X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.122] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4151449 for flyrotary@lancaironline.net; Wed, 03 Mar 2010 20:16:05 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.122; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.0 c=1 a=cA-3C-Av9p8A:10 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=ekHE3smAAAAA:20 a=UretUmmEAAAA:8 a=Ia-xEzejAAAA:8 a=kviXuzpPAAAA:8 a=nUuTZ29dAAAA:8 a=FAudFDUr2tAdk1mkf9IA:9 a=hrMeux8Qg1ubGG02mkEA:7 a=FBvK9Gb6b3mpj7PoWg8wjGD4PuwA:4 a=1vhyWl4Y8LcA:10 a=EzXvWhQp4_cA:10 a=4vB-4DCPJfMA:10 a=yqjm12SAq4PzRAzp:21 a=lqwBmnwAXDiBokRA:21 a=SSmOFEACAAAA:8 a=7ZTLtd6-LCyVYq0Z8RAA:9 a=Lz7O-Ix1V6XUnNNUOMQA:7 a=s72Za0zpL9IqBN3ZS3xLfFq_6akA:4 a=VYdPZi_WzT7MIp8n:21 a=g2Ql6VWoqfevbRvU:21 a=tC6YKQLvsyiDG588E-sA:9 a=sNVqgiWbfm6gx21eht5QA4Equm4A:4 a=1Vq_FK4TplAA:10 a=rK7_Snnp8w1mzslLtbcA:9 a=tY9SOkmA9sggeAwJ54AA:9 a=OZJGW_Z213-B3NEgXKdzjVFaZkcA:4 a=q6PCrga3cWlUD47UAaQA:9 a=CzjJBf81rvx4PltPpKAA:9 a=Cw0yJJRF8uhkOVBUJO4Zf-kaV7wA:4 a=e2n4KQ7JTmKbnDR3ovAA:9 a=Yblhoe6ZdYcz7Y2O:18 a=i6GYtFeWOMyvAXi3:18 a=Uvyq_eEvy86UaCuJ:18 X-Cloudmark-Score: 0 X-Originating-IP: 75.191.186.236 Received: from [75.191.186.236] ([75.191.186.236:4357] helo=computername) by cdptpa-oedge01.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id E7/EE-08284-1B90F8B4; Thu, 04 Mar 2010 01:15:30 +0000 From: "Ed Anderson" Message-ID: To: "'Rotary motors in aircraft'" Subject: Fixed Pitch Prop Thrust was RE: [FlyRotary] Re: single rotor Date: Wed, 3 Mar 2010 20:15:33 -0500 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_00AC_01CABB0E.47A851B0" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 Thread-Index: Acq7HTiCBfNfXWiKSv62P4VHefD/xQAA8knQ In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_00AC_01CABB0E.47A851B0 Content-Type: multipart/alternative; boundary="----=_NextPart_001_00AD_01CABB0E.47A851B0" ------=_NextPart_001_00AD_01CABB0E.47A851B0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Arggg! Props! =20 Ok, Bill =96 here is my stab at it. The following equation tells the = tale =96 well some of it. =20 (1) where: T thrust [N] D propeller diameter [m] v velocity of incoming flow [m/s] additional velocity, acceleration by propeller [m/s] density of fluid [kg/m=B3] =20 (air: =3D 1.225 kg/m=B3, water: =3D 1000 kg/m=B3) =20 =20 =20 Thrust is about increasing the momentum of the air mass passing through = the prop disc. Static thrust occurs while sitting still - therefore v (the = air velocity of air in front of the prop disc) =3D 0. So the addition = momentum imparted to the air mass by our spinning prop is p*DV. Since the air = mass p during our run up is essentially constant ), that leaves two variables - = the diameter of the prop D and the amount the spinning prop accelerates the = air (Dv) to affect the thrust (T) generated.=20 =20 The following are extracts from some of the better article (more understandable) material I have read about props and static thrust. As = it concludes and Tracy points out Static Thrust does not really tell the = whole story. =20 =20 For a typical, fixed pitch propeller, the largest induced velocity = occurs under static conditions, where the efficiency is small. It decreases = with increasing flight speed, until it reaches zero: no thrust is generated. For a given power P, it is always desirable to use the largest possible propeller diameter D, which may be limited by mechanical restrictions (landing gear height) or aerodynamic constraints (tip Mach number). = That's why most man or solar powered airplanes use large, slowly turning props. These catch a large volume of air and accelerate it only slightly to = achieve the maximum efficiency. As long as an aircraft does not move, its propeller operates under = static conditions. There is no air moving towards the propeller due to the = flight speed, the propeller creates its own inflow instead. A propeller, with = its chord and twist distribution designed for the operating point under = flight conditions, does not perform very well under static conditions.=20 As opposed to a larger helicopter rotor, the flow around the relatively small propeller is heavily distorted and even may be partially = separated. From the momentum theory of propellers we learn, that the efficiency at lower speeds is strongly dependent on the power loading (power per disk area), and this ratio for a propeller is much higher than that for a helicopter rotor. We are able to achieve about 80-90% of the thrust, as predicted by momentum theory for the design point, but we can reach only = 50% or less of the predicted ideal thrust under static conditions. So much for theory. My personal experience when I went from the faster turning 68x72=94 prop to the slower turning (2.85 gear box) 76x88 prop = =96 my take off acceleration increased significantly indicating (in my opinion) more thrust was being generated. With the 76x88 prop and my old 13B I would generate 5800 rpm static (for what its worth), with it cut down to 74x88 I picked up 200 rpm for a static of 6000 rpm. Plus I got another = inch of ground clearance =96 needed on my nose geared Rv-6a. =20 =20 Interestingly enough the larger slower turning prop not only did not = hurt my top speed it actually increase around 4 mph =96 perhaps due to the = increased HP due to high rpm of the lighter loaded engine? =20 Ok, Bill that=92s my take and what I could pull out of references. = Don=92t know if it really tells us a whole lot =96 there are some good NACA studies = on Prop =96 but the math makes my head hurt. =20 Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry Sent: Wednesday, March 03, 2010 5:01 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: single rotor =20 I would like to get some educational (for me) discussions going on this. = =20 A prop of 76 X 88 is pretty common in our usage. Tracy, Ed, and I have = a Performance Prop in this dimension. Dennis and maybe others have a = Catto prop in this dimension. We all seem to be getting static rpm of about 52-5400 rpm (except for Dennis with his new DIE manifold). Tracy and Ed = had their prop cut down to 74 X 88 and are getting increased static to = around 6000 rpm. Higher rpm =3D higher HP for the rotary. We should get = higher thrust with a slightly smaller diameter prop? This has something to do = with the idea of sizing the prop to the engine. I wonder what is the proper size? What is the proper static rpm for best performance with the = rotary? What did Tracy and Ed lose in prop performance and what did they gain in total performance when they cut the prop down? =20 It seems to me that a prop sized for climb would allow around 7500 rpm = at about Vx or Vy? Max speed would require 7500 rpm at WOT sea level? I wonder what rpm our props allow at these speeds? If you had a prop that would do the above, I wonder what the static rpm would be? Then since = most of us have fixed pitch props, I wonder where we should try to be for the best of both worlds (a compromise)? =20 We have some really good engineers in this group and they have made = these selections. I know they know why they made the selection they did. How about sharing? :>) Don=92t worry, you can not ramble on too much for me! =20 Bill B=20 =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy Crook Sent: Wednesday, March 03, 2010 2:32 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: single rotor Al is correct about it taking HP to make static thrust with a prop but = the assumption about the relationship between HP and static thrust is = subject to a lot of variables. There is no fixed relationship between static = thrust and HP. If there were, you could not account for the ability of most helicopters to hover. =20 =20 You could easily increase static thrust by 1.18 by increasing the = diameter of the prop and the reduction ratio of the redrive with NO increase in = HP. =20 =20 But my real point was that static thrust is not a very useful = measurement to us. =20 Tracy On Wed, Mar 3, 2010 at 11:06 AM, Al Gietzen wrote: Looking at the two sizes of the engine, it takes 1.6 times as much horsepower to develop 1.18 times as much static thrust! Somehow this = does not compute for me=85.I always doubt the performance figures in a sales presentation and when they don=92t make sense to me=85..??? =20 Bill B (hoping this generates an educational experience for me :>) =20 =20 We=92re talking about the amount of force exerted by the prop with the = plane (motor) standing still. So, it seems to make sense to me that the power needed to accelerate the = air to generate the thrust would go as the cube root; and the cube root of = 1.6 is very close 1.18. =20 To move the amount of air it takes to generate the thrust certainly does take horsepower. Very much the same as the power it takes to drive the = pump (or generator) on a dyno. So I don=92t know how Tracy was interpreting = the question. =20 Al =20 __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com ------=_NextPart_001_00AD_01CABB0E.47A851B0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Arggg!=A0 Props!

 

Ok, Bill – here is my stab at it.=A0 The following equation tells the = tale – well some of it.

 

         &nbs= p; (1)

where:

T

thrust

[N]

D

propeller = diameter

[m]

v

velocity of incoming = flow

[m/s]

additional velocity, acceleration by = propeller

[m/s]

density of = fluid

[kg/m=B3]

 

(air:  =3D 1.225 = kg/m=B3, water:  =3D 1000 = kg/m=B3)

 

 

 

Thrust is about increasing the momentum of the air mass passing through the = prop disc.=A0 Static thrust occurs while sitting still - =A0therefore = v (the air velocity = of air in front of the prop disc) =A0=3D 0.=A0 So the addition momentum imparted to the = air mass by our spinning prop is p*D= V.=A0 = Since the air mass p during our run up is essentially constant ), that = leaves two variables - the diameter of the prop D and the amount the spinning prop accelerates the air = (Dv) to affect the =A0thrust (T) generated. =

 <= /span>

The following are extracts from some of the better article (more = understandable) material I have read about props and static thrust.=A0 As it concludes = and Tracy points = out Static Thrust does not really tell the whole story. =A0

 

For a typical, fixed pitch propeller, the largest = induced velocity = occurs under static conditions, where the efficiency = is small. It decreases with increasing flight speed, until it reaches zero: no = thrust is generated.

For a given power P, it is always desirable to use the largest possible = propeller diameter D, which may be = limited by mechanical restrictions (landing gear height) or aerodynamic = constraints (tip Mach number). That's why most man or solar powered airplanes use = large, slowly turning props. These catch a large volume of air and accelerate = it only slightly to achieve the maximum efficiency.

As long as an aircraft does not move, its propeller operates under static conditions. There is no air moving towards the propeller due to the = flight speed, the propeller creates its own inflow instead. A propeller, with = its chord and twist distribution designed for the operating point under = flight conditions, does not perform very well under static conditions. =

As opposed to a larger helicopter rotor, the flow around the relatively = small propeller is heavily distorted and even may be partially separated. From = the momentum theory of propellers we learn, that the efficiency at lower = speeds is strongly dependent on the power loading (power per disk area), and this = ratio for a propeller is much higher than that for a helicopter rotor. We are = able to achieve about 80-90% of the thrust, as predicted by momentum theory for = the design point, but we can reach only 50% or less of the predicted ideal = thrust under static conditions.

So much for theory.=A0 My personal experience when I went from the faster turning 68x72” prop to the = slower turning (2.85 gear box) 76x88 prop – my take off acceleration = increased significantly indicating (in my opinion) more thrust was being = generated.=A0 With the=A0 76x88 prop and my old 13B I would generate 5800 rpm static (for = what its worth), with it cut down to 74x88 I picked up 200 rpm for a static of = 6000 rpm.=A0 Plus I got another inch of ground clearance – needed on my = nose geared Rv-6a.=A0

 

Interestingly enough the larger = slower turning prop not only did not hurt my top speed it actually increase = around 4 mph – perhaps due to the increased HP due to high rpm of the = lighter loaded engine?

 

Ok, Bill that’s my take and = what I could pull out of references.=A0 Don’t know if it really tells us = a whole lot – there are some good NACA studies on Prop – but the = math makes my head hurt.

 

Ed

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry
Sent: Wednesday, March = 03, 2010 5:01 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = single rotor

 

I would like to get some educational (for me) discussions going = on this. 

A prop of 76 X 88 is pretty common in our usage.  Tracy, = Ed, and I have a Performance Prop in this dimension.  Dennis and maybe others = have a Catto prop in this dimension.  We all seem to be getting static rpm = of about 52-5400 rpm (except for Dennis with his new DIE manifold).  = Tracy and Ed had their prop cut down to 74 X 88 and are getting increased = static to around 6000 rpm.  Higher rpm =3D higher HP for the rotary.  We = should get higher thrust with a slightly smaller diameter prop?  This has something to do with the idea of sizing the prop to the engine.  I = wonder what is the proper size?  What is the proper static rpm for best performance with the rotary?   What did Tracy and Ed lose in prop performance and what did they gain in total performance when they cut = the prop down?

 

It seems to me that a prop sized for climb would allow around = 7500 rpm at about Vx or Vy?  Max speed would require 7500 rpm at WOT sea level?  I wonder what rpm our props allow at these speeds?  If = you had a prop that would do the above, I wonder what the static rpm would be?  Then since most of us have fixed pitch props, I wonder where = we should try to be for the best of both worlds (a = compromise)?

 

We have some really good engineers in this group and they have = made these selections.  I know they know why they made the selection = they did.  How about sharing?  :>)

Don’t worry, you can not ramble on too much for = me!

 

Bill B

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy Crook
Sent: Wednesday, March = 03, 2010 2:32 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = single rotor

Al is correct about it taking HP to make static thrust with a = prop but the assumption about the relationship between HP and static thrust is = subject to a lot of variables.  There is no fixed relationship between = static thrust and HP.   If there were, you could not account for the = ability of most helicopters = to hover.  

 

 You could easily increase static thrust by 1.18 by = increasing the diameter of the prop and the reduction ratio of the redrive with NO increase in HP.  =

 

But my real point was that static thrust is not a very useful measurement to us.

 

Tracy

On Wed, Mar 3, 2010 at 11:06 AM, Al Gietzen <ALVentures@cox.net> = wrote:

Looking at the two sizes of the engine, it takes 1.6 times as = much horsepower to develop 1.18 times as much static thrust!  Somehow this does not compute for me….I always doubt the performance figures in a sales presentation and when they don’t make sense to = me…..???

 

Bill B (hoping this generates an educational experience for = me  :>) 

 

We’re talking about the amount of force exerted by the = prop with the plane (motor) standing still.

So, it seems to make sense to me that the power needed to accelerate the air to generate the thrust would go as the cube root; and = the cube root of 1.6 is very close 1.18.

 

To move the amount of air it takes to generate the thrust = certainly does take horsepower.  Very much the same as the power it takes to = drive the pump (or generator) on a dyno.  So I don’t know how = Tracy was = interpreting the question.

 

Al

 



__________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com



__________ Information from ESET NOD32 Antivirus, version of = virus signature database 3267 (20080714) __________

The message = was checked by ESET NOD32 Antivirus.

http://www.eset.com
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