Servo load calculator
bg
I am looking for a set of equations or spreadsheet template that I could use
to calculate the load on a servo from control surface. I am familiar with
the Multiplex servo analysis calculator on their web site but I am unclear
on how the control horn length and output wheel radius effect the result.
Bill Groft
Robert Steinhaus
caluculator helpful
http://web.egr.msu.edu/~tenneycr/
Best wishes!
Walter Holzwarth
<stei...@earthlink.net> wrote:
>You may find the following link to an excel spreadsheet servo analysis
>caluculator helpful
>
>http://web.egr.msu.edu/~tenneycr/
>
>
>bg wrote:
>
>> Hi,
>>
>> I am looking for a set of equations or spreadsheet template that I could use
>> to calculate the load on a servo from control surface. I am familiar with
>> the Multiplex servo analysis calculator on their web site but I am unclear
>> on how the control horn length and output wheel radius effect the result.
>>
>> Bill Groft
Hi,
I think Craig Tenney's excel sheet is very well done, and I like it.
But we should realize, that the formula for calculating the servo
loads gives too high results. It does not represent, what's happening
in real life.
On 18.04.00 I've put a question to rec.models.rc.air with the topic:
"Wanted: Calculation of aileron control surface loads". Below is the
text of this question, once more. Parts of it are automatically
translated, I hope it's understandable.
Regards
W. Holzwarth
-----------------------------------------------------------------------------------
In a German discussion forum (www.rconline.net), similarly to the US-
rconline.com, we are in search of:
Calculation formula for the aileron servo moment of a pattern or TOC
plane
The pure influence of the aerodynamic forces interests with priority.
Weight moments, acceleration etc. are comparatively easy to determine
and are to be neglected. If there is an Excel file, we can be more
than happy.
We found in the meantime some formulas, but we have the opinion, that
all 12 of them get too high results. On the other hand, with large
planes, the torque of our servos is at the limit, so the calculation
with a more realistic formula appears meaningful.
We believe that the static determination of a stagnation pressure on
the aileron control surface, by calculation or wind tunnel
measurements, results in too high values. In real life the airplane
begins a rolling motion with an aileron deflection immediately. Thus
results a modified angle of attack of the wing, which reduces the
aerodynamic force to the control surface.
A formula, which considers this influence, is further looked up. I
assume there exists something, but probably the correct persons did
not read the problem yet.
Thanks for the assistance. Some details in the link
Walter Holzwarth from Germany
http://home.t online.de/~Walter.Holzwarth /
Details:
In the following only the formulas with the best results, or with
origin from the USA
1. Maybe the best formula, in the English model jet magazine Radio
Control Jet International. It is by Corneliu Rudianu and can be found
in RCJI April/May 1998.
2. Likewise good results come from a diagram by Alasdair Sutherland
in the English Radio Control Model World 08/98. It is based on a
formula, which was published by Carl Risteen in the autumn 1993 in
Model Airplane News. This can be seen on a web page by David Garrison
http://www.dc-rc.org/selecting_servos_for_driving_con.htm
3. Martin Hepperles on-line analysis of profiles (apparent also with
flap deflection) on http://beadec1.ea.bs.dlr.de/Airfoils/calcfoil.htm
4. Multiplex / USA: On-line servo force calculation on
www.critterbits.com/calcservo.htm
5. Servo calculation program in Excel of Craig Tenney
http://web.egr.msu.edu/~tenneycr/
And some more ...
>
>
Jon Stone
momentary load will be as the existing formulas indicate. There is a moment of
intertia that must be overcome to initiate a roll.
Of particular interest to sailplane pilots, is the load required to hold a flap down
80-90 degrees. This load does not reduce as the flap is put down. It does reduce
after the glider has slowed down.
Since the flap servo has the highest torque requirements on a modern day glider, I
would suggest using the formulas as stated, and not the "reduced" values proposed
below.
As an aside, I have found that horn placement is critical to reducing the torque
requirements of the servo driving the surface. With Craig Tenny's spreadsheet, you can
easily experiment with horn placement on the surface, and initial horn angular
placement on the servo.
Feedback welcome,
Jon Stone
Jon Stone
Casey
Jon Stone <ther...@earthlink.NOSPAM.net> wrote in message
news:3933D3F4...@earthlink.NOSPAM.net...
Walter Holzwarth
tahk you for thinking about that theme.
I agree with you that there is the biggest problem, when a breaking
flap must be held against the air flow at a high angle of deflection.
I must admit, I didn't think of this case before. It is a nearly
static problem, as you say, the load only gets smaller with slower
velocity of the plane.
In all other cases (aileron, elevator, and rudder) the plane is moving
this kind, that the deflected control surface gets partly unloaded.
There are not these high loads, as calculated by Craig Tenney's
spreadsheet.
Looking at the aileron of a pattern plane, it's easier to talk about:
As you say, there are several influences: air load, inertia, weight of
the control surface, acceleration, and even flutter may be part of the
whole needed servo moment. Only looking at the influences by air flow
at the aileron example: I think, as soon as the control surface is
deflected, the plane begins to roll. The inertia is more noticeable
with planes of the old days. This rolling motion very soon becomes
steady, depending on the deflection. Then there is an acting load of
the control surface and an equal damping load, produced by the air
flow on the wings. In a roll, there's a spiral slipstream around the
plane. In the fuselage area, there's mostly flow from the front, but
at the wing tips we have an acting air flow , more in the direction of
the control surface. Thus the control surface is unloaded, the
counteracting load for steady rolling is mainly produced by the fixed
parts of the wing, not the movable control surfaces. I think, this
can not be simulated in wind tunnel tests.
Only knife edge flight can be simulated in wind tunnel, in my opinion,
but there's a dampening influence, too, because of the inclined angle
of the fuselage. But as we know, large TOC planes have strong servos
at the rudder.
The placement of rudder and servo horn has some kind of influence, as
can be seen with the spreadsheet,.but there are soon limits because
of the needed throws at the control surface.
So far from my side.
Regards from Germany
Walter Holzwarth