Rivets

[JimParker256]

Yeah, those "whisker" wires produce an amazing amount of drag. The drag difference between a perfectly round wire and a streamlined, airfoil-shaped wire of the same surface area is pretty astounding. Check out this old video: https://www.youtube.com/watch?v=ftq8jTQ ... e=youtu.be

It shows that a round tube has well over 9X the drag of a streamlined airfoil of the same maximum thickness. Likewise, a round wire 1/10 as thick as a streamlined airfoil's maximum thickness will have the same drag as the streamlined shape.

That's one of the reasons why a Cessna (with its airfoil-shaped streamlined struts) is so much faster than an old wire-braced monoplane of similar size and possibly even greater horsepower. And when you look at the Panther, with its airfoil-shaped contours just about everywhere, you realize how it's possible to obtain so much speed on such relatively low horsepower.

This stuff fascinates me... It's why I started out as an Aerospace Engineer, before moving to Computer Science so I could actually get a job and pay off student loans... LOL

[Steamer]

Jim,

An interesting story. It proves once again that there's most likely no free lunch in aviation. It has been written that Spitfires built with flush rivets were faster than those built with universal head rivets. That does make some sense. Careful attention to reducing drag can pay off.

I fly RC model aircraft as a hobby. One famous FAI pylon racer design had two 5/32 diameter music wire "whiskers" about 4" long mounted on the nose to keep it from tipping over on it's nose on landing. They were removed for racing and only used in practice. The model was over 5 MPH faster with them removed.

Stan

[JimParker256]

As for Tony's analogy to golf balls. Wouldn't you need a lot more rivets to get the speed increase enjoyed by the golf ball? Them little suckers are just covered with dimples.

No problem - just leave it on the ramp here in the Dallas area when one of our patented summer thunderstorms comes roaring through... You'll have plenty of "hail dimples" to make your airplane faster... LOL

All kidding aside, one of the fastest Grumman Cheetahs I ever flew was one that was liberally "dimpled" by a really severe hail storm. There were dimples the size of nickles and even quarters all over the plane, including the cowl and upper fuselage. An insurance company had "totaled" the airplane because it was uneconomical to repair the hail damage, and the owner (at that time) bought it at salvage, had it inspected by an A&P/IA, and returned to service. Turns out that none of the hail dents were close enough the the bond lines (Grummans are bonded - glued - instead of riveted) to cause problems. Pure luck! It looked like hell, but flew fine. That airplane was at least 5 knots faster (at the same RPM, altitude, and approximate DA) than the others I flew during my airplane search... The owner attributed it to the hail damage, using the same "golf ball dimple" theory.

A year or so later, I happened to run into the guy who had recently purchased the plane, and learned that he was most disappointed to find out that the tach was reading almost 200 RPM lower than actual. In other words, the additional 5 knots airspeed was because he was running the engine at 2700 RPM when he was indicating 2500 RPM. Fixed the tach, and the airplane was suddenly 5 knots slower in cruise!

[Steamer]

Dan, Tony,

I've had the opportunity to look at an airplane assembled with pop rivets since I made my original post on the subject. I had looked the craft over a couple of times before I noticed the holes in the rivet heads. That and the picture of Tony's tail (the airplane's not the pilot's) leads me to believe it's a non issue.

I would prefer bucked rivets. I worked as an A&P 30 years ago and that's what I'm used to. (I just recently got my license current to work on a CFI friends Cessna 170A. In return he has taught me to fly in it. Saved us both a ton of money and we've had a good time in the process.) But, the pop rivets don't require someone to help buck the rivets and I'm sure they reduce the building time.

As for Tony's analogy to golf balls. Wouldn't you need a lot more rivets to get the speed increase enjoyed by the golf ball? Them little suckers are just covered with dimples.

Thanks for taking the time to respond.

Stan

[danweseman]

Stan
Fillig the small hole in the center would be fine. It would be alot of work, and i thin on would quickly succumb to covering over the entire rivet head, which is bad for many reasons
The first thing i think when i see an aluminum airplane with rivets heads filled , is , what are they hiding.
second the filler around rivet will crack sooner or later looking terrible
you cannot easily inspect or repair the rivets (until the paint / filler cracks per above)
Aluminum aircraft with filled in rivets look terrible. You have a somewhat wavy surface that smooth like composite...

If you do not like the look of the Blind rivets you can always use "bucked" rivets, which would likely be faster in the end than filling in the blind rivets.

Dan W

[Tony Spicer]

Stan,

Anything is possible.

https://picasaweb.google.com/tonyboytoo ... 7395889938

Pulled rivets are supposed to have holes in the center. They're like dimples in golf balls. Fill the holes, and your Panther will be the slowest one on the block.

Tony

[Steamer]

Hello all,

I'm not presently a builder, but if I do decide to build an aircraft it will be a Panther or a Cougar. A thought struck me that I thought would be worth mentioning regarding the pop rivets used on the Panther.

A friend of mine had the pleasure of going to Air Venture 2015 and got a first hand look at the Panther. He thought it looked a bit unfinished with all of the rivets with holes in them. So my question is what's to prevent one from filling the holes with some sort of epoxy putty to make them look more like driven rivets? It would keep water from pooling in the rivet cavity, maybe improve looks, and help hold the rivet stud in place. It would add some small amount of weight too.

So, am I just a crazy newbie or does this idea make any sense?

Stan J.
AKA Steamer