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Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

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Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Old 08-20-2006, 04:03 AM
  #476  
tetsa
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Hello everybody! I also bought the YAK some time ago, and I do have to say it flies beautifully.

How ever: On the 10. flight, when pulling out of a hover, the fire wall ripped off. The engine (Saito 220) wasn't badly damaged, but the plane is a write off.[&o]

I've contacted GP trough my hobbyshop where I got the plane from. It's interesting to see what they say, since this was clearly a case of "bad building". There was no glue in the area where the firewall meets the triangular reincorcements, so there was nothing to hold the firewall in place...

All this came as a total surprice, since I've had numerous GP ARFs before, the 1/4 Extra to name one, and I've had no problems with them at all. I'll try to remember to post a picture a friend took at the field, when I get it.

I'm quite sure this was just an isolated case, but if the GP replaces my plane I'm going to do something to the firewall area. Maybe wrap some carbon fiber around it.

Cheers,

Tero
Old 08-24-2006, 10:26 AM
  #477  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Okay guys, here's a picture I took today. As you all can clearly see, the firewall sides are suspiciously clean of glue... IF there were glue, the would also be schreds of wood stuck to the sides. (Or correctly: If there were glue, my plane would still be flying...) Now here's what I believe happened: The firewall sides gave up the struggle to keep the enginebox together, since the triangular pieces were not properly glued to the sides. And when the last bit of adhesion was lost, the box sides just opened up, and my Saito 220 took a short, but rather spectacular burst forward.


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Old 08-28-2006, 04:50 PM
  #478  
DOC
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I just started to assemble my Yak today! I noticed the Robart hinge point (knock offs ) are of poorer quality than the real thing. The pin has a smaller head , and the peened end, isn't very well peened. I tryed to repair the questionable pins (rivets), but they get too tight and don't work well.
Has enyone had any pin failures? Or is this a non problem.........?
I think I'll use the real thing just in case.
Thanks, DOC
Old 08-28-2006, 05:46 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I too have some question as to the integrety of the firewall ? I don't think a 1/8th inch firewall thickness is adequate for the larger engines. I have laminated in an aditional 1/8 in. acft ply and added 1/2 in. gussets.
Old 08-30-2006, 12:23 PM
  #480  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Okay guys. A couple of days ago I wrote how I wrecked my YAK because of faulty firewall. After sending a bunch of pictures of the nose of my late YAK to GP, they admitted that the firewall was poorly glued to the sidewalls. They will supply me with a new plane.

See, this is how a classy company operates. It would have been so much easier for them to just brush of the little modeler from Finland (where the hell is that, anyway!?!?!) but instead they took the trouble of looking in to the case, and admitted that there was an error in the building of my plane. For that, GP deserves my deepest respect.
Old 08-30-2006, 03:38 PM
  #481  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Great!!!! I hope to have mine done tmorrow and fly this weekend.

(I checked my firewall after seeing your pictures and drizzled in some more epoxy just in case........)

Great Planes has some pretty decent customer service.......
Old 09-01-2006, 05:44 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Where is everyone balancing this thing at. The manual says 5 1/8" back...looking at tthat mark on the wing it seems awfully far forward. I built mine by the book with the Fuji 43 and the rudder servos in the tail. I put it on my GP Balancer and it is WAY...WAY...tail heavy. I'm not talking a little. It is balancing at 6 3/4" back[X(].

Where is the sweet spot on this thing. I like mine flying neutral (inverted and upright with no elevator input).

Old 09-02-2006, 09:39 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I just completed mine with the O.S. 1.60. I agree with BMiracleTX, it is unbelievably tailheavy at the 5 1/8" point. I put some temporary weight on it and tried it at 5 7/8" and still had 17 Oz of weight on it to balance. I have the rudder servo forward in the pull-pull position. I see that many of you with the 1.60 are moving the CG back, I also would really like to know what the sweet spot is. I would be far more comfortable if I could use 6" to 6 1/4" safely. Any comments would be much appreciated.
Old 09-03-2006, 09:24 AM
  #484  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I was all excited to fly mine this weekend until the balancing. Now I am just so frustrated that I put it up for about a week. I will mess with it later. I guess I will be moving my servos to the pull-pull forward position and see how it balances.

Can one of you who have flown theirs yet tell us where to balance it?
Old 09-03-2006, 06:48 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I was all excited to fly mine this weekend until the balancing. Now I am just so frustrated that I put it up for about a week. I will mess with it later. I guess I will be moving my servos to the pull-pull forward position and see how it balances.

Can one of you who have flown theirs yet tell us where to balance it?
I initially balanced mine at 5" by adding 6 ounces of lead in the nose using an Evolution 45 and the pull-pull systems. It flew a little nose heavy, so I took of the 6 ounces off and it came out at 5 3/8". At that location it felt neutral, but not to snapy. I haven't tried yet but I think you may be able to mve it aft as far as 5 5/8" if you add enogh exponential on the elevator.
Old 09-04-2006, 07:16 AM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Doc,

It's not 1/8" thick, it's a 1/4" thick, I think you were just measuring the "notched" part. Plus there are additional laminations on the back, however my DA50 fell right over top of were they ended so I had to laminate around the mounting holes.

Mac
Old 09-04-2006, 09:22 AM
  #487  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I just finished mine today, and I plan to fly it later this week. The CG came out at 5.5". That calculates out to ~28.5%, and that should be perfect for this type aircraft.
It came out at 14.9 lbs, with a Walker Machine 3.2(Sachs). Flying at 5K feet I need the extra power..! I have pull-pull on the rudder and put the elevator servos (HT 5645's) in the rudder servo cut outs.
I'll post flight results when available.
Old 09-07-2006, 06:32 PM
  #488  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I completed my Yak about a month ago, and have been moving back the CG ever since from its orginal 5 1/4 inches (which like AirTech, took 4 oz lead in the nose). It has a BME 44cc with three servos in the tail. After about the 7th flight, I have settled on 6 1/4, which is just at the back of the wing tube. The balance test I have learned is a 45 degree upline, then go inverted, and having the upline maintained with only the slightest down pressure on the elevators. I'm not quite there.

With the balance I now have, the plane flys well, but has more of a tendency to slightly nose up on landing than I am used to. Those who preceed me in giant scale tell me that giving the plane no up elevator, or even a bit of down elevator on landing takes some getting used to - which explains some of my hard landings. When I kept up the speed as indicated, I have done much better. I would appreciate comments/advice from those more experienced.

With all that said, this plane is a blast to fly. Super performance. Way superior to anything I have flown 60 sized areobatic.
Old 09-07-2006, 11:17 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Without the cowl and spinner my CG is at about 6 3/4" back with a Brillelli 46 and push - pull servo's (in the tail). I wish I had known this sooner, now I am going to have to move the rudder servos up and move my throttle servo over and I guess plug up some holes. Using my digital bathroom scale I am around 14 lbs.

This is a little disappointing since the rear rudder servos don't even balance properly with the recommended Fuji engine.

Another problem I found is that the 22x8 Xoar prop doesn't fit in the spinner - though this I can understand.

Thanks BMiracleTX for posting.
Old 09-07-2006, 11:55 PM
  #490  
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Uncus it only takes a little bit of sanding to fit the zoar I had the same problem.
Old 09-08-2006, 04:40 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I flew my Yak today! At 5 1/2" It flew fine. I did notice a nose drop when cutting the throttle on landing. I also needed a Very slight down elevator for inverted flight. The book reccomended throws are not enough, the high rate throws are OK for me. Unlimited rolling verticals, but knife edge to the left causes an RPM loss, due to the carb. position.
I replaced the Kit tail wheel with a sullivan (10-22 LB).........it sucks! A friend is using an old Klett Tail wheel and it works wonderfully. Unfortunatly they are out of business....... I made somthing of my own, I'll try tomorrow.
Old 09-08-2006, 05:36 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

ORIGINAL: DOC

I flew my Yak today! At 5 1/2" It flew fine. I did notice a nose drop when cutting the throttle on landing. I also needed a Very slight down elevator for inverted flight. The book reccomended throws are not enough, the high rate throws are OK for me. Unlimited rolling verticals, but knife edge to the left causes an RPM loss, due to the carb. position.
I replaced the Kit tail wheel with a sullivan (10-22 LB).........it sucks! A friend is using an old Klett Tail wheel and it works wonderfully. Unfortunatly they are out of business....... I made somthing of my own, I'll try tomorrow.

You can get Klett tailwheels from Central Hobbies. http://www.centralhobbies.com/landin...tailwheel.html Scroll down and you'll see them.
Old 09-09-2006, 07:11 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Shakes, Thanks for the heads up. That is a great setup. I'll have my order in ASAP.
Old 09-10-2006, 04:15 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I just completed mine, O.S. 1.60. I took it out this morning for break-in on our test stand but just for break-in not flight, was planning to fly it tomorrow. It ran great for quite awhile until it suddenly shut down. I thought I had run out of fuel. I took the canopy off and saw I had plenty of fuel left. Thinking it was just a minor thing I restarted, couple of minutes later it quit again even though it was running great up to that point. Obviously I had some sort of a problem. All fuel lines clear, engine sucking fuel great, no air leaks etc. Then I found the problem, the head of the engine was really hot. I am pretty sure the engine is overheating due to lack of air flow over the engine. Since that cowling is so big I and my flying buddies are of the opinion that cool air is not flowing properly over the 1.60. Anyone else encountering this problem? I started making a baffle to get air to flow over the engine better (a full plate inside the cowling cut around the engine/muffler but that really makes it impossbile to mount the cowl screws in the back. My real question is wether or not anyone has encountered the overheating problem with thier 1.60 on the Yak?
Old 09-12-2006, 08:28 AM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Dave Patrick has some really functional, nice looking metal tailwheels that are perfect for this arf. The 7-12 lb. tailwheel is on my yak and works perfect.

http://www.davepatrickmodels.com/frame.htm

Mike
Old 09-17-2006, 01:22 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Anymore reports on CG?

I moved the rudder servos to the middle and now I am am balancing around 6-1/4. To get it to balance aroung 5-1/2 I had to put about
2 lbs of weight on the motor standoff box which seems crazy. Am using the GP balancer with great difficulty with this size plane. Looks like it is flyable at 6-1/4.
Old 09-17-2006, 02:22 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Uncas

You should not have to add any weight to this plane, move some thinghs around. Two pounds is crazy!
Old 09-17-2006, 04:09 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

Evfast, if you read the above posts, Uncas and I are in the same boat...we are both running 43 or 46cc gassers on the front (which add more weight to the nose than the recommneded OS 1.60). We built it by the book with the rudder servos in the tail and our CGs were too far back (6 3/4'). Now we have both moved our rudder servos to the front (and now we are both balancing around 6 1/4") which is still 1" aft of te recommended beginning C.G.

I agree with you that we should not have to add weight, but I have moved everything as far forward as I can without risking radio interference from the gas engine....Like Uncas, the only thing I can do from here is add weight to the nose.

Does anyone know if the kits being currently sold are a second production run? Is it possible that they used thicker/heavier wood to build the fuse which would then result in more weight in the tail?

This seems rediculous to have everything forward with a heavy gas engine and still have to add weight. I could put everything up front like the nitro guys are doing, but it would be unflyable due to the radio interference.

Uncas....its nice to know that at least you and I are consistently having the same results with our setups and resulting CGs. Chemoman seems to like hhis set at 6 1/4" so I think I will try mine there...I like mine to fly alot like his sounds.
Old 09-17-2006, 09:32 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

BM,

You are exactly right. The ignition noise issue prevents anymore shifting of weight forward. Though, I did see a pic of a GP Ultimate Bipe in another thread where the throttle servo was in the engine box next to a gas (not glo) engine! This is my first gas plane so I don't know what you can and can't get away with.

Also, I measured my CG without the cowl and spinner. That will add about another 8 oz to the nose. I will probably add another 8 oz of lead to the nose. From there I will gradually remove weight and see how it flys. One of the fella's at the field who flys giant scale planes told me CG is more forgiving in the larger planes.

I noticed in the other GP YAk thread that Marmitus put a 5 cell 3600 mah nimh in the nose of his OS 1.60 version.
Old 09-27-2006, 12:21 PM
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Default RE: Great Planes 25% Yak 81" 12-lb, seen on Fly3D Magazine

I also am heaving problems with CG. I bought my YAK early this year but did not hurry to put it together because I was waiting for BME 55cc. Since that engine never got out yet, about a month ago I got me a KROMA 55. Now kroma is heavy engine. Few days ago I temporarily installed the engine and was shocked to learn that I would need more then a pound of weight to balance it at 5 and 1/8! My rudder servo is in the tail and I will have to move it from there to the middle - pull-pull (which I don’t like) system.

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