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Byron is wrong. Not by much. But he's still wrong My premise is that high speed descents are inefficient because parasitic drag increases by the square of the speed. 150kias is a 56% increase in drag over 120kias. That extra speed in the high speed descent comes at the cost of wasting fuel that is burned off into drag. I tried to carve out some examples off the top of my head based on numbers I'm used to seeing. Granted I didn't test record these numbers from tests but I've got enough 201 time to have a good feel for what to expect. I also did not take into account the change in true airspeed but from experience in a normally aspirated plane, it's about a wash (ias goes up as tas comes down in descent). Wind can change your strategy but I will assume no wind for pure speed comparisons. Let's use a 500nm no wind xcountry cruising at 10,000ft and descending to sea level. No golden showers on this one because everyone's got the range to make this nonstop. We will compare two descent rate strategies. One is to stay high and descend at a high rate at high speed and the other is to start a gradual descent further out at near Carson's speed. For the enroute portion, I am basing cruise on 117kias, 140ktas, 8gph. I'm ignoring the climb portion for this example because it doesn't affect the difference between the two descent strategies. I chose 10,000ft altitude so that we could draw out the descent to make it a more influential component of the flight. Using a 300fpm descent rate, it will take 33minutes to descend 10,000ft at a continued speed of 140kts. The power is reduced to 6gph in order to maintain a descent profile at around carson's speed. This descent will cover a distance of 77nm in 33 minutes so it has to begin a ways out. The same speed as cruise is carried through the descent so the gain is only in fuel savings. This trip takes 3:34 at a fuel usage of 27.3g. What if we target the same descent rate but skip the power reduction and maintain cruise power at 8gph? The descent from 10,000ft will still take 33 minutes at 300fpm but it will cover more ground, 85nm at a 155kts descent on 8gph. This trip takes 3:31 but uses 28.1g. Now we'll look at the Byron high speed descent. I don't have my own numbers for this so I will take Byron's word and use his. 200kts at 10gph in an 800fpm descent rate. The descent will only take 12.5 minutes in a distance of 42nm. You will spend more time at normal cruise and a short time at high speed descent. This trip takes 3:29 but uses 28.3g. So what is the outcome? 3:34 on a carson's speed cruise and descent for 27.3g 3:31 for a carson's speed cruise but same ff descent for 28.1g 3:29 for a carson's speed cruise with a high speed descent for 28.3g You get to save 5 minutes off the trip max for the cost of a gallon of gas. Hardly a golden shower but still that's $5 for 5 minutes. But here's the real kicker that proves that the high speed descent is inefficient and impractical. If instead of descending faster you would just cruise a tad faster and stay with the efficient descent, you'll get there faster for the same or less fuel! Making the trip at 145ktas@8.5gph instead of 140ktas@8.0gph using the carson's speed descent profile (140kts@6gph) gets you across the same distance in 3:28 and uses 28.1g of fuel. So if you're going to waste $5 to go a little faster on your flight, you're better off cruising faster than descending steeper. This should come as no surprise because naturally the parasitic drag from going 5kts faster than 140 is lower than going 200kts. Ok, a bunch of you don't give a damn and only "got a Mooney to go fast." But for those of you who got a Mooney to go fast efficiently, I think Carson's speed for the climb, cruise, and descent is the best way to go. Target 115-120kias for all phases of flight and let Mr Carson earn you the best speed for your buck.