Flanges question from newbie

[DaveNelms]

Howdy all. I'm scratch building a Patrol and have a, perhaps stupid, question:

Will it hurt anything to have the flanges on my flaps and ailerons cut to 9/16" instead of the 1/2" the plans call for?

The reason I'm asking is that when I was making my form blocks to cut out the ribs I made the full length and then cut off the ends for the flaps an ailerons.

Many thanks,

Dave

 

[jaredyates]

I don't think it is a stupid question and I'm glad you came to ask it. I don't know the answer, and I would be inclined to ask Bob. But I suspect his main reasons for the flange dimension would be preserving edge distance on the rivets, and establishing a certain minimum bending strength of the rib. It seems like having longer flanges only helps in those two areas, at the expense of a little weight. If you call Bob to ask about it, please let us know what he says!

 

[SpruceForest]

Mine vary between .525 and .560, which is a consequence of radius on the form blocks and my rout templates. Realistically, unless you figured in the effect of the 0.1" radius on the added width for the flange, it will add somewhere around 0.03" and 0.06" width to the flanges per 90 deg bend (radius dependent).

No interference seen in two airplanes worth of ailerons in dry fit-up, so not a fit issue, and no issue with rivet minimums (plus most of the rib flanges meet fabric versus aluminum, anyway).

Adding mass to the area aft of the spar means more counterbalance mass required. How much? Eight ribs and an extra 1/16" width on top and bottom flange equates to a 1" wide by 13" long by 0.025" piece of aluminum, which adds ~1/2 ounce to total weight of each aileron and an arm relative to the aileron hinge point of roughly -7". With arm from hinge of +4" for the counterweight, roughly 7/4 * 1/2 ounce of counterweight to add, or 1.375 ounces total added weight at 100% C/B per aileron. Sounds like the total penalty for the extra flange width is 2-3/4 ounces on aircraft empty weight. Skip that donut on the way to the airport or forego the grande for the tall coffee and you are golden.

 

[DaveNelms]

I feel like I just put you to a lot of trouble but something tells me you enjoyed the whole process immensely.

Many thanks! I'll throw enough money into the budget to cover the extra ounce of lead shot.

 

[marcusofcotton]

Another negative is at the smaller radius on nose ribs being more challenging to get a nice fit while dealing with that extra material that doesn't want to shrink down and lie flat.

Welcome to the group! Where are you located?

 

[DaveNelms]

East Texas out in the boonies between Winnsboro and Quitman. It's one hour due north of Tyler.

Good thought on the extra material. I'll be dealing with 38 ribs and it wouldn't be too bad to just shave 1/6 off my master block if I do it now. Maybe I'll bite the bullet and just do it. Then I can have that extra doughnut before flights. Doughnuts are good.

 

[SpruceForest]

No real issue for the aileron and flap ribs... pretty much a straight bend - so extra width is not an issue.

 

[spinningwrench]

If you have solid form blocks you could simply have a woodworking friend run them through a thickness planer.

 

[Redneckmech]

I also don't believe there will be any issue with the extra material but I have not assembled my ailerons or flaps yet so have little to no authority to provide feedback on it.

If you decide to, you can easily trim your blocks with a router. Get a 1/2" flush trim router bit and replace the bearing on the tip with a 1/8" smaller diameter bearing (1/16 radius). Adjust the router so the bearing rides on the top edge of the formblock and run around it. It will leave a lip of the original diameter that you can flip the block over and then flush trim with your regular flush trim bit or correct size bearing. I used this for all of my lightening holes since the fly cutter left a rough edge, I would cut them 1/16" or 1/8" smaller than called for with the fly cutter and then trim them with the router bit to the needed size.
I got the idea from N3UW and it worked wonderfully for the lightening holes.

 

[sjt]

If you ask me 9/16 is better. If you want an airplane that has the least amount of weight you would use 1/2. If you want to finish your airplane you would use 9/16. The slightest misdrill in a 1/2 flange might violate the edge to distance sheet metal rule. The extra weight is nothing. I gave up trying to make a perfect airplane. I made my form blocks out of 1 inch mdf. You can't get it at the box stores but it is available from cabinet makers. Also, the extra thickness of 1 inch mdf allows for a single form that can be used for both the right and left version of ribs.

To save material - we cut the blanks at arbitrary angles relative to the grain of the 2024 sheets. When you go to bend them you will find that they do not take the same radius bend on the same form.


Not really a problem. In the case of the Center ribs there are various lengths to accommodate cap strips. Do not pre cut them. What you will find is that along any spar there will be variations. If you do not precut them you can sort the ribs so that they fit optimally along the spar that also is not perfect. If you have already put notches for capstrips you can not sort them for best fit.
A sander can make a notch once the rib is sorted for average best fit at that location of the spar


In the case of the aileron and flap spars I made a bunch of mdf forms. All slightly different to create ribs that match the spars the way i wanted. I recommend up cut spiral bits. The brand I use has ball bearings available that are very slightly differnet in size. When I wanted to make multiple mdf forms that were just ever so slightly different I would swap the bearing and make mdf forms using the sequentially smaller mdf form.


https://www.amazon.com/gp/product/B0012JI78U/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0012JGB2E/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

The picture has the wrong number the B3U is 0.490
This will allow for duplicate mdf forms that are sequentially smaller.
The 7/16 drill rod was used to make a nut to screw on the router bit.



I even put scallops in the 1 inch form so that I could make flute the way i wanted.
I used a press to hold metal and bent the flange with an orange hammer.
I then used a wooden dowel to take up some of the metal in the scalloped area of the mdf . I just use the 1/4 dowel to smack material into scalloped area with a hammer.
You could use a fluting pliers to take up material, I just like the scalloped area method.

I also made a joggle tool out of 5/8 keystock used to match ribs to spar as required:

 

[sjt]

Big fan of upcut spiral bits. In all cases with a router the there will be aluminum chips everywhere. And those little chips are hot when they fly off. An upcut spiral pulls the chips up toward the router and away from your body. This of course has the downside in that the router will ingest the chips.

I made a piece of lexan to seal the router off from the chips as well as a vacuum to pull chips away from router.






I then used tape to further protect against chips ingested into router.

I then used a vacuum to pull chips out of router.

I do not remember why but I made a variable speed controller for router. My first router did not survive - hence version 2 has more precautions.


I usually used a 1/2 spiral bit. But for the aileron I used 1/4 spiral bit. Routers scare me. If that bearing is not firmly against something it can unexpectedly grab and take off.
I have found that you can trim material free hand without the bearing touching so long as you do not try to take of more then the radius of the spiral bit. In the case of a 1/2 bit I probably can trim 3/16 without the bearing touching. A 1/4 bit can probably only free trim something like 3/32 before it grabs.

 

[SpruceForest]

Concur. Flange width on aircraft will vary between a little extra and not enough… I stay on the plus side for when I end up needing that slosh extra.

 

[DaveNelms]

I made my form blocks like you did. My little drill press was working really hard making the big lightening holes so I just went half way through then used the router table to finish them. Worked like a champ. The holes are perfect.

 

[DaveNelms]

Many thanks for this info. I want to come see your work some time. You're not too far away from me.

 

[DaveNelms]

I cut them all at 9/16ths. No turning back now. Thanks again I was agonizing over it.

 

[sjt]

In Texas everything is 200 miles away.
My log: (i recommend using the EAA free log facility)
https://eaabuilderslog.org/?blproject&proj=7XFn3SHmH
stan patrol p284


You might also checkout Propman (Frank Johnson) He is much further along.

Next year make sure you attend Reklaw Flyin
https://www.youtube.com/watch?v=j7sNWLkV218