FAQ: Visually Estimating Electra Tire Diameter - old photos

Heath Smith · June 10, 2012, 01:24:05 PM

I have found several references to the Electra tire size being 35 inches (2000 article) to 36 inches. Glickman's photo analysis suggested that the tire size was also 36 inches.

Some time ago, there was a reference to the size of the hub being 8 inches. Is this the case?

If the hub is about 8 inches in diameter, according to my crude attempt to measure the tire, this would suggest that the tire is only about 26 inches in diameter.

Does anyone have a definitive answer?

If you have better photos, please pass them on.

Thanks in advance.

Chris Johnson · June 10, 2012, 02:25:53 PM

Does this help?

Wheel Of Fortune / Electra wheel details

Heath Smith · June 10, 2012, 02:30:17 PM

Chris,

That does show a hub about 8 inches in diameter but that is not the actual Electra from AEs plane.

That tire also ends up being about 26 inches in diameter.

Andrew M McKenna · June 10, 2012, 03:25:50 PM

The diameter of the tire doesn't change no matter what the size of the hub, it is still a 35 inch diameter tire measured from side to side across the middle, the hub simply takes up the center section and fills the "hole" in the tire.

Looking at the material in the WOF link Chris provided, the standard Electra tire was a Goodyear "Airwheel" - "Goodyear Airwheels and heavy duty tires were standard equipment on all Lockheed Model 10 Electras. The size was 35x15-6. The 35 refers to the uncompressed height of the tire, the 15 refers to the width across the face of the tire, and the 6 is the diameter of the opening in the middle of the tire, all in inches. Lockheed publication EE1135 revised 5/1/36."

So if the hub is 6 inches across, you'd have 14.5 inches of rubber sidewall on either side of the hub for a total of 35 inches in diameter.

Andrew

Heath Smith · June 10, 2012, 04:15:32 PM

As you can see in the 1st photo (below), the rim is measured at 8 inches. Although it is not a perfect picture, the rim is certainly not 6 inches. The diameter of the rim where it meets the tire might be 6 inches, but the outer rim is 8 inches.

If we assume the outer rim is 8 inches as shown, picture #2 shows that the shown tire is not 36 inches. It is more like 26 inches.

Along with these photos is the description "As shown in this photo of the Goodyear Airwheel on Lockheed 10A c/n 1052 at the New England Air Museum".

So the question is, is the tire and rim shown in these photos supposed to be the exact same as those on the Electra?

Greg Daspit · June 10, 2012, 10:44:44 PM

From the catalog in the link Chris posted the hub is 6". The rims on the outboard side is probably 8" and the inboard rim looks even bigger, with a disk brake. The donut shaped balloon tire likely ordered by the hub, not the rim size.

Andrew M McKenna · June 11, 2012, 12:22:31 AM

I think the 1936 Lockheed publication is more accurate for the configuration of AE's Electra. it Clearly states that the standard issue was the 35x15-6 Airwheel.

The Aircraft at NEAM has had many years to be modified, and it is not unlikely that Goodyear offered an 8 inch Airwheel with a smaller tire sometime during the past 75 years, particularly as airport runways improved. I would not take the NEAM aircraft configuration as exactly like AE's, but at least a good example of the Goodyear Airwheel.

Andrew

Heath Smith · June 11, 2012, 04:24:54 AM

I believe this photo is after the Hawaii crash as it has the sector gear for retracting the landing gear. This shows the inboard hub and the brake line. This should be a pretty good reference for measuring the tire size.

Just doing a quick experiment with a wood yard stick, crouching like Earhart was, I am already inclined to believe that the tire shown is also not 36 inches. I am 5'11 and I believe she was 5'7.

Monty Fowler · June 11, 2012, 06:18:38 PM

And, respectfully, this is sliding into Jeff Glickman territory. He's the pro from Dover on all things photographic when TIGHAR wants to know something definitive about a picture.

LTM, who knows an expert is someone who knows when to bring in the experts,
Monty Fowler, TIGHAR No. 2189 CER

C.W. Herndon · June 12, 2012, 07:07:29 AM

Heath, If you look closely at the "guy" behind the tire in your picture he is not sitting but rather crouching just as AE is. When you look at a picture it is very difficult to compare the scale of two items unless they are next to each other and in the same plane.

I am 5'8" tall and tried your experiment with the yardstick. I crouched down and leaned forward slightly as AE is doing in the picture. The top of the yardstick came up to my mouth.

C.W. Herndon · June 12, 2012, 09:07:52 AM

Heath, I concur that the diameter of the tire shown is probably 28 inches. However the caption with the picture in your reference further states "This photo shows a Goodyear Airwheel on Lockheed 10A c/n 1052 at the New England Air Museum with a 4-inch obstruction."

On 5-19-37 the Department of Commerce, Bureau of Air Commerce, re-certified NR-16020 for flight after the repairs necessary from the Luke Field accident. The Aircraft Inspection Report ,which is attached below, says on page 2, that the tires on the aircraft were 35x15-6, 8 Ply Goodyear 6HBA.

Heath Smith · June 12, 2012, 10:00:44 AM

The page that I posted in reference to the 28 inch diameter was not in reference to the one that the museum. You can approximate the museum tire to about around 30 inches just using the tape measure in the foreground.

Landing on the Reef?

Quote"NR16020 was equipped with low-pressure, 28 inch, Goodyear Airwheels. These tires were designed for operations from unimproved airfields. The aircraft should be able to land safely on a hard surface with perturbations not exceeding four inches in height or depth."

Note that this specifically mentions Earhart's plane (NR16020), and is not a generic statement about L10Es nor is it a reference to the one at the museum.

That is interesting about the inspection report declaring a 35 inch tire, that is not what I estimate and seems to be in conflict with the TIGHAR's statement above.

Despite the report, I would say that photographic evidence trumps a document. There are plenty of photographs to analyze as they made their way across Africa, Indonesia, Australia, and Lae.

Martin X. Moleski, SJ · June 12, 2012, 10:32:28 AM

Quote from: Heath Smith on June 12, 2012, 08:24:28 AM

According to this page:

"NR16020 was equipped with low-pressure, 28 inch, Goodyear Airwheels. These tires were designed for operations from unimproved airfields. The aircraft should be able to land safely on a hard surface with perturbations not exceeding four inches in height or depth."

I concur with that measurement.

I am the person who placed that page in the wiki.

I can't find my original source. It may have been an older research paper that is now no longer available on the Forum--perhaps from the Eighth Edition of the Earhart Project Book.

I've revised the article, given that the list of standard equipment as well as the last inspection confirm the larger tire size.

James G. Stoveken · June 12, 2012, 10:54:52 AM

Quote from: C.W. Herndon on June 12, 2012, 09:07:52 AM
The Lochheed 10A was a smaller aircraft than the 10E and used a smaller tire.

I believe all models of the Lockheed 10 series were the same size, the difference between the models being engine make and HP. The Lockheed 12's were smaller. Of course, this doesn't mean that all model 10's used the same size tires. There were probably options available determined by the projected use of the aircraft.

Heath Smith · June 12, 2012, 11:05:26 AM

I can only say that it is good that we have lots of photographs to analyze.

For anyone interested, I believe Earhart was about 5'7", figure a 1 inch heel, she would be about 5'8". The cowling opening is about 37" and I believe the prop is about 9ft.

The drum is more than likely a standard oil drum about 22.5 inches in diameter and 33.5 inches high.