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Author Topic: FAQ: Visually Estimating Electra Tire Diameter - old photos  (Read 46866 times)

John M Kirk

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Re: Electra Tire Diameter
« Reply #15 on: June 12, 2012, 11:57:59 AM »

The following is from a retired Navy submariner... who is not an engineer.. so, be kind and gentle..  This is nothing more than a guess (swag).

Based on the 55 gal drum (actually 44 gallons), divide the drum into 6 sections.  You can then say the tire is approx. 5/6 the height of the drum.

The tire is also squatting approx 3-4" (swag), this needs to be added to the total.

5/6 height of tire = 28"
tire squat =            3-4"
total =                  31-32"

Now, the drum is not beside the tire.  If you move the drum back, you could add 2-3" (swag), which would be around the 34-35" size... See attached (crude) dwg...  Please share your thoughts...

John
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Heath Smith

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Re: Electra Tire Diameter
« Reply #16 on: June 12, 2012, 12:55:23 PM »


John,

No worries about swags, that is all we are doing here.

If you look closely, there is a tiny sliver if light behind the drum and before the shadow (lower-right) suggesting that the back of the drum is very close to the tire.

If you measure the drum at it's left edge, you would need to add approximately 22.5 / 2 inches to the distance of the drum to put the left edge of the barrel next to the tire.

Just roughly calculating a 9% reduction in the barrel height, I would still say that the barrel is 2-3 inches taller than the tire if they were on the same plane.

Just as an experiment, if you assume that the rim in 8" in diameter, what is the height of the tire not attempting to correct for deflection?
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Bruce Thomas

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Re: Electra Tire Diameter
« Reply #17 on: June 12, 2012, 01:31:43 PM »

It’s viewing examples like this video that makes me realize that inferring relative size of various objects in a photograph is best left to those who have mastered the very complicated science of photogrammetry.

From what height was the picture taken?  Was the photographer down on one knee?  That’s what it looks like to me ... and that could help form a mental image of the 55 gallon drum looking “obviously” taller than the tire.

John Kirk’s cogent explanation of how the perspective in the picture containing the 55 gallon drum could be misleading about size comparison is compelling to me ... along with the splendid reminder of “tire squat” (which Andrew McKenna alluded to when he spoke of "the uncompressed height of the tire") for the tire accounting for some of the measurement discrepancy that Heath is fixated on.

My money is on the aircraft inspection report, combined with the training of persons professionally trained and working in the field of forensic photo analysis.

Talking about tires, and making inferences from flawed premises, reminds me of a favorite saying of a famous person who ran the company I spent my career with:  "Si mi abuela tuviera ruedas seria bicicleta."
LTM,

Bruce
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John M Kirk

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Re: Electra Tire Diameter
« Reply #18 on: June 12, 2012, 02:37:27 PM »

Bruce, based on your comments, me having to refer to Webster, the photo, and the inspection report, my final answer is 35",  I believe I came close to the 35".  My swag was 34".  So, this means I could possibly go on the next excursion??? lol.  I am very good with a metal detector..

You guys, keep up the good work.. Very nice site, and very informative.

jk
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John Ousterhout

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Re: Electra Tire Diameter
« Reply #19 on: June 12, 2012, 07:49:05 PM »

Heath's photo doesn't show the bottom of the drums or the tire, so it is not useful to judge relative sizes.
Cheers,
JohnO
 
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John Ousterhout

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Re: Electra Tire Diameter
« Reply #20 on: June 13, 2012, 07:27:39 AM »

Heath,
good catch, I missed seeing the barrel with the 3 guys until I opened the photo.  Now if we could only see the bottom of the tire.  The camera angle/altitude relative to the drums and tire appears to be fairly high, making judging heights difficult.  The drum is roughly on the aircraft centerline (the hose appears to touch the nose), making the port landing gear about 6 feet closer to the camera.  That should make the port tire appear larger than an equally tall barrel, but to be sure the tire and barrel image dimensions need to be measured from top to bottom, not just comparing the tops.  The barrel looks unusually large/tall, relative to the 3 guys.  Maybe they're quite short? 

Is the tall man standing on the wing, wearing dark clothes, Fred Noonan?  Wasn't he about 6 feet tall?  A standard 55 gallon barrel is 35 inches tall, or about equal to a tall man's trouser inseam.

The paint on the leading edge is clearly visible in the photo, which might interest some folks over in the artifact thread.
Cheers,
JohnO
 
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John Ousterhout

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Re: Electra Tire Diameter
« Reply #21 on: June 13, 2012, 08:21:28 AM »

According to The Wreck Photo, the cowling is about 54 inches diameter.  Since it's fully visible, and on nearly the same plane as the tire, and not greatly forshortened by goofy angles, they're rather easy to measure and estimate the tire diameter.  On my screen I measure the cowling as 33 mm, and the tire as 20-1/2 mm, for a tire/cowling ratio of 0.62.  Times 54 inches = 33-1/2 inches diameter for the tire. 
There's obviously some margin of error with my method.  For example, my plastic measuring stick is only useful for measuring to the nearest 1/2 mm, so each measurement has a potential error of +/- 1/4 mm, giving a potential range from 32.9 to 34.2 inches.  There are additional potential errors that make the possible range a bit greater, but I think it is safe to say the tire is more than 30 inches in diameter.
Cheers,
JohnO
 
« Last Edit: June 13, 2012, 03:18:16 PM by John Ousterhout »
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Andrew M McKenna

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Re: Electra Tire Diameter
« Reply #22 on: June 13, 2012, 02:48:33 PM »

Instead of trying to compare the tire with the barrel, why not work it backwards from the wheel hub? 

We know that the 6 inch hub was "standard" issue, and if so, what do you guys calculate the tire diameter to be?  How much "uncompressed" rubber is there above the hub?

We also know that there was also an 8 inch hub, as seen in the NEAM photo, and if that is what we see in the AE photo, what would the diameter be?

AMCK
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Heath Smith

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Re: Electra Tire Diameter
« Reply #23 on: June 13, 2012, 02:57:10 PM »


Andrew,

Assuming that the visible part of the rim is 8 inches, I would estimate the red line shown on this photo would measure 14 inches.

If the tire is deflated as on some of the other photos, it could be a 30 to 32 inch tire.

It not the greatest photo because we cannot see the bottom of the tire.
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Heath Smith

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Re: Electra Tire Diameter
« Reply #24 on: June 13, 2012, 03:04:43 PM »


Here is the shot with the somewhat deflated tire. I estimate the red line to be 27.6 inches assuming the outer rim is 8 inches.
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John Ousterhout

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Re: Electra Tire Diameter
« Reply #25 on: June 13, 2012, 03:35:11 PM »

I worked out the wheel rim diameter a little differently, again using Heath's photo, blown up on my screen to allow better resolution when reading my mm scale, and again using the 54 inch cowling diameter as a reference for comparison.  I obtain a tire diameter of 33.3 inches +/- about a half inch, and a visible hub diameter of 9.6 inches, +/- about the same half inch.  Just how deep is the edge of the rim on an 8-inch, and on a 6-inch hub?  The "8-inch" or "6-inch" measurement is the diameter of the hole in the tire, not the edge of the wheel rim.
Somewhere there must be a record of the actual outer diameter of the 6-inch and 8-inch wheel hubs.
Cheers,
JohnO
 
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Heath Smith

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Re: Electra Tire Diameter
« Reply #26 on: June 13, 2012, 06:07:53 PM »


Double checking Johns work, I came out with the exact same numbers if the hub is 9.6 inches.

The hub that meets the tire is smaller than the outer visible rim. The museum tire for example possibly has a 6 inch diameter hub where it meets the tire and an 8 inch visible outer rim.
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Heath Smith

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Re: Electra Tire Diameter
« Reply #27 on: June 13, 2012, 07:51:35 PM »


Here is something else that we can compare. I do not have time today but perhaps tomorrow.

On the museum wheel, my estimate for the axle tube is 2", the outer rim is 8". Keep in mind that the face the 2" tube is about 6" closer than the rim.

Now if a different rim were used to for larger tires, and that rim was say 9.6 inches, the axle tube should still measure around 2" unless the entire fork was swapped out.
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John Ousterhout

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Re: Electra Tire Diameter
« Reply #28 on: June 13, 2012, 08:49:46 PM »

I was under the impression that AE's Electra was fitted with the oversize tires, requiring custom forks.  I don't know if that would also change the axle tube diameter.  I'll look for a reference...
Cheers,
JohnO
 
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Andrew M McKenna

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Re: Electra Tire Diameter
« Reply #29 on: June 14, 2012, 01:36:47 AM »

Re-reading this thread a bit, it is clear, as Woody pointed out, that the aircraft was equipped with Goodyear 35x15-6 tires and a Goodyear 6HBA Airwheel when it left the Lockheed repair shop, as indicated in the inspection report.

The photo of the Airwheel assembly found here may help explain the apparent diameter of the hub vs the 6 inch designation.



I'm not sure why we're still speculating on the size of the tires given the inspection report.

Andrew
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