Bonding ribs, horizontal stab

[Flyboy66]

When bonding horizontal stabilizer ribs into place, do I bond the sections where the welded structure passes through the ribs? How do I know if I need stiffeners? The ribs are all strait, but will they bend with an air load, or when the fabric is shrunk?

[jrevens]

Hi Steve,

FWIW, I installed stiffeners on most all of the ribs that weren't in contact with one of the steel "ribs"... that includes the elevator ribs. I also bonded to the structure that passes through them.
Here's a representative picture -

[Esser]

I did my rudder with no stiffeners only to find out the humidity caused them to swell and warp. In my opinion, stiffeners are not optional unless you are bonding it to something along side it.

[Flyboy66]

Half (just under) of the horizontal stab done. I need to go glue the ribs with weldments through them. Was waiting to hear/see back from you guys. Dinner, then trimming the ribs for the other side.

After gluing, I went upstairs to show neighbor wings and fuselage, and noticed that KF uses a lot of adhesive to bond the wing ribs in. Did I use enough adhesive to bond in my ribs?

Tomorrow, I will install stiffeners on today’s work and install ribs in the other half.

[jiott]

By all means, use stiffeners on all ribs not otherwise stiffened by a steel structural member. The kit typically does not include enough stiffener material so you will be tempted to skip it on some ribs, but go buy some 1/8" ply from the local hobby shop and cut some more. I skipped some on my elevator and was sorry I did. The fabric shrink process pulled the outer steel tubing in just enough so that some of my unstiffened ribs took on an "S" curve. Not a show stopper, but not good in my book.

[Flyboy66]

I am sold on stiffeners, but it raises another question. How do you clamp the stiffener in place while the adhesive sets?

Any pictures?

The outboard 8 ribs are now installed on the stab. Tomorrow is stiffener day as well as elevator rib day. Also, what about foam versus balsa wood for the outer edge of the stabilizer?

[jiott]

I used small spring clamps to hold the stiffeners.
I highly recommend balsa rather than foam on the stabilizer tips as well as the elevator tips. Much more resistant to hangar rash in these very vulnerable places. Foams OK on the top of the rudder and vertical stab.

[David47]

Recommend you also put stiffeners on the elevator ribs. I didn’t on mine initially and had to go back and do it because they bowed with moisture uptake over time. Suggest you Put the stiffeners on ribs first before you locate and bond in place.

[efwd]

I just put a bit more flox in to make sure gravity didn't take advantage of the situation. I put the stiffener on and just wrapped tape around it in a couple spots along the length. Everything turned out well.
I too would recommend Balsa wood. I won't ever use foam anyplace if I do this again. I have mentioned before, If your using Oratex, foam will melt when forming the fabric around those surfaces.
Eddie

[Delta Whisky]

Steve - after bonding in the ribs in my VS, and then adding the stiffeners, I changed the process a bit when doing the rudder. I first "dry fitted" the ribs (using the ribs in the VS for alignment), then added the stiffeners using a table top to ensure a flat rib, and then bonding them in their final resting places.


As you can see in the pictures, I'm fond of using my most used tool - clamps from the aviation department in Harbor Freight.



Bonding while on the table top also made the job tons easier due to access.


More details can be seen on my build site.

[Flyboy66]

I have only been to the antique tractor section of Harbor Freight. I didn’t even know they had an aircraft section! More clamps are on the list now. I really like the idea of bonding the stiffeners first. I am in the process of doing ribs first than adding stiffeners for the stab. The elevator will be done differently.

On the stiffener subject; are you applying adhesive to both sides, or just one? And do you set up the stiffeners to contact the tubing or does it end just prior to the tubing so that you are bonding on,y the rib to the tubing?

[Flyboy66]

Jrevens: how do you get such a pretty finish on the adhesive?

[jrevens]

I don’t know... I’m just kind of slow and careful I think. I did spend a lot of unnecessary time carefully cleaning up the initial “mess” as well as masking sometimes. A gloved finger dipped in alcohol (or even water) is helpful to do a little smoothing. If you wait until the epoxy is starting to set-up and get a little stiff, the finger wipe can be very effective for helping to produce a nice looking fillet. I think Brandon at the factory is the guy to ask this question of. He makes some of the nicest looking glue joints that I’ve seen.

[efwd]

Get the ratcheting gun with dubble barel syringes with mixing tips if your looking for great filets. If I remember from my visit in April, Brandon has an air driven applicator gun with mixing tips.
Eddie

[aviator79]

By all means, use stiffeners on all ribs not otherwise stiffened by a steel structural member. The kit typically does not include enough stiffener material so you will be tempted to skip it on some ribs, but go buy some 1/8" ply from the local hobby shop and cut some more. I skipped some on my elevator and was sorry I did. The fabric shrink process pulled the outer steel tubing in just enough so that some of my unstiffened ribs took on an "S" curve. Not a show stopper, but not good in my book.

I stiffened all of the HS ribs, but since I didn't have enough material, I did not do the elevator ribs, as they were all nice and straight. Tightening the fabric was enough compression on the steel structure that most of them bowed a little. Fortunately, the elevator ribs follow a linear contour from LE to TE, and you actually can't tell in the finished product, but I wish I would have stiffened them.


Get the ratcheting gun with dubble barel syringes with mixing tips if your looking for great filets. If I remember from my visit in April, Brandon has an air driven applicator gun with mixing tips.You can get this adhesive and a much cheaper non-branded gun from McMaster Carr. I just used mine for the first time, and now that I've seen the light, I would have used this from the beginning despite the cost. You'll need to order a half ton of applicator tips, but you will waste very little adhesive. My glue work does not look as good as John's, but it would have if I'd used this gun from the beginning. Also really nice not to have to mix. Just put the tip on and go!

[jiott]

I used the glue gun on some later items in my build. I ran out of the expensive mixing tips, but continued to use the gun without the tips. It squirted out a nice accurate 50-50 ratio onto a piece of cardboard that I then mixed by hand. Not as handy as with the tips, but still much better than the mess of using the big cans.

[aviator79]

Just as a point of reference, the 1.69 oz cartridges are $20/each, making the epoxy about 6 times more expensive in this form than in the 2.5 lb cans. The tips are $1.26/ea and are obviously not re-usable. That's a little bit more than what I spend on veterinary syringes to use as dispensers. Some of the cost is recovered in the lack of waste, but it's still going to be way more expensive to use this stuff, probably by several hundred dollars if you used the gun exclusively. Despite this, if I had it to do over again, I'd make use of this system a lot more and a lot earlier.

[colospace]

My first Hysol use was on the horizontal stab, and man did it seem messy. Then I developed my technique a bit and it became much nicer to use.
Back when I was mixing/using larger quantities, I would measure out the components with plastic spoons or a scale depending upon quantity needed, and mix in a plastic cup. I then loaded into an appropriate size syringe (local farm and ranch store has them in several sizes). Alcohol on my finger tip after partial setup, as John mentioned, would produce nice fillets.
Now that I usually only need small amounts, I bought the cartridges with no tips and I do as Jim mentioned and just squirt out some on a plastic lid, mix and apply.

[Durham66]

On my model IV, The only place that has the wooden ribs is in the Hor stab. I decided I'm not going to put wooden ribs in the rest of the surfaces in the tail, but I do need to repair on of the ribs in the hor Stab. Although from the look of the ribs in the Hor Stab, they do not look like factory ribs supplied by kitfox, they look homemade and made out of what's looks to me like salvaged wood from some cheap furniture. should I order the rib kit from kitfox and replace these?

[patrick.hvac]

The applicator syringe gun is awesome but as mentioned above will cost 4x as much as the cans.
When applying thickened epoxy I usually just grab a box of freezer ziplock bags, scoop it in from the mixing surface and cut the corner off.
Use it like a piping bag. Then use alcohol on a finger to clean up the corner fillets.