HighPitch

A while back I saw a Lear 24 wing stripped of it's tip tanks and the airfoil really caught my eye! It resembles a pylon foil shape. It was very interesting and I thought about the pilots of these ships...my guess is that a deep stall is nominally unrecoverable without gobbs of altitude.

Ollie

Fullscale airfoils, particularly laminar flow airfoils, do not behave the same at model sizes and speeds (reynolds numbers) as they do in their full scale applications. Thgis is because the boundary layer of flow is relatively much much thicker with models. Also the Angle of attack at which the airfoil stalls is much lower with models.

The post stall behavior of airfoils at low reynolds numbers is best investigated by wind tunnel tests. Some airfoils stall abruptly and some stall gradually. Some must achieve an angle of attack much lower than the stall angle of attack before flow reattaches and lift is restored (hysteresis). Some recover from stall at the same angle of attack as they had when the stall started.

The Clark Y, at a reynolds number of 100,000, stalls at an angle of attack of ten degrees but doesn't loose any lift for an additional five degrees increase in angle of attack. Itrecovers at the same angles of attack that it stalled.

The NACA 2.5411, at a reynolds number of 100,000, stalls very abruptly at an angle of attack of 12 degrees and recovers at the same angle of attack.

A flat plate, at a reynolds number of 100,000, stalls at an angle of attack of seven degrees but doesn't loose any lift for an additional eleven degrees angle of attack or more.

The SPICA airfoil, at a reynolds number of 100,000, stalls at 15 degrees, doesn't loose much lift till 20 degrees but doesn't recover from a deep stall until an angle of attack of about 9 degrees is reestablished.

The NACA 64A010, laminar flow airfoil has a peculiar post stall behavior. The stall occurs at 10 degrees angle of attack. By 15 degrees it has lost only about 20% of its lift and by 18 degrees angle of attack has recovered all but 2/3 of the lift it lost! This is at a reynolds number of 200,000. It exhibits no hysterisis in stall recovery.

In some airfoils the stall (flow seperation) begins near the leading edge and sweeps over the upper surface almost instantaneously, resulting in an abrupt stall. In some airfoils the stall begins near the trailing edge and progresses forward gradually as the angle of attack increases, resulting in a very soft stall.

All the angles of attack mentiond above do not include the induced angle of attack of a wing of finite aspect ratio.

DICKEYBIRD

The Learjet 23 & 24 have an NACA 64A109 root and NACA 64A109 mod at the tip. Dunno what the "mod" means....that always gets my goat when someone lists the airfoil on their design as "mod"

Here's a pic, looks plenty sleek, eh?:

xlr82v2

My Feedback: (1)

I'm around the Lear's all the time...

I've seen the airfoil at the tip several times when the mechanics had a tip tank pulled...

from what I remember, the airfoil is much "flatter" than that.

But that's mostly the Lear 35's, they may have a different airfoil.

CharlieK

Lear 23's through 35's have the same wing the tip is just extended on the 35. It is the nastiest stalling thing you will ever ride behind and they have done all kinds of weird mods to keep the boundary layer stuck to the wing and get it to stall properly. the early one were low speed limited by where the wing gave up and not by the actual stalling speed. When the leading edges are removed it is required to get a lear test pilot to stall test them before they can be returned to service. They want to make sure it will not snap roll at the stall. Any airplane with a t tail or cruciform tail will deep stall when the wing blamks out the tail airflow. Quite an experience to ride through on a test flight-you have to be real fast to get it out before it gets the nose so high it goes to the ground that way(this was in a jetstar)

049flyer

My Feedback: (18)

Stalls are not normal maneuvers in jets, especially Lear Jets. Jets have electronic devices to warn of impending stall conditions but in normal operations you will never get close enough to the stall to activate the device or actually stall the aircraft. Minimum approach speed is about 30% above the actual stall speed with touchdown not much below that.

The only time a jet pilot will encounter a stall is when riding with the test pilot to check the stall characteristics after removal of a leading edge or other maintenance that could affect the flight performance.

If you find yourelf in a Lear Jet near an actual stall you have WAY bigger things on your plate to worry about than the pending stall.

049flyer

My Feedback: (18)

There is a vast difference in the wing leading edges of early 20 series Lear Jets and later 20 series aircraft and 30 series aircraft. The wing itself is the same for the most part but the leading edge was made much thicker in later aircraft to enhance low speed flight characteristics. The thinner leading edge had it's advantages but the more docile thick leading edge won out.

049flyer

My Feedback: (18)

dupe