JC's Planes and Projects

Ryan Aircraft electric P-47 Thunderbolt with geared Himax brushless motor

Specifications:

Wingspan: 31 inches

Length: 27.25 inches

Weight: 15-oz RTF!!!!

Transmitter: Futaba 8UAPS

Receiver: Berg 4-channel “micro-stamp”

Servos: 2 x GWS Pico+ servos on aileron and elevator.

Power: Himax 2015-4100 brushless motor mated to GWS EPS-350C gearbox with “C” gearing. Batteries are 3s1p Etec 1200mah. ESC is Castle Creations Phoenix 10.

Prop: GWS 9x7

Finish: Fuselage is glassed with ½ ounce cloth. Flyer surfaces are covered with Oz Cover Lite. Paint is Testors enamels.

Features: The stock 1-meter antenna was cropped in favor of an internal Azzar 6" long antenna. Pilot in cockpit is scanned image of Walker “Bud” Mahurin.

Have you noticed that I like P-47s? This is my third Jug and my second Jim Ryan design. I had excellent success with the bubbletop design and have enjoyed many flights with it. When I finished it during the winter of 2003 it was close to state-of-the-art. It had a Mega 16/15/5 with the new HeCell 2/3A NiMH batteries and a Hitec 555 RX. This was the about the best “speed 400” performance upgrade available at the time. It proved to be a powerful power system and delivered 7-9 minute flights. The bubbletop Jug came in at 20-21 ounces and flew very well. It had no bad flight characteristics, but the wing loading was evident with a high cruise and landing speeds that resulted in a flight envenlope that demanded the pilot’s attention at all times. Well, a lot has changed in a year. New technologies motivated me to build another Ryan P-47 to see how light I could get it in an effort to approach a relaxing park flyer flight envelope. Lightly loaded airplanes are just more fun to fly and I find that I fly them more.

I started the project by firing up Motocalc and running a lot of numbers. I was impressed with the Himax 2015-4100 that I used on my foamy Yak and chose it as the powerplant. The Himax is an ounce lighter than the Mega. Same goes with the batteries – I had the 3-cell packs of Etecs and decided to use them as well. The LiPo batteries save at least three ounces over the KANs. I also chose the Berg RX and saved some weight over the Hitec 555. I also used a Castle Creations Phoenix 10 and it is much lighter than the Jeti 18-3P that I used on the bubbletop. I decided to drop the rudder servo since I rarely used rudder on the bubbletop in flight. Net savings in electronics and power system was at least four ounces.

I’ll admit to a fairly heavy glassing job on the bubbletop. I decided to try something lighter for the finish on the razorback. The fuse was glassed and I did a much better job than last time. This time around I used a 50/50 mix for the first coat to attach the cloth and a 25/75 (epoxy/alcohol) for the second coat. This worked fine and added very little weight. Hey, I’m learning all the time! For the wing and tail feathers I decided to try the Oz Cover Lite paint-able iron-on covering. This product is very pliable and went on and around the parts very well. Added weight was negligible and not filling or sanding was needed. I probably saved an ounce over the bubbletop in the covering. The downside of Oz Cover is that the enamel primer and paints that I used do not get a good purchase into the material. Even very low-tack tapes and stencils can pull up the paint. If I had to do it over again I would glass the entire structure as I did the fuselage.

Early on I decided to model the P47C of Captain Walker “Bud” Mahurin. Capt. Mahurin was a very interesting subject. He was attached to the 63^rd FS of the 56^th FG also known as “Zemke’s Wolfpack.” He had great success as the fifth-ranking ace in the ETO scoring 19.75 kills before being shot down while attacking a Dornier. With the help of the “resistance” he was able evade capture for 6-weeks and make his way back to England. The policy at the time was that anyone having knowledge of the “underground” could no longer fly in the ETO lest he be captured and forced to talk. He was transferred to the Pacific theater where he added one kill to his total while flying P-51s. Like Col. Gabreski, Capt. Mahurin flew F-86s in Korea. There he claimed a further 3.5 kills. How is that for service to your country? He also brought down a B-24 by getting “too close” to it. He bailed out of his tail-less Jug and the B-24 crash landed. He expected to be court-martialed but Col. Zemke just chewed him out and he was flying again – but maybe not so close to the friendly bombers!

Capt. Mahurin’s best known mount was the P-47D “Spirit of Atlantic City” war-bond presentation aircraft designated UN-M. Before that he had success with a P-47C designated UN-V. I chose to model UN-V because I could not think of a way to paint “Spirit of Atlantic City” on the side of this little airplane! “Bud” Mahurin was also a good photo subject for the American press. All of his photos inevitably show him with his distinctive big smile. I scanned a popular cockpit photo of Captain Mahurin and placed it in the cockpit of my model.

Captain Walker “Bud” Mahurin flashing his big smile in the “greenhouse” of my Ryan P-47C Razorback

The installation of the Himax with the GWS gearbox required very little modification. Formers F1 and F2 were modified to accept a 3/8” hardwood stick to mount the gearbox. Just take care to preserve the thrust-line shown on the plans. Once I had everything installed it was time to mount the battery and balance the model. Guess what? With the Etecs all the way forward on the battery mount the ship was still quite tail heavy. Arrrrgghhhh! All that work to make the model light and I have to add lead? After taking a breather I started poking and prodding the battery around in the fuse and found that it fit very well in the chin of the fuselage in front of the wing. But how was I going to mount the battery up there? My solution was to build a small balsa box and position it in the chin. The Etecs just slip down and into the box and are held securely. The balance came out right on the money! Wahoooooo, no lead!

Now that she was really finished I got out ye olde digital fish scale and it read 15 ounces! That’s right, a full 6-ounces lighter than the bubbletop. I charged up a pack of Etecs and did a run-up. The static thrust is definitely more than 15 ounces! Motocalc predicted about 16 ounces. At full throttle the little Jug definitely had greater than 1:1 thrust to weight ratio as it wanted to climb to the ceiling if unrestrained. While not scale this P-47 will have unlimited vertical flight.

Like the first P-47, this project was a lot of fun. I found it very relaxing to build a second airplane of the same type. Knowing exactly how it goes together allowed me to do a better job. Most of the parts were made from scratch and I haven’t done that in nearly 30 years. I look forward to getting this airplane in the air. Lighter airplanes are just more fun to fly!

Flying the little Jug

5/1/04 – I have not flown the little Razorback yet. I am waiting for some nice weather. I’ll post a full report soon.

Left rear photo of the little Razorback. All insignias and lettering are painted on.

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