Sherpa

Recently a lot of concentration has gone into designs that would fill an empty space in the stable of slopers carried by FSD. One particular goal was to design a true ultra-light sloper that could fly in extremely light conditions. Another goal was to develop a sloper that could be easily broken down into three major parts for easy transport such as in a backpack. This would allow pilots to pursue more exotic slopes that can only be reached on bike or foot. Thirdly, we wanted to design a sloper that could successfully SAL (side arm launch). We hope that the newly designed Sherpa will fulfill these requirements.

The purpose of this page is to outline the steps taken in the design and development of the Sherpa. As the project progresses, more entries will be posted on this page.

The Sherpa Project

The original design was scratched out on a piece of paper about 2:00 a.m. in the morning. By 12:00 noon the next day, there were several variations of the original idea mapped out using Adobe Illustrator. The concept for the design was to develop a sloper that would have an AUW of around 6-6.5 oz. In addition, I wanted the Sherpa to have the ability to break down into three major parts for transporting in backpacks. It is hoped that this added feature will be integrated into the design in a future version. Finally, the Sherpa will have the ability to be a SAL plane for those days when conditions on the slopes are not ideal. The graphic to the right was the version to be taken to the shop for development.

Here are a couple of images of the first “hand-cut” version. This means that no tooling for the Sherpa had been developed or used. The exact parameters came from scaled up drawings done on Illustrator. Without an airfoil template, a set of Raptor 36 wings were temporarily used. (Airfoil PLA001A)

Handcut Sherpa 1.0 without elevons.

Handcut Sherpa 1.0

without elevons.

A word about the airfoil for the Sherpa...

The airfoils for the Sherpa are an exclusive design by Todd Jurhs. Todd is

a slope enthusiast with a special interest in airfoil design. His effort

here was to develop plank specific airfoils with minimum drag and moment

characteristics while maintaining sufficient lift at very low Reynolds

Numbers. The Sherpa wing panel is semi-symmetrical employing two separate

airfoils for the root and the tip. Both airfoil designs are the property of

the designer and are exclusive to Future Slope Designs.

The first step after developing the hand-cut version was to generate templates for both the ATJ airfoils and fuselage,

Once the wing panels were cut, a groove to receive the fuselage tube was cut into each root. Special tooling to insure consistency remains to be developed.

Next, the tail was cut with a scrap piece of tubing to determine an accurate cut.

Finally, the fuse pod is cut to include the center balsa piece with paper template.

The Sherpa now consists of three sections, the wing section, the tail section and the fuse/pod section.

The fuse after two coats of Goop

Sherpa Elevon being prepared for covering with blue packing tape.

Protective strapping tape applied to the leading edge.

Preparing to attach elevon to the right wing panel.

The Sherpa covered and ready for installation of gear.

Hi Todd,

I had been waiting for a few days for the winds to turn around so I could test the Sherpa (aka - Enigma). Today the winds at the launch site were around 7-11 mph. This is unusual because where I fly it is either nothing or at least 15 mph. The conditions today were perfect for testing both the plane and more importantly, your airfoil.

I have posted a short video of today's effort on the FSD web site. You can go to:

http://futureslopedesigns.com/Sherpa.html

Go to the bottom of the page to see the Vimeo movie.

I'm not sure where to begin...

I have been designing and testing slope planes for a long time. For whatever reason (which I haven't quite figured out yet), today's test of this particular plane and your specific air foil was unlike anything I had experienced in the past.

The winds were very light, but the plane had no problem gaining altitude. The lift ability of your airfoil was outstanding. It seemed to lift with no effort at all. I was completely amazed.

While it lifted with ease, I couldn't seem to get it dialed in with regard to throws and the balance point. In the video it looks like it is flying pretty well. However, I had to constantly make corrections and "actively" fly it. It was rare that I could take my hand off the stick.

It did everything it could to make flying it very difficult.

I moved the CG around at least a dozen time. Sometimes it would fly better and other times it wouldn't hold a line. Then there was the constant hyper-stalling. Once again, I made several adjustments with little or no improvement.

I am convinced that dialing in the proper CG will be difficult at best.

I noted that the sloper would suddenly nose up and then porpose off and on.

Here's the deal...

Even with the issues outlined above, I KNOW that this will probably be my most successful design (due in large part to your airfoil). I simply need to put the time in to make the proper adjustments. I will probably go out again tomorrow and continue my testing.

You will note in the video that I didn't even attempt any rolls or inverted flight. I was too busy trying to keep the plane on some sort of consistent tract.

And therein lies the biggest issue I faced...That the sloper did not track well. It wasn't a left/right issue as much as it was a pitch issue...Once again...back to the CG adjustments.

I am so excited about this plane and I also know that a 55" or 60" version will be even better.

Once I get everything dialed in properly, I will be able to evaluate your airfoil completely. Rest assured though, that it does do two things well: It has great lift ability and it has a great speed range.

I hope that this brief report encourages you to keep designing more airfoils.

Thanks for your efforts.

-Paige

The following is an email I sent to the airfoil designer for the Sherpa. It is a brief “flight report” from the first tests.

Future Slope Designs introduces its first ultra-lite sloper, the Sherpa 36. The Sherpa employs the highly researched and tested ATL airfoil for maximum lift and lowest drag. This combination allows the Sherpa to fly in light conditions on almost any slope. In addition, its semi-symmetrical design makes inverted flight near effortless. The Sherpa is also designed to break-down into three major parts. This “packable” feature makes the Sherpa ideal for transporting via backpack to those remote sites that no one else has tried yet. While at an average AUW of 7.25 oz. the Sherpa still penetrates well and shows an amazing speed range. Its top end speed allows for crisp rolls yet it can slow down to a crawl so you can impress your friends with creative hand-catches. FSD is proud of this well-researched and highly tested sloper. We hope that you will enjoy it as much as we have.

SHERPA SPECS

WINGSPAN 36”

WING AREA 252 sq. in.

WING LOADING 4.20 oz/sq. ft.

AUW 6 -10 oz.

SUGGESTED GEAR

RADIO W/ELEVON MIXING

TWO DYMOND 47s an Up

BERG MICROSTAMP RECEIVER

4 CELL 1/3 AAA Rx BATTERY