wmartin@brl-tgr.ARPA (Will Martin ) (07/16/85)
Regarding the "slow four-point roll" mentioned about the 707 -- this started me thinking in general terms about acrobatics. I'm sure this is obvious to those of you out there who have really studied aviation, but I have some novice questions: 1) On the stages in a slow roll, where you hold the positions for some period of time, and where you are on your side: what is holding the airplane up? Momentum? Faith? (The wings are vertical at those times.) 2) We have seen diagrams and descriptions of wing cross-sections and airfoils in basic physics classes, describing the differential airflow over the top and bottom, and how this creates lift. OK; so how does a plane fly inverted? Is it just by holding enough of an angle of attack that you get some lift from the inverted airfoil? Thanks for basic knowledge! Regards, Will Martin USENET: seismo!brl-bmd!wmartin or ARPA/MILNET: wmartin@almsa-1.ARPA
tel@cbnap.UUCP (T. E. Lester x3259 3E257) (07/21/85)
In article <11624@brl-tgr.ARPA> wmartin@brl-bmd.UUCP writes: > >1) On the stages in a slow roll, ...what is holding the airplane up?... > On wing edge the plane must assume a nose high attitude. The combination of down thrust from the engine and wing effect from the fuselage side give the lift. This requires a rather high speed. >2) ....describing the differential airflow... how this creates lift. >OK; so how does a plane fly inverted? ... >Will Martin > >USENET: seismo!brl-bmd!wmartin or ARPA/MILNET: wmartin@almsa-1.ARPA Common misconception, differential airflow causes lift. Basic laws of physics will tell you "action = reaction" Lift is caused by the acceleration of a mass of air downward, period. The airfoil is just an efficient way of doing this. A lot of aerobatic planes have symetrical wings with zero dihedral and get lift purely from angle of attack. Hope this helps. Tom ihnp4!cbnap!tel
dbp@dataio.UUCP (Dave Pellerin) (07/23/85)
> >>2) ....describing the differential airflow... how this creates lift. >>OK; so how does a plane fly inverted? ... >>Will Martin >> >Common misconception, differential airflow causes lift. Basic laws of >physics will tell you "action = reaction" Lift is caused by the acceleration >of a mass of air downward, period. The airfoil is just an efficient way >of doing this. A lot of aerobatic planes have symetrical wings with zero >dihedral and get lift purely from angle of attack. Hope this helps. > Tom ihnp4!cbnap!tel Sorry, lift is created by two factors; increased air velocity over the upper surface, and the so-called "action = reaction" lift. The first factor accounts for (in normal aircraft) about 80% of the lift produced. "Action = reaction", where air is deflected downward, accounts for only 20% of the total. If Newton's law were the only factor, the perfect airfoil would probably be a flat plate! Most asymetrical airfoils will produce a significant amount of lift at slightly negative angles of attack. A "symetrical" airfoil becomes quite asymetrical with a little angle of attack. Dihedral has little or no affect on lift, it only provides yaw stability. Dave Pellerin ..uw-beaver!entropy!dataio!dbp
ron@brl-tgr.ARPA (Ron Natalie <ron>) (07/25/85)
> >of doing this. A lot of aerobatic planes have symetrical wings with zero > >dihedral and get lift purely from angle of attack. Hope this helps. First, dihedral is the angle of the wings to each other and have nothing to do with the symetricallity of the wings. They can be symetrical with the dihedral being anything. > > Sorry, lift is created by two factors; increased air velocity over the > upper surface, and the so-called "action = reaction" lift. The first > factor accounts for (in normal aircraft) about 80% of the lift produced. > More correctly, lift is caused because the increased velocity over the upper surface causes a decrease in air pressure on the top comared with the bottom. -Ron
price@magic.ARPA (07/26/85)
In article <726@dataio.UUCP> dbp@dataio.UUCP (Dave Pellerin) writes: > ... Dihedral has little or no affect on lift, it only provides yaw >stability. > I thought dihedral provided roll stability. Of course, if you kick in rudder on a wing with a lot of dihedral, it will bank up. Thats how many model sailplanes work. Dihedral tends to make the wing return to level flight if banked, does it not? But...but...hmmm, it also converts yaw to roll. So, is it really providing yaw stability or roll stability or both? **Hang gliding lore: Hang gliders incorporate some amount of anhedral in order to allow the wing to be weight-shifted. Increasing the amount of anhedral reduces roll initiation resistance, but also increases the tendency to overbank. A balance is typically struck between anhedral at the tips of the wing and dihedral near the root. You really can't yaw a weight-shifted hang glider, as far as I know. If anyone figures out a way to do that, let me know! -See you at cloudbase! chuck price
dsmith@hplabsc.UUCP (David Smith) (07/27/85)
> Regarding the "slow four-point roll" mentioned about the 707 -- this > started me thinking in general terms about acrobatics. I'm sure this is > obvious to those of you out there who have really studied aviation, but > I have some novice questions: > > 1) On the stages in a slow roll, where you hold the positions for some > period of time, and where you are on your side: what is holding the > airplane up? Momentum? Faith? (The wings are vertical at those times.) > Watching the Blue Angels do this, they pull up just before they start the roll, and fly an arc. At the end of the roll, they have to pull out of a shallow dive. When they are knife-edged, the nose is up a bit, so I suppose they get some lift out of the fuselage. > 2) We have seen diagrams and descriptions of wing cross-sections and > airfoils in basic physics classes, describing the differential airflow > over the top and bottom, and how this creates lift. OK; so how does a > plane fly inverted? Is it just by holding enough of an angle of attack > that you get some lift from the inverted airfoil? > Yes. High speed airfoils are fairly symmetric, although I suppose the supercritical airfoils may be less so. I once read of an exchange where a pilot claimed his plane flew very well upside down, even better than right side up. To which the other pilot replied that the designers must have done a poor job. David Smith ucbvax!hplabs!dsmith