X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost05.isp.att.net ([204.127.217.105] verified) by logan.com (CommuniGate Pro SMTP 5.4.6) with ESMTP id 5646224 for flyrotary@lancaironline.net; Tue, 10 Jul 2012 18:13:05 -0400 Received-SPF: none receiver=logan.com; client-ip=204.127.217.105; envelope-from=bbradburry@bellsouth.net Received: from desktop (adsl-74-235-237-236.mco.bellsouth.net[74.235.237.236]) by isp.att.net (frfwmhc05) with SMTP id <20120710221229H0500h5e3de>; Tue, 10 Jul 2012 22:12:29 +0000 X-Originating-IP: [74.235.237.236] From: "Bill Bradburry" To: "'Rotary motors in aircraft'" References: In-Reply-To: Subject: RE: [FlyRotary] Re: On the step Date: Tue, 10 Jul 2012 18:12:31 -0400 Message-ID: <2E164DC17C9D4BDB9FD8A6C03B5DA0B8@Desktop> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_002D_01CD5EC7.93137080" X-Mailer: Microsoft Office Outlook 11 Thread-Index: Ac1eyL66YAQFb+6fS46WfSa4SsuEDgAH7bIg X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18463 This is a multi-part message in MIME format. ------=_NextPart_000_002D_01CD5EC7.93137080 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Charlie, You could be right about this. I think I remember him telling me that he runs the engine at 2450 rpm at cruise. I don't know what his fuel burn is, but I looked at several of his flights on FlightAware and he is doing a ground speed of 150 knots just about everywhere he goes. I realize that ground and true are only the same under no wind conditions, but I haven't seen anything higher than 159 anywhere. Bill _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Charlie England Sent: Tuesday, July 10, 2012 2:20 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: On the step Here you go: http://www.vansaircraft.com/public/rv-7per.htm Van's numbers are: 75% cruise at 8k ft is 207 statute mph. This is with a constant speed prop, but even with a wood fixed pitch, he shouldn't lose more than 5 mph unless he has it pitched for climb (not much need for that with 200 hp...). If google's math is right, assuming 200 mph cruise that would be 173+ kts. Assuming 150 hp, .45 lbs/HP/Hr properly leaned fuel burn & 6 lbs per gallon fuel weight, that's ~11.25 gal per hour fuel burn (say 11.75 gph for sloppy and/or paranoid leaning practice). I bet he's burning a lot less than that, right? I bet that he's running at far less than full throttle at 8000 ft & turning closer to 2400 rpm than the rated 2700 required to get 75% power at that altitude. Charlie On 07/09/2012 10:38 PM, Bill Bradburry wrote: Hi Charlie, I don't have any idea what Van's performance numbers are?? Where would I find those? Bill B _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Charlie England Sent: Monday, July 09, 2012 3:45 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: On the step Hi Bill, There's something seriously outside the norm if he's only getting 150 kts at 8k ft full throttle. Any properly built -7 will come very close to Van's spec performance numbers. The fixed pitch prop would have little effect on cruise, if pitched properly for the plane & HP. 160 hp -7's with FP props can easily hit that cruise figure. Charlie On 07/09/2012 02:02 PM, Bill Bradburry wrote: Brian, Getting "on the step" might get you at your terminal velocity/hp/rpm equilibrium sooner, but no matter when, at some time it will all level out at the equilibrium point. You might be able to dive and pick up 9% more, but it will not hold and will eventually bleed off the same point no matter how you got there. It seems true that you can judge the rotary hp by its rpm, but in the case of the shallow dive, you are actually reducing the load on the prop and the engine uses the hp not needed to pull the plane to increase the prop rpm. When the load from the plane comes back, when you level out, the rpm will drop back because the hp is now being used to pull the plane as before. If this didn't work this way, you could carry a plane with a 3 hp lawnmower engine up to 30K feet and drop it out and the engine would be producing 10,000 hp by the time it got down to sea level!! It would then level out and maintain mach 2!!! :>) My next door hangar neighbor has an RV-7 with a 200HP fixed pitch prop and he is pretty consistently running 150 knots of true airspeed at 8K feet. You could probably use him as a guide for performance on your plane. At 8K feet he is at close to 75% power. Say 150 HP. B2 _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of bktrub@aol.com Sent: Monday, July 09, 2012 12:43 PM To: Rotary motors in aircraft Subject: [FlyRotary] On the step I commented on here recently about how I took a cross- country flight to Walla Walla from Everett, Wa recently and was only seeing 140-150 mph cruise at 11,500 feet. It got me to thinking- I was getting about 6200 rpm on the engine which is 2175 at the prop. So, I'm a little overpropped/ underpowered. So, there's the old chestnut about how you can get a few more knots from an airplane in cruise if you go a little above your cruise altitude and then descend to your cruise altitude, thereby getting "on the step" . Some pilots swear by this, others dismiss it. I have a theory- if I climb to a cruise altitude and stay at full throttle while doing so, I will only get the engine to run up to a certain RPM and therefore a certain hp will be achieved, and no more and so the airplane will settle into an equilibrium at a certain speed- say at whatever hp/speed - 140 mph at 6200 rpm- lt's say x hp. Now, If I were to descend to my cruise altitude in a shallow dive, I will be acheiving a higher rpm and hence horsepower, say 6800 rpm and horsepower will be x + 9%x for a hp of 109% of the hp achieved at 6200 rpm, so I should be able to achieve and maintain a higher cruise speed if I descend to my cruising altitude. ( I picked 9% arbitrarily for the sake of argument) . Anyone want to shoot me down on this one? This is just an theory, If I want to go faster first I have to clean up my drag. My cooling scoop is effective, but obviously draggy. And It needs a flap on it. That's a project for this winter. Brian Trubee ------=_NextPart_000_002D_01CD5EC7.93137080 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

Charlie,

You could be right about = this.  I think I remember him telling me that he runs the engine at 2450 rpm at = cruise.  I don’t know what his fuel burn is, but I looked at several of his = flights on FlightAware and he is doing a ground speed of 150 knots just about everywhere he goes.  I realize that ground and true are only the = same under no wind conditions, but I haven’t seen anything higher than = 159 anywhere.

 

Bill

 

From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Charlie England
Sent: Tuesday, July 10, = 2012 2:20 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = On the step

 

Here you go:
http://www.vansai= rcraft.com/public/rv-7per.htm

Van's numbers are: 75% cruise at 8k ft is 207 statute mph. This is with = a constant speed prop, but even with a wood fixed pitch, he shouldn't lose = more than 5 mph unless he has it pitched for climb (not much need for that = with 200 hp...). If google's math is right, assuming 200 mph cruise that would be = 173+ kts. Assuming 150 hp, .45 lbs/HP/Hr properly leaned fuel burn & 6 = lbs per gallon fuel weight, that's ~11.25 gal per hour fuel burn (say 11.75 gph = for sloppy and/or paranoid leaning practice). I bet he's burning a lot less = than that, right?

I bet that he's running at far less than full throttle at 8000 ft & = turning closer to 2400 rpm than the rated 2700 required to get 75% power at that altitude.

Charlie


On 07/09/2012 10:38 PM, Bill Bradburry = wrote:

Hi Charlie,

 

I don’t have any idea what Van’s performance numbers are??  Where would I find = those?

 

Bill = B

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironlin= e.net] On Behalf Of Charlie = England
Sent: Monday, July 09, = 2012 3:45 PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = On the step

 

Hi = Bill,

There's something seriously outside the norm if he's only getting 150 = kts at 8k ft full throttle. Any properly built -7 will come very close to Van's = spec performance numbers. The fixed pitch prop would have little effect on = cruise, if pitched properly for the plane & HP. 160 hp -7's with FP props = can easily hit that cruise figure.

Charlie


On 07/09/2012 02:02 PM, Bill Bradburry wrote: =

Brian,

 

Getting “on the step” = might get you at your terminal velocity/hp/rpm equilibrium sooner, but no = matter when, at some time it will all level out at the equilibrium point.  = You might be able to dive and pick up 9% more, but it will not hold and will eventually bleed off the same point no matter how you got = there.

 

It seems true that you can judge = the rotary hp by its rpm, but in the case of the shallow dive, you are = actually reducing the load on the prop and the engine uses the hp not needed to = pull the plane to increase the prop rpm.  When the load from the plane comes = back, when you level out, the rpm will drop back because the hp is now being = used to pull the plane as before.  If this didn’t work this way, you = could carry a plane with a 3 hp lawnmower engine up to 30K feet and drop it = out and the engine would be producing 10,000 hp by the time it got down to sea = level!!  It would then level out and maintain mach 2!!!  = :>)

 

My next door hangar neighbor has an = RV-7 with a 200HP fixed pitch prop and he is pretty consistently running 150 = knots of true airspeed at 8K feet.  You could probably use him as a guide = for performance on your plane.  At 8K feet he is at close to 75% = power.  Say 150 HP.

 

B2<= /u1:p>

 

From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of bktrub@aol.com
Sent: Monday, July 09, = 2012 12:43 PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] On = the step

 =

I commented on here recently about how I took = a cross- country flight to Walla Walla from Everett, Wa recently and was only seeing 140-150 mph cruise at 11,500 feet. It got = me to thinking- I was getting about 6200 rpm on the engine which is 2175 at = the prop. So, I'm a little overpropped/ underpowered. =

 <= o:p>

So, there's the old chestnut about how you can = get a few more knots from an airplane in cruise if you go a little above your = cruise altitude and then descend to your cruise altitude, thereby getting = "on the step" . Some pilots swear by this, others dismiss it. I have a = theory- if I climb to a cruise altitude and stay at full throttle while doing so, I = will only get the engine to run up to a certain RPM and therefore a certain = hp will be achieved, and no more and so the airplane will settle into an = equilibrium at a certain speed- say at whatever hp/speed - 140 mph at 6200 rpm- lt's = say x hp.

 <= o:p>

Now, If I were to descend to my cruise = altitude in a shallow dive, I will be acheiving a higher rpm and hence horsepower, say = 6800 rpm and horsepower will be x + 9%x for a hp of 109% of the hp achieved = at 6200 rpm, so I should be able to achieve and maintain a higher cruise  = speed if I descend to my cruising altitude. ( I picked 9% arbitrarily for the = sake of argument) .

 <= o:p>

Anyone want to shoot me down on this = one?

 <= o:p>

This is just an theory, If I want to go faster = first I have to clean up my drag. My cooling scoop is effective, but obviously = draggy. And It needs a flap on it. That's a project for this winter. =

 <= o:p>

Brian = Trubee

 

 

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