A4-e skyhawk - building report

[YOAVHOZMI]

Thank you Isaac for understanding us with your knowledge. Well done.

YOAV

[nando]

First of all, the fantastic model, as usual. When I follow you to design and build your own models, I can not believe how simple and easy it is, but I know that all that ease lies primarily in your creativity and this thought frightens me.

I can not even believe that you choose all of my favorite planes: amazing.

Originally Posted by YOAVHOZMI

boundray layer trubulators

The work on these small parts was very tiring and Sisyphean.
Each part is the size of a millimeter.
And there are 72 pieces.
And then we have to paint the edge thickness for each and every one of them.
for a guy like me is Very frustrating.

YOAV

You are welcome in a large group. You can see how Sisyphean is to cut, bend, paste, paint and place 51 motors in the model I'm currently working on (see my signature).

Anyway I have to give me courage and try to start one of your beautiful models (Mirage, Kfir, F-15, Phantom, A-4, ....: eek

Best, Nando

[YankeeBoy]

Originally Posted by Isaac

A technical clarification on the tail surfaces

Those are called horizontal stabilizers , not elevators ...

Isaac

Common usage term for "all flying" horizontal control surfaces is "stabilator." Not sure if this ever reached "official" status. "Flaperons" is another example of crunching two aircraft control functions and the associated names together.

[nando]

Originally Posted by Isaac

A technical clarification on the tail surfaces
[...]
If you notice, the rudder on the real plane has all of its structure exposed on the outside as it sandwiches the rudder single inner surface. Again, this is a cost and weight reduction aspect
[...]
Isaac

I read somewhere that the odd design of the rudder was motivated mainly to solve vibrational problems in the test flights of the protoypes.

I have to dig for the source.

Best, Nando

[Robotaleem]

Originally Posted by YOAVHOZMI

you are killing me.

YOAV

YOAV Tower, should I call emergency services to increase your level of building (impossible); Robot two.

[nando]

Found it here, where you can read:

"The hydraulically actuated rudder is of a unique design, consisting of a single central skin with external riblike stiffeners. According to the interesting account of the development of the A-4 given in reference 164, this design feature was found to offer a solution to problems of rudder buffet or buzz."

Best, Nando

[Isaac]

Originally Posted by nando

Found it here, where you can read:

"The hydraulically actuated rudder is of a unique design, consisting of a single central skin with external riblike stiffeners. According to the interesting account of the development of the A-4 given in reference 164, this design feature was found to offer a solution to problems of rudder buffet or buzz."

Best, Nando

the buzz is due to a single flat surface resonating. Like a thin sail on a boat. So there will always be a natural frequency that will resonate this like a drum. The outside ribs are both structural and also break the flat plate of the rudder into smaller sections thus changing its resonance frequency ( buzz ) out of the operational range.

However, if they made a full skin rudder, this would not occur. Douglas went the low cost way with a single flat sheet for a rudder.

Isaac

[YOAVHOZMI]

4 Armament carriers

And I think I'm done for tonight.

YOAV

[nando]

Digging more i found more information.
First I found this picture of the Skyhawk prototype with a "normal" rudder with the skin outside.



Then I found this description on Google books, about the early "buzz" problems with the original rudder during the test flights on April of 1955.
They tested more solutions but no one was suitable: for the weight or for the inefficacy. They left the rudder with the external ribs as a workaround, but the solution was effective and the temporary solution became definitive when the production started. Heinemann regretted never doing a "proper" solution.

Sorry for hijacking the Yoav's thread, but I can't resist to deepen the history of the planes I love.

Best, Nando

[Isaac]

Nando


Nice article and it showed that Douglas chose the low cost approach instead of fixing the resonance issue. Every other airplane that has a rudder uses the external skin design which is aerodynamically cleaner and has less drag. Because this was a little scooter and no one really cared too much about the speed penalty, the US Navy just agreed to the temporary solution and kept it ( I think it was cost and weight driven ).

Anyhow, for modeling affect, the external ribbing is really nice.


Isaac