I always thought max range was calculated at L/D airspeed.  I don't
think, historically, it's been done at 65% power.  Besides, max
endurance has nothing to do with distance, it has to do with *time*
aloft.  Max range is a no-wind DISTANCE, while max endurance is a max
time.  I may be wrong, but that's how I've always thought of those
terms.

Thoughts?

Walter


On Apr 19, 2005, at 7:06 AM, Matt Hapgood wrote:



Can someone explain to me if this makes sense (Max endurance has greater
range than max range)?  Conceptually this doesn't make sense to me...

The data is from Lancair Production website for the 400.

Cruise Data
  Max Power Speed (FL180) . . . . . . . . . .  230 KTAS  (265 mph)
  Max Recommended Cruise Power Speed (FL25) .  235 KTAS  (270 mph)
  Max Range (65% Power, FL180, 200 KTAS). . . 1071  Nautical Miles*
  Max Endurance. . . . . . . . . . . . . . .. 1320  Nautical Miles*

 

Walter is correct.  Using "Aerodynamics for Naval Aviators" as a reference for reciprocating engines and the Navy as a respectful organization that might find it useful to teach its' pilots to make use of max range and endurance so as to eliminate flights ending up in the sea, the following info was found to be pertinent. 

 

Max Range is indeed to be flown at Max L/D and must take into account the changing weight as fuel is burned.  Even more important in airplanes whose total weight is significantly influenced by fuel weight (like our wee lawn darts). At some constant altitude, a 10% increase in weight would require a 5% increase in velocity (IAS?), 15% increase in power and a 9% decrease in specific range( NM/lb fuel).  If compressibility effects are negligible, range variation related to altitude is a function of prop/engine performance (except for the fuel consumed in climb). However, turbocharging may improve range at higher altitude.  Anyway, Lancair just gave a range number for a specific power setting, altitude and speed (implying weight).

 

Also, endurance is defined by time aloft.  The time that the airplane can be held in level flight at the lowest fuel flow.  Generally, the velocity would be around 75% of the speed for max range.  Calculations indicate that the lowest practical flight altitude would yield the max endurance.  Any distance calculated from the speed would be greatly influenced by the winds since so much time would be spent aloft.  I am sure Lancair just did a calculation for the distance one could cover at some max endurance speed and reduced fuel flow. 

 

Matt, note that max range and max endurance were "starred", and that text was:

 

* Includes climb, descent and 45 minute reserves