Great thread!

Thanks, Jason

Oli,
I am having some issues with figuring out the correct parameters for a Flap calculation and I was wondering if you could help?


Here are the parameters that I have tried:


The issue I am having is selecting the correct values for Rs +/- and Rc +/-
I believe that Rc + should be 0 deg and Rc- should be 60 deg, but this yields a strange diagram in the excel program.
The flap uses a live hing and the hing point is on the bottom skin of the wing.

I drew up the surface in Autocad to visually verify, and it should work, can you help?

That's because you do not use the offset function "0c".
Here is how you should do it. 0c is specifically designed for flaps.
In the example below i used a takeoff position of 15 degrees and offset the control by -15 degrees.
The deflection then becomes 45 down to keep the max deflection of 60 degrees.



Note that the torque requirement for a deflection of 15 degrees at 75 mph is 61 oz-in. This is good.
As you deflect your flaps towards 60 degrees you want to slow down, as 75 mph would require 257 oz-in of torque from the servo at least.

Oli,
Great thread especially for us scratch builders. Got a question on flap servo requirements-where the hinge pivot point is below the wing surface. This occurs when using Fun-Key hinges (from Yellow A/C) for their F/A-18 and similar jets. With their medium size hinges, the pivot point is about 10 mm below the wing/flap surface. This type of hinge yields a semi-Fowler type movement of the flap. Also, what is the recommended position of the flap control horn with this setup.? I'd appreciate your thoughts and guidance on this. Thanz in advance.
Rgds,
Art ARRO

Thank you Oli for the explanation, is there instructions for the spread sheet that identifies the input parameters and how they are used in the calculations?


I entered the same numbers you used and came up with the same results, however I still have a question, see photo.



In the cad drawing I have the servo arm drawn as I though it should be which is different than the diagram in the simulation.

It is good to see that the program yields very close results as the drawing, in this case the distance from center line to the tip at full deflection, the Autocad drawing shows 9.7cm and the program shows 9.3 cm, which I think is close...

I would be interested in learning how to set up the offset hing also, below is a drawing of my flap example above only with an offset hinge.
I am not sure how to lower the hing point in the program.

Other interesting information

I was making a chart from my flap example with declining air speed when I accidentally selected the servo reverse function, the torque requirements went down...
I charted both normal and reverse servo functions.

I was looking at a hidden linkage design as follows, not sure this is correct.

Yes, on my blog:

http://www.ultimate-jets.net/blogs/f...ols-on-rc-jets

Yes, this is correct.

I have not had the time to implement offset hinges in the program yet...

The servo arm offsets itself to ensure the cinematics entered ( servo position, horn position and servo/ control deflections ). This is done by simple trigonometry formulas.
There is always one possible solution to ensure a proper cinematics with reasonable inputs.

The red curve is non linear in this example because the servo arm is nearly aligned with the control link for almost all the deflection between 0 degrees and -15 degrees.

The difference between your CAD and the simulation is the servo offset at neutral. Note that this can be changed by entering a different value of Oc.

It's got a weird result because some of your figures are not right, you have not matched the centre of servo travel to the centre of flap travel. Total flap travel is 60 degrees but you have defined its centre at 15 degrees which is 1/4 rather than 1/2 travel, so the program has had to work out how to make the flap travel 15 degrees one way with 1/2 servo rotation whilst making it travel 45 degrees with 1/2 servo rotation in the other direction. In reality you don't do that mechanically, which is what the program has calculated, you do it electronically in your Tx servo settings, e.g off-setting the centre value.

Since flap travel is 60 degres, half flap (which will equat to servo centre) is 30, so in the Oc box put in -30, not -15. Then your Rc+ and Rc- both should be +30, i.e. 30 degrees either side of a -30 centre value (the Oc value). Now you will get a proper diagram showing a sensible servo output arm, and sensible torque graphs.

At first, when you put the Tx switch to the mid position the flap will go to about 30 degrees down. Simply adjust the Tx flap control/servo centre point until you get the required travel.

Oli and HarryC

Thank you very much, I corrected the chart and the torque numbers appear more favorable, I created a new chart using the HI TEC HS 7955TG as the servo.
The chart does illustrate what happens when deploying full flaps too soon.

With the proper Oc and Rc+ & Rc- numbers the geometry looks good as compared to my drawing and the strange anomalies are gone.