Great Planes 25% YAK-54

[flyman1948]

Anybody have any experience with the GP 25% YAK? This will be my first gas plane and I'm concerned about balance. GP says the rudder servos can be in the tail, or mounted midship. I understand that mounting the servos in the rear means I have to add weight to the front to balance out. Any comments?

[Black Bird]

I owned the GP Yak. I did not have any balance issues at all. Just let me know what motor you are thinking about and I can tell you the weights. I used an OS 160 first, it came out a little over 13 pounds. The rudder servos were mounted in the middle. I wanted a little more power so I upgraded to a Fuji 50. I put the servos in the tail and I still did not have a balance problem. Then you can use your radio equipment to find the correct cg for you.

Either way you go, you should not have to worry about extra weight as long as you do not use a motor lighter then a 160.

[yaks]

it's better to fly 3d when the plane is a little tail heavy.. it prop hangs better it flat spins easier etc.. qq yak-54 85" has the servo at the middle..

[flyman1948]

Black Bird.......

I intend to use a FPE 2.4/40cc engine. It should weigh with muffler and ignition around 53.4 Oz. I don't know if stand-offs are required yet. What servos did you use?

[JOSE S]

I used to have one with a f.pe. 52cc an mount one servo for rudder using pullpull system an mount the 19-6 onz. fuel tank as close as posible to the wing tube and the cg was by the book an came out on 15.0 lbs with gas. if you need help with you biuld let me know will be glad to help.

[JOSE S]

with the 52 cc engine i have to use 1 inch and 3/4 wood spacers to get the cowling foward so the instalation of the canopy will be easy, i use on mine hi tec 5925 and 5625 and a std servo on engine one lipo bat for the servos and a 2700 4.8 for the engine

[flyman1948]

I'm getting ready for final assembly of the gas YAK and placed all the parts in the plane to get an idea where the CG would end up. The factory calls for 5 1/8 back from the leading edge at the fuse...my CG is another 1 1/4 towards the tail at 6 3/8 from leading edge. Servos were to be installed in the tail but now maybe not. What CG points have you tried that have worked well....? Thanks

[Black Bird]

Hey little buddy, sorry I have not answered your questions, but you seem like you are coming along pretty well. As I am sure you have found out, you are not going to have any balance issues such as adding weight. I had the servos in the tail. I like to fly very tail heavy, so it was perfect for me. Your engine is amost 20 ounces lighter than my F50.

Are you using the aft servo tray. I am assuming that you did considering that you thought that you would be nose heavy. I had a redundant power system and put all three batteries right under the wing tube. If after you have done this, your CG does not mover forward enough for your flying styles then you may have to consider putting the rudder servos in the middle. FWI, my CG was about 2 inches behind recommended and flew inverted hands off, but ballooned on landings.

You did not mention what servos that you are going to use. I really recomend using something around 130ozs minimum. Hitec 5645s are very nice. The yak has to much surface area on the ailerons for a 90oz servo to give you the centering and response needed to fly this plane.

I will be checking back to see how your progress is coming. What is your weight. Do you have a redundant power system. It is also possible to put your batteries over the motor box under the cowl. If you are worried about EMI, just twist the wires coming from your battery pack to your reciever. This can be easily down by sticking the male end into a drill, and momentarialy pressing the trigger.

[flyman1948]

Black Bird
I'll move the rudder servo test weight location to mid-ship. I did the CG test with the appropriate amounts of weight at the desired location. I'm using HS-645MG's, 133 Oz @ 6Vt. Weight with metal connecting rods is over 2 Oz each, so I added 8+ Oz. at the tail to simulate servo weight. Ingition battery will be in engine box mount. Rx battery 10" behind engine. FPE 2.4 engine/muffler/ignition system weighs 52 Oz. If I have to add weight I'll consider redundant battery.I'll check CG with test servo weight at mid-ship location and see what I end up with.
Did you fly the plane at the recomended CG (5 1/8 back) and how did it handle....? I'm impressed it flies well for you at 2 inches back...7 1/8". I'm interested in what ranges the CG location can be at and still fly well. Some posters have stated the factory location of 5 1/8 is way too conservative for their taste, one going so far as to say it felt nose heavy.
Thanks for the twisted wire tip..............

[Black Bird]

I always start an inch back from the recomended CG location. If you are going to fly some IMAC pattern work, the forward CG would be optimal. If you are going to do 3d, that is when you are going to need to shift the CG back. More experienced pilot than me go further back. Ofcourse there are advantages and disadvantages with both CG locations. If just depends on the flying styles. I figure that it easy to fly fast and more difficult to fly slow.

Flight Lesson: This is common knowlege, but what is wrong with a little review. The forward CG will give you a faster high end speed and a faster approach speed with a nose low attitude on landing requiring a flare. It is easier to recover from spins because the nose naturally wants to drop. This is good with altitude but not so good in a hover. When you loose the hover, with the forward CG, the nose with vilantly drop and more airspeed is needed to recover from the dive because of less horizontal stabilizer control throw effectiveness . The aft CG will make the plane more manuverable, slower approach with a nose high attitude on landing requiring down elavator to prevent the aircraft from entering a stall. One of the purposes of an aft CG is too increase the effectiveness of the tail surfaces at a slow airpseed and high angles of attacks. The aft CG reduces the amount of down force required by the horizontal stabilizer to keep the nose at an high angle of attack in high alpha flight.

A word of caution of the landing gear on the Yak. The two piece aluminum landing gear is supported by an 1/8 inch peace of ply. I would recommended reenforcing the piece of ply. I had a couple of belly flop landings and it would not have been so bad if the ply was a little thicker. A small 1/32thick 8.5" long x 2" accross rectangular sheet of aluminum would work nicely for this. Shim the aluminum until it fits with the landing gear inserted. When you are satisfied with the fit, mark the locations for the retaining screws. Drill the wholes and epoxy the piece of aluminum to the ply. THis may not seem much, but it will help on windy days.

[GremlinX]

KrisW has one..

[MikeStak]

I used the Fujimac 43cc engine, and the Futaba S3305 Hi-torque servos on the tail as instructed by the manual. I have added nothing to this plane that is not mentioned in the manual, everything is stock and only what they suggested in the manual.

My problem is that this plane is horribly tail heavy when using the Great Planes CG Machine at 5-1/8” back from the main wing leading edge. I moved the battery and extra wire to the forward platform, but it is still extremely tail heavy. It is so tail heavy that I am convinced the 5-1/8” measurement has to be a misprint. Can somebody please lend some assistance who has either built and flown this plane before, or knows the answer to this as I cannot be the only one who has purchased this plane and has run into this same issue? I am at a stand still and will not fly this plane as if it is really this tail heavy will certainly lead to a crash.