#2 GEE BEE Z Replica

Tiger Tim · **Posted:** Wed Apr 20, 2011 6:39 pm

ProfromDover wrote:

I thought the original Z crashed due to a fuel cap coming off and coming through the windscreen...

That was the suspicion at the time and I believe all later Gee Bee racers had armoured glass windscreens as well as fuel caps that were safely concealed under streamlined hatches. Belt and suspenders approach, I guess. I've read elsewhere that if you watch the original crash film the wing comes apart before the airplane goes out of control, not the other way around as you would expect with the gas cap explanation. Two popular modern theories are structural failure due to wing damage from a day or two prior or flutter, or both.

-Tim

lotus49 · **Posted:** Thu Apr 21, 2011 10:00 am

The Granville bros as much as acknowledged this, when they stated there would never be another structural failure of a Gee Bee wing, after the Z.

If you look at the subsequent structure of the R1/2 and follow on wings, it can be seen that they essentially built a fully internally braced wing, then skinned it for good measure.
The spars are incredibly beefy, the wires big and the fittings massive, all really over engineered.
There is actually no need for the internal brace wires with the skin, but they added them anyway.

I think the gas cap theory had been thoroughly reviewed and discounted by the principles of the day.
this was discussed at length during the EAA Air Racing events, and it was decided this was probably more rumor than fact.

As mentioned it was a structural failure, plain and simple, perhaps compounded by some previous damage, or maybe from a built in error.
One little discussed factor is the workmanship of the day was quite appalling compared to what we now see as standards, they were not adverse to simply drilling bigger holes to make things fit, edge distance was rarely considered, and try finding an inspection panel on an original racer.
these were machines built in terms of weeks and months, not years.

dxlyj · **Posted:** Wed Jun 01, 2011 12:10 pm

ProfromDover wrote:

The GBs used the latest high tech to get the edge on the competition. That being said they employed the M-6 airfoil on their aircraft. The Monk airfoils were the latest greatest airfoil series of the time. Low drag allowing higher speeds and performance. That being said the M series airfoils had one major flaw. When the airspeed decayed there was a major shift of the center of lift and center of pressure.

Mind you I am not an aerodynamicist (sp?) but what this means in layman's tongue is that when the airfoils reaches a slow speed it basically stops flying. Period. Not like modern airfoils which sort of slowly play out and you can feel the break coming. Lots of aerodynamic advancements since the 1930s. The M series were sort of an all or nothing type of airfoil. If you check the NACA L/D charts on the M series and compare it to something like a 23012 (Cessna 100 series) you will see quite a large difference in personality.

Aerobatic pilots *like* airfoils that that have a sharp break at the stall. Better snaps/spins. The 23012 is an excellent compromise (used on the T-Craft) and was my dad's choice to build the "better" Taperwing (which we never got around to). It has very good negative G performance which allowed Duane Cole to do the amazing things he did on 90 hp.
--
Dave Lyjak

cwmc · **Joined:** Fri Jan 28, 2011 2:43 am **Posts:** 322

ProfromDover wrote:

The GBs used the latest high tech to get the edge on the competition. That being said they employed the M-6 airfoil on their aircraft. The Monk airfoils were the latest greatest airfoil series of the time. Low drag allowing higher speeds and performance. That being said the M series airfoils had one major flaw. When the airspeed decayed there was a major shift of the center of lift and center of pressure.

Mind you I am not an aerodynamicist (sp?) but what this means in layman's tongue is that when the airfoils reaches a slow speed it basically stops flying. Period. Not like modern airfoils which sort of slowly play out and you can feel the break coming. Lots of aerodynamic advancements since the 1930s. The M series were sort of an all or nothing type of airfoil. If you check the NACA L/D charts on the M series and compare it to something like a 23012 (Cessna 100 series) you will see quite a large difference in personality.

If you notice, everything Delmar did with the GB was fast. Rolls fast, knife edge fast, upside down fast, landings fast. Everything fast. Delmar has enough aeronautical piloting and engineering skill to know exactly what to expect. They are great airfoils when you are going fast. They are killers if you fly them slow like a Waco or a Travel Air. Many other aircraft used that series of airfoils with some success. The little poky Buhl Bull Pup even had a M-12 (12%) airfoil on it...

I thought the original Z crashed due to a fuel cap coming off and coming through the windscreen...

Pitts Specials with "flat" bottom wings have M-6 airfoils and are very docile, trying to get one to break in a snap or competition spin took technique and practice.
Sounds like, at best, an exaggeration that the cl shift was quick or destabilizing.
Chris...

F3A-1 · **Posted:** Sat Dec 24, 2011 11:56 am

I have finally seen a video of the Kimball/Eicher Gee Bee Z flying.

While visiting Fantasy of Flight I was shown a few minutes of Kermit Weeks first of two flights in his newly purchased Z. Kermit did his usual great job of flying. It is available to see while visiting FoF in a booth near the Gee Bee's. It sounds just like the R-2.

Pirate Lex
http://www.BrewsterCorsair.com

10kDA · **Posted:** Tue Jan 10, 2012 7:41 pm

The Munk M6 has a very soft stall due to the reflexed camber line. It's basically the same airfoil as on the Waco Taperwings, except the Taperwings have no cusp on the top surface. The numbers for the M6 and M12 show a very small change of center of pressure, that's why the racers used them - low trim drag, and predictable handling from the point of horsing the airplane off the ground at the racehorse start, climbing out, and attaining racing speeds. Benny Howard's Mike and Ike used the M6 as designed. Mr Mulligan used a M12. The M6 was a 12% thick airfoil. The Gee Bees used a M6 thinned to 65% of the original thickness, which gives about 7.8% thickness. Thin airfoils don't give a lot of warning at stall, and not a lot of margin for recovery, and don't always behave like a thicker version with the same camber line.

Chris

GeeBeeZ1931 · **Joined:** Tue Feb 28, 2012 7:54 am **Posts:** 3

"As mentioned it was a structural failure, plain and simple, perhaps compounded by some previous damage, or maybe from a built in error.
One little discussed factor is the workmanship of the day was quite appalling compared to what we now see as standards, they were not adverse to simply drilling bigger holes to make things fit, edge distance was rarely considered, and try finding an inspection panel on an original racer.
these were machines built in terms of weeks and months, not years."

Lotus49 :shock:

You were doing great on your post until you got to this paragraph. YES structural failure likely because of wing flutter at over 300 MPH per Kermit Weeks and an 90 year old flutter experts analysis.
NO to shoddy craftsmanship! They built fast but that did NOT mean they didn't build well. Whoever gave you that idea was no better than the hacks that labeled the Gee Bees as widowmakers. Consider how fast they could put together a B 17 at Boeing. Then consider how much smaller the Z was and how many workers there were versus the time to finish. Quite a bit longer than building a huge B 17 wouldn't you say. Also consider how long it took to build the first Mustang from concept to flight? What was it? 6 weeks?(I think) A considerably more complex aircraft. And these warbirds were not shoddily constructed.

GeeBeeZ1931 · **Joined:** Tue Feb 28, 2012 7:54 am **Posts:** 3

10kDA wrote:

The Munk M6 has a very soft stall due to the reflexed camber line. It's basically the same airfoil as on the Waco Taperwings, except the Taperwings have no cusp on the top surface. The numbers for the M6 and M12 show a very small change of center of pressure, that's why the racers used them - low trim drag, and predictable handling from the point of horsing the airplane off the ground at the racehorse start, climbing out, and attaining racing speeds. Benny Howard's Mike and Ike used the M6 as designed. Mr Mulligan used a M12. The M6 was a 12% thick airfoil. The Gee Bees used a M6 thinned to 65% of the original thickness, which gives about 7.8% thickness. Thin airfoils don't give a lot of warning at stall, and not a lot of margin for recovery, and don't always behave like a thicker version with the same camber line.

Chris

I have to ask this not being an airfoil expert. If an M6 airfoil is supposed to be 12% thick then reducing it to 7.8% would mean it's no longer an M6 wouldn't it?

mustanglover · **Posted:** Wed Feb 29, 2012 12:04 pm

GeeBeeZ1931 wrote:

Also consider how long it took to build the first Mustang from concept to flight? What was it? 6 weeks?(I think) A considerably more complex aircraft. And these warbirds were not shoddily constructed.

3.4 months or 102 days to be exact. That is from design start to delivery of completed aircraft to the flight test division.

F3A-1 · **Posted:** Fri Mar 02, 2012 11:05 am

skooterN2767K wrote:

I have been looking everywhere for airshow pics and especially video of the Kimball/Eicher Gee Bee Z replica. I believe Delmar flew it to Oshkosh '97 or '98 and did his aerobatic routine with it. I have found pics of it at OSH, but have never seen video anywhere of it flying. Anyone know of any place to find a video of it?? Thanks

Fantasy of Flight has just posted this video of Kermits first flight of his Gee Bee Z. It is intended for a somewhat younger audience. I loved it!

http://www.geebeefun.com/zeevideo.htm

Pirate Lex
http://www.BrewsterCorsair.com

airnutz · **Posted:** Mon Mar 05, 2012 5:37 am

Would you be mine? Could you be mine? Won't you be my neighbor?

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#2 GEE BEE Z Replica

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