I read a post here indicating this might be a bad combo of build techniques.

Will not covering adhere to the sharp steps on a KFm airfoil?

I am looking to try my first build with covering and would like to know the advisability of combining the two techniques.

I covered my So.45 plane with film covering from Hobbyking. The plane itself is made of DollarTree foamboard with a KFm3 airfoil. If there's a problem between these airfoils and film covering, I haven't found it yet.

I've used the 'New Stuff' (document laminating film) in two thicknesses / weights applied over EPP, Depron & fanfold foam with great results. It will bond well at temperature settings well below what deforms the foam. I've also used it to reinforce the leading edges of thin horizontal stabilizers, & to stiffen thin Epp wings to eliminate flutter. It's very versatile stuff!

Viking

And looking at the massive number of builds that have been covered with clear and colored package sealing tape I'd have to say that covering foam with some type of thin light film has no bad effects at all.

I like the 2.2 mil or so colored tape best on a balance of cost and ease of use. Applying it to follow the steps has been possible but is a tricky and time consuming process that really requires two or more sets hand to accomplish. So I usually trim the tape even with the vertical drop at the step and then resume it on the horizontal flat at the bottom leaving the vertical steps uncovered.

It has been found that the cleanly defined and sharp 90 degree step works better than a step with any eye-pleasing curves, rounded corners, and angled or airflow smoothing attempts.

I use 3M77 or Duro #01-81088 aerosol spray adhesive on bare foam to improve the adhesion of the foam.

And has been mentioned, it can contribute a lot to the strength of components like the tail feathers. I use a single layer of tape covered 1/4" FFF foam for vstabs and hstabs whereas the bare foam by itself would not be strong enough.

And with the tape the hinging of control surfaces becomes an a thrown in for free or inherent part of the covering process.

Jack

Not a great picture for showing the step covered (was to show the servo for ailerons) But this is a KFM1 wing and at each side of the picture, you can see the step with Packing tape covering. I tape the top, then use the handle of an Xacto knife to "roll" or slide it into the step corner, then press the surface aft of the step. Followup with a Monokote iron to set the adhesive and it's all good.

I thought the question was about covering over the step, as if you started at the leading edge and attached to the trailing edge as you would for a built up wing, not covering the individual pieces.

But I don't know the answer anyway

Azarr

Firstly I'm no expert. Reading through some of the advanced theories about KFm steps then some people seem to be suggesting that the step itself is a factor in the usefulness of the airfoil rather than just the overall profile of the laminates. If this is the case then covering the wing in a way that chamfers/blends the steps by pulling the covering tight might mitigate the effects. Covering in a way that adds strength and keeps the steps would conversely be a positive.
IMOH, and I like KFm airfoils, it won't make enough difference for us average joes to worry about.

Originally Posted by Azarr

I thought the question was about covering over the step, as if you started at the leading edge and attached to the trailing edge as you would for a built up wing, not covering the individual pieces.

But I don't know the answer anyway

Azarr

I read the question as being that of the pros and cons of covering the steps but following the original right angled contour of the steps with a thin layer of material. Done that way, I think covering can be done without losing much or anything.

But in the past when steps were covered or shaped in a manner that masked the right angle steps or rounded or blended the right angled corners, there was a loss in some of the desirable KF qualities.

Jack

Originally Posted by Thechittyfather

Firstly I'm no expert. Reading through some of the advanced theories about KFm steps then some people seem to be suggesting that the step itself is a factor in the usefulness of the airfoil rather than just the overall profile of the laminates.

That is absolutely the case. The effrects at the steps or that result from the presence of the steps is what makes the foil work.

If this is the case then covering the wing in a way that chamfers/blends the steps by pulling the covering tight might mitigate the effects.

That is the case and it will mitigate the effects.

How do I know that?

Who else knows that?

I know if from experience as a builder and flyer and from my experiences and anecdotal evidence contributed by others over the past five years or so. And the others are those that have gone through the same or similar experiences that I have. We are not scientists, we don't have wind tunnels, we still have questions and wonder about how and why it works.

But we don't wonder much about what does work. Our gauge of effectiveness is in the seats of out pants and the emotions of happiness we get out of our builds.

Covering in a way that adds strength and keeps the steps would conversely be a positive.
IMOH, and I like KFm airfoils, it won't make enough difference for us average joes to worry about.

And I think that is the best way to do it. Cover while keeping the shape of the steps to the greatest extent possible and it works fine.

Jack

Haha. I'm must have been paying attention for a change.

Originally Posted by Thechittyfather

Haha. I'm must have been paying attention for a change.

Don't forget, the building thing is a big factor in the KF thing. Especially if you like to build with cheap and readily available materials. And can take some joy out of anything that will fly.

Do you have a plane with a KF foil? If not, it is easy to build one and it will fly well. What might be more interesting would be to build a flat plate wing plane of some type that is a quick and easy build and not hard to fly too.

The NutBall, best damn RET foamy yet..... - http://www.rcgroups.com/forums/showthread.php?t=836389

Buiild and fly something like that. Then build and fly something like davereap's KFm4 version of that plane:

KFm4 build on a 36" Nutball using 6mm Depron or FFF - http://www.rcgroups.com/forums/showthread.php?t=1049935

If you don't see a difference I would be very surprised. You could even just build the Nutball and then tape a KFm1 (bottom) or KFm2 (top) step on it and the effects of the step it will be apparent.

Jack

To clarify, my question was regarding the ability of the new stuff/doculam to adhere to the 90deg steps.

Another question...is there a good substitute fo 3m77 that will not eat fff/eps? The new formulation will eat foam in my fff test.

Originally Posted by roo_ster

To clarify, my question was regarding the ability of the new stuff/doculam to adhere to the 90deg steps.

Another question...is there a good substitute fo 3m77 that will not eat fff/eps? The new formulation will eat foam in my fff test.

Haven't used the Doculam and don't normally try to cover the vertical on steps (only the flats or horiizontals) so can't answer that one.

The 3M77 ($12 a can or more) and Duro 01-81088 (about $8 a can cheaper and works well) both have some Acetone in them that will attack foam. But if you hold the part at arms length (wear an old sweatshirt sleeve and a disposable glove) and spray on one or two light coats it will not "pecker up" little holes in the bare FFF. And the plastic skinned side is not bothered by it.

Jack