propeller designs

Hi everyone,

I have often noticed the wide variety of propeller manufacturers during the war, especially German. Has there been any studies on the properties of these propellers, both allied and German, and how they effect aircraft performance (level speed, climb rate, range, etc.)? I realize that a propeller's pitch, diameter and number of blades can have a profound effect on an aircraft's performance.

I have also noticed that the SSW DIII and DIV were phenomenal climbers. Was this due to a large extent because they had a four-bladed prop? Or was this an incorrect assumption during the war, just as the thin, cambered airfoil was felt to have less inherent drag then the thick, flat airfoil, which was later proven that the opposite was true? ??? ???

Looking forward to your thoughts,

JASTA75

[StephenLawson]

Greetings Jasta75:

The propeller variances you mention can be a sticky subject. *Nonetheless it was covered expertly by the great research devotees *Mr. Alex Revell *and J.M. Bruce in Aeroplane Monthly *from about June - Oct 1977 in a series about RFC 56 sqdn. *In Sept they discussed '...the right props for the job...' *The subject of coure was the change from the 4 bladed prop on SE 5 with the Hispano-Suiza 8Aa to the two bladed version found on SE 5 and 5a types with the increased horse power of the newer available direct drive Hispano-Suiza 8Ab and SE 5a types with the great Wolseley VIPER W4a. *These motors were installed in the SE 5 airframes when available. *Noteably the designation according to memos from the Air Board *showed the differences between the SE 5 and 5a designation layed in their wing designs. *But the rigging diagrams labels denote (I) SE 5a, 200hp Hispano-Suiza. (II) SE 5 , 150hp Hispano-Suiza.

In Alex Imrie's book on the Fokker Triplane we note the unusual prop found on 528/17 after its refurbishing. *The thng is much heavier than the Axial or other props found on the Oberursel Ur.II 120hp. *Yet this was an advanced develpoment? As the development and design of propellers was still progressing how this helped the Goebel Goe.II 100hp function on 528/17 is anybodys guess.

[Dan_San_Abbott]

StephenLawson:
Steve, I would like to make correction to your thread.
The S.E.5 was delivered with the 150 hp Hispano Suiza 8Aa engines with a 2 bladed right hand propeller. The S.E.5a were delivered initially with the Hispano-Suiza 8Ca 200 hp geared engined and used a 4 bladed, RAF Dwg No. T.28096 left hand propellers. This same propeller was used on the Wolseley built geared 200 hp "Adder I and II", both of these engines had a gearring ratio of 21 : 28.This commenced with the second production order of 50 machines, serial numbers, A8898-8947 and all subsequent orders. The 4 bladed propeller was used on the French Hispano-Suiza with the geared engine with the gear ratio of 24 : 41. Some of the later S.E.5a machines fitted with the French built Hispano-Suiza 200 and 220 hp engines were delivered with 2 bladed propellers ,A.B. 8080 and T.28137M. The charteristic of these later S.E.5a aircraft was the rounded top one piece radiator.
With the gearred engines the propeller turned at a slower rpm, i.e. with the 21 :28 ratio the propeeper turned @ 1500 rpm and the engine was turning 2000 rpm, the 24 : 41 ratio, the propeller was turning @ 1170 while the engine was turning @ 2000 rpm. The four blades was used to utilized the engine horsepower.
The direct drive Wolseley Viper I and II were all delivered with right hand two bladed propellers. The "Viper" engine installation is characterized by the two box radiators and the squarish nose.
Blue skies,
Dan-San

[Dan_San_Abbott]

Jasta75:
* * An important characteristic in propeller design is the operating range of the engine's rpm. *An example was the propeller use on the SSW D.III was the slow rpm of the bi-rotary engine required a large diameter 2 blade propeller. With the large diameter of the propeller required a high undercarriage. *When the engineers at SSW changed to the 4 blades and a smaller diameter, they were able to utilize the engine's power and reduce the height of the landing gear.
* * Another example, is the Alb.C.V and the LVG.C.IV with the 8 cylinder, 220 Ps Mercedes D.IV geared engine. The engine rpm was 900 rpm and turned a 2 bladed propeller 3300 mm (10.82ft.) propeller.
* * * * * * * * * * * * * * * * *Blue skies,
* * * * * * * * * * * * * * * * * * *Dan-San
* *

[dbahn]

As for the wide variation in design of propellers, it certainly was not limited to German props only. *Particularly prior to the end of WWI, and for at least some time after that, propellers built by US, British, and French manufacturers used a wide variety of design variations, all hoping to achieve some performance advantage over the rest, but in reality there was not a great deal of difference from a design standpoint. *(That's not to say some propellers didn't perform better than others, but it was more by luck than design). *If you look at propellers built into the 30's and 40's, the design of most of those are similar (straight centerline with symetrical leading and trailing edges, tapered tips), in contrast to WWI era props with curved and/or offset centerlines, asymetric leading and trailing edges, etc. *

There was so much variation in design that it is nearly impossible to identify a propeller merely by its shape, other than to perhaps provide a good guess at the manufacturer. *Fortunately, most of the British and French propeller manufacturers stamped the drawing number (design or series number) on the hub of the prop. *Most US manufacturers did not.

You have all made some good points on propellers, stuff that I was not aware of. Can anyone tell me if there was any great differences between the German propellers and allied propellers? This would include efficiencies, pitch and general propeller shapes.

Regards,

JASTA75

[dbahn]

I don't know about the relative efficiencies, and pitch of course is variable in the sense that it was designed as part of the propeller design, i.e. there might be a number of propellers that used the same basic design but with a number of choices in pitch. (Most propellers will have the diameter (length) and pitch stamped on the hub, the pitch is expressed as the distance the propeller would move forward in one "theoretical" revolution, and can be looked at as the distance between threads if the propeller were a complete screw)

As for general propeller shapes, I would say that German propellers almost characteristically were designed with a straight centerline and tended to be balanced symetrically around that centerline. While some Allied props had that same general configuration, most had curved (scimitar) centerlines and there was much more variation in leading vs. trailing edges. In many ways, I think the German propellers were more "modern" in the sense that later propellers evolved to look more like them, and in the same sense I think they are a little "boring" in their appearance compared to other propellers.

Look through a series of frontal views of German airplanes and compare them to similar views of Allied planes and I think you will quickly see a general difference. Obviously, there will also be exceptions.

[David_Layton]

As respects to German Aircraft, the Type Acceptance pages shown in many of the Datafiles and WWI Aero (long German word begins with a B, I am away from my book collection) courtesy of Peter Grosz, gives propellor diameter and pitch. *Pitch = the linear distance the propellor would move forward were it 'screwed' forward 1 revolution using the blades as its threads. *In essence, this is the effective pitch.

The best source on British (and French Aircraft if used by RFC/RAF) is the propellor datafile.

In WWI Aero, I believe Nov. 1997, Javier Arango describes how his repro Fokker D.VII with a 160 hp Mercedes with proper WWI repro propellor (over 9 ft in diameter) flies better than the ex Blue Max repro D.VII re-engined with a 230 hp Gypsy (inverted so as to give it the proper thrust line) and a 6 foot propellor. *

In a past issue of OTF, there was a comparison of fighter aircraft to determine the best fighter. *The one area I took issue with was that thrust was not measured, instead the author only took into account the engine's horsepower. *This simple assumption is wrong as the correct measure should be thrust (or the increase in air pressure behind the propellor.) *

Do we have any aeronautical engineers who could give us a fairly accurate, say 90-95% accurate, simple formula for combining propeller and engine data to determine thrust? *