V Speeds

Sep 07, 2011 2 Comments by

One of the major differences between full-scale flight and radio control is obviously no one is in the cockpit.  But, if we could be in the cockpit, what would we be likely looking at throughout the flight?  My experience tells me airspeed would be a continuous part of my visual scan of the instruments.  On the ground we really have no commonly used method of determining our airspeeds but we fly our remote control planes exactly the same way as full-scale planes even though we are not in the cockpit.  Airspeeds associated with flight actions and characteristics are typically referred to as V speeds.  Even though we don’t know the actual airspeed from the ground, we can still commonly refer to the V speed parameters.

Going fast may or may not be your style.  Being in control may be a better description of your flight goal.  Achieving max speed before auguring into the ground or making neck breaking fly-bys are too completely different ways to define speed.  The reality is speed is a valuable way to assess your flying and more importantly how your plane performs.  In aviation V speeds are used to describe everything from maneuvering speed, flap and gear deployment maximum speeds to stall speeds and maximum airspeed.  Let me introduce you to a few of these so the next time you are discussing speed and handling performance everyone will understand.

The first V speed you should know is VR.  This is the speed at which your aircraft is designed to rotate off the ground.  It works in conjunction with VS speeds which are your stall speeds.  It seems obvious to say that in order for flight to occur you have to exceed the stall speed.  It should also be obvious that VR andVS speedsare closely tied to the weight and balance of your aircraft; more on weight and balance in my next article, but as a teaser know that as weight goes up, stall speed goes up for a given aircraft and as balance moves aft stall speed goes up, both then require a higher VR.

The second V speed you should know is VNE or the maximum speed your aircraft should never exceed.  I realize standing on the ground is totally different than being in the plane when the wings shear off, but there is a speed that should not be exceed.  Along with higher speeds come other linked limitations such as loss of control surface deflection, stripped servo gears and/or control surface flutter.  If you do get slowed down on the backside of a loop then those problems will go away, but if not maybe it was not the loss of receiver reception, but maybe just plain going too fast that caused your crash.

Associated with VNE is VA or your design maneuvering speed.  This is the speed at which abrupt and quick maximum deflection of control surfaces will not create a situation where the aircraft goes beyond its maximum design G-force parameter.  We assume the VNE is in straight and level flight but VA may not be at a normal attitude.  If you decide to do a snap roll while flying your high wing trainer at high speed the result might be a wing shear or your self determination of the approximate VA speed.  One may get lucky a few times, but sooner or later VA will catch you.

Flap and Gear V speeds for single engine planes would be the VFE and the VLE speeds.  The VFE speed is the maximum speed for extension of the flaps and the VLE speed is the maximum speed for dropping the landing gear.  For both of these the risk of servo damage is present.  Exceeding the VFE and VLE speeds puts extreme pressure servos through the flaps and the landing gear.

Finally, V speeds you often hear are VX and VY speeds.  Angle of climb is indicated as the VX speed and is the speed that best gets your aircraft over an obstacle during takeoff.  It is basically indicating that at this speed your plane will have the best angle and altitude gain over the object ahead without loss of airspeed and ultimately stalling.  This is a steep climb rate.  The VY speed on the other hand is the best speed to give you the most altitude over a given period of time.  Most of us have experienced the climb out that we feel as we dial in the climb rate to the fastest speed without losing any airspeed.  This is a shallower climb angle.

So, this weekend at your local flying field share this information and before you know it everyone will be talking V speeds.  And while you are there tell them you heard gliders are the fastest radio control aircraft at over 300 mph.  See what they say.

David Vaught

About the author

A frequent contributor to Model Airplane News and Electric Flight, Dr. Dave is a true RC enthusiast with over 40 years of flying experiences as well as a private pilot license. He flies and writes about everything from ornithopters to giant-scale aircraft, building and flying an average of 20 planes a year.

2 Responses to “V Speeds”

  1. fhhuber says:

    Then you should also talk about “getting behind the power curve”… an easy way to cause a crash in full scale aviation.

    This is usually not a big a problem for models since our available thrust often exceeds aircraft weight.

    But its fun to play with.

    • David Vaught says:

      Great comment. I agree as often the planes I fly have plenty of power and I tend to be drawn to those as I like having some power curve left. We also many times can firewall the throttle and gain a much quicker response then we might in a real airplane. On the other hand I also like to fly a Cub that stays on the runway until I can safely rotate and climb out without a Viking departure! Thanks for your contribution.

Copyright © 2014 Air Age Media. All rights reserved.