LET Model JS1 is here!

[tewatson]

Moving to the main wing panels, the inner ailerons suffered from the same malady as the tip ailerons, with the same results: Significant double-centering, excessive load on the servo, and limited upward surface movement. The OEM linkage geometry is a bit less of a problem here, as the wing is slightly thicker and thus slightly more moment arm. So, I decided to see if just addressing the wiper and sub-TE problems would cure the symptoms.

The process was identical...disconnect the linkage rod, then pivot the aileron down about 70-80 degrees, and secure it in position. Re-shape the wiper (to the extent possible) by extensively block-sanding with 180 and then 220 grit. These wipers are also molded with the wrong profile, so re-shaping ability is somewhat limited. See the pics for an idea of how grossly out-of-profile and thick they were. As I previously stated, completely unacceptable.

Next, the sub-TE overhang was reduced approximately 1mm by marking the new profile with blue tape, and using a thin sanding block to sand the edge to the new line.

With the OEM linkage back in place, there is still very slight double-centering (less than 1mm), but surface throw is correct with only minimal binding. It really does need new linkages here as well, and I will likely do that at some point in the near future. For now, it is adequate to get the plane flying. Next, we tackle the flaps (all 12 linear feet of them)...

[tewatson]

Finally, we come to the flaps. The primary problem is wiper profile and thickness, and with the additional down throw required, the binding produced very excessive load on the servos. With limited upward movement needs (as flaperons), the sub-TE was not a factor. The OEM linkage geometry is again even less of a problem with a thicker wing section here, although to be optimal the surface horn pivot point should be a little forward of the hinge line. Not enough to warrant ripping the linkages out right now.

Same wiper adjustment process as before, although with 70" long flaps, there are two servos per surface. I also needed a more robust jigging process, to ensure there were no prolonged twisting forces applied to these long surfaces, and to prevent the panel from moving around (or worse, slipping off the table.) The incorrect wiper profile is most impactful here with the increased down throw needs, and re-shaping ability is limited as well.

Re-engaging six feet of flap wiper requires a bit of forethought, and I came up with a scheme that worked perfectly: Playing cards and a second set of experienced hands. Took the wings over to Dennis Brandt's house and with the nearly 20-card hand dealt, each of us took an end. Took about 10 seconds per flap and worked perfectly.

Using the OEM linkages, there is no double-centering, but there is some servo howl at max flap. I figure this is OK since landing configuration is not used for long. By design, flap throw is limited to no more than 25 degrees, so energy management will be key. On the other hand, there is 12 feet of flap so they are more effective than one might expect.

[yyz]

I'm amazed at how much technical hand work you guys have had to do to get these planes in flying shape. Yeoman duty for sure. I guess shipping it back to LET isn't exactly an option. Did you talk Steve off the ledge or vice versa?

[tewatson]

A little of both. He was first out of the gate and discovered the problem. We talked about it for a while, and he actually flew his first with just some wiper work and all the OEM linkages intact. Up until then, we were hoping that the ~9mm upward tip aileron throw would be enough. It was not, so we came up with the linkage re-do idea. His is a little different, with ball links for the tip ailerons instead of the MP Jet clevises on mine. You know me...I like to think about things for a long time before building and I learned a lot from what he went through.

LET/Topmodel basically would not admit there was anything wrong, and shipping it back was really not a practical option anyway. One thing that really boiled my blood was during the discussions we had early on with LET, they sent us videos of the prototype airframe showing them running a steel ruler freely back and forth between the sub-TE and wipers, saying "see - nothing wrong." Yeah, but that's YOUR plane...OURS have problems. One of the risks of being first in line for a new design, I guess.

I estimate to have spent about 40 hours on the wings alone, for the wiper and linkage work.

[ARUP]

It's amazing how much time it takes to finish these things! I hope I will be at an aerotow where you will fly it! It's a beautiful model!!!

[tewatson]

Hoping to debut at the February aerotow in Visalia.

[tewatson]

Another helpful bit was this test harness I made. Wanted to program the radio early on, and repeatedly mounting the wings to the fuse for testing while doing all the wiper work was not a viable option. This made things easy.

[yyz]

It's all about the DB9 (D-Sub not Aston Martin). Keep up the great work! Like Steve's this is really going to be a gorgeous ship.

[tewatson]

DB15, I'll have you know. Five servos per wing, with no doubled-up connections.

[tewatson]

Assembled the complete airframe today for CG check and overall function testing. This is only the second time it has been all together, and the first time everything was powered up at once (the latter is always a satisfying milestone to attain.)

It took 1/2 oz. (yes, half an ounce, or 14 grams!) to CG it at the recommended point, so no need to cast up a large block of lead shot and epoxy. Nice. Apart from a couple small details such as re-securing wing servo covers and some minor cockpit/pilot items, it is ready to fly. Looking to maiden at the Visalia Aerotow in a few weeks.

[ARUP]

Noyce! Wish I could be there to see the first flights!

[jgallacher]

Tom good news, send pics for the PRCF club newsletter.
Jim Gallacher

[JimD]

Hi Tom, we posted a link to this thread on the Scale Soaring website, check out the Home Page listing... https://www.scalesoaring.com/

[tewatson]

Thanks, Jim. That’s nice.

[stevecondon]

Can't wait until you maiden yours, Tom! Love the way this model flies and I am still uncovering the potential. Besides aero-towing, I am looking forward to another ripping day at Torrey Pines to fly my JS1...this time I will attempt to get there when there is little to no traffic competing for airspace! Too stressful. This was a fairly short but very exciting flight!

[ARUP]

Excellent photo!

[lenb]

you're killing me Steve, not only is a great aircraft, BUT that spot!!!!

[tewatson]

Spent a few hours this week on remaining details like final cockpit arrangements.

As mentioned, I'm using the PowerBox Champion SRS unit for battery and RX management, with dual (redundant) JR DMSS serial bus RXs. It will handle up to 18 channels, has 24 output connections with unrestricted assignment capability, dual redundant voltage regulators which can be independently set if you have both HV and non-HV equipment, plus much more. Additional information here: https://www.powerbox-systems.com/pro...mpion-srs.html

The plane is ready to fly; now just need the weather to cooperate.

[Mark Taylor]

Dude! That is sick! Real Gucci stuff right there! Based on the purchase price, was it worth it?

[tewatson]

The control surface wipers and linkages should have been far better designed and implemented for a model at this price point. Other than that, I would say yes. Final judgement will come after it flies.

[tewatson]

No towing this month...everything is too soggy. Going to be a few more weeks until maiden. Rats!

[jgallacher]

Bring it out to Johnson Field we can get you a tow pilot.

[tewatson]

Rained out again. Now aiming for first flight at the March Visalia Aerotow.

[tewatson]

Maiden day at Visalia was largely uneventful. Got four flights in, and after correcting a minor landing gear issue, everything went without a hitch. The JS-1 displays good manners on tow, thermals well and has really outstanding L/D. My only complaint (if you can call it that) is the rather limited flap throw, which simply requires good approach planning and energy management. On the third flight, flew the GPS Triangle course and did nine laps in average air. So, it shows promise.

Felt good to finally fly this thing. Looking forward to lots more air time.

Tom

[ARUP]

Awesome news! It sure is a 'purdy' sailplane!!! Hopefully the travel limits secondary to manufacture will be remediated. I couldn't imagine landing this slippery monster at some of the fields from which I fly with the limited glidescope control from which the pilot is forced to endure!