All pilots understand that aircraft V-speeds depend on factors such as weight, altitude, and aircraft orientation. For instance, a pilot might reduce the approach speed for a lightly-loaded aircraft to avoid float or a hard landing, since the stall speed is decreased from that for an aircraft at maximum allowable gross weight. And, of course, pilots should be particularly aware of the maneuvering speed when flying in turbulent air. The numbers quoted in spec sheets, magazine articles and the Pilot’s Operating Handbook are usually for an aircraft in wings-level flight at sea level altitude and at maximum gross weight. As the density altitude changes in response to changes in temperature or barometric pressure (e.g., from increasing altitude), or the gross weight changes as fuel is burned, the V-speeds also change. This add-on provides a table of V-speeds for the A2A Piper Comanche that change in real time as the flight parameters change. The table appears as an AxisAndOhs “gauge” either on the desktop or in-game (or both).

V-speed formulas

I have used V-speed correction formulas from the official Piper PA-24-250 Comanche POH (1958-1960) when available. These are specified in the POH for VX, VY, and best en route rate-of-climb speed as follows:

The figures for VX and VY are based on a 2800 pound gross weight. Both VX and VY decrease approximately one mph for every 100 pounds that the airplane is below maximum allowable gross weight.

VX increases approximately 0.25 mph for each 1000 foot increase in density altitude above mean sea level.

VY decreases approximately 0.75 mph for each 1000 foot increase in density altitude above mean sea level.

Best en route rate-of-climb speed decreases approximately 0.75 mph for each 1000 foot increase in density altitude above mean sea level.

For corrections not specified in the POH, I have used an approximate dependence on weight as the square root of the ratio of current gross weight to maximum allowable gross weight. This seems to be an approximation widely accepted in aviation circles for maneuvering speed, glide speed, and stall speeds. I have also included the dependence of stall speed on bank angle as inversely proportional to the square root of the cosine of bank angle (that is, as the square root of the increase in G-force for a typical GA aircraft, which is inversely proportional to the cosine of bank angle, for angles sufficiently distant from 90 degrees). Note that stall speeds given as indicated airspeed (i.e., read from the airspeed indicator) are not significantly dependent on altitude.

The attached graphic shows the specific formulas I used to determine the following V-speeds in mph indicated airspeed:

  • VERC Best en route rate-of-climb speed
  • VA Design maneuvering speed
  • VX Best angle-of-climb speed
  • VY Best rate-of-climb speed
  • VGR Best engine-out glide speed for range
  • VS0 Stall speed (power off – full flaps and gear extended)
  • VS1 Stall speed (power off – clean)
  • VAPP0 Approach speed (1.3 times wings-level VS0)
  • VAPP1 Approach speed (1.3 times wings-level VS1)

(Note: VERC, VGR, VAPP0 and VAPP1 are my own non-standard abbreviations.)

In these formulas, DA indicates the density altitude in feet, B indicates the bank angle, GW indicates the current gross weight, and GWM indicates the maximum allowable gross weight (2800 pounds without wing-tip tanks, and 3000 pounds with wing-tip tanks).

Using the AAO gauge

To use the table as an AAO gauge, unzip the file and place the folder ComancheVSpeeds in the folder

...\Documents\LorbyAxisAndOhs Files\UserGauges

Then, select the drop-down menu “gauges” in the AAO application. Tick “Desktop FIPs” to use the table as a gauge on the desktop, either alone or with other AAO gauges. Tick “Web FIPs” to use the gauge in the in-game AAO panel. This panel may be opened from the usual MSFS menu. The in-game panel works well in VR and can be moved to a convenient location (see the various screen shots inside the cockpit, which were taken in VR). The desktop gauges can be moved to any monitor, and the web gauges may be accessed from a networked computer or tablet – see the AAO manual.

Notes

The V-speeds shown in this app are for simulator use only! Do not use them for actual flying (I hope that goes without saying.)

This gauge was developed using version 4.0 of AAO. Be sure that you have the latest version installed.

How well these speeds reflect your experiences in MSFS depends on the flight model. I don’t know how well A2A incorporates certain variables into their model for the Comanche, but they do pride themselves on the accuracy of their flight models. So it will be interesting to see how well the simple formulas used in this app correlate to your flying experiences.

As always, the suggested approach speeds should be adjusted to account for gusty winds, anticipated wind shear, or excessive turbulence.