TT2
Posts: 648
Joined: 3/19/2002
From: Osborn, MO, USA
Status: offline
|
I bought the GSP Katana to fill the gap for a somewhat large, somewhat scale, 'every day' 3D-capable aerobat. After considering many engine choices I ended up using a used OS 1.60fx with a Bisson Pitts muffler, Perry VP30 pump, Mezjlik 18x6 prop. After assembly and test flying I'm convinced that this is a near-perfect combination. The first two flights of this plane were nothing short of amazing...I have never seen a plane of this size that flew so well.
During assembly I changed some things around:
1. I replaced the aluminum anti-rotation pins in the tail with a CF tube that extends from one stab half, through the fuse, then into the other stab half. A bit lighter and stronger.
2. I pinned the firewall and ran thin CA around every joint I could get to from the engine box to the wing tube.
3. Instead of adding washers to achieve the proper thrust angles, I mounted the OS 160fx squarely in the mount then using a belt sander I sanded the rear beams of the engine mounts until the proper angles were achieved. The cowl will completely clear the OS 160fx...only holes for the glow ignitor and needles are required.
4. I enlarged the servo hole in the side of the engine box so I could stuff a micro servo behind the firewall for the throttle. This provides a 'straight-shot' to the throttle with no bends in the pushrod. What more could you ask for? I covered the hole with clear Ultracote.
5. That heavy (8.9 oz) fiberglass landing gear had to go so I made some carbon fiber gear (around 5 oz) for this plane (available soon at [url]www.fiber-lite.com[/url]). I have never used fiberglass gear, but I recently witnessed a flying buddy's Creek Staudacher shatter it's fiberglass gear on the second landing...not much of an impact either...I don't think that the GSP Katana's gear would hold up any better.
6. This plane leaves alot to the imagination when it comes to installing the fuel tank, receiver and receiver pack. I wanted my tank near the CG and didn't feel like using the supplied tank so I used a Hayes (my favorite) 16 oz. For the fuel tank I glued a couple 1/8" x 3/4" ply beams across the inner-most topside wing tube brackets, then padded and wrapped the tank (using vet-wrap), and zip-tied the tank firmly around the wing tube. Seems to be VERY solid. The receiver was padded and secured to the back of the wing tube bracket with velcro. The battery pack was padded and secured to the front of the wing tube bracket, but after test-flying I will move it to the back to shift the CG further aft.
7. I didn't feel like fooling around with the stock linkage and horns so I used #332 Robart 1" ball link horns for the ailerons and elevators, 'home brew' carbon fiber 4-40 pushrods and dubro 4-40 ball links attached to dubro HD servo arms (I'm NOT a big fan of these, but I wanted to check the geometry before ordering aluminum ones from SWB). On the rudder I used the same types of pushrods. I made a much larger (3 5/16" hole to hole) carbon fiber servo horn to enable full travel of the rudder while maintaining the 'parallelogram' linkage geometry. At the rudder I used parts from the #886 Dubro HD control horn system and some 8-32 threaded rod going all the way through. If you look closely at the pictures you may notice that the screw plates for the aileron and elevator horns aren't visible on the tops of the surfaces...that's because they aren't there! I drilled 1/8" holes at the screw locations, soaked the wood with thin CA, redrilled, installed lengths of inner nyrod and CAd them in place. I find that this is easier to do than trying to get the screws to match up to the screw plate on the opposite side of the horn, plus it looks a helluva lot cleaner and is super rigid and strong. Anyway, the horns and linkage are probably overoverkill but to me it's worth the added expense (around $25-$30) for the amount of peace-of-mind it provides.
8. I used a 10-22 lb Sullivan tailwheel bracket...the stock tailwheel looks like someone's idea of a practical joke.
9. I added 18g of lead to the left wingtip to correct the lateral imbalance.
10. I added a homemade fiberglass tube down the bottom of the fuselage interior to route the elevator and rudder servo leads through. I routed the antenna wire along the top interior of the fuselage (far away from the servo leads) all the way back to under the rudder servo.
Still reading this? Good. For radio gear I used (2) Hitec HS-5925 digitals for the ailerons, (3) Futaba S9402 for the elevators and rudder, and a Hitec HS-81 micro for the throttle. Currently installed is an old Hitec Supreme 8 ch (50.800Mhz) and a Nimh 1650mah 5-cell pack. Yes, I have more money in the servos than the airframe and engine (bought used) combined...but man, do those surfaces MOVE! If you want to know my radio setup just let me know...I use a JR 10x and can email you my setup file if you want it.
I didn't have a chance to weight the plane but it feels very light for it's size. My CG with everything installed ended up being about 1/2" behind the recommended CG range. Since I find that most aft-CG recommendations are typically on the VERY conservative side, I decided to leave it where it was for initial flights. The engine fired up without hesitation and I taxied it out onto the runway. I took off at about 3/4 throttle when WHAM! I hit a light pole. Just kidding...the plane flew off very nicely. I circled around, added maybe two beeps of right aileron and one beep of up elevator. I gained a bit of altitude and then pointed her straight up to check how it was tracking. The rudder and engine thrust looked correct. I kicked up the low rates to middle rates and did some loops and rolls. Nice. A few more loops and rolls then I slowed down to see what landings would be like. No wing wobble or stall at very slow speeds. Great. Next tried some knife edge with my 'approximate' elevator and aileron compensation mixing turned on. Pretty close on the mixes and the plane tracked BEAUTIFULLY in knife edge. Tried some high-alpha knife edge but found that my mixes were getting kinda wacky toward the ends of the rudder travel...I've got the elevator and aileron mixes setup as point-curve types so that very fine-tuning of KE mixes is possible. I'll get it nailed with more flights. OK, now time to land her. Setup on approach, cut the throttle to 1/4 and basically watched it land. Too easy.
At this time I'm thinking to myself 'Wow...what a great flying plane!', but I hadn't seen anything yet. The second flight I decided to get a bit more aggresive and fly like I normally do. I pegged the throttle on take-off and the plane was in the air and climbing in maybe twenty feet. Pointed it straight up and did some axial rolls while watching the Katana get smaller and smaller. Hammerhead, cuban eight, then set up for a hover. Held the hover for about two seconds then the plane began to torque roll like a top! WOW! I was so shocked at how axial the TR was that I froze and fell out of it. At this time I was still on middle rates so I kicked it up to high rates...FULL surface travel. I went on a shallow upline and added quite a bit of elevator to see at what point the plane would snap...it didn't...it did a PERFECT 'wall'. I was so freakin' happy that I yelled at a flying buddy and said 'Man, you have GOT to see this!'. I was flying dead level at about 1/4 throttle setting up for another 'wall'. I pulled the elevator, the plane pitched up perfectly then we heard a loud 'POP'. Oh crap. I brought the Katana in as fast as I could. We immediately noticed that some sheeting had split near the end of the (very short) wing tube. I disassembled the plane and we were looking over the wings. One guy looked down the inside of the wing and said 'well...there's the problem'. I took a peek and noticed (for the first time) that the grain of the shear webbing was running parallel with the top and bottom spar caps. The shear webbing had split from the leveraging force being applied by the wing tube. When it all let go it split some of the ribs while the top and bottom surfaces of the wing were trying to get away from each other. I was bummed! Not because of the fact that the plane had broken, but because I couldn't fly it any more that day! I really wanted to see how elevators and harriers were with this plane. Judging from the 'wall' they should be excellent.
I called GiantScalePlanes and told them how great the plane flew and how the wing had popped at the shear webbing. Irwin promised to send me a new set of wings and asked that I took pics of the damage and sent it to him...which I did. Maybe I got a bad set of wings and the rest have the shear webbing grain in the right direction...so look down YOUR wing and post your findings.
The fix: I removed the covering from the three bays where the damage occurred. Using 3/16" medium balsa I made and installed shear webs in the three bays between the end of the wing tube and the wing servo. Then I used popsickle sticks and glued one to the top and bottom spar and to the rib in front of the wing tube. The other was glued to the same rib behind the wing tube (see the pics). I hope that this fix will do the trick. I'm dying to fly this plane again and don't want the wings pulling off during one of my very violent blenders.
Even though there is a serious issue with the wings I still think that this is an incredible airplane. Sure, the covering leaves a little to be desired but I bought this plane to FLY not to stare at. The workmanship is better than most others ARFs I've seen...all the parts are nicely laser cut and the fit of the parts is near perfect. The covering scheme is very visible in the air and greatly contrasting top from bottom. You certainly don't have to think too long about which side is 'up'. For the price it can't be beat IMO. I'm going to buy another one of these just so I can have a backup...
-Tom
< Message edited by RCadmin -- 10/4/2003 1:10:55 PM >
_____________________________
As complexity approaches infinity, mean time before failure approaches zero...
|
Printable Version
All Forums >> RC Airplanes >> ARF or RTF >> GSP Katana 72"...DETAILED BUILD and 3D FLIGHT REPORT 
GSP Katana 72"...DETAILED BUILD and 3D FLIGHT REPORT - 
Way to early for that kind of shock.
