Question about Lear wings.

[JordanD]

I've been noticing the difference in the wings on the earlier lears (like the 25) and the lear 35. I'm wondering why on the 25, the wing is swept all the way to the tip tank, but on the 35, the wing is straight for the last foot or so.
Here's one of a 25.
and here's one of a 35.
Does it make it slightly easier to handle, or have anything to do with stall performance? Does it cost it any speed?

[screaming_emu]

angle of sweepback has to do with reduction in shock waves. The more swept back the wing goes the smaller the "thinness ratio" (yeah, I know...that's what its actually called). This reduces the size of the shockwave created as an aircraft gets closer to the speed of sound. Since shockwaves are waves of energy, they create their own drag, so the smaller you can make them, the less gas the plane needs to burn to fly at high speeds.

Now I'm not too familiar with the speed of the 35 vs the 25, but I'm guessing the 25 goes faster (or burns less fuel while doing so). That's about all I remember on the subject. I would look up more, but I lent my high speed aero book to my brother.

[JordanD]

angle of sweepback has to do with reduction in shock waves. The more swept back the wing goes the smaller the "thinness ratio" (yeah, I know...that's what its actually called). This reduces the size of the shockwave created as an aircraft gets closer to the speed of sound. Since shockwaves are waves of energy, they create their own drag, so the smaller you can make them, the less gas the plane needs to burn to fly at high speeds.

Now I'm not too familiar with the speed of the 35 vs the 25, but I'm guessing the 25 goes faster (or burns less fuel while doing so). That's about all I remember on the subject. I would look up more, but I lent my high speed aero book to my brother.

Ah I see. I think the 25 did burn more gas though, but that was probably because of the turbojets.

[CAPFlyer]

Actually, the change was part of the modifications that Dee Howard made when helping to design the Lear 35. The Lear 23/24/25 was already in production and he only added the tip tanks to them but didn't refine the wing design any. They found that on the earlier Lears, the air flowing over the tip tanks interfered with the airflow near the tip of the wing, causing a lot of drag. By putting in the "straight" section, they were able to solve the problem and get a smooth interface of the two airflows, thus reducing the amount of drag encountered at higher cruising speeds.

Cruise speeds for the different models -

Lear 23 - Mach .78 (Max .81)
Lear 24 - Mach .78 (Max .81)
Lear 25 - Mach .78 (Max .81)
Lear 35 - Mach .78 (Max .81)

Range for the different models -

Lear 23 - 1400 nm (840 gallons)
Lear 24 - 1100 nm (834 gallons)
Lear 25 - 1770 nm (900 gallons)
Lear 35 - 2000 nm (931 gallons)

Fuel Efficiency (Miles/Gallon)

Lear 23 - 1.67
Lear 24 - 1.32
Lear 25 - 1.97
Lear 35 - 2.15

As you can see, speed remained the same on all models, but range and fuel efficiency increased markedly with the Lear 25 and Lear 35.

[JordanD]

Thanks for the info CapFlyer!

[LRJet Guy]

20 series Lears came from the factory with tip tanks.

There are at least 3 different wing mods for the 20 series. I flew a straight 24 (converted from a 23) with the original wing. It had numerous vortex generators in front of the ailerons, horrible slow speed handling, a curved strake between the leading edge and tip tank, and no preselected flap detents.

The other Lear I flew was a 25B, which had a Softflite wing, I think a III. It had no VGs, and long straight strake in the gap between the wing leading edge and inboard surface of the tip tanks. It also had flap preselect detents.

I believe you're exactly right on the straight leading edge on the 30 series. If I remember it right, the 25 I flew had it as well.

The 20 series had GE CJ-610 turbojets. Down low, the engine is ungodly thirsty. There is considerable difference in fuel burn even between FL350 and FL 410. We never flight planned under 410 for this reason. During my checkride, we never got above 15,000 ft. It lasted just about an hour and a half, and the low fuel light was on during the last landing. Take it to 410, and it would stay aloft about 3 hours, maybe a bit longer if you didn't mind the light.

The 25 was a bit heavier and had 100 lbs more push per side. Didn't seem to burn too much more per hour than the 24. We managed almost 4 hrs out of one, but landed on fumes. It held I think another 600 lbs of fuel than the 24.

Both are very sexy airplanes, but shitty systems wise. Been a while since I flew one, and my memory is a bit rusty on that airplane. Had a blast flying them though.