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Newsgroups: rec.aviation
From: gl...@hpnmdla.HP.COM (Glen Baker)
Date: 25 Sep 90 14:46:46 GMT
Local: Tues, Sep 25 1990 10:46 am
Subject: Re: Downwind turn confusion (was: Re: Rotten advice given in a magazine)
l...@hao.hao.ucar.edu Dirk Lummerzheim at High Alititude Observatory writes:
>/ hpnmdla:rec.aviation / l...@hao.hao.ucar.edu (Dirk Lummerzheim) / 2:24 pm Sep 24, 1990 / Sure there's doubt about it. In fact, it's not true! >In article <7480...@hpnmdla.HP.COM> gl...@hpnmdla.HP.COM (Glen Baker) writes: >> As long as you are just *flying* (not attempting to navigate or >> land) the wind direction has none, zero, effect on the ability of your >> aircraft to generate lift. ALL that matters is the velocity of the airframe >> relative to the airmass...the motion of the airmass relative to ANYTHING >> else is COMPLETELY irrelevant. >Well, this statement isn't quite right either. And every pilot knows >about that, even if he hasn't experienced it. >GROUND SPEED has a significance for the aerodynamics of the plane. >There is no doubt about that. >The laws of physics that I wish to See previous postings by other folks, the airmass DOES constitute an >draw attention to are the conservation of momentum and energy. Both >depend on the velocity of the plane in an inertial frame. If you are >moving through an accelerated airmass, that airmass does not constitute >an inertial frame. But the ground always does! inertial reference frame. >The example that I am getting at is the effect of wind shear. The plane You're changing the problem! We were talking about a plane in a constant >keeps moving with the same GROUND SPEED, but the relative wind suddenly >changes (i.e. when you go through a microburst it might change from >headwind to tailwind). You can see that the plane "feels" the ground >speed here. velocity airmass (the velocity of the airmass being measured relative to some arbitrary point on the ground). However, I submit that the plane does not "feel" the groundspeed in the above argument, rather it "feels" the delta (i.e. acceleration) of the relative wind. >Velocity is always relative. And if you don't like Fine. I'll add the velocity of the airmass over the ground. Now we can >the ground as a relative point, add any constant velocity to it.) get rid of the ground in this discussion! >This is not saying that you gain anything by turning the plane into Accelerate the plane relative to what? Relative to the airmass ALL of the >the wind (which was the starting point of this discussion). That >(directional) change of velocity is always so slow, that other forces >(friction, lift) which are applied during the turn have enough time >to accelerate the plane, such that the conservation laws are not >that easily applied, and one fares a lot better with just considering >the entire problem in the reference frame of the moving airmass. plane's acceleraion is supplied by the turning forces (lift vector, yaw, etc). The motion of the airmass relative to the ground is not a part of the equation unless you are planning on having the ground and the airplane mate. There is nothing special about the ground as a reference plane! Consider O.K., I'll carry my reductio-ad-absurdum one step more. I mount the entire I submit that anybody who uses the ground as some magic reference point is ..glen You must Sign in before you can post messages.
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