Fluting and straightening the ribs

These are fluting pliers and the resulting fluted rib. What is fluting you may ask? This is a process where small crimps are made in the flange of each rib to help bring the flanges to 90 degrees perpendicular to the web or main flat part of the rib, and to correct the bow in the web or flat part of the rib that results from bending the top and bottomflanges of each rib. The process of attempting to bend two 90 degree flanges on a thin piece of aluminum causes the larger flat part of the metal to bow in one direction. Fluting the flanges is necessary to straighten the bow in the metal by counter-acting the bending moment that occurs. Easier to see than to explain. Since I have already straightened all the flanges and fluted all the HS ribs, I will try to show a pic of the Vertical Stab ribs later on so you can see how pronounced the bow really is, and how fluting works to straighten it out. It really does work nicely.

HS 404 and 405 Continued - marking the rivet hole locations

SO these are the marks for the rivet holes that ensure that they have enough edge distance. 4 holes are required for the main rib flange, while only two are required for the flange on the nose rib. The whole point of the exercise of clamping the two rib sections together was to determine where the edges of the flange of the nose rib will line up with the flange on the main rib as shown in this pic. It is otherwise difficult to figure out where these holes go since the front spar fits in between the two ribs.

The vertical lines represent the edges of the trimmed flange of the nose rib and where it will be positioned in relationship to the main rib once positioned on the other side of the front spar. This allowed me to "transfer" the position of the shorter flange of the nose rib onto the larger flange of the main rib so that I can better determine where the center rivet holes needed to be drilled to maintain proper edge distance. Van's wants everyone to locate these holes themselves, so they do not pre-drill any of the holes in either flange.

This was a major pain in the ass to figure out, but I am confident that all the holes are now properly marked. Basically the marks all represent rivet hole locations that 1/4 inch away from all edges of each flange in each rib. The distance needs to be 2x the diameter of the rivet used. IN this case, they are 1/8 inch thick rivets, so 2x 1/8 inch is 1/4 inch to meet minimum edge distance.

HS 404 and 405 rib flange aligment continued.....Mounting hole alignment shown

A better shot showing the two forming holes underneath the clamp that I used to alig the two rib sections. Alslo shows the finished front rib after the nibbling and edge smoothing was completed.

Also don't forget to radius the inside corners where the flange is trimmed or nibbled away. Another thing to notice from this pic is the reference line drawn with a sharpie next to the area that has been trimmed away. Always perform major trimming or cutting so that you are not quite to the final trim line. Then perform final sanding, trimming, or grinding up to the established trim line. It's always easier to trim a little more metal away than it is to replace it after it's gone! Many builders have had to order new parts here, either due to improper trimming, or because they mess up the edge distance when trimming the flange or marking and drilling the holes. Thanks to Ron Duren's posts about these problems in his site, I was able to avoid this problem, and my finished parts all came out fine.

HS 404 adn HS 405 Rib flanges aligned and clamped, and center lines marked

Not a very clear pic, but it shows the alignment of the two rib sections.

Drilling holes correctly in the HS 404 and HS 405 flanges - my method

This is the source of great controversy, discussion, and advice as to how to go about marking and drilling the holes for the rivets that end up attaching this main rib to the front spar and subsequently to the nose rib - sort of a 3 layer sandwich of thin alumimum that must be solidly attached by riveting them all together. The controversy revolves around measuring and marking the holes to be drilled, while maintaining proper edge distance from the material. Setting a rivet too close to the edge can cause cracks or failures in the part, so this does have to be done correctly.
After spending lots of time reading and studying the plans, I had an epiphony of sorts. Realizing that the front spar is just the middle layer of the sandwich, the real challenge was to get the rivet holes of the ribs in the right spot, while making sure that the two rib pieces line up correctly. I also realized that the mounting holes in each rib that are used when forming each part appear to be in alignment with each other. As shown here, I simply clamped the two pieces together, lining up the two forming holes as closely as possible, while checking the outer edges to ensure they also were aligned.

I also used two pieces of aluminum from the trim bundle and placed them on both sides of the ribs where the flanges join to further ensure that the ribs are in proper alignment. Then youn really need to pay attention to the lovely drawing in the plans, which, much to my disappointment, is a bit too small to properly show all of the detail regarding how the edge distance and marks for each hole are determined. Be careful, and spend quality time here to fully understand how each set of refernce lines for each rivet hole are determined. Posts on VAF also very clearly discuss this problem.

More nibbling......

Your's truly nibbling away at the rib.

Nibbler tool

The nibbler tool, and some scrap aluminum showing my less than great cuts made with the dremel cutoff wheel, and the rib undergoing the trim...

Nibbling the HS 404forward rib flange to clear the angle support brackets

On to the ribs! I used a nifty tool called a nibbler to trim away the metal outside of the marks as shown. Others have used a dremel with a reinforced cutoff wheel to do this work, but I did not seem to have very good control when practicing with my Dremel tool on some scrap aluminum. This nose rib has to be trimmed to clear the reinforcement angles on the front side of the spar. The tape is "frog tape," which is mainly used for masking very clean trim lines when painting. As it turns out, it also makes a good straight edge for marking lines. Note the chunk missing on the right side which has been "nibbled" away a little at a time.

HS 702 Bend Angle

So this pic is rotated 90 degrees - cannot figure out how to rotate it in the blogger tools. Anyway, this is a clearer pic that shows the detail of what concerned me about the bend line. I was not sure if I would be creating a stress riser since the bend line and the corner radius of the flange intersected. Turned out it was no big deal for a 6 degree angle, but may very well have become a big deal requiring additional fabrication and trimming of metal if the angle for the bend was greater.

Using angle template to check angle of bend on HS 702 Spar

Checking the angle - 6 degrees on the nose! One of the things I found out while talking to Ron about this is that the RV7 construction is a bit different. The RV7 plans require some fabrication of the front spar where this bend line occurs, but the RV8 HS front spar does not.. Many folks try to purchase completed tail sections from other Van's aircraft, thinking that they will fit their RV because "they are all the same." This is not true.

Hobbs now about 40 hours - bending the HS 702 Front Spar Web

Probably should have removed the blue vinyl covering before making this bend, but it did not seem to matter. I took 2 pieces of particle board, cut them so that they were slightly smaller than the actual width of the spar at the bend line, clamped them together as shown, and made the 6 degree bend.

Tribute to Patrick Swayze

Hey Ron Duren, if you are following along - ditto on your post a while back about the loss of Patrick Swayze - a fellow pilot and great actor. I could not add anything more to what Ron stated in his post. Check out his blog entry for more.

POST MORTUM NOTE AFTER RESEARCHING THIS WELL AFTER I HAD LEFT IT ALONE!! This may vary for each different model of Vans Aircraft. I have since found out that the RV-8 plans do depict relief holes in the this area, but only in the pictures. The instructions in the plan book make absolutely no mention of putting relief holes on this location, so this is an area where Vans really needs to update their instructions for the RV 8.


So, another great thing about Chapter 301, they have a lot of active RV buildes and fliers. I found one post on the Van's Air Force website where someone mentioned the need to trim this area of the front spar, and I became even more perplexed. I contacted the Chapter 301 president to ask him who I could contact about the bend line problem I posted earlier. He put me in touch with Bill Truax, a really nice person and Technical counselor who has build at least 13 airplanes I think. He took the time to come to my work shop and look at the problem in person. He told me that it probably would not be a problem and to go ahead and make the bend. So that is what I did, and it all worked out fine. On to the next step......

Joined Chapter 301

So, after attempting for the past 6 months to visit another local EAA Chapter, Chapter 301, I finally made it. What a great time that was - I met the pilot of "Rare Bear," a highly modified F8F Bearcat fighter aircraft from WWII. This is a long time crowd favorite of the Reno Air Races. If you think what I am doing is crazy, you should have heard all of the things they have done to that aircraft just to get a few more knots of airspeed out of her to win the race - it would boggle your mind. I got his autograph. More importantly, I joined Chapter 301. I also met some old friends - including Jack Buschmann, a former Civil Air Patrol Colorado Wing Commander, and a old CFI that I used to work with named Roger. Jack announced that he just finished his DAR final airworthiness inspection after working on a quickbuild RV7 for the past 2 years, and just got his signed paperwork that same day! Now he has to finish putting it back together and conduct the test flying period required by the FAA. I can only imagine being at that stage of the build for my own aircraft. Totally cool.

Bending the HS702 Front Spar Web to Match the Angle Support Brackets

This is the nature of the entire project - you finish one sub assembly and move on to the next challenge or problem at hand. The next step was to bend the center flange of both front spar halves to the same 6 degree angles as the support brackets. If you look closely I have drawn a mark with a black shrpie to show where the bend line is supposed to be, and took this photo to show that the bend line seems as though it might interfere with the radius of the 90 degree bend of the flange at the top of this photo. I stressed over this for some time, since I was not sure if I would have to trim this flange so that it would not interfere with the bend line.

Scotch Brite Tool - An amazing piece of 3M Technology

The angle fabrications work was finished up by using this..... a scotch brite polishing wheel. This is a specialty tool designed for aluminum. I installed it on one side of my grinder. It does not bind up with aluminum, which is what happens to a normal grinding wheel.

Sanding Dust after grinding down the angle support brackets

.....It leaves an awful lot of fine aluminum dust particles - probably not the best thing to be breathing.

My table sander

.....My electric sander. I think I had and 80 grit belt and disk which came with the sander - All they had been used for up to this point was several Pinewood Derby cars throughout the boys cub scout years. This actually worked pretty well, but........

Finished taper on angle support bracket after sanding

One of finished edges after utlizing my sanding method of removing the aluminum........
I believe it was an 80 grit belt, followed by the Scotch Brite wheel, and then again with 220 and 320 aluminum oxide sand paper, sanding by hand to remove any silicon particals from the sanding belts, which can cause corrosion, and to create the final smooth form of the tapered edges of the angles.

Marking Material to remove from Angle Support Brackets

This is a bit blurry - was still trying to figure out my wife's digital camera. These are the marks to show the taper line and the amount of aluminum that needed to be removed from the ends of each bracket. Many have used a band saw for this, which I don't currently possess (Xmas is just around the corner!). Some have used a dremel cutting wheel, but my attempts to do this on some practice pieces proved to be less than satisfactory. The wheel was too hard to control on such thick aluminum.

Used my Sander to grind these down - worked very nicely but left a lot a metal dust - recommend wearing a respirator when you do this.

HS810 and HS 814 Angle Support Brackets Bent

Upper and lower support brackets for the front HS spar with 6 degree bends on both sides. I decided to deviate from the instructions a bit by performing the bend before tapering the ends of both suppot brackets. There was more surface to bang the mallet on and less chance of warping the aluminum during the bend.

Hobbs now at about 35 hours

So it has been a while again - I just cannot bring myself to entering daily posts for some reason. About 35 hours in now - about to start final drilling the frame and skins for the horizontal stabilizer. Winter building in the garage is going to be challenge. This is a pic of a small electric heater I bought from Home Depot to help heat up my work area, since I have no ducted heat in my garage at this time. Between this heater and several 150 watt flood lamps, I am finding that the work area gets pretty comfortable, even with the snow falling outside, as long as I keep the garage door closed.