Propeller Air-Screw Research...

[xylstra]

I have a few topics that I hope will provoke some interesting discussion as well as yield answers to questions I have.

Experimental PROPELLER AIRSCREWS for piston engine aircraft.

Topic #1: During the 1920's on through to the 1940's and even a few beyond that there have been some advocates and indeed, practical experimental hardware made to investigate speed changing fixed-pitch propellers. Nearly all have been low/high 2-speed reduction gearboxes. However, I have never yet been able to locate any substantive detail (i.e. research papers, pictures, diagrams, etc, etc). I believe Armstrong-Siddeley conducted some research into this topic in the 1920's/'30's and very late, the mighty LYCOMING XR 7755 sported a high/low speed propeller gearbox this, in particular would have been of interest to learn more of its inner workings but none, so far as I've been able to find. Moreover, such little information (mostly, often just a single sentence) as I've been able to find has usually originated only from Western, English-speaking countries but nothing of, say, middle/Eastern Europe or the the Asian far-East...

which conveniently leads me into....

Topic #2: What and how was propeller airscrew research was conducted in the axis countries for example, look at the far-reaching Japanese experimental R D work conducted and evidenced by the 6-blader unit employed on the gorgeous Kyushu Shinden J7W1 and other late prototype aircraft. But of Japanese airscrew R D we seem to know very little e.g. the names of the researchers and the institutions they worked for, testing facilities (wind-tunnels, etc), published technical papers, photographs, etc.

So, is there anyone out there with their hand on the valve controlling the information-fountain who wouldn't mind giving it a flick and putting me out of my misery!

(NB. Just a useful hint: try taking a look at: enginehistory.org/References/UKNA/Prop-AVIA.shtml which contains a brilliant table of papers held at discover.nationalarchives.gov.uk )

 

[xylstra]

Hi Folks,
In the intervening month since I made my initial post I have been a little disappointed with the lack of information but for my part, I've not been idle! With much further digging I've hit pay-dirt albeit not the mother-load but still, a rich vein of glinting gold specks which I will share with you now.
Though not confirmed, it appears the Armstrong-Siddeley research I referred to was undertaken by one Thomas Pitt (TP) de Paravicini whose technical research paper (Reference: PA1716/3/3/8, 10th March, 1941) is recorded - though frustratingly - not accessible on the discovery.nationalarchives.gov.uk database, entitled "2-speed multi-speed airscrew gears". The paper is physically held at the Coventry History Centre (U.K.). Anybody able to swing by and grab a copy?!
Also, have a look at his British Patent: GB460149(A)-1937-01-19.
Another extremely interesting fountain of information has emerged in the form of US Patent#: 2,482,460A assigned to Wright Aeronautical Corporation. What is of additional interest is that if you scroll doen to the bottom of the patent (off-screen), additional links to other related patents appear - VERY interesting! NB You'll need to use Google's CHROME browser for the patent information to render properly (Web-Search: Google Advanced Patent Search).
Although all of this has in some way helped to answer my own question, don't slack-off, there's still much more information out there somewhere so everyone keep on digging!

 

[WJPearce]

Hello,

Attached are the two patents you referenced. Perhaps making this information easily accessible will help bring more info to light.

For a fee, you can get some documents from the Coventry History Centre. I think what they charge is based on how much work they need to expend digitizing the documents. I don't think they do it regularly as there is not a set process in place. If you are interested in paying for the document, I can send you contact info to try and get the process started. It took me two months to get what I wanted, so patience is required.

For the Lycoming XR-7755, different nose cases would allow the engine to be single-speed and single rotation, two-speed and single rotation, single-speed and dual rotation, and two-speed and dual rotation. The single speed would have a .32:1 reduction while the two-speed would have .38:1 and .24:1 gear reductions. The XR-7755 in the NASM is the -3 which has contra props and two-speed gear reduction, but I don't know how it works.

Detailed below is how the two-speed propeller gear box worked for the Studebaker XH-9350 (the what?). The engine was never built but the gear box was. It was a remote unit that was not attached to the engine. The 24-cylinder XH-9350 was meant for use in large, long-range bombers and transports.

The XH-9350 employed a two-speed gear unit between the engine and the final contra-rotating gear reduction unit. The two-speed gear reduction unit was used to keep the propeller rpm within the range of maximum efficiency for its size. With the XH-9350 running at cruise speed (low rpm), the two-speed unit allowed a direct drive (1:1) between the engine and contra-rotating gear reduction unit. With the engine running at take-off, military, or climb power (high rpm), the two-speed unit provided a 1.428:1 (.700) reduction. The reduction was achieved through the use of six planetary pinions. The speed change was accomplished through the use of a wrapping spring clutch. The two-speed unit was approximately 37" long and 22.6" in diameter. It weighed 560 lb and at least one unit was built.

The engine was coupled to the input shaft of the two-speed gear unit via a drive shaft. The unit's input shaft was coupled to a housing (green) with a ring gear mounted inside. Fitted inside the ring gear was a carrier housing six planetary pinions (blue). Attached to and passing through the center of the planetary carrier was an output shaft (still blue) that extended to the end of the two-speed gear unit. Here, the output shaft was coupled to another drive shaft that led to the contra-rotating gear reduction unit. Inside the two-speed gear unit and between the output shaft and the planetary carrier was a sun gear shaft (red).

For direct drive (1:1) or low engine speed operation, the wrapping spring clutch (Xs) held the sun gear shaft (red) to the output shaft (blue). This essentially locked these two shafts, the planetary carrier, and the ring gear (green) together so that they all turned the same speed as the input shaft (engine rpm).

For reduction drive (1.428:1) or high engine speed operation, the wrapping spring clutch (Xs) held the sun gear shaft (red) to a stationary member (gold) within the two-speed gear unit. The sun gear shaft (red) not rotating forced the planetary carrier with the output shaft attached (blue) to rotate at a reduce rpm compared to the ring gear / input shaft (green). Thus, the input shaft (green) rotated 1.428 times for every single rotation of the two-speed gear unit's output shaft (blue).

For changing speeds, the wrapping spring clutches altered the rpm of the sun gear shaft so that it was either rotating at the same speed as the output shaft (1:1) or was held stationary (zero rpm) and allowed gear reduction (1.428:1) to occur. The wrapping spring clutch allowed the sun gear shaft to make a slow and smooth rpm transition, thus not causing any stress or shock on the engine, drive shafts, contra-rotating gear reduction unit, or propellers.

Orange is where the teeth of the ring gear (green) are contacting the teeth of the planetary pinions housed in the carrier (blue).

Purple is where the teeth of the planetary pinions housed in the carrier (blue) are contracting the teeth of the sun gear (red).

Regards,

 

[WJPearce]

Attached are two more patents and a link to Robert Neal's description of the two-speed Liberty.
https://books.google.com/books?id=9y8cBQAAQBAJ&lpg=PR2&pg=PA301#v=onepage&q&f=false

 

[xylstra]

Hi Bill, Thanks for the additional info which helps add to the body of additional history. I am still holding out for that first phase I mentioned, the very early (say, WW1 --> ~ late 1920's) pioneering experiments. Probably less likely to be as well documented, but you never know!
Cheers.

 

[xylstra]

Hi Bill,
During my last reply I neglected to mention a web-site that may interest you: aeroclocks.com
They sell a range of books dedicated to German WW1 propellers which seems to be a personal obsession of the author, Bob Gardner who I suspect may also be the web-site operator. Hope it's of interest.
Cheers.