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-   -   I Don't Get It - FP vs CS (https://vansairforce.net/community/showthread.php?t=80855)

LeeM_2000 02-29-2012 09:47 PM

I want a C/S, but will likely end up with a FP for the cost savings both in initial purchase price and maintenance.

trackdom 03-01-2012 12:04 AM

By the way, who are the best wood propeller manufacturers in USA?
Thanks

ao.frog 03-01-2012 02:17 AM

I'd think that...
 
.... when a carowner has tried automatic transmission, he'd never want to go back to manual gearshifts anymore...

That's the case for me at least... :D

Get a ride in a -7 with a C/S prop: do some short field takeoff and landings, some acro and then decide....

Flyguytki 03-01-2012 03:00 AM

Quote:

Originally Posted by ao.frog (Post 634792)
.... when a carowner has tried automatic transmission, he'd never want to go back to manual gearshifts anymore...


Again personal preference, I would rather have a manual transmission over automatic any day. But that right theres proves the point. It all what you want, if you want simple, you cant get much more simple than one lever for power, push forward go fast pull back slow down.

-david

NickAir 03-01-2012 03:46 AM

C/S or F/P
 
The simplicity of a fixed pitch has benefits:
- no moving parts
- no grease
- no leaking Zerk's
- no down time for rebuild
- no high $$ for rebuild
- no problem out performing spam cans w/ your F/P
- Top end speeds are same as F/P
- There are fixed pitch props that flex flatter at max rpm when airspeed is low, (for better climb performance.) This will never compete with a C/S although appears to be a great compromise.
- Tri blade F/P is supposed to provide more thrust at lower airspeed although it may be slightly less efficient.
- Tri blade creates higher prop clearance to ground.

If a RV pilot wants more performance at take off and climb then you can still stay with a F/P by going with a tri blade and/or a higher pitch. This will limit the top end to a lower speed as a direct trade off for the higher performance on take off and climb. This is common with small power bush planes for reasons mentioned above.

pierre smith 03-01-2012 05:01 AM

Quote:

Originally Posted by trackdom (Post 634787)
By the way, who are the best wood propeller manufacturers in USA?
Thanks

In my opinion, Craig Catto, although they're really composite but the most bang for the buck.

Best,

Mel 03-01-2012 06:47 AM

Quote:

Originally Posted by NickAir (Post 634803)

If a RV pilot wants more performance at take off and climb then you can still stay with a F/P by going with a tri blade and/or a higher pitch. This will limit the top end to a lower speed as a direct trade off for the higher performance on take off and climb. This is common with small power bush planes for reasons mentioned above.

I think you mean "lower pitch" for take-off performance. Lower pitch allows the engine to turn up faster thereby producing more power.

PerfTech 03-01-2012 09:20 AM

Best FP prop
 
Quote:

Originally Posted by pierre smith (Post 634813)
In my opinion, Craig Catto, although they're really composite but the most bang for the buck.

Best,

I second that! Craig Catto is one of the nicest, most sincere, helpful and accommodating people you will ever meet and makes a fabulous product. He will work with you to be certain you have the perfect propeller for your airplane. Very hard to improve on that! Allan :D

paul mosher 03-01-2012 09:37 AM

C/S
 
Grease on windshield? High maintenance? I've used C/S props for years and never experienced either problem. Get what you want.
It'll be cheaper to buy a C/S than buying a F/P and changing your mind later.
But get what you want.

rockwoodrv9 03-01-2012 09:37 AM

additional workload for CS?
 
I have flown almost always with a FP prop. I flew some in a 182 that had a CS, but I didn't operate the prop since I didn't have experience with one - the plane's owner did the prop adjustments. That was several years ago and I don't remember much about it. How much more complex is it for a low time pilot? If I remember correctly, LSA does not allow it for that reason. I plan to go with a fuel injected engine to reduce the leaning needs and chance of error and engine repairs. The cost is an issue too and my major flight profile is traveling to visit kids and grandkids. I like the idea of increased climb and the ability to slow down getting in and out of smaller airports, but the -9 with a 360 or a 320 will not have any performance problems for sure with either type of prop.

Does the extra knob add that much workload for a low time pilot? It may be a question that may not have an answer more than a standard transmission - vs - auto would have. I appreciate the expertise here - it is hard to find something that people don't know about on this forum!

paul mosher 03-01-2012 09:44 AM

Prop
 
C/S use is not a big deal. Look at all the extra knobs and switches people add to their airplanes with the EFIS systems they install.

PerfTech 03-01-2012 09:48 AM

C/S or F/P
 
Quote:

Originally Posted by Flyguytki (Post 634797)
Again personal preference, I would rather have a manual transmission over automatic any day. But that right theres proves the point. It all what you want, if you want simple, you cant get much more simple than one lever for power, push forward go fast pull back slow down.

-david

Manual verses automatic isn't an accurate comparison. A far more accurate comparison would be a high tech constant velocity, infinitely adjustable automatic transmission verses a manual trans that is stuck in one gear for life. Allan :rolleyes:

Mel 03-01-2012 10:45 AM

I've heard this ONE too many times!
 
Quote:

Originally Posted by PerfTech (Post 634922)
Manual verses automatic isn't an accurate comparison. A far more accurate comparison would be a high tech constant velocity, infinitely adjustable automatic transmission verses a manual trans that is stuck in one gear for life. Allan :rolleyes:

Comparing a fixed pitch prop to a manual transmission stuck in one gear is also not an accurate comparison.
If that were "apples-to-apples", there would be many cars running around with a "one-gear" transmission. Only place I've seen this is on the drag-strip.
There are MANY airplanes flying just fine with F/P props.
When is the last time you saw a car on the road with a one-gear transmission?

LeeM_2000 03-01-2012 11:47 AM

Does this count?
 
Quote:

Originally Posted by Mel (Post 634953)
When is the last time you saw a car on the road with a one-gear transmission?

It has a fixed pitch prop.


paul mosher 03-01-2012 12:38 PM

aerocar
 
Yes it does. And it's neither a good car or a good airplane.

Mel 03-01-2012 01:03 PM

DO YOUR RESEARCH GUYS!
 
This car did NOT drive on the road with a single speed transmission!

LeeM_2000 03-01-2012 01:38 PM

No, but it drove on the road with a fixed-pitch prop. I thought these were one in the same.

It had a 3-speed on the floor for driving the wheels. That's just like having a constant speed prop. ;)

NickAir 03-01-2012 01:49 PM

Car Transmission analogy.
 
Mel is correct. The car trans analogy is flawed in showing a comparison between a F/P vs. C/S.

Fixed pitch: $ lower entry price; low maintenance; no mechanical rebuild needed; lighter weight; no loss in top speed.

Constant speed prop does have the advantage of helping to move the CG forward for a more usable useful load, depending on mission. Also C/S has the advantages of a climb prop at slower airspeeds, therefore allowing shorter takeoffs and climb capability.

rv7boy 03-01-2012 01:51 PM

Air is a Compressible Fluid
 
You guys are off in Never-Never Land.

There's LOTS of difference between turning a propeller (either CS or FP) in a compressible fluid and driving a tire on a paved road.
(Different way of saying that Mel is right again.)

Reminds me of a debate by a buddy who challenged a so-called expert on model airplane propellers after the "s-c e" wrote an article in the AMA (Academy of Model Aeronautics) magazine.

Put your thinking caps on. :)

Mark Albery 03-01-2012 02:34 PM

Where I work, we're building a car with a single gear fixed transmission and no clutch.

The trick is to use an electric motor that produces 100% torque at 0 RPM:D:D

ao.frog 03-01-2012 02:41 PM

I was just...
 
.... poking you guys... :D
(with my comment automatic vs manual transmission)

As already mentioned, I bet this post is just to poke us... ;)

Jerry Cochran 03-01-2012 08:06 PM

HP=TxR
 
Since HP=Torque X RPM, I like to think of the blue and black knobs as 2 ways to add or subtract power, together or individually...

Darn handy and works every time it's tried...

trackdom 03-02-2012 12:43 AM

Quote:

Originally Posted by pierre smith (Post 634813)
In my opinion, Craig Catto, although they're really composite but the most bang for the buck.

Best,

Thanks to you

Sig600 03-02-2012 01:58 AM

Constant speed prop just gives you some extra versatility. Depends on the operator if that is worth the cost. To each their own.

William Slaughter 03-02-2012 07:21 AM

It's really simple.
 
Do you want great performance at a lower cost, or do you want maximum performance and are willing to pay the difference. Excellent results either way.

Ron Lee 03-02-2012 12:47 PM

Flying out of mountain airports the CS prop can be VERY useful.

Moura 03-03-2012 02:25 PM

Stupid question
 
What setting will slow down an airplane with CD, blue knob all the way forward or all the way back?

Mel 03-03-2012 03:02 PM

Quote:

Originally Posted by Moura (Post 635884)
What setting will slow down an airplane with CD, blue knob all the way forward or all the way back?

Blue knob forward results in fine pitch and maximum drag.
Blue knob pulled back results in coarse pitch and max glide.

NickAir 03-03-2012 03:02 PM

C/S control
 
C/S Prop control:
Forward: Flatens the pitch for take off, climb or slowing.

Back/out: Increases the pitch for high speed cruise/extended glide.

Moura 03-03-2012 03:34 PM

Another stupid question, if I want To slow down in circuit and move blue knob all the way forward, the engine's rpm will go up. Can it in any way damage the engine due to over reving? Same would apply in formation in a dive!

paul mosher 03-03-2012 03:37 PM

read a book
 
prop governor. look it up.

Moura 03-03-2012 03:41 PM

Quote:

Originally Posted by paul mosher (Post 635897)
prop governor. look it up.

Thank you Paul.

L.Adamson 03-03-2012 05:53 PM

Quote:

Originally Posted by Moura (Post 635896)
Another stupid question, if I want To slow down in circuit and move blue knob all the way forward, the engine's rpm will go up. Can it in any way damage the engine due to over reving? Same would apply in formation in a dive!

You don't have to move it all the way forward. It still acts like a brake. In fact, if you move it forward too soon, it is like quick shifting into lower gear. Throws you towards the panel, and doesn't do well for the engine either. Just push all the way in on short final, when power is pulled back. I'd just usually leave mine, at the 2350 cruise setting. You'll only notice that the blue knob isn't full forward, if you do a go-around or touch and go. You'll notice a definate decrease in power.

Moura 03-03-2012 10:14 PM

Thank you L. But I was wondering what would be a reasonable / aceptable RPM in such a situation. Max. Take off rpm? Or could we go higher?

PerfTech 03-03-2012 10:25 PM

Quote:

Originally Posted by Moura (Post 636018)
Thank you L. But I was wondering what would be a reasonable / aceptable RPM in such a situation. Max. Take off rpm? Or could we go higher?

The max is set by the prop manufacturer, most Hartzell or Whirlwind compact is 2700 rpm red line. Allan

paul mosher 03-03-2012 11:17 PM

gov
 
actually prop rpm is restricted by prop manufacturer. Exceed rpm limits and it is a mandatory overhaul.

NickAir 03-04-2012 02:59 AM

Max RPM
 
Also, Lycoming engine O-320/O-360 Max rpm is usually 2700, therefore many prop designs are same.

smokyray 03-06-2012 08:32 AM

Not so fast...
 
Quote:

Originally Posted by paul mosher (Post 636025)
actually prop rpm is restricted by prop manufacturer. Exceed rpm limits and it is a mandatory overhaul.

Not quite. 2700 Max RPM on C/S props is correct for most manufacturers recommendations for certified applications and has carried over on experimental props sold to be installed on Lycomings. Being an IA I'm sure you know once you paste "experimental" on your type certificate, all bets are off. You don't have mandatory limits on anything per say, except your conscience, your posterior and the approved limits/maneuvers posted in the logbook during the test phase. If you follow certified standards and limits for your RV experimental airplane's engine/prop, good on ya. Years of testing, NTSB investigations and lawsuits have set the ultra-conservative limits on most parts sold by major aircraft parts companies. They do however perform very well beyond posted limits...

Even Hartzell likes racing airplanes and their custom made props for Dave Anders, the Reno Lancair Legacies and others have higher RPM limits (2900-3200) and were built specifically to run at higher RPM's. How are they different form a stock Hartzell? Call Kevin Karam at Hartzell, he'll tell ya. Craig Catto's background is Reno racing. His props come into their own around 2850 and "posted limits" up to 3200 for my 2 blade. Lycoming's limits running above 2700? That's another discussion for another day. Ask Mahlon, he's on the site.

FYI...

V/R
Smokey

MauiLvrs 03-06-2012 10:43 AM

Quote:

Originally Posted by rockwoodrv9 (Post 634917)
Does the extra knob add that much workload for a low time pilot?

No....
Quote:

Originally Posted by rockwoodrv9 (Post 634917)
I plan to go with a fuel injected engine to reduce the leaning needs and chance of error and engine repairs.

I don't see how fuel injection would in any way reduce the leaning needs in a noticeable way :confused:

gasman 03-06-2012 05:26 PM

What is the maximum and minimum pitch of a c/s prop on a RV7 180hp?

Sensenich is fixed at 85 inches.


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