Kris' GP Yak-54 buld thread

[GremlinX]

Dont take me wrong, I enjoy this build! Wouldnt stand offs be a whole whole lot easier and lighter to do the mount? Thanks.

[KrisW]

I look at it this way. you can use standoffs if you like. To me they concentrate stresses in a small area, allowing more flexing, less stability, and the possibility that sometihing is going to give way under high stresses. I've always felt that tying in the sides and top of the motorbox as directly as possible to the back of the engine is a more structurally sound practice than using standoffs, such as 1" diameter dowels or sluminum studs.

The weight savings would be noticeable, I'm sure, but through hollowing out the center, and then relieving the back of the spacer as much as possible, a lot of excess mass was removed, and the whole assembly is a lot stiffer. I've been known to completely remove the front of a motorbox and lay up a whole new one with 1/8 ply and CF. This is an exercise in doing it more simply, with as little likelihood of failure, as possible, and is meant to show considerations of what is necessary for this buildup.

So, yeah, I could have. . I'm cheap. .lazy. . do things differently, and had the stuff on hand to get it done. i didn;t even have to waste any gas running down to the store to pick up a piece of 1" diameter dowel.

[RTK]

Kris--I hope you follow up this great build thread with a video. I am looking for a home for my new 55 when it arrives. Oh and yes there is nothing wrong with being cheap, lazy and doing things differently I am the same way, always marching off the beaten path and sometimes getting lost

[bodywerks]

This is one of those planes that is anxiously awaiting that new BME 55. To me, a 60+ ounce engine is really gonna load those little wings. Then again, if this is a low-buck IMAC approach, the extra wing loading might be OK...

[KrisW]

A few comments, if I may.

Bodywerks, the BME55 will be about 1.25 lbs less total weight, with everything in place, and will still requre a standoff to fit this aircraft. Figure 34 ounces for the engine, 6-7 ounces for the JA muffler, and 7 ounces for the ignition/battery/switch. That's 48-50 ounces. Can we say the SAME weight at the OS-160 setup?

SICK SICK SICK ! ! ! ! !

Commentary #2. .

I do not know WHO decided that it's okay to use Clevises on controls where the servo's arm pivots in one axis, and the control pivots in another. It's RIDICULOUS!!!!!!!!!!

Please note the accompanying photos of a PROPER servo/control linkage setup for ANY control surface where the servo is mounted straight into the wing/stabilizer, and then is forced to move an aileron/elevator/rudder that has a hinge line 90 degrees off the servos axis of rotation.

I've long touted the advantages and simplicity of using clevises for installations where the servo arm moves in the same plane as the control surface (such as the elevators in this case), but when you mount them 90 degrees to eachother you are going to run into instant binding any time you get more than about 20 degrees off center. The only solution to this engineering boondoggle is to use Ball Links on the pushrods.

Clevises are good for 3-5 degrees of off-line pivot, side-side, and unlimited motion in the proper axis of orientation. Ball Links can handle up to about 20-25 degrees of off-axis inclination before they start to have problems.

My advice on this plane (and any other where clevises are included for a setup such as pictured) . . do NOT use Clevises. Spend $10 and invest in a 10-pack of HD Dubro 4-40 Ball Links. use them on both ends of the control rod, use 4-40 screws and LOCK nuts, and do it right the first time. Your servos, control surfaces, and airplane (due to lack of flutter. . . ) will all thank you.

Note that the servo and control surface are both moving 40-60 degrees in each direction, showing a freedom of motion and lack of binding, and close to 1.20:1 ratio. The servo arm is actually about 20% shorter than the moment arm on the control horn, giving the servo a bit of mechanical advantage, which is desirable with such large ailerons. This is a good compromise setup for intitial flight testing, and you can mix the aileron throws up pretty drastically with just this basic setup. It ought to be sufficient for 90% of a flyers needs, unless he wants to dedicate the plane to strictly 3D (with EXTREME roll rates) or IMAC style Pattern (with very mild roll rates, but a lot more precision).

Also, please note that the ball link on the servo arm is UNDER the arm, not on top of it. Putting the link under the arm reduces twisting forces on the arm, reduces angular deflection of the servo on it's mounting pads, and reduces side-side forces on the servo's bearings because the link is more closely aligned with the actual top output shaft bearing. Putting the link on top causes a lot of unwanted movement and stress on the installation, which can never be a good thing.

Also note the use of locking nuts on the 4-40 screws. You gotta keep things tight, with no loosening or slop, when you use composite arms on a servo. Even Aluminum arms can develop wear if the screws back out even a little bit. Best bet is to always use an aircraft locking nut, with nylon insert in the nut, to prevent anything coming loose.


Okay . . . now that I have that off my chest. . .

Please note in the photos that these are JR 8411's on the ailerons. Also note the "output shaft brace" installed. When I first started using the 8411's. . way back when they first came out, I got a lot of premature gear wear. So I sat down one day and watched the servo as it moved, to see if anything was amiss. I noticed that under light loading nothing bad was going on, but when you started to load the servo as it moved the output shaft would move around a LOT. It not only moved end-end, but also side-side. Well, think about it a bit and you come to realize that every time the shaft changed angles, so did the teeth on the output gear, against it's drive gear, so it was causing undue wear because of the improper alignment of the gear teeth.

I did some searching on the Horizon site, and found these "Servo Output shaft Brace" kits, for about $10 each. It struck me as kind of ironic that you bought a $115 servo and then had to brace the output shaft with a $10 kit, but that is what was happening. After installing the brace kits, I saw almost zero end-end movement in the output shafts, and my gear wear problem dimished a good bit, to where I was getting about 3 times the flights before the servos needed new geartrains. Of course, these kits do not stop the shaft from rocking side-side, but that motion is still less prevalent after intalling the kit, probably because any hysterisis is reduced and the bearings have less load to make them go off center.

So, this is the basic servo installation for the ailerons and rudder on this plane. I'll have pics of the elevator setup when I get to that point.

[KrisW]

Internal Radio installation:

I installed the "rear radio plate" in the fuselage, so that I would have someplace to mount my Fromeco regulator and battery. The throttle servo uses the front of the two hole originally intended for the dual rudder servos in a pull-pull setup, and the Receiver rests at the rear of that mounting plate.

Note that all wiring is tied down at regular intervals to prevent movement. A simple technique for this is to drill a 3/16 hole througha fuselage former, about 1/8" from the edge of the wood, then slide a small zip tie through the hole and use it to hold down the wiring. It's quick, and makes a neat looking installation.

I'll install the receiver battery last, to help achieve the proper CG. Mocking up the battery, after all the components were in the plane, showed that having it centered on the rear mounting plate gave me a slightly tail heavy plane, with no prop or spinner in place. When they are installed I expect the plane to be slightly nose heavy. Right now the ignition battery is inside the motor box. By moving it to the gear plate I can make the plane more tail heavy, or add lead to the tail if necessary.

The throttle servo uses a .060 CF rod with a clevis at the servo end and a plastic
snap ball" link on the throttle arm, to control the engine. I like using the CF rods because they give you a stiffer installation than a plastic rod-in-sleeve setup, but have fewer temperature change issues than a steel cable or rod. Any normal control rod setup will work fine with this application, though. Use whatever works best for you.

[KrisW]

And now for some pics of the finalized fuel/control/engine setup.

The ignition is not in place at this time, but will mount on the side of the motor box where the throttle servo would have mounted in a Glo engine setup. The fuel line has an in-line filter and will use a "Fuel Dot" for filling. It passes through a 1/4" hole drilled through the standoff mounting plate. The throttle control rod passes through the same way. Vent tube exits onto the right LG leg, and is zip-tied in place. It uses the same slot that the gear leg uses to slide into the fuselage.

[Bryant330L]

Hey Kris, email me your address so I can get your decals in the mail.

[bodywerks]

Kris, how are you holding that breather foam onto the carb's diaphram cover?
I remember those shaft supports back when the 4131 was considered THE servo. Do they still make them? The supports, that is...

[KrisW]

Bodywerks, I just use Thick CA on the carb cover, after cleaning it with 409, then apply the foam. I use it to shield the diaphragm from direct airlast, while still allowing it to breathe. Works very well.

[KrisW]

Okay .. . . . .

Great Planes lists the weight of this little beastie as 12.5-15.25 lbs.

I still need to add the elevator control rods.

My digital Bathroom Scale says it weighs 15.5 lbs

My Digital Wally-World fish scale says it weighs 15 lbs 7 ounces.

That's one DARNED accurate Bathroom Scale!!!!

I can reduce weight by 3-4 ounces by going to a smaller ignition pack (2 ounce reduction) using a mini-servo for throttle (1 ounce reduction) and. . . hmmm. .. and???? Well, I could go to a 2400ma Li-Ion pack instead of the 4800. That would save another 3.5 ounces or so. (I have a pair of 2400's on the way, for another plane) So, I could, feasibly, get it down to 15 lbs even by using smaller battery packs, which I am definitely going to explore as an option, as well as the smaller throttle servo option. I have some HS-81's sitting here that would do well in that role.

let's see. . no pilot figure. . no IP. . no floor for the canopy area.

This is right at the limit of the power capability of the BME-44 to pull out of a hover, and within 3-4 ounces of what a Fuji-43 powered plane would weigh. I'm using only 1 rudder servo, and one lservo ead split to a Y for the elevators, instead of the advised separate leads.

DA-50 guys, you will come in about this weight. . .same for the BME-50, ZDZ-50. . heck all the 50cc engines out there weight about the same except for the heavier 3W50.

So, for a gasser (except for the BME 55) you can expect to come in right at 15 lbs or so. For a Glo setup, expect 13.5-14 lbs, which is a BIT more than I'd want to have with an OS-160.

I'm REALLY glad I wanted to experiment with IMAC with this plane. At this weight it ought to be very stable for Pattern FLying.

And, figuring out the wing loading, it comes out to 1138 sq-inches and 15.25 lbs (for arguments sake) or 244 ounces DRY. 7.9 square feet of wing, 244 ounces, makes it 31 ounces/foot.

For comparison sake, a 40% model with 2650 inches of area and 38 lbs of weight comes in at 33 ounces/foot, and a 35% model with 2050 inches of area and 26 lbs come in at 29.2 ounces/foot.

I'd really rather see another pound off this airframe. . just because it will fly so much better at a lighter weight. Can't weight for the BME-55 (pun intended).

[red_z06]

Kris: It looks super (looks only). I also wanted one after building GP Cap 232 for its light weight but turned off by Yaks weight.

My cap currenty weigh 13.25lb as shown. I'll go with stock DA muffler, smaller batteries and it will be at 12.75lb dry. I wish I had your BME55 in it. Where are you using that engine?

How about trying that engine on Cap 232? I'll bet if you go all out, you can get it under 12.0lb mark.