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Any advice on mimimum mountain emergency
approach landing speeds for a LNC2?<
We need to understand that the airplane sees only dynamic pressure (IAS) and aerodynamically it would not know if it was in the mountains or at sea level. In other words, the proper approach IAS at sea level would be the same at high density altitudes for a given GW, CG and turbulence condition. The TAS during approach will of course be much higher at high density altitudes requiring a longer rollout. Thus the desire to lower
the approach IAS. The second important thing to realize is that the Lancair is not a Champ. A 1.2 Vs short field approach in a Champ will not be safe in a Lancair. This is another
topic. Knowing that the aircraft's stalling speed varies with GW, CG and bank angle, the approach speed is based on the higher of what feels comfortable and provides adequate margin above the stalling speed. But, WHAT IS THE STALLING SPEED?
The difference between a short field approach and a normal approach is nil in a Lancair. The major difference is the approach flight path angle. Certainly the AOA should be the same. In effect, all approaches in a Lancair are short field approaches.
As you know, I use AOA to gauge and maintain a fixed margin above the stalling speed for all approaches. Only the flight path angle varies (throttle) depending upon field length and approach obstructions. All approaches are stable
below 300 feet AGL (no turns or big changes in descent rates or IAS/AOA). For my particular aircraft, 8.5 degrees AOA during approach works well and usually results in an IAS of about 79 to 85 knots. This approach AOA provides
a fixed 6.5 degrees AOA margin above
the critical angle. These numbers will not
be the same for your aircraft.
For my Lancair 360 this 8.5 degree AOA for all approaches provides enough energy to stop the descent in the flare without excessive float down the runway with the engine at idle regardless of GW or CG.
Every custom built Lancair will be slightly different and airspeed errors will vary. In addition, each pilot will have to establish their own comfort level.
Finding a good approach IAS is like asking what IAS the aircraft stalls at.
It depends upon GW, CG, bank angle and other factors and must not be considered
a constant --- Nor does the bottom of the green and white colored radial on your IAS meter tell you where the aircraft stalls!!!!
Many of our fellow Lancair pilots that perished in fatal accidents briefly forgot about the limitations to flying IAS, nor were they
protected with an AOA (stall) warning.
Tip - For aerodynamics think AOA. For speed
think GPS. For FARs think IAS.
Jim Frantz
LML website: http://members.olsusa.com/mkaye/maillist.html
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Please send your photos and drawings to marvkaye@olsusa.com.
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