Top Flite P51 - 65" span

[Nigel R]

" In theory, therefore, tilting the retract support rails by 10 deg should produce the required effect."

All looks good, and the value of the mockup is clear to see, but I'm sure adjusting the tilt will mean the wheels are further back (1/2" or so?), when they are extended and down. Are they still a good distance in front of the CG when extended?

[Bruce Collinson]

Peter,

A post “Anyone use these” this am reminds us that sheets of epoxy glass suitable for horns, servo arm extensions and ... u/c doors? ... are readily available with a helpful link. Of course it may be that you welcome an opportunity to laik about with carbon mouldings custom made for the profile.

Good build.

BTC

[Peter Jenkins]

Ron and Nigel R you have both raised the issue I had been pondering about bringing the main wheels back when reducing the tilt by 10 deg. I measured the distance from the CG point marked on the wing to the centre line of the retract unit. That came to 5.8 cm. I did some trig and based on the length from the top of the strut to the bottom of the wheel (21 cm), tilting the retracts back by 10 deg moves the bottom of the wheel backward by 3.64 cm.

So, would changing the wheel contact position (albeit on a fully extended oleo) from 9.44 cm in front of the CG to 5.8 cm in front of the CG make the aircraft more likely to tip onto its nose during a landing run especially on grass? Since pilots report that the aircraft can tip onto its nose during landing then clearly this might not be such a good idea after all.

I thought the best way to analyse the options was to do a scale drawing of the wing box at the centre line of the retracted struts. I then drew on the measured position of the wheel within the wing under the tipping back by 10 deg. By judicious use of the real ply ribs attached to the mock up, I was able to determine that removing 2 mm from the rib nearer the wheel would produce a 2 deg droop of the leg and allow the now tilted wheel to sit low enough to provide the required clearance for the door above the wheel. The leg mounted door is also able to sit on top of the wing skin without fouling the leg. This, of course means that when the legs are extended, they will not sit perfectly vertically downwards but we are only talking a degree or two.

By this stage of the day, I only had time to glue up the main wing strut and reinforcing piece before time ran out. So, while I've technically started the wing build it's hardly worth putting up the picture.

[Peter Jenkins]

Posted by Bruce Collinson on 15/04/2020 12:50:04:

Peter,

A post “Anyone use these” this am reminds us that sheets of epoxy glass suitable for horns, servo arm extensions and ... u/c doors? ... are readily available with a helpful link. Of course it may be that you welcome an opportunity to laik about with carbon mouldings custom made for the profile.

Good build.

BTC

Bruce, thank you for that suggestion. However, as I am just as likely to use thin ply and make up the detail inside the door with balsa and bend the ply by steaming it, there is little point in putting out a request as you suggest. It will depend on the final wing profile exactly how difficult a task this will be. If I do need to use some of my carbon cloth, I have a plan to sandwich it between two sheets of plastic and weight the whole lot down onto the wing with a pile of mags on the top of the wing. That way, the resultant curved sheet will match the wing contour exactly. That is not a big investment in time and will cost nothing more as I've already got the stuff to hand.

[Peter Jenkins]

Today was a pretty simple sort of day. Construct the port wing. Just needed to follow the very good building instructions. It started with making the spars which require two parts to be glued together.

A total of 4 spars are needed. While they were drying, I remembered I needed to make the access holes for the servo lead to the aileron servos. While the plan shows a single centrally mounted aileron servo with a bell crank in each wing (rather shows the designs age) I decided to go for two wing mounted aileron servos. The simple way to do this was to put all the port wing ribs inboard of the aileron servo together, aligned with the spar slots and use my pillar drill to drill a 10 mm hole through all of them. The hole needed enlargement as it wasn't quite large enough to allow a servo lead lock though. Once that was done, it was just a case of pinning down the spar and then gluing the ribs into place making sure they were truly vertical and right on top of their required positions.

Suffice to say that the accuracy of the die cutting meant this was a pretty painless task. I made sure that the rib tabs were pinned to the board and also pinned the ribs in front of the spar. Once that was dry, I glued on the rest of the wing parts. Some, like the spar for the aileron hinging needed to be glued together and roughly sanded to shape and others, like the moulded LE, needed to be cut a joined to create the distinctive kink in the Mustang wing. The flap trailing and side edges followed and then the whole lot has been left to dry overnight.

The clamps you can see in the photo above are holding the u/c ply formers that will hold the u/c mounting spars. I also meant to add the servo hatch rails for the aileron servos but decided that I'd leave that operation till the glue was quite dry. Talking of glue, I'm using aliphatic for the first time. While it's nothing like as fast as Cyano, it's a huge improvement on PVA, my previous glue of choice.

So, tomorrow, it will be a case of remove the port wing panel, turn the plan over, and build the starboard wing panel. That will no doubt take a lot less time to construct as I shall be utilising today's knowledge. The washout on the wing is quite noticeable when you look at the construction as a whole. No tip stalling if I can maintain the design washout angles!

[Peter Jenkins]

Incidentally, I've now read through about half of a very long thread on RCU on building this Mustang with contributions from a wide range of folk. One poster was particularly helpful in his description of how he'd constructed the inner u/c doors and another provided a link to the TF Beech Staggerwing in which they provide very helpful detail on making tailwheel doors using two rubber bands to close them and an aluminium spreader attached to the tail gear to push the doors open. That's solved that problem so things are looking up as regards the things I need to research. The other interesting bits were the AUW of the model. The guy with the detailed u/c doors, covered his with glass and then went to town on weathering. His model tipped the scales at 11.5 lbs. He had a OS 120 FS in it and reported that the power was adequate. He found he needed to go to full throttle, allow the aircraft to accelerate, and then it would loop well. Otherwise, there was the danger of the loop degenerating as speed decayed. Interesting as I am going to power mine with an OS 120 FS!

[Mike Rieder]

Looking good Peter, re strengthening the landing gear support area, i would consider glass clothing the inside of the wing area. I can give you some sutable cloth at some point or pos even drop off if needed.

I had a similar issue with the spit as i had to remove most of the rib to get the wheels in.

[Peter Jenkins]

Hi Mike, my plan was to install a ply doubler to both ribs supporting the U/C blocks and extend them back towards the rear of the rib to provide a path to transfer the impact forces of landing. I have also decided to use my supply of carbon cloth to reinforce the whole of the bay from around the LE, along the upper skin line, down the face of the spar and then back up via the bottom skin. Only problem is that I think the instructions call for skinning the bottom of the wing first. That might do as the torque on landing that the wing has to take will be to place the upper skin in torsion and lower one in compression. Need to think that one through a bit more.

I'm also going to build some structure around the wheel well both to reinforce and area where most of the rib has been cut away and also to box in the opening probably just inside the door opening to reduce the ingress of oil and dirt while allowing easy cleaning of the area.

[Peter Jenkins]

I haven't managed to do as much as I wanted today but I have carried out the first phase of reinforcing the wing to soak up the landing loads. The first part was to cut out and glue in a 3/32" ply rib to W4 and W5 . Here are the reinforcing ribs:

and here they are glued to their respective wing ribs. It was only after I had glued the W5 support rib in place that I noticed I'd forgotten to drill a hole for the aileron servo lead! Ah well, another awkward little job that will take up valuable building time!

You can also just about see the u/c rails which I glued in yesterday evening using Hysol.

Tomorrow, I shall reinforce the ply ribs with light weight carbon fibre cloth.

[Peter Jenkins]

I have been wanting to draw out the tail wheel retract and doors so that I had a good idea of how I was going to position and build them. The link to the TF Beech Stagger Wing manual (that I got from the RCU thread) shows how to use the retract to open and rubber bands to close the u/c doors. So, the drawing below, is how I'm going to implement this on the Mustang.

I will need to check how long the tail wheel doors need to be by reference to the photos I have of the Polish Mustangs. The other interesting thing about the retract is that the tail wheel is steered by a horn that is controlled by pull-pull wires. As the leg retracts, the wires go slack and a spring centres the tail wheel. There isn't much movement of the tail wheel to steer the aircraft and this is down to the tiller contacting the support structure. I'm going to investigate filing the plastic support structure a tad to see how much that improves the steering angle that can be achieved.

[john stones 1 - Moderator]

Coming on well Peter, I had my 120 in a seagull Yak, the first version, over 10lbs and it flew it with ease, nice big maneuvers.

[Peter Jenkins]

That's good to know John. I note that the OS 155 FS Alpha has the same mounting holes as the 120 FS so if the grunt ain't there for big verticals like the full size that might be an option if I can find a second hand one. I have to balance expenditure on this project with my F3A needs! However, as we cannot fly this is the next best therapy!

[Peter Jenkins]

A couple of posts above I said the stbd wing was complete for now and I'll start on the port wing. Wrong. I'd turned over 2 pages in the manual! There were quite a few jobs to do and an error to be fixed - caused by reading two steps that sounded the same except that one referred to the top spar and one to the bottom spar! That took almost 2 hours to fix! At least I shouldn't make the same mistake on the port wing - fingers crossed! The key parts were to glue in the shear webs on the front and rear spars. This photo shows work in progress on the front spar webs.

The next photo shows both sets of webs glued in. The key thing was to make sure the wing was flat before gluing in the webs as once you've built in a twist with the webs it's quite difficult to undo!

You'll notice there's a gap in the webs where the u/c rails are attached. This is to allow me to reinforce the additional ply rib with carbon fibre and to make that job easier I've left off the web. Once I have the port wing at the same stage, I'll do both together to save on mixing resin twice.

So, the last job today was getting going on the port wing.

I might see if I can creep out and glue in the top main spar before my absence is noticed!

[Martian]

Looking great Peter makes me want to start building again

[Peter Jenkins]

Well Martian, you'll have plenty of time before we get to fly again.

OK, today I was going to try and finish the starboard wing. Unfortunately, several things conspired to defeat that aim. First, there were no 1/8 square strip left! There was only 1/8 x 3/16 strip. Having turned out all the wood bundles I still couldn't find any. So, I searched my meagre store of balsa and there were none there. Worse still, I didn't have any 1/8 sheet so I could strip it. After half an hour of running round in ever decreasing circles, I was about to go and get the other Mustang kit down and pinch the 1/8 square strip out of that when I remembered that there might be some spare 1/8 sheet in the die cut left overs. Success! So, as I don't have a balsa stripper, I produced the strip using steel rule and knife!

Then the washing machine died and to cut a long story short, the only quick solution was to research and buy a new one! Then the electric sun blind wouldn't work..... You get the picture!

So, getting back to the build, I've done quite a lot on the wing and also glued in the ply reinforcing ribs to rib W4 and W5 - the ribs that have the u/c blocks fitted to them. I also decided to reinforce rib W2 as it had a lot of material cut out of it to accommodate the retracted wheel. So, this is what the starboard wing now looks like with the clamps holding the reinforcing ply ribs in place while the glue sets.

[john stones 1 - Moderator]

Coming on nicely Peter.

Bad luck tends to come in cycles, washing machine eh.

[Peter Jenkins]

Oh, I forgot to say that I was considering fitting a couple of hard points for the wing pylon and making some drop tanks. It occured to me that a wheels up landing might be when the drop tanks earn their keep! As ever the position of the pylon is in-between 2 wing ribs! So, I'll have to add in a rib or even a pair of ribs to support the hard points. I'm thinking of just having a couple of balsa blocks with a bling nut to attach the pylon. That would allow me to leave building the pylon and drop tanks until after the maiden.

Does anyone know if you can buy a set of 1/7 P51D drop tanks?

[Peter Jenkins]

Thanks John.

[Martin Harris - Moderator]

Posted by Peter Jenkins on 20/04/2020 23:36:34:

Then the washing machine died and to cut a long story short, the only quick solution was to research and buy a new one! Then the electric sun blind wouldn't work..... You get the picture!

I have to ask - had you forgotten to put a shilling in the meter?

[Peter Jenkins]

Shilling! In which century are you living Martin? More like a £1 coin at the very least!😂

[Nigel R]

Build is looking good Peter

[Danny Fenton]

Looking great Peter

Cheers

Danny

[Peter Jenkins]

Oh dear Danny, I'd better not bodge anything is you're watching!

Made good progress on the starboard wing today. Still need a few bits to get it to the same state of the port wing and then go through the fiddly bit of joining them.

Based on my port wing u/c setup, I decided that I needed to tilt the retract mount a little more to drop the retracted wheel 3-4 mm more into the wing. So, I filed off about 1 mm from the inboard mount and after a bit of work with my drum sander it all fitted in nicely.

After a bit more sanding, the whole unit was lined up against the plan markings below it.

However, when I looked at what was left of the innermost rib, the answer was - not a lot!

I am going to be building a box structure to both add strength to the wing structure and to form the u/c wheel well. I also put a washer under the outboard retract when bolting that up and that dropped the wheel on the port wing to a similar position as the pictures above. That did mean the wing skin might need relieving a tad to clear the retract bolt heads at the front. Might be OK as it's difficult to see without putting a sheet of balsa across the wing.

[Peter Jenkins]

Bit of a fiddly sort of day. Got the starboard wing up to the wing joining stage but as I was gluing in the u/c rails, I paused to think about how else I could strengthen their fitment. So, I came up with this idea.

The left hand piece is likely to be a bit weak at the front but the wing curvature prevents anything larger. On the RHS, the u/c leg precludes a one piece reinforcement so 2 pieces are needed by at least with the support lower in the wing there is room for a bit more meat in the ply reinforcement at the front. So, this is what it looks like on the rails.

And this is what it looks like installed on the wing - dry fit at this stage.

I've now glued the reinforcements onto the port wing setup and the u/c rails and reinforcements are all now in the port wing. Will leave it to dry overnight.

This will either make a significant improvement to the u/c rail strength or pull an even larger bit of wing out if I managed to test the gear to destruction!

[Ron Gray]

Softly, softly on those landings Peter, at least we have a tarmac runway!