Why Maneuvering Speed Changes With Weight

[Music] greedy's folks I'm rod Machado thank you for tuning into part two of this short video series on maneuvering speed and I hope you had a chance to watch part 1 otherwise you're going to be staring at me like a dog looking at a fan in other words you're going to be confused so off to part 1 with you on how maneuvering speed is determined if you haven't already watched it then again since I'm a big softy I'm going to review part 1 with you anyway in our previous video we learned that the GeForce experience by the airplane is derived by the ratio of all the upward acting forces on the airplane which we'll call lift divided by all the downward acting forces on the airplane which we'll call weight simply stated lift divided by weight gives us the g-force experienced by the airplane and its contents now if it takes a four point five degree angle of attack at 110 knots to produce 2,500 pounds of lift sufficient to keep our 2500 pound airplane in level flight we feel a g-force of 1 2500 pounds this way and 2500 pounds this way equals a g-force of 1 now if turbulence suddenly quadruples on an angle of attack 218 degrees our wings will suddenly produce four times as much lift or 10,000 pounds of lift with a weight of 2,500 pounds will experience a g-force of 4 now if the airplane limit load factor was plus 4 G's and it's typically 3.8 G's but 4 G's makes for well is your math then we won't exceed this value since the wings have reached an angle of attack of 18 degrees which is the critical angle of attack for this airplane increase the angle of attack further and the airplane will stall ok let's talk about how maneuvering speed is affected by weight the airplanes posted maneuvering speed VA is based on the airplane B net max gross weight that's right maneuvering speed is technically only applicable to the airplane when it's at max gross weight when the airplane operates at less than gross weight its maneuvering speed decreases and is given a new name called operational maneuvering speed or operating maneuvering speed otherwise symbolized as vo in fact many pilot operating handbooks show three different operational maneuvering speed for weights less than gross weight now the question is or at least it should be on your mind why does the operational maneuvering speed decrease as the airplanes weight decreases well here's one let's say that it takes a four point five degree angle of attack at 110 knots to maintain level flight in an airplane that is operating at its maximum gross weight of 2,500 pounds now let's reduce the weight of that airplane by opening the door and tossing your flight bag out great now the airplane weighs one thousand six hundred and sixty-six pounds yes that's a mighty big flight bag but you need a big bag to carry all 20 of those portable GPS units and that Van de Graaff generator you use to keep other airplanes away from you when they get too close in the traffic pattern flying it the lesser weight of one thousand six hundred and sixty-six pounds at the same speed of 110 knots means the wings can operate at the lower angle of attack of three degrees in producing the lift necessary to maintain level flight with the speed of 110 knots at the lower weight of one thousand six hundred and sixty-six pounds a sudden and very strong gust could increase the angle of attack from three to eighteen degrees in other words the angle of attack would increase six times over its starting value of three degrees and that would increase the lift our wings produced by six times giving us a g-force or load factor of six GS now if our limit load factor was 4 G's then this is beyond the limit of what our airplane can safely handle since our weight is 1666 pounds it's less than the maximum allowable gross weight so we need to do something to keep from exceeding our example limit load factor of 4 G's 3.8 G's really in turbulence so what should we do well the answer is to slow the airplane down let's say we slow the airplane down to 95 knots this allows us to maintain level flight at an angle of attack of 4.5 degrees at 1666 pounds at this speed we can increase the angle of attack 4 times above its original value before the wings reach their critical angle of attack and the airplane stalls therefore 95 knots becomes our new maneuvering speed if we want to limit ourselves to 4 G's thus decreasing weight requires a decrease in the airplanes maneuvering speed if your poh pilot operating handbook doesn't provide operational maneuvering speed for different weights then here's how to roll your own for every 2% reduction in weight reduce VA by 1% in other words if the gross weight decreases by 20% reduce VA by 10% now here's one last thought to consider when flying at 110 knots at a weight of 2,500 pounds a strong vertical gust would increase our angle of attack four times over its original value before the wing stalls we would pull 4 G's and the airplane wings would suddenly generate 10,000 pounds of lift in the process at 1666 pounds the same strong vertical gust would increase our angle of attack six times over its original value before we stall we would pull 6 GS and the airplane wings which suddenly generate 10,000 pounds of lift and the process wait a minute the wings in both instances are developing the same amount of lift while in the latter instance the G loading is greater because the airplane is lighter so why will two extra G's hurt the wings if the total instantaneous lift developed in both instances by the wings is the same well the fact is those two extra G's won't hurt the wings the instantaneous lift developed by the wings at both the heavier and lighter weights is the same therefore the wings experience the same amount of force applied to them in other words a force for which both wings have been designed to handle you see the problem here is not with the wings it's with something called the airplanes fixed weight components now think about the airplanes engine mounts they are designed to handle four G's or four times the weight of the engine without being damaged again it's really three point eight GS if the engine mounts are subject to a g-force of six GS they could break or deform and the same idea applies to the floor of the baggage compartment the floor under the seats of your airplane and for that matter the seats themselves these are all considered to be fixed weight components and they have an allowable stress limit of 4 G's if you pulled 6 G's at lower weights because you didn't reduce your maneuvering speed to a new operational maneuvering speed then these fixed weight components could become overstressed and be damaged thus damaging the airplane so this is why we reduce our speed to some new operational maneuvering speed at weights lower than maximum gross weight and just to be clear I've used 4 G's here as the airplanes limit load factor to make the math easier in reality the normal limit load factor for a standard air where the airplane is 3.8 positive G's and negative 1.5 to geez well I hope this makes the concept of maneuvering speed a little bit easier to understand I've been rod Machado say fly to you

Channel: Rod Machado

Views: 52,308

Rating: 4.9840479 out of 5

Keywords: Airplane, Maneuvering Speed, Pilot, Flying, Rod Machado, Machado, Rod's Aviation Learning Center, Aviation, Flight Training, Flight Instruction, Private Pilot, Flight Instructor, CFI, Commercial Pilot, Learning to Fly, Become a Pilot

Id: BAy4w3SYCTo

Length: 8min 54sec (534 seconds)

Published: Sun Dec 11 2016