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Author Topic: Own Design Glider.  (Read 145 times)
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Fergy
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« on: June 30, 2020, 09:59:37 AM »

As a long retired aeromodeller I am very lucky to be living in a quiet and beautiful part of south west Scotland, with the added bonus of having plenty of nearby fields.

Most of my aircraft are electric powered R/C gliders of my own design. Recently these have evolved into a series of similar types of around 5 feet wingspan, so that fully assembled they will fit in my car.

For many years I have used Sailplane Calc by Mr. Curtis Suter to ensure everything works as hoped for. Thank you Mr. Suter.

While they are of conventional balsa and tissue construction I have been building the wings using the methods of Dick Mathis in his Head Hunter and Bounty Hunter designs. The resulting wings are extremely stiff and warp resistant.

For covering and doping I use Ben Buckle wet strength tissue applied wetted with very dilute Eze Dope, using cheap full strength PVA as the adhesive. Several more coats of not quite so dilute Eze Dope complete the job. I hate covering models, and find these materials the easiest to use so far.

All the gliders have weighed in at around 19 ounces, resulting in a wing loading of under 6.5 oz., per square foot.

My radio equipment is a FlySky FS-i6 Tx., with modified firmware allowing a FlySky CAT-01 altimeter to be used. The receiver is an FS-ia6b with iBus telemetry.

Controls are motor, rudder, ailerons and elevator. The ailerons are mixed with the rudder, giving co-ordinated turns.

I flew full size gliders for over 10 years and, when flying my model gliders, sorely missed hearing a variometer beeping away. With my modified FlySky gear a CAT-01 Altitude sensor is used. This allows temperature and altitude to be displayed on the transmitter, and provides a fairly authentic audible vario tone, greatly enhancing the speed of thermal detection without looking away from the glider. All of the FlySky equipment is very reasonably priced (pension friendly), while the added functionality weighs virtually nothing.

As the transmitter auxiliary switch C is nearest to the elevator stick I use the comprehensive Tx., mixing options to designate the switch as an elevator trimmer. I always build in down-thrust but never get it exactly right, so I simply flick the switch when making the transition from power to gliding. I find this to be much easier and more repeatable to use than a stick trim, and once the optimal trim has been established it need not be changed. Plus, unless the switch is in the Up (powered) position the Tx., will not switch on. This ensures that the switch is always in the launch position.


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Own Design Glider.
Own Design Glider.
Own Design Glider.
Own Design Glider.
Own Design Glider.
Own Design Glider.
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dosco
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« Reply #1 on: June 30, 2020, 10:45:01 AM »

Fergy:
Very neat!

Have you tried any of the Drela airfoils?

Also, do you have a "bones" pic of the outboard wing panel? It looks like you have false ribs (half ribs(?)) there, and not in the inner wing panel.

Regards-
Dave

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Fergy
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« Reply #2 on: July 02, 2020, 04:58:18 AM »

Thanks for your reply Dosco,

Yes I tried a few of the Drela airfoils some years ago , AG03, AG04 and AG16, but as I haven’t flown in a competition for nearly 60 years so have no simple way of comparing any of them. They did all seem to work well enough though.

The sections I settled on for the last several years were MH42 for thermal flying and E374 for slope soaring and aerobatic biplanes.

Flying on my own means that I just want the glider to hang around up there for a reasonable length of time looking for any thermals or wave lift. Raptors and gulls are very common around here and have been my main aid to finding lift, but the big breakthrough for me has been fitting a variometer. I can’t recommend this enough. All full size glider pilots will use them…..a lot.

Curiosity made me want to try out Dick Mathis style airfoils. Firstly, I wanted a change of construction method, and then I wondered how well they would perform, which seems to be as well as any other airfoil. I now believe that thickness is the most important variable, as good penetration can be useful.

The wing in the photos has only three solid ribs in each wing half. At the centre section, the tip and at the root of where the ailerons start from. The rest uses identical sticks and riblets. It gives a very stiff warp resistant and lightweight wing. I suppose if it hadn’t been a good airfoil Dick Mathis wouldn’t have stuck with it, or won any competitions.

My next job is to slim down the fuselage a lot.
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flydean1
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« Reply #3 on: July 02, 2020, 08:12:30 AM »

Fergy,

Dick's "birdcage" wing featured stick diagonals behind a full depth main spar, and full depth riblets forward.  You have modified this and might possibly be an improvement.  He used this construction all the way up to a 1000 sq. in. monster!  All flew well.

I built a 1/2A Bounty Hunter a few years ago and was impressed with the light weight and stiffness.
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Fergy
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« Reply #4 on: July 04, 2020, 05:08:37 AM »

Good morning flydean1,

Much as I would like to take the credit for this wing design, Dick Mathis used it in his Head Hunter with a sheeted upper leading edge. I think the Bounty Hunter came slightly earlier. I like the thinking behind his designs. Simple but very, very effective.

What strikes me is the low power he usually used, except in the case of Head Hunter. This tells me the glide had to be fairly good.

My next wing will be Bounty Hunter style, mainly to save 1/16" sheet. I'm fairly sure there will be no detectable performance difference.

As you say, stiffness is excellent.

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