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paul.mcallister
Joined: 09 Jan 2006
Posts: 177
Location: Waukesha, WI USA
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 Posted: Thu Jul 13, 2006 2:55 pm Post subject: PROBABLE SPAM> Re: Maximum Range flights. |
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Patrick,
Being someone who is easily confused can you help me understand the difference between best endurance and best range.
My interest is coming up with a way of determining the best speed to fly for a given head wind component that would yeild the maximum distance across the ground.
Paul
do not archive
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hurstkr(at)growzone.com.a
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| Posted: Thu Jul 13, 2006 4:08 pm Post subject: PROBABLE SPAM> Re: Maximum Range flights. |
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Hello Paul,
You said :-
> Being someone who is easily confused can you help me understand the difference between best endurance and best range.
"Best Endurance" is the maximum amount of TIME you can spend in the air. This would be accomplished at the minimum power (hence minimum fuel flow) necessary to sustain level flight. This is used for situations like carrying out a search when you want to stay in the air as long as possible but don't want to cover great distances. Wind has NO affect on Endurance.
"Best Range" is the maximum "DISTANCE" you can fly under the prevailing wind conditions.
> My interest is coming up with a way of determining the best speed to fly for a given head wind component that would yield the maximum distance across the ground.
To achieve best "Range" when there is wind, one should slow down with a tailwind and speed up with a headwind. The question of course, is "how much" to slow down or speed up. If the figures are not published anywhere, I think it would be necessary to log fuel flows at all flight true airspeeds and then do the maths necessary to construct a graph.
To try to make the point clearer, let's take a case to its logical extreme. Consider an aircraft with a 120 kts max speed and best L/D of 70 kts. If this aircraft flew at 70 kts into a 70 Kt headwind, its range would be zero because it would be stationary over the ground. Now if it flew at 120 kts, it would make headway at 50 kts GS and the range would depend on the amount of fuel it could carry. If it was to fly at 80 kts into the same 70 kt headwind, it would have a GS of 10 kts so would take five times as long to cover the same distance as if it was flying at 120 kts. Therefore, if it burns less than five times the amount of fuel at 120 kts as it does at 80 kts (it would want to!) then with a 70 kt headwind, it would achieve a much greater range flying at 120kts than 80 kts.
Sorry Paul, I just typed the last paragraph before I realised you already understand the problem. Ah well, I'll leave it there anyway. Maybe somebody else can explain the best way to do the flight testing and how to draw the graphs so we can all learn. If I ever get flying myself, I will want the answers too!
Best regards
Kingsley
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