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Lockheed P38 lightning - Part 1

by Phil Niewand

Plan No.697

Features Construction Articles

Plan Detail:
Plan No. 697
Price: AU$85.00 (3xSheets) 
plus P&H (AU$7.00 within Australia).
Moulded Canopy: AU$27.50 plus postage.

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When talking to the editor of this mag one day, in passing I asked what plans that he had that needed to be built and tested. John went through a list of about half a dozen and the last on the list was the Lightning, probably thinking that I wouldn't pick that one. My ears pricked up and after a few more details about it, the answer was yes for the Lightning! I explained to John that it would probably take me a year or so to get it completed, because the reviews I also do for airborne had to take a front row seat and the Lightning would have to fit in around them. Well it actually ended up taking two years, but I think the wait was worth it!

The plan arrived and on opening the separate sheets it revealed that it was the early P model, which had the smaller swept back engine cowls. The plan showed side mounted 46 two-stroke engines that would stick out the right hand side of each cowl. After a bit of thinking and knowing that I was going to use the small for their size, Magnum AR 61 FS's, the answer was to mount them inverted, but again they would stick out the front of the swept back cowls. Now the only problem was that they would stick out even further that the 46's. After a few phone calls to John, he gave in and let me change it to the later ' L ' model, which had a larger frontal engine area, which would completely enclose the motors. Having run these Magnum engines inverted in most of the review planes, I had no reservations about their reliability mounted up side down.

The plane that I have copied is the Lightning that was flown by the American Ace, Major Ted McGuire Jr. He was killed in combat in the Pacific theatre, trying to protect his wingman involved in a dogfight with a Zero. McGuire banked his Lightning too steeply and stalled the top wing and went into an unrecoverable spin and was killed on impact. He had the second highest amount of kills of all the P38 pilots, with 38 kills to his name, before his untimely death. The nose art on the plane is the nickname that he had for his wife. Pudgy 5 (bet his wife liked that!) was the last P38 that he flew.

Getting Started
Well let's get started on the building! It is advisable to kit up your parts before you start, so the photocopier ran hot to make up ironing templates to transfer the images onto the balsa and ply pieces. For those not familiar with this technique, photo copy all the various parts of the plan that need to be cut out of balsa or ply. These photo copies can then be cut out and then laid face down onto the wood and a domestic iron run over the photo copy. The image on the paper is then transferred onto the wood much the same as one of those temporary tattoos we had from the lolly shop when we were kids.

There is a fair amount of cutting involved and on Fathers Day a nice little band saw arrived, so it got a very good test out! The ribs were cut in pairs, as was anything that had to be duplicated. A few hours had me covered in balsa dust and the parts ready for some building.

The centre section of the wing needs to be built first and then the two booms and tail are built over it using the jigs made from the plan. Each boom and the centre pod, are built flat on the plan over the wing and then once completed, turned over and then the bottom sections are glued on to complete the rounded shape. The horizontal stab was built up and covered with 1.5mm balsa. This sits in a pair of jigs that holds it at 0 degrees to the datum line, while the wing needs to be packed to 1 1/2 degrees of positive incidence. You will need to get yourself a good incidence meter to allow you to get everything lined up perfectly, otherwise you just might create a dog of a machine! Take your time with this part of the job, and double check everything several times before committing glue to the wood. I tended to use PVA for a lot of this work, as it gave me a bit of jiggling time. The balsa formers and spruce stringers then just join up the tail and the wing, making sure to keep them square over the plan. I completed each boom before moving on tho the centre pod.

I had brought a set of spring-air retracts and fitted them without too much effort. They were all set up as firewall mounted units and this didn't suit the boom installation. So I made up an aluminium plate to bolt them to and then bolted the assembly to the mounting plate. A bit of mucking around, but the end result worked a treat. Once the retracts were in the booms (under the wings), they could be sheeted and the centre pod built over the wing in the same manner as the booms. This is built up using the building board surface with formers and some spruce stringers, just like the booms, whereas the booms are just sheeted with 3mm balsa, the pod is tapered in all directions and needs to be covered using the planking method. A bit time consuming, but the end result is worth the effort. The booms require the 3mm balsa to be wetted out with liquid ammonia to allow it to follow the tight curves at the tail end of the boom. I fitted it in place and used thin cyano to hold it there, before applying some PVA glue to permanently fix them in place. I placed the sheet joins along the stringers to help support them. A lot of time was spent thinking out the best way to tackle things as I went along. But better to waste a bit of time than stuff the job up!

The wing end sections are made to be removable to allow for easy cartage of the plane. These were built over the wing plan and I put 2 degrees of washout in each tip. This required the rear of the tips to be packed up by 5mm, tapering back to zero at the root. This will help prevent the dreaded tip stall, both at high speed and on the all important landings. The wing joiners on the plan are just 3mm x 15mm bar iron and I replaced them with high tensile 6006 aluminium bar of the same size. These have worked fine, with no sign of them bending in loops and rolls. I could see this plane becoming too heavy if some weight saving measures weren't taken. I did also cut sections out of the ply motor mounting boxes and hollow out a few ribs towards the wing tips. Trial fit everything, and check it with the incidence meter as you go along. This will save you from depression after it rolls into the ground on its maiden flight. While the wing ends were still pinned down, I sheeted to top surface with 1.5mm balsa and made sure the washout was still there as the glue dried. The rudders were built up over the plan and sheeted like the rest, with 1.5 mm balsa. A rough sand had them close to the right profile for a final finishing sand after they are attached to the plane.

SERVOS
With a total of 13 servos needed on the original plan, I just had to see if I could bring the number down without compromising the safety of the plane. Originally it had 2-aileron servos, 4 flap, 2 rudder,1 elevator, 2 throttle, 1 retract and 1 for a steerable nose wheel. I was able to make up a piano wire linkage that would go from the inside flap, through the boom and connect into the outside edge of the outer flap. That got rid of two! The rudder was just a matter of fitting a pair of bell-cranks each side of the rear edge of the horizontal stab and running a wire across to connect them up together. Then a pair of linkage arms made the rudders move in unison with each other. Sweet! That had it back to 10 servos. I was able to get a great deal on some Hitec 225BB mini servos and they have more than enough power to operate all surfaces with authority. Now where to put them all?

I had my suspicions that the plane would turn out on the tail- heavy side, but I fitted the elevator and rudder servos mid-way down the right boom where the dummy radiator covers would go. This was where the plan had them! They stayed there until I was about to fit the covers in place (more on that later). The wing servos were screwed onto ply plates and hatches cut out for them to fit into. The throttle servos went underneath the fuel tanks and had to be built in, so the throttle travel was checked before the balsa covered them up. The retract servo to operate the air retracts went as far forward as I could get it in the nose pod and the nose wheel servo was placed just in front of F2. Let's get back to some more building now.

Cowls
The plan shows carved block balsa cowls and radiator covers. Because there are two cowls and four covers, I decided to head in the fibreglass direction. A foam plug was made for each item and they were covered with 2 layers of 6oz cloth and then wet out with epoxy resin. They were then covered with a mix of Q-cells and epoxy to fill and imperfections in the surface. Once cured they were sanded back with various grades of wet and dry sandpaper. Now we had two plugs that some moulds could be made from. I think these will be available as a set with the plan and canopy in the not too distant future. Even though it took a bit of time, I still think that I would be still sanding all those awkward curves if they were balsa.

Engine Mounts
The engine mounts went on the firewall with blind nuts and high tensile bolts. The plastic mounts required a section cut from them to allow the carby to rest next to the firewall. This was necessary to keep the proper length of the cowls. I marked on the plan the position needed for the firewall when using a four-stroke motor. With the retracts in and operational, I had to decide whether to put some doors on to hide them. Last year a gentleman by the name of Rod Mitchell attended the big Hamilton fun fly and swap meet on the last weekend in November( free plug!) Rod brought along his 'YippeeÓ P38 Lightning and thrilled the crowd with some precision flying. I was able to have a good long talk with him and he showed me his simple door actuating system, using just fishing line and a few torque rods to open them. Thanks Rod, because I really had no idea how I was going to get them working. Another option is to use a Robarts sequencing valve which will control all three doors and will save heaps of time and headaches.

Next issue we'll finish off the Lightning then get to what most of us really like, flying.
Just as a teaser I'll let you into a secret, it flies just great.

Go to Part 2 of construction article >>>

All components cut out prior to construction.
All components cut out prior to construction.

 

Engine pods are ply and locked into the wing.
Engine pods are ply and locked into the wing.

 

Commencing the tail booms.
Commencing the tail booms.

 

All balsa build up empenage.
All balsa build up empenage.

 

With tail booms, centre wing section and empenage sheeted, it's time to start the nose and cockpit.
With tail booms, centre wing section and empenage sheeted, it's time to start the nose and cockpit.

 

Strip planking being laid onto the nose and cockpit
Strip planking being laid onto the nose and cockpit

 

Bottom of booms now sheeted with tops about to be stripped on.
Bottom of booms now sheeted with tops about to be stripped on.

 

Wings are all balsa/wood build up construction.
Wings are all balsa/wood build up construction.

 

Wing root and engine pod. The top will be sheeted over.
Wing root and engine pod. The top will be sheeted over.

 

Note how the engine pod locks into the wing.
Note how the engine pod locks into the wing.

 

Trial fit of the Magnum 61FS. Note the planking on the nose. Take your time for a good job.
Trial fit of the Magnum 61FS. Note the planking on the nose. Take your time for a good job.

 

Retracts fit neatly into place.
Retracts fit neatly into place.

 

Before and after painting. Brown paper was used over the balsa sheeting then painted.
Before and after painting. Brown paper was used over the balsa sheeting then painted.

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