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Author Topic: RES 50 inch RC Hand Launch Glider  (Read 874 times)
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Sundance12
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« on: July 27, 2018, 11:37:00 PM »

This design is in keeping with the early 1986 period of RC Hand Launch Gliders that were just becoming popular as a lead in to futer DLG sized airplanes. The micro servo had just made its debut on the scene an this contribute to the class. 50 inch spans were typical and 11 oz was the norm. I have been preparing a design in the style of the period and present a rough draft design to perhaps stimulate conversation in the class of sailplanes.

Opinion on this work is appreciated.

Sundance12
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Konrad
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« Reply #1 on: July 28, 2018, 06:37:37 AM »

I found that the javelin or grenade (Bridi) launch worked best with a finger hole in the bottom of the fuselage. To cut down on drag I added a spring door that close this hole after launch. I did not like the finger rests often added to the side of the fuselage. I found that with the Eppler 205 that these flew best at 12oz plus. Any lighter and I couldn’t get the height I wanted on launch. I did fold a few wing at the dihedral joint. Of the smaller 50” HLG I built the Bridi Tercel and Flipper. In the same time frame I much preferred the Larry Jolly 60” Flinger. A little later I built the 60” DJAerotech Monarch. The performance gains from the sheeted foam core wing was huge.

On your model as drawn, I’d thin the airfoil as it looks like you are also adding spars to what looks to me like a foam sheeted wing. I’d also use a modern airfoil from the likes of Mark Drela. I'd also do away with any spoilers. To get out of thermals I'd fly inverted if I couldn't find sink. (Like I couldn't find sink) Grin  Also I'd use a bolt on wing to reduce weight and drag.

All the best,
Konrad
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Sundance12
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« Reply #2 on: July 28, 2018, 11:45:56 AM »

Hi Konrad

I will be launching this with a lightweight histart. I never liked hand throw with these things. 11 to 12 oz was my target I don't think I will have trouble getting to that. The aerofoil is 8% and the wing is all built up, no foam here. Sheeted leading edge. No spoilers on this plane. I have built the Flinger in my long past. (1986) wing is strap on like the Bird of Time design, there will be little drag with that. Fuselage is quite narrow. Thanks four your observations, it's good to have a critical look. I will recalculate my aerofoil thickness. This airplane is really a fun flyer for the local park and not for contest performances. It is a design to test out a series of design rule of thumbs for gliders that has been published in model aviation literature from the 50s and 60s. The design structure is typical of the 80s. I may publish my page of design numbers.

Sundance12
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« Reply #3 on: July 29, 2018, 04:44:03 AM »

The aerofoil is 8% and the wing is all built up, no foam here. Sheeted leading edge....
I will recalculate my aerofoil thickness.

You will find that 8% thick is around the practical limit for structural stiffness in a built up model although a little thinner can be better for aerodynamic reasons with a refined airfoil design (they tend to be very thin in the rear portion/trailing edge area, which makes it a struggle to get a stable TE with traditional techniques.) I'd suggest looking at the F3-RES style build techniques which use carbon strip caps on the spars (unless you're specifically after 80's style construction.)

If you are sheeting the D-box I'd suggest the AG37-38 airfoil series. There are better airfoils around now (try BC30-BC70 if you're ok with undercamber) but the AG35-38 series was designed for built up construction with flat faceted upper surfaces.

I'm afraid 11oz (311g) is rather heavy in a 50" model (My 60" Skidoo was 200g without ballast.) Try for as light as you can without compromising stiffness but give yourself the option to add ballast. You'll find more thermals Smiley especially in light wind conditions.

I would suggest running your design through Curtis Suter's SailplaneCalc (http://www.tailwindgliders.com/Files.html) to check you have the right stability and control. Over a few R/E models I have settled on:

  • EDA around 11 degrees.
  • Horizontal Tail Volume around 0.4
  • Vertical Tail Volume around 0.04
  • Tail moment arm 3.5-4 times the mean chord

Jon
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« Reply #4 on: July 29, 2018, 08:05:01 AM »

Hi Jon
Thanks for the evaluation regarding airfoils and what the trend to thinner is all about. I am agreement that thinner may give more performance but that requires a move to space age materials that I was not intending. Yes I am keeping this design a period piece of the times (1980s).  I always buold light so I will strive for lighter I will have to rethink a location for ballast if I can.
thanks for the link to design calculators I will try them.

Sundance12
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« Reply #5 on: July 29, 2018, 08:44:12 AM »

Jon,
Thanks for the link and your design interpretation.

Sundance,
With these time frame builds it is a problem as to where to draw the line as to what technologies to use.
As I recall Bob Violet had introduced the use of carbon strips to the hobby market in the 80’s. Also Selig and Donovan had introduced low Reynolds number airfoils with the Princeton wind tunnel publication.
So in keeping with the 80’s theme the use of computer airfoils and carbon is still inline with the 80’s theme. The real changes since the 80’s has been in the radio weight and size and the introduction of the discus throw.

"It is a design to test out a series of design rule of thumbs for gliders that has been published in model aviation literature from the 50s and 60s." As I recall in this time frame R/C sailplane design was still aimed at "hang time". The idea of "covering ground" wasn't introduced until the Graupner Cirrus.

All the best,
Konrad
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« Reply #6 on: July 29, 2018, 08:56:53 AM »

To add to the good advice that you have been given I would strongly suggest that you try to at least have thinner airfoils at the tip, tapering from the centre panel. The lighter, less draggy tips will improve performance and response.
How thin? I would be aiming for at least 6% or even better right at the tip. I have used 4.5% at the tip on a 2m model(RE) but that was glass on foam, and was very happy with it's performance.
With conventional construction - DBOX LE and a shear webbed much wider sheet TEs with solid balsa right at the TE and cap strips may be the way to go.
It will need good light stiff balsa - possibly around 1/32".

John

PS Re Konrad's post - I had an early javelin launch 1.5m RE RC hand launch glider(1996) which used a SD4082 - 8% thick and 4% camber but glass on foam. It was too heavy at 13oz but with a hook was quite capable of beating 2m RE models
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« Reply #7 on: September 06, 2018, 07:36:54 AM »

This design is in keeping with the early 1986 period of RC Hand Launch Gliders that were just becoming popular as a lead in to futer DLG sized airplanes. The micro servo had just made its debut on the scene an this contribute to the class. 50 inch spans were typical and 11 oz was the norm. I have been preparing a design in the style of the period and present a rough draft design to perhaps stimulate conversation in the class of sailplanes.

Opinion on this work is appreciated.

Sundance12


Sundance:
I like the looks of your layout.

Of course, the devil is in the details. Some thoughts (for whatever that's worth (not much, I think)) which are informed by current info ...

- Use actual airfoil sections for the tail feathers, particularly a non-symmetrical one to avoid control hysteresis (i.e. "mushiness")

- Concur with the suggestion to use Sailplane Calc ... many designers in the 80s apparently did not understand dynamic stability, or chose to ignore those considerations due to constraints (for example, 36" stock wood lengths)

- Also concur with the thoughts on airfoil thickness ... size materials and geometry for stiffness
  -- Remember that the bending moment is non-linear and the majority of the stress is within about 1/3 of the half-span (from the root)
  -- To work within the constraints of wooden construction, you may want to try a thickness distribution across the span, say a 10% thick root chord, thinning to 5% at the tips
  -- Keep the tips light, and try to concentrate the structural mass (of the plane) near the CG ... taper the spars, use bass or hard balsa for the tip panels, etc.

Perhaps it would be interesting for you to articulate the "design rules" you have in mind ...?

Regards-
Dave



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« Reply #8 on: September 06, 2018, 08:01:06 PM »

Here's a copy of the model I manufactured in the mid 90's, Fred Mallett's Airworks Epsilon. It was one of the last HLG planes to get a rush of interest at top levels before DLG's came out. Double taper planform with pod and boom, all made from scratch out of raw materials save for the arrow shaft booms. I was blessed to have a good teacher in Fred, but life changes and my professional model building career transitioned into Austin slacker for a decade or so. Smiley
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« Reply #9 on: September 06, 2018, 08:10:44 PM »

Weight is still 9oz ready to fly.  Grin You can always add ballast, but the hardcore competition guys demanded the lightest planes. As any good manufacturer will do, there is a strict quality control process for all planes, but the best of the best, the lightest that passed structural inspection, always got set aside for special flyers. As close as we were cutting the weights, that often meant some visual flaws on the lightest units, but that didn't matter in competition.
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« Reply #10 on: September 07, 2018, 11:32:36 AM »

Thanks for all the input on this project design, I will be writing up my design thesis soon. With the opinions expressed in this forum, I had to rethink a number of things toward this design. I certainly am using design techniques from the 30's, 40's and 50's and some of these new points of view make me change tack a little bit. However, the intent was not to develop any kind of competition performer, I wanted a design that would meet my needs in simplicity and perhaps, do that for others as well. This plane is a Sunday Flier for sure and with limited construction materials at my disposal composites are out. I suppose I am having a bit of a time qualifying my design point of view. The initial motivation for this creation was that I "needed to build something and my drafting board was only big enough for 36 inches" problem. Such is life, I will make a study of all the individual points and suggestions, and re-develop. This project has taken on a bit more direction than anticipated but that is a good thing for a better product.

Sundance12

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« Reply #11 on: September 07, 2018, 11:26:02 PM »

My favorite small (58") glider is Ed Depue's "Tossette". I use mine as a park flier and it loves light/small thermals. Have had 3 of them, 1st two were just over 8oz. #3 is almost finished. It was kitted by Midway Models along with the 60" "Gnome". Plans are available through AMA Plan service in the Model Builder collection. The Tossette is similar in shape and construction as your drawing. One difference is a much larger rudder. I have found this to be helpful flying the very small thermals.

Norm
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« Reply #12 on: September 08, 2018, 09:51:45 AM »

My favorite small (58") glider is Ed Depue's "Tossette". I use mine as a park flier and it loves light/small thermals. Have had 3 of them, 1st two were just over 8oz. #3 is almost finished. It was kitted by Midway Models along with the 60" "Gnome". Plans are available through AMA Plan service in the Model Builder collection. The Tossette is similar in shape and construction as your drawing. One difference is a much larger rudder. I have found this to be helpful flying the very small thermals.

Norm

Neat.

Your comment about the rudder ... this is (sort of) the reason for suggestions to use Sailplane Calc. Verifying the fin sizing (area, moment arm, etc.) prior to building will help ensure a nice flyer.

-Dave
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Sundance12
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« Reply #13 on: September 08, 2018, 10:40:16 AM »

Thanks for all the input everyone, I accept all of the points of view. I am familiar with the Sailplane Calc you are referring to and I am using it for a different 2 meter sailplane project. This small sailplane has been designed using design criteria established by other sources of knowledge established in the 40s to 70s published in period publications of the time. I may work this design in the sailplane Calc just to see how traditional methods compare.
I like the design you presented Norm, I am familiar with it. It was not in my list of previous desidns that I had been uaing for analysis.
yellow is my favorite color. I will look at the percentage my rudder is compared to the fin on my design.

More to follow

Sundance12
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« Reply #14 on: September 08, 2018, 11:13:53 AM »

Quote
This small sailplane has been designed using design criteria established by other sources of knowledge established in the 40s to 70s published in period publications of the time. I may work this design in the sailplane Calc just to see how traditional methods compare.

Sundance:
If you're looking to replicate the areas and moments of the older designs, which I can appreciate from a nostalgia point of view, I'd still recommend using Sailplane Calc to ensure the design has the "controllability" attributes necessary for a good design (and verify the heuristics you're using are valid).

It would be no fun to design something, build it, and find out after the fact that it's a pig ... and then have to redesign it to fix it.

I'd posit that Drela has brought the math associated with a modern understanding of stability and control to model aircraft design. Even through the 1960s these concepts were not well known or understood.

Anyways, I suspect you've heard enough. I hope you post some pics of your finished bird.

-Dave
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« Reply #15 on: September 19, 2018, 03:57:13 PM »

Hi Dave

I did run the design through the Sailplane Calc and was pleased with the numbers regarding typical stability parameters. I will be including these results as I finalize design details. Plans will be available when locked down and the prototype tested. I am in the last stages of a workable plan that I can work from. The images of the plan in the earlier post are preliminary and served to provide foundation. The plans are being created by Ratz and I on an ongoing unstructured schedule and we have been through plan revision 4 at least. I did change the airfoil to a AG35r that seemed appropriate. The section is slimmer at 8.7%. Building this fine wing will be interesting indeed. The rest of the features have remained much the same.
I will be posting a build log here as I get to that point.

Stay Tuned.

Sundance12
 
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« Reply #16 on: September 19, 2018, 04:49:40 PM »

Alright, a modern old-timer! Cheesy

Please correct me if I'm wrong. I thought the AG35 was designed to be sheeted for the first 40% of the chord. Will you be bringing the top sheeting back this far?
The (r) in my search is just an indication that the airfoil was rotated a bit over 1.5° in the wind tunnel to give consistent relevant data against the other airfoils being tested (comparing apples to apples).

All the best,
Konrad
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