Glider design

[dusty IV]

I'm playing around with the idea of using a Multplex Cularis glider wing,WS of 103" . I have a fiberglass /carbon fus I made several years ago but never used. Both the Cularis and my fus are about 50" long . The Cularis has a center mount wing while my fus has a small pylon for wing mount.

Building a strong 10' wing is a big project and I can buy the Cularis foam wing for about $100. That's tempting. The intent is to have a gas bag type glider which can fly hands off for long periods of time on lazy summer days.

The ratio of the wing area and stab is about 11%. Is that a good number for pitch stability or how high you go? There must be some rough rules of thumb for this. I've made some gliders with the now popular tooth pic size stabs but didn't really like them for my use. Distance between the wing and stab is about 34 " I think. I can move this number around depending on where I mount the stab.

[BMatthews]

If you're after a floater then I'd suggest you're aiming at the wrong wing. From looking up the Cularis it seems to be more solidly built and likely uses an airfoil that wants to fly fairly quickly. It also lacks the polyhedral style wing that you'd want for those "set the Tx down and just watch it fly" style of sessions.

The amount of stabilizer area you need is not cast in concrete. There's a number called the Tail Volume Coefficient that is used to determine where the airplane's neutrail stability point is located. From that you can determine your CG. If the tail is short then 11% will be too small. If it's longer then 11% would be fine. If it is REALLY long then you can get away with an even smaller stabilizer.

But still, if you're after a calm evening floater then from what I see and read you're on the wrong track.

[dusty IV]

If you're after a floater then I'd suggest you're aiming at the wrong wing. From looking up the Cularis it seems to be more solidly built and likely uses an airfoil that wants to fly fairly quickly. It also lacks the polyhedral style wing that you'd want for those "set the Tx down and just watch it fly" style of sessions.

The amount of stabilizer area you need is not cast in concrete. There's a number called the Tail Volume Coefficient that is used to determine where the airplane's neutrail stability point is located. From that you can determine your CG. If the tail is short then 11% will be too small. If it's longer then 11% would be fine. If it is REALLY long then you can get away with an even smaller stabilizer.

But still, if you're after a calm evening floater then from what I see and read you're on the wrong track.

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Good tip.that was what I wanted to know. All I could up with was some comments on a nasty tip stall and keep it flying fast which backs up your comments.

So what's a good airfoil? Seems like I remember an E208 being decent but I will research this.

[Ralph Walton]

couldn't find an E208 but I know E205 was popular in the 1970"s It has an unusual shaped LD curve with a pronounced bump at one point.

Something like a S3010 as used on the very popular great planes Spirit would outperform rings around a 205 except in a very narrow range of conditions.

After the era where gas bags were king Late 70"S?(some say they still are!) top gliding contestants figured
their airfoils had too much lift, and lower camber foils started to gain popularity.

These days camber changing foils seem to be the "thing" to have.The Mg06 springs to mind. Its a relatively thin 7.3% thick foil and peculiarly flaps and ailerons are hinged at 30% of the chord. Its extremely low drag at low Cl but when cambered its got almost as much lift as the old gas bag profiles. A great way to have the best of both worlds!

They now had foils that could thermal reasonably well, but could also penetrate to come home from along way downwind, quicly get out of sink or get to the next thermal quicker.

[dusty IV]

I just plowed through a stack of long forgotten prints of planes I have built. Found a 2M polyhederal Gnome from Midwest. There sure have been a lot of improvements in the past 20- 30 years. Forgot how some of these things looked. Sweptback rudder and stab were popular. Always hated that look and could not see why it was done that way.

It has a very thick airfoil. Clary Y looking. No idea what it is. As I remember is was a good stable flyer

I found a MH 32 that looks like it might be a good choice. Would this work on a polyhedral plane intended to fly slow?

[Shedofdread]

For an unflapped thermal soarer, may I recomend SD7032. You dont need flaps and it's thick enough to be strong without mega tech.

MH32 will soar well but needs flaps (22% chord).

S

[dusty IV]

For an unflapped thermal soarer, may I recomend SD7032. You dont need flaps and it's thick enough to be strong without mega tech.

MH32 will soar well but needs flaps (22% chord).

S


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What are flaps used for other then landing on the MH32? If it's for landing only, can spoilers be used on a polyhederal? If polyhedral is causing problems with flaps or spoilers maybe I should use a flat center section or a simple V. Not married to any particular design layout yet.

In the advanced gliders I see a lot of comments about varying speed as in chasing thermals and getting out of sink. However for this application which is sport only the electric motor can be used for all this and I should not have to worry about wind penetration or sink.

[Shedofdread]

MH32 used to be a very popular F3b section and by varying the camber [with the flaps], the flight speed can be varied. 3 or 4 degrees down flap and it floats, neutral for best glide and say -2 degrees for high speed flight. Really for landing, the flaps should go down and the ailerons up, to give 'crow' braking

From what you say, I presume that rudder / elevator is your prefered method of control? If so, steer clear of sections that are intended for flaps (most modern F3b/j sections) - they won't have a sufficient CLmax at 0flap (ie no flaps, just a plain wing) for the sort of flight you seem to require.

SD7032 floats well and with ballast, will move around (if you have motor - not relevant). Flat centre section and tip dihedral, whilst not the optimum will work and is structurally very efficient for a 3 piece wing. Also with the centre panel being flat, it makes the install for the torque tube to drive letter box 'brakes from one central servo, very simple.

Get some foam cut!

S

[dusty IV]

[QUOTE=Shedofdread]MH32 used to be a very popular F3b section and by varying the camber [with the flaps], the flight speed can be varied. 3 or 4 degrees down flap and it floats, neutral for best glide and say -2 degrees for high speed flight. Really for landing, the flaps should go down and the ailerons up, to give 'crow' braking

From what you say, I presume that rudder / elevator is your prefered method of control? If so, steer clear of sections that are intended for flaps (most modern F3b/j sections) - they won't have a sufficient CLmax at 0flap (ie no flaps, just a plain wing) for the sort of flight you seem to require.

SD7032 floats well and with ballast, will move around (if you have motor - not relevant). Flat centre section and tip dihedral, whilst not the optimum will work and is structurally very efficient for a 3 piece wing. Also with the centre panel being flat, it makes the install for the torque tube to drive letter box 'brakes from one central servo, very simple.

Get some foam

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I pulled up the mh32 vs SD7032 and agree the 7032 is a lot thicker and better suited for my needs. Good call.

I really think a wing this big needs ailerons. Our field is small and landing is tight. How about a flat center section with a flap/brake for landing and ailerons in the tips? Adverse yaw I've found is easily controlled by mixing rudder with the ailerons. Or I could split the flap and use it as flaperons.

[Shedofdread]

I used to have an aileron and flap equipped SD7032 model (still do have it but no gear in anymore) and it worked well. Also it was no lightweight but still floated.

So the design -
Flat centre section, tip dihedral
Flaps on the centre panel, ailerons on the tips
SD7032

Now you need to decide on the planform. Google 'Liftroll' by Jeff Hazel. It's a planform design spreadsheet.

It'll be done by the weekend!

S

[Ralph Walton]

The SD7032 is a hugely lifting foil. Looks kinda draggy

[Shedofdread]

The SD7032 is a hugely lifting foil. Looks kinda draggy

True, no good for F3B but for the purpose intended, it works rather well.

S

[BMatthews]

For calm air gas bag style "hang it up there and watch it meander around" an airfoil with more camber is what you want. But with this goal in mind a very light weight becomes paramount when you're looking for a 4 to 6 oz/sq-ft wing loading (that's what the old classic gasbags used to fly with). And if you really want to get silly you'll be wanting a 3 to 4 oz wing loading.

BUT.... along with this light weight comes a desire to avoid a lot of wing sheeting which means your airfoil has to work more on basics and rather sweeping shape cues rather than a hyper critical trailing edge cusp shape where if you deviate more than a fraction of a % then you don't get the benifits.

Such is the design of the Selig 7032. It won't translate well at all to open framed design that uses turbulator spars to control the shape of the wing. For this you need to switch over to free flight technology and airfoil practices.

Or if you're happy with a medium slow flying model then just plant a basic (but properly shaped) Clark Y airfoil on the drawing board and call it good to go.

If you want to go REALLY slow then dig up some plans for the older built up FF A-2 Nordic glider class of models. Adapt the nose and fuselage to hold your gear and go enjoy seeing your model all but hover up there and ride the lightest of lift whisps.

Or if you don't mind building you could buy one of the JASCO Termic 72's from http://www.tmrcsailplanes.com/SAM-vintage-sailplane-kits.html . This would be a floater with extreme CLASS once finished. Obviously some mods would be needed to adapt it to RC. Just watch the weight buildup. You'll want to keep it to around 20 to 24 oz ready to fly for the ultimate floater experience.

[dusty IV]

Still messing around dreaming. That's as much fun or even more then building to me. Use to get notes sent home to my folks saying "he daydreams to much".

Is there anything better then daydreaming?

So now I've pulled prints on a Playboy cabin. Never built one of these but looks interesting. I'm far from a purist and the original construction needs some help with Warren Trusts and such. Drawn up to 84+" with the original undercambered airfoil or maybe I should use a modern D tube with a modern airfoil.

Lots of thing to dream about.

[Texas Buzzard]

We pick our tools to fit the job.

Pick the type of flying you want to do THEN pick a ship. Not all ships will fill all weather conditions and pilot's preferences.

You don't pick up a pair of pliers to solder two wires together - right?

[Ralph Walton]

We pick our tools to fit the job.

Pick the type of flying you want to do THEN pick a ship. Not all ships will fill all weather conditions and pilot's preferences.

You don't pick up a pair of pliers to solder two wires together - right?

Great advice. I started with the "I want a plane that can do everything " stage, I now design or adapt planes to suit whatever conditions I'm likley to encounter at my chosen flying sites.

Sorts of things to think about would be "whats the landing zone like?" If its tight you may need crow braking. Open fields leave the braking choice open. If its really tight and rocky , maybee epp is the only option.

Whats the typical wind like or what conditions do I want to fly in? generally light and flukey conditions requires a light wing loading.

Do I want scale or do I want performance? There's a bit of leeway here, but the two don't usually go hand in hand.

What size? There's no doubt that when it comes to planes, bigger is better. Bigger has better allround performance and is easier to fly and see, BUT, bigger costs more, takes up more space to store and transport and crashes bigger

You get the general idea :)