AUW and Sailplane Performance (what I learned from building a 10' Gentle Lady)

[JimD]

Just about every sailplane pilot either started with or at least has had some stick time on a Carl Goldberg Gentle Lady. Larry, one of the guys in our local club had a Gentle Lady that he would hand launch and make multiple circles before landing and doing it again. After watching him have so much fun, I decided to build my own Gentle Lady. Following the "lighter is better" school of thought, we carefully constructed the airframe with Carl Goldberg Super Jet instant glue and covered it with MonoKote, nice and light weight!

Hand launching my Gentle Lady proved frustrating...I was lucky to make a 180 degree turn and get back to my feet, much less the multiple circles Larry was making!

So what was the reason? One day while flying with Larry, I asked him if I could see his plane. When he handed it me it was like lifting a brick!!!!

Lead weight added, problem solved.

Fast forward to 2009. Funny that prior to meeting LenB for the first time I was already leaning toward the "bigger is better" school of thought. During the winter of 2009, I decided to scratch build a 10' span version of the Gentle Lady...the Ginormous Lady...the Giant Gentle Lady.

Here is the uncovered airframe sitting on my 8' long workbench. Wow, I thought it was huge!



The completed model at the 2009 Cumberland, MD Fall Soar for Fun.



The first flight.







So...how did it fly?

Back to school...built it very light...very short flight...would not penetrate into even a slight breeze...lesson learned, AGAIN!"

Added a bunch of lead and it was a totally different sailplane.

Point is, consider the optimum AUW (All Up Weight) of the sailplane you are building and then judge whether it is better to have a stronger but heavier airframe structure or added lead weight!

[lenb]

2009 was my first year at the event and I can distinctively remember the plane.

[Stew2]

And aerodynamically you want as much weight as you can get in the wing. You want a very strong, light weight fuselage and tail and the ballast located on your balance point. Your trying to increase the wing loading with minimized increase in roll, pitch and yaw inertia. That is what allows a glider to have good penetration and remain light on the controls, which means minimal control input for direction changes. Minimal control inputs minimizes drag... All working in the right direction. If you are ever around when a Baudis Antares is being put together, ask if you can feel the weight of a wing panel, you will be amazed. Sailplanes are not light, they are very slippery! You will notice on most big glass ships that the majority of the mass is in the wing panels, and they don't put the water ballast tanks in the wings because they couldn't fit them anywhere else...

[JimD]

2009 was my first year at the event and I can distinctively remember the plane.

...and I can distinctly remember the guy that showed up with a trailer and this "giant" sailplane!

[Asher Carmichael]

As a "professor" from Davis and Elkins once told me......"gravity is what energizes our sailplanes and mass with altitude is potential energy". Thanks for the reminder, Jim.

[lenb]

...and I can distinctly remember the guy that showed up with a trailer and this "giant" sailplane!

Oh, that little thing?

[Xroadie]

It's Giant Scale Gentle Lady!!!

[JoeN]

So where is the giant gentle lady now? I would like to see her fly at THE March Fly In.
I am late to the large concept. Just got a Blanick! I do have a large sailplane, first flight was at the Soar For Fun last November, the Sky Bird. Only had one flight due to flight control problems, which should be OK now. Plan to fly the big sail plane at the March fly in two weeks away from now. I pLan to pester every one who shows up with a Blanick about how to set her up. So, please be be gentile and tolerant with me. Thank you in advance. Joe

[pete914]

I have a "smaller" 5 meter ASW 28. It's loaded down with 2 x 4000 mah 4s batteries and other gear for a nose mounted SLS system and feels quite heavy in the hand. I think pulling the system out could save me 2-5 lbs. However, I want it to fly like it's full scale counterpart and worry that the lighter wing loading won't help.
Two questions:

1. If we want less inertia to roll and pitch it seems like the best place for weight is at the CG point inside the fuselage right? I've also read to put the weight in the wings. Heavy wings are like heavy lever arms and it seems would be akin to a tight rope walker with a pole. So why do we want the weight in the wings, it seems counter intuitive.

2. I have seen some "formulas" for determining ideal wing loading for a glider, slow flyer, acrobatic plane, etc.

Using this formuls my 1:4 DG 100 is a brick with 3x the recommended wing loading for a glider. On paper it would not soar. However, it soars and climbs remarkably well. The weight seems to help. What guidelines do people use to figure out how much their sailplane should weigh? What characteristics are most apparent when a sailplane is too heavy? Too light?

[ingrahal]

Another factor is the airfoil. Some airfoils perform better at higher speeds. The best L/D and minimum sink and all that stuff. The heavier the sailplane the faster it flies. This improves performance with some airfoils. Back in the day we found that the Lawicki Duck flew better ballasted even in light lift.