[clam]

Gents,
Had an odd development yesterday while dimpling my rudder spar (R-802). After dimpling with a squeezer, the spar was bowed just like a punched rib would be prior to fluting. Haven't seen this before. Anybody know what would cause this? Too much squeeze on dimpling (is that even possible)?
I ended up fluting the spar and it straightened out perfectly. I did not experience this at all on the VS or HS. I'm planning on using the spar, but will check with my tech counselor first. Any thoughts out there?
Thanks,
Jeff

 

[scard]

In fact, make sure you are squeezing the dimples hard enough. The material will curl right up if a series of dimples are not formed with a lot of force. I wouldn't be too keen on fluting the spar.

 

[Rick6a]

......the spar was bowed just like a punched rib would be prior to fluting.......I ended up fluting the spar and it straightened out perfectly......Any thoughts out there? Jeff

At 52" more or less, the R-802 is a fairly long and supple part. I used my pneumatic alligator squeezer to dimple its holes as I do on most parts. Still, I did not notice any undue bowing of the spar. It is highly likely your R-802 would have clecoed into place just fine but I further OPINE that it is perfectly acceptable to flute it to a reasonable straightness condition before clecoing to the R-801PP skin.

 

[briand]

I had my flap spar bow quite a bit after dimpling. I sent vans a pic and they said that it was fine and "build on".

I actually backed off on the pressure a bit for the 2nd spar and it helped a lot. I think there is probably a sweet spot that you need to find. I have a pnuematic squeezer and set it so the dies would just touch then added an AN960-10L (thin) washer at 80psi. I got these instructions from someone else here (don't remember who).

 

[dan]

In fact, make sure you are squeezing the dimples hard enough. The material will curl right up if a series of dimples are not formed with a lot of force. I wouldn't be too keen on fluting the spar.

Exactly what Scott said. And in essence, you have already fluted your spar! By not dimpling fully. Go back and hit each dimple properly (squeeze it good), and you should see it straightening right out.

 

[clam]

Thanks guys. It appears I had "under-squeezed" the dimples as ya'll mention. I tend to think the fluted spar is ok, but I will call Van's on Monday to verify. It didn't take much fluting. (The AN426 rivets sat nicely in the spar dimples in the first place, which is why I tried the fluting prior to re-dimpling.)
Jeff

 

[cytoxin]

squeezer yoke spread from overpressure.

been through this several times, and i am sure it can be found if you have all day to search. however the squeezer yoke tends to spread and you get a high pressure point in the throat side of dies.if it bowed away from you as held for squeezing then this is what happened. very closely veiw the piece and look for the crush on one half of the dimple. take a scrap peice of hinge (cause its soft) and try over squeeze and under squeeze. you'll see the over squeeze causes the banana effect. now i am not sure under squeezing will cause this but i will bet you a dollar to a dime oversqueezing will.


if you adjust your squeezer with washers try and adjustable set. the one from my avery hand squeezer works fine in the pneumatic. the alligator doesnt seem to do the banana because it evenly loads the dies. as does a c-frame or probally even a drdt deal.

 

[szicree]

I gotta go along with the last post. Undersqueezing can cause a bend also, but it would not be corrected by fluting, since the direction of bend would be the same.

 

[clam]

thanks. i did notice the "uneven" dimples when oversqueezing as well as the yoke flexing. spar did banana "away" from the yoke side of the dies on the oversqueeze. (pneumatic squeezer w/ adjustable holder)

 

[cytoxin]

oversqueezing

oversqueezing effectively lengthens the flange area (displaces the material. like a penny on the train track.) while fluting effectively shortens it. fluting should correct if vans says that is ok. \

NOTE: what dan and scott are saying is true but will probally result in a banana toward the squeezer as the metal is just bent like a flute and not formed . when properly dimpled the metal is formed to the dies. over pressure stretches the metal and lengthens it. resulting in the away bend.

DONT OVER DO IT

 

[clam]

oversqueezing with pics

here's the evidence. you can see a slight mark at each dimple where the dies were coming together on the yoke throat side. also just barely evident is a slightly mis-shaped dimple with the low side matching the throat side. this evident oversqueezing caused the ends of the spar to go away from the flange side (ie, lengthening the flanges) just as cytoxin/zsicree mention. appears an undersqueeze would have done just the opposite as dan and scott are saying. you can see the small amount of fluting that straightened it out (ie, shortened the flanges). i did not re-dimple as i believe i was oversqueezing. i'll post van's reply when i get it. thanks for all of the inputs.

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[clam]

if anybody's still interested, van's response:
"a fluted rudder spar? i would have just clecoed hole by hole until it lined up and straightened out, then riveted. but fluting works too and will not cause any problems. build on."
so, onwards i build....

 

[Rick6a]

....van's response.....i would have just clecoed hole by hole until it lined up and straightened out, then riveted. but fluting works too and will not cause any problems......

Good news Jeff. Van's is almost always the place of choice to get a truly informed opinion. In the end, much ado about nothing.

 

[John Courte]

I had the same problem, and got essentially the same response from Van's. They said it was OK to flute the rudder rib. I did, but it wasn't pretty.

Part of the reason I'm on my second rudder.

 

[clam]

Rick, I tend to agree. There are some extremely talented folks that contribute to this site and offer invaluable advice to us "first timers". Can't thank you folks enough. That said, I still gotta pay that long distance phone call charge and get "dad's" blessing...

break, break:

John, you're talking the rudder spar right? Not either of the end ribs? I had some issues on my horiz stab that I was considering rebuilding for. Had my tech counselor come over to take a look before I completely closed it up. He told me that my work at that stage would not win any awards, but was absolutely safe to fly. His advice: if you want a work of art, redo it and add years to the build. You want a safe flyer sometime this decade, press on.

Still kinda nags at ya though when that part isn't just perfect.....

ps. he also told me i better lighten up on the primer unless I just wanted a 900 lb tail . he enjoys the sarcasm. good luck....