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Top Flite P51 - 65" span

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Bob Cotsford02/07/2020 14:50:02
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8646 forum posts
483 photos

I guess that's why we saw the pilots of these models back in the '70s and '80s as God-like creatures, filthy rich and skilled beyond our wildest dreams. A .60 was a big expensive engine back then, or at least it was beyond my budget at the time.

Nigel R02/07/2020 15:00:59
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3987 forum posts
722 photos

Sometimes kit wood selection leaves a lot to be desired and needs to be thrown out and replaced with better.

Peter Jenkins03/07/2020 01:06:33
1624 forum posts
305 photos

Trouble is Nigel it rather negates the whole point of buying a kit if you do that plus it doubles the cost! On the whole, I'm quite happy with most of the wood in this kit and it looks like it will come in under 11 lb so the 120 should do what I would like it to do - give a nice large manoeuvres.

Peter Jenkins03/07/2020 01:10:16
1624 forum posts
305 photos

I've been held up for various bits and pieces but this evening I implemented Plan B on the tail wheel retract door operation. Looks like Plan C is now required!

However, by using the servo delay function on my Tx, it rather looks like I can dispense with the u/c door sequencer and get some control over u/c deployment speeds. It is surprising how much aggravation this part of the build is creating! Just makes me more determined to find a way to make it work!

Adrian Smith 103/07/2020 11:53:22
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2472 forum posts
1273 photos

I feel your pain, Peter. I have had jobs in the past that have driven me up the wall. Even when I seemingly found a solution I was not happy with it again and went back to the drawing board. We are a tenacious lot we modellers and I am sure you will come up with something to solve it.

Peter Jenkins03/07/2020 12:01:06
1624 forum posts
305 photos

Thanks Adrian. Plan D is starting to form - just in case!

Ron Gray03/07/2020 12:07:27
2235 forum posts
978 photos

KISS! And that’s not a 💋

Peter Jenkins04/07/2020 23:33:28
1624 forum posts
305 photos

Well, Plan D eventually came good and it certainly matches KISS! I tried having separate pushrods to connect each door to the servo arm. I started with both pushrods with Z bends through one hole in the servo arm but that brought problems with a slightly different geometry causing one door to be pulled further in than the other. The light bulb finally went on and I ended up using different holes in the servo arm to give a difference in total door movement. That worked! Phew - sadly it's cost almost 3 weeks while I have fiddled around with rubber bands and different arrangements using a servo.

mustang 129.jpg

mustang 130.jpg

I had to bend the top end of the port pushrod so that it would clear the retracted tail wheel but the whole operation is now smooth with no binding and, most importantly, the doors and the tail wheel miss each other during operation! I ended up using the Servo Slow function on my Tx (JR XG11).

On opening the doors open with around 0.3 sec additional to normal. The tail wheel is set at just over 3 secs slower than normal and that gets the doors open pronto allowing the wheel to travel unhindered. On retraction, this is reversed so that the tail wheel travels at 0.3 secs slower than normal while the doors are set at just under 4 secs longer than normal.

As I've yet to work out how to post videos on You Tube, and you can't post a video in the Album, you'll have to take my word for it that the retract function now works well.

I can not carry on with the rest of the build. Phew!

Adrian Smith 105/07/2020 15:26:02
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2472 forum posts
1273 photos

I knew you would sort it in the end, Peter. As for videos I upload the clip on to youtube first (reasonably quick if you have a decent upload speed) , then copy the youtube link into the MF thread URL box icon (car?) on the second row third from the left that shows up when you start a new post. There are other ways that it can be done, but it works for me. yes

Peter Jenkins05/07/2020 17:20:32
1624 forum posts
305 photos

Thanks Adrian. It's getting the video onto YouTube that I've never done and, frankly, never felt the need - until now! Too many other things to do which are higher up the priority list I'm afraid. I'll get there one day!

Ron Gray05/07/2020 17:49:31
2235 forum posts
978 photos

Do you want me to do it for you Peter (from the one you sent me)?

Peter Jenkins05/07/2020 18:45:38
1624 forum posts
305 photos

That would be very helpful Ron. Then could you drop me or note, or we'll chat on the phone, on how you do it and I'll try and educate myself! Be handy for the main u/c doors in due course.

Ron Gray06/07/2020 22:04:50
2235 forum posts
978 photos
Peter Jenkins06/07/2020 22:27:15
1624 forum posts
305 photos

Thanks for posting that Ron

I should explain that the "background" music is from Classic FM to which I was listening when I took the video.

Since taking the video, I've tweaked the servo slow speeds so the retraction operation is much closer in timing. Quite happy that there is sufficient separation to allow for air forces on the mechanism. Have to wait till I can fly it.

Adrian Smith 107/07/2020 19:33:49
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2472 forum posts
1273 photos

Neat, Peter. Funny how such a short clip masks hours of toil. yes

Peter Jenkins07/07/2020 20:22:11
1624 forum posts
305 photos

Thanks Adrian. There was a moment when I almost decided to junk the doors but a little voice said "no way"!

Peter Jenkins08/07/2020 19:59:50
1624 forum posts
305 photos

After a detour to the dentist to get one of my molars almost out - he had to give up after 1.30 mins of tugging, drilling and heaving - I've managed to get a couple of small jobs done on the Mustang.

The tailplane and elevators have had their tips sanded to shape and the inboard end of the elevator construction, the addition of a coupling of fairing blocks added to the elevator, shaped and then cut off and glued to the fuselage. I'm not sure why this is called for as I cannot see this on the full size. Still, it's done.

mustang 131.jpg

The next small job was to glue the rest of the upper fuselage formers in place including the instrument panel that is provided with a gauge to get the angle of tilt correct. Again, not sure why this is designed this way as the full size instrument panel if vertical and not sloping.

mustang 132.jpg

Peter Jenkins18/07/2020 00:21:14
1624 forum posts
305 photos

Things have slowed down a tad so I've not posted till I had made a decent bit of progress.

I've now added the stringers to the front and rear of the fuselage top formers. The next job was to cut the sheeting for the front top of the fuselage from 1/8" sheet. The instructions tell you to glue the bottom of the sheets to the fuselage and, when the glue is dry, to damp the sheeting and bend it over to glue it to the other formers. I decided to cut the sheet so that it ended at the mid point on the stringer at the top of the fuselage before I glued the sheeting in place.

This photo shows all the stringers in place and the 2 forward fuselage sheets glued into place.

mustang 133.jpg

and the view from the front end:

mustang 134.jpg

Once the glue had set, as suggested by the instructions, I dampened the back of one of the sheets, made sure that it would wrap around and end at the mid point of the top stringer and then glued it in place supporting it with pins:

mustang 135.jpg

Once that was dry, I dealt with the other side in the same manner. The next picture shows the two skins glued into place with all the supporting pins removed.

mustang 136.jpg

Peter Jenkins18/07/2020 00:31:30
1624 forum posts
305 photos

The next step was to cut the rear fuselage sheeting to shape and then glue that in place. Again, because of the curvature of the fuselage formers, I chose to glue the skins to the fuselage at the bottom and, when the glue was set, to glue and then clamp and pin the fuselage sides to the formers.

mustang 138.jpg

mustang 139.jpg

Once set, it was back to the razor plane and sanding block to trim the fuselage skins level with the formers.

mustang 140.jpg

mustang 141.jpg

A hunt through the remaining wood in the kit box produced the 1/2 inch fuselage top decking. This had to be shaped to fit over the tailplane and rest against the front of the fin. I at last had a decent job for my curved Permagrit sanding block - the one with the grit on the outside! Once that was done and the decking roughly trimmed to the fuselage top, I glued that in place.

mustang 142.jpg

Once that was set, it was out with the razor plane to get the bulk of the balsa removed in shavings rather than dust! Razor planes really are worth their weight in dust!

mustang 143.jpg

Final shaping was done with a long Permagrit sanding block, coarse first and then finishing with the medium grit.

mustang 144.jpg

Richard Clark 218/07/2020 03:27:25
424 forum posts
Posted by Peter Jenkins on 02/07/2020 14:41:12:

Nigel, you are right provided that the wood in the kit is designed for a light build. In practice, in these older kits, my experience has been that they were built to survive a crash landing so, those of us who learned how to land, pay the penalty in weight. Today's light weight models with formers fretted out to save weight do not survive a robust arrival and tend to have the u/c plate ripped out early on.

So, you have to be realistic about the issue of what size engine to fit. I flew a friends TF Spitfire with an OS 90. It was grossly underpowered given its weight. You had to dive at full throttle to work up the speed required for anything other than a tight loop. It was not fun flying it as I was always on tenterhooks lest it stall. Even a pull out had to be gentle lest it tip stalled.

On that basis, I decided that the OS 120 was a better bet as I want to be able to fly the Mustang like the full size and carry out large sweeping manoeuvres.. It doesn't need all the power to be used all the time. I fly F3A competitively and learning how to use the throttle properly is something that took me 2 years. OK, I'm a slow learner but when I watch newcomers to aerobatics they struggle just as I did with both throttle, and the other essential control, the rudder.

This is not to say that I think it's a good idea to fit a 30 cc petrol in this model but if proper throttle control is used then it shouldn't be a problem. The problem is, what is proper throttle control! Back to my earlier point.

 

You and Nigel both make valid points, but remember these TF kits were designed for the non-schnuerle ported 60's of the period and flew perfectly well and in a scale like manner. (The  tip stalling you mention may be a 'high speed stall' caused by an over-weight plane  in a high G manoeuvre.)

Though your 120 won't do any harm as the planes are strongly built, as you say. The Spitfire wing excessively so - I actually had to boil the top ones of the two gigantic basswood main spars and pre-bend them while hot and wet to fit.

A purely personal opinion but I don't think these TF kits were very good originally, and the 'Gold Editions' are no better. The Spitfire has a grossly over-thick wing which ruins the appearance (the Spitfire had the thinnest wing of any WW2 fighter) and there are several other severe  construction faults, all of which would greatly  puzzle those without  enough experience to make their own changes..

And pre-warned about the Cessna Skyhawk tearing its wing  off carrying half the cabin with it in a 'sudden'  manoeuvre I greatly modified mine.    

As for 30 cc in the P-51  I think it's barmy

Edited By Richard Clark 2 on 18/07/2020 03:40:43

Edited By Richard Clark 2 on 18/07/2020 04:00:53

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