Wooden Propeller Forum  

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

Reply
 
Thread Tools Display Modes
Old 04-28-2019, 11:47 AM   #11
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

Hello Pierre-Michel,

It seems that Scout D were fitted with 80HP Le Rhone 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?

Yes, I think there is enough evidence (documentary and photographic) to be sure that the Bristol Scout D was operated with the 100 hp Gnome Monosoupape B.2 engine during WW1.

Jack Bruce's Windsock Datafile 44 says:

The 100-hp Gnome Monosoupape was fitted to some of the later Scouts D delivered to the RNAS. This engine had a full-circular cowling with a large frontal opening and, on its starboard side, a peculiar bulge to improve exhaust outflow.

The 'peculiar bulge' in the cowling (also described as a gumboil) is a distinctive feature, and shown in several photographs, including one I have when the Mono engine itself is clearly seen.

The Bristol Scout D that I am researching is described as having a 100 H.P. Mono[saupape] Gnome engine, No. 5812, in the RNAS weekly operations report for that period.

The RNAS serials book by Sturtivant and Page lists the contract for that batch of aircraft, and notes that it was ordered with 110 hp Clerget but delivered with 100 hp Gnome Monosoupape.

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.


The first question: I think we can be sure it was the 100 hp Gnome Monosoupape engine. According to Wikipedia -
Power output: 86 kW (115 hp) at 1,300 rpm (Maximum power)
Compression ratio: 4.85:1

Unfortunately, Jack Bruce's Datafile doesn't give performance data for the Bristol Scout D with the Mono engine. But he does have the following, not sure if it helps:

Weight and performance
Bristol Scout D
Engine: 110-hp Clerget

Weight fully loaded: 1,442 lb
Max. speed (mph)
- ground level 107.3
- 3,000ft 109
- 7,000ft 108
- 10,000ft 100 (est.)

The second question: The standard approved pitch used was 1800. That is based on drawing number P3012, as given in Bob Gardner's book. A possibility is that the source data is incorrect. I'm not sure why (but then I know nothing about this subject!) a Bristol Scout and a Sopwith Pup fitted with the same engine would require such different pitches.

When I look up the Bristol Scout D in Bob's book for the Mono and other engines, I see the following pitches:

Bristol Scout D with 110 hp Le Rhone - P2710
Bristol Scout D with 100 hp Gnome Monosoupape - P1800
Bristol Scout D with 110 hp Gnome - pitch not listed
Bristol Scout D with 80 hp L Rhone - P2400
Bristol Scout with 80 hp Clerget - P3300
b3rn is offline   Reply With Quote
Old 04-28-2019, 02:40 PM   #12
pmdec
Forum Contributor
 
Join Date: Nov 2006
Location: France
Posts: 539
Default

Hi,

I have quite not to very approximative knowledge about English aircraft and have to refer to some credible documentation. The joined pic is from Flight, 1958-1, p0697 PDF. Does it seem right?
Are we talking about the Scout n°8976?

Anyway, there is a measure which can give some information: the central hole diameter and the thickness of the hub of your prop. The "80HP" and the "100HP" Gnome had not the same metallic hub. I have to search about the Le Rhône 80 and 110.
BTW, it would be pleasant for forumers if you post some pics of the markings!

Regards,
PM
Attached Images
File Type: jpg Specs.jpg (58.4 KB, 2 views)

Last edited by pmdec; 04-28-2019 at 03:23 PM.
pmdec is offline   Reply With Quote
Old 04-29-2019, 04:46 PM   #13
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

PM, I'm writing an article, and don't want to post too much specific detail because Google will spoil the surprise!

I am trying to connect an aircraft (RNAS Bristol Scout D with 100 hp Gnome Monosoupape engine) with a prop in a museum.

All the evidence links the two, except that the hub data on the prop shows P2640, whereas the published information in Bob's book (based on drawing numbers) shows that the Bristol Scout D prop as P1800.

This is the only discrepancy in the argument I'm trying to build.

So far, it seems you think P1800 is unlikely for a 100 hp Mono engine? (For me, I'm also not sure why there would be such a difference between the Bristol Scout and the Pup with the same engine.)

The joined pic is from Flight, 1958-1, p0697 PDF. Does it seem right?

Yes, but unfortunately, that table doesn't include the Bristol Scout D with 100 hp Mono engine. Only a relatively small number (8951-9000 and perhaps a handful more) were ordered by the Admiralty in this configuration for the RNAS.

Anyway, there is a measure which can give some information: the central hole diameter and the thickness of the hub of your prop. The "80HP" and the "100HP" Gnome had not the same metallic hub. I have to search about the Le Rhône 80 and 110.

The prop is in a museum. I took a number of photos but unfortunately did not measure the thickness of the hub. Also the central hole is covered over by a plaque!

BTW, it would be pleasant for forumers if you post some pics of the markings!

Attached is a good image of Bristol Scout D N5393 with 100 Mono engine and distinctive gumboil on the cowling.

Also attached is my photo of the hub in the museum.
Attached Images
File Type: jpg N5393.jpg (19.9 KB, 3 views)
File Type: jpg IMG_0449.jpg (96.6 KB, 2 views)
b3rn is offline   Reply With Quote
Old 04-29-2019, 08:50 PM   #14
pmdec
Forum Contributor
 
Join Date: Nov 2006
Location: France
Posts: 539
Default

Hi,

Also the central hole is covered over by a plaque! It seems that the plaque bolt had marks of (un)screwing... It would be the easier way to have, perhaps, an answer...

[boring writing ON]

About pitch, "in general". Airscrews are exactly what means their name: a screw for air! At the rotating speed they are used (around 1000 km/h or 600 mph at the tips of the blades), the air is as hard as wood for a screw. There is very little "slip" or "skid" (I don't know the right word): the "skidding" of a good airscrew is no more than 10% at max or cruising speed (depends of usage). For a very good one, 6%, even 5% can be reached. But, sometimes, you need to have more skidding to prevent the engine running to high, using a "too high" pitch and wide blades: you will never reach the max speed.

So, the maths are very simple:
- the pitch marked on the hub is the geometric pitch: It is the distance the airscrew would travel forward when it turn 360° if it was not "skidding". Say, for example, a prop with 1800 millimeters pitch (quite all English propellers of the WW1 era are marked using millimeters, for the diameter and for the pitch).
- For each complete rotation of the prop, the plane travel forward about 0.9 x pitch, say ~0.9 x 1800 mm = ~1620 mm with 10% "skidding".
- With a Gnome monosoupape engine running at 1300 rpm, each minute the propeller attached to the engine made 1300 rotations.
- So, each minute the propeller travels forward 1300 x 1620 mm = 2,106,000 mm = 2106 meters = 2.106 kilometers = ~ 1.31 mile.
- Each hour, the propeller, and the aircraft!, travels 60 x 2.106 km = 126 km. It is flying at 126 km/h. Or 78 mph.
It is impossible without running the engine faster to exceed that speed at level flight. You can't screw the prop in the air more that the pitch for each rotation. And if you run a Gnome past, say, 1400 rpm, I think it will be destroyed.

And don't forget that Gnome monosoupape did not have any air intake command: there is no carburator. The only way to slow the engine is to cut the magnetos (or some of them on some engines) and/or close the gazoline line. So, if you fit a too low pitch prop on the engine, it will exceed its max rotation speed.

With 2640 mm pitch, the prop you show could reach 185 km/h (115 mph) at 1300 rpm.
It could be a prop for a 9N monosoupape, used on Sopwith Camel. It is strange it has neither serial number nor aircraft indicated.

[boring OFF (I hope!)]

The "multiple" pitches Bob Gardner shows in his books for "Monosoupape" could be for different monosoupapes engines, because there was the 7 cylinders ("A"), and at least 3 engines with 9 cylinders : 9B, 9N and 9R... I don't know if it is linked to or it is by chance, but the 7A had in France a "type A" metallic hub (60 mm central hole and around 100 mm thick) and the 9B a "type B" metallic hub (70 mm central hole, around 140 mm thick). But there could be exceptions... and in England it was perhaps different!

Regards,
PM

Last edited by pmdec; 04-29-2019 at 09:05 PM.
pmdec is offline   Reply With Quote
Old 04-29-2019, 11:34 PM   #15
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

That's very interesting and not boring at all, PM. I appreciate it!

I think we can assume this is a British-built Gnome Monosoupape Type B-2. All references in contemporary reports use the designation 100-hp Mono.

For that particular Mono, here is some data gleaned from Google!

Power rating: 75 kW (100 hp) at 1,200 rpm
Source: https://airandspace.si.edu/collectio...-rotary-engine

Power output: 86 kW (115 hp) at 1,300 rpm (Maximum power)
Compression ratio: 4.85:1
Source: https://en.wikipedia.org/wiki/Gnome_...ape_9_Type_B-2)

Applying PM's method:

0.9 * 2640 mm (pitch) = 2376 mm (allowing 10% skidding)

100 hp, 1,200 rpm

1200 rpm * 2376 = 2,851,200 mm = 2851.2 metres = 2.8512 km = 1.77165354 miles

60 * 2.8512 km = 171.07 kmh
60 * 1.77165354 miles = 106.23 mph

At maximum power, 115 hp at 1,300 rpm

1300 rpm * 2376 = 3088800 mm = 3088.8 metres = 3.0888 km = 1.91929134 miles

60 * 3.0888 km = 185.33 kmh
60 * 1.91929134 miles = 115.16 mph

These speeds seem reasonable, but perhaps all I have done is confirm the propeller's hub data! And the manufacturers weren't resorting to Google.

So PM - my question: Is the pitch relevant only to the engine, or to any characteristics of the planes or fuselage?

Why would the drawings show such a difference in pitch between two aircraft using the same engine?
Attached Images
File Type: jpg Gnome B2 Section from Instruction book No.2.jpg (88.6 KB, 0 views)
b3rn is offline   Reply With Quote
Old 04-29-2019, 11:39 PM   #16
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

The "multiple" pitches Bob Gardner shows in his books for "Monosoupape" could be for different monosoupapes engines...

Possibly. But Bob's table for Bristol shows 100 hp alongside each Mono prop, suggesting the B-2. My assumption is that "100 hp" was used to distinguish the engine type.

This is from Wikipedia, and I haven't cross-checked.

7 Type A - 80 hp
9 Type B-2 - 100 hp
11 Type C - ?
9 Type N - 150 or 160 hp
Type R - 180 hp
b3rn is offline   Reply With Quote
Old 04-30-2019, 06:32 AM   #17
pmdec
Forum Contributor
 
Join Date: Nov 2006
Location: France
Posts: 539
Default

Hi,
Quote:
Originally Posted by b3rn View Post
.../... So PM - my question: Is the pitch relevant only to the engine, or to any characteristics of the planes or fuselage? .../...
Yes, the pitch, but also the diameter and the blade width depend of many parameters, but I dont't know how all this was computed in WW1 era, neither in France nor in England.

Since the 20's (and perhaps before) it is known that the propeller efficiency depends of its diameter: larger is the prop, higher the efficiency could be... but the prop tips have to stay away from sound speed*** and from the ground!
Blade width is more difficult: it depends of the choosen profile of the cross-sections. You have to look at NACA history, but I think all about profiles of cross-sections was empirical in WW1 era.
To compute the pitch, propellers manufacturers could use only max power and regime of the engine AND the speed the aircraft is presumed to reach. This last data is very difficult to know by the aircraft manufacturer and was also, I presume, empirical in this era. It depends of the engine power, the weight of the aircraft, its wing area, its running resistance (size and number of struts, ...).
And then, you can also choose between an aircraft which would have a high speed OR a high climb rate. But for speedy aircraft you have to verify that the aircraft could take-off! At low speed, a propeller designed to reach high speed has a pour efficiency: it is why variable pitch propeller are used (pitch can be changed in flight). The low pitch is computed for a maximised efficiency at take-off speed and high pitch computed for max efficiency at cruise speed. The difference between them could be in the order of 10 to 20 degrees for aircraft with a max speed in the order of 200 km/h.

So, yes, there are different propellers for different aircraft using the same engine, even for the same aircraft for different uses: Dave told you could have a "cruise prop" and and a "for performance" one and he is right, but the difference would be low. It why there were adjustable pitch propellers (that is, only on the ground with stopped engine).

*** To compute the true speed of blade tips, forward speed vector has to be added to tangential speed vector. IMHO, if only max speed is considered, this could be ignored until 200 km/h (1000 tangential + 200 forward > ~1020 true speed).

Regards,
PM

EDIT: Forgot the sound speed limit! The blade tips speed has to be kept subsonic. It is why "modern" props for small aircraft have a smaller size than WW1 ones: engine rotation speed is higher but gears are costly, so on "small" aircraft of nowdays (which have about the same power), the propellers are smaller. And with more efficient shape than during WW1, the prop efficiency is good even with a smaller used air surface.

Last edited by pmdec; 04-30-2019 at 08:56 PM.
pmdec is offline   Reply With Quote
Old 05-21-2019, 11:13 PM   #18
b3rn
 
Join Date: Apr 2019
Location: Sydney, Australia
Posts: 9
Default

A recap. Bob's book has drawing numbers, and for the 100 hp Mono-engined Bristol Scout D, a pitch of 1800 is shown in that table. (In comparison, the 100 hp Mono-engined Pup - same drawing - has a pitch of 2640 mm.)

I followed PM's formula for the pitch of 1800 mm, and the maximum speed is 78.5 mph.

That seems too low?

Bob has checked his data and confirmed what's in the book. My guess is human error in the original documents, an early/transition period that was superceded, or it was practice (just not recorded here) to supply the prop specified for the 100 hp Mono Pup for the 100 hp Mono Scout D. I'm going to note the anomaly in my article but assume that the prop in question (P1620) is from the Bristol Scout D.

Here's my working in case I got it wrong:

0.9 * 1800 mm (pitch) = 1620 mm (allowing 10% skidding)

At maximum power, 115 hp at 1,300 rpm:

1300 rpm * 1620 = 2106000 mm = 2106 metres = 2.106 km = 1.3086077 miles

60 * 2.106 km = 126.36 kmh
60 * 1.3086077 miles = 78.516462 mph

Thanks for your help!
b3rn is offline   Reply With Quote
Old 05-27-2019, 08:19 AM   #19
pmdec
Forum Contributor
 
Join Date: Nov 2006
Location: France
Posts: 539
Default

Hi,

I think you are right. Perhaps there was a typo in "old papers"... Or the pitch measured was not the true one. I don't really know... but maths are a compulsory base!

The joined pic came from a Ratier workshop notebook. It is about test runs for an automatic variable pitch propeller which had only two positions: one for take off, one for max speed at level flight. The "trouble" for racer was to be able to take off with high pitch propeller which could permit high speed. What is of interest for you, IMHO, are the simple maths used:

- "V" is speed in kilometers per hour ("sol" is the French for "ground": those racers flew at low altitude, so there was no need to compensate for air pressure),
- "N" is rotation speed of the engine in rpm,
- "T" is the power delevered by the engine (note that the power at 2400 rpm is very higher than at 2200 rpm).
- "H" is the pitch in meters. H=2m30 à 0m60 means the pitch is 2,30 meters at 0,60 meter from the prop center (those props had not a constant pitch along the blade, but higher near the tip),
- ° and ' are angular degrees and minutes
- gr is another angular unit frequently used by Ratier (400 "grades" = 360 degrees = 1 rotation), I don't know which word is right in English,
- "PF" is for French "Point Fixe" (ground run full throttle).

You can see that 360 x 1000 [speed in meters by hour] / 60 [speed in meters by minute] / 2400 [advance by engine rotation] x 1.10 [10% slip] = 2.75 meters = pitch near the tip (the prop is 1,90 meter long).
This will be the higher speed the plane can do at 2400 rpm with the blades blocked at 31°20'.
But the prop is constructed with best efficiency when the pitch is 2.60 meters at 0.60 meter from prop center, that is 34°35', which gives 410 km/h at 2500 rpm for a plane with a 240HP engine. So they diminished the pitch to use it with the 160 HP engine by 3°15' (from 34°35' to 31°20').

And that 180 x 1000 x 1.1 / (60 x 2200) = 1.50 meter = pitch when the blades are blocked at 21°40' (the automatic system rotates the blades 31°20' - 21°40' = 9°40' after take off).

To be noted : the word "variable pitch" is a poor term, because the blade torsion doesn't change, only the global incidence changes. A true variable pitch propeller would have a variable torsion : This has been tried with blades made of "articulated" sections. Seems it didn't work...

We are far from WW1 props... Sorry for the digression!

Regards,
PM
Attached Images
File Type: jpg 1232b_cr_sh_900px_97k.jpg (96.7 KB, 3 views)
pmdec 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 07:53 AM.


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