I Am Having "CG" Issues...

[Smacka]

I am very close to completing my Aeroworks 1.20 Yak 54. I am having a very difficult time with the "CG" as follows:

1) In one of the attached photos you will see that I have 3-marks on the wing tip (each wing tip). The first mark from the leading edge is the 3 3/8" mark the manual states is the proper "CG" balance point. The second mark from the leading edge is at 4-inches. The third mark from the leading edge is at 4 1/2-inches.

2) One of the photos shows my current voltage regulator position, which is up by the fuel tank. I first started with the receiver battery right next to the receiver (just in front of my pull-pull rudder servo). In this configuration the aircraft's "CG" balance point was at just over 4 1/2-inches.

3) I moved the receiver battery onto the cowling above the top of the engine box. The "CG" moved slightly toward the forward end to the 4 1/2-inch mark (see photo).

4) I added a ridiculous amount of lead (11.875 ounces) just in front of the receiver battery and the "CG" balance point is now halfway between the 4-inch mark and the 4 1/2-inch mark (see photo).

I am not sure what I did wrong to have the bird so dog gone tail heavy. Adding that much weight plus the receiver battery onto the top of the engine box seems flat wrong, and it looks extremely bush league.

Can anyone help and tell me what I am doing wrong?

Thank you!

[ledsled]

I'm not sure about the Aeroworks YAK. But most instructions use the mark at the fuse.. I'm not sure that will change the CG mark for you.

[Tired Old Man]

Unless a manual specifically states the root or tip for the measuring point it's typically done at the root. Bipes are a different story.

[jfstrama]

The Aeroworks manual shows them marking the CG AT the wingtip (really nice color photos!)

Before adding weight, what engine are you using (they show an OS120 2-Stroke with a pitts muffler and what looks like a Saito 150 4-stroke neither lightweight engines)and how far out is it mounted? I would move the engine further forward (with shims or standoffs) before I would add weight.

Just my 2-cents.

MadDog Joe

[Flatlandman]

Take more pics showing all of the plane some of the tail some of the insides and some of the motor box area and let us see if there's any help we can give ya. With the pics you have there isnt enough information to tell you anything isnt quite right.

[krayzc]

R U using a CG machine or your fingers for balance?

[jfstrama]

	Quote: Originally Posted by Flatlandman
	Take more pics showing all of the plane some of the tail some of the insides and some of the motor box area and let us see if there's any help we can give ya. With the pics you have there isnt enough information to tell you anything isnt quite right.

I have to agree. Remember, for most planes every 1oz in the tail is multiplied by the distance from the CG over nose weight. You may only have to find 2-3oz in the tail to fix your issue.

MadDog Joe

[SleepyC]

From your picture the spinner looks to be almost inside the cowl. I would say you would want your spinner backplate almost 3/4 to 1" in front of the cowl. (So move your motor 1" forward) I bet by moving your motor forward your CG issues will be gone.

[Smacka]

	Quote: Originally Posted by SleepyC
	From your picture the spinner looks to be almost inside the cowl. I would say you would want your spinner backplate almost 3/4 to 1" in front of the cowl. (So move your motor 1" forward) I bet by moving your motor forward your CG issues will be gone.

Here are some more pictures. I have mounted the engine to where the thrust washer is 5 11/16-inches from the fire wall. This is what the AW manual said to do, and you know how I do follow the written word, eh Sleepy? Having said that, though...the manual shows the engine more forward on the actual mount than mine is. The manual shows the actual engine mount lugs flush with the end of the engine mount BUT then it would be almost 6 1/2-inches from the fire wall. I am really confused by the numbers stated versus the pictures shown in the manual.

I hope the added pics make it more clear. Oh, and no CG stand to check it...two people with fingers on the wing tips per, you guessed it, the manual

Thank you all!!!

[Flatlandman]

I dont see any problems other than what sleepy said about the engine. But i do see 2 or 3 oz in the tail area that can be removed without any issues.

The double trusses you used for the ele and rudder control horn you installed per the instruction. You should remove one side of the trusses per ele half and one from each side of the rudder. Thats some easy weight to remove from the tail and will go a long way to help cg the plane.

There are lighter tail wheels you can get also if it comes to that.

[Smacka]

Here is the photo right from the manual. I have the thrust washer set right at 5 11/16-inches from the fire wall, as shown.

It's a puzzler...

[Flatlandman]

I wonder if its showing a differnt distance or you have a diff motor mont the one on that pic is at the end of the mont and yours is near an inch in ?

[Flatlandman]

I just scanned the manuel and they used only one control horn truss per ele and 1 per side of the rudder so maybe i was on to something with that.

[SleepyC]

Also... when it comes to CG you move what you have to.

To me the manual is showing the minimum clearence needed. So if you have a heavier engine you would need that much room. All the Yaks i have ever had 68" - 72"- 85" - 88" - 110" all needed the motor pulled out quote a bit.
my 35% yak had the spinner back plate 1.5' out from the cowl and it worked great and looked nice as well.

[Smacka]

	Quote: Originally Posted by SleepyC
	Also... when it comes to CG you move what you have to. To me the manual is showing the minimum clearence needed. So if you have a heavier engine you would need that much room. All the Yaks i have ever had 68" - 72"- 85" - 88" - 110" all needed the motor pulled out quote a bit. my 35% yak had the spinner back plate 1.5' out from the cowl and it worked great and looked nice as well.

I was actually afraid this was the final answer That means I have to scrap the current set of motor mounts, the cowling (because it will no longer line up with the current cutouts) and the throttle linkage. The throttle linkage was such a beyotch that I had to solder the end hooked to the throttle servo while it was in the aircraft.

Oh well...once complete, I know I will love this bird!

Oh, and Flatlandman:
You are absolutely correct. This size Yak 54 should have had single control horns. Aeroworks' assemblers screwed up when they built my ARF and predrilled this bird for the 50cc hardware. Aeroworks was gracious enough to recognize the error and, after the fact, sent the 50cc hardware my way. I do believe the 50cc hardware will work just fine BUT it has no doubt contributed to my "CG" issue.

It looks as though I need to shift the motor forward so that the engine lugs are flush with the end of the motor mounts.

Thanks folks!!!