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Old Jan 01, 2013, 07:22 PM
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rayonnair's Avatar
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Originally Posted by Dead View Post
Yes that is 20 extra grams in tail plus the extra weight of the tail wheel. That explains it.

I would not worry at all about "measuring" CG. Just set it in flight. You should be able to fly hands free upright and either hands free or just a slight bit of elevator while inverted to keep the nose up. If it flies like that you are golden.
It flies exactly like that now

Just wanted to measure for JetPlaneFlyer's benefit.
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Old Jan 01, 2013, 11:58 PM
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What aftermarket tailwheels are you using, or did you just modify the stock version?

I have gone with an aftermarket tailwheel on my X and it is fantastic and far less impact on my rudder (I tend to land tail wheel first most of the time). However, it has changed the angle of attack on the ground and the tail is a little to tall on the ground for my liking. It forces me to make longer takeoff runs....
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Old Jan 02, 2013, 12:16 AM
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Originally Posted by bsbauman View Post
What aftermarket tailwheels are you using, or did you just modify the stock version?

I have gone with an aftermarket tailwheel on my X and it is fantastic and far less impact on my rudder (I tend to land tail wheel first most of the time). However, it has changed the angle of attack on the ground and the tail is a little to tall on the ground for my liking. It forces me to make longer takeoff runs....
I bought something from dubro. Sorry, I don't remember what it was. I just popped by my LHS (the friendly one), asked what tailwheel for something around 47" monoplane WS size, and bought that one. It didn't come with a wheel, I provided my own wheel. There is a picture in post no. 7319.

I don't think mine helps with the impact on the rudder servo... if the rudder is deflected, that poor servo is going to feel the strain.
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Old Jan 02, 2013, 12:24 AM
how'd I do that....oh
chop stiX's Avatar
South Africa, GP, Pretoria
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I have the stock wheel on mine and no problems at all with it.I still wonder how the CG could be so different,as I have mine balanced as per manual and need slight down elevator when inverted to keep the nose up
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Old Jan 02, 2013, 03:02 AM
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Originally Posted by rayonnair View Post
I'm not sure where my CG ended up. I added 5g, which didn't really work 100%, then I added another 5g and it was good. I left it at that. I'll measure it later - how do you determine CG anyway, is it when the fuselage is level with the ground? I'm not sure what imaginary line to use on the AMR.

I suspect it is the servos + the modified tail wheel. I changed the tail wheel because of this thread. My servos are TGY-306Gs, they're actually quite heavy at 22g each. In comparison the HS-65MGs are what, 12g? That's a lot of weight. But I'm liking the servos so far. Fast, and strong enough. I should get a camera up there some time and check for blowback.
Yes, the servos explain it for sure. Due to the fact that the tail is longer than the nose 20g added in the tail will take at least 50g in the nose to balance. If it were me I'd swap them out for something lighter which would mean you could take the noseweight out and move the battery back a bit. The tailwheel mod I did added 2g which I'm prepared to live with, but 20g in the tail is a whole different story.

When balancing the fuselage should be level. The join line between the battery hatch cover and the main fuselage is a good reference point
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Old Jan 02, 2013, 03:16 AM
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Originally Posted by chop stiX View Post
I still wonder how the CG could be so different,as I have mine balanced as per manual and need slight down elevator when inverted to keep the nose up
Please double check because from my own experience I'll stick my neck out and say It's impossible. The manual's recommended 59.5mm CG position produces crazy climb when inverted and generally tail heavy handling. Some people have thought they were on the recommended CG but when checked they weren't. In my experience and that of pretty much everyone who has taken the time to check properly about 47-48mm produces hands off level inverted.

I've posted this photo before but the story here is:
  • I marked the manual recommended 59.5mm CG location on the tip with black tape.
  • I went and flown the AMR and adjusted CG until I had hands off level inverted.
  • I then balanced the model on home made CG test rig, checking the fus was level with a spirit level
The photo is reasonably clear as to where the CG ended up relative to the tape marks. the 'actual' CG ended up 47-48mm i.e. about 12 mm ahead of the position stated in the manual.



Note that when you check the CG on the AMR it's vital to accuracy that the fuselage is perfectly level. Because the support point is the top wing, and so high up above the vertical CG position any 'tilt' on the fus will mean that the true CG is not where you are supporting the plane. A 5 degree nose down tilt would produce an error of about 10mm between where the CG actually was and where you were holding the tip. I think this is what leads people to believe they are balanced as per manual, many people believe (wrongly) that the nose should hang down when you check the CG.
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Old Jan 02, 2013, 05:11 AM
how'd I do that....oh
chop stiX's Avatar
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I'll go double check Steve,but DemonGti put mine together and he flies his on the cg as per manual aswell.
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Old Jan 02, 2013, 05:21 AM
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Originally Posted by chop stiX View Post
I'll go double check Steve,but DemonGti put mine together and he flies his on the cg as per manual aswell.
or thinks that he does I've yet to see anyone demonstrate their trimmed CG to be as per manual in the same way as i showed in the post above. Most (including myself usually) justs roughly balance their model on finger tips and if the fuselage is 'near enough' level then that's good enough to test fly, then adjust from there.
Not many people ever take the time to accurately check where the CG ends up after they have fine tuned by flight testing.
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Old Jan 02, 2013, 05:47 AM
how'd I do that....oh
chop stiX's Avatar
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hehe
He's pretty strict to his setups and always helps me so I really trust it.but I'll measure it later when I get home
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Old Jan 02, 2013, 08:59 AM
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JetPlaneFlyer, near as I can determine my CG point is 54mm from the leading edge of the tips of the top wing. I tried to put my fingertips at 48mm, but that dipped the tail. I tried to put them at 58mm, but that dipped the nose slightly. So, I figure 54mm is it. In the air and inverted, it drops the nose veeeeery slightly. You have to hold it there for a second or two before it becomes apparent.

Limitations: fingertips were used, and I don't have a spirit level. To try and eliminate these error points I used different fingers and eyeballed the horizontal by using a mirror and lining it up against horizontal backgrounds (beds, table).

I'm going to stick with the TGY-306Gs. They've served me well so far, even through 3 or 4 rough harrier landings (one of which I suspect brought about the beginnings of a de-lamination of the CF on the landing gear). They're pretty fast too. I thought I'd take a video of them in a static test so that you could see.

PA Ultimate AMR on TGY-306Gs (0 min 24 sec)
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Old Jan 02, 2013, 11:48 AM
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hello Rayonair

do you have a possibility to make a picture of the servo installed on the plane.
I am using the original name of the servo (KST) and do have some problems with the installation - lugs are very near to the case...and this leaves me with very few wood to fix the screws - did you find a solution?
Greeting
Jonathan (France)
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Old Jan 03, 2013, 04:08 AM
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Hi jonathan, I'll try soon as I get home. What is the issue exactly? Is it that you cannot slot the servo into the hole? I'm not sure what you mean when you say there is not enough wood for the screws.
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Old Jan 03, 2013, 04:26 AM
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Hi

I had the problem that after making the opening for the servo a little larger, I was under the feeling that the position of the lugs was not really ok and that the screws to fix the servo had to hold in the balsa wood only

Regards
Jonathan(France)
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Old Jan 03, 2013, 05:33 AM
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Originally Posted by lecaidduvol View Post
Hi

I had the problem that after making the opening for the servo a little larger, I was under the feeling that the position of the lugs was not really ok and that the screws to fix the servo had to hold in the balsa wood only

Regards
Jonathan(France)
I'm afraid that's why you should not go enlarging the holes The plywood plate isn't very big and if you put in a larger servo the servo mounting holes will hit balsa rather than plywood, as you have discovered.

If you have already cut the holes then you are into a repair situation. If it were me I'd get some suitable size servos (Hitec HS-65MG, Savox SH-0257 or similar) then glue in a small piece of plywood to replace the bit that you have cut out.

Larger servos will likely be too heavy anyway and will upset the CG even if you did find a way to fit them.
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Old Jan 03, 2013, 05:38 AM
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Oh I see! I understand now.

For the elevator/rudder servos, I had no problems. My elevator (or was it rudder?) servo hole broke because I made a mistake, and the servo fit right in. I glued in an extra bit of plywood behind for reinforcement. The rudder servo hole, I filed it just big enough to fit the servo.

For the aileron servos, I added some plywood to fit the servo. The servo is very tall so when you slot it in the bottom part of the servo will poke out the top covering film.

Pictures attached, hope it helps.

Edit: remember to pre-drill your holes. GENTLY! If you don't then when you screw the servos in you will unstick the ply from the balsa.
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Last edited by rayonnair; Jan 03, 2013 at 05:44 AM.
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