter Jenkins10/04/2020 23:39:32
1529 forum posts
256 photos

I did some more research on the use of Oracover Chrome and found the following thread on another forum that indicates that practical experience with a "covering" called Flite Metal (which is real aluminium sheet) found that:

After the initial test of the Futaba© system it became apparent receiver & antenna placement was of little concern because evaluation results were the same as when the system sat outside of plane on a board. Please re-read that sentence again before continuing.

I will be doing my own tests but it is good to see that others have found virtually no effect on 2.4 GHz radio when enclosed by aluminum sheet itself.

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