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Scratch built 2m RES Glider

Old 11-20-2022, 09:43 PM
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aaindthu
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Default Scratch built 2m RES Glider

Hello!

I have previously tried building an RES glider and had to give up several times because it flew poorly. I learnt a lot from that especially about the weight limits for a 2m glider. Then I built this glider.
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It weighs just 615 grams and has a 2 meter wingspan (78.7 inches). It has c20 micro brushless motor, powered by 3s 1000mah lipo. It flew great and it also had a very low descent rate. I did some flight time with this glider, but still it had the same problem as my previous RES gliders which is, it was sluggish and won't turn spontaneously. After watching some more youtube videos for answers about RES gliders, I am convinced that the length of wing section that has the dihedral in my glider was not sufficient to make an effective turn with the rudder. My previous glider also had same wing dimensions, so everything makes sense now.

Now, I am building another wing for the same glider with dihedral starting from the wing root itself. Both wings will be straight with dihedral of 7 degrees at the centre. The wings are made from 5mm depron sheets. They have semi-symmetrical airfoil. This wing will be held to the fuselage with elastic bands, to keep the weight down.

I have already glued the left wing to the centre "block" of depron that has the dihedral. The wing has 4 ribs on each side, glued with epoxy. I did not make any spars because the upper and lower wings are folded with tape into airfoil shape. This curvature provides necessary strength along the length-wise axis of the wing, so there are no extra spars. This wing is 100 grams heavier than the previous one, but it has thicker airfoil than the previous, so I am not concerned.

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The ultimate goal for me is to build a slow flying thermal glider that can be launched and landed safely from the terrace of my house. Because sometimes I hate to carry my models to a field that's a few kilometers away from my house. I have a somewhat big terrace with minimal trees and the terrace is well above the powerlines. If it flies well, I could enjoy flying from my house terrace.

Last edited by aaindthu; 11-21-2022 at 10:19 AM.
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Old 11-22-2022, 09:55 AM
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This wing ended up weighing 330 grams. I thought of a better way to make the same type of wing. So I made another wing with same dimensions but instead of the block of depron in the middle, I glued spars and ribs in the mid-section. And finally glued the depron sheet onto the spars and ribs covering the top of the wing. I put tape for the leading edges and trailing edges. The wings weigh 305 grams.. almost 30 grams less than the previous one.
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Now to make a base on the fuselage for the wings to be seated.
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Old 11-22-2022, 03:53 PM
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aaindthu
A 2m span lightweight RES glider is bound to be 'sluggish' in roll. The only way to get a positive roll effect is to have considerable dihedral angle. This will reduce the efficiency and thus the sink rate of the wing.
Ailerons provide a positive roll and actually work best with no dihedral at all although that would also remove any sort of roll stability!
Technically for the same deflection the down aileron creates more drag than the up so although the ailerons will make it roll the different drag cause the plane to yaw the opposite way to the intended turn.
In a conventional control layout the rudder is also used to counter the aileron yaw but is not actually used to cause the turn, only to keep the plane flying correctly.
It is possible to virtually eliminate the aileron adverse yaw by arranging that the up aileron travels further than the down so equalising the drag they create. It is called differential ailerons.
Using aileron differential a big wing glider with efficient limited dihedral can fly perfectly well with no rudder at all just a fixed fin. It is called AES control.

If done well an AES glider will glide better and have more control than RES.
A big wing with limited dihedral and no rudder..
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It is both pretty powerful and can fly slowly.
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Old 11-22-2022, 05:05 PM
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Originally Posted by quorneng View Post
aaindthu
A 2m span lightweight RES glider is bound to be 'sluggish' in roll. The only way to get a positive roll effect is to have considerable dihedral angle. This will reduce the efficiency and thus the sink rate of the wing.
Ailerons provide a positive roll and actually work best with no dihedral at all although that would also remove any sort of roll stability!
Technically for the same deflection the down aileron creates more drag than the up so although the ailerons will make it roll the different drag cause the plane to yaw the opposite way to the intended turn.
In a conventional control layout the rudder is also used to counter the aileron yaw but is not actually used to cause the turn, only to keep the plane flying correctly.
It is possible to virtually eliminate the aileron adverse yaw by arranging that the up aileron travels further than the down so equalising the drag they create. It is called differential ailerons.
Using aileron differential a big wing glider with efficient limited dihedral can fly perfectly well with no rudder at all just a fixed fin. It is called AES control.

If done well an AES glider will glide better and have more control than RES.
A big wing with limited dihedral and no rudder..
It is both pretty powerful and can fly slowly.
The model is beautiful. I agree that aileron wings can be more effective than dihedral wing, but I just want to save weight on the two servos that are required. 20 grams plus the necessary cables. And, it also complicates the building of the wing and fuselage joining area due to the aileron cable.
RES is simpler to build and lighter than the AES one. I am also thinking to add FPV equipment to my model at some later point.. so I'm keeping the weight as low as possible without sacrificing strength of the wings.
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Old 11-23-2022, 01:22 AM
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aaindthu
Ailerons heavier?
Remember you are using two servos so they can be smaller and lighter.
The powered glider in the video uses micro 3.7 g servos. In addition the servo cable as fitted to such a servo is 32 swg which is only half the weight per m of that fitted to a normal 9g servo.
Overall any weight penalty can be very small particularly if the cable extensions are done by soldering rather than using plugs and sockets. I do agree the wing construction is a bit more complex however as the structural work to provide ailerons is out towards the wing tip it is nothing that effects the inherent strength of the wing.
It will be most interesting to see how your big RES glider pans out. Do keep posting.

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Old 11-23-2022, 06:26 PM
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Finished with my glider. AUW is 732 grams. Feels light enough. The pictures show the amount of dihedral.
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I am just waiting for the rains to stop. Got two planes waiting for maiden flight .
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Old 11-24-2022, 01:42 AM
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aaindthu
That tail assembly must be pretty heavy to require the motor and battery to be so far forward. Such a layout does not effect the glide performance but it will add to the already significant inertia of the big wings that the rudder has to overcome to initiate a turn.
Until the plane actually starts to yaw it will not bank and then commence a proper turn. Remember the motor torque will tend to make the plane bank to the left so it is likely the rudder will appear more effective to a left turn than a right when under power.
At 732g and with those big wings I am sure it will fly ok but i fear it will still be pretty sluggish to both get in to and out of a turn.
Hope both maidens go well
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Old 11-26-2022, 02:49 PM
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When building, Try to keep the Weight towards the Front, Its best NOT to have the Servos attached at the Rudder and Elevator, That makes a plane tail heavy, then you have to add nose weight. Place the CG at 25% Behind the Leading edge of the main wing, Thats a very good place to start, Build as Light as possible with out sacrificing strength, Its Best to build From Kits at First so you get a good Understanding of building Procedures and Designs, Its ok to make mistakes from time to time, Thats how we all learn, Then Learn from your Mistakes, I have made many many mistakes, but I have learned from them and I try not to make those mistakes again.
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Old 11-26-2022, 03:07 PM
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I have actually removed the two servos from the top of the tail fins. I will update once it's finished.

I was thinking about what Quorneng mentioned about inertia of the tail and I have come up with an amazing analogy.
An airplane or a glider tail is like a wind turbine, the lighter the turbines are, the faster they turn and heavier turbines need lot of airspeed to start turning. In a lot of ways, airplane tail is like a wind turbine trying to turn the airplane around, especially the RES type glider.

So I understand now the importance of removing the weight off of the tail surfaces. Thanks a lot. You guys are great. I will update soon.
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Old 11-26-2022, 03:15 PM
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Give the Rudder Lots of Travel, Gliders need Lots of Rudder Movement and Area because Gliders are so Slow, I Learned how to fly with a 2 meter Glider
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Old 11-26-2022, 03:25 PM
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Originally Posted by CHELLIE View Post
Give the Rudder Lots of Travel, Gliders need Lots of Rudder Movement and Area because Gliders are so Slow, I Learned how to fly with a 2 meter Glider
Understood, thanks for the advice. I will update once I have finished modifying the glider.
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Old 11-26-2022, 03:37 PM
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I Have a Pen Pal In India, and She also Builds Rc Planes and Boats, She is A Real Sweetheart, I Would Love To Travel to India one day, I love the Culture and People There, My Doctor is from India, and my Son had to have surgery on his brain from a Aneurism , his doctor is from India, he had a 2 percent chance of surviving the Operation and he Survived, IMHO Doctors from India are World Class, I also use natural healing herbs and spices from India and China,
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Old 11-26-2022, 03:57 PM
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Originally Posted by CHELLIE View Post
I Have a Pen Pal In India, and She also Builds Rc Planes and Boats, She is A Real Sweetheart, I Would Love To Travel to India one day, I love the Culture and People There, My Doctor is from India, and my Son had to have surgery on his brain from a Aneurism , he had a 2 percent chance of surviving the Operation and he Survived, IMHO Doctors from India are World Class, I also use natural healing herbs and spices from India and China,
I am happy your son survived. I hope he's good now.. I wish him good health and take care.
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Old 11-26-2022, 05:31 PM
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Originally Posted by CHELLIE View Post
When building, Try to keep the Weight towards the Front, Its best NOT to have the Servos attached at the Rudder and Elevator, That makes a plane tail heavy, then you have to add nose weight.
To be exact tail mounted servos do not by themselves make the plane tail heavy provided there are necessary items towards the front that counter their weight.
What tail mounted servos do do is raise the lateral inertia which can be significant in a RES glider.
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Old 11-30-2022, 01:24 PM
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I sent my glider to a weight loss program and now it weighs 682 grams. Joking aside, here's what I did to lose 50 grams. I removed all the cable extensions with sockets and plugs (27 grams), I removed the extra plywood for the motor mount along with nuts and bolts (10 grams), now I am using cable ties to hold the motor. And I removed the two 9 grams servos (26 grams) and installed the 3.7 grams micro servo on the cf tube ahead of the tail plane. I was also able to cut short the nose by 8 cm due to the reduced weight in the tail and overall without affecting the CG. This should reduce the innertia along the lateral plane to some extent... I will do maiden flight some day this week or the next...
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