How does the broader blade propeller affect performance?

[Bilbo_Baggins]

The F model BF109 has a broader prop than the E, and the G2 an even broader prop than the F. I am not sure if the K model had an even wider propeller from the G however? Also the Yak 1b according to dev diaries has a broader blade prop than the earlier Yak machines. I don't know about the Lavochkin machines as they underwent so many continuous changes.

 

You can actually see the difference in game, which is cool.

 

What I’d like to know is how exactly these broader propellers affect performance/speed/acceleration at different altitudes and with different powerplants. 

 

Could anyone help explain?

 

RGDS

Edited February 28, 2019 by Bilbo_Baggins

[Field-Ops]

There is a lot to it than what I can bring up but my understanding is that broader bladed props allow for faster acceleration reaching top speed along with better climb speed. There is a downside from what I understand as well being lower top speed in a dive because the larger blades act as sort of a brake when not properly pitched. 

[JtD]

The guy who can answer this question in that depth conclusively will be hired on the spot by an aeronautics company with a top salary.

 

Sorry man, but that's advanced engineering with a complex case by case answer.

 

In general a wider prop will lead to a shallower angle of attack of the prop bladed, given that the prop blade load goes down. This is the similar to an aircraft receiving a larger wing while maintaining the wing span. The best point of operation will shift towards lower speeds or, more importantly, towards higher loads (more power (same as higher weight in the aircraft case)). A wider prop will support a more torque (i.e. a more powerful engine or lower speed flight regimes such as climb) or more efficient operation at low rpm.

 

Therefore, as a very general trend, you'll seed wider props increase take off and climb performance (in particular at high altitude) at the cost of top speed and you'll also see installations of wider props as more powerful engine revisions are mounted on an aircraft.

 

Similar effects can be achieved by increasing prop diameter or number of blades. All three solutions have specific advantages and disadvantages.

[Ehret]

This video could be helpful:

 

[Bilbo_Baggins]

8 hours ago, JtD said:

The guy who can answer this question in that depth conclusively will be hired on the spot by an aeronautics company with a top salary.

 

Sorry man, but that's advanced engineering with a complex case by case answer.

 

 In general a wider prop will lead to a shallower angle of attack of the prop bladed, given that the prop blade load goes down. This is the similar to an aircraft receiving a larger wing while maintaining the wing span. The best point of operation will shift towards lower speeds or, more importantly, towards higher loads (more power (same as higher weight in the aircraft case)). A wider prop will support a more torque (i.e. a more powerful engine or lower speed flight regimes such as climb) or more efficient operation at low rpm.

 

 Therefore, as a very general trend, you'll seed wider props increase take off and climb performance (in particular at high altitude) at the cost of top speed and you'll also see installations of wider props as more powerful engine revisions are mounted on an aircraft.

  

 Similar effects can be achieved by increasing prop diameter or number of blades. All three solutions have specific advantages and disadvantages. 

 

That's a great explanation. This correlates with what I feel in the game with the G2 wide propeller blades... it seems to have tremendous thrust and acceleration in the lower speed/high load range. 

[Elem]

In short. The more power you have available, the larger the blade area required to absorb that power and turn it into thrust most efficiently.

[Bilbo_Baggins]

19 minutes ago, Elem said:

In short. The more power you have available, the larger the blade area required to absorb that power and turn it into thrust most efficiently.

 

So what if you were to put the broad blade G model 109 propeller on a E model machine? How would performance be affected? 

Edited February 27, 2019 by Bilbo_Baggins

[Elem]

30 minutes ago, Bilbo_Baggins said:

 

So what if you were to put the broad blade G model 109 propeller on a E model machine? How would performance be affected? 

The rpm, (hence thrust) would be reduced as the engine does not have the power to turn that area of blade to its optimum efficiency. Put a Fiat 850cc engine in a Roll-Royce Phantom chassis, what would be the result?

Edited February 27, 2019 by Elem

[BlitzPig_EL]

10 hours ago, Elem said:

 Put a Fiat 850cc engine in a Roll-Royce Phantom chassis, what would be the result?

 

An unreliable Rolls Royce.

[Bilbo_Baggins]

21 hours ago, JtD said:

 

Similar effects can be achieved by increasing prop diameter or number of blades. All three solutions have specific advantages and disadvantages.

 

Does anyone know any reports of WW2 machines that have been tested back to back with only different propellers, and their effect on maximum speed or climb performance? 2 vs 3 blades or 3 vs 4 blades.

[JtD]

There are several performance tests with different props on the http://www.wwiiaircraftperformance.org site.

 

The P-47 was tested several times with a large number of different 4-bladed props: http://www.wwiiaircraftperformance.org/p-47/p-47.html

 

The Spitfire IX was tested with different props, different reduction gears and 4- vs. 5-bladed prop: http://www.spitfireperformance.com/spitfire-IX.html

 

The Spitfire I was also tested with different props, 2-bladed 2 pitch vs. 3-bladed constant speed, for instance: http://www.spitfireperformance.com/spitfire-I.html

 

I recall having read several other aircraft prop test reports, but can't point you there. Might have been on the same site, feel free to keep browsing.

Edited February 28, 2019 by JtD

[Kurfurst]

K-4 got a wider prop, visibly so, as did all the later high altitude late G series (/AS, G-10).

 

The key factor on the later models was connected to higher operating altitudes, where wider propellers act similar to larger wings, as JtD explained very well. The downsize is similar, increased drag, which may reduce performance at lower altitudes.

 

I guess the intent was the same on the earlier models as well, since new models always seem to progress towards higher operating altitudes and wider propellers.

 

[Bilbo_Baggins]

4 hours ago, VO101Kurfurst said:

K-4 got a wider prop, visibly so, as did all the later high altitude late G series (/AS, G-10).

 

The key factor on the later models was connected to higher operating altitudes, where wider propellers act similar to larger wings, as JtD explained very well. The downsize is similar, increased drag, which may reduce performance at lower altitudes.

 

I guess the intent was the same on the earlier models as well, since new models always seem to progress towards higher operating altitudes and wider propellers.

 

 

G14 had same propeller as the G6 and G2?

 

K4 hits an incredible 600kmh at SL, I have to wonder what it could achieve with a F4 propeller.

[Kurfurst]

Yes, its the same Prop on g2, G4, g6 and (non AS) G14.

 

The K-4 would be likely faster at low levels, this is what shows between the broad propellered G-14/AS and the G-14 with the older prop. Despite the same power, and the AS versions cowling having + 6 km/h worth better aerodynamics, the AS version is some 7 km/h slower at SL.

 

So I would say the old would add 10 to 15 km/h to the K-4, but that would also kind of defeat its purpose of being primarly a high altitude fighter, where the broader bladed Prop was simply better - and those altitude were far more important from the operational point of view, than tree top level performance.

[CUJO_1970]

More blades lead to more turbulence for WW2 era props don't they?

 

My layman's understanding has always been generally that wider chord blades increase climb performance at the expense of top speed, but of course I'm sure there are exceptions to that rule.

 

I seem to have read over the years that FW-190 pilots driving the late-war 190A-9 and D-9 preferred those broad-chord wooden props to absorb the extra engine power, over 2,000hp, as they lead to better performance (especially at higher altitudes).

Edited February 28, 2019 by CUJO_1970
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[Kurfurst]

Could be the case with the 190D, where there was a lot of power to go around, but perhaps not enough prop to handle it. In the case of the late 109G/K, the wide bladed props definitiely appear to be inferior flow climb compared to the earlier prop, by about 1 m/sec, at least at low altirudes (higher alts being difficult to compare, since the engine powers were also different there).

 

But they also tried various new designs with thinner blades, and even swept back props, so tuning the prop was definitely an art of its own.