under the large model guide lines it says the MAC sgoulf be 2-3% less than 25%. Is this a requirment or something they recommend to prevent flutter. Thanks

Are you referring to full flying control surfaces pivot points?

If so, it is more about giving a balanced surface control authority...which incidentally translates into less tendencies for flutter; servo torque is dependent on relative arm lengths (servo/control surface), airspeed and total surface area...

Servo torque has absolutely nothing to do with arm length. Servo torque does not change unless you change the voltage to the servo.
Al

I guess I should have said servo torque needed...I thought that would Have been understood. I guess not

del, off-topic

Well on a jet its a full flying stab, and I was wondering since some of the larger jets require LMA1 sign offs to be legal to fly. It this a must do for certification or something they recommend to prevent the flutter. I understand why the recommend it but is requirement or suggestion.

del, OT

He is not talking about the cg placement. Rather the pivot placement on a stabilator.

Looks like a requirement to me as far as the LMTA is concerned

Seems I didn't have enuf info abt what the Q is to reply with a useful answer. Can you cite the rule at issue?

It is in B.), 13.) f.) of


http://www.modelaircraft.org/files/520-a.pdf

Tnx, Matt

I agree with you that it appears to be a requirement, implicit as there is no prescribed way for demonstrating adequate servo torque as required by the rule for any case other than the specified stabilator pivot axis.

I noticed there are only a couple of dozen model jets currently with permit under the program..........pretty exclusive club!

cj

Well from what I have read it would appear that lots of people havent done the right thing and got the certification.  I was reading one of the jet events is having people on site to certify but, it would appear they are not holding everyone to the standard since a few people will be flying a certain jet that unless modified have a MAC of 27.5%.  I am working on my LMA1 stuff so I can certify people and I really wanted to know so I had the right idea. When I read the above reg, I read it as a must have and wanted to make sure. Thanks guys

Pick up the phone and call Technical Director Greg Hahn, I'm certain he can get you the right information

Its just the way AMA words things sometimes, they need to really watch how they use "should" . Like they say words have meaning

I agree. NATOPS was pretty clear, "Should" was recommended, "Shall" was mandatory, "WARNING" meant follow this or get hurt.

Good show on working to take on that job for the benefit of fellow modelers. Watch out for trick questions on the test, tho.

Ex: A currently permitted model is listed as "40% Cub - White LTMA-1." Explain that.

I just started reading it all, but my back ground is perfect for this plus I like helping however Ican.

Well after reading and talking to a few people it would appear this MAC noted in the regulations is not a must have requirement for the Large model sign off.

How do you figure that?

Unless I missed it the rules it says nothing about your MAC "will or must" be per the recommendation. I talked to Lewis about this since a few people will be flying the large f-14 at his event. If this was a requirement the only way it would be legal was if they moved there stabs or some kind of mod. I guess AMA said it was not a rule just a guidline, I will call monday and ask myself.

The section F does talk about servo torque and arms to allow for full defection but does not say anything stating the MAC will be per the diagram.

Does Greg Hahn know you are referring to FEJ F 14's?

The model is irrelevant to rule, the rule cannot apply to certain products and not others.

So I called AMA today and the above mentioned jet since its an ARF must be flown as is. Adjusting the shaft to give it a new MAC isn't actually legal.  The MAC is there for people designing and building something from scratch. Also there some math not being done right from what he stated due the swept wing and the curvature of the inside portion of the stab. Nice guy by the way very helpful.

Well, the model is relevant to to the rule, according to this item on p.3:

"13. If the model airplane is built from a commercially available kit, all servos installed must meet or exceed the
kit manufacturers’ specified torque."

Apparently scratch builders are subject to sticking with the specified pivot axis, but ARF and kit builders can defer to the mfgr, who is presumed to know the minimum safe servo torque required.

Scratch builder needs to produce an additional kit or two for sale to his buds, then the required torque per the rule is whatever he says.

The 400oz servos will rip any stab or control apart before u stall the servo. Plus the funny part is the plastic mounting arms will break before stalling as well. This is why u always see load testing with the servo clamped to the table instead of normal mount. Another reason I'm glad futabas 500+ oz servos are now completely metal. Any I got the info I needed thanks for the discussion.