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Mar 12, 2013, 04:40 PM
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Build Log

P-51D "Gunfighter" - 1600mm Starmax PNF (9.5/10) (Crashed - destroyed)

This large P-51 has been awaiting completion for quite a while now! For the moment I can't say how this particular one will fly, but all P-51's fly fantastically so this should be totally fine too.
Looking over the plane and its parts and design ideas, it all looks very well done. As always, some things can be done better, but the base of it all has everything important covered - no major flaws that will need a lot of effort. Though some areas I do make a lot of effort for changes that I want.

At US$208 PNF in Australia, that is a very cheap and large P-51 ! And great value for a plane that could be flown almost just as it comes anyway.
Starmax are not quite up there with FMS in finer details, but at a fair bit under half the price of the FMS 1700mm it is a very cost effective way to get a large P-51 ! If you really wanted all the finer details that the FMS come with, you would be better off just paying more for that instead of a LOT of TIME yourself, and also likely to be costing towards the same total as the FMS in the end.
(Though the FMS still needs things fixed here and there - as per all foamies do really).

It was a LONG time coming, to complete(!!!) but it finally is 99% done and ready to fly!!

I gave it a rating of 9.5/10 because it is a great base to work from, but COULD be flown just as it comes too! The landing gear is a weakness, but all else is fine/good. This is quite a good bargain large P-51 really!!

Last edited by PeterVRC; Jan 06, 2019 at 05:47 PM.
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Jun 21, 2014, 09:58 PM
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Change the landing gear

The stock landing gear is pretty plain to see that it won't last that long! The retracts are too small and the legs are too thin/small and weak really. It could last IF you fly from a hard runway AND grease the landing every single time! hehe

Thus right away I decided to change the retract to larger PK-514's and to use some heavier duty sprung alloy oleos. This also means making mounting plates to replace the stock sub-standard plastic things they have.
Doing this gave an extra benefit.... by setting the LG mounts into the wing "horizontally across the plane" - not in line with the wing, which has dihedral - then 90deg retracts will work properly! Totally storing the wheels/legs and not needing 85deg retracts to cope with the dihedral.

I stuck to the same sized wheels as stock, but changed them to FMS wheels, but they are quite a bit too small really (stock also)! Scale says 91mm !! These are 70mm. WAY too small really. I will look at changing those in future....

I bought the HobbyKing 161mm P-51 oleos, which are too long. So I modded them down to the required size. One problem is they can only fit a 70mm wheel anyway! So I will have to change the oleos if I want to use larger wheel diameter!

I made plywood plates from 4mm plywood, cut to shape and PU glued (Gorilla Glue)
into the recesses I 'hacked' out in the wing for them. They sit a fair way into the wing, to allow the whole oleo/leg and wheel to totally store away.It is quite easy to cut out the wing to suit that. A little bit tricky to check and align each side to match a 'straight line' horizontally across both sides, so that they are both level to the ground surface and not inclined.

They are a strong as anything!!! A great result! The PZ-514 are very robust and easily adequate - with the metal trunions fitted to those.

Last edited by PeterVRC; Jun 21, 2014 at 10:04 PM.
Jun 21, 2014, 10:08 PM
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Removable Drop Tanks

I am not sure WHY I had this idea..... lol
I think the real P-51 had a hard-point on the wing for the drop tanks, so instead of making the whole tank and hardpoint the one unit as it comes, I cut them apart so the hardpoint is fixed to the wing. I will have to re-check if that was a good idea or not (realistic)....

It would have been easier to leave them as one piece and then use rare earth magnets IN the wing 'slots' for the tanks to attach onto - as per they came to attach into those slots.
It seems that I may have glued in the tanks first, and then decided to remove them... I forget....
This plane took well over one year to complete - due to lack of making it any priority! sheesh.

Jun 21, 2014, 10:17 PM
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Pilot and FPV

I decided this plane will be "FPV capable" so I needed to make the cokcpit "Dual Purpose".... to have a pilot in there, or change him out easily for an FPV pan/tilt gimbal setup.
To do this, I cut out the pilot area and made a "plate" that the pilot is screwed onto. The plate is screwed onto mounts and can be changed out for another 'FPV plate" version.

To get INTO the cockpit I made it a screw on canopy, thus it can be removed to get full internal access.

I bought a HobbyKing pilot that seemed a good size, but is probably a fraction too big. But it looks pretty good!
He had a permanent 'leftwards look' so I cut off his head and re-glued it back on facing straight ahead!! WHO makes these things!!!?? Looking left might be ok for some static model, but not for a pilot supposedly flying a plane!! hehe
I also had to 'scratch out his eyes'!! LOL. So that I could repaint them looking straight ahead too!

The stock supplied instrument panel is of some modern Cessna or something!! It looks ok, but is totally wrong of course! I do not want to spend time on the cockpit, because no one ever sees that!!! I only do "Stand-off scale" so no one can see such details from that "3metres" distance. hehe

I made my own FPV pan/tilt gimbal from alloy plate, THEN found Fatshark had one very much the same in moulded plastic, for $25 including the two servos!! DOH. Mine took HOURS to make.... so I bought a Fatshark one also.

I haven't decided on the layout of the rest of the FPV stuff for now.....

The cockpit/canopy surround needed some plywood plates for the canopy screws to go into.
I had also extended the main hatch to be much longer - almost all the way to the front firewall. To have total access to the fuselage interior.

Last edited by PeterVRC; Jun 22, 2014 at 09:51 AM.
Jun 21, 2014, 10:22 PM
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Stock motor and ESC

After some power testing, and also cutting open the ESC to check it out internally, I decided the stock motor and ESC should be totally fine!
The ESC had proper contact of all FET's to the thermal pad that 'sticks' them onto the heatsink, so that was fine.
I still used a separate SBEC... in case.... So I unplugged the red power wire from the servo plug to the RX.

Power tests on the stock prop showed 66Amps peak, which fall away to 60Amps region. For 850W reducing. The ESC is an 80Amp one.

Jun 21, 2014, 10:38 PM
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Extended hatch, ESC bay and Battery tray

First I extended the hatch length by cutting off more of the top deck up front and attaching that to the stock hatch/canopy. This is to give total access into the fuselage to make fitting things EASY!

Who knows WHERE they want you to put the ESC and battery..... so I set that up to my own aims.

By cutting the "Floor" out of the fuselage front area, it opened up into a cavity that there is up under that nose area. Very deep into the belly. So then I put in a 'false foam floor' so that I could put a 2.5mm Bass-Ply plate onto that, to velcro the ESC onto. By doing this it means to the top - heatsink - of the ESC is in line with the airflow that comes through the firewall 'hole'. I was also putting a longer battery tray into the plane, so that covers the ESC up but the airflow still passes under that tray and over the ESC.

The battery tray was also 2.5mm Bass-Ply and runs from almost the firewall - just short of that to allow the motor wires to come up, plus airflow to head up over the battery too.
This HUGE tray area means a HUGE variety of battery setups can be used!! My aim was to use 4S 4400mAH. but it can fit TWO of those side by side easily! 8800mAH !!
The empty weight of the plane (when it was all completed) is 2919g. So with ONE 4S 4400 it is about 3450g... still a light weight for it s size really! This thing could carry over 4.0Kg EASILY... so twin 4400's is no issue really. IF you wanted some really long flying time!!!

When investigating HOW to get some more airflow into the plane, I noted how the under nose 'scoop' up front was not even open to allow airflow! Hmmm, simple... open that up!!
The front nose 'ring' portion is actually held on by magnets, but you have to cut it free with a knife first - I think the stickers were holding it a bit, or else they used a bit of CA to lock it on(?). But putting it back with just its magnets felt totally fine in strength terms.
So I cut open the full scoop opening, so there is plenty of airflow coming in via there now! A bit MORE than the actual rectangular hole size in the firewall! Hmmm.... I figured it will 'ram' air through that. The ratio of sizes looked well suited so I did no make the firewall hole larger. Flight testing has shown it is all totally fine like that.

So a large Bass-Ply battery tray is added into the front fuselage area, with velcro 'tracks' on it so that battery/s can be placed over a large range of positions, as required for CofG balancing.
I also added a velcro strap - it does the real work of holding a battery down. The velcro floor is for lateral and longitudal control.

Last edited by PeterVRC; Jun 22, 2014 at 09:53 AM.
Jun 21, 2014, 10:41 PM
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Tail wheel steering wires and RX aerials

I HATE push-pull steering wires!! hehe
But with a retracting tail-wheel that is pretty well ALMOST the only way to do it viably. A pushrod system is messy to fit into the small area - yet COULD be done....

I made some "Looped Sliders" to go into Linkage Stoppers I put onto the Rudder servo arm. Doing this means you can ADJUST the wiring - to align the tail-wheel separate from the Rudder drive, but also adjust taughtness of the wiring. This system works very well really, DEFINITELY very useful for push-pull wire systems!

I mounted two FRsky 40cm base loaded aerials in the rear fuselage, one taped to each side - one vertical and one horizontal, for Diversity. Access to them is via the underside rear cooling door.

Last edited by PeterVRC; Jun 22, 2014 at 09:56 AM.
Jun 21, 2014, 10:47 PM
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Re-assigning servo and pushrods, plus Wing Wiring

WHO makes dual rudder pushrod systems!!?? WHY???
How much 'pressure' do they think a Rudder will have?? In a warbird....
Yes, MAYBE in an aerobatic plane that will do Knife Edges.... but not in a warbird!

So to clean up the pushrod paths I changed the servos to do the opposite tasks than stock. Elevator to Rudder, Rudder to Elevator.
I also made BOTH just use ONE pushrod each, and NOT have then 'running over the other servo" like stock either!!
It also means the tail-wheel push-pull wiring can remain ON ITS OWN and clear too!

I modded their 'pushrod guide plate' and also added another one of my own - so that both Elevator and Rudder have a guide plate to limit the pushrod flex dramatically. Something that ALL planes with this sort of pushrod setup should have!!

I made a 2.5mm 5ply Plywood 'cross plate' for the Elevator - to ASSURE both Elevator halves move IDENTICALLY at all times! In stock form it is just a 'foam bridge'!! Pathetic really.... and asking for trouble one day!

For the Wing Wiring, to keep the wing easily removable, I used Futaba Extensions for lengthening all servo leads - by soldering them, NOT connectors. Futaba type are 'better' than JR (all the same costs) because Futaba plugs are "flat" whilst JR get 'wider" at the wire end of their plugs. This means when you plug in a row of plugs into a RX, JR type need to 'wedge in' tighter and tighter as you have more! Futaba just all go straight in like a plug SHOULD!!
This allowed gluing all the wing plugs into on 'big plug block' so you can just plug that into the RX as one unit easily then!
It is not hard to plug in, or get out, but will also never fall out by itself either!

Note also, I epoxied my P-51 wing halves together into one wing.

Last edited by PeterVRC; Jun 22, 2014 at 09:58 AM.
Jun 21, 2014, 11:03 PM
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Maiden flight and issue

The maiden flight went flawlessly. What a GREAT plane it is!!
The huge 4 bladed prop sound fantastic!!
It has ample speed on the 4S - easily a 'proper' scale top speed - and the 4 blades give it HUGE 'Torque'... pulling power. So vertical climbs are VERY strong!
I was VERY happy with the total of all aspects of the plane!

I used about 120mm CofG, from where the wing TRULY meets the fuselage - that is including the 'fillet' the P-51 has. It flew inverted great too. But I will check moving it more REARWARDS too. In 5mm steps... but by the way it flies I expect it can do 10mm EASILY, if not 15mm or 20mm.
The main aim for THAT is to prevent the nose-overs it wants to do all the time! And if it flies fine with a more rearwards CofG then that is fine too!

I had ONE 4S 4400mAH Nano 65C battery all the way forwards for that 120mm CofG - which was another reason I didn't use 110mm as most people do! LOL.
For two of those batteries you just move them half their length rearwards approx. So all in all the layout and balances worked great too!

3.5Kg region of AUW and it flies like on rails!!
The prop sounds fantastic.... the inertias are excellent, thus a very stable 'linear' flying plane. But it needs a LOT of Rudder to form co-ordinated turns, whcih is no issue to do - you just have to REMEMBER to do so! INITIATE turns with Rudder!! As you should do with all planes that have Rudders anyway.
The AUW 'linearity' also makes landing a CINCH to grease in perfectly.
At this aircraft size and mass - inertias - things become far more 'flowing' and linear, thus the easier flying of them.

As it comes... 9.5/10... but with my 'fixes'... a 10/10 AWESOME plane!

One ISSUE.....
I did not grind FLATS onto the retract 5mm pins!! I forgot.... DOH.
So one of the legs rotated on the retract pin, on the maiden landing... and then on the second flight during the take-off run. So it NEEDS those flats put onto them!
But this is MY FAULT of course... so the plane itself, once modded to fix 'shortfalls' is that perfect 10/10. I would say it is the BEST prop aircraft I have by far! 1100/1200mm P-51, FW-190, Spitfire.... good planes, but this beats them hands down!

Jun 22, 2014, 10:05 AM
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Landing gear mod/upgrade

It turns out I FORGOT to add "flats" the the retract pins! On the retract trunion portion AND the oleo portion!
So OUT they came, and had those ground onto them.....
That will solve the 'rotating oleo' issue!!

While I was at it, I tried out how large a wheel I can fit.
3.0".... 76mm
Not quite as big as I would like, but a fair bit more than the 68mm it had!!
I had some light weight HobbyKing wheels, which fit very well and are a PU Rubber. Totally fine for GRASS, but might wear out on asphalt over time.
I also had some other 'scale detail tread' wheels, but only the 2.75" version (70mm). They look great, but are HEAVY too! I could get 3" version of those, but it is not really worth doing that.

3.0" wheels also fit perfectly into the stock wheel bays... just 2mm clearance around the wheel. So the retract pins better not bend ever!

I will still look into some 85-90mm solution eventually....

Jun 22, 2014, 10:08 AM
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Maiden flight video

P-51 Mustang - 1600mm Starmax "Gunfighter" - Maiden Flight (5 min 7 sec)
Jun 24, 2014, 08:36 AM
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Alloy Fairings and Doors

I did some Filling around the retracts area, and made up some new landing gear leg fairings. This is because of the larger wheels, and also the slight difference in lengths etc of the landing gear now.

I made up stiff card templates and then made 0.5mm Aircraft Alloy fairings. They are 1g heavier than the stock plastic - but they are also a bit larger area overall too. They are a good color match to the plane just as they are so I won't need to paint them, just put a black tape Invasion Stripe on them.

I have planned how to attach them, but will need to make either alloy or nylon 'mounting blocks' to the oleos. I will do that over the next few days....

I also made templates for inner gear doors, but I am not sure I want to bother doing everything required for that! I half do and half don't.....
They would also be 0.5mm Aircraft Alloy, and they overlap the fairings some amount. But anyway, I will think about that over time...

Jun 24, 2014, 08:43 AM
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Bombs, Drop Tanks and some wingtip weight

I had laterally balance checked the wing before the maiden flight, seeing this is a BIG and quite heavy wing. It was 12g out of balance.... so I cut a circle recess under the wingtip and put a few washers totalling 12g into there.

I had cut the Drop Tanks off there 'Pods" long ago, and glued those wing attachments on. I have to check a bit more, but I see pics of P-51's with none on... or some with the mounts on... so I suspect they bolted on the mounts and used Drop Tanks, and some pics are when a plane came back with no tanks. They probably DON'T put the mounts on unless the plane is going to do something long range.....
I might cut the pods flush off the wing, and make a 'dual purpose' system that can have the mount on, or off, the wing, as well as the Drop Tank fittable of course.
I began that, but will do more tomorrow....

I also checked fitting the Quanum Drop Bombs I have a pair of for the P-51. I will makes their mounts removable too, so that if I want them on then I put them on, and if not, then the wing will be clean there.

I set them out to have the Drop Tanks and Bombs side by side if I wanted to do that too, but I don't think they would ever have run BOTH really. This was also why I stopped, so I could ponder over whether I make ONE mount system to take EITHER the Bombs or the Tanks.... which seems a better idea really.
I have to check over pics and do some reading one that....

Sep 11, 2014, 07:03 PM
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Tail Wheel Mod - Redone!! Major change

The Starmax P-51 comes with a steerable tail wheel, but they use a Pull-Pull wire cable system for that. Pull-Pull cable systems are RUBBISH!!
It is difficult to get the cabling taught so that the control system (steering in this case) is accurate, and also to keep it taught ongoing. Plus when the landing gear folds up (via retract) the cables go loose and can foul things, or not go back to their 'extended' position cleanly when it comes back out.
It is just a sub-standard system/idea!
Direct Pushrod steering is FAR better.... and operates perfectly, and reliably, if done well.

Another thing is that the tail wheel is too far rearwards compared to the full scale P-51. And it is missing doors.....

I cut out a huge "Bay" in the rear underside where the tail wheel goes. You need to use the "Medium" PZ retract size to get decent size to allow proper control arm and leg 'storing' operation - the "Small" size PZ really limits what you can do effectively. But the Medium size retract is quite a bit bigger and needs more depth into a plane to recess it. This is even more limited down the tail end of a plane!
But if you go down deep enough into the underside of the P-51 tail end (eg plane inverted and working "down" into that then) you will reach a 'separate level' of foam moulding. All the prior stuff above was another main structure and there is a small section of space/cavity before that next level. So you can hack out all the 'above' stuff to get to that next level. This also means removing the 'Fin bolt plastic circle thing' - you won't need that later, it gets done another way.
This "level"/depth is just perfect for setting up a Medium sized retract system!

I had only used ONE Rudder pushrod and that normally passes through that cavity area, but now it would get squashed under a "retract mounting plate" if it was left there. So I made a channel for it and used a 3mm carbon fiber tube to protect its passing through that retract region. Even if you had the stock two pushrods, you would just do that same thing twice.

A large retract mounting plate is made - very large so is strengthens the area and also allows has room to mount the steering servo and doors servo (if one is used).
I use captive nuts (3mm) on all these retract mount plate setups so that the retracts are bolted in with 3mm bolts - not just wood screws or self tappers.

The stock tail wheel leg and wheel are used still, but the 'kink' is modified to suit a better scale look. It is also modified to have a groove in its top end, so that it can be held in the retract by the retract's SIDE grub screws - this allows easy removal of the leg, without dis-assembly of the retract unit!
I made my own alloy steering arm setup, so that it could be made to suit the sizes needed - but any steering arm could be used and modded to suit.

The under-belly ahead of the tailwheel is glued back in, and a balsawood plate is made to go after the tail wheel - leaving just the area to be covered by operating doors.

Last edited by PeterVRC; Dec 23, 2014 at 08:15 AM.
Oct 15, 2017, 07:55 PM
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Main gear leg fairings - 3D printed

Whilst the alloy fairings I had made up looked somewhat nice, there was no good way to attach them to the oleo legs. At some stage I had also looked at full scale P-51 pics and videos and noted they are not actually 'free standing' fairings, as per most model P-51 aircraft do it, but are attached with hinging to the wing itself. This actually made the best solution obvious and easy!
I designed some 3D Printed fairings AND mounting plates to cover the retracts which had the hinging for the fairings included. This system also had the added bonus that the fairing 'changes' its position along the oleo as the leg extends or retracts. Due to the hinging being offset away from the actual retract pivot point. This is what the full scale also does!
It makes the fairing 'higher' up along the oleo when the gear is stored, and it 'moves down' more over the wheel as it extends out. Only by about 10mm difference, but that makes the inner gear door system more suited to the wheel shape too. (again, exactly as per the full scale does).

The left and right sides are not quite 100% equal, so each mounting plate and fairing had to be custom made to suit. But they are very close to the same, so visually you cannot see any difference.

I have not made up inner gear doors covers yet, as that needs the servo/drive setup done too and I will do that over coming weeks or so.

The leg fairings temporarily use 'flat elastic' to hold them against the leg, until I get some finer round elastic to use.
You need them attached with elastic to allow the oleo to KEEP moving deeper into the wing even after the fairing plate has already hit the wing underside channel/stop point.
It all makes for a very nice, true to scale, flush fitting gear system which also pulls the fairings in tight to the wing seating. And will just be even better once the inner doors are all done too!

I did the test prints in RED PLA, seeing I have a lot of that around. The final parts will be done in 'silver' PLA but for now (lazy) I just painted the red ones to suit (silver with black stripe). They looked quite good so I just haven't done the silver versions yet! I will do those once the main inner doors get designed and printed also.
I will also take more pics of the new silver ones not installed as I forgot to do that when I made these up. Plus some pics of the red ones painted up as they are now.


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