I need to do the Fowler thing and I notice that the NACA reports show the retracted and the fully deployed configurations, so my question is: What should happen in between?

I can make the flaps slide backward most of the way before rotating... but that forces them to slide down and out parallel to the wing UPPER surface and jut into the airflow below.

I can make them rotate evenly throughout their travel... which is what I know a lot of models do, but that makes them fairly draggy, even at fairly low deflection angles, so I wouldn't get maximum bennefit for takeoffs.

I can make them rotate just a little as they slide backward and then rotate at a much higher rate once they're back... seems like the most practical thing to me.

Any insight on how "the big boys" do this, or how you've always done it, or how's a bad way I should avoid, or a textbook right way, or ....?

Hi Al,

Visit this thread:

http://www.rcuniverse.com/showthread...=slotted+flaps

It's a discussion on multi-slotted fowler flaps, but the drawings and model(s) I built can easily be standard single slots.

I still have the drawings (AutoCAD) and can scale/arrande them to your liking.

My gallery has photo's of the mechinism in action.

Hope this helps...

Craigg

Another thing you might look into is Robart sells Fowler Flap hardware which might solve your problem.

Ted

Your third option seems to be how the commercial airliners I've flown on do it.

.
The first motion on the Fowler flap is to extend the wing area, not make a flap per se.. Most commercial planes will use this first motion with a slight amount of deflection for takeoff. On the Tristar, takeoff flap is 10 degrees. Lots of rearward motion, little down deflection.
Landing flaps, OTOH, are 33 degrees (CAA cert) or 42 degrees (FAA cert). Lots of down deflection after the 10 degree position to add -drag-, not lift!
Doing this on a model can be intricate as the parts are small and easily jammed.
A Youngman (Fairey Firefly) style flap might be more easily mechanized on a model.

Al...The best fowler flap arrangement I have seen up to now is a Dave Platt set-up using jackscrews and flap carriages......seems like they were on an OV-10....but not sure.......very similar in nature to B-727/B-737 T/E fowler flaps although I dont think they are triple-slotted....might want to ck with him on that ........Bill......

Thank you gentlemen... good stuff all 'round. Here's the plan for now... first wing will have single element Fowler flaps with the following action...

• First, flaps will do most of their rearward movement (probably 75% or 80%) while they rotate the first 10 degrees and open a slot as specified in the NACA documentation. (In this stage I expect increased lift without significant drag penalty for shorter takeoffs).
• From there, they will continue rearward as they pivot to as much as about 25 degrees. (In this phase, I expect parallel increase in lift and drag to allow slower speeds with little further effect on glide path... may be useful if wanting to extend an approach).
• The final stage of deployment has the flaps already translated to their full rearward positions and involves only rotation toa total deflection of 40 degrees or, perhaps, a little more, (In this phase, increased drag outstips continued increases in lift for slower glides at steeper decent angles).

I'm planning on implementing all that by having leading edge and a point on the body of the flaps pinned, and the pins riding in curved tracks/guides that will force the correct placement and angle... they'll be actuated by feed screws that will keep the all ends at the same location relative to their travel.

So, there's probably pros and cons involved with the details... how can I improve the implementation concept?

Al, your method sounds like what I was going to do many years ago, until I got to trying to find the materials that would let all that happen without jamming.
Keeping the flap segments aligned in the deflection tracks is the difficult part. Any lateral misalignment will jam the flap.
It got to be too much of a construction hassle for me to actually proceed with it.
.
I do recall seeing one of Dave Platt's flap systems detailed in MAN many years back..

The only way I can see you reliable extending the flaps without a jam is to place a pushrod (or whatever) at each end of the flap, where the tracks are. This ensures an equal force at the tracks and will prevent mis-alignment. How you do it is up to you.

Just a thought.

-Q.

Yep, I see the jamming problem... I'm thinking of either a jackscrew or pushrod at each end of each flap.

Once I was happy with my track/guide geometry on paper, I realized that actually producing the parts is a whole 'nother problem... for which I have a couple of ideas, but it sure would have been nice if I'd buiot a CNC router last year.