How do you measure that? I assume the "best" isn't the steepest, because although you get to critical altitude quickly, you have very low ground speed while climbing.
As a general 'rule' the longer the leg the more advantage there is in speed; on shorter legs climb performance is the key. That's why -in the 2008 race- some of the Cabin Class a/c were often almost as fast on Duenna time (300nm legs) as many of the fighters in tests.
The first thought is to reach your best altitude and speed ASAP to spend the longest time at top speed with the most efficient fuel burn. However some aircraft have poor climb performance when loaded, and others accelerate slowly. My preferred test method is to:
1. determine the optimum cruise altitude (remember winds will ultimately play a part in the race). Perhaps slightly above CA may be best as it will give a bit more range for a small loss of speed but that can be adjusted enroute.
2.Determine the highest sustainable climb rate (fpm) - some a/c will climb fast initially but then have to be eased off significantly as you get higher to maintain speed.
3. Fly a few tests using a stopwatch or timer and DME for distance. Measure how long & far it takes to get to altitude at max rate - then keep going and measure how long and far until you accelerate to max speed. Make notes. (note: some feel that climbing slightly above and then descending to cruise altitude helps you accelerate - scientific testing has not come up with a universal answer)
4. Repeat the tests using a lower rate of climb/higher airspeed (say 20% different) and compare the two. In both cases note the amount of fuel used to get to cruise.
Now, you use science or intuition! In many cases the differences will be small, but in a few it can be significant - compare the results. Small differences can be compromised by erratic flying or weather so don't fret the small stuff. Ballpark numbers are around 200KIAS in the climb for fighters (dccs P-38 may be a bit lower but at a higher rate of climb, for example), 150-170 KIAS for things like the DC-7, 210KIAS for large jet tubes (but many require a step-climb until fuel burns off before being able to reach optimum altitude).
When I've been looking at aircraft options I reckon the Vne speed is important (I think that's the "max_indicated_speed" in the aircraft.cfg file). Being able to descend steeply/quickly certainly helps.
Because this is "racing" and not totally realistic (we don't care about pax - just don't overspeed or overstress), descent can be a big difference. A/c with a lower Vne have to be planned (can you watch the airspeed as you descend thru cloud, keeping the needle just below Vne? and leaving room for gusts?) - you may have to start a more gentle descent, further out and sacrifice GS as you get lower. Higher Vne allows a faster (and often steeper descent allowing longer at cruise speed/altitude. A high Vne plus "aids" such as dive flaps or spoilers are even better... but remember you also have to slow to gear/flap speeds which can sometimes take a while.
Once you find a couple of "good" aircraft in each group, practice, practice, practice so the techniques come naturally.. and have a Post-it note with critical speeds in front of you for reference when you race.
The ultimate answer is "block time" (aka Duenna Time) so that's your confirmation... fly several a/c and/or flights to see what comes out fastest.
(then again, some people pick planes because they fly nicer, easier, safer
-- and the last is the true test - crashes are deadly)
Rob
