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[70.196.201.113]) by mx.google.com with ESMTPS id t22sm139036anh.20.2012.07.10.16.41.05 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 10 Jul 2012 16:42:32 -0700 (PDT) Subject: Re: [FlyRotary] Re: On the step References: From: Tracy Content-Type: multipart/alternative; boundary=Apple-Mail-40677A2A-94E1-4FF4-BC25-0FDB2EF051EC X-Mailer: iPad Mail (9B206) In-Reply-To: Message-Id: <6E0B0F36-460B-4A89-87FB-F3F1FA38558A@gmail.com> Date: Tue, 10 Jul 2012 17:40:38 -0600 To: Rotary motors in aircraft Content-Transfer-Encoding: 7bit Mime-Version: 1.0 (1.0) --Apple-Mail-40677A2A-94E1-4FF4-BC25-0FDB2EF051EC Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 Everybody likes to quote 75% cruise power performance numbers for their airp= lane but in the real world very few recreational fliers actually fly at thos= e numbers. Unless you time is EXTREAMLY valuable or you are running out of= daylight or weather, those last 25 kts are not worth the fuel cost. =20 =20 Hey, I actually LIKE being in the air, why would I spend a lot of money to g= et down sooner? Tracy Sent from my iPad On Jul 10, 2012, at 4:12 PM, "Bill Bradburry" wro= te: > Charlie, > You could be right about this. I think I remember him telling me that he r= uns the engine at 2450 rpm at cruise. I don=E2=80=99t know what his fuel bu= rn 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 g= round and true are only the same under no wind conditions, but I haven=E2=80= =99t seen anything higher than 159 anywhere. > =20 > Bill > =20 > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Be= half Of Charlie England > Sent: Tuesday, July 10, 2012 2:20 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] Re: On the step > =20 > Here you go: > http://www.vansaircraft.com/public/rv-7per.htm >=20 > Van's numbers are: 75% cruise at 8k ft is 207 statute mph. This is with a c= onstant 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 2= 00 hp...). If google's math is right, assuming 200 mph cruise that would be 1= 73+ kts. Assuming 150 hp, .45 lbs/HP/Hr properly leaned fuel burn & 6 lbs pe= r gallon fuel weight, that's ~11.25 gal per hour fuel burn (say 11.75 gph fo= r sloppy and/or paranoid leaning practice). I bet he's burning a lot less th= an that, right?=20 >=20 > I bet that he's running at far less than full throttle at 8000 ft & turnin= g closer to 2400 rpm than the rated 2700 required to get 75% power at that a= ltitude. >=20 > Charlie >=20 >=20 > On 07/09/2012 10:38 PM, Bill Bradburry wrote: > Hi Charlie, > =20 > I don=E2=80=99t have any idea what Van=E2=80=99s performance numbers are??= Where would I find those? > =20 > Bill B > =20 > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Be= half Of Charlie England > Sent: Monday, July 09, 2012 3:45 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] Re: On the step > =20 > Hi Bill, >=20 > There's something seriously outside the norm if he's only getting 150 kts a= t 8k ft full throttle. Any properly built -7 will come very close to Van's s= pec performance numbers. The fixed pitch prop would have little effect on cr= uise, if pitched properly for the plane & HP. 160 hp -7's with FP props can e= asily hit that cruise figure. >=20 > Charlie >=20 >=20 > On 07/09/2012 02:02 PM, Bill Bradburry wrote: > Brian, > =20 > Getting =E2=80=9Con the step=E2=80=9D might get you at your terminal veloc= ity/hp/rpm equilibrium sooner, but no matter when, at some time it will all l= evel 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 m= atter how you got there. > =20 > 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. W= hen the load from the plane comes back, when you level out, the rpm will dro= p back because the hp is now being used to pull the plane as before. If thi= s didn=E2=80=99t work this way, you could carry a plane with a 3 hp lawnmowe= r 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 m= aintain mach 2!!! :>) > =20 > 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. Y= ou could probably use him as a guide for performance on your plane. At 8K f= eet he is at close to 75% power. Say 150 HP. > =20 > B2 > =20 > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Be= half Of bktrub@aol.com > Sent: Monday, July 09, 2012 12:43 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] On the step > =20 > I commented on here recently about how I took a cross- country flight to W= alla Walla from Everett, Wa recently and was only seeing 140-150 mph cruise a= t 11,500 feet. It got me to thinking- I was getting about 6200 rpm on the en= gine which is 2175 at the prop. So, I'm a little overpropped/ underpowered. > =20 > So, there's the old chestnut about how you can get a few more knots from a= n airplane in cruise if you go a little above your cruise altitude and then d= escend to your cruise altitude, thereby getting "on the step" . Some pilots s= wear by this, others dismiss it. I have a theory- if I climb to a cruise alt= itude and stay at full throttle while doing so, I will only get the engine t= o run up to a certain RPM and therefore a certain hp will be achieved, and n= o more and so the airplane will settle into an equilibrium at a certain spee= d- say at whatever hp/speed - 140 mph at 6200 rpm- lt's say x hp. > =20 > Now, If I were to descend to my cruise altitude in a shallow dive, I will b= e acheiving a higher rpm and hence horsepower, say 6800 rpm and horsepower w= ill be x + 9%x for a hp of 109% of the hp achieved at 6200 rpm, so I should b= e able to achieve and maintain a higher cruise speed if I descend to my cru= ising altitude. ( I picked 9% arbitrarily for the sake of argument) . > =20 > Anyone want to shoot me down on this one? > =20 > 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 f= lap on it. That's a project for this winter. > =20 > Brian Trubee > =20 > =20 --Apple-Mail-40677A2A-94E1-4FF4-BC25-0FDB2EF051EC Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
Everybody likes to quote 7= 5% cruise power performance numbers for their airplane but in the real world= very few recreational fliers actually fly at those numbers.   Unless y= ou time is EXTREAMLY valuable or you are running out of daylight or weather,= those last 25 kts are not worth the fuel cost.   
 = ; 
Hey, I actually LIKE being in the air, why would I spend a= lot of money to get down sooner?

Tracy

Sent= from my iPad

On Jul 10, 2012, at 4:12 PM, "Bill Bradburry" &l= t;bbradburry@bellsouth.net&g= t; wrote:

=

Charlie,

You could be right about this.  I t= hink I remember him telling me that he runs the engine at 2450 rpm at cruise.&nbs= p; I don=E2=80=99t know what his fuel burn is, but I looked at several of his fli= ghts 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=E2=80=99t seen anything higher than 15= 9 anywhere.

 

Bill

 

<= span style=3D"font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weig= ht:bold">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 t= he 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 mor= e than 5 mph unless he has it pitched for climb (not much need for that with 2= 00 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 pe= r 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 & turn= ing 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,

 <= /o:p>

I don=E2=80=99t have any idea what Van=E2=80=99s performance numbers are??  Where would I find those?

 <= /o:p>

Bill B<= /o:p>

 <= /o:p>

<= span style=3D"font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weig= ht:bold">From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Charlie England<= br> Sent: Monday, July 09, 2012 3= :45 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: On t= he 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 =E2=80=9Con the step=E2=80=9D m= ight 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 t= he plane to increase the prop rpm.  When the load from the plane comes bac= k, when you level out, the rpm will drop back because the hp is now being used t= o pull the plane as before.  If this didn=E2=80=99t work this way, you co= uld carry a plane with a 3 hp lawnmower engine up to 30K feet and drop it out an= d 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 knot= s 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.&nbs= p; Say 150 HP.

 =

B2

 =

<= span style=3D"font-size:10.0pt;font-family:Tahoma;font-weight:bold">From: Rotary motors in aircraft<= /st1:personname> [mai= lto:flyrotary@lancaironline.net] On Behalf Of bktrub@aol.com
Sent: Monday, July 09, 2012 1= 2:43 PM
To: Rotary motors i= n aircraft
Subject: [FlyRotary] On the s= tep

 

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 pr= op. 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 crui= se 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 wil= l only get the engine to run up to a certain RPM and therefore a certain hp wi= ll 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 h= 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 680= 0 rpm and horsepower will be x + 9%x for a hp of 109% of the hp achieved at 62= 00 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 fir= st I have to clean up my drag. My cooling scoop is effective, but obviously dragg= y. And It needs a flap on it. That's a project for this winter.

 

Brian Trubee

 

 

= --Apple-Mail-40677A2A-94E1-4FF4-BC25-0FDB2EF051EC--