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propellerdesign(at)tele2. Guest
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Posted: Tue May 29, 2007 12:01 pm Post subject: Stoped / windmilling propeller drag |
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Hi Guys,
I have a question from a Polish Pilot, if drag is less or not from a free spinning propeller (engine with clutch) or stopped propeller, when engine is stopped or out, and how much it will do on sink rate?
I think we all agree on the fact that drag is higher if propeller is rotating and driving the engine, then if propeller and engine is stopped.
I can't think about a better place to ask this question then here on this active list with all different engine / prop setup that exists on kitfoxes.
The Polish guy is replacing his VW with a modern BMW with a 2,75/1 reduction on a Tulak airplane.
Best
Jan Carlsson
[quote][b]
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wingsdown(at)verizon.net Guest
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Posted: Tue May 29, 2007 1:27 pm Post subject: Stoped / windmilling propeller drag |
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For those that would argue differently. If the prop did not create drag in free rotation helicopters could not auto rotate. As far as how much. It take some nerve to test that feature. I never intentionally shut off the engine in flight. There must be some formula to do the math. I did once go beta and full power. That was way different being pulled forward while in the air. Went back to regular flight real quick. Fun though.
Rick
[quote]
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crazyivan
Joined: 25 Aug 2006 Posts: 62 Location: Pensacola
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Posted: Tue May 29, 2007 2:23 pm Post subject: Re: Stoped / windmilling propeller drag |
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There are a few guys on this list that like to shut the engine off in flight.
I, on the other hand, am too chicken. What I can offer is the drag difference between different pitches of prop. I had my IvoProp set for a flat (climb) pitch and it was tough to get the prop to spin at 2000rpm at idle on final at 55mph but the drag was noticable. When I had a fatter pitch set for cruise, I had to be careful to keep the rpm above 1800 (gear box chatter) and I had a harder time slowing down...I had to make a flatter approach.
There wasn't a big difference, but it was noticable. If I lost the engine on final, I'm certain that there would be reduced drag from a stationary prop. I'm not sure how much and I ain't gonna find out on purpose unless I'm over the great salt flats.
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_________________ Dave
Piper PA-22/20 |
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rjdaugh
Joined: 30 Aug 2006 Posts: 195
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Posted: Tue May 29, 2007 2:42 pm Post subject: Stoped / windmilling propeller drag |
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Rick,
Shut off the engine.
Perhaps it helps that I started out as a glider pilot, but I enjoy shutting off the engine and enjoying quiet flight. Sometimes I do it just to show passengers that it is no big deal. Sometimes, like this past Sunday, I do it to work the thermals. The Kitfox does not have a great glide ratio, but that is not what is needed to work thermals. What is needed is a low sink rate – lower than the vertical speed of the thermal. I get about a 500 fpm sink rate at about 63 mph airspeed. That’s not too bad for a starter glider, but a high performance glider can get under 200 fpm.
If your engine is off for a long time, start it early enough so you can warm the engine before you get close to the ground. Usually, unless you are going to do a dead stick landing this will be only 6 – 12 minutes anyway so your engine is still warm.
To get back on topic, with my old prop, I had to slow nearly to full stall to get the engine to stop windmilling. So it was easy to measure sink rate with it windmilling or without. I didn’t test it real carefully, but sink rate was over 600 fpm with the prop windmilling versus 500 with the prop stopped.
With my new prop, I can get the prop to stop windmilling if I just slow to about 55 mph. I haven’t tried to measure windmilling versus stopped.
To start the engine, I just have to bump the starter and it starts right off with the air pushing it.
Try it. You will like it! And it will make you a more confident pilot.
Randy
Randy Daughenbaugh, N10NH
Black Hills of South Dakota, - Near Mount Rushmore
Home Strip, Grass Room in Hangar for visitors
Series 5/7 (7 Firewall Forward) 912S, Warp Drive Taper Tip
Gross Weight 1320 lbs, Flying since November 2004
From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Rick
Sent: Tuesday, May 29, 2007 3:26 PM
To: kitfox-list(at)matronics.com
Subject: RE: Stoped / windmilling propeller drag
For those that would argue differently. If the prop did not create drag in free rotation helicopters could not auto rotate. As far as how much. It take some nerve to test that feature. I never intentionally shut off the engine in flight. There must be some formula to do the math. I did once go beta and full power. That was way different being pulled forward while in the air. Went back to regular flight real quick. Fun though.
Rick
[quote]
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_________________ Randy
Kitfox 5/7 912S
Black Hills, South Dakota |
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kirkhull(at)kc.rr.com Guest
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Posted: Tue May 29, 2007 3:30 pm Post subject: Stoped / windmilling propeller drag |
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From the aerodynamics classes that I took ( what I remember of them anyway) a freewheeling prop looks like a solid circle to the air. In other words a lot of drag. As far as stopping the engine in flight , it was removed from the training curriculum for a reason.
From: owner-kitfox-list-server(at)matronics.com [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Rick
Sent: Tuesday, May 29, 2007 4:26 PM
To: kitfox-list(at)matronics.com
Subject: RE: Stoped / windmilling propeller drag
For those that would argue differently. If the prop did not create drag in free rotation helicopters could not auto rotate. As far as how much. It take some nerve to test that feature. I never intentionally shut off the engine in flight. There must be some formula to do the math. I did once go beta and full power. That was way different being pulled forward while in the air. Went back to regular flight real quick. Fun though.
Rick
[quote]
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lcfitt(at)sbcglobal.net Guest
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Posted: Tue May 29, 2007 4:08 pm Post subject: Stoped / windmilling propeller drag |
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I have never done it but this topic came up during the trip to So. Cal. and
the other three pilots had done it and our most experienced pilot said he
guessed it would be 20-30° greater glide. That corresponds pretty well with
Randy's experience.
Lowell Fitt
Cameron Park, CA
Model IV-1200 R-912 UL Warp
1998 850 hrs.
---
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N81JG(at)aol.com Guest
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Posted: Tue May 29, 2007 4:15 pm Post subject: Stoped / windmilling propeller drag |
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A wind-milling, undriven rotor (no motor drag) is what allows a helicopter to descend in autorotation. A stopped rotor will not allow an autorotation, only descent like a brick. Hence rotating blades have more drag.
John Greaves
VariEze N81JG
See what's free at AOL.com.
[quote][b]
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akflyer
Joined: 07 May 2007 Posts: 574 Location: Soldotna AK
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Posted: Tue May 29, 2007 6:29 pm Post subject: Re: Stoped / windmilling propeller drag |
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[quote="N81JG(at)aol.com"]A wind-milling, undriven rotor (no motor drag) is what allows a helicopter to descend in autorotation. A stopped rotor will not allow an autorotation, only descent like a brick. Hence rotating blades have more drag.
John Greaves
VariEze N81JG
Close... In a helicopter, autorotation is possible from the stored energy in the blades. If you can go to negative pitch, you can acutally gain rotor RPM. To auto rotate, you go negative on the pitch and fly with the cyclic as you normaly would. you start you flare a little later than normal and pretty much arrest forward speed then you pull the pitch to gently set her down...all this happens very fast. A huey can store enough energy to autorotate, land then lift off do a complete pedal turn and set back down... if it was empty to begin with..
This is an issue I am wrestling with on my Avid with the clutch.. If I have an engine out, I still fall like a rock with the prop windmilling and cant stop it.
See what's free at AOL.com.
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_________________ DO NOT ARCHIVE
Leonard Perry aka SNAKE
Soldotna AK
Avid "C" / Mk IV
582 (147 hrs and counting on the rebuild)
IVO IFA
Full Lotus 1450
#1 snake oil salesman since 1-22-2009
I would rather die trying to live, than to live trying not to die.... |
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msm_9949(at)yahoo.com Guest
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Posted: Wed May 30, 2007 11:43 am Post subject: Stoped / windmilling propeller drag |
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Leonard,
Have you actually tried it in your clutch-equipped Avid? I.e, turn off power and let the prop freewheel? If so, please advise as to sink rate and other performance characteristics you experienced. I'd like to know what to expect before I try it myself.
akflyer <akflyer_2000(at)yahoo.com> wrote:
Quote: |
This is an issue I am wrestling with on my Avid with the clutch.. If I have an engine out, I still fall like a rock with the prop windmilling and cant stop it.
--------
Leonard Perry
Soldotna AK
Avid "C" / Mk IV
582 IVO IFA
Full Lotus 1260
95% complete
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Marco Menezes
Model 2 582 N99KX
Shape Yahoo! in your own image. [url=http://us.rd.yahoo.com/evt=48517/*http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.asp?a=7]Join our Network Research Panel today![/url] [quote][b]
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akflyer
Joined: 07 May 2007 Posts: 574 Location: Soldotna AK
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Posted: Thu May 31, 2007 6:19 am Post subject: Re: Stoped / windmilling propeller drag |
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I have not flown the Avid yet as I am still one wing short... But, I have flown my Brothers KF II with the clutch set up. You dont have to kill the engine to get it to free wheel just pull the power back to an idle. With the power at idle and the prop free wheeling, at 55-60 I am dropping around 1000' min. I would hope this would go up if the prop stopped turning.
I have tested it on a cub with the prop windmilling and with the prop stopped. When starting from 6000' and crossing cook inlet, it was a matter of making the far shore and having to slip to hit the beach with the prop stopped, and having to re-start or swim about a mile to mile and a half in real cold water to get to the beach if I let it wind mill.. Until I had tried it I would never have figured it would make that much difference.
I put the clutch on my avid as most of the time I will be dealing with cold weather (rough starts and warm up) and float flying (nice to warm up without moving).
I hope to have mine in the air by the end of the month and will do some testing with fine and coarse pitch and see how much of a difference that makes.
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_________________ DO NOT ARCHIVE
Leonard Perry aka SNAKE
Soldotna AK
Avid "C" / Mk IV
582 (147 hrs and counting on the rebuild)
IVO IFA
Full Lotus 1450
#1 snake oil salesman since 1-22-2009
I would rather die trying to live, than to live trying not to die.... |
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msm_9949(at)yahoo.com Guest
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Posted: Thu May 31, 2007 6:48 am Post subject: Stoped / windmilling propeller drag |
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I've also cut power to idle at altitude in my clutch-equipped model II. In this configuration, I can usually hold the descent rate to about 600 fpm, at 50-55 mph indicated. I suspect that with the engine completely off, it will sink much faster.
akflyer <akflyer_2000(at)yahoo.com> wrote: [quote]--> Kitfox-List message posted by: "akflyer"
I have not flown the Avid yet as I am still one wing short... But, I have flown my Brothers KF II with the clutch set up. You dont have to kill the engine to get it to free wheel just pull the power back to an idle. With the power at idle and the prop free wheeling, at 55-60 I am dropping around 1000' min. I would hope this would go up if the prop stopped turning.
I have tested it on a cub with the prop windmilling and with the prop stopped. When starting from 6000' and crossing cook inlet, it was a matter of making the far shore and having to slip to hit the beach with the prop stopped, and having to re-start or swim about a mile to mile and a half in real cold water to get to the beach if I let it wind mill.. Until I had tried it I would never have figured it would make that much difference.
I put the clutch on my avid as most of the time I will be dealing with cold weather (rough starts and warm up) and float flying (nice to warm up without moving).
I hope to have mine in the air by the end of the month and will do some testing with fine and coarse pitch and see how much of a difference that makes.
--------
Leonard Perry
Soldotna AK
Avid "C" / Mk IV
582 IVO IFA
Full Lotus 1260
95% complete
Read this topic online Sick sense of humor? Visit Yahoo! TV's [url=http://us.rd.yahoo.com/evt=47093/*http://tv.yahoo.com/collections/222]Comedy with an Edge [/url]to see what's on, when. [quote][b]
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kerrjohna(at)comcast.net Guest
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Posted: Thu May 31, 2007 9:20 am Post subject: Stoped / windmilling propeller drag |
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the conclusion below might not prove out in practice. with the reduced drag of a stationary propeller the 50-55 mph indicated will be attainable at a lesser decent angle.
John Kerr
[quote]-------------- Original message --------------
From: Marco Menezes <msm_9949(at)yahoo.com>
I've also cut power to idle at altitude in my clutch-equipped model II. In this configuration, I can usually hold the descent rate to about 600 fpm, at 50-55 mph indicated. I suspect that with the engine completely off, it will sink much faster.
akflyer <akflyer_2000(at)yahoo.com> wrote: Quote: | --> Kitfox-List message posted by: "akflyer"
I have not flown the Avid yet as I am still one wing short... But, I have flown my Brothers KF II with the clutch set up. You dont have to kill the engine to get it to free wheel just pull the power back to an idle. With the power at idle and the prop free wheeling, at 55-60 I am dropping around 1000' min. I would hope this would go up if the prop stopped turning.
I have tested it on a cub with the prop windmilling and with the prop stopped. When starting from 6000' and crossing cook inlet, it was a matter of making the far shore and having to slip to hit the beach with the prop stopped, and having to re-start or swim about a mile to mile and a half in real cold water to get to the beach if I let it wind mill.. Until I had tried it I would never have figured it would make that much differen ce.
I put the clutch on my avid as most of the time I will be dealing with cold weather (rough starts and warm up) and float flying (nice to warm up without moving).
I hope to have mine in the air by the end of the month and will do some testing with fine and coarse pitch and see how much of a difference that makes.
--------
Leonard Perry
Soldotna AK
Avid "C" / Mk IV
582 IVO IFA
Full Lotus 1260
95% complete
Read this topic online Sick sense of humor? Visit Yahoo! TV's [url=http://us.rd.yahoo.com/evt=47093/*http://tv.yahoo.com/collections/222]Comedy with an Edge [/url]to see what's on, when. | [b]
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clint_bazzill(at)hotmail. Guest
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Posted: Thu May 31, 2007 12:41 pm Post subject: Stoped / windmilling propeller drag |
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That much sink at that airspeed. Like a Cessna with full flaps. Clint
From: Marco Menezes <msm_9949(at)yahoo.com>
Reply-To: kitfox-list(at)matronics.com
To: kitfox-list(at)matronics.com
Subject: Re: Re: Stoped / windmilling propeller drag
Date: Thu, 31 May 2007 07:45:35 -0700 (PDT)
I've also cut power to idle at altitude in my clutch-equipped model II. In
this configuration, I can usually hold the descent rate to about 600 fpm, at
50-55 mph indicated. I suspect that with the engine completely off, it will
sink much faster.
akflyer <akflyer_2000(at)yahoo.com> wrote:
"akflyer"
I have not flown the Avid yet as I am still one wing short... But, I have
flown my Brothers KF II with the clutch set up. You dont have to kill the
engine to get it to free wheel just pull the power back to an idle. With the
power at idle and the prop free wheeling, at 55-60 I am dropping around
1000' min. I would hope this would go up if the prop stopped turning.
I have tested it on a cub with the prop windmilling and with the prop
stopped. When starting from 6000' and crossing cook inlet, it was a matter
of making the far shore and having to slip to hit the beach with the prop
stopped, and having to re-start or swim about a mile to mile and a half in
real cold water to get to the beach if I let it wind mill.. Until I had
tried it I would never have figured it would make that much difference.
I put the clutch on my avid as most of the time I will be dealing with cold
weather (rough starts and warm up) and float flying (nice to warm up without
moving).
I hope to have mine in the air by the end of the month and will do some
testing with fine and coarse pitch and see how much of a difference that
makes.
--------
Leonard Perry
Soldotna AK
Avid "C" / Mk IV
582 IVO IFA
Full Lotus 1260
95% complete
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=115755#115755
Marco Menezes
Model 2 582 N99KX
---------------------------------
Sick sense of humor? Visit Yahoo! TV's Comedy with an Edge to see what's on,
when.
_________________________________________________________________
PC Magazine’s 2007 editors’ choice for best Web mail—award-winning Windows
Live Hotmail.
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msm_9949(at)yahoo.com Guest
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Posted: Thu May 31, 2007 3:13 pm Post subject: Stoped / windmilling propeller drag |
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Pretty draggy. Alot like full flaps on a 172. In fact, I've also used the big fan to steepen glide on short final.
Clint Bazzill <clint_bazzill(at)hotmail.com> wrote: [quote]--> Kitfox-List message posted by: "Clint Bazzill"
That much sink at that airspeed. Like a Cessna with full flaps. Clint
From: Marco Menezes
Reply-To: kitfox-list(at)matronics.com
To: kitfox-list(at)matronics.com
Subject: Re: Re: Stoped / windmilling propeller drag
Date: Thu, 31 May 2007 07:45:35 -0700 (PDT)
I've also cut power to idle at altitude in my clutch-equipped model II. In
this configuration, I can usually hold the descent rate to about 600 fpm, at
50-55 mph indicated. I suspect that with the engine completely off, it will
sink much faster.
akflyer wrote: --> Kitfox-List message posted by:
"akflyer"
I have not flown the Avid yet as I am still one wing short... But, I have
flown my Brothers KF II with the clutch set up. You dont have to kill the
engine to get it to free wheel just pull the power back to an idle. With the
power at idle and the prop free wheeling, at 55-60 I am dropping around
1000' min. I would hope this would go up if the prop stopped turning.
I have tested it on a cub with the prop windmilling and with the prop
stopped. When starting from 6000' and crossing cook inlet, it was a matter
of making the far shore and having to slip to hit the beach with the prop
stopped, and having to re-start or swim about a mile to mile and a half in
real cold water to get to the beach if I let it wind mill.. Until I had
tried it I would never have figured it would make that much difference.
I put the clutch on my avid as most of the time I will be dealing with cold
weather (rough starts and warm up) and float flying (nice to warm up without
moving).
I hope to have mine in the air by the end of the month and will do some
testing with fine and coarse pitch and see how much of a difference that
makes.
--------
Leonard Perry
Soldotna AK
Avid "C" / Mk IV
582 IVO IFA
Full Lotus 1260
95% complete
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=115755#115755
Marco Menezes
Model 2 582 N99KX
---------------------------------
Sick sense of humor? Visit Yahoo! TV's Comedy with an Edge to see what's on,
when.
_________________________________________________________________
PC Magazine’s 2007 editors’ choice for best Web mail—award-winning Windows
Live Hotmail. [url=http://us.rd.yahoo.com/evt=48250/*http://searchmarketing.yahoo.com/arp/sponsoredsearch_v9.php?o=US2226&cmp=Yahoo&ctv=AprNI&s=Y&s2=EM&b=50]Pinpoint customers [/url]who are looking for what you sell. [quote][b]
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