Kangke Super Kraft REARWIN SPEEDSTER 1/5th Scale
I receintly ordered a KANGKE Super Kraft 1/5th scale Rearwin Speedster for my next project. This ARF is actually classified as a Sport Scale ARF. However, it's close enough for me. My engine choice for this bird is an Evolution 26 GT II. This engine uses standard rail mounts. It has a front carb and side exhaust just like a typical glow engine so installation will be easy and identical to its glow counterpart. The benefits of gasoline power is it's clean, inexpensive, and very low maintanance. As 26cc engines go, this engine is very much on the upperend in price. By the time you purchase the engine & muffler... a good $500.00 will be invested, but I can assure you that it's money very well spent. This engine is super reliable, easy starting, and excellent service from HORIZON HOBBY
is no mention anywhere in the literature regarding this aircraft being built for a
gasoline engine. So if you decide to do this, you may be on your own regarding warranty.
No big deal, I put gasoline engines in all of my airplanes regardless if it's made for gas
or not. However I do have a list of things that need to be beefed up for gasoline engine
1) The firewall gets
It really dosen't take much effort to make ANY aircraft gas engine worthy, but you do need to plan your build to include the necessary changes. Always make Safety your FIRST priority.
ABOUT the Engine:
ABOUT the ARF:
A closeup of the GP Hinge
Some people like to glue their hinges in place, and this will work fine. However, I prefer to anchor them with #2x3/8 button-head screws.
Here is the horizontal stab hinged and ready for elevator halves. This is a very clean and easy install. I am very pleased with the quality of this ARF. It is well designed and well fitted. The hardware is of good quality and it has semi-phenumatic tires instead of those crappy foam tires often found in most ARF's. I do think the tires are a bit small though. I switched to 4" diameter and they fit perfectly in the wheel pants.
As you can see, the Evolution 26 is a perfect fit! I did make a change in the engine mount. by using an aluminum one instead of the plastic mount provided in the kit This is just my personal preference for gas engines. The nylon/plastic mount is OK for most all engine applications. I am using a full-length Tuned Pipe on my 26 GT and it fits nicely. The purpose of the pipe is, I get an extra 800 RPM out of my engine. The available Pitts Style muffler will work FINE as well, however I prefer power over looks. Again, its just another personal preference. A gas engine historically vibrates more than a glow engine. This engine is an exception since its origin is glow. On the other hand, I am putting a 1.60 engine into a .90 sized aircraft so special attention is manditory. The firewall MUST be re-enforced to support the extra weight & power.
Here is a close-up of the engine installation.
The stand-off box needs to be fiberglassed and/or screws installed at the intersection of the box. I would also suggest additional tri-stock wherever possible. Other than that, it's ready to go. You'll notice the engine is inverted... Again, my personal preference. With the engine being inverted the cowling will need minimum cutting to fit, and it will have a much cleaner look. So far, this aircraft has been my EASIEST gasoline engine conversion to date. The supplied fuel tank is an 18.5 ounce glow fuel "stopper style". You can use this tank if you change the stopper to a gasoline compatable stopper. I replaced the factory tank with a B&B Specialties tank which is specifically for gasoline. It's a 16 ounce, which is really too big for my gasser. It will easily fly 50 minutes in a single fill-up.
Unlike J-3 Cubs and Monocoupes the Rearwin Speedster has a semmetrical wing profile similar to a Taylorcraft or a Citabria. Also, the fuselage is fairly narrow and tall which will make air penetration a little less difficult. The tall fuselage will make for excellent knife-edging. The large vertical fin has a slight draw-back for some aerobatics, but that's easy to overcome. The coupling ratio is fairly long so you can expect the aircraft to track nicely with minimal yaw.
In order to counter balance the extra weight of the engine, I added a second elevator servo and moved them both to the rear of the fuselage. (You can see the left one in the photo above.) this balanced the aircraft perfectly AND it gives the aircraft precise elevator control. The aircraft balanced perfectly in the neutral position with the servos moved to the rear.
I kept the original rudder servo location but changed the wood dowel to a fiberglass arrow shaft with .093" rods. This is much more ridged. You may install a PULL-PULL system if you like, as the proper cutouts are already in the fuselage. For servos, I used a pair of Hitech HS 625 Metal Gear for the ELEVATOR, and HS 5625 MG Digital for the ailerons & rudder. The throttle servo is an HS525MG. My radio is a SPEKTRUM DX-7, operating at 2.4Ghz. The receiver is 6.0 volt and the ignition is 4.8 volt, and both are 2700 Mah NiMh. You won't need high capacity batteries if you use standard servos.
Because I will have two batteries (ignition & receiver) I had to look for a unique place to put them. I wanted them accessable, AND beneficial for balancing the aircraft if necessary. I came up with installing them in the bellypan. This turned out to be fantastic! I did secure the bellypan with covering AND the supplied screws to insure it stays on.
Kangke got a little carried away with cut-outs for weight reduction. You will want to cover these off cut-outs to keep the fuselage from getting pressurized, AND to keep fuel vapor out! I just covered these cut-outs with Ultrakote.
The Rearwin Speedster is done. Its weight came in at 11 pounds, 12 ounces, having a wing-loading of 28 ounces per foot. She's going to fly like a charm!
All I'm lacking now is a maiden flight!
After one final check of the controls, I taxiied out and lined up into the wind. At about 1/3rd throttle she rolled out smooth & straight, not needing any rudder correction at all. I pulled back on the elevator and she climbed straight up as high as I wanted to go. I leveled off, and she locked on to course headed north. I needed NO AILERON TRIM, NO ELEVATOR TRIM, NO RUDDER TRIM! Amazing! After about 7 or 8 laps around the field I had to add left aileron trim. I knew Something was up... I landed only to find the left strut came lose at the wing. After a little creative re-work it was ready again. The next flight was flawless. It knife-edges perfect... It flat-spins perfect in both upright & inverted... It's capable of a rudder snap on demand, but you have to want it to snap, as it takes a sudden full rudder. It's also capable of an elevator snap, but you have to force it by increasing your elevator travel as far as it will go. It's a very graceful snap, and easy to recover from! Next time out, I will "try" some 3D type maneuvers just for fun. I'm not expecting it to perform well, but it may be surprize me...
UPDATE Oct 28, 2007
UPDATE July 12, 2008
Copyright © 2007 M. B. Fuess- Greater Southwest Areo Modelers