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Oct 22, 2019, 02:51 PM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
Quote:
Originally Posted by BMatthews
If you decided to change the airfoil I'd say go with the airfoils used on the Allegro Lite. And use the width of the sheeting and all since that is part of the airfoil's design to have the covering supported over the width of the sheeting instead of sagging between the ribs.

The stock GL design was always at its best on slower wind days and not all that great in windy conditions. Folks have and do ballast them. But I recall seeing how abysmally the Electra with that same wing flew when loaded down with the big can motor and heavy 6xC size battery packs back in the day For my money it sure looked pretty obvious that the GL is basically a calmer day sort of model.

But it excels at that light floating sort of performance. Trying to make it fly well in high winds and blustery conditions makes as much sense to me as that silly transport truck racing.

On the other hand plagiarism is a long respected and utilized mode of designing. I've often thought that it would be fun to take the GL layout and areas and fill in the outlines with a slicker wing airfoil and construction, slim down the fuselage and streamline the tail sections with a little more of an airfoil shaping and cleaner trailing edges. But you're right, it would not be a Gentle Lady any longer. But I'll bet it would be a nice flying glider.
I am a GL owner. Built mine back in 1985. It was built so that I could enter a one-design event which was popular to commemorate Carl Goldberg after his passing. I made every effort to make mine very light. It flew well but it suffered the ability to penetrate any breeze > 5mph or so.

One day I was out with it on a breezy day and decided to strap on about 4oz of lead to the CG. I simply taped it to the top of the wing. What a difference! It was performing much better than I had expected.

To this day I consider the GL to be somewhat of a compromise in performance. I say that because I always felt it was marketed as an entry point into the hobby. It is an easy build and performs quite well. I don't think by removing the washout will make that much of a performance difference due to the fact that it is a flat bottom airfoil.

I built my GL to specs. However if I were ever to build one today I'd make a few changes including moving to something like a S3021 airfoil and adding spoilers. Just with those 2 changes I believe the overall design will perform much better but still be docile enough for the beginner.

What comes to mind is the Harley Michaelis Easy Eagle. It is in the same class but it having a much more efficient airfoil (SD 7032) performs much better.

Just some random thoughts.
Kurt

https://augiemckibben.wixsite.com/harleys-easy-eagle
Last edited by kzimmerm; Oct 22, 2019 at 03:00 PM. Reason: Added Link
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Oct 22, 2019, 05:35 PM
B for Bruce
BMatthews's Avatar
I had a GL of my own many years ago and while helping out as an instructor got to fly a dozen or so GL's built by beginners. The weights ranged from quite light in the low 20's to maybe as much as the low 30's. And at those weights they all flew well. The slightly heavier ones handling moderate 5 to 7 mph winds in an OK manner.

I'm pretty sure that the Electras flown with the heavy can motor and heavy 6 or 7 cell packs made from sub C cells was up closer to the mid 40 oz range. And THAT much was way over the top.

Looking at the Easy Eagle I see that Harley included a bunch of turbulator spars to aid with supporting the covering. I've done this too but typically we'll see an issue with the covering sharply sagging between the ribs and behind the top spar. The fix that came out at the time was to extend the top sheet to some distance behind the high point. I've sort of done that on a couple of models by adding an additional turbulator spar behind the upper spar. I suspect that the airfoil on the Easy Eagle might gain some slow speed performance by using one as well.

But that's a different discussion....

I've thought from time to time about an updated GL. But then I look at the lessons learned over the years that have given us more recent designs like the Allegro Lite and the many great flying F3RES designs and just sigh and go find something else to do....That and the simple fact again that it would no longer be a Gentle Lady.
Oct 22, 2019, 08:30 PM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
Agreed. So many great designs..... so little time. When I choose a model I’m looking to fill a criteria. For entry level I have often suggested the GL. If one wants to advance their skills I’d choose something like the Easy Eagle. Once one’s skills are advanced then something in the STD class or 3 meter category works.

I just love to build and fly. Woodies are top on my list. My vintage Inventec designs Grand Esteem and Pelican are also top of the list. I can go on and on.

That’s the best part of this hobby..... endless supply of building projects

Kurt
Oct 22, 2019, 11:47 PM
Registered User
Quote:
Originally Posted by AChacon
snip

I don't plan on winch launching so I will stick with the stock Sophisticated Lady structure w/ 3-piece wing. Plan is to revitalize my old Dyna-Flite Upstart.

Since I'm building from plans I think that there is no extra effort to build the SL wing. Just have to remember to allow for the additional sheeting when cutting ribs. Speaking of which... The Gentle Lady has 44 of them. Doing anything 44 times by hand is going to take a while. It took me a week of spare time.

First photo Oct 13, getting ready to cut the first rib. Last photo Oct 19. That's a full set of ribs ordered the way they will be on the wing, on one of the wing spars.
Wimp! I once made a 2 meter wing with almost 80 ribs. I'll admit it was a pain, and the result was kind of ugly, but it flew ok.

You don't have to fear the winch if you learn to tap and don't go up on super gusty days. If the SL has the same size joiners as the GL, you'll get quite a bit of warning before anything breaks, as the tips will get up to a fairly steep angle. (I never broke mine. Someone else smashed into it on the slope.)
Quote:
Originally Posted by Steve Corbin
snip
Then the guy made a flight and while making a crosswind landing the left wing dropped just enough to catch a bush, and the glider spun 180 and stopped.
Instead of the Nylon bolts shearing as intended they ripped the nut holding part out of the fuselage which fractured heavily.
Since then I've seen similar damage to models using the bolt on technique. My self I prefer the GL method of using the longitudinally mounted rubber bands.
snip
If bolts are used it would be prudent to make sure they are properly sized so they will shear instead of wrecking the fuselage. Inflight loading will be in tension, and very little Nylon is required to match the strength of that balsa trailing edge and the bulkhead the nuts are on.
snip
I've used a single, strong bolt next to the spar and either friction or something quite weak to keep the wing from yawing. In a cartwheel, the friction isn't strong enough to hold it or the weak pin or bolt breaks, and the wing pivots, reducing the twisting load on the fuselage. The Mantis, or at least some versions, used a single bolt and friction. I didn't tighten the bolt once and had a flight with something like 20 or more degrees sweep, plus and minus. Still quite flyable, but it did hurt the performance a little. An RES or REF Mantis, of course, wouldn't be flyable in that condition! I guess the one big bolt trick wouldn't help very much in a perfectly straight, nose-in crash.
Quote:
Originally Posted by mawz
I'd suggest going S3021 over E205, it's basically an E205 without the poor slow-speed performance.
According to Profili, the E205 looks considerably better if you add a turbulator at 40 percent. Isn't that where the end of the sheeting is? This is based on a Reynolds number of 90,000 X (1/sqrt Cl), i.e. what a model in steady flight would experience at various speeds.
Quote:
Originally Posted by Sailhigh
The stock GL airfoil is actually pretty good for what it was designed to do. The performance that many think is lacking is actually not related to the airfoil, but to the high drag producing wing twist. The washout is like a training wheel for a bicycle. Great aid for learning, but a detriment to better performance. You do not have to include the washout in your build and the plane will fly just fine with a lot more efficiency.
More efficiency at high speed, anyway. Possibly less efficient at low speeds, since it has wide tips, resulting in a less than ideal lift distribution.
Quote:
Originally Posted by kzimmerm
snip
One day I was out with it on a breezy day and decided to strap on about 4oz of lead to the CG. I simply taped it to the top of the wing. What a difference! It was performing much better than I had expected.

To this day I consider the GL to be somewhat of a compromise in performance. I say that because I always felt it was marketed as an entry point into the hobby. It is an easy build and performs quite well. I don't think by removing the washout will make that much of a performance difference due to the fact that it is a flat bottom airfoil.
snip
Kurt

snip]
I used to fill the area under the wing of my HOB Two Tee with a whole lot of pennies (plus some crumpled up paper, I think). Was much better in the wind that way, but of course if I did something wrong, it would hit the ground harder that way.

With something like 2 degrees of washout, I suspect the tips would get separated flow underneath at maybe a 1 degree lower angle of attack than if flat. I think that would correspond to something like a Cl higher by 0.1. So it would be at least a little slower.

Quote:
Originally Posted by BMatthews
I'm pretty sure that the Electras flown with the heavy can motor and heavy 6 or 7 cell packs made from sub C cells was up closer to the mid 40 oz range. And THAT much was way over the top.

snip
A flying student of mine built one. I think it was over 50 ounces! If memory serves, he used one of those Master Airscrew prop/gearbox/motor combinations. It would reach a decent altitude in a minute or two as opposed to a week or two with the stock motor and prop. It wasn't so good with thermals, as I recall. One day, he pushed up when I told him to pull up. I took the transmitter back, but by that time it was going so fast that the wing broke when I pulled up. I don't think I pulled up all that hard, either.

I suspect that a slow airfoil is a plus in a beginner's airplane. If you don't think that's true, or you're not a beginner, you might consider the 2 meter Chrysalis. I hear it flies quite well, with a wide speed range. A friend sold me a Jester, which I kind of like, because he liked the Chrysalis he buitl much better. I imagine an F3-RES would be even better, if strong enough.
Oct 22, 2019, 11:49 PM
Registered User
P.S. I don't think my obsession to laziness ratio is high enough to cut 80 ribs any more!
Oct 23, 2019, 12:18 AM
Slope Soarer
Thread OP
Spar joiners (at the top). They are long and thin and a pain to fabricate. I've lost skin on my knuckles to my wood plane(s) while trimming to size. I needed a clamp of some type to hold them. Also the wing ribs laid out on the plans.
22-Oct-2019.

Regarding the wash-out. I once read an article someplace that said wash-out on constant chord wings was not so bad since it reduces lift near the tips and gives a pressure distribution closer to the elliptical ideal. The GL has a slight taper so the wash-out might actually help things. I like the fact that I can put the plane into a 60-70 degree climb, hold it, loose speed, stall out, and it won't do anything bad. I also can put it in a 90 degree bank, pull full elevator, and nothing bad happens. Slope soaring folks do that sometimes to avoid other planes or rocks. Or dive bombing eagles.

I also owned a Easy Eagle (as kitted by Ace). My recollection was a very nice wing and a light-ply box for a fuselage. It ended up being heavy. I tried slope soaring it (as I did with the GLs). My recollection was that the GLs could out maneuver the Easy Eagle. But the flaps on the Eagle made landings easier. I don't know about thermal performance. But for what I am doing (re-starting flying) I think that the GL is a better choice. I'm not sure about high-starting a Easy Eagle, I think it was designed for a winch.

As for bolt-on wings, I'd only use those if I was planning on not crashing. I've crashed two such planes. The first (Dynaflite Skeeter) had the wooden dowel rip through the bulkhead. The second (an RCM PSS P-51) had all the ribs in one wing break and the bolt was fine. In the P-51 I put on a brass tube on the bolthole to make a nice edge to shear the bolt, and drilled a small hole through the bolt cross-wise at the edge. but still the bolt held. Might have something to do with the dummy air scoop on the P-51.
Oct 23, 2019, 07:11 AM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
RE: Easy Eagle.... on the site I referenced above Harley does mention that Ace took some compromises in the kit fabrication and produced a kit far heavier than the original design. Some time back someone was offering a short kit with laser cut parts. The remaining wood needed to be sourced by the builder. If the builder knew what he/she was doing the result would be a glider weighing less than 30 ozs. Is is a nice weight for a 2 meter. My GL weighs in at 28 ozs.

Sourcing your own wood to keep things light is one of the major benefits of scratch building.

Kurt
Oct 23, 2019, 03:39 PM
B for Bruce
BMatthews's Avatar
A side note that might explain some of the GL's preference for lighter wing loading.

The airfoil used by Carl in this design was the same used on a number of his later free flight gas jobs from the early 1960's. Even the buried spars in the ribs is right from his high thrust Viking free flight design. And at the time of the appearance of the GL we were all flying lightly loaded gliders that were later on referred to as "floaters" or "gasbags". So likely why he chose to use his favorite free flight airfoil on the GL. And so it's no surprise that the GL shares a bit of a dislike for heavy wing loadings and trying to fly faster with many of the designs from back in the day.

Looking at the GL plan on Outerzone I see that the GL first saw the light of day back in 1980. That's coming up rapidly on 40 years ago now.
Oct 24, 2019, 12:57 AM
Registered User
Pretty sure that the GL,doesn't "dislike" heavier wing loading. It's the only way you're going to get back upwind on sufficiently windy days. (Unless your name is Tom Keasling.) It might not handle the same as a normal GL. In some ways it will handle better if the increased weight is concentrated near the cg. A model that has a fast airfoil won't need a heavy wing loading, and in fact, like any other aircraft, will suffer if the weight is more than desirable for the conditions. Bigger turning radius, somewhat increased sink rate, faster landings that must dissipate more kinetic energy, preferably not by breaking something. I used to put rocks in my Oly II on windy days.

------------
A given amount of washout works best at a given speed. As you go faster, less is required, and having more than you need may cause extra drag because the airfoil may be operating outside of its best range of CL. Also, induced drag will be more than it needs to be, though at high speeds this may be somewhat less of a problem. Flown fast enough, a washed out wing may be lifting down at the tips and up in the middle.

A constant chrd wing will have less induced drag if given a little washout. At least at low speeds. Ditto a wing with tips that only taper a little. A wing that has a lot of taper may need washout to prevent tip stall if other aerodynamic tricks aren't used. However, this washout doesn't help with induced drag because it makes the lift distribution less like an ellipse. It can get a lot more complicated than this if the airfoil changes along the wing, there is sweep, or the lift distribution is adjusted to lessen bending stress and/or reduce adverse yaw. I'll admit I haven't done much of the math for this. One way to reduce the amount of calculation required is to use Schrenk's approximation, which can be graphical. You can just do a few drawings. Presumably, there are ways to adjust Schrenk's approximation to account for twist. I don't know whether it can be fudged to account for sweep. Schrenk's might be a good check on fancy software to make sure your results are reasonable. Software may not give you a dope slap if you feed it garbage. My fingers are tired, but I'm sure you can look up Schrenk's approximation on the web. It seems to me that there was an understandable paper about it from NACA, eons ago when dinosaurs ruled the earth and aerodynamicists placex centers of pressure out in space as far as Alpha Centauri. But that's another story.
Oct 25, 2019, 02:41 PM
Slope Soarer
Thread OP
Nope, I'm not yet finished. Photos are old ones of Gentle Lady number 2. Not sure when it was built, but it has a AMA membership sticker for 1991 on the side of the nose.

Location is Coyote Hills in Fremont CA near San Jose, If you go to the East Bay Regional Parks District web site and find the map, the place I was flying at is called "Glider Hill". The hill has a couple of miles of SF bay to the west (upwind 90% of the time) as in the first photo, and is covered mainly by grass as in the second photo. I never realized how lucky I was since I'd never flown elsewhere,

I made the wing tips different colors to aid in determining orientation. I don't think that I'd choose these colors again since the black tip heats up in the sun and goes slack more so than the orange one, I had a later plane that had tips that were white on the top and black on the bottom and that worked just as well visually.

Building wings at the moment.
Last edited by AChacon; Oct 25, 2019 at 02:52 PM.
Oct 25, 2019, 02:51 PM
Slope Soarer
Thread OP
Quote:
Originally Posted by kzimmerm
RE: Easy Eagle.... on the site I referenced above Harley does mention that Ace took some compromises in the kit fabrication and produced a kit far heavier than the original design.

Kurt
I read that someplace as well. From my perspective back when I built it the problem was that it was hard to maneuver in a slope soaring environment and the construction suited for winch launching was not needed. Too fast for light wind days and too hard to maneuver for high wind days. But it might work well here here in AZ.
Oct 25, 2019, 05:28 PM
Registered User
In a post earlier in this thread, I mentioned joiners. Just to be clear, I meant the wires joining the three piece version of the wing.
Nov 02, 2019, 10:34 PM
Slope Soarer
Thread OP
Quote:
Originally Posted by lincoln
In a post earlier in this thread, I mentioned joiners. Just to be clear, I meant the wires joining the three piece version of the wing.
I guessed as much. One wonders how the GL ever survived. Maybe some did not. I built my first GL with a one-piece wing and the second with removable tips. After a crash on the first plane showed that there is more than one way to remove the tip panel, I rebuilt it with removable tips. I was working from the GL plans at the time so I used their design with a small modification: I added a short pin at the rear spar to make the alignment metal to metal, not by the tape.

The SL plans show two joiner rods, and that makes a cosmic balance: two spars, two rods. So that is what I used here. Took a bit of work to figure out how to make the two joiners parallel so they won't bind when putting the tip panels on. With a single rod this is not an issue.

The photos show the removable tip with just enough epoxy for me to verify everything will work. The sequence shows the tip panel coming off. Success, now it is time to really glue it up.

I'm hoping the left wing will go faster. Every time I've cut a part for the right side, I've cut a mirror image part to use on the left.
Nov 02, 2019, 11:14 PM
Registered User
dsdemer's Avatar
Yes, the world could always use another build log. The specific sailplane doesn't matter...
Nov 03, 2019, 06:00 PM
Slope Soarer
Thread OP
Quote:
Originally Posted by kzimmerm
RE: Easy Eagle.... on the site I referenced above Harley .....

Kurt
Oddly enough there is a discussion on RC Groups about Easy Eagles:
https://www.rcgroups.com/forums/show...ort-fun-flying


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