Mass Balance requirements history

[TimMcK_Aero]

Hey,
Does anyone know of the history behind the mass balance load factors?

e.g. (limit loads perpendicular to the control surface):
[ul]
[li] MIL-S-5706, Para 4.9: 36g <= 9x(symmetric pull up load) <= 60g [/li]
[li] FAR23.659: 24g [/li]
[li] MIL-A-8870 Para 3.2.1.1.1.3: 100g [/li]
[/ul]

Tim

 

[Sparweb]

"History" + "aircraft" = NACA

https://ntrs.nasa.gov/

Investigated thoroughly in the 1940's as wartime aircraft needed to fly much faster.

STF

 

[WKTaylor]

TimMcK_Aero... Very precise mass/balance requirements [static/dynamic] and very high structural safety factors equate to minimal anticipated forces and very high stiffness margins.

Here is how ARDCM 80-1 HANDBOOK OF INSTRUCTIONS FOR AIRCRAFT DESIGNERS [1958] summarized the design problem for control surfaces.

NOTE. HIAD skips around and is a-pain to follow. HIAD was replaced by AFSC Design Handbooks which took the HIAD apart and updated and reorganized the data/material/concepts/etc.

CONTROL OF VIBRATION, NOISE AND AEROELASTIC PHENOMENA HIAD Chapter 5

5.1 FLUTTER

... MIL-F-25352 lists detailed measures required by ARDC for avoiding flutter, ...

a. High torsional rigidity of fixed and movable control

b. Adequate mass balance or high rotational rigidities of movable control surfaces.

c. High rotational and torsional frequencies of control surface tabs or adequate mass balance of tabs.

d. Mass distribution such that the airfoil surface centers of gravity lie close to the airfoil
quarter-chord for the wing-aileron, stabilizer-elevator, and fin-rudder combinations.

e. Spans, masses, and moments of inertia of control surfaces and tabs kept as small as practicable.

f. Irreversible tab mechanisms located as close to the tab horn as possible and designed so that play can be kept to a minimum and within allowable limits.

g. Minimum coupling for tab flutter modes by locating the tab near nodes of important vibration modes of the supporting control surface.


HIAD Part B Airframe Design

5.2 TRIMMING CONTROLS

Design trim systems according to MIL-F-9490

5.2.2 TAB BALANCE

See MIL-F-25352 for mass balance of tabs.





Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[WKTaylor]

Fud-4-Thot...

Some fear flutter because they do not understand it. And some fear it because they do. — Theodore von Karman, aerodynamicist.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[TimMcK_Aero]

OK, so based on service experience, the static strength requirement has been set to meet the stiffness requirements to prevent flutter. I was hoping that there was some kind of rational analysis behind the numbers (24g? why not 22g or 27g? why the sudden jump in the mil-spec?) I just found the FAA simplified flutter prevention, which just asserts the 24g load.

Thanks for your input anyway. (The HIAD looks like my next stop).

Tim