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#11
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"The OTHER Kevin in San Diego" skiddz *AT* adelphia *DOT* net wrote in message Man, I hope you've got better seat cushions than I'm sitting on. After about 90 mins, my ass is asleep in the R22.. Yep, Call Oregon Aero http://www.oregonaero.com/ they make these magic portable seat cushions that are a total godsend. If I had a 600SHP turbine behind me instead of 124hp of Lycoming 4 cylinder, I could get much higher. I dont have 600HP... Im only allowed to use 275 of the available horsies in cruise because doing otherwise tends to rip the teeth off the transmission. THIS is one of my greatest fears in flying. Right now, if I even see a tower of any kind, I fly right over the top of it. I dont mean to be preachie, but you've got to be carefull when going straight over the top of a tower, especially on lower viz days. Sometimes the lights are out of service and you cant see the actual top. BTW: never trust the charted tower heights, they are frequently very wrong. ( I reported one to NOAA that was about 800 ft taller than what the chart said, and its still not fixed two years later.) CYA, Bart |
#12
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B4RT wrote:
I dont mean to be preachie, but you've got to be carefull when going straight over the top of a tower, especially on lower viz days. Sometimes the lights are out of service and you cant see the actual top. BTW: never trust the charted tower heights, they are frequently very wrong. ( I reported one to NOAA that was about 800 ft taller than what the chart said, and its still not fixed two years later.) No kidding about lights not working... pull up notams for pretty much any airport, and you get one or several "Tower 4.5 SW 419 AGL lights OTS" (or along those lines). Some folk wisdom about towers, once told to me- if you picture the tower falling over as you fly past it, and you are far enough away that it will miss, then you are probably safe from the guy wires. Note use of "probably." Best bet is watch out and be careful. There is a big (1300') tower in our instrument practice area where I work. During the day I keep track of it with one eye and often check the altimeter with the other. At night I keep a bit farther away to be sure. The students tend to do a decent job holding altitude (under the "hood") after I mention that tower |
#13
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Not sure on the exact altitude where the efficency is, but I remember
something about 8,000' with a single engine turbine. Not that you would find me that high in a helicopter anyway, unless the terrain dictates it. On Fri, 29 Oct 2004 22:10:53 GMT, "Steve R." wrote: Hi! I had a long drawn out reply to your first sentence (about TAS, CAS, and IAS) until I re-read it and paid more attention to the "ignoring the winds" part! ;-) I agree, assuming absolutely NO wind, TAS should equal ground speed if we're doing the calculations correctly. Since that's never the case (the part about absolutely NO wind that is), for all intents and purposes, I try to never equate airspeed and ground speed as the same thing although the first will obviously have an impact on the second. The only reason I mentioned tail winds in my original question was to clarify that if you've got a good enough tail wind, your ground speed will be up enough to compensate for any airspeed losses that occur due to the increased altitude. I hear what you're saying about less drag on the lift producing surfaces (wings!) but aren't you also having to fly at greater collective settings in the "relatively" thin air? From what I think I'm getting out of all this, that minor change isn't hurting you enough to offset the gains of climbing up to 5000 feet and the improved fuel burn (5-6 gallons/hr isn't chump change these days!) doesn't hurt a bit either. In the turbine helicopter you fly, where is the point of diminishing returns? In other words, how high can you go before any improvement in TAS or fuel consumption quits netting you any gain? Thanks for the reply. Fly Safe, Steve R. hellothere.adelphia.net wrote in message .. . Remember, TAS is your airspeed (ignoring the winds) in relation to the ground. IAS is to the air around you. The higher you go, the less drag on the fuselage and same as a fixed wing, less drag on lift prducing surfaces mean more efficiency, which means a little better airspeed. That IAS maybe lower due to less power, but for that amount of power you are more efficient. That all adds up to higher TAS and lower fuel burns. In the turbine I fly, I see up to a 5-6 gallon an hour less burn at 5,000'. On Fri, 29 Oct 2004 13:56:01 GMT, "Steve R." wrote: "B4RT" wrote in message ... I usually use about 2000 agl for medium cross-countries and 45-55 hundred for long ones. (My turbine works really good here + I get a free TAS increase from the altitude) The other reason to fly higher on cross countries is that you'll have less worry about towers & wires. Bart Ok, I'm a bit confused here. So Bart, or Kevin, or anyone who cares to put in their 2 cents worth, have at it. :-) My issue is with Bart's statement that there's a free TAS increase in his helicopter with altitude. I'm sitting here, thinking about how I want to word all of this and I'm starting to think that I'm about to answer my own question so I'll put it to you kind folks and see what comes back! I understand that fixed wing aircraft gain efficiency with altitude. The simplified explanation is that as the aircraft climbs to greater altitudes (ie: thinner air), there's less frictional drag on the airframe and the aircraft achieves a higher TAS (true airspeed for those who may not know) as long as you're not flying so high that you're no longer able to pull standard cruise power from the engine. Assuming the same power settings from the engine/engines, you'll achieve a higher cruising airspeed (TAS) at altitude than you will at sea level. All of this happens automatically. As for helicopters (any rotorcraft), the airspeed of the "wings" (ie: the rotor blades) is limited to the maximum rpm that the rotor system can sustain. Because of this, as the helicopter climbs to altitude, the rotor blades can't see the kind of TAS increase that a fixed wing aircraft enjoys because the speed of the rotor blades is tied to the max rpm of the rotor system. Consequently, as the air thins with increased altitude, the helicopter has to fly with ever increasing collective settings to maintain the same lift/thrust levels. When you can't increase airspeed (rotor rpm), you have to increase AOA (collective) to maintain a given lift/thrust level!? One negative side effect of this is that the helicopters Vne speeds lower as the altitude rises. What I've always been told is that because of this, it doesn't generally pay for a helicopter to go to altitude on a x-country flights unless there are sufficient favorable winds (ie: tail winds!) to make up the difference. (?) Now to the part where I might be answering my own question. Just as the fixed wing aircraft sees in increase in TAS at altitude as long as it can still maintain cruise power (generally 65 to 75% power), I'm starting to think (I hadn't really considered it this way before!) that as long as the helicopter isn't pushing it's Vne limits at altitude (due to higher collective settings), the fuselage will see an increase in TAS also, even if the rotor blades themselves are not, because of rpm limitations on the main rotor system. Of course, if the fuse is seeing a higher TAS, then the rotor blades will also see in increase, at least on the advancing side..........but I don't think I want to get into that too deeply! ;-) Am I getting this anywhere near right? I hope this makes sense. Thanks for any replies! :-) Fly Safe, Steve R. |
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