Leading Edges

I was going to be silly with the following in another topic :

> I'd also like a razor plane. > >Can't imagine shaping LEs without it.

And I started to be a wise guy and ask why the fellow shaped the leading edges, and then, I thought that mine was a very good question. We were talking about scratch-building and shaping square-stock leading edges.

So what if we do not shape that leading edge?

Consider the power we have in our engines/motors.

Consider the turbulation we would get from those wings when flying at a high angle-of-attack.

OK, I propose the following. Build a general sort of trainer and only shape one leading edge.

Fly said model. I venture that the square wing will lift first, will stall last, and appreciable yawl won't occur until well up in speed.

If the wing is a "D" section, the covering can be put on the wing to the trailing edge of the leading edge stock, leaving the leading edge bare wood.

After testing that way, then leave the tip third of the span square and slowly shape the leading edge as it approaches the root.

Fly again. The yawl will be a little less, the speed up a bunch, and the square wing will still stall last...and possibly at nearly the same angle.

By the way, leaving the square leading edge stock uncovered would be a good idea. It can be shaped later and covered. Even if both wings were to have square leading edges, I would not cover them with film. I think I would not even sand them but just brush some butyrate on them...and not sand after that either.

Or I could just be all wet about all this. But if you think I am, say why.

Ken

Reply to
Ken Cashion
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[snip]

OK, I know I'm being nit-pickety, but "yawl" is bothering me.. It's YAW...

Reply to
The OTHER Kevin in San Diego

No. You are not nit-picking but you are exactly correct. Thank you. I know what "yaw" is and I know what a "yawl" is. And the other "yawl" is sorta' the plural of "you."

Ken

Reply to
Ken Cashion

Depending on where you happen to live...

I think I should try finishing my coffee before I peruse usenet - I wouldn't be so punchy then...

Reply to
The OTHER Kevin in San Diego

Yawl is a type of two masted sloop rig sail boat. Y'all is the southern for you all.

But all y'all knew that!

Reply to
Paul McIntosh

And a ketch is another type of two-masted sloop rig sailboat. Tell us the difference.

As is said in southern South Mississippi, "By George, you is right! You be one bad dude!"

Ken

Reply to
Ken Cashion

Neither is a sloop-rig sail boat, since a sloop (at least in modern terms) has one mast, and typically carries a single headsail; a cutter, the other common kind of single-mast boat, carries two headsails, and typically has the mast stepped slightly further aft; cutters also often have modest bowsprits, from which they fly the jib (the "outer" headsail), and a wire parallel to the leading edge of the jib, a little farther aft, from which they fly the "staysail."

As for the difference between a yawl and a ketch...it's in the relative sizes of the main and the mizzen (the smaller sail behind the mainsail). On a ketch, the mizzen and main are reasonably similar in size; on a yal, the mizzen is tiny. (Example: mainsail might be 300 ft^2, mizzen 75 ft^2).

Not surprisingly, on a yawl the mizzen tends to be closer to the stern; on a ketch it's somewhat closer to the bow. This leads to the characterization that "on a yawl, the mizzen is behind the steering wheel (or tiller, or, sometimes, the "steering post"), while on a ketch it's ahead." But that's really nonsense. You can put a yawl rig on a boat with a transom-hung rudder, and it'd be silly to say that it just became a ketch.

But I digress :-) Then again, so did you. :-)

(On the topic of leading edges: the most sophisticated boats around don't just hang their sails from wires; they spend a lot of time working on the leading edges. C-class catamarans are a nice example: the top ones don't have sails -- instead they have "wings" where you'd normally have a mast, i.e., something that looks like an airplane wing with its root on the deck and its tip way up in the air. On a less-sophisticated level, my old Tornado catamaran had a jib that didn't "hank on" to the forestay, but instead folded around the forestay and was fastened with a zipper to hold it there.)

--John

(When I say "a sloop, in modern terms", I do so because "sloop" was (ca 1800) also a term used to denote a vessel commanded by an officer of a certain rank in the Royal Navy, regardless of the rig the vessel carried.)

Reply to
John F. Hughes

Er, no, its a particular form of sailing craft.

Reply to
The Natural Philosopher

I was repeating the question so as to not confuse the issue but you are correct...if you don't go too far back...1850? There were some pretty strange, small commercial boats sailing in East Anglia England back then...there is no telling what the locals would be calling them.

That was it. I had always seen the little drawings as showing the mizzen ahead or aft of the rudder post, but again, like you say, there is a problem with terminology when the rudder is on the transom. And this is some of the strange things I have seen sailing in shallow British waters.

I have one on video and there was very little current but a goodly wind, and the closest he could point was 45 degrees...and the channel was not real wide. He was carrying enough weight that he could easily tack through the wind but then, he would fall off on a broad reach to get his speed back before he could start pointing again.

I liked his red canvas sails though.

Now, that I think about it, in the whole video scene, he couldn't have gained 75 yards...he might still be there, tacking back and forth. (I am reminded of "Charley on the MTA.")

And again...

That sounds neat. I only sailed one cat...a Pringle or something...wait...isn't that a potato chip..maybe it was something else. It was rented and the sheet was so short, I couldn't go wing-and-wing, actually, I had to be careful not to gybe on a run. I told them about it and they said something about beginners tearing out the main stays. I told them if they didn't give a little more line on the sheet, they were going to start ripping out cleats next...and knocking people in the head.

John, I think it is funny that I posed a thought about leading edges and we are approaching an instruction manual on sailboats and no one has said anything about the topic yet.

I love the usenet.

Ken

Reply to
Ken Cashion

If a Southern boatbuilder throws a party, he says, "Yawl come!"

Reply to
Geoff Sanders

From Geoff=A0Sanders:

A yankee would say, "I didn't quite ketch that!" :-) oc

Reply to
Bill Sheppard

That's 'cause them Yankees is all a bit dinghy! :-)

Reply to
Geoff Sanders

I've noticed that the stall strips on most full-sized light aircraft are shaped like half of an unsanded balsa square. That shape probably creates turbulence and or flow separation faster than a round shape does. Those strips are located near the wong root to cause root stall before tip stall. That, of course, is always a good idea if you like using ailerons!

Geoff

Reply to
Geoff Sanders

Geoff, I was both aircraft safety officer and aircraft mission manager on a Lear 23 and that was not a good wing. It would fall out from under you pretty quickly. We wanted to cruise high and fast, and we wanted to fly low...and with the scanners, meant slow.

How could we do all of that?

There is a thing called Soft-Flight II modification. Trippers were glued to the upper wing surface in front of the ailerons. Large fences were added to stop the air going down the swept leading edge and shoot it over the ailerons. Turbulators were glued to the top of the wing near the root...these were to buffet the air at higher angles of attack.

But the main thing was a series of triangles screwed to the entry point of the wings. These were about 3/8" triangles, maybe1/16" thick. They were placed with a flat edge longitudinal with the wing

-- and the tips of the triangles were touching each other.

At the cruise attitude these were getting little linear air-flow, but as the nose went up the linear air-flow increased and this caused turbulence to keep the air a little closer to the wing a little longer.

It was a great mod. We could fly at altitude at the same speeds on just a little more fuel but we could fly lower and slower safer, and landing became less of a controlled crash. Without this mod, the Lear had to fly lower and lower until it touched the runway, and there the pilot stuck it and held it down...then the throttle could come back.

I remember seeing exactly these triangular leading edge turbulators on A-1 and A-2 towline gliders and many rubber free-flight models in the

1960s.

Ken

Reply to
Ken Cashion

Thanks, Ken - good info!

Geoff

Reply to
Geoff Sanders

last, and appreciable yawl won't occur >until well up in speed.

The squared leading edge will stall first, by a wide margin. Leading-edge "turbulators" designed to create vortices to keep flow attached work on an entirely different principle. Any deviation from the roundness designed into a leading edge will alter the stall behavior; enlarging the LE radius will usually drop the stall speed, reducing it will raise the stall, and introducing sharp corners will aggravate it mightily. At high AOA the stagnation line (the point on the LE where the airflow divides and goes either over or under the airfoil) is well back under the LE. See

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and scroll down to section 3.5 for a description of the stagnation line and stall effect. Imagine, now, the air having to travel around a couple of sharp corners in doing so, without creating rolling turbulence that brings on the stall. Stall strips are used on some aircraft to start the stall sooner. Typically seen on the Beech Bonanza, they are triangular cross-section strips that run for a few inches along the LE at the root. They start the wing stalling inboard to prevent stall starting at a dangerous place like the midsection which will normally result in a violent stall, wing drop and subsequent spin. Stall strips will raise the stall speed some, but it's in the interest of safety. They alert the pilot and get the nose coming down before things get too far out of control. They are often fitted during testing of a new design to get the stall behavior the designers were after; it's cheaper than redesigning the wing to introduce more washout or complex airfoil mods.

Dan

Reply to
Dan_Thomas_nospam

*I* know who that was and why he was there, but how many others even have a clue?
Reply to
Six_O'Clock_High

On Thu, 13 Apr 2006 22:34:51 GMT, "Six_O'Clock_High"

Probably, the same number who thought this topic ("Leading Edges") was about boats.

Ken

Reply to
Ken Cashion

On 13 Apr 2006 11:41:25 -0700, Dan_Thomas snipped-for-privacy@yahoo.com wrote:

last, and appreciable yawl won't occur >until well up in speed.

Finally, someone understood what the subject was!

Yeah. That makes sense but I think our models work at different Reynolds numbers and I am not so sure that big plane rules apply...at least not in the same degree. I remember the discussions about horizontal tails aerodynamic problems if we left the flat plat without a sharp leading edge and it didn't seem to make any difference. And I do know there was a difference in pitch control whether the elevator trailing edge was left "blunt" or "tapered" in cross section. Additionally, I remember all the discussions about diamond cross-section full-flying tails and how ineffective they were around neutral...and they really shouldn't have been. I agree with everything you said and have experience with some of it on full flying aircraft...slow and fast ones, but again...our models don't act like real airplanes in many cases. By the way, I had a (semi) scale Storch that I had flown two different models for years and one day, I decided I wanted to add the fixed slots to the leading edge. I wet some 1/32" balsa, put it to the leading edge at the correct place and wrapped the wing with Ace bandages. When dry, I put balsa standoffs so the slots would be in the right place. All the increased high-angle-of-attack lift I was expecting cost me so much in drag, the danged model would not ROG! Before the slots, it would in about 40'. After the mod, it would not. I got a fast, strong kid to hand-launch if...a practice that I hate. He gave that sucker a carrier catapult sort of launch and as soon as it left his hand, it slowed down and I knew better than to give it anything but some down. It settled in pretty quickly. I took a razor blade from the flight box, cut the slots off, fired it up, and made a nice takeoff in 40' and it was back to doing really nice outside loops. I was surprized...and those slots really looked neat.

Dan, I appreciate the inputs. I know what the Bonanza strips look like and I had forgotten about then until you described them. The Bonanza was an old (relatively) design for those. So another question comes up...since you are so informed on this, what do you think the first commercially produced aircraft for the non-commercial user was that had such turbulators, fences, trippers, and the like on them. (I don't meet slats...they might have been the first of that sort of thing and they certainly go back to the ...what? Late, 1920s...mid-1930s? I am thinking about the DeHaviland planes. We had some small 1" square sections on the Lear wing that seemed to have done nothing but introduce a physical turbulence on the surface of the wing. Before they were added, the pilot (by feel) got no warning of an approaching stall and a soon-to-be-dropped wing. After this mod, the airplane made noises, vibrated -- well...like a lot of airplanes did automatically without little pieces of aluminum glued to the wing.

Ken

Reply to
Ken Cashion

On Thu, 13 Apr 2006 22:34:51 GMT, "Six_O'Clock_High"

Of course, 'these are the times that try men's souls...'

Reply to
David Hopper

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