Great Planes 25% Yak 54 Build Comments
10-23-2007, 12:12 PM
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Great Planes 25% Yak 54 Build Comments
Well, now that I've got my CG issue squared away, I thought I'd post a few pics and add some commentary about the build.
I found a build thread over on www.theForumThatMustNotBeNamed.com filled with with lots of great advise. I read it through a couple of times before and during the build and incorporated some of the advise and hints given.
All up weight with the CG at 5 5/8" aft of the LE is 15lbs 4.3 oz. Heavier than the ideal but I can work on that later by replacing the gear and the wing tube with CF.
Propulsion
Brillelli 46
CH Auto-Advance Ignition
Single cell Li-Po pack
Xoar 21x8 prop
JR / Spektrum
Spektrum DX7 Tx
JR921 with one satelite receiver
JR Data logger
5 JR8611a high torque servos
1 JR821 digital servo
Electrical - Fromeco
2600mAh Li-Ion receiver battery
Regulator w/ two power outputs
Swtich harness
Other
SWB control horns all around except rudder
Jersey Modeler fueling system
I've attached some photos with overall views and a couple of detail shots.
For some reason, I guess was I was bored waiting for the motor to arrive, I modified the cabin hatch a little. The kit configuration has a solid balsa floor but since I wanted to be able to look inside to visually check the ignition cutoff and regulator status LEDs, I cut-off the forward cabin floor. I then went kinda nuts on the cockpit and fabricated an instrument panel just for the heck of it.
To get a constant CG, I relocated the tank from immediately behind the firewall to the CG. Since the wing tube was in the way, I had to mount the tank high which required a relief cut in the hatch. Not very scale but it's balanced by the cockpit detail.
I actually like being able to eyeball the tank so over all it's a good thing though not very pretty.
I'm using a JR921 (9-ch Spektrum) radio with a Data Logger. I wanted to be able to check for signal fade and such immediately after a flight without having to pop the canopy so I mounted the display in a cutout on the fuselage side. Yeah, a little much but waht the heck.
Finally, I used SWB control arms (I should have gotten shorter ones) and spherical bearing clevis' all around for control system smoothness.
After 2 flights today, I experienced 3 fades on one antenna, 1 fade on another, and zero on the remainder. Since up to 50 or so fades is considered normal this is really exceptional.
I found a build thread over on www.theForumThatMustNotBeNamed.com filled with with lots of great advise. I read it through a couple of times before and during the build and incorporated some of the advise and hints given.
All up weight with the CG at 5 5/8" aft of the LE is 15lbs 4.3 oz. Heavier than the ideal but I can work on that later by replacing the gear and the wing tube with CF.
Propulsion
Brillelli 46
CH Auto-Advance Ignition
Single cell Li-Po pack
Xoar 21x8 prop
JR / Spektrum
Spektrum DX7 Tx
JR921 with one satelite receiver
JR Data logger
5 JR8611a high torque servos
1 JR821 digital servo
Electrical - Fromeco
2600mAh Li-Ion receiver battery
Regulator w/ two power outputs
Swtich harness
Other
SWB control horns all around except rudder
Jersey Modeler fueling system
I've attached some photos with overall views and a couple of detail shots.
For some reason, I guess was I was bored waiting for the motor to arrive, I modified the cabin hatch a little. The kit configuration has a solid balsa floor but since I wanted to be able to look inside to visually check the ignition cutoff and regulator status LEDs, I cut-off the forward cabin floor. I then went kinda nuts on the cockpit and fabricated an instrument panel just for the heck of it.
To get a constant CG, I relocated the tank from immediately behind the firewall to the CG. Since the wing tube was in the way, I had to mount the tank high which required a relief cut in the hatch. Not very scale but it's balanced by the cockpit detail.
I actually like being able to eyeball the tank so over all it's a good thing though not very pretty.I'm using a JR921 (9-ch Spektrum) radio with a Data Logger. I wanted to be able to check for signal fade and such immediately after a flight without having to pop the canopy so I mounted the display in a cutout on the fuselage side. Yeah, a little much but waht the heck.
Finally, I used SWB control arms (I should have gotten shorter ones) and spherical bearing clevis' all around for control system smoothness.
After 2 flights today, I experienced 3 fades on one antenna, 1 fade on another, and zero on the remainder. Since up to 50 or so fades is considered normal this is really exceptional.
10-23-2007, 12:16 PM
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RE: Great Planes 25% Yak 54 Build Comments
Landing Gear Reinforcement
I read about issues with the strength of the langing gear mounts and was proactive.
I fabricated one triangular brace for each side and one beam brace to oppose it. These were epoxied in place with one 2-56 bolt and blind-nut per side for reinforcement. The install leaves a gap of about 1/16" to allow the gear to flex under normal landing loads but a hard one will land on the brace and distribute the load more efficiently into the structure rather than breaking it.
Though overall I was very satisfied with the kit, three issues; the LG mount strength, the use of large amounts of gasoline-soluble foam in the fuselage, and the stab mounting method - which I'll discuss later - were my only complaints. The plywood they used in this area should be the higher-strength 5-ply variety, not the light 3-ply stuff.
I read about issues with the strength of the langing gear mounts and was proactive.
I fabricated one triangular brace for each side and one beam brace to oppose it. These were epoxied in place with one 2-56 bolt and blind-nut per side for reinforcement. The install leaves a gap of about 1/16" to allow the gear to flex under normal landing loads but a hard one will land on the brace and distribute the load more efficiently into the structure rather than breaking it.
Though overall I was very satisfied with the kit, three issues; the LG mount strength, the use of large amounts of gasoline-soluble foam in the fuselage, and the stab mounting method - which I'll discuss later - were my only complaints. The plywood they used in this area should be the higher-strength 5-ply variety, not the light 3-ply stuff.
10-23-2007, 12:31 PM
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RE: Great Planes 25% Yak 54 Build Comments
Stabilizer Attachment
I didn't take any photos (all I have is one grainy image from the manual) when I did this but here's my commentary:
The instructions, which are very well done in nearly every way, are surprisingly limited with respect to this one very important step. In effect, after a detailed series of steps to ensure accurate alignment, all it says is basically "apply epoxy and glue in place." The issue is twofold:
First, a fundamental "How do I do that?!?" question:
The stab slides through close-tolerance, airfoil-shaped openings in the fuselage side. How, exactly, do I apply epoxy to the fuse and the stab center section without, a) getting glue all over everything while simultaneously leaving enough in the joint to result in a strong, durable bond, and b) clean-up the excess glue without ruining the alignment?
Second, will the joint between the stab and the 1/8" thick balsa fuselage sides be strong enough to withstand the pounding they're going to get from a gas motor?
I ended up aligning the stab per the instructions and used copious amounts of thin CA to glue it in place. Later, since there's no other way to access the area, I cut open the fuse bottom at the nearest open bay to give me access to the bottom of the fuse-stab joint. Next, I epoxied 2 pieces of 5/8" balsa triangle stock to the interior of the fuselage. Each piece was custom-cut to clear stringers, and since the stab is airfoiled and curves away, I kerfed the forward-half of each piece. There is no way to access the top of the stab joint.
Once the epoxy set, I ended up with an incredibly strong joint that I feel much better about and didn't have to clean up a bunch of smeared epoxy. Since the plane ended up tail heavy, I would recommend going with a slightly smaller stock size but still believe the joint needs to be reinforced.
I didn't take any photos (all I have is one grainy image from the manual) when I did this but here's my commentary:
The instructions, which are very well done in nearly every way, are surprisingly limited with respect to this one very important step. In effect, after a detailed series of steps to ensure accurate alignment, all it says is basically "apply epoxy and glue in place." The issue is twofold:
First, a fundamental "How do I do that?!?" question:
The stab slides through close-tolerance, airfoil-shaped openings in the fuselage side. How, exactly, do I apply epoxy to the fuse and the stab center section without, a) getting glue all over everything while simultaneously leaving enough in the joint to result in a strong, durable bond, and b) clean-up the excess glue without ruining the alignment?
Second, will the joint between the stab and the 1/8" thick balsa fuselage sides be strong enough to withstand the pounding they're going to get from a gas motor?
I ended up aligning the stab per the instructions and used copious amounts of thin CA to glue it in place. Later, since there's no other way to access the area, I cut open the fuse bottom at the nearest open bay to give me access to the bottom of the fuse-stab joint. Next, I epoxied 2 pieces of 5/8" balsa triangle stock to the interior of the fuselage. Each piece was custom-cut to clear stringers, and since the stab is airfoiled and curves away, I kerfed the forward-half of each piece. There is no way to access the top of the stab joint.
Once the epoxy set, I ended up with an incredibly strong joint that I feel much better about and didn't have to clean up a bunch of smeared epoxy. Since the plane ended up tail heavy, I would recommend going with a slightly smaller stock size but still believe the joint needs to be reinforced.
