Short field take off

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jon1746
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Re: Short field take off

Post by jon1746 »

I have the Vortex generators on my plane. When I was getting my multi, the flight instructor could really tell a difference. He normally flies a NG without them.
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ememic99
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Re: Short field take off

Post by ememic99 »

I'm reviving this old thread to check what you think about data published by DAI in "SUPPLEMENT S07 TO THE AIRPLANE FLIGHT MANUAL DA 42 TAE 125-02-114 ENGINE". It's supplement that covers changes in procedures and operational speeds for CD-155 equipped DA42.

Attached you can find screen-shot of normal operating speeds table. According to it, rotation speed with flaps in APP position is higher (76 KIAS – circled red at picture) than with flaps in UP position (72 KIAS) in case of mass above 1700 kg. I’m not sure this is correct (at least it's not logical) because I don’t understand how rotation speed with lowered flaps can be higher than with flaps up. What do you think about this? The same speed (76 KIAS rotation speed with flaps in APP position) is mentioned later in the document in "Short Field Procedure (Take-Off with Flaps APP)" checklist.

For mass below 1700 kg rotation speed for APP position is 71 KIAS while in UP position it’s 72 KIAS which seems to be logical.

BTW Vmca is 66 KIAS for flaps APP and 70 KIAS for flaps UP while Vyse is 86 KIAS.
speeds.jpg
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ememic99
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Re: Short field take off

Post by ememic99 »

I gave it a try yesterday and took off with flaps in APP position. I didn't feel any special left turning tendency so usual right trim for take off was sufficient. However, the aircraft had weird tendency to take off at very low speed (as low as 60 KIAS) and definitely no rotation was needed (like C172). I pushed the nose down until reaching 71 KIAS and then, after releasing the stick a bit, it went up in the air but at somehow strange angle. It reached easily 82 KIAS but even with gear up the speed wasn't increased much - some 85 KIAS with pitch at some 7 degrees and 800-900 fpm. At 300 feet AGL I retracted the flaps and increased pitch up ("flaps up-nose up"); the speed increased almost immediately to 92 KIAS and then seconds later to 100 KIAS with pitch more than 10 degrees and over 1200 fpm.

So first conclusions: it might be useful for soft and short runways but degrades climb performance, it seems as designed more like landing aid rather than take off aid - too much breaking effect comparing to benefit of additional lift. I'm not sure what would happen in case of EFATO with such low speed and whether I would be able to retract flaps to get decent rate of climb and at the same time not causing stall or flight below Vmca.

Further tests to be done to measure accurately take off distance and to evaluate pros and cons.
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