QQ 102" Yak Gen I build and recover

[jbdesigns]

this thread will describe what i did during the building of this Generation 1 QQ 102" yak 54.

The build started by completely removing all of the covering. I wanted to accomplish two things, recover in a scheme that is different from the stock kit, and to repair, re-glue and add some structure to the airframe where needed.

Equipment specs:
Gen 1 plane, purchased in summer of 2005.
BME 110 extreme.
KS headers supplied through DA aircraft. originally the flex style but modified. (described later)
Pefa canisters. MS sized i think. they are the exact same cans that QQ used on his prototypes and are shown in the manual. 2" diameter.
Z-line carbon spinner.
27x10 break in prop. 28x1 mezjlik now.
TNT alum gear (the tall version)
white rose tail wheel
Hitek 5955 for rudder and elevators. 2x for rudder, 1 per elevator
Hitek 5985 for aileron, 2 each
Jr 571 for choke
Futaba 9101 analog for throttle
Spectrum 9100 receiver
2x 2300 A123 receiver batteries (hand made from Dewalt pack)
1 2300 A123 for ignition
monokote covered
paint from Radio south

i took pictures during the build so i wil simply post each photo with explanations of what i was doing and why.

i hope to show how an ARF can be improved and customized somewhat to be a better plane overall. i typically build my planes so modifying this was just sort of natural and i just couldn't fly it completely stock. i hope that some of you will find at least one thing interesting that will help you on your next airplane build or ARF build.

John

[jbdesigns]

like i said,the first thing i did was strip off all of the covering. it came of very easily, which is a bit disturbing. the covering techniques used layered sometimes three layers of covering. i feel that there was extra weight in the covering that i will not be putting back in when i recover.

the first reconstruction that i did was the bottom of the fuse around the gear. the portion of the fuse in front of the gear is a few 1/8" square sticks. they broke on me just handling the plane. i replace several of the sticks with some spruce stringers 1/8" x 1/2". see picture. i made notches in the sticks so that they fit into the same spots that the original sticks were glued into. placing the stringers on their edge makes it very strong to resist breaking when lifting the plane from this area. tiny weight gain, a few grams.

[jbdesigns]

because this area directly in front of the gear gets a lot of abuse, i wanted to toughen it up a bit more. from my experience, the open stringer area right behind the exhaust area just gets alot of abuse. oil, heat, handling damage, etc. i have always had to recover this area on my other planes after a year or two.

so, i added a skin of 1/64" plywood over the stringers. i carefully sanded a small relief in the balsawood sides to allow the ply to set down in and be flush with the balsa. i glued on the ply with Titebond on the stringer areas and zap on the edges. i glued one edge down first with the zap. i then added the titebond to the stringers and then rolled it over and zapped the other edge. before gluing, i cut and fit the ply so that it was perfect length. i let it hang over the bulkheads just a tad so i could sand that flush after glue dried

when it was done, it is very tough with just a little extra weight. worth it for me to have less trouble here.

[jbdesigns]

another picture of the area with the 1/64 ply added. really is much stronger than before and will be durable when picking up the plane from underneath.

[jbdesigns]

another area under the fuse that i strenghtened is right behind the gear. the 1/8" stringers are really a little flimsy. they do the job of holding the covering into a pleasing outline, but for this area, it gets alot of abuse too. it is common place to pick up the plane from. i didn't think they would stand up to my handling. so i added some light weight 1/8" balsa sheeting between the stringers. not too difficult to do and again, not much weight. i am not too worried about a little weight up front since i am using the BME engine and will need some additional weight up front. after gluing in the sheet pieces with titebond, it really got strong. the openings are for pipe cooling.

[cap231jim]

John,

I've thought about doing exactly what you are doing. My thoughts were to have a different color scheme (so it doesn't look like every other ARF of that type!) and to add some improvements to some areas so it becomes a little more durable in everyday handling. I think you're still ahead of the game; you will end up with a unique looking and proven airframe that is a little more practical. Still quicker than building the thing from the ground up!

I'll be watching.....

Jim

[jbdesigns]

here is another look at the pipe exit area with the balsa sheeting. if you look inside, you will also see that i added 1/16" light balsa sheeting to any opening inside the tunnel area to keep heat and wind from going into the fuse.

[mflander]

Subscribed. Do you plan on going into detail about your covering techniques when recovering an arf? Are all the surfaces still hinged? How do you plan on making sure the covering is good in these areas?

[jbdesigns]

Ok, been building rockets with the kids. the plane is already done and was test flown at the Nall this year. i will keep making posts as to what i did until i get all the way through. this may take a week or so, who knows.

one of the most important improvements that i wanted to make on this ARF is adding cross bracing. as you can see, there is very little wood in the rear section of the fuse. great for light weight, but the builders neglected a very critical piece of construction, the cross bracing. I can understand why, as cross bracing is not easy for mass production. it takes fitting and sanding and such that will really slow down the process. Well, i have that time. omitting the bracing is allowing the rear portion of the fuse to twist quite a bit from engine pulses and from flight forces. in the short run, there is not likely to be problems. but one complaint i think i have heard alot from ARF owners is that the plane isn't as good 100 or more flights later. things have loosened up, covering is falling off, the plane isn't tight anymore etc.. There will certainly be those that do not notice this or will claim that it didn't happen to them, ok, maybe so. but for me, i know what the forces are and where the weak areas are and i will strengthen them.

the two pictures here show the 3/8" balsa sticks i used for bracing. i picked medium hard wood that was straight. don't use soft wood for this. i glued them in using titebond wood glue. epoxy might be the ideal glue but that is really time consuming. the wood glue works well, but fillets are not too practical as the glue shrinks up so much the fillets tend to go away after drying. whatever, the key is to get parts that fit well and are not too tight. if they have to be forced into position, you risk distorting the air frame permanently.

the bracing alternates top side to bottom side. i extended the bracing all the way to the start of the engine box on the top side. i went to the back of the pipe box on the bottom side.

for this plane, to get the bracing in well, i had to remove some of the bulkhead material on the bottom side. i wanted the sticks to glue to the bottom plywood forming the fuse and part of the bulkheads prevented this. look closely, you will see what part i cut off using a dremel and carbide bit.

i know for sure that this addition will stiffen up the plane torsionally and prevent glue joints from loosening up over time. the air frame is light, i have a hard hitting engine, so this is important.

weight gain was about 1.5 to 2 oz as i weighed the sticks i used before construction.

and yes, mflander, i will describe some of the covering techniques i used. for now, go and look at this post i made about covering with monokote. http://www.flyinggiants.com/forums/f...ee-finish.html

John

[jbdesigns]

mflander,
the hinges were never installed or glued prior to this recover. so, all covering was easy to remove and was also of course easy to cover again. i never built or flew the plane prior to this work. i know it is gen I kit, but family, extensive house remodel, a ton of travel for work, and a non functioning work shop kept me away from building until just this spring. basically, until i got the shop back up in the new section of the basement, there was no building going on. included a picture of the shop. it is long and skinny as that was the shape of the addition. 9.5' x 50' shop.

i used Klett large hinges instead of the kit hinges as they move more freely and are more precise IMO.

John

[cap231jim]

Cross bracing is an EXCELLENT idea!!!!!

(adds very little weight but much strength)

[jbdesigns]

Rudder servos. i don't know if this was the next step i took, but that is not important.

as i said earlier, i mounted the rudder servo horn onto a bellcrank to take up the pull forces from the tensioned cables. i mounted the horn onto a nelson bellcrank hardware assembly. this bellcrank was mounted onto a small plywood block to get the correct height to the servos. A blind nut is installed under the plywood plate for the bolt.

the servo arms are SWB units. the ball link inbetween i can't remember where i ordered it. i wanted the double ended ball link. Dubro doesn't make it. i had to search for it then and apparently, i don't remember now where it was from.

the cable end attach points are also from SWB. i don't like the threaded rod with small hole in it method since it cuts into the cable with such a tight bend radius. you can also see that after attaching the crimp fitting, i put heat shrink tubing over the wire. looks better and i also used the shrink tubing to hold the plastic tubing on the rudder cable, you know, the tube that keeps the two crossed wires from rubbing directly on each other.

i personally like the belcrank. even with the cables tightened, it does not take much effort to move the belcrank. and i know i am saving wear and tear on the servo output shaft. i added approximately 2 oz.

John

[jbdesigns]

since i couldn't leave well enough alone, i also changed the rudder horn.

the stock kit includes dubro hardware for the rudder. The rudder is drilled and ready to accept this hardware and this hardware will work. it will not fail as far i can tell and many many have been using it.

i don't like it though. at extreme control throw angles when the forces are probably the greatest, this rudder horn deflects. the plastic arm at the extreme throw angle is pulling 50 degrees angle on this plastic piece. it cannot take that and deflects. anyone who has this can try this them selves by holding the rudder over hard and then pulling on it with your hands. look at the control horn and you will see it deflect. engineering wise, this is not a good solution so i made new horns out of the G-10 fiberglass material. previously, i had Nelson hobbies custom cut me some from drawings i made. i didn't have the luxury of time for this one. so i drew it up, stuck it two a double stack of 1/16" G-10 and cut it on the band saw. final sand it with the band sander and then drill the holes for the clevis while they are still stacked together. carefully mark a center point between the two clevis holes and use that when gluing into the rudder.

i used the band saw to cut a slot into the rudder. before cutting, i had the rudder hinged to the fin and made marks where the control horn should be with the rudder cables pulled tight. it was slightly off from where the drilled hole was so i made this correction when cutting the slot.

i played around with plywood stacks until i found the right combination that was the same thickness as a 4-40 ball link. this plywood stack was cut to be the same outside width of the rudder.

i used slow set epoxy to glue the horn and spacer into the rudder. some simple care is used to get the horn spacing correct so that each ball link hole is equally spaced from the rudder hinge. also, care is taken to have the horn square to the rudder. epoxy gives time to check every thing several times to be sure.

i put the width between control clevis's basically the same as what the dubro hardware would have done. it was about 4" or just slightly less. i believe 3.875 to 4" was the dimension. whatever i picked, it worked out fine as the cables do not go slack at extreme throws.

John

[jbdesigns]

If you look close at the rudder horn, you will also see that i added balsa sheeting to the side of the fuse where the rudder cable exits the fuse. for best clearance, the stock slot is not long enough. so i carefully traced the outline of the plywood side and cut balsa to fit the space. for ease of gluing, i added some scrap balsa to the inside of the plywood to give a ledge for the sheet to lay against. that way you can just push the sheet up against the ledge and hold while the super glue cures. a touch of filler in the cracks and you are finished. the long slot works great and the horn can go all the way to the side of the fuse without the cable rubbing on anything.

i used sulivan 4-40 threaded eyes for the cable to "tie" to at the rudder horn. this eyelet gives a nice smooth edge for the cable to bend around and will not chafe or cut the wire over time.

i don't think the rudder horn added any weight over the stock hardware. i like the looks of this horn and i know it is strong and stiff.

a couple more pictures of the horn and then how it looks on the rudder installed on the plane.

[jbdesigns]

i also added some wood to strengthen and stiffen the rear of the fuse where the stabs mount. squeezing back there, i felt that it was too weak from side to side directly where the stab mounts. specifically, the areas of the fuse where the front edge of the stab mounts. since the fuse is providing the base for the stabs to mount to, i wanted it stiffer.

look at this picture here. you can see a balsa wood "floor" that goes right between the two sides just where the stabs go. it is 1/8" contest balsa and is cross grain. you will also notice a smaller piece of this balsa that goes vertical (perpendicular to the balsa floor). this added significant strength as well to this area. finally, there is a little stick of balsa behind one of the plywood side vertical ribs. this gives that skinny piece of ply some stiffness as well. all told, i added no more than 1/2 oz if that. but it is loads stronger now.

i don't think i took pictures, but i replaced the metric blind nuts back there for the stabs with 6-32 blind nuts. this will make it easier to replace the bolts if i loose one. not necessary, but i did it. the time that i loose that bolt will be when i don't have all of my other hardware around. then i have a chance of getting the bolt from a fellow modeller at the field where ever i am.