11

# inverted flight

Diest TKO

1
Mon 9 Nov, 2009 07:21 pm
@georgeob1,
georgeob1 wrote:

Diest TKO wrote:

georgeob1 wrote:
The little winglets one sees on modern airliners are there to minimize the energy lost in these vortexes.

I'd add that elliptical wings are the most efficient at minimizing vortexes, but winglets are designed because they make for significantly easier manufacturing.

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It is an eliptical distribution of lift (from tip to tip) that minimizes, not vortexes, but rather induced drag. This is a result that was discovered in the 1930s by the British fluid mechanicist, G.I. Taylor. This can be achieved with an eliptical wing, but there are easier ways to do it.The British Spitfire fighter was an early example of a rather literal application of the principle. However the Germans achieved much the same outcome with the BF 109 using a, much more easily manufactured, trapeziodal wing planform and decreasing camber towards the wingtips.

Perhaps you are referring to something different with the "winglets". I was referring to the small airfoils that one often sees eminating from the wingtips of airliners, often inclined about 45 degrees upward. They add to manufacturing complexity, but significantly reduce the energy in the trailing vorticies and thereby reduce drag & fuel consumption.

No. I meant what I said.

A trapezoidal wing is a mere approximation of a elliptical wing that is much simpler to build.

Induced drag is only applicable for a finite wing. The drag you refered to being created by the vortexes is said induced drag. The only wing that has no induced drag is a infinite wing... but the complications of that are obvious.

Vortex creation comes from the pressure difference on the top and bottom of a wing. The pressure difference equalizes at the wing tips creating the vortex flow. An elliptical wing with a high aspect ratio is the most efficient wing possible.

Two wings with the same aspect ratio where one has winglets and the other is an elliptical wing will have different coefficients of induced drag, with the elliptical being the superior. Winglets are more complex in manufacturing, but simple in comparison to the mass production of elliptical wings.

Winglets are great and decrease vortxes (compared to a wing without winglets) but they are not as good as a elliptical wing.

Plane wings are not "inclined" by 45 degrees. I think you meant they have a dihedral (sometimes polyhedral) of 45 degrees.

Ionus - Prolonged is a key word there yes, but a few can do it and reach an inverted equilibrium for a sustained period of time.

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georgeob1

1
Mon 9 Nov, 2009 09:21 pm
@Diest TKO,
I believe you are confused and are trying to demonstrate more understanding than you really have, Read my posts again, this time more carefully, and you will see that you are eagerly, and in part incorrectly, correcting mistakes I didn't make. Perhaps you will even understand.

I was clear- and entirely correct - about the G.I. Taylor principle with respect to an elliptical distribution of lift from tip to tip (infinite wings don't have tips): the principle holds that an elliptical distribution of lift minimizes induced drag. An elliptical distribution of lift can be achieved in several ways - the Spitfire did it with a wing that itself was elliptical: as I explained the BF 109 did it with a trapezopidal wing and varying camber. The latter option led to an aircraft that was much easier to manufacture.

All wings, elliptical or otherwise, produce wingtip vortices. Winglets, usually inclined (and that is indeed the right word) about 45 degrees above the plane of the wing help to minimize the energy dissipated in these vortices and thereby reduce drag. They have nothing whatever to do with induced drag.

The inclination of the wings above the horizontal is - as you noted - referred to as dihedral. This has nothing to do with winglets. Dihedral is used to couple yaw and roll and thereby reduce the tendency of an aircraft to "Dutch Roll". Modern fighter aircraft generally have very little or occasionally negative dihedral, precisely to decouple yaw and roll, thereby achieving greater maneuverability.

Diest TKO

1
Mon 9 Nov, 2009 09:51 pm
@georgeob1,
This is literally my field. I do know what I'm talking about here.

wikipedia wrote:
A rectangular wing produces much more severe wingtip vortices than a tapered or elliptical wing, therefore many modern wings are tapered. However, an elliptical planform is more efficient as the induced downwash (and therefore the effective angle of attack) is constant across the whole of the wingspan. Few aircraft have this planform because of manufacturing complications " the most famous examples being the World War II Thunderbolt and Spitfire. Tapered wings with straight leading and trailing edges can approximate to elliptical lift distribution. Typically, straight wings produce between 5"15% more induced drag than an elliptical wing.

Inclination refers to the angle a wing (also canard or horizontal stabilizer) chord makes with the fuselage such that the fuselage is level. Inclination is related to angle of attack.

Dihedral refers to how a wing meets the fuslage in terms of how the wing is "bent." Anhedral is bent down, Dihedral is bent upwards, and Polyhedral would be a wing that had multiple angles.

Winglets are directly related to induced drag because if a wing did not terminate, there would be NO induced drag. Infinite wings do not have induced drag.

I know what you are talking about...
wikipedia wrote:
The lift distribution may also be modified by the use of washout, a spanwise twist of the wing to reduce the incidence towards the wingtips, and by changing the airfoil section near the wingtips. This allows more lift to be generated at the wing root and less towards the wingtip, which causes a reduction in the strength of the wingtip vortices.

however it is still an approximation. The only true elliptical lift distribution comes from an elliptical wing. I never said an elliptical wing doesn't create wingtip vortexes, only that it is the optimum at minimizing those vortexes and minimizing induced drag.

wikipedia wrote:
Wingtip vortices are associated with induced drag, an essentially unavoidable side-effect of the wing generating lift.

wikipedia wrote:
The primary concern in low speed flight is the aspect ratio, the comparison of the length of the wing measured out from the fuselage, wingspan, compared to the length from front to back, chord. Wings with higher aspect ratios, that is, wings that are longer and skinnier, have lower drag for any given amount of lift than a wing of the same area that is shorter and fatter. This is due to an effect known as induced drag, caused by airflow around the tip of the wing. As the size of the tip decreases compared to the wing's overall size, the magnitude of the induced drag is reduced.

This is why designers of gliders, who want a high lift to drag ratio, use very long and skinny high aspect ratio wings and winglets. At higher speeds, however, different forms of drag become more prominent, meaning that the large aspect ratio wings found on gliders become very inefficient. Another issue is strength; it is harder to build a longer wing with sufficient stiffness than a short one.

There are other ways to reduce induced drag, mostly by changing the shape of the wing to reduce the size of the tip. The elliptical wing found on the Supermarine Spitfire and Republic P-47 is the most efficient, but difficult to build. A practical compromise is to taper the wing towards the tip, a feature that can be found on almost all modern aircraft (including gliders).

I know exactly what I'm talking about, I'm not sure why you want to fight me on this one.

Here's an aerobatic plane I designed and built in college for my senior design. If I (or the the other 8 team members) was getting the terms wrong here, my Professor would have noted so in the several hundred page report we had to turn in after the year. Why not just trust me on this one.

I can't find anything on this G.I. Taylor Principal. Can you assist me with a link. I believe if we find a source, it will confirm my suspicion that a trapezoidal wing with twist will still not match an elliptical wing and that it's lift curve is still an elliptical approximation.

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georgeob1

1
Mon 9 Nov, 2009 10:00 pm
@Diest TKO,
You disguise the fact well. It has been my field for many years. I have advanced degrees in Aeronautical Engineering and fluid mechanics from Caltech; am a graduate of the Navy Test Pilot School and have over 6,000 hours in fighters.
Diest TKO

1
Mon 9 Nov, 2009 10:24 pm
@georgeob1,
georgeob1 wrote:

You disguise the fact well.

Har.

georgeob1 wrote:

It has been my field for many years. I have advanced degrees in Aeronautical Engineering and fluid mechanics from Caltech; am a graduate of the Navy Test Pilot School and have over 6,000 hours in fighters.

That's pretty cool. I have some friends who do test flight engineering on the JSF out in Maryland. They've got to spend some good time in the planes. I'm really jealous. If I get bored with my current job, I think I might try to move over to that.

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farmerman

1
Mon 9 Nov, 2009 10:25 pm
@georgeob1,
My second two favorite warbirds are the Spitfire and The P51. I always wondered which plane would prevail in air to air because they were essentially the same speeds and even though the climb ad was to spit, the dive was to P51.

Good thing they fought on the same side. Both planes owed much of their designs to Germany though. The p51 was designed by a German escapee and the Spit copied much of its stuff from the Heinkel He70. I sat in on several confabs with a buddy who flew a Texan for the Confederate Air Force.
Diest TKO

1
Mon 9 Nov, 2009 10:26 pm
@farmerman,
farmerman wrote:
Confederate Air Force.

I don't know what this is, but the phrase alone deserves repeating.

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georgeob1

1
Mon 9 Nov, 2009 10:43 pm
@farmerman,
I know the Mustang had an early NASA 6000 series airfoil. I don't know about the German expat designer. Who was it?

I knew the Texan as the SNJ. They had been phased out when I went through flight training. We flew the T-28 - the USAF version had an 800HP engine, while the Navy version had a 1,300 HP engine - we loved to jump Air Force guys.

I would bet on the Mustang over the Spitfire. It had higher speed and could therefore control the engagement and disengagement. It also had much longer endurance. In everything but extreme low speeds it could (almost) match the Spitfire in maneuverability, and could prevail in a vertical scissors maneuver. The Spitfire had a serious flaw in that the British version of the Merlin engine had a carburetor, while the Mustang had fuel injection. Engine stalls during a zero or negative g maneuver were a serious defect - something that BF 109 pilots used to good effect.

Still, considering that it was designed several years earlier, and at a time when advances in aircraft design were coming fast and furiously, the Spitfire was a marvelous aircraft.

My regret is that I never flew an F-8 Crusader. Too much time in Demons and Phantoms.
Diest TKO

1
Mon 9 Nov, 2009 10:49 pm
The longer I post here, it's strange how many people have worked with planes, in the aerospace industry or been pilots.

A2K is a bunch of propellerheads

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Ionus

1
Mon 9 Nov, 2009 11:02 pm
@Diest TKO,
They are a bunch of aeronautical history buffs who have spent large fortunes restoring aircraft and can now boast at least one of the finest collections in the world.
0 Replies

Ionus

1
Mon 9 Nov, 2009 11:03 pm
@Diest TKO,
I am sure you meant to include rotor heads, too !
0 Replies

farmerman

1
Tue 10 Nov, 2009 06:00 am
@georgeob1,
Quote:
something that BF 109 pilots used to good effect.
I read (I have no "backseat experience in either a Spit or a P51 but have been told that the RAF pilots figured out how to keep from totally crapping out in dives and they overcame this "shortcoming").
The Mustang designer was a guy named SChmuel. HE escaped the NAzis in the early 1930's and came to the US and got a job at Vought and did the Mustang as a "walk on" design. I think its ultimate long range made it a hit for the Southeast Asia bombing escort and , of course , later, in the Allied bombing of Germany where the Mustangs would take the entire herd of bombers in and bring em home(more or less) safely.

0 Replies

farmerman

1
Tue 10 Nov, 2009 06:03 am
@georgeob1,
Quote:
Too much time in Demons and Phantoms.
A high school friend who flew in phantoms and then F 16's in a carrier squadron called the DIAMONDBACKS would tll me that the F4 was living proof that, if you strapped on enough power, you could make an anvil fly.
Ionus

1
Tue 10 Nov, 2009 06:31 am
@farmerman,
We used to joke the F-4 had the glide ratio of a brick. The Diamond backs originally flew the Corsair II if my memory serves me. Is that why you were curious about the wing design ?
farmerman

1
Tue 10 Nov, 2009 06:37 am
@Ionus,
yeh, the history of the squadron was compiled into a photo album with some shots of all kinds of early and late craft. The only thing I knew about the Cosair was what i watched in the Black Sheep Squadron.
Ionus

1
Tue 10 Nov, 2009 06:42 am
@farmerman,
Great viewing but historically inaccurate as to the personalities involved, but who cares ! Look at the aircraft !
0 Replies

Chumly

1
Tue 10 Nov, 2009 08:20 am
Sufficient lift for inverted flight is a function of the "angle of incidence" (this is the correct term). Witness a symmetrical wing.
0 Replies

georgeob1

1
Tue 10 Nov, 2009 10:22 am
@Diest TKO,
Diest TKO wrote:

The longer I post here, it's strange how many people have worked with planes, in the aerospace industry or been pilots.

A2K is a bunch of propellerheads

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That's what hapens when you get a collection of old farts around -- they have had so much time that one or two of them have done just about everything.

The Phantom was actually - despite many defects - a remarkably good aircraft in terms of versatility, payload and carrier suitability. In fact it's design is traceable to the F101 Voodo: and it is true - as someone here suggested - that two J79 engines made up for a number of aerodynamic flaws. However, compared to its contemporary competitors like the F-100; F105 and others, it was the champ.

The military services, particularly the Air Force, tended to design aircraft to win the budget wars in the pentagon instead of the real ones they were fighting. This was the mindset that produced such fiascos as the TFX (later called the F-111), the B-1 and others. There was in fact a major revolution behind the introduction of the F-16 in the Air Force and the F-18 in the Navy - coming as it did very soon after these services introduced the F-15 and the F-14 respectively. The key force behind them was a real maverick in the Air Force, a Col. John Boyd. Not a very likeable guy personally - very single-minded and obsessed - but right about many things. There's an interesting biography of him in the bookstores now.
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High Seas

1
Tue 10 Nov, 2009 04:29 pm
@georgeob1,
georgeob1 wrote:
...This vortex is real, and when an airliner rotates quickly at takeoff it sheds an opposite vortex which stays behind on the runway. ... That's why small aircraft aren't allowed to land or takeoff for a few minutes behind a "heavy" .

That's true, and it's also true that towers don't always remember to tell single-engine private aviation about the heavies before giving them permission to taxi - sometimes I suspect them of doing it on purpose, but that's probably unfair.
farmerman

1
Tue 10 Nov, 2009 07:54 pm
@High Seas,
Thanks a lot. Not being a comfortable flyer, Im supposed to be leaving on a private plane on a runway normally used by commercial buses. Ill be sure to put a death grip on the pilots neck. Weres already in a damn weather delay.
0 Replies

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