X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail-qy0-f182.google.com ([209.85.221.182] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4151404 for flyrotary@lancaironline.net; Wed, 03 Mar 2010 19:04:40 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.221.182; envelope-from=rwstracy@gmail.com Received: by qyk12 with SMTP id 12so1388607qyk.7 for ; Wed, 03 Mar 2010 16:04:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to :content-type; bh=qjMt6U4BgpmBRGmhJtDbN2UGHk4tYhaKw66J5Wqbq7Q=; b=OLROjfKYZOyqqqRWbOSRlFmAxgQbPeCatbGTX5HPGk15YDEPiAI9bNqhvR0MfxKk5D 7R/P28uIKJWrCgdbPVOAOrzxaISIT9HWrR01uO08FRT6UtwL/GLt1WwINRzDhP0wAltH q2gbs80UIxXmjeFimzE1R0GXDZkWo/UfxMnpA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type; b=fPYEgX1B4XEGY7V4BlVPji/AdueI2CaKwFxqa5HlbqO9OHPNgVBwsqSSHJ7P3g3IVQ h2TK/GmVmWBu2XdoCeBdJIjlT3MslnPxvVmbqmuKKUsKpJninDZO9YPpyPs3alVuNLfB /F3Bvp2a7UyvyJDHzm3+v9sxDmWDSRa1srGGY= MIME-Version: 1.0 Sender: rwstracy@gmail.com Received: by 10.224.91.144 with SMTP id n16mr4962396qam.316.1267661044161; Wed, 03 Mar 2010 16:04:04 -0800 (PST) In-Reply-To: References: Date: Wed, 3 Mar 2010 16:04:04 -0800 X-Google-Sender-Auth: 7d8a40247feb57a2 Message-ID: <1b4b137c1003031604i41c89422tea414dba5f6b4144@mail.gmail.com> Subject: Re: [FlyRotary] Re: single rotor From: Tracy Crook To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=00c09f99e37a3bab770480ee56a6 --00c09f99e37a3bab770480ee56a6 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable "Did you lose a little =93top end=94 when you trimmed the prop?" Nope. Short props work well at high speeds. Long props favor low speed performance. But this ignores HP. The HP gain with the higher engine rpm= s obtained with the shortened prop overshadows the minor 2" change in diamete= r on both climb and top speed ends of the scale. Matching the prop to engin= e (and aircraft speed envelope) was the object in shortening the prop, not optimum theoretical prop length. Tracy On Wed, Mar 3, 2010 at 3:18 PM, Bryan Winberry wrote: > Tracy or Ed, > > Did you lose a little =93top end=94 when you trimmed the prop? > > Bryan > > > ------------------------------ > > *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] *O= n > 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 w= ith > 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 mo= st > 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=92t worry, you can not ramble on too much for me! > > > > Bill B > > > ------------------------------ > > *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] *O= n > 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 th= e > 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 diamet= er > 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 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 doe= s > 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..??? > > > > Bill B (hoping this generates an educational experience for me :>) > > > > We=92re talking about the amount of force exerted by the prop with the pl= ane > (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 o= f > 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 p= ump > (or generator) on a dyno. So I don=92t know how Tracy was interpreting t= he > question. > > > > Al > > > --00c09f99e37a3bab770480ee56a6 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable
"Did you lose a little =93to= p end=94 when you trimmed the prop?"
=A0
Nope.=A0=A0
=A0
Short props work well at high speeds.=A0 Long props favor low speed pe= rformance.=A0 But this ignores HP.=A0=A0 The HP gain with the higher engine= rpms obtained with the shortened prop overshadows the minor 2" change= in diameter on both climb and top speed ends of the scale.=A0=A0 Matching = the prop to engine (and aircraft=A0speed envelope) was the object in shorte= ning the prop, not optimum theoretical prop length.
=A0
Tracy

On Wed, Mar 3, 2010 at 3:18 PM, Bryan Winberry <= span dir=3D"ltr"><bryanwi= nberry@bellsouth.net> wrote:

Tracy or Ed,

Did you lose a = little =93top end=94 when you trimmed the prop?

Bryan

=A0

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:<= /b> [FlyRotary] Re: single rotor

=A0

I would like to get some educational (for me) discuss= ions going on this.=A0

A prop of 76 X 88 is pretty common in our usage.=A0 T= racy, Ed, and I have a Performance Prop in this dimension.=A0 Dennis and ma= ybe others have a Catto prop in this dimension.=A0 We all seem to be gettin= g static rpm of about 52-5400 rpm (except for Dennis with his new DIE manif= old).=A0 Tracy and Ed had their prop cut down to 74 X 88 and are getting in= creased static to around 6000 rpm.=A0 Higher rpm =3D higher HP for the rota= ry.=A0 We should get higher thrust with a slightly smaller diameter prop?= =A0 This has something to do with the idea of sizing the prop to the engine= .=A0 I wonder what is the proper size?=A0 What is the proper static rpm for= best performance with the rotary? =A0 What did Tracy and Ed lose in prop p= erformance and what did they gain in total performance when they cut the pr= op down?

=A0

It seems to me that a prop sized for climb would allo= w around 7500 rpm at about Vx or Vy?=A0 Max speed would require 7500 rpm at= WOT sea level?=A0 I wonder what rpm our props allow at these speeds?=A0 If= you had a prop that would do the above, I wonder what the static rpm would= be?=A0 Then since most of us have fixed pitch props, I wonder where we sho= uld try to be for the best of both worlds (a compromise)?

=A0

We have some really good engineers in this group and = they have made these selections.=A0 I know they know why they made the sele= ction they did.=A0 How about sharing?=A0 :>)

Don=92t worry, you can not ramble on too much for me!=

=A0

Bill B

=A0

From: Rotary motors in aircraft [ma= ilto:flyro= tary@lancaironline.net] On Behalf = Of Tracy Crook
Sent: Wednesday, March 03, = 2010 2:32 PM
To: Rotary = motors in aircraft
Subject:<= /b> [FlyRotary] Re: single rotor

Al is correct about it taking HP to make static thrus= t with a prop but the assumption about the relationship between HP and stat= ic thrust is subject to a lot of variables.=A0 There is no fixed relationsh= ip between static thrust and HP.=A0=A0 If there were, you could not account= for the ability of most helicopters to=A0hover.=A0=A0

=A0

=A0You could easily increase static thrust by 1.18 by= increasing the diameter of the prop=A0and the=A0reduction ratio of the red= rive=A0with=A0NO increase in HP.=A0

=A0

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

=A0

Tracy

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

Looking at the two siz= es of the engine, it takes 1.6 times as much horsepower to develop 1.18 tim= es as much static thrust!=A0 Somehow this does not compute for me=85.I alwa= ys doubt the performance figures in a sales presentation and when they don= =92t make sense to me=85..???

=A0

<= /div>

Bill B (hoping this ge= nerates an educational experience for me=A0 :>)=A0

=A0

We=92re tal= king about the amount of force exerted by the prop with the plane (motor) s= tanding still.

So, it seem= s to make sense to me that the power needed to accelerate the air to genera= te the thrust would go as the cube root; and the cube root of 1.6 is very c= lose 1.18.

=A0

To move the= amount of air it takes to generate the thrust certainly does take horsepow= er.=A0 Very much the same as the power it takes to drive the pump (or gener= ator) on a dyno. =A0So I don=92t know how Tracy was interpreting the questi= on.

=A0

Al<= /p>

=A0

<= br> --00c09f99e37a3bab770480ee56a6--