AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  explain full throttle height          AirTalk.org Forum Index -> Aviation (Students) View previous topic :: View next topic   Author Message d&tm Guest Posted: Tue Apr 06, 2004 8:24 pm    Post subject: explain full throttle height I am trying to understand the factors that determine best range and endurance, and keep coming across this term full throttle height, what does this mean? Dont know if I have the right books but I am finding this range and endurance stuff a bit confusing. Graphs of power versus airspeed make sense academically but what I want to know in practice is what power setting do I require, what attitude do I need and what altitude should I fly at. my instinct says that best range is going to be at highest altitude ( less air resistance) and the minimum power required to hold height at level attitude ( least drag) likewise endurance would be at lowest altitude where the air is thick so can get lift to stay up with less power and presumably best lift to drag ratio attitude again , ie level. Are there any good web sites that explain range and endurance well? ( I am flying a Warrior II) if there is anything specific. thanks Terry Back to top Ben Jackson Guest Posted: Tue Apr 06, 2004 11:36 pm    Post subject: Re: explain full throttle height In article <c4vbkg$9ct$0 (AT) pita (DOT) alt.net>, Highfllyer <highflyer (AT) alt (DOT) net> wrote: Quote: For most normally aspirated airplanes those altitudes will fall between 8000 and 12000 MSL. You might have to modify the altitude because of equipment considerations. That seems pretty low. Looking at a C-152 range chart, full throttle would intercept best-glide-power (which isn't a line on the chart, I assume it'd be a little to the right of 45% which is 77KTAS at sea level) well above the service ceiling of the airplane (12000' or so). Now best range *at full throttle* starts increasing at 8000' because full throttle becomes lower and lower. It just won't increase to max until it gets way down (35% maybe?). Of course in the POH these lines curve back because they take into account climb time, but I'm thinking of the 'pure' case. -- Ben Jackson <ben (AT) ben (DOT) com> http://www.ben.com/ Back to top Julian Scarfe Guest Posted: Wed Apr 07, 2004 7:09 am    Post subject: Re: explain full throttle height "d&tm" <tfmann (AT) iprimusREMOVEME (DOT) com.au> wrote Quote: I am trying to understand the factors that determine best range and endurance, and keep coming across this term full throttle height, what does this mean? The maximum recommended continuous power for an engine (well most standard aero-engines) is 75% of its maximum sea level power. With full throttle you get "100% power" (unsurprisingly, as that's the reference for the percentages). As you go up, there's less pressure and density, so for a given throttle position the engine gets less air with each gulp. By the time you get to the altitude at which the pressure is about 75% of sea level, you get to the point where even with full throttle you're developing only 75% power. So for 75% power the full throttle altitude might be around 7000 ft, for 65% power it might be 10,000 ft. Quote: Dont know if I have the right books but I am finding this range and endurance stuff a bit confusing. Graphs of power versus airspeed make sense academically but what I want to know in practice is what power setting do I require, what attitude do I need and what altitude should I fly at. For best range (limited fuel) at a given power setting, you'll do better at higher altitude. A given IAS takes slightly more power to achieve than at sea level, but gives much more TAS. If you look for absolute best range, it will occur at a speed not very far from minimum drag speed, which is the same as your best angle of glide speed. Down at that speed, altitude matters much less, and you achieve similar range at any altitude, with a slight preference for higher altitudes because the engine will turn fuel into power more efficiently with the throttle further open. Endurance is pretty much directly related to power setting. Again, altitude plays a minor part, as producing say 65% power takes slightly less fuel at altitude. Absolute best endurance occurs at an IAS for minimum power required. A particular IAS requires more power with altitude, so absolute best endurance happens at sea level. Anything much more sophisticated than that requires some math. Julian Scarfe Back to top d&tm Guest Posted: Thu Apr 08, 2004 9:45 pm    Post subject: Re: explain full throttle height Thanks for the input guys, its helping me think it through, we have two different answers however for best ensurance. one saying full throttle height the other sea level. Which one is correct. terry "d&tm" <tfmann (AT) iprimusREMOVEME (DOT) com.au> wrote Quote: I am trying to understand the factors that determine best range and endurance, and keep coming across this term full throttle height, what does this mean? Dont know if I have the right books but I am finding this range and endurance stuff a bit confusing. Graphs of power versus airspeed make sense academically but what I want to know in practice is what power setting do I require, what attitude do I need and what altitude should I fly at. my instinct says that best range is going to be at highest altitude ( less air resistance) and the minimum power required to hold height at level attitude ( least drag) likewise endurance would be at lowest altitude where the air is thick so can get lift to stay up with less power and presumably best lift to drag ratio attitude again , ie level. Are there any good web sites that explain range and endurance well? ( I am flying a Warrior II) if there is anything specific. thanks Terry Back to top Julian Scarfe Guest Posted: Fri Apr 09, 2004 10:14 am    Post subject: Re: explain full throttle height "Highfllyer" <highflyer (AT) alt (DOT) net> wrote Quote: As Julian points out correctly, this requires a bit more power. Highflyer takes the position that the efficiencies gained by running the engine without restriction and leaning it agressively for the higher altitude allow you to burn a bit less fuel for that power. Which is correct depends on whether the increased efficiency of full open air passages and appropriately lean mixture will reduce fuel consumption below the fuel consumption required to produce the requisite power for the proper airspeed at sea level. Completely agree with that. The engine manufacturers' data doesn't go down to the sort of power settings we're talking about, so it's very difficult to say which effect wins out. Here are some representative numbers: An IO-320B at 20" 2200 produces 76 BHP at sea level, and 96 BHP at full throttle altitude (~10,000 ft). [The Lycoming nomograms suggest that the fuel flow for this is actually the same as for producing 96 BHP at sea level -- I can't believe that, as I agree that some of the extra power at least must come from the reduction of pumping losses, which is "free" in terms of fuel flow.] At 10,000 ft it takes 16% more power to overcome the same drag. That would suggest that it takes 88 BHP at altitude to overcome the same drag as 76 BHP at sea level. Practically speaking you'll be looking for max endurance only in a hold or similar, in which case the altitude may not be something you have a choice over! Julian Scarfe Back to top John T Lowry Guest Posted: Mon Apr 12, 2004 3:31 pm    Post subject: Re: explain full throttle height I finally got around to calculating how (calibrated) airspeed for best range (Vbr) varies with density altitude (it doesn't!) and with gross weight (it goes up as weight does) for a fixed pitch propeller airplane. For a standard Cessna 172 in no headwind or tailwind, weighing 2400 pounds, Vbr = 73 KCAS at any altitude. At 2000 pounds, Vbr = 67 KCAS. The specific range figures (nm per pound of fuel) also do not vary, for a given weight, with altitude. But if your airplane is heavier, specific range is lower. The maximum is quite broad; three or four knots off the optimum airspeed, in either direction, only makes about 1% difference. I calculated specific range (also specific endurance) figures for various airspeeds in my book (Performance of Light Aircraft), and graphed them as functions of airspeed, but I failed to there see what the altitude effect was. I wish I had. So for best range, don't move a darned inch, vertically, unless it's to avoid some rocky obstruction in your path. But don't forget to slow down as you burn fuel. If you run into a headwind, speed up (about 6 KCAS for a 20-knot headwind, for this airplane); if you run into a tailwind, slow down. John. -- John T Lowry 5217 Old Spicewood Springs Rd, #312 Austin, Texas 78731 (512) 231-9391 [email]jlowry100 (AT) earthlink (DOT) net[/email] "d&tm" <tfmann (AT) iprimusREMOVEME (DOT) com.au> wrote Quote: Thanks for the input guys, its helping me think it through, we have two different answers however for best ensurance. one saying full throttle height the other sea level. Which one is correct. terry "d&tm" <tfmann (AT) iprimusREMOVEME (DOT) com.au> wrote in message news:40731202$1_1 (AT) news (DOT) iprimus.com.au... I am trying to understand the factors that determine best range and endurance, and keep coming across this term full throttle height, what does this mean? Dont know if I have the right books but I am finding this range and endurance stuff a bit confusing. Graphs of power versus airspeed make sense academically but what I want to know in practice is what power setting do I require, what attitude do I need and what altitude should I fly at. my instinct says that best range is going to be at highest altitude ( less air resistance) and the minimum power required to hold height at level attitude ( least drag) likewise endurance would be at lowest altitude where the air is thick so can get lift to stay up with less power and presumably best lift to drag ratio attitude again , ie level. Are there any good web sites that explain range and endurance well? ( I am flying a Warrior II) if there is anything specific. thanks Terry Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         AirTalk.org Forum Index -> Aviation (Students) All times are GMT Page 1 of 1   Jump to: Select a forum Aviation----------------alt.aviationAviation safety EnhancementPlanes, gliders and flying in AustraliaAviation et pilotage (Français)rec.aviationAviation (Aerobatics)Hot air, gas balloons and airshipsHang-gliding, paragliding, foot-launched flightAircraft Design & BuildingInstrument Flight RulesAviation (Classifieds)Military AircraftNaval AviationAviation (Miscellaneous Topics)Owning AirplanesAviators (General Discussions)Aviation related productsAircraft RestorationHelicopters and rotary wing aircraftsFlight SimulationSailplanesAviation (Students)Light aircraftFlying related activities in the UK Airports----------------alt.airportsEdinburgh Airport Glasgow Airport Humberside Airport Luton Airport Aberdeen Airport Glasgow Prestwick Airport  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.