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Old Nov 01, 2012, 03:04 AM
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#47 Model Airplane Building Clinic >> “Great Planes P51 Mustang"

Hello everyone (or anyone)

As I use the internet as a great source of information for building but never added anything myself I decided to join in on the clinic. Normally I do house modifications and that sort of stuff but I am all finished at home and with family members. So it was time for a new hobby and thought building models will be fun. After lots of build reads and the Airfieldmodels website I decided it should be fun and would give it a try.

I was planning on building a trainer such as a SIG Kadet, Robbe Charter or something like that. Unfortunately there is not much choice for kits here in the Netherlands and these were all not in stock so my wife got me the P51 from great planes for my birthday. As I have no flying experience this just means I get to build a trainer after the P51 .

Anyway to keep it short I have built a couple of Guillow rubber band models when I was 12 or so 20 years ago so I will consider myself a newbie. I will be building the plane by the book as I have no idea what to expect. As the price of everything is high I want to extend the build time and I will do this by adding the optional mechanical retracts. There are many threads on how frustrating retracts are so I guess I will see if this was the right choice along the way.

I have completed several steps all ready and so will add these the coming days.
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Old Nov 01, 2012, 03:36 AM
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The first build requirement was the fin and stabilizer. These are made of solid balsa blocks/sheets as seems standard for Great Planes. I prefer built up structures as they look better but I guess it doesn't make that much difference if you cover them with non-transparent covering. Not much to remark on the gluing and sanding except the amount of dust produced. I will be building everything with wood glue as I think this will give me more time to line everything up the whole time.

I have epoxied the wire joining the control surfaces on the stabilizer but not yet on the fin for the tail wheel. I don't see any photos or descriptions on that join and it seems a bit fragile to me as only the wire stuck gets glued and the wire down the side cant be else the hinge will be fixed. More of that later on in the build I guess.
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Old Nov 01, 2012, 03:45 AM
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The next step was the wings and top sheeting. I liked the idea of using magnets so order a couple online and found some sheet metal lying around. I was planning on building some help pieces but until now the magnets seem suitable as they are. I will see if this is still true with the fuselage.

In order to get the leading edge mounted two v's had to be cut put for the bending (actually breaking). As I had dreaded, while getting it in place and sanding the groves to accept the ribs, it broke in half at one of the breaks. Once it was mounted it is not noticeable but I don't like how the fractured wood looks. This will have to be filled in and sanded flat. Not sure if was expected to break and look smoothly.
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Old Nov 01, 2012, 03:55 AM
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The next step was installing the shear webs and other webs and rib cross joints. The choice of wood glue over CA was well done as I have glued many pieces incorrectly. A new baby in the house (2 weeks old) doesn't increase your alertness in the evenings.

The inner ribs are angled and have to be installed using a angle gauge included in the kit. This was a bit of a pain and could be a lot easier as I noticed installing the shear webs. Included in the kit are three webs between the last two inner ribs. These are all die cut to the correct angles and so I will use them as guides on the second wing. The angle seems ok but it will ease my mind if I can use the extra measuring points.
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Old Nov 01, 2012, 04:16 AM
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This is the last post on my progress already done. The wing seems to be flying together, took about a week or so mainly due to the drying time and hour or two I spend each night.

This step, several actually, required adding the sheeting to the top of the wing. The sheeting on the leading edge front needs quite a bend and so needs to be wet. Here one of the pieces of tape loosened up over night and so the sheet was not flat down. I had to cut off the last few ribs and glue it again. Luckily this worked out better than expected and it looks as if was always that way.

There were several tricky angles and corners to fill up with sheeting at the tail and leading edge. I used some cardboard to make cutouts and overlarge sheets that I sanded down to fit. I am very happy with the way it was all turned out till now. There is only one corner that needs some filling up but this was due more to the 3D bends in the sheeting and wing. In the last picture you can see me framing up the second wing, haven't gotten much further than gluing the doublers on the spars and checking that all fits in place.

Next step is a repeat on the other wing over the next few days. While waiting for the "paint to dry" I went out and got myself a OS MAX 46 AX as a power source. Looks like it will be a lot of fun getting that run in, as a mechanical engineer I cant get myself to go electric.
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Old Nov 02, 2012, 04:40 AM
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I have gotten the second wing well under way. The ribs and spars are glued in in the first photo. I took care with the leading edge so as not to break it. This was done by wetting the joint, but it still broke. Next time I will cut them to the correct angle and just use a butt joint.

The second photo are the shear webs being glued in place. Luckily I could use all my clamps so I could prove to my wife that I needed them all. When not in use they are entertainment for my daughter.

The last photo is the major part of the top sheeting being glued down. There are only a couple of triangles left over in the corners for gluing this evening.

The weekend I will be planning how to but the retracts in. I bought a set of Thunder Tiger Superlite Retracts size 60. The retract frame is a bit smaller than the ones indicated on the planes but for the rest looks like I can just follow the manual. Should be interesting.
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Old Nov 02, 2012, 01:38 PM
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United States, NH, Bedford
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Subscribed. Really nice clean build, Harare.
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Old Nov 02, 2012, 02:53 PM
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Thank you very much.

I have finished the top sheeting of the second wing and its waiting to dry. Now I am wondering if I should install the retracts or carry on with the fuselage. I am rather dreading the retracts after reading all the comments on internet about installing them. Ill give it a nights sleep to see how the wings turn out once layed togethor. That should help decide whether to carry on building on the fuselage or finish off the wings.
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Old Nov 03, 2012, 06:45 AM
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United States, NY, Eldred
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In regards to post #2 about the strength of wire joiners on the control surfaces, one trick is to use fiberglass cloth over the wire that lays in the gap you cut for the wire to be flush with the surface. This will add significant strength.
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Old Nov 03, 2012, 08:47 AM
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Thanks for the information on the fibreglass. When I connect the wings togethor with fibreglass I will add a bit to around the wire joiner grooves.

The top of both wings are sheeted now with still some small bits of work to be done. Like sanding and putting strips ontop of the ribs.

The angles of the ribs are nice and identicale but there is a slight curve in the length of both of them. This leaves about a millimeter gap at either the leading edge or trailing edge. I never thought about checking the straightness of the ribs, just the angles. The leading edge ribs are bent a little inward on both sides. I will think how to solve that along the way to joining them. Next time I will use a straight edge clamped to the outer ribs. Live and learn I guess, still annoying though.
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Old Nov 21, 2012, 09:16 AM
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Hi back from a very busy couple of weeks at work in combination with a sick baby so nothing has been happening. First off I got myself the power plant which is an OS Max 46.

The next step has been trying to get the retracts installed. Unfortunately nothing fits that well and so its a lot of modifying and moving stuff around.

I got the retracts nearly completely fitted, just have to epoxy the rails in and fine tune the spacing. The next step is then to cut the holes for the control rods. After that the bottom sheeting needs installation and the retract holes neatened up with sheeting. Sounds simple, hope it is.

One of the uncertainties I have is if the rails and wood connections are strong enough for landing. As I have never flown, landed or even seen it I am not sure how much stress they endure.

I think next time to ensure, I don't need to trim the rails, the retracts will be installed at an angle to the wing. The wheels can then be rotated to ensure they are correctly lined up when dropped down.
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Old Nov 24, 2012, 11:58 AM
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I didn't think the retract rails were strong enough compared to the pictures out of the manual so I added pine planks under the rails. These are connected to the leading edge, not that that is very strong, and to the spar. I think this will be strong enough but with out ever seeing any model planes flying or landing its all based on my imagination. An additional advantage is that it will give the screws some more meat to grip too.

The most time consuming was getting the wheel wells bent. I had hoped to bend them in one sheet with the grain. After lots of steaming and soaking it still was not flexible enough so I had to accept that i needed to bend parallel with the grain.

The next step is figuring out where to put the retract servo and whether to cut out and put in the rails before I glue the wings together.

I got myself some easy connectors for the retracts but the screws are longer than the servo clearance rendering them unusable. There should be a solution but I can't think of it with out grinding down the screws. Sorry about the photo I don't have macro on my compact and didn't feel like getting my big camera. Its a pity because I really liked the feel and quality of them.
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Old Nov 24, 2012, 12:00 PM
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I purchased a propellor today out of boredom as I wont be needing it for quite a while still. However it doesnt fit tightly on the engine shaft and can move a lot. Does it need a bushing or prop filler?

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Old Nov 25, 2012, 07:32 AM
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The retracts are installed and working smoothly. Now I have to figure out where to put the servo and the connecting rods. Temporarily clamped the wings together so I can measure it up. I think I will get the servo in and the retracts working before I sheet the open side of the wing. This is because I am not sure how much rotation I need on the wire for the turning of the servo.

Its a lot higher off the ground than I thought it would be, wonder what it will look like with the fuselage attached.
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Old Nov 27, 2012, 05:41 PM
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Maple Ridge B.C. Canada
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I built this kit a few years ago. I put a Saito .72 in mine. It is a fantastic flyer - very stable and almost like a trainer. It is still going strong and I purchased a second kit just to have on hand.
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