Author Topic: Spitfire Mark Vb  (Read 745 times)

Offline AKA_Wiley

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Spitfire Mark Vb
« on: July 09, 2017, 04:45:44 pm »
 S! Well what can I say the mere thought of flying the spit again finally lured me to buy BOK,plus the P39 and the A20 coming didn't hurt,havent been flying much of late,but hope to be flying more in coming weeks. 

Offline AKA_Relent

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Re: Spitfire Mark Vb
« Reply #1 on: July 09, 2017, 07:03:42 pm »
Sounds good Wiley - she's a fun aircraft to fly, like you I'm also looking forward to flying the P-39 and A-20.

S! Rel

Offline AKA_Goshawk

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Re: Spitfire Mark Vb
« Reply #2 on: July 10, 2017, 01:43:23 pm »
Question:  When lowering the prop pitch, it results in a lowering of the RPM. It would seem that lowering the pitch would cause an increase in the RPM, since the propeller is doing less work. Please explain how lowering the prop pitch lowers the RPM.
Thanks.

Gos


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Offline AKA_Wiley

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Re: Spitfire Mark Vb
« Reply #3 on: July 10, 2017, 04:10:21 pm »
 S! Gos lowering the prop pitch changes the prop blades angle to take a bigger bite of air thus lowering engine rpms,increasing prop pitch to a "fine" setting lets the prop take a smaller bite of air thus letting the engine increase rpms,think of it like this try running your car as fast as it will go top end in overdrive unless you have major horsepower you car will only go so fast as the engine doesn't make enough power to overcome the very high gear ratio while in overdrive,(coarse prop setting)now try running as fast as you can go but not in overdrive (fine prop setting)you will in most cases find that you go much faster as the engine can overcome the much better gear ratio when not in overdrive.

Offline AKA_Wayno

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Re: Spitfire Mark Vb
« Reply #4 on: July 11, 2017, 11:14:48 am »
 8)I agree with Gos. "Lowering" the prop pitch (Decreasing pitch) will make the prop take a lesser cut of air, thereby decreasing engine load and increasing RPM? I think the Russians at IL-2 have had this backwards for a long time?
« Last Edit: July 11, 2017, 11:17:56 am by AKA_Wayno »

Offline AKA_Relent

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Re: Spitfire Mark Vb
« Reply #5 on: July 11, 2017, 11:55:06 am »
This all depends on the interpretation of increasing and decreasing prop pitch.

The way I see it, and how I think Wiley is interpreting it, is as follows:

Increasing prop pitch:  Rotating the blades such that from a side view, the blade is getting closer to vertical ( | ),  or a finer pitch.  Thus the engine RPM increases as there is less load on the engine (i.e. The prop is biting off less air, so it's easier on the engine).

Decreasing prop pitch:  Rotating the blades such that from a side view, the blade is getting closer to horizontal ( -- ), or a coarser pitch.  Thus the engine RPM decreases as there is more load on the engine (i.e. The prop is biting off more air, so it's harder on the engine).

S! Rel
« Last Edit: July 11, 2017, 11:57:00 am by AKA_Relent »

Offline AKA_MattE

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Re: Spitfire Mark Vb
« Reply #6 on: July 11, 2017, 12:52:26 pm »
It is just semantics. 

MattE

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Offline AKA_Scorp

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Re: Spitfire Mark Vb
« Reply #7 on: July 12, 2017, 08:48:28 am »
I don't think you directly control the prop pitch on any of the Russian AC.  The lever controls the governor which attempts to maintain a certain RPM by automatically adjusting the prop pitch.

 
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Offline AKA_Relent

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Re: Spitfire Mark Vb
« Reply #8 on: July 12, 2017, 03:03:58 pm »
Interesting, I've never researched that aspect - although the principals above would still apply I'd think, with respect to the relative loads on the engine.

Offline AKA_Goshawk

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Re: Spitfire Mark Vb
« Reply #9 on: July 12, 2017, 09:49:57 pm »

Increasing prop pitch:  Rotating the blades such that from a side view, the blade is getting closer to vertical ( | ),  or a finer pitch.  Thus the engine RPM increases as there is less load on the engine (i.e. The prop is biting off less air, so it's easier on the engine).

Decreasing prop pitch:  Rotating the blades such that from a side view, the blade is getting closer to horizontal ( -- ), or a coarser pitch.  Thus the engine RPM decreases as there is more load on the engine (i.e. The prop is biting off more air, so it's harder on the engine).


So, this being the case, wouldn't the higher prop pitch cause longer engine life than having the prop pitch lowered?
Why then do people want to cruise around at 80 prop pitch instead of 100, which would be easier on the engine?

Us curious, but smallish, bird-brains wanna know?

Thanks again.

Gos
-the most curiouserest accipiter


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Offline AKA_Relent

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Re: Spitfire Mark Vb
« Reply #10 on: July 13, 2017, 07:45:04 am »
In my explanations, I was speaking to the act of increasing (finer) or decreasing (coarser) pitch, and the immediate effect on the engine.  Beyond that, you have to look at airspeed and altitude.

At higher altitudes, the air is thinner, at high/fine pitch there isn't as much bite as at low altitudes.  So you would probably need to decrease pitch (coarser) to get the same amount of bite at lower altitudess

At higher speeds, the load on the engine would generally be less than at lower speed with the same coarse pitch - simply because it should take less throttle (i.e. engine effort) to maintain a certain higher (e.g. cruising) speed than being at a lower speed and attempting to gain speed or climb (more engine effort), where you would likely use a higher/finer pitch.

Cruising at 100% pitch would require more engine RPMs and would lead to quicker overheating on many of the aircraft we fly in BOS/M.  That said, if you are in a close in dogfight, and you need more acceleration, then you would need a higher/finer pitch setting, at the risk of higher RPMs and overheating the engine.

S! Rel
« Last Edit: July 13, 2017, 10:03:07 am by AKA_Relent »

Offline AKA_Scorp

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Re: Spitfire Mark Vb
« Reply #11 on: July 13, 2017, 09:43:57 am »

Increasing prop pitch:  Rotating the blades such that from a side view, the blade is getting closer to vertical ( | ),  or a finer pitch.  Thus the engine RPM increases as there is less load on the engine (i.e. The prop is biting off less air, so it's easier on the engine).

Decreasing prop pitch:  Rotating the blades such that from a side view, the blade is getting closer to horizontal ( -- ), or a coarser pitch.  Thus the engine RPM decreases as there is more load on the engine (i.e. The prop is biting off more air, so it's harder on the engine).


So, this being the case, wouldn't the higher prop pitch cause longer engine life than having the prop pitch lowered?
Why then do people want to cruise around at 80 prop pitch instead of 100, which would be easier on the engine?

Us curious, but smallish, bird-brains wanna know?

Thanks again.

Gos
-the most curiouserest accipiter

"Harder on the engine" should be harder for the engine just as starting off in 4th gear is harder for the engine than starting in 1st.  Think how hard it would be on your car's engine if you drove about in 1st gear all the time.



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