Mark's Models Sensor 117 2009! - RC Groups
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Jan 06, 2009, 05:53 PM
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Mark's Models Sensor 117 2009!

Greetings, the snow is piling up outside and here's the start of my 3rd Sensor. The kit is in perfect condition, although my how that balsa can get curved over time. This one is going to be polyhedral with flaps but no spoilers. Flap servos will be in the wings. I think the flight surfaces will have white over the sheeting and a couple of transparent colors over the open bays for that stained glass effect. The plans evidently got wet sometime before I acquired the kit. My first Sensor got a slab balsa fuselage that carried a 35mm film camera, talk about antique technology. Anyway, I haven't stick-built in a few years and am doing this project to sharpen the old skills before starting the Dumas YMF-5 Waco kit of Pat Tritle's wonderful design. That will be the highlight of this building season.
I was hoping there were people out there with a fondness for this sailplane that would enjoy knowing they haven't all disappeared yet.
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Jan 06, 2009, 06:14 PM
I need some building time in t
scaflock's Avatar
I remember the Sensor will. I used to live close to Marks' shop in San Marcos and saw them out flying often. Alas... the shop is gone and the field in now an industrial park. Yet another reason I left S. California.

Jan 06, 2009, 07:11 PM
Mark LSF # 3792
Hey, G&S I see your in Steamboat. Good to hear the snow is piling up. I am going to be there next week with the Texas Ski Council doing some "slidin". Don't pack it to hard!

Strange last week I was out "glidin" in a t-shirt. Our building seasons, yes plural, come inconsistantly here. I remember the Sensor, Mark had some good designs. My first real good glider was a '99 and it really taught me how to thermal. Good luck with the build!

Jan 09, 2009, 01:05 PM
Registered User
Bought one of these at a swap meet last spring. Fiberglass fuse, one servo controlling both the flaps and blade spoilers. Is a beautiful plane both on the ground and in the air.

I here that this was a cutting edge sailplane of its day.

Enjoy the build and the results.

Feb 02, 2009, 10:38 PM
Registered User
As an update, the wing panels are built, along with the tail surfaces. Wings are joined and ready to be mated to the fuselage. It's been fun going back to a kit that was a Big Project in my early days of modeling. I'm taking time with it, going out to ski or play with our Dog Alyeska. There's no hurry, we've got feet of snow in the yard.
Feb 02, 2009, 11:57 PM
K5054 & K5083
wrinkled's Avatar
I'm still flying mine now after 19 seasons. Its been relegated to the woodies and RES now that I've moved on to moldies. Other than the monokote being a little worse for wear, I'm still pleased with the kit.

If I were building one today, I'd consider putting in mechanical spoilers (If they are still made) with the servo mounted in the wing. The worse part about putting it together is hooking up the spoiler actuator strings. If I recall I used .021 CF on the top spar and .14 on the bottom. So far no wing failure and I push it a little harder than I ought too. I don't like the flap setup but I'm not sure there is a better way on THIS model.

The fuse needs bracing (side to side) at the point where the wing leading edge meets it. My first semi-dork landing nearly crushed the fuse at that point. It probably wouldn't hurt to reinforce the fuse in the servo tray area. Seems to me I had to fix that area once or twice.

Feb 03, 2009, 12:10 PM
Registered User
Yes, good advice, the fuselage will get something like a 3/8" dowel between the leading edges. I'm not building for winch launches or contest landings, so this one's going without carbon fiber or spoilers.
I want the fuselage secure with the fin vertical before mounting the wings to it. What I've done is wrap the fuse with tape and then glued a couple of shaped foam blocks to it with Titebond. Beans and rice are weighing things down. Hopefully I'll be out of the kitchen before my wife gets home. This way I think I'll be able to measure the wings square to the fuselage and level with the countertop and get accurate results. The tape will leave the fuse free of glue.
Feb 08, 2009, 05:48 PM
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The 1/4-inch balsa stabilator pushrod would be okay if braced; but the long, thin fuselage made that seem difficult. I like pull-pull cable setups so I've rigged one for the Sensor. The rudder will also be pull-pull. I'm using Spectra kite line.
The stabilator bellcrank is actuated by one cable running directly to the servo arm while the other cable runs back and around a pulley, then to the other servo arm. The pulley is 3/8" O.D. brass with 1/16 ply sides revolving on a 11/32" O.D. piece of aluminum arrow shaft. The arrow shaft is epoxied to the fuselage sides with plywood brackets. While the pulley weighs a bit, I think overall there will be a weight benefit along with the positive, slop-free control of the stabilators.
Feb 10, 2009, 07:12 PM
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I'll be watchin'

I will be watching with great interest because I have a Sensor started but put on hold some time back. This just might get the firew under my but to get her back under way again. We have got to keep the old girls around and flying. I have a 20 plus year old R08 2m that was given to me and I still enjoy flying her. Jim holland
Feb 11, 2009, 10:33 AM
Registered User
Thanks, Jim, I'll try to keep moving and updating as I go. I have to add the top pieces of sheeting, rib cap strips and sand all the flying surfaces, glue in the stab mounting, hinge the rudder, then run all the controls. I'm going to run a Y-shaped control rod out through the fuselage sides underneath the wings to external flap control horns. So much simpler than the kit design.
Feb 12, 2009, 04:16 PM
Registered User
Stan asked for some fuselage information, his disappeared and he'd like to build one for the wings and tail surfaces he has finished. I think a simple wood fuselage with box cross-section would be an easy project to design and build. I did one myself to carry a film camera.
I have limited imaging capability, but would like to provide as much info as possible. If anyone can help with his project, please jump in!
Apr 02, 2009, 07:33 PM
Registered User


Here's the covered flight surfaces in transparent Monokote and White Ultracote. The Spectra pull-pull cables are run to the rudder and stabilators. The fuselage is mostly ready for paint and radio installation. It's gone pretty well and I'm satisfied with the results.
Apr 02, 2009, 10:18 PM
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Buran's Avatar
Around 1985.
Sep 11, 2009, 10:06 PM
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finally, a test flight

A couple of weeks ago the Sensor got hand-tossed off a 10-foot bank across a ball field to set the elevator and rudder trims. Today, with a trip out of town coming up that will eat up the rest of the month and winter closing in on our Rocky Mountain home, the Sensor was carried up the Steamboat ski resort slopes to the top of a run called SeeMe that's a couple of hundred feet above the base area. It's about the only grassy slope available around town. It faces west and had a nice lively breeze coming straight in to the slope. The Sensor left my hand with hardly any push, immediately rising about 25 feet, moving straight ahead a ways and rising another 50, then it just went up the elevator, at least another hundred feet. Very steady but with that kind of lurching motion polyhedral planes seem to rely on. Anyway, after about a half hour of zooming around, circling upward and such an approach was attempted to the top of this hill and the Sensor circled a bit too far behind the slope and dropped into tall grass behind the ridge, undamaged. Oops. Anyway, it was great to finally see it soaring. I'll be eager to try its thermalling abilities from a heavy-duty high start, hopefully this fall.
The photos show the control setup with Hitec gear. Rudder servo on right is HS 422, elevator on left HS 475HB, and flaps up front another HS 475HB. Battery in the nose is 4 AA NiMH, with a casting of lead in the very nose adding about a quarter of a pound. I wrapped the nose of the fuselage with two layers of aluminum foil, making an exterior "mold" which was set into a can of kitty litter. A bit too much lead was melted and poured into the mold. Then the Sensor was assembled and balanced and the lead drilled out until it was the right weight. Then it was glued into the nose with Shoe Goo. It fit really well once the front point of it was cut off leaving room for the extra fiberglass wadded up there in the very nose of the fuselage.
The switch is mounted above the wing just behind the canopy. The receiver is stuffed beneath the servo tray behind the servos with some foam rubber.
I ran Spectra kite line pull-pull cables to the two rudder horns and the bellcrank and pulley arrangement for the elevator. At the rudder horns I just knotted the Spectra into Sullivan brass clevises which were crimped and CA'd. The rudder horns are a single piece of Formica glued into a slot in the rudder with Shoe Goo. At the servos short threaded control rods were bent into eyehooks. The Spectra was looped through the eyehooks and secured with little copper tube ferrules which were crimped and CA'd. These control rods are secured to brass Sullivan clevises with locknuts and Loktite.
The single flap servo drives a "Y" shaped control rod with a Du-Bro ball link at the servo and Great Planes steel clevises at the flaps. With the clevises Loktited they can't rotate and change the adjustment with the wings off.
Nothing fancy, but the rudder and elevator control is slop-free and tight, while the flap actuation actually has some softness thanks to the multiple bends in the control rods. This seems to maybe be a good thing. The flaps are bumped securely against the wings when fully up, but when dropped seem like they can easily absorb impacts with the ground when landing.
Last edited by glidin'n'slidin'; Sep 11, 2009 at 10:18 PM.

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