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TurnKey RC P-40

Fitz takes a brief departure from "helis", and gives a review of a very fine semi-scale kit from TurnKey RC, a 1/14 scale P-40B "Tomahawk", which was design specifically for electric Speed 400 power, and based on Gus Morfis plans.

Splash
Specifications
  • Wingspan: 30 in.
  • Wing Area: 144 sq. in.
  • Length: 26 in.
  • Flying Weight: 18 oz.
  • Wing Loading: 18 oz/sq. ft.
  • Motor: 6V Speed 400
  • ESC: Castle Creations Pixie 20
  • Prop: Master Airscrew 5.5 x 4.5
  • Cells: 7 or 8-cell packs, 500/600mAh
  • Manufacturer: TurnKeyRC
  • Available from: TurnKeyRC

Introduction

The Curtis P-40 remains one of the most instantly recognizable planes of WWII, if not for its success in the hands of the American Volunteer Guard (AVG) who were known as the "Flying Tigers", then for the unmistakable shark's teeth motif wrapped around the large air-cooling intake of the P-40s flown by the AVG. An appropriate and mean looking design that also showed a little intimidation couldn't hurt as well. To this day, P-40 keeps its place as one of the classic WWII fighter plane designs. It was a moderately successful front line fighter that flew in the European and Pacific war theatres. While it couldn't dogfight with the lighter and more nimble Japanese planes, armed with multiple .30 and .50 cal machine guns, the P-40 was a durable and stable gun platform that, in the right hands, could be an effective fighter against the Japanese forces.
The people at TurnKeyRC (www.turnkeyrc.com) have introduced a short kit of the venerable P-40B "Tomahawk" in 1/14 scale, specifically for electric flyers. Based on Gus Morfis plans and designed for inexpensive speed 400 drive systems, it is an all-wood, laser cut kit that includes precut wing ribs, fuselage formers, and even tail parts. TurnKeyRC has also taken the effort to include vacuum formed canopy, machine gun blisters, exhaust stacks, and the distinctive chin air cooler. All the builder has to supply is the wood sheeting, sticks and various hardware bits (I understand that TurnKeyRC now offers a full kit that includes all the wood, motor, prop, spinner, adaptor, hardware, and even speed controller).
Short kits have the advantage of allowing the builder to have a better selection of the wood to be used in building the kit. Since you want to build as light as possible, I suggest you try to use contest grade balsa for your wood selection. This is made easy as the instructions include a complete list of hardware and wood required to complete the model. The instructions, printed on three sheets of double-sided paper, offer a sectioned and step-by-step logical building sequence that includes several black and white progress photos. Full size plans are also included and were shipped rolled up. Supplementary building instructions are also printed on the plans as well. The kit, while easy to build, does require that the builder have some previous kit building experience.
For a "short kit", there sure are allot of pieces! The plans are clear and concise.
The kit as received contained quite a few parts. For a short kit, it seemed to have more parts than many full kits that I have built. The wood was very good and quite light as well. The quality of the laser cutting was quite good as expected. All the parts had the requisite breaks in the cutting so that the pieces stayed attached to the wood sheets during transit.

Construction

Wings

Construction starts with the wing. Since the model uses a basic flat-bottomed airfoil, the wing halves are built flat on the plans. However, before this is done, you must first butt-glue two sheets of 1/32" sheeting a little larger than the size of the wing half. This will become the lower sheeting of the wings later, so be sure to make two sets.
Make two sets of lower wing sheets
Follow the plans and instructions for building the wing using the balsa spars and precut ribs. (Note: the 1/8" x 1/4" hard balsa wing spars appear to be missing from the bill of materials; this should be corrected in subsequent kits). Don't forget to notch the spars near the wingtip. The tip ribs have a shallower cutout in them (ostensively to make the tip ribs more durable during assembly). Another thing to note is my hobby shop didn't have the 1/4" x 5/16" size balsa leading edge listed in the parts list. It appears to be an odd size that some wood manufacturers don't carry. I substituted it with 5/16 square, which worked fine. Also, be sure to set the wing dihedral by gluing the wing root rib at the pre-defined angle using the included laser-cut angle bracket (nice touch).
Lower wing sheeting is added after the wing half is framed up Even the cross-grain shear webbing is laser cut. Cool!
Once the bottom sheeting is glued to the wing, slit the trailing edge of the wing ribs at the pre-defined marks and install the 1/8" strips to form the aileron split. The plans show an optional design for removing part of the wing sheeting to save a bit of weight. That, along with cap striping the wing ribs are not necessary, and a viable option for the truly weight conscious. It should also be noted that the spar shear webbing is also precut and pre-tapered for the builder (yet another nice touch). However, the instructions don't seem to indicate they were included, almost causing me to miss using them.
The trailing edges of the ribs have marks to indicate there they will be trimmed to make the ailerons. Once the aft balsa strips are added, then the ailerons are cut free and sheeted along with the wing.
Finish the wing half by applying the D-tube wing sheeting, while making sure to block up the wing tip trailing edge for the correct amount of washout (very important). Repeat for the other wing half and follow the instructions for joining the wings. Before sheeting the ailerons, I added some extra internal balsa reinforcement where the aileron torque rods would be inserted and glued.
Nearly completed wing half The wing tip, while laser cut, needed some scrap balsa reinforcement as it kept breaking.
column 1 column 2
The DuBro 1/2a aileron linkage (part # 231) listed in the parts list is a little unusual in its construction and must be soldered correctly. The link threads are springs that must be soldered onto the rod ends. To do this correctly, you should first sand or file the rod to provide a good soldering surface. Next, slide the springs on and apply some soldering flux to the outer surface. Using a good soldering iron (recommend 30+ watts), carefully apply the solder while heating the rod with the iron. Do not apply too much solder! The point is the use solder and spring to form threads with a light coating only.
Follow the aileron linkage assembly instructions carefully, or you may have problems with it.

Fuselage

The fuselage builds pretty fast, but care must be taken in its construction and sheeting to prevent any warping (it almost happened to me). TurnKeyRC has provided a neat "crutch" (upper frame), which forms the basis of the fuselage construction. The crutch is pinned to the plans and the formers are then glued to it (the fuselage is initially built upside down). Before you pin the crutch in into place, take note of the station/former numbers, as they become hidden when the crutch is in place.
The fuselage is built inverted on a "crutch" for the first few steps.
When gluing the formers into place, be sure to be extra careful to keep them perpendicular to the crutch and aligned with the plans. The next steps are to simply glue on the precut lower fuselage frames, 1/8" wood strips, and the wing saddles. At this point, you have the option of using the vacuum formed nose scoop (includes internal support), or to make an all balsa one carved from block wood (not included). I used the vacuum formed scoop, which has since survived some rather hard landings with no problems.
The frame for the fuselage builds very quickly.
As noted in the manual, basic fuselage construction goes fast. However, the next step, applying the fuselage sheeting, must not be rushed or else you may end up with a twisted fuselage.
Follow the instructions carefully and take your time. Before I started on the sheeting process, I first raised the whole assembly off the plans a little by using some scrap wood pieces. This makes it easier to apply the sheeting. It is quite easy to induce warping if the sheeting is not applied in the manor described in the instructions. Window cleaner applied to the outer side of the sheeting not only makes it much easier to bend around the frame, but also prevents the wood from splitting.
Spraying window cleaner on one side of the sheeting only makes it bend much easier. Sheet the fuselage in sections and take your time. It is starting to look like an airplane now.

Nose

A balsa block, lightly tack-glued to the top front of the fuselage is sanded to shape and will later serve as a battery access hatch, while the nose is formed from some half dozen laser cut balsa rings. Each ring is a different size and starts (largest ring) from the now sheeted fuselage. The rings form a rough taper that is then sanded smooth while the precut plywood motor mount forms the final ring. (You may want to inset the mount to reduce the spinner gap, depending on the prop adaptor used.) This worked quite well for forming the nose cone and alleviated a lot of work that would be required for making the nose from scratch. I also used a little bit of balsa filler to smooth out any unevenness after sanding the rings to a taper.
A balsa block is carved to form the front deck and access hatch. You can also see the precut rings that form the tapered nose. Here is another image showing the rings after they have been sanded. Note the support for the plastic chin intake.

Rear stabilizers

The rear stabilizers are also precut so there is very little work to assemble them, except to glue in the cross grain end pieces (another nice touch to prevent warping when covering). Do not glue the tail parts to the fuselage yet, as they will be covered separately.
The tail fillets are formed before the tail parts are glued on. Scrap balsa blocks a glued using temporary spacers, then trimmed and sanded to shape.
I then separated the top access hatch from the fuselage, as it will be covered separately. To hold the hatch in place, I used cobalt magnets purchased at Radio Shack (see photo below). This simple solution works almost too well and I highly recommend it.
With the wings and fuselage done, I noticed a few pieces were left unused. For the life of me, I could not figure out their purpose. One part was shown separately on the plans, but it wasn't labeled. I felt bad, since time and effort were taken to cut them out. Hopefully TurnKeyRC will clarify their use in future kit versions.
Here's the P-40 all framed up and ready for covering. The tail pieces are not glued yet, as they will be covered separately.


UBOs, Unexplained Building Objects, were spotted on my workbench after the plane was done. The US government denies their existence.

Finishing

The fuselage and wing tops were covered using flat tan Monokote iron-on covering. Likewise, the bottom of the wings, fuselage, and horizontal stab were covered with dove-gray flat Monokote.
Parts were covered with iron on film covering
The camouflage pattern was simply sprayed (airbrushed) on using Tamiya acrylic paint taken from my plastic model paint collection. Tamiya model paints were also used to paint the plastic vacuum formed pieces.
Plastic model paints were used for painting. Vacuum formed parts were cut out and painted separately.
The decals were home made and printed in my computer's inkjet printer using a suitable graphics manipulation program (in my case CorelDraw) and self-adhesive Avery brand label paper that can be found at office supply stores. The source of the decals came from various photos off the Internet that were resized and cropped. The wing markings were actually drawn using a CAD program, and then the blue was filled in using a simple paint program. It must be noted that the Avery adhesive is not particularly strong. Therefore, it may be necessary to spray the back of the decals with 3M 77 adhesive spray (or its equivalent) for better adhesion. For those who don't feel inclined to go through such work can use Major Decal 1/12 scale decals. I also understand decals are available directly from TurnKeyRC.
The decals were home made on my computer. The wing emblems were purposely made a lighter color on the top of the wing to simulate a sun faded look. The landing gear blisters are made from scrap balsa.
The final steps were to glue on plastic pieces such as the gun blisters and exhaust stacks. These pieces were carefully cut out with a hobby knife and a pair of small curved Lexan scissors. In addition, the parts and were painted separately before being attached to the model with medium CA. I left a little extra material on the pieces when I cut them out, which provided some additional gluing surface. The empty airframe weight at this point came to about 6.5 ounces.

Electronics

Lastly, I mounted the motor, battery, and associated electronics into the airframe. The elevator servo was mounted using simple balsa "rails" and was connected to the elevator with a 2-56 pushrod. I chose to mount the aileron servo by cutting a small slot in the upper wing and installing it upright. The receiver and battery pack were mounted using Velcro (the latter requiring a scrap balsa mounting plate).
Here you can see the magnets that hold the front hatch in place. There is ample room in the model for all the electronics.
The directions don't specify the type of speed 400 motor, prop size, or battery configuration to use. Therefore, I decided to start with a 6-volt speed 400 and Master Airscrew 5.5 x 4.5 propeller for preliminary flight-testing. I also used a DuBro plastic spinner (red), which worked, but unfortunately was a bit heavy and left a somewhat unsightly gap between it the fuselage. Perhaps a vacuum formed spinner and inset motor mount would be better (simple solution would probably be to install the motor mount a few rings inset from the end ring).
Two different battery packs were used during testing. I used a seven and eight cell 500AR from my personal inventory. A Castle Creations Pixie-20 speed controller completed the power package.
A 6-volt Speed 400 motor and Castle Creations Pixie 20 are used in lieu of a micro Allison engine.
The ready-to-fly weight came to 18.4 ounces (514 grams) with the eight-cell pack, which is about two ounces greater than the advertised weight. This is still only an 18 oz/sq. ft. wing loading.

Flying

A diamond in the rough?
For those still awake after reading the above, now to the exciting part! The P-40 was balanced slightly nose heavy on the spar, which measured at about 1-3/4" from the leading edge. There were no problems getting the balance correct. The control setups were ~3/8x" for elevator throw and x1/4" for the ailerons up and down (I went with more throw on the elevator than stated in the manual). To be sure to have adequate power on the first flight, I decided to use the eight-cell pack first (nothing more sour than no power).
With some trepidation, the first flight was made at a local fly-in. A fellow flier was kind enough to act as a launching service. While I usually launch my own models, for the first flight, I like to have someone else throw the plane so that I can keep my hands on the controls in case of a severely out-of-trim plane.
Well, two seconds after launch, I knew I was in control of a sweetheart. My "launcher" gave a nice and level launch into the wind. The P-40 climbed briskly and was quite stable with very little trim needed. The control throws felt good for my flying style, responsive but not twitchy (i.e. fun).
Launches are easy and if there is any wind, you have to do little more than simply let go of the model.
After the trims were set, it was time to test the model's flight envelope. The flight speed is best described as moderate (some call it scale-like). While it is not particularly fast, it is not a slow poke either.
As with any new plane, I wanted to test its stall characteristics first. Power on stalls usually resulted in a small amount of left wing drop (presumably a result of the motor/propeller torque), from which the P-40 was able to quickly recover. Power off stalls showed no wing dropping, as the plane just "mushed" in the stall until elevator pressure was released.
Loops were quickly and easily done from level flight. Rolls were also pretty quick, although slightly barrel like. The model will fly inverted, but it would still descend slightly even with full down elevator and full power. Since the wing has a flat-bottomed airfoil, this didn't surprise me.
Landings are quite easy as well. The plane is somewhat "draggy", so you don't need to set up a long approach. That said, the glide is pretty flat, and the plane can slow down to an amazing crawl and still have good control. All subsequent launches have been self-done and are very easy, as the model needs very little speed to fly.
Looking for Tokyo Joe Being chased by Tokyo Joe
The model flew well with both the seven and eight cell packs. I prefer the eight cell packs, as they have a bit more power available.

Conclusion

Hits

  • Looks cool and is a surprisingly a rare model for s400 electrics
  • Good flying qualities

Misses

  • Instructions are a little rough around the edges with relatively few pictures
  • Some parts on plans not labeled
  • Would have preferred a semi-symmetrical airfoil (just my personal preference)
In summary, the model builds into a fine and attractive little war bird that has good presence in the air and flies good. While not for absolute beginners, anyone who has built a couple kits and can fly an aileron-equipped plane can build and fly it. Hopefully TurnKeyRC will come out with a Nakajima to chase around!

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