Propeller-Clearance Question

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Zipper730

Chief Master Sergeant
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Nov 9, 2015
I'm curious if there were any figures that existed in the years leading up to and during the early years of WWII (later on larger propellers and the desire for superior performance led to these requirements being relaxed) regarding the minimum propeller clearance from tip to ground for aircraft in the US and UK (as well as Germany, the USSR, and Japan if applicable)?

I'm curious if the numbers vary for conventional-geared and tricycle-geared aircraft.

fubar57 , GregP , M MIflyer , MiTasol , P pbehn , S Shortround6 , swampyankee , W wuzak , X XBe02Drvr
 
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SaparotRob said:
Well, it can't be that critical. The renowned Dr. Christmas, a man asked by the Kaiser to take over the German aircraft industry, just sawed off some of the propeller that didn't clear the ground.
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Yes, but he did have to know how much to cut off didn't he? For example did the propeller have to be 5-6" off the ground? Was this with the shock-absorbers uncompressed or fully compressed, etc?
 
SaparotRob said:
Rules? Regulations? Dr. Christmas was a fraud.
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Well I know he was a fraud, but the plane was nonetheless built (and offed two pilots who flew the plane). I was curious by the 1930's if the USAAC or RAF had some kind of rule in place that dictated propeller clearance.

There seemed to eventually be a rule that dictated 7" between the propeller and the ground in a tricycle-gear and 9" in a conventional gear when in when the gear is statically deflected and in the level takeoff/taxiing atitude. I'm not sure when this came into being.
 
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The Bf 109 E certainly looks to be below the 25cm figure in the horizontal flying position. I am making the tip clearance less than 25cm with the aircraft on jacks for gun sighting checks.
In the rigged position, the aircraft is usually supported on the underfuselage trestle and the tail trestle taking the 2,000kg+ weight, with the mainwheels just lightly touching the ground and the aircraft restrained with tie-downs. So the undercarriage legs are not compressed and at full travel will be similar to the clearance shown, meaning, very little clearance with a firm touchdown in a horizontal position!
Someone might have the factory diagrams of the prop clearance?

Eng

Here is a pic of a Bf 109 E having weapon sighting checks.

 
Thumpalumpacus said:
A little less than ten inches for the Western audience.
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In the USSR, 250mm was considered to be the height of a "standard hummock".

There was a comical case - Sylvansky's I-220 - may be, too comical even for the USSR, when the clearance was 220 mm, the designer decided to shorten the propeller blades by 100 mm (according to legend it was done with a hacksaw), as a result the airplane could hardly take off.
 
The rigging diagram in the ModelArt Bf109B-E had the top of the propeller at 3,432mm when vertical and in flying attitude. And the propeller diameter as 3,150mm. Which give a clearance of 282mm (a little under 3 hands for that country which will use anything but metric system ).
 
It also appears to have a relief area cast in the concrete as a safety measure.
 
Engineman said:
The Bf 109 E certainly looks to be below the 25cm figure in the horizontal flying position.
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It's probably an illusion. I tried to estimate the clearance from several drawings taking into account the compression of the undercarriage legs under loading, I got a minimum of about 300 mm.
For example, according to this drawing the clearance is about 350 mm:

In fact, I believe the actual clearance in Soviet aircraft may have been less than recommended. According to the La-5FN test report at Rechlin, the clearance was considered too small for safe takeoff/landing. The Yak-7M-82 could not be fitted with a propeller of the required diameter because the landing gear legs were too short - in general, different propellers were used on the Yaks, differing in diameter by 200 mm, so I don't have a full understanding of the situation yet.
 
The Royal Navy had issues with early Seafires 'deck pecking' if the nose dipped on braking. The on board solution was just to saw off 6" from the propellor tips which slightly improved performance and solved the 'deck pecking '. The problem was not airframes nor engines being damaged but they were simply running out of replacement propellors on board. As to how they balanced them I do not know.

In the words of EmileLevassor 'c'est brutale mais ça marche'. Crude but it works. He was speaking of the crash car gearbox pre Great War.
 
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