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Old 12-05-2017, 04:19 PM   #51
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Ok.. so this thread is reminding me a lot of the conversation I had with Jim Doyle (Chopmo) back when I was buying my fuel tank from him. Jim was a stress analysis engineer with Lockheed. I mentioned my observations about flexing of wooden spars, and my wonder about how strong that kind of construction could actually be. After a brief explanation of truss engineering in our biplanes, he then assured me that a wooden spar is best for our application and will flex forever without undergoing the fatigue failure that an aluminum spar can eventually face (as in bending a coat hangar back and forth)... as long as you don't overload or bend it to the point where the wood fibers fail. So, given the reports that I've read regarding the substitution of Fir for Spruce being acceptable, I would much prefer going that route over trying to make up a metal spar. Just my opinion.


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Old 12-05-2017, 05:40 PM   #52
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OK, Here is another point of reference.

If you go to the EAA Museum, on the wall is bolted Neil Loving's Wayne Racer. The spar is one laminated assembly, continuous from tip to tip, shaped as a gull wing. The top and bottom spar caps are constructed of layers 1/4" thick. Each layer is a series of scarfed together segments. Held together with resourcinol glue.

Flight, not static, tested to +6G at the Cleveland National Air Races in order to qualify.

Building the jig to hold the laminations in the gull wing shape while the glue dried must have been as much work as building the whole wing. Compared to that, building a straight laminated spar looks easy.

Best of luck,

Wes


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Old 12-05-2017, 07:38 PM   #53
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Well I’m going to throw it out here since nobody else has. Why not use the stronger Douglas fir spars and reduce the weight like Great Lakes and Fairchild did by routing them. I know the FAA doesn’t like it but lots of planes from the20’s and 30’s has routed spars and flew for years.
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Old 12-05-2017, 09:04 PM   #54
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Rick I was going to mention that as well. But I was wondering if routing would lead to another series of unending calculations to see if you are making any stress risers or making one area to weak while making one area to strong?

I need to re read a thread where Kevin Kimball said something about the reason not to sub fir for a spruce. He seemed to have a very good/strong opinion that it shouldn’t be done if I recall. In all other places I see where it “can” be done. The Stearman guy have been doing it for along time.
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Old 12-06-2017, 04:25 PM   #55
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For what it's worth, ACS claims they can ship me a set of plain Spruce spars with 2-3 weeks leadtime. That order is going in today or tomorrow, we'll see how close to reality their ship date estimate is.
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Old 12-06-2017, 04:50 PM   #56
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ACS and Wicks may be in collusion. Collusion is a recent buzz term that triggers the sheeple. Next month ACS will make a "spruce supply all depleted" announcement and drive some business in Wicks direction.
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Old 12-06-2017, 11:00 PM   #57
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Collusion? There’s zero collusion here. So what the Wicks wood guy had a ACS hat on and sent his girlfriend I❤️ACS text messages.
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Old 12-07-2017, 09:33 AM   #58
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Default ACS and Wicks

My policy for years has been to buy everything except spruce from ACS. All spruce from Wicks. I recently had to change that when I found ACS was again selling 4130 sheet in condition A. I now buy all 4130 plate from Wicks. I have no issues with the quality of ACS spruce, just the accuracy of the dimensions. If I have to I will buy the spars slightly oversize from ACS and buy a thickness planer to finish them.
I get consistent second day delivery from ACS on 90% of my orders, UPS ground.I am 250 road miles from ACS Corona.
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Old 12-07-2017, 10:58 AM   #59
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Rick I was going to mention that as well. But I was wondering if routing would lead to another series of unending calculations to see if you are making any stress risers or making one area to weak while making one area to strong?

I need to re read a thread where Kevin Kimball said something about the reason not to sub fir for a spruce. He seemed to have a very good/strong opinion that it shouldn’t be done if I recall. In all other places I see where it “can” be done. The Stearman guy have been doing it for along time.
First, it should be noted that during WWII, Boeing model 75(Stearman) spars were made from both spruce and routed Doug fir. The fir spars were routed or pocketed between plate areas. This was done to decrease the stiffness of the fir more than it was to save weight. Doug fir is more prone to splitting in bend loads like a ground loop than Sitka spruce. So routing the spars allows them to flex a bit more. Stearman wings built with new wood today generally have solid spars of fir or spruce no pockets. It is about 5 pounds per wing.

As for my statement on substitution, you have it backwards. It is fine to put fir in a wing designed for spruce just not the other way. The model 12 wings were designed with Doug fir spars since the load capacity of fir is about 25% greater than spruce. It is not ok to use spruce spars in a model 12. Doing so would mean you are 40% under rated on the spars. For example, the lower front spars on a model 12 are 1” thick. In spruce they would need to be 1.5” thick.

As another point of reference, the model 12 spars are Doug fir. All 4 rear spars are .6875” (11/16” for the tape measure type folks) thick, upper front .875”(7/8”), and lower front is 1” thick.
If spruce were used and sized for the same loads, it gets heavy. Doing the math for 1” thick rear spars, 1.25” upper front and 1.5” lower front all in spruce shows how fir is the right choice. Not to mention 1.25” and 1.5” thick spruce isn’t typically available so they would have to be laminated, less room for ailerons and so on.
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Old 12-07-2017, 11:52 AM   #60
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Here are a few pictures of the Gee Bee Z wing to show the use of spruce spars. The first shows the spars on a table after I shaped them. Note the rear spars are thicker than they are tall. Rear spars 1.5" with 2 laminations, front 2" thick of 3 laminations. I glued them up in our wooden propeller blank glue press(we used to make certified wooden props).
Second shot is putting T88 on the structure before leading edge ply went on. Note the front spars are full height and shaped to the airfoil. Nose ribs and main ribs butt against the spar instead of spars inside cap strips.
Third pic is the varnished wing outside for a photo.
Forth pic is me holding the wing vertical recreating the same photo by Bob Hall when building the original. for reference, I am 5' 9" tall.
IMG_E6741.jpg   IMG_E6744.jpg   IMG_E6743.jpg   IMG_E6742.jpg  
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Old 12-07-2017, 12:24 PM   #61
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Kevin,
How do you cut the scallop in the leading edge skin behind the spar? Is it done prior to or after the skin is glued on?
Thanks.

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Old 12-07-2017, 12:30 PM   #62
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Kevin,
How do you cut the scallop in the leading edge skin behind the spar? Is it done prior to or after the skin is glued on?
Thanks.

Steve H
Did it before skin went on the wing. Skin was tack nailed to the wing, locations for scallops marked, take off wing and band saw scallops close then sand to the line. Nothing fancy.
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Old 12-07-2017, 12:48 PM   #63
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Those scallops sure will make the fabric transition look nice. I've always liked turtle decks that have the scallops.
Thanks for the info. Appreciate it.

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Old 12-07-2017, 12:58 PM   #64
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The scallops on these wings is not for looks. The skin acts as a gusset onto each rib since the ribs are butted to the rear face of the spar. That along with the corner blocking makes for a great load path. The wing loading is 31 lb per sq ft.
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Old 12-07-2017, 01:37 PM   #65
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Those scallops sure will make the fabric transition look nice. I've always liked turtle decks that have the scallops.
Thanks for the info. Appreciate it.

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Old 12-07-2017, 02:12 PM   #66
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I just read a 1943 Aerodynamics text book my mother gave me. Towards the end there is a brief paragraph about the demise of old growth wood fit to make spars. I was amused by what is old is new again.
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Old 12-07-2017, 03:01 PM   #67
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Kevin. Thanks for clearing that up. Awesome pictures of the GeeBee! Pretty wild how much different this wing looks vs the R1. Seems like the r1 used a lot of routed ply ribs.

On a Stearman because it was made with both fir and spruce. I assume it’s load limit numbers are all based on the lower strength spruce? Adding the extra strength doesn’t hurt or help that particular design?

Thanks again for clearing it up. I remembered something about the model 12 only using one wood for spars but had it backwards on what it was designed for and the “why” not the other wood.
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Old 12-07-2017, 03:16 PM   #68
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Forth pic is me holding the wing vertical recreating the same photo by Bob Hall when building the original. for reference, I am 5' 9" tall.
Who is that young kid?
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Old 12-07-2017, 03:51 PM   #69
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Kevin-Thanks for those fantastic pictures. Did you use T88 for the laminations? Years ago there seemed to be opposition to using epoxy for laminations, now it seems to be common.
Did Kermit fly both Gee Bees?? Did anyone else besides Delmar fly your Z??
I saw your Z at Lakeland, maybe before it flew?? Still amazed at the workmanship as well as the incredible amount of work a project like that takes.
I saw Delmar fly a show in the R in Ft. Worth area. A black wall of weather was rapidly approaching from the west. He finished about the time the rain hit just to the west. Single runway, 90 degree crosswind variable plus minus 30 degrees and blowing really hard. He greased it on the upwind wheel, rolled for a while and then gently let the other wheel down. I was pretty close and could not see the slightest deviation directionally. I know Delmar is an incredible pilot but after that landing I was left wondering if the R is not quite as bad as some believe. Just very blind with some weird quirks but is it any more blind than a Sea Fury or F8F with the tiny bubble canopy. Hoot Gibson wrote a report on Strega, one of the interesting comments was the visibility for takeoff and landing being much better than the Sea Fury.
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Old 12-07-2017, 04:02 PM   #70
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Roughly 6" spacing on the wing ribs??
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Old 12-07-2017, 05:39 PM   #71
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Who is that young kid?
I know, Right! I was 30 years old then, 53 now.
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Old 12-07-2017, 05:45 PM   #72
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Kevin-Thanks for those fantastic pictures. Did you use T88 for the laminations? Years ago there seemed to be opposition to using epoxy for laminations, now it seems to be common.
Did Kermit fly both Gee Bees?? Did anyone else besides Delmar fly your Z??
I saw your Z at Lakeland, maybe before it flew?? Still amazed at the workmanship as well as the incredible amount of work a project like that takes.
I saw Delmar fly a show in the R in Ft. Worth area. A black wall of weather was rapidly approaching from the west. He finished about the time the rain hit just to the west. Single runway, 90 degree crosswind variable plus minus 30 degrees and blowing really hard. He greased it on the upwind wheel, rolled for a while and then gently let the other wheel down. I was pretty close and could not see the slightest deviation directionally. I know Delmar is an incredible pilot but after that landing I was left wondering if the R is not quite as bad as some believe. Just very blind with some weird quirks but is it any more blind than a Sea Fury or F8F with the tiny bubble canopy. Hoot Gibson wrote a report on Strega, one of the interesting comments was the visibility for takeoff and landing being much better than the Sea Fury.
Kermit flew the Z but has not flown Delmar's. I don't think Delmar's was assembled 100%, just static.

The Original airplanes in 31-32 were the equivalent of transonic flight today for a cub pilot. There were no pilots with experience going as fast as these planes were capable of going. Bob Hall practiced for hours in the Model Y flying it on approaches at cruise speed to simulate what the Z would be like. He was 26 years old and had 281hrs in his logbook when he test flew the Z. I think these planes are successful today because have good brakes, better airports and pilots with experience in airplanes with similar or greater performance.

I think there was a little bit of "Big man" talk by those who flew the airplanes. If you tell everyone it is impossible to fly yet you can do it, you look like a super hero, right?
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Old 12-07-2017, 05:50 PM   #73
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Roughly 6" spacing on the wing ribs??
Close. Ribs are 5.4" on center per written spec from Bob Hall Himself.

The Z construction is like that of Hall's other designs leading up to the Z. Pete Miller designed the R1, R2. Pete was hired after Bob Hall quit in protest of the 1340 being put on the Z for the speed record attempt in which the plane crashed. Hall went on the design and build the Hall Bulldog, Cicada, the gull wing stinsons, and then to Grumman where he was chief engineer on all the grumman cats up through the F14. Ever notice how the grumman wild cat, hellcat, bearcat, etc. have similar look to a Gee Bee Z? The cantilever gear in the Gullwing stinsons, the gull wing, all from the Bulldog.
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Old 12-07-2017, 08:00 PM   #74
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"If you tell everyone it is impossible to fly yet you can do it, you look like a super hero, right?"

Hey! Isn't that what all of us high performance biplane drivers do?

Best of luck,

Wes
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Old 12-07-2017, 09:02 PM   #75
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I felt pretty great after jumping from the C120 into the Pitts but after a few hours figured out the little smile between Pitts drivers was telling each other not to let the secret out that they were NOT supermen. Not to say one doesn't have to pay attention......

What bothered me were a few offers I got to fly other airplanes I had absolutely no business flying. It seemed people thought if you could fly one you could fly anything.

Biggest issue is that they are like heroin, once you fly them nothing else quite satisfies.....

I think Kevin is exactly right. I don't have that much time/experience but it's enough to know that there's a lot I don't know and not ready for. Those relatively low time guys in the 30's with the race planes and the 200 hour young lads in WW2 flying 51's, F4U's, etc. continue to amaze me.


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