Top Flite P51 - 65" span

[Peter Jenkins]

So, this is the top of the wing showing the sheeting completed. If you look carefully, the aileron servo recess has all the strings sitting in it. I will probably use it to hold the Robart control box and will need to attach the retract sequencing card to the top of the wing as well.

And, this is the bottom of the wing. The construction at the rear is for the radiator intake. As I chose the cover the flaps separately from the main wing sheeting, you can see where I've left the gaps for cutting out the flaps. Strangely, that happens in the fuselage build section!

I've still got the wing tips to glue on and the ailerons to shape and dry hinge. That's tomorrow's job. Then I will build the fin and rudder before starting on the fuselage proper.

[Richard Clark 2]

Posted by Peter Jenkins on 14/05/2020 18:49:51:

Hi Richard,

Having completed the wing sheeting I weighed the wing and then all the bits that will go into the wing. The outcome was as follows:

• fully built and sheeted wing 24 oz
• Wing tips and ailerons 1.5 oz
• 12 Robart 3/16" pin hinges 0.2 oz
• 4 standard servo 5.6 oz
• 2 mini servos (doors) 2.0 oz
• 2 Robart electric retracts inc wheels 12.6 oz
• Retract sequencer and Robart contol 1.7 oz
• Servo lead extentions (estimated) 2.0 oz
• 2S LiPo for gear operation 2.0 oz
• GRAND TOTAL 51.6 oz or 3 lb 3.6 oz

I will need to cover it obviously and put on the decals but I can't see that adding more than say 8 oz so say 3 Lb 11.6 oz.

I don't understand your wing weighing 7 lb. The only guess I've made is the weight added by Oracover the rest are actual weights. Also, the u/c doors will be made out of 1 mm ply reinforced with balsa. As I'll have to cut the same amount of wing skin out the additional weight will not be very much.

Peter,

I don't understand it either, and as I said I ignored the warnings of the model shop owner and of course I did not initially notice the three pound difference between TopFlite's 'advertised on the box' weight and the actual 'in the instructions' weight of their original.

During the build I thought the Spitfire would be quite light, It does fly 'just about adequately' but I consider it one of my only three 'disasters' in a lifetime of modelling, the other two being a DH88 Comet racer scaled up to 65 inch span from the excellent Aeromodeller control line plan by 'L Last' but which I made for RC, and which despite the washout, section change, and the skills of the hand-carved Wallace and Gromit in the cockpit, is a tip stalling nightmare, and a well-known, grossly overpriced, and much hyped US/Chinese made EDF.

From the weights you give I am sure your P51 will be fine so I will now shut up

[Peter Jenkins]

Well, after the whole issue of wing weights, I decided to weigh all the wood that I have for the fuselage build. The heaviest parts were all the plywood formers and they tipped the scales at 7.2 oz. The total for all the material for the fuselage came to 6 lb 7.5 oz and that allowed for 4 oz for glue (not sure whether that's realistic) and 5 oz for the covering. I have yet to weigh the prop and spinner. I suspect the 4" spinner will be around 4 oz with a Xoar wood prop coming in at 2 oz. That will push the fuselage up to almost 7 lb. This does include the tailplane, fin and rudder.

If I add in the estimated wing weight of 3 lb 6 oz, I get an all up weight of 10lb 6oz. Top Flite quote a range of 8-10 lb. I suspect 8 lb is for a fixed u/c setup. 10lb would be perfectly reasonable for a 90 2 stroke. I will be happy to hit 10.5 lb dry weight. The RCU forum had folk with an 11.5 lb airframe that flew well.

I should say, I've been off sick with a gammy eye but that's now cleared up so today, I was finishing off the wing (added the wing tip blocks) and while that was drying, I cleared the building board and put the fuselage plan on it. I then assembled all the fin and rudder parts and set them out on the board.The fin TE and rudder LE had to be prepared by gluing together two identical parts - they are the ones with the clamps on them. The ribs need to be pinned down and the fin LE and TE then glued to them. Given the fun and games with sticking the wing LE on, I think I'll cyano the to and bottom ribs to the LE and TE and use aliphatic for the ones in between. That way, I'll reduce my dosage of cyano fumes!

While the fin/rudder parts were drying, I brought the four pieces of diecut balsa out and checked their fit. On the whole, the die cutting was pretty accurate just needing some minor sanding to get the all four pieces to fit together snugly. The instructions warn you that it is easy to make 2 sides the same. I have, therefore marked the inside face of each fuselage side with Port Inside and Stbd Inside. I hope that will mean I won't fall into the trap of making 2 identical sides!

The photo shows the 2 sides pinned down and drying after application of aliphatic glue.

Following my weight exercise, I examined all the balsa and ply parts provided and I think they are all a reasonable weight for the tasks they are required to perform. I will keep a close eye as the fuselage build proceeds to examine the scope for replacing ply formers with balsa formers.

I have a SLEC building jig and I might bring that out to build the fuselage on as it will help to avoid building a banana fuselage. That will require my centre bench to be used which will give easy access to both sides of the build.

The final bit of preparatory work I did was to offer up the retracting tail wheel to the fuselage plan and it was clear from that exercise that it would be helpful for the tail wheel to retract a bit further into the fuselage. I took a close look at the tail wheel mechanism and it looks like there is a way of retracting the tail wheel a bit more by cutting back the plastic spacers that provide the limit to travel for both extension and retraction.

I'm going to soft mount the OS120 using a proprietary soft mount. Apart from the motor, this mount is the next heaviest part tipping the scales at 7.9 oz. The plan shows a very similar mount and the size is virtually identical so that was good to see.

[Mike Rieder]

Hi Peter, got round to weighing the top flite spitfire wing,

its fully glassed, sprayed on camo and markings, lights, 4x servos, scale bits and bobs, electric retracts, canons wheels etc.. it will get a final coat of clear but it wont add much to the weight. It came in at a shade under 4lb.

 

Hi Peter, got round to a part in the build where i can take the wing off to weigh it,

so its a fully glassed wing with sprayed on camo and markings, 4x servos, electric retracts, lights, scale bits and bobs! Etc.. it will get a light coat of clear but want add much weight. It comes in at a shade under 4ld.

Edited By Mike Rieder on 17/05/2020 20:51:09

[Peter Jenkins]

Hi Mike,

Wow, that looks really good. That's a pretty amazing outcome. Glassed and painted wing with flaps, retracts and all the scale details and still come in under 4 lb - very well done.

I'm looking forward to having a Spit and Mustang formation when we get back to normality. I'd better speed up my building looking at where you are with your Spit.

[Peter Jenkins]

Managed to squeeze in some shed time today and glued up the fin frame. Hope to get the fin and rudder completed tomorrow.

The fuselage sides dried overnight so I game them a rubdown concentrating on the external side and then glued in the first of the plywood doublers. I took a good look at all the doublers and in all honesty I cannot see a safe way of reducing their size. However, having done a weight budget for the fuselage yesterday, I decided to press on with the kit as is. What is worth saying is that the die cutting of the 5 parts that are glued together to form the fuselage sides was very accurate. The ply doubler you can see on the second skin in the photo below only needed the residual stalks that held the ply to its plate removed otherwise they were both very accurately cut. As they say, you can never have too many clamps and I ran out when clamping up the first fuselage side and doubler so the second one is still awaiting it's fate!

I will follow the instructions and cut off the plan view of the fuselage over which the fuselage has to be built. I'll transfer the plan to my SLEC building board when I start that section.

[Peter Jenkins]

Well, I didn't manage to get the fin and rudder completed but made good progress with them. The next shot shows the fin half done with the sheeting on one side completed. I need to add the structure so that I can cut out the aerodynamic balance tab as I did for the elevator before adding the sheeting for the other side. You can see the rudder at the top of the picture clamped up to dry. The instructions had the rudder plate being glued to the fin hinge post and the balsa blocks forming the fin top and bottom to be glued on afterwards. I decided to glue the blocks on first and then glue the whole lot to the rudder hinge post. Much easier that way and don't know why they didn't tell you to do it that way! The double lines at the front and rear of the rudder are so you can position strips of 1/8" balsa.

I had a couple more bits to glue to the fuselage sides, being the aft top doubler and a a strip doubler which I did while the rudder was setting. I then spent 30 mins looking for the balsa strip that I needed for the rudder ribbing. Could I find it - no! I had just decided that I'd have to use some of the waste balsa from the die cut sheets to cut out the required strips when I noticed the missing strips sitting on the building board where I'd put them yesterday! do you get that happening to you?

The instructions tell you to just cut off rectangular bits and glue them to the rudder using the twin lines on each side of the rudder as guides. You then sand them to shape. I decided it was easier and used less balsa if I cut triangular pieces to fit and get 2 pieces of of every length of rectangular balsa. Result. The photo below shows the 2 fuselage sides now ready to begin the second stage of glueing them together with the ply formers and the completed rudder (sitting between the fuselage sides) awaiting final sanding of the top and bottom. The good thing is that I have made a left and a right side for the fuselage! One is always grateful for small mercies!

The rudder is rather an elaborate structure and is actually quite heavy. I'm beginning to wonder if cutting some lightening holes in the sheet rudder shape might not be a good idea. I think that first I'll sand off what looks like 50% of the block tip and bottom before deciding on any lightening holes.

[Peter Jenkins]

Today was going to be crack on with the fuselage day. However, the issue of fitting the retracting tail wheel and its steering took up much of the afternoon! I did get my SLEC building board out of storage and did as TF recommends and cut off the plan view of the fuselage and placed that on the SLEC board, covered it with SLEC plan protector and set to to dry assemble the fuselage.

I also offered up the tail wheel to the plan and noted that I would need to tilt the tail wheel towards the front of the aircraft at the top of the retract. This I eventually achieved by packing the rear of the retract with a 3/32" piece of balsa sanded to zero at the top end. This arrangement allows the wheel to come out at the the right place and to retract completely to allow the doors to close.

The final issue was how to steer the tail wheel. The Robart tail wheel I'm using has a steering mechanism that uses a pull-pull cable arrangement. This allows the unit to retract thus relaxing the steering wires. I dry assembled the fuselage to check for the best position for the retract servo and for a pull pull bellcrank arrangement that would be connected to the rudder servo. As the pull pull wires will cross on their way down the fuselage this conveniently allows one arm of the rudder servo to control the rudder and the other side of the servo arm to be used to control the pull pull bellcrank moving it in anti phase.

So, now that has been sorted out, I will be able to get on and glue something together tomorrow!

[Peter Jenkins]

I forgot to add the photo I took yesterday with the fuselage dry assembled in the SLEC fuselage jig. I took this to check out the pull pull run would be OK as it would be running below the rudder and elevator pushrods - just to be sure! The two holes you can see at the bottom of the picture are the holes for the rudder and elevator pushrod guides. The pull pull wires go to the just the outside of the former with the O in it you can see at the top of the photo. The entry holes for the wires will be either side of the former at the centre of the photo - the tailwheel is bolted to this former.

The next job was to make a new servo plate to move the servos forward to free up space for the pull pull yoke and retract servo as in the photo below. The pull pull yoke I fashioned from a servo arm, a 3 mm bolt a 1/8" ply plate with a further 1/8" ply spacer under the servo arm. Rather than glue this assembly into the fuselage, I put some hard balsa strips under the ply plate and secured the two together with some servo screws. I will glue the hard balsa strips to the fuselage and the will allow me to remove the pull pull servo arm if I ever need to. Probably won't now that I can remove it!

The next job was to drill holes in the remaining ply formers to support the retract rod guides. I had kept all the ply former press outs so looked for the Former 9 push out and cut a bit out of it, glued it into Former 9 and used that to drill the support hole. This next photo shows the extra holes in the formers marked: R for rudder, E for elevator, TW for tail wheel retract.

Having satisfied myself that I had done all the necessary preparation work, I go the glue out and glued in the first two formers and the servo mounting plate. They were all trued up using 2 try squares to keep them at 90 deg while the glue set.

Tomorrow, I hope that my pull pull wire will arrive so that I can take a further look at how it will all work before any further gluing.

The last fiddly bit will be making and fitting the tail wheel doors. The good news is that the RCU forum Mustang build identified a detailed account of how to do this from the Top Flite Beech Staggerwing manual. Needless to say, I went on line and downloaded the relevant parts of the manual. This shows the bits I need to make so that the doors are opened by a pusher fitted to the tail retracts and then closed by two sets of rubber bands! I guess they might need to be replaced relatively frequently as they are bound to end up being contaminated by glow exhaust!

[Robert Parker]

Hi Peter,

Your build rate is quite something I wish I could get so much done in a session.

With regard to your retracting tailwheel, I have done exactly the same with my TF P40 Warhawk which I'm currently finishing off after a 6-year layoff.

BTW my painted wing came out at 4lb 1oz with flaps retracts and 4 standard servos and covered with tissue and dope.

Keep up the good work

Regards

Robert

[Peter Jenkins]

I have to say Robert that I was thinking along the lines of this build going quite slowly! I just haven't been able to devote the time to it that I would like because of the other calls on my time. There have been times when a particular problem has really slowed, nay stopped, any building, while I work out what to do.

Good to hear that your P40 wing came in at that weight.  I am confident now that I will hit somewhere between 10.5 and 11 lb for the Mustang without fuel.

So, today I felt that all the immediate issues associated with the retracting tail wheel (making sure it retracted far enough, could be steered with a pull pull arrangement, and found a place for the retract servo) had been resolved so I should get on and glue the main formers and fuselage sides together. I re-read the instructions to make sure that if I glued the whole lot at the same time I wasn't asking for trouble! They recommend the use of cyano and do the gluing in stages. As I'm using aliphatic, I felt that would give me the time to glue the right fuselage side to the 4 formers, then glue in the left fuselage side to the same formers (this included the fuselage wing bolt cross piece, and then deal with the rear of the fuselage after that.

The key for me is to make sure I've assembled all the clamps, tape and anything else that needs to be involved in the gluing before starting. To that end, the SLEC building board supports were all set up for the right fuselage side (this looks like the left side in the photos as the fuselage is upside down) and the clamps on the other side just slackened off enough to allow them to be twisted to one side to let the second fuselage side in.

Taking a deep breath, the glue application began. All told, it took about 15 mins to get to the stage of all bar 1 former (which comes later) glued into place, vertical checked, either clamps applied or tape used to pull the fuselage sides aft of the centre section into the required curve to stick to the formers.

And this is what it looks like from the other end!

I'm pleased to say that the fuselage sides at the extreme rear are right on top of the plan outline! Phew!

A couple of days ago, I had been modifying the Robart tail wheel to allow more steering angle. This required the tail wheel tiller to be removed and then the actuating arms to be filed to allow the tiller to move further. I had removed the centreing spring to make life easier. However, when I came to put the spring back into the tail wheel, there was a loud sproing and the spring disappeared into the worst corner of my shed! I queried Robart on buying a replacement part but the cost of shipping was absolutely prohibitive! $30 for delivery in anything up to 12 weeks or $49 for "within the next 5 days". Inwoods came up trumps with some 0.9 mm piano wire and today I made my replacement cetreing sping. Inwoods also supplied the pull pull wire and some small hinges that I wanted for the u/c doors.

So, the final part of today's effort was to glue in the support structure for the servo arm to drive the pull pull steering mechanism on the main servo tray as shown in one of the earlier photos above. That will allow me to make up the pull pull cables tomorrow, attach them to the tail wheel tiller and the servo arm by the servos. I'll then be able to check how much movement I need from the servo arm to allow the full movement of the tail wheel.

Edited By Peter Jenkins on 21/05/2020 20:44:28

Edited By Peter Jenkins on 21/05/2020 20:46:18

[Peter Jenkins]

After yesterday's rapid progress, today was spent on chasing detail again.

After removing the clamps and tape that had held the fuselage together while the glue dried overnight, I set to to check the pushrod outers in their relevant holes in the formers. It became clear that I had made an error in routeing for the tail wheel retract pushrod! So, I marked where the pushrod was hitting Former 8 and managed to get my mini drill inside the fuselage to drill out the new hole.

As you will see from the above photo, I had mounted the rudder, elevator and tail wheel gear retract servos to aid in checking the pushrod runs.

The next problem was with the run for the pull pull wire. F8 was again the problem so by sighting through the holes I had drilled in the tail wheel former, F10 I was able to determine that F8 only needed a bit of work with my round file to enable line of sight between the two holes for the pull pull wires.

Next job was to bolt in the tail wheel and check the retraction and extension. Shock horror! This is what I saw when I squinted along the side of the fuselage!

Almost half an inch of wheel was still exposed when the gear was retracted! The bottom sheeting is only 3/16" so that wasn't going to make a difference - the wheel would still be showing! The first thing to do was to lose the triangular packing piece from behind the tail wheel mount. That still left a bit of wheel exposed so there was no other option than to unbolt the wheel assembly and reposition it further into the fuselage. That necessitated gluing in some more 2 mm ply to allow the top mounting screws in the tail wheel retract into which to bite.

By careful positioning, I have now marked the new bolt holes and will drill those tomorrow.

I did cut the exit slot for the rudder pushrod and that all now lines up very well. The elevator is operated by a horn silver soldered to the elevator saddle wire that will be inside the fuselage. So, it will be a case of fit and then only ever see again if you cut into the fuselage!

I finished off the day by connecting up the servos to the Rx and checking that the servo arms were set for neutral or as neutral as I could get them by repositioning on the servo splines. Then a tweak from the sub trim to get the servo arms at 90 deg at neutral. Rather than operate the tail wheel from the main u/c sequencer box, I decided to give the tail wheel retract servo direct transmitter control. I'm using an 11 ch Rx so took one of the Aux channels for the tail wheel retract servo. That enables me to use the Tx servo slow function for retraction and extension. 1.5 secs seems to be about right for moving from retracted to extended with the same delay on retraction. Will have to see what it looks like when I get the mains operating as well.

[Robert Parker]

Hi Peter,

I recall having a similar problem with my TF P40 when I was building it.

Although with the TF P40 there is a curved underside to the fuselage which helped me hide the wheel when retracted.

I see from your photos that the Mustang is a lot wider at the tail wheel, I was pushed for space as you can see.

The instructions for the P40 also said to use cyano for most of the build. I'm not a great fan of building entire models from it, not to mention all of the fumes in a confined space, I used PVA or epoxy throughout the build, this allows me to make any adjustments if needed.

Regards

Robert

[Peter Jenkins]

Hi Robert, yes, I don't know why Robart cannot supply a P51 tail wheel retract that actually mimics the full size for the position when retracted and when extended. It cannot be that difficult! I think the reason the Mustang has more room for the tail wheel compared with the P47 is that the tail wheel is mounted quite far forward - it is in front of the tailplane by a good margin.

I started to use aliphatic glue a short while ago and I find it a lot better than PVA as it has a much quicker drying time and also has a good "catching" function when you first press joints together. I use Cyano very sparingly these days and only when speed of gluing is essential.

I had to raise the tail wheel retract further into the fuselage in order to get the wheel no more that 1/16" above the fuselage side.

There is a 3/16" sheet that provides the bottom of the fuselage. I will be cutting this away for the tail wheel retraction and decided, after studying the photos of the Mustangs in my 303 Sqn Mustang book, the door size. I now need to construct a pusher in ali or brass sheet that will be screwed to the tail wheel retract so that it pushes the doors open. The doors will be sprung loaded closed with rubber bands so the pusher is needed to open them against the rubber bands. The TF manual for their Beech Staggerwing shows this arrangement clearly so its now just a matter of making the doors out of 1 mm ply, hingeing them (I'm going to use Kavan like hinges) and arranging the hooks for the rubber bands plus some blocks to allow the doors to close against something solid.

Having repositioned the tail wheel, I had to relieve some of the structure to allow the quick link to be attached to the retracting arm. Then it was a matter of setting up the pull pull wires for the steering function.

Note that I have included a "pigs' ear" to terminate the pull pull wire in the ferrule. Since all this is going to be inaccessible once the bottom sheeting is in position, I don't want this to come adrift!

I've set up the retract servo so that the wheel is as low as possible when retracted. This leaves the retract mechanism very close to a geometric lock which I hope will not be the case when the fuselage is the right way up. Then, the weight of the wheel will, I hope, avoid the slight hesitation for the tail wheel to move from the fully retracted position. Setting up the steering mechanism was a bit of a faff as I needed to determine which holes to use on the servo arm and the jockey bell crank. With max rates selected, I can get the maximum tail wheel movement without any binding.

[Adrian Smith 1]

A real builder's job there, Peter

Those SLEC building boards are an absolute boon too.

[Peter Jenkins]

Thanks Adrian.

The SLEC board is excellent but you must supplement it with tape to hold the top of the fuselage sides together as well as clamps. I need to order some more plastic side pieces although once you have got the fuselage bent to the right shape aft of the wing it usually all stays straight to the rear without any additional encouragement. I'm sure there will be cases where that isn't true though!

[Peter Jenkins]

I hope that today marks the end of the very fiddly bit of work that's been needed to set up the retracting tailwheel and to implement a steering solution that uses the rudder servo. So, now I have a tail wheel that retracts, extends and steers using a mini servo as the retract servo and a spare servo arm driven by the rudder servo to provide tail wheel steering when the gear is extended. You can see this clearly from the photograph.

You will note that the quick link and threaded coupler are sheathed in shrink wrap. This was to deal with the problem of having the pull pull steering wires slack once the tail wheel was retracted. The uncovered quick link would sometimes jam in the opening cut in the former. So, out everything came, shrink wrap was installed which necessitated removing the Q links and then re-setting the pull pull overall length until the tail wheel was in the fore and aft position with the rudder servo arm at 90 deg to the servo and the steering tiller parallel to the rudder arm. You can see the pull pull's slack in the photo below. The photo was taken when all the control rod guide tubes had been glued into place.

The Q link and threaded coupler now have a nice smooth cover that will not jam in the hole through the former.

That then allowed me to move on to the final few steps before the wing is mated with the fuselage. This is to build the radiator up. The next shot shows the two radiator formers glued into position. The next move is to cut out a 3/16" sheet cover for the radiator bottom and then to wet it and glue it in place to conform to the curve of the formers.

I've also got to finish off the wing by sanding the wing tips and dry fitting the ailerons while the fin and rudder still need to be progressed.

[Peter Jenkins]

I've just re-read the last post and realised I'd not put in the photo showing the two radiator formers! so, here it is:

The next thing to do was to cut piece of 3/16" balsa to rough shape and bend it to fit in with the radiator formers. As I said above, I had to wet the balsa and then starting at the rear, I glued it in place and followed up with masking tape across it and down the fuselage to hold the balsa in place till the glue set. I did this a few more times until I arrived at the front and then left it to dry.

Once that was dry, I sanded the top and fuselage sides so that they paralleled the underlying formers and then it was time to add the sides. These I cut to the shape shown on the plan from 3/8" balsa. This I again wet and then glued down. This was a bit more difficult to persuade into shape as the wood was stiffer. However, with the help of some long T pins I managed to nail it all down and left it to dry.

Once dry, I did the same for the other side. While that was drying, I made up a ply template to get the downthrust angle right. I then mixed up some 30 min epoxy and painted the insde of the cowl with it and then glued in the first of the 3 formers into Position 1.

You can see the template in the photo just under the clamp. There was a minor tweak needed to get this former, to get the correct downthrust. As you can see, the downthrust angle is spot on so it will be interesting to see if they got their sums right when I fly it!

The final part of the day was to sand some triangle section balsa to fit the sloping F3 and glue to the Former 1B. A lot of this triangular stock will end up being sanded away. I'm not looking forward to that as I shall have to wear my mask while I do that. I'll make as much use of my razor plane to cut down the sanding of course.

Meanwhile, I've also been finishing off the fin and rudder. No photos this time but I'll put some up next time.

I'll glue on the block that makes up the bottom cowl tomorrow and then the fuselage will be ready for mating with the wing! Exciting! But...there's still a long way to go!

[Peter Jenkins]

I took the bandages (sorry sticky tape!) off the radiator construction today and it looked a bit chunky! Incidentally, this is the 100th photo in the album!

It's amazing what 5 mins with a razor plane can do!

The next task was one that I've been looking forward to for a long time! The first time of mating between the wing and the fuselage. Having slid in the 2 wing mounting dowels and taped some 1/32" ply to the wing over the wing seat position (to emulate the 1/32" ply wing fillet), I was amazed to find that the wing slid into place. It wasn't quite the right place but I was still impressed. Says a lot for the accuracy of the die cutting and the method of construction that you have to follow.

The next job was to stick some packing into the back end of the fuselage to simulate the fin post, and stick a large pin into the centre of the dummy fin post. Next the piece of string trick to make sure that the distance from the fin post is the same to each wing tip. That required some easing of the wing centre leading edge and then it was a case of taking a deep breath and drilling through the hole in the wing mounted plate into the fuselage mounted plate.

You can see one wing bolt temporarily persuaded into the drilled hole in the fuselage plate. I'm using 5 mm bolts that will bolt into 5 mm spike nuts. The TF plan calls for the hole in the fuselage ply plate to be tapped so accept the wing bolt but I prefer a spike nut!

The final job for the day was to tack glue the dowels into place.

Tomorrow, before I remove the wing, I'll check the wing incidence since the fuselage is sitting on a flat surface and I can measure the downthrust in degrees as I have a template angle that I can measure with my protractor.   Then, I'll remove the wing and epoxy the dowels into place.

Edited By Peter Jenkins on 27/05/2020 20:51:46

[Peter Jenkins]

Didn't get much done today but did manage to finish gluing the wing dowels, plane the lower chin pieces to a 45 deg angle and fitting the T nuts for the 5 mm wing bolts. After that, I decided to measured the wing incidence. I started my making sure the building board on which the fuselage was resting was level.

I reckon that's close enough to 0!

On with the wing, bolt it down and then stuck the incidence meter onto the wing.

The plan states that the wing should be at +1/2 deg incidence. When you look at the incidence reading in the photo below, you will see that Top Flite has done a very good job of die cutting!

Before someone says that the incidence gauge is showing a negative incidence, do remember that the fuselage is upside down.

I was so astonished at this outcome that I had to go and lie down!

The next task according to the instructions is to fit the tailplane and then the fin. However, I always prefer to deal with fitting the engine before I have a fuselage encumbered with the tailplane and fin while I'm trying to drill holes and fit an engine. So, tomorrow's jobs will be to:

• rotate the carb on the OS 120 to get the throttle arm on the same side of the fuselage as the throttle servo
• mark out the firewall and drill the holes for the soft mount, tank feed and throttle rod
• glue in the firewall and rear supports and complete the fuel proofing of the tank bay with 30 min epoxy.

Till then, tara!

[Adrian Smith 1]

Like the progress, Peter.

I have a Robart Incidence meter and I wouldn't without it. I has thrown up some interesting numbers on one or two of my smaller ARTFs! That's why I like Extreme Flight's bigger ARTFs because enclosed in the box are the incidences of all wings of that particular kit.

[Adrian Smith 1]

like so.

[Peter Jenkins]

Yes EF are good in providing detail. Some F3A kits come without this vital information but I've not found that to be the case with the ones that I have had. As you may know, most F3A models come with wing and tailplane incidence adjusters and you can play tunes on the motor up/down and side thrust as well which is when having an incidence gauge such as Robart's is essential if you want to know your starting and end points.

I was just surprised at the accuracy of the Mustang's wing incidence. Of course, once the model is finished I shall just have to live with this as changing the incidence, if required, will compromise the scale appearance! F3A models are provided with adjustable wing and tailplane incidences on the whole although some don't necessarily come with the initial set up data! Resorting to the various fora does produce the answers although many will tweak the incidences to eliminate any aileron or elevator trim required to fly level. One can also play tunes on the motor side and vertical thrust lines much more easily.

It will be interesting to see how good the Mustang set up is once it's in flight.

Edited By Peter Jenkins on 29/05/2020 12:33:06

[Peter Jenkins]

Not a very productive day today! It began by me tracking down a user manual for the OS 120 FS. It was clear that turning the carb through 180 deg to put the throttle arm in the correct place was relatively easy. So, order of work was to do that first and then sort out the firewall to get the holes for the engine mount drilled.

Having rotated the carb, I found that I had made the classic mistake of forgetting that the fuselage was upside down on the building board and that the carb had been in the right place all along. So, turn the carb back to the original position! While I had tools to hand, I decided it would be a good idea to check valve clearances. That gave the minimum reading for valve clearance so that was fine. Nothing like a bit of unnecessary work!

I then carefully marked up the firewall as per the instructions. There are punch holes for the two centre lines for the firewall and also the displaced centre line so that the spinner comes out in the right place given the side thrust. I'm using a Dubro Softmount for the OS 120 and after carefully examining the mount it looked like I would have to drill and tap the mount for the 5 mm engine retention bolts. That then sent me back to do a Google search for the correct size of drill required for a 5 mm tap. I had the tap but not the 4.2 mm drill. I took a look at the UK Drills website and as my Bosch drill set is now well past the time it needed sharpening, a bit of retail therapy had a boxed set of cobalt drills and a 4.2 mm drill (almost half the cost of the boxed set!) on its way. Hope they'll be here for Monday next so that I can then drill out and tap the engine mounting holes in the Softmount. Never having mounted an engine like this before, I shall have to make very certain that the holes are drilled in exactly the right place!

Back to the shed to drill out the holes for the Dubro mount and forgot they would, being American, be imperial sized. Still a 5 mm drill hole is not too far off the required 3/16" hole required. Having drilled the holes I used the T nuts mounted with the smooth side facing the bolt to bolt the the mount to the firewall. With both mounts "bolted" in place I did feel that the 3/32" firewall was a bit flexible. It will be glued to another 3/32" plywood former that I had previously glued to the fuselage. In the end, I decided that I'd like to make another firewall but out of 1/8" ply as that felt a little bit less prone to flexing. Currently, the combined formers will be 7/32" thick and will be backed up by some 1/8" ply pieces for the T nuts to bite into. I'll see how the glued up formers feel and will decide then whether an additional full width 1/8" ply sheet would be advisable to reinforce the firewall further.

I then used the existing firewall as a template to cut a replacement one out of 1/8" ply taking the opportunity of making it a better fit than the original piece. I drew in the 2 centre lines and the displaced centre line. That allowed me mark out the required width of 46.6 mm for the OS 120 crankcase to be a snug fit between the bearers. I measured up and marked out the position for the four bolts on the firewall and trial fitted the soft mounts. Pleased to say that when looking down each mount hole, the cross marking the bolt hole was centred.

As you can see, I have also marked out the centre line on the 2 engine mounts as well as the bolt hole centres on the lower of the 2 arms.

Dubro state that before using the mount, all 4 rubber "grommets" should be removed and washed in glow fuel before being returned and bolted up. I presume that is to provide some form of lubrication to allow them to work more easily. There is no information about the life of these rubber inserts so that might be something to find out about.

Once I've got the engine mounted, I'll return to the manual and install the fin and tailplane.

[Peter Jenkins]

I spent another day looking at the engine installation and, in particular, the routing of the throttle pushrod.

Productive work was limited to drilling all the engine mounting holes, which I'm pleased to report were all spot on - the first time I've achieved that! The increase in stiffness of the 1/8" ply was noticeable once I'd bolted the softmount to the firewall and then clamped the engine in place.

It was immediately apparent that my burblings of yesterday about the carb being correctly setup were wrong. It's amazing how difficult it is to get an inverted engine mounting sorted out when the fuselage is upside down! Anyway, I repositioned the carb for the 3rd time and once the engine was clamped into place it became clear that there was a problem with getting the throttle pushrod to the throttle arm. The tank and softmount arm are in the way of a direct route so after much deliberation it looks like I will have to misuse a servo arm to create a bell crank to route the throttle rod run through 180 deg. I haven't worked out whether to glue a small hardwood block to the softmount arm or drill and tap the arm to take a short bolt to act as the servo arm bearing. I don't like the idea of drilling and tapping into the metal arm so I think a hardwood block will be the way to go.

There is a cavernous space for the tank. I'm using a 12 oz tank as I don't really want much more than 12 min flying time. However, I do need to have the option to increase the tank size so my method of tank positioning is to use some blue foam (from packaging!) to construct a tank size hole that will position the tank in the right place. The trial fit showed that I need to have a piece of string tied around the tank to pull it back against the grip of the foam!

All that was left to do was to glue in the firewall and the third part of former 1 which gives the rounded top for the top cowling and the plywood supports for the T nuts.

I've left it to dry overnight and will then drill through the rest of the firewall and pull in the T nuts. Since the lower mounting bolts will be pointing straight at the tank, I might cut them to being only just longer than the T nut. That will allow the soft mount to be bolted on and the throttle linkage mocked up.