Wednesday, August 18, 2010

Curtiss F-6C4 Re-Cover - Way to Go Mark!

It was hot and dirty work - happy to be done

My friend Mark Julicher of Bulverde, TX has been sending updates to his latest project to recover a Curtiss F6C4 aircraft for the National Museum of the Marine Corps. He has graciously allowed me to add his photos here for the followers of Barnstmr's Random Aeronautics to enjoy.

Here are some of his reports below. I will add more as he nears completion of this wonderful airplane.

AUGUST 17, 2010

It is traditional when school restarts to write an essay titled, "How I spent my Summer". Here is a short picture essay of how I spent my summer. Please enjoy my small indulgence here.

This plane is slated to hang in the National Museum of the Marine Corps when they complete the new aircraft gallery. It is a Curtiss Hawk originally flown in 1928, 98% of this one has been rebuilt - my task was to apply new fabric and dope which I accomplished at a facility in San Antonio, Texas. The plane will be re-assembled for final inspection in the next few weeks and then shipped overland to Virginia.

The structure is an amazing combination of construction techniques including riveting, welding, wood & glue, wire bracing, sheet metal and of course fabric. The fabric process here is Ceconite with Randolph dope. The engine is a P
ratt & Whitney 1340 rated at 650 horsepower. Save for the magnetos, there is no electrical system. The plane was aircraft carrier qualified which is amazing in itself, although the landing approach speed was probably only 60 knots which would make for a quick stop with any kind of wind over the deck. Armament is one .30 cal and one .50 cal directly in front of the pilot and firing through the propeller arc via a synchronizer. I imagine the pilots were mostly deaf after firing a few rounds!

The upper wing required 28 yards of fabric sewn into five panels for the top side and five for the bottom. I counted 1070 rib laces - give or take a few. It took four days to rib lace the upper wing plus a day each to rib lace each lower wing. There is one gallon of dope for each coat on the upper wing and there are 13 coats on it.
I shall complete the fabric work on Tuesday August 17 and then a local artist will paint the Eagle-Globe&Anchor insignia plus a few last minute touches on the fuselage. As a final step the plane will be assembled for a good looking over before it it crated and shipped.

All the best,

Click on Images to Enlarge Photo

Upper wing ready to cover

Tail feathers in the spray booth

Vertical stabilizer awaiting squadron insignia

Rudder - huge!

Lower left wing being taped

Upper wing top side - complete. 46 inch diameter national insignia, 26 inch high letters

Upper wing bottom side

Fuselage being prepped

Pilot seat. The perforated bins are ammo cans. Red knob is a manual fuel pump for the aux tank.

Fabric starts out saggy-baggy

Fuselage ready for tapes and dope - engine being assembled

Mark says, "Yes I sat in the cockpit and it IS way cool!"

Fuselage getting silver dope.

Random Correspondence from Mark

MAY 3, 2010
Buell and Terry,
Have either of you ever covered a wing that uses a wire trailing edge?
If so, is there anything special I need to know about how to do it? It appears that I will get a contract to cover this F6C-4, and the wings have wire trailing edges. I have the original fabric to look at (already removed) and there are probably some clues there, but any pointers I can get would be appreciated.
Perhaps I need to go discuss this with Roger Freeman? I don't know, but you guys are the restorers I trust most in these parts so I thought I would first ask you two.

Mark Julicher

MAY 4, 2010
The trailing edges will indeed scallop. I think there may be nothing you can do about that with wire edges. I'm concerned about how to keep the glue from puckering the fabric because it will probably try to touch the opposite surface and stick on it. Sort of like when you get too much glue on a tube and the fabric wraps around too far and leaves a dimple.
All the best,
June 02, 2010

Prior to dis-assembly
31 foot span
2000 rib stitches on 2 1/2 inch centers in the top wing alone.
According to the owner, it is a replica, but that is sure enough a legitimate data plate. And no, it is never going to fly.

The Curtiss F-6C4 was flown by the USMC. This remaining example belongs to the National Museum of the Marine Corps. The technology is fascinating.

Here are two photos taken during the restoration so far. One is an example of a lace-in panel frame. New boot hooks will be swaged onto this frame after a 4 inch fabric tape is applied - thereby capturing the fabric under the hooks. We are purchasing boot hook swages that mount in an arbor press to do this task.

Next photo is how I covered the wire trailing edges of the lower wings. Per advice from Jim and Dondi Miller, I could have done an overlapped glue joint over the wire, but I decided to go in keeping with the original fabric. I had to dissect some old linen to figure out the secret of covering the wire. I'm happy to say the zillion stitches held perfectly when the iron hit the fabric.

More on the Doped-In/Lace-up Inspection Panel
- Pay Attention Curtiss Robin Restorers!-

When Mark first began the process of restoring the F6C-4, we had some interesting dialog floating around via email on just how to accomplish this type of Doped-In Lace-Up Inspection panel. Here is the string of emails....

Thanks. After a lot of figuring, I believe you have the correct solution in fabricating a sub assembly. Now to go purchase a pot load of boot hooks...

On Jun 4, 2010, at 11:40 AM, wrote:
Curtiss Robins had this type of panel near the tail when new (although Dad did not keep this purity in the restoration of our Robin 82H). If this were up to me, I would first cut out a pinked-edge fabric rectangle approximately 1.5 inches larger than the overall dimensions of the aluminum rectangle and then go ahead and prepare it complete with the swaged lace-hooks on the bench.
This would result in a fabric/aluminum sub-assembly. Then hold on to that until after the fabric cover is stretched on the airframe. Then I would dope in the panel/fabric sub-assembly into position wherever it goes. You could cut out the middle portion (to result as a 3 or 4-inch pinked edge tape) or just leave it there and have 2 layers of fabric full span across the panel. An additional layer of pinked tape could be added if you were worried about strength, but evidently, the last restorer decided its not necessary.
I'll bet you will have a bigger challenge preventing dope runs from forming around those little lace-hook buggers. Perhaps you'll want that surface to be horizontal while doping.
p.s. My wife is knowledgeable about some of the fabric swaging tools. I will see if she has any
sources for you.>
Sent: Thu, Jun 3, 2010 10:51 pm
Subject: Fwd: Help with Lace Panel
Nope, it is not at Doc's, and it would be a tight fit.
Here is an e-mail I sent to the vintage aircraft guys, perhaps you may know the answer to my predicament, BTW, the vintage aircraft folks were not very satisfactory on my query about wire trailing edges, so maybe they will do better on lace-in panels.
All the best,

Begin forwarded message:
June 3, 2010 9:23:02 PM CDT
To: andrew>
Subject: Re: Help with Lace Panel
Andrew,Many thanks for the reply. I went through the same thought processes, but none of the proffered solutions appear to be correct. Allow me to share some photos of this project and discuss each in turn. At least that way you will have as much to go on as I do. Beg your pardon if I overwhelm your e-mail.
First let me say that this plane is a replica built in the mid 1970s, even though it has an original 1928 data plate. (that could start a donnybrook all by itself, but I digress). I am guessing the build-date based on some date stamps on wood in the wings. Furthermore, much of the AN hardware in not from the 1920s.
Second, the lace-in panels in this plane are a work of art. Someone far more clever than myself built this jewel. If I can capture enough photos etc, I feel a how-to magazine article coming on...

Photo One is the project before it was disassembled and moved to the shop in San Antonio. Lace-in panels are prominent. I asked the owner (USMC museum) if I could re-use the current panels, but it appears he wants new ones. The workmanship in this plane is phenomenal, and it will take my best effort to cover this to museum quality. BTW, the slipper fuel tank hangs down a few inches because one machine gun's expended brass chute empties straight down.

Photo two is self explanatory. This gem is mounted above the pilot's left shoulder. These planes were mostly based in San Diego. According to various reports, the straight nose F-6's were kept by the Navy, and round engines were the favorite of Marines. The plane was carrier capable.

Photo three is one lace in panel. The 3" fabric tape covers both sides of the panel and it has not been split. That kills the theory of doping on a panel then cutting it out before installing the boot hooks. None-the-less, I still may have to do the job that way because it makes good sense.
HOWEVER this puzzle is really a stumper... read on.

Photo Four. Here I peeled some of the fabric back to see if it went under or around the boot hooks. The old fabric (linen) tears right up to the hooks and I'm convinced it goes under them. Besides, how would you punch perfect little holes in the tape for each hook to protrude through?
So now I'm thinking the frame was doped on and taped. Then the holes were made in the fabric, probably at pre-drilled locations in the frame, and finally the hooks were installed and swaged in place by a tiny A&P who crawled into the fuselage.

Or perhaps the fuselage sides were covered, the lace-in panels were doped to to the fuselage, the hooks swaged on while someone could reach in from below or above, and lastly the turtle deck and belly were covered???

Photo 5. Here is the reverse side of the lace-in panel. The panel frame is elegant. It is one piece of aluminum which has been stop-drilled and then MOSTLY split down the centerline. The inner frame and outer frame are still attached at the corners as shown and also at the center point of each side. This makes a beautifully straight frame with perfectly parallel edges. I am impressed by both the technique and the craftsmanship.

My next step is to contact a boot hook maker and find out what sorts of tools could be used to set the hooks. This might offer a clue, especially if there is some sort of two piece tool using a set and a buck. Many thanks for your ideas.
Mark Julicher

On Jun 3, 2010, at 8:03 AM, andrew king wrote:
I think that the answer might be that they installed the inspection opening framework in the fabric before they covered the fuselage. In '28 they would have been using an envelope with sewed seams on the longerons, so they would have been able to place inspection openings where they wanted them. I've seen original Jenny fabric that had the metal grommet drain openings in the wing installed with no patch, that must've been done before covering, haven't seen an inspection opening done that way, but it's possible. Or perhaps they installed the frame, then cut the fabric from the opening, and then installed the boot hooks reaching the backside through the now open hole. My best guesses...
Sent: Jun 2, 2010 4:27 PM
Subject: FW: Help with Lace Panel
Andrew, I know what he's talking about, but I'm not clear on the actual install. I think you've done this, so would you mind answering him and ccing me on your reply? Thanks! H.G.

-----Original Message-----
From: Mark Julicher []
Sent: Tuesday, June 01, 2010 7:52 PM
To: vintage
Subject: Help with Lace Panel
I am trying to locate ideas on how to fabricate a lace-on inspection panel. Allow me to introduce myself. My name is Mark Julicher, EAA 605278, also a member of NAFI and a technical counselor and flight advisor, and I have rebuilt several aircraft, mostly fabric. But I'm stumped.
I am replacing the fabric on a 1928 biplane that uses lace-on inspection panels. It is easy to figure out how to build the aluminum framework, but after that it gets dicey. It appears that the framework is applied to the fuselage in the usual manner with dope and fabric, but the boot-lace hooks on the original framework were installed AFTER the framework was doped and taped on. Boot lace hooks are swaged on, so how was that done without access to the back of the panel?
I am in the process of contacting boot hook makers to see how these are swaged on Perhaps I'm barking up the wrong tree and the solution is just dirt simple.... ??

So my question is, is there WW I or 1920's expert I might speak to about how this process is done? Or is this a lost art and I'm on my own?? Any help would be appreciated.
Best regards,
Mark Julicher


And for a final related Treat... Check out this historic video with Curtiss F6C-4 airplanes.

US P-12 and F-6C4 aircraft in formation flight at Cleveland National air race in Ohio.
Cleveland National air races in Cleveland, Ohio. A formation of 18 US Navy Curtis F-6C4 aircraft in flight at the air race. 18 bi winged aircraft in flight in three rows of six planes each. Another formation of 18 bi winged aircraft in flight. Bi winged aircraft in flight. Three US Army Air Corps P-12 aircraft execute an inside loop while in flight. A large crowd gathered to watch the air race show. A P-12 aircraft executes a barrel roll. A bi winged civilian aircraft executes several 180 degree loops and flies upside down. A parachute descends as a pilot of an aircraft lands in parking lot. Aircraft crashes into the ground. A bi winged aircraft flies low over the ground and then pulls up.

US Government Archive number for this historic video is: 342 USAF 23961 (DBVT)

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