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Losing rpm on takeoff
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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Dec 01, 2010 6:18 am Post subject: Re: Losing rpm on takeoff

Recently, when I was doing a pre-purchase inspection on a Sonex with Jabiru 2200 engine, the static rpm at WOT on the ground was 3250, just 50 rpm short of redline and max continuous rpm limit of 3300. During take-off the rpm drops to 3,000 rpm at full throttle climb at Vy. This is with a Sensenich wood prop (fixed pitch). That is 250 rpm drop on a 3300 max rpm engine and this is perfectly normal. Within a few rpm, that is the same thing I get on my Kolb Slingshot with almost identical engine, but with a Tennessee wood prop.



On a 6300 rpm engine, a 500 rpm drop sounds about right.



Perhaps your test pilot does not have a complete grasp of what normal fixed pitch prop/rpm behavior is during various flight regimes.

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Wed Dec 01, 2010 6:23 am Post subject: Re: Losing rpm on takeoff

 	  Dick Maddux wrote: 	
		  

 Interesting LS ,my Warp taper tip has never done that in the 2 years it has been on my aircraft. I get 5200 WOT on take off roll and on climbout it accelerates to about 5400 rpm on my 80 hp 912.

  I am now using a Kiev and it too never drops. It,however stays at 5200 rpm thru take off and climb. I have been watching these numbers very closely comparing the two propellers.I am staying with the Kiev as it isï¿½lighter and much,much smoother.

	




No idea.... On my tornado, tho, it was very noticeable especially at the beginning when I had it overpropped. 



Once I got it dialed in, tho, it was a lot more steady. When I put the coals to it it'd go up to about 5300 and stay there until I was off the ground and climbing at Vy. It would creep up about 50 to maybe 100rpm if I sped up to about 80mph. It went up to about 5550 or thereabouts at WOT, straight and level (about 110mph!).



My powerfin, OTOH, really lugs the motor when starting my TO roll (I can barely get 4800 rpm) which is why I sloooowly advance the throttle. But it unloads a bunch as I approach TO speed. At 65mph at its current setting I get about 5180, if I speed up to 80 I bump up to about 5400 rpm. It'll exceed redline in level flight the way I have it set right now (estimated, of course, never actually tested that ). I live at 7000' MSL so I need all the climb I can get and don't care about top speed (I'm about an 85mph airplane with the PF fitted). 



Interestingly, looking at the logbooks, the actual pitch I've settled on with the powerfin is virtually identical to the pitch I used with the WD (about 14 degrees at the tips). Yet, the WD had zounds more speed range and a much more constant-speed prop behavior. The PF is much narrower, tho it generates more thrust than the WD.



So dunno.....



PS: for comparison purposes, the WD is a 68" 3 blade taper, the PF is a 70" 3 blade F model. The WD is unfortunately unuseable on my plane due to a fluke harmonic vibration on this particular aiframe. The PF has stiffer blades so it doesn't have the same resonance, smooth as silk on this plane. 



But if I could make the WD work on this plane, it'd be back on in about 2 seconds  (I still have my WD in case I ever get another 912ULS powered plane or project to use it with).



LS

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LS
Titan II SS

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Wed Dec 01, 2010 8:24 am Post subject: Losing rpm on takeoff

On 11/30/2010 4:13 PM, FLYaDIVE wrote:

 	  Quote: 	
		   Your data does not make sense.  If you were over pitch and started to 

 roll you would be unloading your prop and the RPM would Go UP. 

  ANYTIME you start your take off roll the RPM goes UP.  If not.... 

 Then something else is wrong.

 Even if you were under pitched there would be a increase in RPM ... 

 Not as much as if you had the correct pitch or over pitched... But it 

 would still go UP.


	


Barry,

     I never found an analytical solution, but if the prop's stalled at 

static run-up due to too high angle of attack it will then "slip", 

unloaded, until the angle attack reduces enough for it to un-stall. 

Increasing airspeed reduces the angle of attack on the prop, hence my 

deduction that my prop un-stalled, loaded up, and pulled the RPM's down 

on the 582. Yes it's all theoretical, but I wasn't able to come up with 

a better excuse, particularly after reducing the pitch solved the 

problem entirely.



Guy Buchanan

Kitfox IV-1200 / 582-C / Warp 3cs / 500 hrs.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Wed Dec 01, 2010 8:39 am Post subject: Losing rpm on takeoff

Thom, I'm aware of prop stalling, you could actually hear the engine slow down on my friend's IO-360 powered LongEZ, but as I recall he was running a Catto prop with 93" of pitch and blades wide enough to provide shade to several children and small adults. Standing still it truly looked like an "airscrew".:-} I do not get the effect everyone is referring to with my 582 and 3 blade, square tip, straight blade Warp Drive prop at all. By the numbers Dave supplied for static RPM I should since I set my prop for 5900 RPM static and it kisses 6000 once I'm rolling. Climbing at 50 mph, it stays on 6000 until I change to my cruise climb setting of 5600. I have to reduce throttle to maintain that cruise RPM once I level off so I don't see where the prop is suddenly getting more "bite".

 The hard part, with a Kolb Mk IIIC and its crappy aerodynamics is knowing what part all that blockage from the fuselage, wing, bad gap seals, and engine standing tall and proud have to do with it. Since my engine is set as low as I can get it with a prop tip / boom clearance of only about an inch, there's also the phenomenon of how much efficiency I gain or loose by having the wing direct air into the prop from its underside versus what is lost or gained by the turbulent air coming over the top. I do know that if I get too aggressive when climbing out that I can hear when the prop begins to cavitate. 

 I did go out last night and check the prop pitch to send to Dave for comparison with his. 14 degrees 20 minutes according to the WD protractor (20d30m down side, 8d10m up) which translates to just a smidge more than 50" pitch.

 



Rick Girard



On Wed, Dec 1, 2010 at 8:18 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 	  Quote: 	
		   --> RotaxEngines-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

 

 Recently, when I was doing a pre-purchase inspection on a Sonex with Jabiru 2200 engine, the static rpm at WOT on the ground was 3250, just 50 rpm short of redline and max continuous rpm limit of 3300. During take-off the rpm drops to 3,000 rpm at full throttle climb at Vy. This is with a Sensenich wood prop (fixed pitch). That is 250 rpm drop on a 3300 max rpm engine and this is perfectly normal. Within a few rpm, that is the same thing I get on my Kolb Slingshot with almost identical engine, but with a Tennessee wood prop.

  

 On a 6300 rpm engine, a 500 rpm drop sounds about right.

 

 Perhaps your test pilot does not have a complete grasp of what normal fixed pitch prop/rpm behavior is during various flight regimes.

 

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 

 

 “Everyone is entitled to his own opinion, but not his own facts.”

 Daniel Patrick Moynihan

 

 

 

 

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 http://forums.matronics.com/viewtopic.php?p=321912#321912

 

 

 

 

 

 

 

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-- 

Zulu Delta

Kolb Mk IIIC

582 Gray head

4.00 C gearbox

3 blade WD

Thanks, Homer GBYM

It is not bigotry to be certain we are right; but it is bigotry to be unable to imagine how we might possibly have gone wrong.

  - G.K. Chesterton



 

  [quote][b]

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Dec 01, 2010 8:53 am Post subject: Re: Losing rpm on takeoff

Rick,



What you describe seems to be common with the Warp Drive props based on what I've heard from others with a WD prop. I've never owned one so don't have personal experience with them. On all the airplanes I've owned with fixed pitch props, what I described is the norm. No idea why the the WD behaves differently but it sounds like a very good thing... almost like the performance advantage of a constant speed prop allowing full power RPM during takeoff and climb without limiting cruise speed. For climb performance limited aircraft in high density altitudes, that could be a real advantage compared to other props.

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

flyadive(at)gmail.com
Guest

Posted: Wed Dec 01, 2010 10:06 am Post subject: Losing rpm on takeoff

Thom, Rick & Gaggle:



Many years ago, back around 1975 I worked on a prop for the Gossamer and Gossamer Albatross.  Remember those planes?  It was the first man powered plane to fly a closed figure eight course.  The prop was made from FOAM with a very thin fiberglass (3/4 oz cloth) coating.  It also had a 25 degree washout.  We did not talk inches of pitch back then.  At high speed the pitch would flatten and after the plane gained altitude and stabilized flight the prop would un-load, prop slowed down which let the pitch increase.  From this information I would guess-ta-mate that the same is happening to the Warp Drive Prop.  There is a small flexing in the twist that changes with RPM.

 



Barry





On Wed, Dec 1, 2010 at 11:53 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

  

 

Rick,

 

 What you describe seems to be common with the Warp Drive props based on what I've heard from others with a WD prop. I've never owned one so don't have personal experience with them. On all the airplanes I've owned with fixed pitch props, what I described is the norm. No idea why the the WD behaves differently but it sounds like a very good thing... almost like the performance advantage of a constant speed prop allowing full power RPM during takeoff and climb without limiting cruise speed. For climb performance limited aircraft in high density altitudes, that could be a real advantage compared to other props.

  

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 

 

 “Everyone is entitled to his own opinion, but not his own facts.”

 Daniel Patrick Moynihan

 

 

 

 

 Read this topic online here:

 

 

http://forums.matronics.com/viewtopic.php?p=321931#321931

 



 

 

 

 

 

 

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[b]

grahamsingleton(at)btinte
Guest

Posted: Wed Dec 01, 2010 4:35 pm Post subject: Losing rpm on takeoff

Barry

Gossamer Condor and Albatross were fantastic but I don't think the Warp drive has any flex, it's far too stiff. I think it's the stall characteristics of the section which was an odl RAF section I think. That sharp leading edge has something to do with it I suspect. btw Paul McCready was a genius!

Graham

From: FLYaDIVE <flyadive(at)gmail.com>

To: rotaxengines-list(at)matronics.com

Sent: Wednesday, 1 December, 2010 18:03:49

Subject: Re: Re: Losing rpm on takeoff

Thom, Rick & Gaggle:

Many years ago, back around 1975 I worked on a prop for the Gossamer and Gossamer Albatross.  Remember those planes?  It was the first man powered plane to fly a closed figure eight course.  The prop was made from FOAM with a very thin fiberglass (3/4 oz cloth) coating.  It also had a 25 degree washout.  We did not talk inches of pitch back then.  At high speed the pitch would flatten and after the plane gained altitude and stabilized flight the prop would un-load, prop slowed down which let the pitch increase.  From this information I would guess-ta-mate that the same is happening to the Warp Drive Prop.  There is a small flexing in the twist that changes with RPM.

Barry

On Wed, Dec 1, 2010 at 11:53 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

Rick,

 What you describe seems to be common with the Warp Drive props based on what I've heard from others with a WD prop. I've never owned one so don't have personal experience with them. On all the airplanes I've owned with fixed pitch props, what I described is the norm. No idea why the the WD behaves differently but it sounds like a very good thing.. almost like the performance advantage of a constant speed prop allowing full power RPM during takeoff and climb without limiting cruise speed. For climb performance limited aircraft in high density altitudes, that could be a real advantage compared to other props.

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 â€œEveryone is entitled to his own opinion, but not his own facts.â€

 Daniel Patrick Moynihan

 Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=321931#321931

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occom

Joined: 26 Aug 2006
Posts: 404

Posted: Thu Dec 02, 2010 2:54 pm Post subject: Losing rpm on takeoff

I have received enough email to establish a plan of  action here. Despite the fact that reducing pitch WILL result in an overspend  situation with my particular experimental installation, I will reduce the pitch  and see what happens during high speed taxi and then climb. Many people actually  using Warp props tell me that I achieve the results I am looking for.  

  

 I understand it is counter-intuitive, but  apparently it is at least somewhat common. I have a couple of theories, but for  now I'll accept positive results and remain in doubt about the actual reason.  Over a long work life I've had to do that on many occasions, because results are  what really matters. 

  

 Thanks to Guy, Lucien and those who contributed  positive and helpful advice off list. To those who offered unhelpful advice and  lectures, thanks for the efforts. It all reminds me of a saying a friend  repeats from time to time. 

  

 "In theory, theory and practice are the same; in  practice they are quite different!" This may be one of those cases.

  

 Dave Goddard

KF IV 1050 / 582 /  Warp

 [quote]   ---

occom

Joined: 26 Aug 2006
Posts: 404

Posted: Tue Dec 14, 2010 2:40 am Post subject: Losing rpm on takeoff

Problem solved, although what is actually happening is a subject of some  debate.



Those who operate the Warp drive taper tip props or have  experience with them were exactly right and ignoring static RPM was clearly the  way to go. I ended up with a very nice smoooth prop after reducing pitch  significantly. 

It is now pitched to allow 6200 rpm in full throttle climb at  0 deg temp. I expect we will have to revisit this when it warms up. The engine  will overspeed quite easily on the ground until speed builds. I have spoken to a  

few others with the same type of prop and their expereince is  similar.  



Thanks to those who offered asistance, it would have  taken somewhat longer to get it right without it. 

   [quote][b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Tue Dec 14, 2010 6:10 am Post subject: Re: Losing rpm on takeoff

Hi Occom,



Glad it worked out, now it's time to just kick back and have fun flying.



I have lots of people ask me what static rpm to set. My standard answer is; the static is only a place to start when putting on a new prop and you have no real idea of an exact pitch and final rpm. I always tell them set a general static rpm and go fly. Flying is the only way to be exact and sure of the final results. This is the only way to dial in a prop/engine rpm to match your plane and local flying conditions.

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Tucson, Az.
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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Tue Dec 14, 2010 6:53 am Post subject: Re: Losing rpm on takeoff

 	  occom wrote: 	
		  Problem solved, although what is actually happening is a subject of some  debate.



Those who operate the Warp drive taper tip props or have  experience with them were exactly right and ignoring static RPM was clearly the  way to go. I ended up with a very nice smoooth prop after reducing pitch  significantly. 

It is now pitched to allow 6200 rpm in full throttle climb at  0 deg temp. I expect we will have to revisit this when it warms up. The engine  will overspeed quite easily on the ground until speed builds. I have spoken to a  

few others with the same type of prop and their expereince is  similar.  



Thanks to those who offered asistance, it would have  taken somewhat longer to get it right without it. 

   	




That sounds pretty close to me. On my Kolb/503, I got about 6300 on a normal climbout (tho I don't actually remember that speed offhand), tho that was slightly underpropped for WOT at straight and level IIRC.



But like I said, tho I love my powerfin, I wish I could make my 68" taper tip work on my tornado. Once I had the pitch dialed in I was able to do 100mph indicated (about 110mph true) at only half throttle (about 5100rpm) at 10,000' MSL. Plus, I could get a virtually constant 5400rpm on climbout even varying between 65 and 80mph indicated. 



The static rpm always seemed to settle at about 5200 rpm no matter what the pitch was set at (I went from 13.5 to about 15 degs in the course of the dialing in and the static was always the same).....



LS

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Titan II SS

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