---------------------------------------------------------- RV-List Digest Archive --- Total Messages Posted Fri 06/04/10: 6 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:50 AM - Airspeeds (Wheeler North) 2. 08:09 AM - Re: Airspeeds (Denis Walsh) 3. 01:09 PM - Re: some approx V speeds (HCRV6@comcast.net) 4. 01:38 PM - Re: some approx V speeds (thomas sargent) 5. 04:42 PM - Re: some approx V speeds (Ed Anderson) 6. 05:39 PM - Re: some approx V speeds (Kevin Horton) ________________________________ Message 1 _____________________________________ Time: 07:50:23 AM PST US From: "Wheeler North" Subject: RV-List: Airspeeds While I think we can prove that an airplane will perform best at some specific speed like 91.23098 kts I would defy anyone to be able to keep it at that airspeed, particularly on a gusty day with thermals and in an emergency, while you are actually supposed to be looking out versus pegging your eyes to interior gauges. Reduce your mental workload by keeping it simple. 90kts for everything in the ATA or an emergency, 70kts for anything with flaps out. On this latter one if you are not comfortable with the airplane kick that up to 75 or 80 kts, but know that this will cause you to float a bit as you rotate to touch down. Practice slow flight ASAP and often, we should all do this... the advice is straight from the mouth of Dick VanGrunsven. Then use 70 kts for all flaps down operations. The 90kts value also gives you more time to process things, see other aircraft, make sounder decisions etc. as opposed to screaming into downwind at warp factor 12 only to piss off some poor C150 as you climb up their static port... ________________________________ Message 2 _____________________________________ Time: 08:09:51 AM PST US From: Denis Walsh Subject: Re: RV-List: Airspeeds Wheeler, this one will likely stir up a blizzard of responses. Piloting techniques do vary quite a bit. I look forward to reading a lot of information and misinformation. As for me, I want to go on record as agreeing with you 100%. D. Walsh On Jun 4, 2010, at 8:49 , Wheeler North wrote: > > While I think we can prove that an airplane will perform best at some > specific speed like 91.23098 kts I would defy anyone to be able to > keep it > at that airspeed, particularly on a gusty day with thermals and in an > emergency, while you are actually supposed to be looking out versus > pegging > your eyes to interior gauges. > Reduce your mental workload by keeping it simple. 90kts for > everything in > the ATA or an emergency, 70kts for anything with flaps out. On this > latter > one if you are not comfortable with the airplane kick that up to 75 > or 80 > kts, but know that this will cause you to float a bit as you rotate > to touch > down. > Practice slow flight ASAP and often, we should all do this... the > advice is > straight from the mouth of Dick VanGrunsven. Then use 70 kts for all > flaps > down operations. > The 90kts value also gives you more time to process things, see other > aircraft, make sounder decisions etc. as opposed to screaming into > downwind > at warp factor 12 only to piss off some poor C150 as you climb up > their > static port... > > ________________________________ Message 3 _____________________________________ Time: 01:09:41 PM PST US From: HCRV6@comcast.net Subject: Re: RV-List: some approx V speeds Please explain: Whether you have fixed pitch or constant speed prop makes a difference. Harry Crosby RV-6 N16CX, 693 hours ________________________________ Message 4 _____________________________________ Time: 01:38:52 PM PST US Subject: Re: RV-List: some approx V speeds From: thomas sargent Yes. I have a fixed pitch prop and a 180hp IO-360-B2B On Fri, Jun 4, 2010 at 1:08 PM, wrote: > Please explain: > > > Whether you have fixed pitch or constant speed prop makes a difference. > > Harry Crosby > RV-6 N16CX, 693 hours > > -- Tom Sargent ________________________________ Message 5 _____________________________________ Time: 04:42:08 PM PST US From: "Ed Anderson" Subject: RE: RV-List: some approx V speeds Harry, When I first did my airspeed checks with my fixed pitch prop RV-6A, I couldn't get anywhere near the performance/airspeed figures that Van quoted. It turns out his figures are for engines with a constant speed prop. My best climb speed Vy turns out to be 120 MPH IAS, considerably higher than the Van's figure. I'm sure there is someone out there that can give you a more understandable explanation - but it goes something like this. Here is how I see it - with a constant speed prop, you can get more HP at slow airspeeds by making the pitch finer producing less load on the engine, which results in more RPM which results in more HP. When you are discussing climb it's the EXTRA HP above that required to maintain level flight than causes you to climb. If you can increase your HP above that necessary for level flight, you can increase your climb rate at any airspeed (well, just about).. With a fixed pitch prop, you have the maximum load on the prop and therefore the engine at slower airspeeds during climb-out, that keeps the rpm lower and therefore HP down compared to a constant speed prop. Therefore, in order to get more climb you need to produce more HP, with a fixed pitch prop you do that by flying a higher airspeed unloading the prop and engine a bit thereby permitting more rpm and HP and higher climb rate. 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 _____ From: owner-rv-list-server@matronics.com [mailto:owner-rv-list-server@matronics.com] On Behalf Of HCRV6@comcast.net Sent: Friday, June 04, 2010 4:09 PM Subject: Re: RV-List: some approx V speeds Please explain: Whether you have fixed pitch or constant speed prop makes a difference. Harry Crosby RV-6 N16CX, 693 hours ________________________________ Message 6 _____________________________________ Time: 05:39:22 PM PST US From: Kevin Horton Subject: Re: RV-List: some approx V speeds I was messing around a few months ago, making some charts to illustrate a magazine article on climb performance that I intend to finish someday. I used the combination of CAFE Foundation drag vs speed data for the RV-6A, Lycoming O-360 power charts and some Hartzell prop efficiency maps. I used that data to predict climb performance at various altitudes and speeds. I didn't have any fixed pitch prop efficiency data, so I used the Hartzell data, but forced it to use the same pitch for all conditions. The pitch was selected to give 2700 rpm at full throttle at 8000 ft. The attached chart shows how Vx and Vy are predicted to vary with altitude for both fixed pitch and constant speed props. You will note that Vx and Vy are quite a bit faster with fixed pitch props, as the rpm and power increase as the airspeed is increased. You will also note that there is a significant variation of Vx and Vy with altitude. I caution that this is a very crude prediction. It may not match the actual performance at all, so use at your own risk. It is interesting to note that the predicted fixed pitch Vy at sea level (105 kt, or 121 mph) is close to what Ed found. That may be blind luck. Kevin Horton Ottawa, Canada On 04/06/10 07:41 PM, Ed Anderson wrote: > > Harry, > > When I first did my airspeed checks with my fixed pitch prop RV-6A, I > couldn't get anywhere near the performance/airspeed figures that Van > quoted. It turns out his figures are for engines with a constant > speed prop. > > My best climb speed Vy turns out to be 120 MPH IAS, considerably > higher than the Van's figure. > > I'm sure there is someone out there that can give you a more > understandable explanation -- but it goes something like this. > > Here is how I see it -- with a constant speed prop, you can get more > HP at slow airspeeds by making the pitch finer producing less load on > the engine, which results in more RPM which results in more HP. When > you are discussing climb it's the EXTRA HP above that required to > maintain level flight than causes you to climb. If you can increase > your HP above that necessary for level flight, you can increase your > climb rate at any airspeed (well, just about).. > > With a fixed pitch prop, you have the maximum load on the prop and > therefore the engine at slower airspeeds during climb-out, that keeps > the rpm lower and therefore HP down compared to a constant speed > prop. Therefore, in order to get more climb you need to produce more > HP, with a fixed pitch prop you do that by flying a higher airspeed > unloading the prop and engine a bit thereby permitting more rpm and HP > and higher climb rate. > > 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 > > ------------------------------------------------------------------------ > > *From:* owner-rv-list-server@matronics.com > [mailto:owner-rv-list-server@matronics.com] *On Behalf Of > *HCRV6@comcast.net > *Sent:* Friday, June 04, 2010 4:09 PM > *To:* rv-list@matronics.com > *Subject:* Re: RV-List: some approx V speeds > > Please explain: > > Whether you have fixed pitch or constant speed prop makes a difference. > > Harry Crosby > RV-6 N16CX, 693 hours > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message rv-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/RV-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/rv-list Browse Digests http://www.matronics.com/digest/rv-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.