Wooden Propeller Forum  

Go Back   Wooden Propeller Forum > Wooden Propeller Identification > "Early" Wooden Propellers

Reply
 
Thread Tools Display Modes
Old 04-23-2019, 07:31 PM   #1
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default Props and pitch: Used on an aircraft type different to the drawing specifications

Hello all,

I'd like to describe a scenario in general terms, and ask you whether you've encountered something similar.

I've interpreted a propeller's hub data using Bob Gardner's excellent books. The data narrows the prop down to a particular engine (100hp Mono), and two aircraft (Bristol Scout D and Sopwith Pup).

I think I know the aircraft from which the prop came, but confusingly, the pitch is not the pitch listed in the drawing for that type (Bristol Scout D). It corresponds with the other of the aircraft (Sopwith Pup).

It's possible - due to supply lines and availability, or a decision on the ground - that the prop with a pitch for one aircraft type was used on another.

Have you come across similar scenarios?
b3rn is offline   Reply With Quote
Old 04-23-2019, 08:32 PM   #2
Dbahnson
Administrator
Site Admin
 
Join Date: Nov 2008
Posts: 973
Default

Are you going by a listed drawing number or just stamped diameter and pitch?

Can you post photos of the hub data, and do you know the manufacturer?
Dbahnson is offline   Reply With Quote
Old 04-23-2019, 10:47 PM   #3
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

I'm looking at 'Known Bristol Drawing Numbers' (in Bob Gardner's book), specifically drawing number P3012. These are all for 100hp Mono engine.

D2550 P1800 BAT Bantam
D2550 P1800 Bristol Scout D
D2550 P2610 Sopwith Pup
D2550 P2640 Sopwith Pup
D2550 P2310 Sopwith Pup
D2550 P2300 Sopwith Pup
D2550 P1800 Sopwith Pup
D2550 P2610 Sopwith Scout

The hub data:

100 HP MONOSAUPAPE
D2550
P2640
B&C 2851

As you can see, this suggests the propeller comes from 100hp Mono Pup, but I'm reasonably sure it was from a 100hp Mono Bristol Scout D.

Have forum members seen instances where a prop for one type is used on another type?

In short, I'm trying to establish whether I must rule out the Bristol Scout D definitively.
b3rn is offline   Reply With Quote
Old 04-24-2019, 07:45 AM   #4
Bob Gardner
Moderator
 
Bob Gardner's Avatar
 
Join Date: Jan 2006
Location: The North of England
Posts: 1,689
Default

Greetings Bernard,

I'm glad that Dave Bahnson has enrolled you in this forum.

But it would appear that my emails have not reached you. I wondered why you had not replied. I enclose a precis of my answer below.

The short answer is that it is quite feasible that the 2640mm pitch prop and the 1800mm was fitted to both the Scout D and the Sopwith Pup. Both the Scout D and the Sopwith Pup used the same engine and therefore the same hub. Both were used by the RNAS. But I do not wish to imply that it was officially authorised.

I am aware of lots of variations within published data of this era. There is evidence that British pilots during WW1 sought certain props from certain makers believing them to be better than others, even though both were made to a similar specification, a process which included wishful thinking and superstition, as well as comparative trials. Often a RFC pilot would sing the praises of a prop made by a specific maker, so his chums in his squadron would try to find a similar one.

The same thing happened with German flyers. The German Flying Troops document, the Propellermerkbuch der Prufenstalt und Werft der Fliegertruppen of 1916, published by P & W at Aldershof, emphasises that all propellers were rigorously tested by them and a prop made by one maker was just as good as those made by other makers. Variations in the performance of a propeller could depend, the Buch states, on fuel, the plugs and even on certain periods of the engine rev range which had to be avoided; for example the Mercedes 160hp engine at 1320-1340 rpm.

Considering these aspects of human behaviour it is quite likely that the RNAS at unit level tried out the 2640mm and the 1800mm pitch prop on both the Bristol Scout D and the Sop Pup. There might have been advantages at different parts of the envelope.

Also Mesopotamia, which I think is where your Scout D was shot down, is at the end of a long supply line and perhaps fitting the Pup prop to a Scout D was due to a shortage, either at the RNAS airfield or in the RN supply chain from the factory in GB by ship to Malta and hence to Mesopotamia.

Perhaps a forumite versed in the mathematics of flight could offer a view on the different flying characteristics of each prop on each aircraft?

But, the short answer is that there is no reason to rule out your Scout D.

With kind regards,

Bob


With kind regards,
__________________
Bob Gardner
Author; WW1 British Propellers, WWI German Propellers
http://www.aeroclocks.com

Last edited by Bob Gardner; 04-25-2019 at 07:18 AM.
Bob Gardner is offline   Reply With Quote
Old 04-24-2019, 07:58 AM   #5
Dbahnson
Administrator
Site Admin
 
Join Date: Nov 2008
Posts: 973
Default

I might add that if a fighter airplane was to be transported a long distance in a non-combat setting it would make sense to install the propeller with the higher number pitch, even though it might not correspond to its "authorized" usage. It would serve as a "cruise" prop rather than a climb, or performance prop.
Dbahnson is offline   Reply With Quote
Old 04-24-2019, 08:32 PM   #6
pmdec
Forum Contributor
 
Join Date: Nov 2006
Location: France
Posts: 528
Default

Hi,

The 80 HP Le Rhône and the 100 HP Gnome Monosoupape were respectivly 84 and 105 HP at 1200 rpm at ground level (Sopwith Pup data).
The Bristol Pup was given to have a max speed at ground level of 100 mph, that is 161 km/h. The minimum propeller pitch to reach this speed at 1200 rpm is 2300 mm.
It is absolutly impossible to reach 100 mph with the 1800 mm pitch indicated above (the engine have to run at 1550 rpm!).

Just my two cents...
PM

EDIT: typo

Last edited by pmdec; 04-24-2019 at 09:03 PM.
pmdec is offline   Reply With Quote
Old 04-27-2019, 06:15 PM   #7
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

Many thanks for the information.

I must admit that I know nothing of the performance of propellers.

A question for PM: My interest is the Bristol Scout D. How would it affect that aircraft using a propeller of pitch 2640 rather than 1800?
b3rn is offline   Reply With Quote
Old 04-27-2019, 06:21 PM   #8
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

Quote:
Originally Posted by Dbahnson View Post
I might add that if a fighter airplane was to be transported a long distance in a non-combat setting it would make sense to install the propeller with the higher number pitch, even though it might not correspond to its "authorized" usage. It would serve as a "cruise" prop rather than a climb, or performance prop.
The aircraft were shipped by sea to the main island base in the eastern Mediterranean, then flown to the various stations. These could be from 65km to 100km away. Some missions look to have involved a 200km return journey. And of course, the aeroplanes were mostly flying over sea.

That might offer a reason for employing a "cruise" prop, if I understand you correctly.
b3rn is offline   Reply With Quote
Old 04-28-2019, 07:19 AM   #9
pmdec
Forum Contributor
 
Join Date: Nov 2006
Location: France
Posts: 528
Default

Quote:
Originally Posted by b3rn View Post
.../... How would it affect that aircraft using a propeller of pitch 2640 rather than 1800?
Hi,

IMHO, for a 2550 mm propeller, the incidence difference at ~2/3rd of the blade between 1800 and 2640 mm pitch is ~7.7 degrees. It is high enough to make the take-off impossible with 2640 mm pitch if 1800 mm pitch was the standard one. And also high enough to make the engine rotate past its maximum regime using 1800 mm pitch in place of a standard 2640 after take-off (and even during engine run-up).

To have an answer about your question, you need to know:
- which engine is used and what is its max torque regime AND its max power regime AND its highest possible regime,
- what was the standard approved pitch used.

It seems that Scout D were fitted with 80HP Le Rhône but some were intended to be fitted with 100 HP monosoupape. Does it exist a picture of WW1 era showing a Scout D with this 100 HP engine?

Regards,
PM
pmdec is offline   Reply With Quote
Old 04-28-2019, 10:43 AM   #10
Bob Gardner
Moderator
 
Bob Gardner's Avatar
 
Join Date: Jan 2006
Location: The North of England
Posts: 1,689
Default

Thank Goodness we have Pierre-Michel!

With kind regards,

Bob
__________________
Bob Gardner
Author; WW1 British Propellers, WWI German Propellers
http://www.aeroclocks.com
Bob Gardner is offline   Reply With Quote
Reply

Tags
hub, pitch

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 10:41 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.