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Author Topic: Propeller Clearance  (Read 22554 times)

Ric Gillespie

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Propeller Clearance
« on: November 28, 2012, 08:14:36 AM »

This thread is for discussions of the probable height above ground of the propeller tips of Earhart's Electra when it was parked on a flat surface.
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Tom Swearengen

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Re: Propeller Clearance
« Reply #1 on: November 28, 2012, 08:42:21 AM »

Hum--Ok----what is the slope of the reef, from the surf line to the beach? The more distance from the surfline, the less water there is on the reef, towards the beach, and the more clearance for the prop. IF the Electra was closer to the beach, then the prop could clear the water, even at a higher tide. If thats the case, and the Electra was closer to the beach, then how was the plane obscured from Lambrechts overflight----unless of course, the theory of the tide coming in an taking the plane over the reef edge is valid.
Tom
 
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Ric Gillespie

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Re: Propeller Clearance
« Reply #2 on: November 28, 2012, 08:49:18 AM »

Hum--Ok----what is the slope of the reef, from the surf line to the beach? The more distance from the surfline, the less water there is on the reef, towards the beach, and the more clearance for the prop. IF the Electra was closer to the beach, then the prop could clear the water, even at a higher tide. If thats the case, and the Electra was closer to the beach, then how was the plane obscured from Lambrechts overflight----unless of course, the theory of the tide coming in an taking the plane over the reef edge is valid.
Tom

That's not what we're discussing. I say again, "This thread is for discussions of the probable height above ground of the propeller tips of Earhart's Electra when it was parked on a flat surface."
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John Ousterhout

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Re: Propeller Clearance
« Reply #3 on: November 28, 2012, 09:38:27 AM »

Knowing the normal clearance from prop tip to the surface the tires are sitting on has some important ramifications to an Electra's ability to run its engine in any particular water depth.  A cross section of the Niku reef surface can be found here.  Depth of water over any particular portion of the reef at any particular point during normal tides is discussed elsewhere, largely in reference to radio transmission times (citation TBD).

(originally posted in Post Loss Transmissions. Solved?) In this Purdue collection photo, AE is standing in the same plane as the prop hubs, making it easy to make a fairly accurate measurement of their height compared to hers, without significant parallax.<snip>  Combined with her range of heights as 67 to 68 inches, these translate into indicated hub heights of 81.8 to 83.4 inches.<snip>  Simple pencil scaling indicates something close to 27 inches clearance from tip to ground, but there is some out of plane parallax foreshortening still needing to be accounted for, in that case.

In a subsequent post, Greg Daspit uses AutoCAD to obtain a tip clearance value of about 26 inches.

Alan Harris estimates a clearance of about 30 inches.

In absence of a direct measurement of Amelia's aircraft, we are seeking other means to calculate or estimate prop tip clearance over the parking surface.
Cheers,
JohnO
 
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Tom Swearengen

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Re: Propeller Clearance
« Reply #4 on: November 28, 2012, 11:23:58 AM »

Pardon my stupidity, but we wanted to know that why? To see if she could have run the engine, and how much water could be on the reef before the prop would hit the water. I respectfuly submit, that the water height is different at the surfline, than near the beach. If the Electra was at the surfline, that is one dimension, if nearer the beach a different dimension.
At least the beaches I've been to, slope toward the ocean. Some more than others. I'm not trying to be stupid Ric, but if you have 6 inches of water at the surfline, and the reef slopes upward to the beach level that is 5 feet higher in elevation, then if the Electra is nearer the beach, the props would NOT hit the water, and she could have run the engine successfully.
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Jon Romig

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Re: Propeller Clearance
« Reply #5 on: November 28, 2012, 05:00:39 PM »

Would measuring the Electra at the New England Air Museum going to help? I can visit over the Christmas holidays...
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Tom Swearengen

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Re: Propeller Clearance
« Reply #6 on: November 28, 2012, 05:09:28 PM »

Jon, I would think so, IF that plane was configured like NR16020. Same tires, wheels, landing gear (if there were any differences that had to do with tires and wheels), prop diameter, etc.
Thats an interesting question? To accomodate the larger tires and wheels for unimproved landing strips, I wonder if Lockheed put different gear with a gear fork (axle distance) on different Electras? WE know AE's was special.
Tom
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Ric Gillespie

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Re: Propeller Clearance
« Reply #7 on: November 28, 2012, 05:22:42 PM »

Pardon my stupidity, but we wanted to know that why? To see if she could have run the engine, and how much water could be on the reef before the prop would hit the water. I respectfuly submit, that the water height is different at the surfline, than near the beach. If the Electra was at the surfline, that is one dimension, if nearer the beach a different dimension.
At least the beaches I've been to, slope toward the ocean. Some more than others. I'm not trying to be stupid Ric, but if you have 6 inches of water at the surfline, and the reef slopes upward to the beach level that is 5 feet higher in elevation, then if the Electra is nearer the beach, the props would NOT hit the water, and she could have run the engine successfully.

We already have the information about water levels on the reef in different locations at different times.  We already have a hypothetical location for where the plane was parked on the reef. What we need to establish is the distance between the prop tip and level ground.
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Ric Gillespie

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Re: Propeller Clearance
« Reply #8 on: November 28, 2012, 05:28:24 PM »

Would measuring the Electra at the New England Air Museum going to help? I can visit over the Christmas holidays...

We've measured and photographed the wheels and tires on that airplane and they're different from the ones on NR16020 - but it would still be good to know the prop clearance for that airplane.  It's always good to have an excuse to visit an air museum.
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Bob Lanz

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Re: Propeller Clearance
« Reply #9 on: November 28, 2012, 06:04:14 PM »

Pardon my stupidity, but we wanted to know that why? To see if she could have run the engine, and how much water could be on the reef before the prop would hit the water. I respectfuly submit, that the water height is different at the surfline, than near the beach. If the Electra was at the surfline, that is one dimension, if nearer the beach a different dimension.
At least the beaches I've been to, slope toward the ocean. Some more than others. I'm not trying to be stupid Ric, but if you have 6 inches of water at the surfline, and the reef slopes upward to the beach level that is 5 feet higher in elevation, then if the Electra is nearer the beach, the props would NOT hit the water, and she could have run the engine successfully.

We already have the information about water levels on the reef in different locations at different times.  We already have a hypothetical location for where the plane was parked on the reef. What we need to establish is the distance between the prop tip and level ground.

Ric,

What criterion did you use to for the "hypothetical location for where the plane was parked"?
Doc
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Ric Gillespie

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Re: Propeller Clearance
« Reply #10 on: November 28, 2012, 06:33:44 PM »

What criterion did you use to for the "hypothetical location for where the plane was parked"?

That's not the topic of this thread. That will be covered in Brandenburg's tides paper.
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Alan Harris

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Re: Propeller Clearance
« Reply #11 on: November 28, 2012, 07:06:17 PM »

Knowing the normal clearance from prop tip to the surface the tires are sitting on has some important ramifications to an Electra's ability to run its engine in any particular water depth.
Exactly right, I agree about the importance and relevance.

Quote
Simple pencil scaling indicates something close to 27 inches clearance from tip to ground, but there is some out of plane parallax foreshortening still needing to be accounted for, in that case . . . Alan Harris estimates a clearance of about 30 inches.
My 30" is the result of using your hub height numbers and calculating/estimating the "foreshortening", although I used different words for it.  Actually I got 30 plus or minus 0.8, corresponding to your range of heights, but this is all so approximate it doesn't matter much.  As stated on the previous thread, we're never going to be precise.  Unknown variables include the Electra's fuel load (weight) in any given photo; and in the photo you used, John, the plane is on uneven sandy ground, giving uncertainty as to depth of the tires sinking into the sand and whether the plane is pitched up or down.  Note that I am not criticizing John or his work, the fuzzy data situation just "is what it is".

I will admit that I still have an unsupported and currently indefensible "gut feel", from looking at the various photos, that it's even greater than 30".  (Don't bother to attack that, as I can't/won't offer any reasoning, lol.)
« Last Edit: November 28, 2012, 07:27:53 PM by Alan Harris »
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John Ousterhout

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Re: Propeller Clearance
« Reply #12 on: November 28, 2012, 10:08:06 PM »

Alan Harris adds:
"(Don't bother to attack that, as I can't/won't offer any reasoning, lol.)"

Thanks for responding - no attack observed or intended. Like you, I prefer to avoid offering any "reasoned" line of defense, preferring to offer data, and opinions.  That being said, I'll simply try to apply known art to the question.  By projecting implied vanishing point construction lines to the photo, I still cannot visualize prop clearance greater than about 28 inches in the photo provided.  Please understand that the photo does not represent the hypothesized condition of an Electra on a Niku reef.  The loaded condition of the aircraft in the photo is unkown, as is the tilt or condition of the "landing" surface (Niku has no cacti, for example).  There are more unknown variables that would effect a "reef landed" condition.

There have been some other, previous, suggestions of prop clearance, based on things like Harney drawings, Museum representations, etc, that I think would be appropriate to add in here.  Please do so...
Cheers,
JohnO
 
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Dan Kelly

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Re: Propeller Clearance
« Reply #13 on: November 28, 2012, 11:08:59 PM »

Hum--Ok----what is the slope of the reef, from the surf line to the beach? The more distance from the surfline, the less water there is on the reef, towards the beach, and the more clearance for the prop. IF the Electra was closer to the beach, then the prop could clear the water, even at a higher tide. If thats the case, and the Electra was closer to the beach, then how was the plane obscured from Lambrechts overflight----unless of course, the theory of the tide coming in an taking the plane over the reef edge is valid.
Tom

That's not what we're discussing. I say again, "This thread is for discussions of the probable height above ground of the propeller tips of Earhart's Electra when it was parked on a flat surface."

With respect Mr Gillespie I would suggest that as the ability of Earhart to send messages depends upon the height of the Electra's propellor above the surface it was parked on then I'd say any discussion of tides and water levels at Nikumaroro that might prevent the propellors from turning is relevant to that. When I read this thread and the thread that was closed the big topic in everybody's minds isn't some hypothetical height on the Lockheed runway at Burbank, but on the reef at Nikumaroro because it is in that place that the capacity to send radio messages while on the ground is crucial to TIGHAR's theory. You have promised a new paper from Mr Brandenburg that will quieten the discussion but when is that going to be available - if you'll forgive the suggestion it ought to be sooner rather than later. Otherwise folks will discuss it.   
« Last Edit: November 28, 2012, 11:13:08 PM by Dan Kelly »
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Greg Daspit

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Re: Propeller Clearance
« Reply #14 on: November 29, 2012, 05:54:53 PM »

This PDF shows two different pictures.

A side view where the drawings was scaled to get the cowl to 53.5” then the prop drawn in in at 9’. A line was projected from the wheel and a prop clearance obtained of 3’-0 1/16”. I found it difficult to find where the top of the cowl was and used my best guess.

The head-on picture was re scaled so the prop was 9'-0". AE ended up being about 5’-7  1/16” tall doing this. The clearance obtained was 2’-3 7/16”. The side view was used  to determine the angle so I could get the prop ellipse. Note, if AE was aligned with the prop at the angle shown, the prop would be in front of her at its lowest point and the dimensions obtained would be different (basically moving the line under AE's feet closer to the bottom of the photo and getting a bigger clearance number.)

The method used obviously has some error to it and/or there are other factors such as fuel load, ground level, ground stability, camera angle, etc., causing different numbers. I'm not sure about the prop dimension and cowl dimension. (I got that 53.5" number from another thread and in this link)
3971R
 
« Last Edit: November 29, 2012, 08:18:15 PM by Gregory Lee Daspit »
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