Re: Kitfox abrupt departure sensitivity to low speed stalls
I'm just playing with semantics now. I have no intention of flying below Vy except to clear obstacles.
I now understand that operating below Vy adds risk to flight operations. I would NOT have had this revelation without everyone contributing your experience. Thank you.
I can see myself landing and taking off in a farm field with obstacles.
So do you clear obstacles faster by getting to Vx and climb at Vx. Or, entering ground effect, accelerating, overshooting Vx, then climb with a higher angle of attack with an airspeed dropping towards Vx with the stored energy built during ground effect. (the later was taught to me at one time by a CFI, though managing when to make transitions for me is vague).
Does available HP at gross weight change Vx ? Especially from one Kitfox to another.
I happened to think that a 180 hp Kitfox (and the weight of its engine) is able to sustain a climb at lower airspeed than a runout engine making a 40 hp Kitfox. Lots of different engines are used, from automobiles, motorcycles, snowmobiles, aircraft engines; with influences from CG, humidity, and % of TBO (loss of HP).
Does higher HP just allow for accelerating faster to Vx (20 feet), and does the propeller wash lower Vx? Is Vx only affected by a couple of knots by HP, or is engine HP a significant influence in Vx?
https://generalaviationnews.com/2016...-first-flight/
Vx was never a real consideration with my Varieze, short fields and grass strips were never considered. With the blade in the rear, much of an angle of attack meant trimming the propeller on asphalt, or digging ditches.
I do NOT have a Kitfox, and am training in a Taylorcraft getting ready for taildragger operations. Depending upon the configuration of the Kitfox I buy, I am anticipating the V speeds are going to be different.
I understand that because the Kitfox "Wants to Fly" well below Vy on takeoff, get up into ground effect and let speed build.
From the Youtube videos of Kitfox, these are often transitions measured in seconds, and even fractions of a second.
Kitfox 582 and 912 competition
https://www.youtube.com/watch?v=vpxDqe5gbcs
These were both racing and flying likely at or above Vy. The extra HP provided certainly different performance. Potentially indicating that engine HP may influence angle of climb and not just airplane structure.
How would a pilot determine Vx for their particular aircraft WITHOUT experimenting near the limits of aircraft performance?
========== Proposed Target to blast holes in ==========
I haven't found Vy or Vx published for Kitfox aircraft.
To determine Vx for a particular Kitfox:
Load near center of CG at MTOW
At greater than 1000' AGL, watch engine temperature closely, and anticipate the potential to enter a stall.
Enter a sustained climb at what is believed to be Vx at full power. Using a GPS, record the temperature, ground speed, airspeed, and vertical change in altitude (indicator, or change in pressure altitude and start & finish times).
Do the ground speed vs change in altitude calculation.
Get set up like before and repeat at a slightly higher airspeed.
Get set up like before and repeat at a slightly lower airspeed.
By using this method, search for Vx at that Density Altitude
Repeat process again by increasing altitude by 3000 feet and repeat.
Find Vx at that increased altitude.
Use the two points to derive if Vx changes with density altitude, and what airspeeds are actually associated with Vx for that aircraft.
Or, possibly there is an Android App that does glide slope automatically (angle with reference to ground), and just reference airspeed.
In this way, a pilot is not deceived by assumption.
Correction: I am not deceived by assumption.
Originally Posted by jtpitkin06
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