OK, let's do some more analyis for the landing at Jasna!
I was complacent because I had no trouble landing at a similarly short airfield before, several times. Just looked at RWY lenght, seemed comparable, so instead of calculating landing performance and target speeds, I spent more time with weather checking
And then here are the facts.
My earlier experienced short field:
LHJK: RWY 14/32
600 X 18 m, CWY 200 + 200 m grass, ARP elevation 364 ft, no sloping
And the field in the video:
LZJS: RWY 08/26,
544 x 15 m, CWY 50 +50 m, ARP elevation 641 m, 2103 ft (middle), both thresholds at 639 m / 2096 ft. (with grass outline, 644 x 35).
Only 10% shorter, little narrower, but what's the big deal?
Well, it's 1700 feet higher, much shorter clearway at both ends, and I was always there in LHJK with 2 persons (instructor or passager), i.e, greater weight.
Let's check the aircraft actual performance. I took a few screenshots from original video recording and enlarged them to see instruments better:
Aircraft:
- weight MTOW 730 kg, approx. actual weight 520 empty +68 pilot +10 baggage + 43 fuel (58 lit) = 641 kg
- flaps - landing flaps deployed (confirmed in video at 10:55)
- throttle cut at +50 feet/+15m (2110 baro alt), 90 m from threshold, manifold pressure idle (11:55 in video, also correlates to GPS track
- threshold - crossed at 63 KIAS at 2080 ft baro alt with VSI 900 fpm (11:59 in video)
- wind - windsock on hangar confirm calm (12:02 in video)
- flare - flew by taxiway exit at 54 KIAS, 2065 ft baro alt with VSI 500 fpm
- touchdown - 41 kts, 2060 ft baro alt VSI 200 fpm, at the 4th outer grass runway marker, which is according to Google Maps, c.a. 360 meters from threshold, (12:11)
- stop - came to a halt in remaining 184 meters, giving a total of 90+360+184 = 634 meters from +50 feet/15m point, using 100% runway.
This is what the DV Aircraft Flight Manual (AFM) says for landing performance:
Conditions: - - Idle
- - Maximum T/O Mass (Weight)
- - max RPM
- - Approach speed 59 kts
- - level runway. paved
- - Flaps in landing position
- - Standard setting. MSL
Landing distance over a 15 m (50ft) obstacle: approx. 454 m
Landing roll distance: approx. 228 m (*note by me = this means touch down 454 - 228 = 226 meters from threshold)
For each 750 m (2500 ft) additional height above MSL add 1 0% to the landing distance. (*note by me, the landing roll distance doesn't change with altitude)
So let's adjust this to the actual performance:
Adjustment for MSL: 2060/2500 * 10 = +8.3% 454 * +8.3% = : 491 m landing distance
Adjustment for speed: (65 kts^2)/(59 kts ^2) --> +21% = 595 m
Adjustment for weight = 730/641 = -->+13% = 677 m
Landing point = 677 m-90 -228 =359 m (66% of runway)
Stopping point: 677 -90 = 577 = 587 m (43 meters over end of runway, 7 meters left from 50 m clearway).
Fairly close, the actual landing roll was shorter due to lower weight, clear runway, good traction, hard breaking.
Then how should it have been done well?
Target
approach speed for lower weight: Square root (641 /730) * 59 =
55 kts.
This woud give us the following distances in the AFM model:
Adjustment for MSL: 2060/2500 * 10 = +8.3% 454 * +8.3% = : 491 m landing distance
Adjustment for speed: 55^2/59^2 = -13% (491 *0.87 = 427 m)
Adjustment for weight: 730/641 = -->+13% (427 * 1.13) = 482 m
Touchdown point: (482-228 -90 = 164 m from threshold, at 30% of runway length, right at the taxiway exit !
Stopping point: 482-90 = 392 m from threshold, using 72% of runway length)
So in short, 55 kts on approach, cut throttle at +50 ft/15m and I land at 1/3 of runway and stop in the next 1/3, leaving the last 1/3 for reserve. It could have been just like a textbook landing!
Now let's play more - how about landing at MTOW? Assume I take fat passenger, top up fuel, and after takeoff, he remembers leaving his wallet on the ground.
Adjustment for MSL: 2060/2500 * 10 = +8.3% 454 * +8.3% = : 491 m landing distance
Adjustment for speed: 59^2/59^2 = +0% (491 m)
Adjustment for weight: 730/730 = +0% (491 m)
Touchdown point: 491 -228 - 90 = 173m at 31% of the runway
Stopping point: 491-90 = 401 m m from threshold, using 73% of runway length.
No problem either!
