Cambria P-51 Mustang Funfighter

[David Hayward.]

Well I couldn’t find a Cambria Funfighter build blog on here so I thought I would do one as I have just started building a Cambria P-51 Mustang funfighter. I believe they are intended to be easy and quick to build, so here goes.

 

Cambria funfighters website can be found here: https://www.funfighters.co.uk/

 

They also have a very useful facebook group here: https://www.facebook.com/groups/1460474474245610

 

A quick view of what you get to start with. All wood is good quality and laser cut, nice pair of veneer foam wings with washout built in. Pretty much everything you need is included in the kit, you just need to add engine, spinner and finishing materials.

 

Engine wise, you can use anything from 20 to 35, many use a 32 which is what the Cambria display team use at shows and I have managed to acquire an OS 32 for this build.

 

 

There is a comprehensive set of instructions and a plan with excellent detail is also provided. Note, the plan quotes 15 to 25 engines, I’m guessing this dates back to the 70’s when these models were first introduced.

 

 

Following the instructions, the build starts with the fuselage. Balsa sides with ply doublers, 4.5mm sq longerons also added to bottom of fuselage. Engine bulkhead comprises of 2 X 3mm ply formers laminated together which I did first so they will be ready to fit with formers F3,F4 & F6 at the next stage.

 

 

Formers F2, F4 & F6 glued in place, it was a bit tricky holding former 3 in place and at 90 degrees to the fuselage side so I decided to fit that at the same time as fitting the second side of the fuselage when it will be held captive between the two sides. Very easy build so far, formers key into slots formed by the ply doubler – no excuses for getting in the wrong position.

 

 

Second side of fuselage being glued in place, former F3 which was due to go in at this point turned out to be about 3mm too wide, so I will trim it and fit when this is dry as it can easily be slid into place and glued then.

 

 

While this is drying, I thought I may as well glue the leading edges onto the wings.

 

 

F3 trimmed and glued in place after second side of fuselage glued to F2, F4 & F6 and dry. So that’s the parallel section done, now in the jig to bring the tail together and fit F7 & F8 toward the tail.

 

 

Next is gluing in place the two radiator sides and then 2mm sheeting to the tail.

 

[David Hayward.]

At this point upper rear fuselage sides 13 are next to be glued into position, although there is a note at the end of this instruction (8) to fit the elevator snake first, however this must have changed at some point because the elevator is now linked to the servo via a pushrod which actually passes through the side of 13.

 

In addition, you have the option of using either a single or double ended pushrod, and I believe the advice is, if you are fitting one of the larger size engines, go for the double ended pushrod.

 

If you go for the single ended pushrod, the two sides 13 can be glued into position, followed by internal doublers 12, the pushrod can then be made up and passed through one of the sides later.

 

If you go for the double ended pushrod, this will need to be made up and passed through both sides 13 with doublers 12 already fitted, at the same time as gluing each side in place. I have gone with double ended as I am fitting an OS32.

 

The standard build has a fixed rudder, however, I have also elected to have an operational rudder and decided to link this vis a pushrod as well.

 

One final note regarding the two upper fuselage sides 13, they weren't quite deep enough to reach the top of formers F6, F7 and F8, so just needed a strip adding to the top.

 

Hopefully these images will make all of the above clear.

 

 

 

 

 

 

 

 

 

Moving attention to the front end, tank bay floor in place along with triangular section for this and bulkhead F2. The engines in these models are typically canted over to about a 45 degree angle, so engine mount fixings installed to achieve this.

 

 

 

While this is drying I sanded the wing leading edges to profile and glued on the wing tips.

 

 

Edited January 8 by David Hayward.

[David Hazell 1]

Ooh I like that they now include a 6oz SLEC tank as standard. That's what I stuck in my Hien. I approve!

[David Hayward.]

5 minutes ago, David Hazell 1 said:

Ooh I like that they now include a 6oz SLEC tank as standard. That's what I stuck in my Hien. I approve!

Yes, its a perfect fit and being 'square' optimises the space for maximum fuel capacity in a small space.

[David Hayward.]

 

 

 

 

 

 

 

Fuselage sides 13 dry and sanded down to top of formers F6, F7 & F8, fuselage spine 16 glued in place and sanded to shape.

 

The upper front fuselage sides are next to be added and here I deviated slightly from the instructions which tell you to fit former F5 prior to the two sides 14. However, I decided to fit F5 after the two upper fuselage sides 14, to ensure I got the slight forward inclination of F5 correct.

 

So I glued the two doublers 15 in place first which span between the upper front and rear fuselage sides, then glued the upper fuselage sides initially only to the top of the lower fuselage sides 10, then fitted F5 and then glued the two side 14 to formers F2, F4 & F5.

 

I did preshape doublers 15 first by wetting and banding round a bottle as they tended to pull the rear fuselage side out of shape otherwise. I also wetted the fuselage sides 14 prior to pulling in to the formers.

 

A couple of pictures which again hopefully help to make sense of my text.

 

 

 

While that’s drying I carried on with the wings where I marked out the ailerons using the supplied template. Almost got this wrong in spite of the well labelled template, but fortunately corrected my error before cutting anything.

 

 

Lined the aileron cutout with supplied balsa, not noted in the instructions but clearly detailed on the plan.

 

[David Hayward.]

Once the upper front fuselage sides were dry, the next step in the instructions is to glue on part 17, front fuselage top, however, now is a good time to fit the throttle snake and fuel proof the tank bay with epoxy while I still have easy access.

 

That done, front fuselage top glued in place and at this point I sanded front and back upper fuselage sections pretty much to shape.

 

I have skipped a couple of steps because I am waiting for a few supplies to arrive, including a spinner which I need to position the engine as specified. So while I wait for delivery I went ahead and fitted the servos; pushrods will be connected once I have the rudder and elevator in place which will then enable accurate measurement of the wire ends.

 

 

 

Next I thought I would progress the wings a little further so cleaned up the aileron cut out facings, sanded the tips to shape and cut the ailerons ready for hinging.

 

 

[David Hayward.]

Spinner has arrived, so I’m now able to go back to the engine mounting point. Back of spinner should be 85-90mm from F2, just had to shape fuselage top 16 to allow engine to sit in place.

 

For the next step of fitting front cowl parts I deviated from the instructions and used the ‘Peter Miller’ technique of fitting the nose ring to the engine spaced back to give clearance to spinner and prop. (I call it the Peter Miller technique because I first came across it when building his Ballerina) In the picture you can see a piece of balsa that is temporarily glued with a couple of spots of contact adhesive to the nose ring. Cowl parts are then fitted between F2 and the nose ring, gluing as you go.

 

Cowl parts in place and glued, silencer fitted to check clearance and all good. Time to get some shape to the cowl….

 

That’s it roughly, still a bit more to go plus I’ll do another test fit of the engine to ensure spinner and nose ring flow nicely.

Edited January 11 by David Hayward.

[David Hayward.]

Finished shaping front end and while I had the engine in for final check I installed the throttle snake and soldered clevises each end.

 

I trial fitted the canopy and found the fuselage sides only just meet the canopy, so I added a little depth each side to ensure the canopy has enough area for the glue to bond to.

 

 Glued in place the hardwood bearer to the underside of the fuselage.

 

 

While that’s drying did a bit more on the wings – preparing to glue the aileron torque rods into the wing, so channels cut into the wing, balsa caps made for the channels, masking tape in place to protect the wing from the epoxy that will be poured into the channels followed by the rods, coated with vaseline, channels then topped up with more epoxy and then the cap strips fitted. Crucial thing here is don’t forget to coat the rods with vaseline or that could be awkward!

 

 

 

[David Hayward.]

Thought it might be useful, particularly for anyone like myself who has never used this method of fitting torque rods before to make a video of this part of the build...

 

[Geoff S]

Never seen that technique before.  Did it actually work, and the torque rod still moved once the epoxy had cured?  Your video stopped too soon 🙂  I don't normally use torque rods for ailerons and prefer a separate servo for each one.  One of the reasons is the pain of fitting them, which this method avoids to some extent.

 

btw I like the Mew Gull in your logo.  Looks very like mine, which represents G-HEKL - a modern replicate of the original, which I chose for a change from Alex Henshaw's better known Gull.

[David Hayward.]

17 minutes ago, Geoff S said:

Never seen that technique before.  Did it actually work, and the torque rod still moved once the epoxy had cured?  Your video stopped too soon 🙂  I don't normally use torque rods for ailerons and prefer a separate servo for each one.  One of the reasons is the pain of fitting them, which this method avoids to some extent.

 

btw I like the Mew Gull in your logo.  Looks very like mine, which represents G-HEKL - a modern replicate of the original, which I chose for a change from Alex Henshaw's better known Gull.

Hi Geoff, yes it has worked just fine. It is rather counter intuitive to drown your torque rod in epoxy I have to admit, but it's a well proven technique amongst those who have built the Cambria FunFighters and the crucial step is to coat the rod well with vaseline of course.

 

Ref the Mew Gull, you may remember this post...

https://forums.modelflying.co.uk/index.php?/topic/40939-chorus-gull/page/2/&tab=comments#comment-811305

 

Edited January 14 by David Hayward.

[Geoff S]

For some reason, I either missed or (quite as likely!) forgot your Chorus Gull build.  It seems we both decided to be 'different' the same way 🙂  

[David Hayward.]

The torque rods in and the epoxy dried, both rods moving freely, one was a bit sticky to start with but freed off after moving back and forth a few times. Ailerons then hinged with supplied Mylar strip.

 

Joining the wings with epoxy came next and required four blocks made up to 25mm depth to be placed under leading and trailing edges at the tip each side, everything held in place with weights while drying.

 

I was preparing to epoxy the wing bandage in place when I realised I hadn’t glued the two leading edge blocks in place, parts 30; its not actually mentioned in the instructions but is quite clear on the plan. Just need to be aware the instructions for the wing are I suspect generic across the various funfighter models, so inevitably, there is some variation.

 

Anyway, blocks glued in place and wing bandage epoxied over join in wing.

 

Edited January 16 by David Hayward.

[Petrogli]

David,

 

Thank you for posting this build.

 

I am a couple of weeks behind you having started my P51 build yesterday and really appreciate having your posts to supplement the manual.

 

Thanks,

 

Neil

[David Hayward.]

5 minutes ago, Petrogli said:

David,

 

Thank you for posting this build.

 

I am a couple of weeks behind you having started my P51 build yesterday and really appreciate having your posts to supplement the manual.

 

Thanks,

 

Neil

Glad you are finding it useful Neil, what engine are you putting in yours?

[Petrogli]

14 minutes ago, David Hayward. said:

Glad you are finding it useful Neil, what engine are you putting in yours?

Mine will be electric so there will be some differences in the front end build!

[David Hayward.]

14 hours ago, David Hayward. said:

Anyway, blocks glued in place and wing bandage epoxied over join in wing.

 

Prior to epoxying bandage I made a 6mm hole through the front of the wing for the front screw fixing which has to line up with the threaded hardwood bearer* fixed in the fuselage. This is down the line of the join in the wings and 32mm back from the front. I didn't drill this hole as it's just two very thin obeche skins separated by polystyrene with epoxy right down the middle and a drill will just kick off to the side and generally make a mess, so I went through first with a small terminal screwdriver with a pointed end. This was slightly off centre, again due to the epoxy, so I then used a needle file, to file into the epoxy and bring the hole back to the centre. I then used a 6mm diameter file to open the hole out to the correct size. Part 29 a circular ply ring is glued to the bottom side of the wing to reinforce where the screw head sits.

 

 

*A belated note about the threaded hardwood bearer, this would I believe be best glued into position when the two fuselage sides are joined as it sits in slots formed by the balsa sides and the ply skins, however, the instructions leave this until point 22 making it more difficult to fit.

 

Edited January 17 by David Hayward.

[David Hayward.]

Fixing wing in position with the front screw and ensuring its straight and true relative to the fuselage, the radiator block 22 is to be glued to the underside of the wing. In preparation for this the dihedral angle has to be chamfered into the bottom of the block so it fits snugly against the wing.

 

Then ply former 23 has to be positioned and glued to 22. It was about 10mm too deep so having trimmed it to size I held it in position on the fuselage by the two 6mm dowels just extended enough through from the fuselage, then holding radiator block firmly in place tacked 22 & 23 together with a couple of drops of cyno; removed 22 & 23 and fully glued together, again with cyno. The two 6mm dowels were then glued into the radiator assembly.

 

Preparation done, it was time to epoxy the block to the wing. Applied masking tape to wing and epoxy to the block, fixed together and weighed down to dry.

 

 

 

[David Hayward.]

Sheeted rest of radiator housing on fuselage and sanded along with the block now attached to wing. I think that’s as far as I’m going with the shaping of the radiator, perfectly adequate for what it is.

 

[David Hayward.]

Now I have the wing in place I’ll move on and fix the tailplane, my order of doing things has differed a little from the instructions but only due to personal preference. I like to physically have the wing in place when I am fixing the tailplane so I can make sure they are level with each other.

 

Tailplane dry, fin followed and squared against the tailplane.

 

 

Now came time to hinge elevators and rudder. A note here about the fin/rudder if you’ve decided to have an operating rudder (the standard build doesn’t), the hinge line of the rudder, true to scale, would be slightly further aft of that on this kit (marked on plan). It would be easy to move the hinge line slightly aft if you wanted to, or, build with parts supplied and angle the elevators to clear the rudder movement – see images.

 

Hinges done followed by fitting control horns and connecting push rods at the tail end.

 

This then enabled me to finish off the pushrods at the servo end, binding and gluing threaded rod to dowels for final connection to servo’s.

 

[David Hayward.]

This just leaves the aileron servo, I elected to sink the servo into the wing and fix to bearers epoxied to the wing surface rather then the side mounted arrangement on the plan, again just personal preference.

 

At this point I thought I would put it all together, fit the tank, engine, battery and check the balance, which turned out to be nose heavy with the battery installed under the fuel tank. So I’ll relocate this further back, possibly behind the cockpit if necessary and I do also have a slightly smaller silencer I could fit if needed. Hopefully won’t need to add any weight to achieve CG.

 

Looking for a suitable pilot and will then put in a cockpit floor plus front and rear panels to finish off cockpit area. Then onto covering...

[David Hayward.]

Prior to covering, I need to check CG, which should be 95mm back from the front edge of the wing adjacent to the fuselage sides. It turned out to be quite nose heavy actually with the battery mounted under the tank at the front, so I relocated the battery to just behind the cockpit and now it balances at 89mm, so I’m happy with that.

 

 

Now I’ll get on with final rubbing down/filling and covering....

[Eric Robson]

Whatever covering and paint you are using David, there will be more going on behind the c of g than in front. No doubt you will recheck after painting. 

[David Hayward.]

7 minutes ago, Eric Robson said:

Whatever covering and paint you are using David, there will be more going on behind the c of g than in front. No doubt you will recheck after painting. 

Yes indeed, its slightly in front of spec now and I can also adjust battery position if needed as I would like to keep it a little less than 95mm back from LE to hopefully keep it on the tame side to begin with at least.

[David Hayward.]

Made a start with the covering and using MacGregor iron on film for the first time. So far so good, made it round the curves at the nose ok with a few cuts to help. One minor niggle, where you slightly overlap sections as when covering a fuselage for example, the adhesive bleeds out from the overlapping edge onto the finished film, leaving a white line along the length of the overlap.  Iron is set to recommended temperature as per instructions so I don't believe it's too hot. Fortunately, I've found it can be cleaned up with meths so it doesn’t permanently ruin the finish, however, never had this issue with any other iron on film; on the plus side it’s considerably cheaper than some other options.

 

Progress so far...