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Old 21 March 2008, 01:49 PM   #1
Varese2002
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Exclamation Kees' Korner #7

In the very irregular series of Kees' Korner.

On August 10, 1918 at Talmas (France) a German giant bomber was shot down. This machine was the Staaken R.XIV R 43/17 in its last configuration with 5 Maybach Mb.IVa high compression engines of 245 hp each (1). The giant bomber was severely damaged because of the crash naturally, but also by an explosion of a bomb still inside the fuselage.

(1) G W Haddow and Peter M. Grosz. The German Giants.

The machine was examined by the British (as it was probably in their part of the front) and parts were salvaged for later analysis.

Analysis were made by the Air Ministry - Directorate of Research - who published reports on different aspects of this machine. One of these reports is H.706 Enemy Engine Report No.16 dating from June 1919, with the title 'Reduction Gears used on Five-Engined Giant Gotha Bomber'.



The following is said about the PROPELLER HUB.

Quote:
The propeller hub is of the same construction as that used on the standard 300 H.P. Maybach engines, but is, of course, of very much larger proportions.
.....
As the air screws revolve at half engine speed, and have therefore a moderately light centrifugal load, they are made of a common wood which would scarcely be safe for direct driving screws.
Although fitted to 300 H.P. Maybach engines, they are marked 260 p.s. (h.p.) Mercedes. The diameter is 14.2 ft. [4,32 meter], and the pitch 10.82 ft. [3.30 meter] for the pusher screw, but unfortunately, owing to the propellers being badly damaged, not only by the crash, but by fire, it is not possible to state whether the tractor screws are of the same dimensions and pitch.

The construction is very interesting; each screw is made of seventeen laminations of what appears to be soft pine, and these laminations are themselves in pieces, and do not run continuously from tip to tip. They are, of course, staggered, so that the joints in successive layers do not coincide. Two plies of very thin birch veneer are wrapped round the blades. The grain of this veneer runs across the blade instead of along it.
This part of the report brings a few questions:
  • power of the Maybach is differently quoted 300 hp <-> 245 hp makes quite a difference
  • the remark over the use of lesser wood. Thinking about it, it is safe to use this lesser wood as (through the reduction gear) screws were revolving at half the speed of the direct drive version. THere was no reason for extra strength.
  • Lightly tipped over by the British, but it is decidedly incongruous to use a specially designed 260 hp Mercedes airscrew on a 300 hp Maybach? Or is it?
  • The 17 laminations seem to be a record number for one airscrew. It seems to me the total airscrew is a rather special construction.
  • Any data what german manufacturer made this airscrew?

And last but not least, as this reduction gear and as I think one propeller were closely examnied by the British, has this propeller made it to a museum or did it end in the fire for heating?

Cheers

Kees
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Old 22 March 2008, 07:41 AM   #2
m9a3r5i7o2n
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The thing I find interesting in this is the very fact that the British found it necessary to even examine and publish a report on the gears/pinions & idlers of a downed aircraft. Just why would go to all this trouble if there wasn't something different in this particular case.
I wonder if the reduction wheels did or did not have, for that time, a special type of tooth and or a special heat treatment that made an examination of extreme interest to the gear cutting industry?
A reading of the report would be of extreme interest to the gear manufacturers as a whole if that were the case
M.L. Anderson
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Old 22 March 2008, 09:11 AM   #3
Varese2002
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Quote:
Originally Posted by m9a3r5i7o2n View Post
The thing I find interesting in this is the very fact that the British found it necessary to even examine and publish a report on the gears/pinions & idlers of a downed aircraft. Just why would go to all this trouble if there wasn't something different in this particular case.
I wonder if the reduction wheels did or did not have, for that time, a special type of tooth and or a special heat treatment that made an examination of extreme interest to the gear cutting industry?
A reading of the report would be of extreme interest to the gear manufacturers as a whole if that were the case
M.L. Anderson
You have an interesting point. Why doing all this analysis and measurements if there is nothing special in it or something to learn for. In the complete report (17 pages inclusing drawings and photographs) there is not a single word pointing to a special construction or something to 'learn'.
I have not seen other reports from those times about German technology, but almost certainly none of them would praise German construction techniques or designs. It was just after the war so admitting that there was something in the technology of the 'looser' was not even a possibility.

So, from the report one cannot see the actual reason why it was done and published. Surely someone thought it worthwhile, but it was improper to say so.

I have not found anything about this report in the contemporary avaiation magazines like Flight. The number 16 in this Engine Enemy Report gives the impression that quite an effort was made by the English to analyze and study German technology.

Cheers

Kees
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Old 24 March 2008, 03:42 AM   #4
YavorD
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In my humble opinion, French, British and German engine manufacturers went into a deep trouble trying to produce reliable high-speed geared-down engines. Small wonder any example was worth studying.
Regards,
Yavor
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Old 24 March 2008, 04:34 AM   #5
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gearing down

this is interesting... can someone help me understand the physics of this?
does the gearing down work like a bicycle gear so that one r.p.m. of the engine translates into less than one r.p.m. of the propeller? and why is it an advantage to have the propeller turn more slowly? is it a question of same power with less torque?

as a non-engineer, these are the sorts of questions that haunt me when i try to understand the technical descriptions. much obliged!
marc
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Old 24 March 2008, 06:40 AM   #6
Varese2002
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Quoting from the original report

Quote:
GENERAL DESCRIPTION.
In each reduction gear the ratio of engine to propeller speed is the same, the gear reduction being approximately half engine speed -i.e., 41 / 21 - and, as shown in the illustrations, the design of the reduction gear is such that the axis of the propeller is raised 217 mm above that of the crankshaft.

The use of these reduction gears necessitates the fitting of a light flywheel to each of the engines. The flywheels are 400 mm. in diameter. and are made of cast-iron. On the inside of each flywheel is fitted the female portion of a flexible coupling. These couplings are of a similar design to the couplings used with the 240 H.P. Maybach engines in the earlier types of Zeppelin airships, and consist of a male and female drum made of aluminium, each
furnished with circumferential recesses, into which are fitted a series of twelve flat leather pads or blocks which take the drive. These leather blocks are built up of a number of small strips of tough leather clamped and rivetted together by two steel plates at the edges.
The general design of the flexible driving coupling is shown in section in the General Arrangement Drawing, Fig. 12. The male portion of the coupling, which is also of aluminium, is secured by eight bolts, and engaged by means of sixteen splines with the flanged end of a sleeve, which is mounted on the rear end extension of the driving pinion.
This sleeve is fitted to the driving spur pinion extension by six splines, and is secured in position by a screwed plug, as shown in section in the drawing.
This is the general arrangement drawing



When you click on this one you go to Webshots and get the original size of the drawing.

Looking from a distance in time to this construction, I think it is an engineering marvel, roller bearings, flexible couplings etc. And that was only a small (but essential part of the Staaken R.XIV).

Why all this work to throttle down from high revs to (lower) revolutions of the propeller. Well others are better equipped to tell this (Yavor ?) but it comes down theoretically that a slow turning airscrew moves a lot more of air.

I have a correction on my earlier piece of faint praise of the British. In the first sectence I read:

Quote:
The following illustrated report on the design and construction of an interesting type of oil-cooled reduction gear, used in the most recent enemy Giant Bomber,.......................
Mark the word interesting

Cheers

Kees
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Old 25 March 2008, 11:28 AM   #7
m9a3r5i7o2n
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Kees
I wonder if the leather pieces were there to also do a double duty possibly not only to take care of flexing of the propeller shaft but also to do some reduction of some torsional vibration? Altogether it is very interesting. One must also remember that this was after the Torsional Vibration Dampener for Six Cylinder engines was patented by Frederick William Lanchester around 1910 or so.

Also interesting is the place where it states the dimensions are on pages 10,11 & 12 I would like to know if it is straight cut tooth, i.e. is it a helical tooth or what, how wide is the gear and pinion?

You also mention Oil Cooled gears & pinion wheels to which I add that the oil cooling of the teeth is probably more important than the lubrication of the teeth as the oil cannot lubricate if gets overly hot and loses its viscosity.
M.L. Anderson

Last edited by m9a3r5i7o2n; 25 March 2008 at 03:11 PM.
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Old 25 March 2008, 12:40 PM   #8
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Kees,

Thank you for publishing details of the report. I would like to use the drawing of the reduction gear in my book on German props if I may.

A record of props from shot down German aircraft from the NRO Kew states that this prop was made by Garuda. The quality of the wood indicates the desperate shortages existing in Germany towards the end of the war caused by the successful British blockade by ships of the Royal Navy. Idflieg progressivly authorised the use of poorer quality woods from 1916 onwards.

With regards,

Bob
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Old 25 March 2008, 02:33 PM   #9
Varese2002
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Quote:
Originally Posted by m9a3r5i7o2n View Post
Kees
I wonder if the leather pieces were there to also do a double duty possibly not only to take care of flexing of the propeller shaft but also to do some reduction of some torsional vibration? Altogether it is very interesting. One must also remember that this after the Torsional Vibration Dampener for Six Cylinder engines was patented by Frederick William Lanchester around 1910 or so.

Also interesting is the place where it states the dimensions are on pages 10,11 & 12 I would like to know if it is straight cut tooth, i.e. is it a helical tooth or what, how wide is the gear and pinion?

You also mention Oil Cooled gears & pinion wheels to which I add that the oil cooling of the teeth is probably more important than the lubrication of the teeth as the oil cannot lubricate if gets overly hot and loses its viscosity.
M.L. Anderson
Hi M.L. Anderson.

About lubrication the following is stated in the report

Quote:
LUBRICATION SYSTEM.
In action, the efficient lubrication of the spur gears and their bearings is assured by the constant supply of cooled oil from the radiator below the gear case (a separate test report of which is attached). Oil is forced by the pump through an external pipe to the front of the main roller and thrust bearings, and also fed on to the spur gears through a union screwed into the tope of the case, the oil returning by gravity through the case to the oil radiator below.
So oil was constantly cooled as the engineers were aware that too hot oil would loose its lubrication power and everything would come to a halt . Of course if the oil cooler malfunctioned the same would happen.




The measurements made are certainly very detailed







Interesting is the remark on page 12 that the material resembles Duralumin. From the outside it also looks special that measuremts are a mix of metric and inches.

There is no further mention in the text about the leather pieces, probably your explanation about reduction of torsional vibration fits. I looked a bit around for the patent of Lanchester, Frederick William but got quickly that he had 119 patents on his name !!


Cheers

Kees
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Old 25 March 2008, 02:43 PM   #10
Varese2002
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Quote:
Originally Posted by rc.gardner View Post
Kees,

Thank you for publishing details of the report. I would like to use the drawing of the reduction gear in my book on German props if I may.

A record of props from shot down German aircraft from the NRO Kew states that this prop was made by Garuda. The quality of the wood indicates the desperate shortages existing in Germany towards the end of the war caused by the successful British blockade by ships of the Royal Navy. Idflieg progressivly authorised the use of poorer quality woods from 1916 onwards.

With regards,

Bob
Hi Bob. These are the only pictures in the report showing the rest of the propellers.



Shortage of propellers was probably so great at the end of the war that a propeller for a Mercedes was fitted to a Maybach.

Cheers

Kees
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