"DOUBLE FLUSH RIVETS"

[NYTOM]

I'm sure this is something only found on a " Classic RV" but I need a little advice here. I'm installing a aileron mounted electric trim and the tab which is nothing more than a modified piano hinge, calls for double flush riveting.
Am I right in assuming I would counter sink both ends of my rivet hole then back rivet to the point of filling the counter sinked hole on the shop head side them filing smooth? I'm going to experiment a little but wondered if anybody had some of that magic advice I'm used to getting here. This must be something from the very early days of the RV since I have yet to see one of these cute little tabs anywhere at least that I can remember.

 

[morlino]

Not sure about your trim tab application but the double flush rivets are pretty common on the pre-punched models. They are used on the trailing edge of the RV7 rudder and I think on some other control surfaces of some other models too.

Van's build manual describes the double flush shop head as an acorn sitting inside of a dimple. But you are correct about the process - back rivet them. I think I set them most of the way with a back rivet set and then finished them with a flush set. The build manual also warns against trying to use a longer rivet so that the shop head fills more of the dimple. Evidently this just results in bent rivets.

If you search the forum you'll find some good info about the rudder trailing edges that you can probably apply to your situation.

There are also some threads in the forum about correcting rigging problems. If I recall correctly, an aileron trim tab is one of the last resorts. I would do some searching.

Good luck!

Edit: if you want to practice, one of the practice projects that Van's sells on their website has a foot or so worth of double flush rivets...

 

[L.Adamson]

There are also some thread in the forum about correcting rigging problems. If I recall correctly, an aileron trim tab is one of the last resorts. I would do some searching.

The-- electric-- piano hinge aileron trim tab, was common practice on the older models, and sold as an option. Not to correct rigging problems; but just a way of balancing for fuel and passengers. My 6A has one.
For whatever reason (that I haven't figured out), I just don't like "bias" springs, and prefer the old way. Of course, built in flush tabs, would look great for ailerons and rudders too. Just some more work, though.

L.Adamson

 

[NYTOM]

My Old Fashion Trim

For whatever reason (that I haven't figured out), I just don't like "bias" springs, and prefer the old way

I agree on this point. After failing to find among my countless pictures of RV's a similar tab and wondering why, I did a little research and found the "bias" system Van now sells right along side the servo/trim tab for the left aileron system that I bought with my slooow build kit so long ago.
The trim tab seems more of a true trim system rather than a "hidden helper hand" on the control stick in the "bias" system. IMHO it seems like the "bias" system although invisible on the exterior of the plane would cause unnecessary constant stress on the control links.
I'm not implying one system is better than the other, its just how I see it.
Also agree that a little tab like the one on the elevator would look much nicer.

 

[airguy]

I went through this last week on my 9A rudder, here's how it turned out...

http://websites.expercraft.com/airguy/index.php?q=log_entry&log_id=25231

 

[L.Adamson]

I agree on this point. After failing to find among my countless pictures of RV's a similar tab and wondering why, I did a little research and found the "bias" system Van now sells right along side the servo/trim tab for the left aileron system that I bought with my slooow build kit so long ago.

Well, here is "the tab"...

I stuffed everything on the right wing, to offset my weight!

L.Adamson -- RV6A

http://img329.imageshack.us/img329/6535/dsc05247reducednq1.jpg

 

[rvbuilder2002]

The trim tab seems more of a true trim system rather than a "hidden helper hand" on the control stick in the "bias" system. IMHO it seems like the "bias" system although invisible on the exterior of the plane would cause unnecessary constant stress on the control links.

The reason the spring system works so well is because the control forces are very light for small roll inputs (the forces start to climb an appropriate amount with more control deflection). Only small control inputs are needed to produce enough roll trim force to compensate for fuel imbalance. Because of this, the springs are not very stiff. They are not very noticeable in the system and are much less expensive than a 100 + dollar trim motor and it is less work to install...but as already mentioned both work equally well.

 

[MNellis]

Here is a link to my aileron trim tab that I built quite a few years ago.

http://bmnellis.com/wings_ailerons_trim.htm

 

[NYTOM]

ONE HAPPY CAMPER

Reason 613.4b-3 sub part section C: Why I love this site
Want to thank Mark & Greg for their help and suggestions on the the double flush rivets but the response by MNellis has changed everything!
What he created on his 6 is exactly what I wish my trim tab could be.
He even included step by step instructions with pictures for Gods sake.
I swear if this site ever goes away I'm going to have to kill myself.
It just can't get any better than this.
I considered getting the "bias" system Scott explained since it seems much easier to install but Van lists a 7A kit adaptable to a 6A for $310.00 which is a lot more than the $172.00 I already paid way back in 95. Current price for my kit is now $280.00.
And lastly I want to thank Mr.Adamson. You probably don't remember but you've helped me before in the past and as part of the "RV Brotherhood" I want you to know I do appreciate it. Its reassuring to know I have experts looking over my shoulder. Also, awesome looking A you have there. Hope mine turns out even half as nice.
Nuff said. I'm heading down to the shop to build "The MNellis Tab"
Hope everyone has a safe Sunday.

 

[rvbuilder2002]

I considered getting the "bias" system Scott explained since it seems much easier to install but Van lists a 7A kit adaptable to a 6A for $310.00 which is a lot more than the $172.00 I already paid way back in 95. Current price for my kit is now $280.00.

Eek is right!
That must be the electric version which uses an expensive trim motor to adjust the bias centering of the springs.
I was talking about the manual version (which I think works just fine) which is available for about $45 for a 6,7, or 9. As I said before... it is a cheep way to go if you can get past the need to have a button control on the stick grip.