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aaindthu 06-11-2019 02:08 PM

Yes, Mr. Jools, you are right. These wings are definitely not strong enough.
So, I am going to glue 3mm thick balsa strip on top of each wing. That should make it strong enough.
Thanks,
Aaindthu

aaindthu 06-11-2019 02:32 PM

1 Attachment(s)

Originally Posted by quorneng (Post 1019166)
Just a crude test but with every thing, including the battery, in place does the wing feel strong enough to allow it to be lifted just by its wing tips? If it can the wing should be adequately strong enough to do a loop without breaking.

So I did the test with two batteries, esc and motor in place. Because the glider is not finished yet and it is likely to end up heavier when finished I used two batteries for this test(one 3s/2200mah, and 3s/1000 mah,) even though I will be using only one for flying.

The wings flex, but not too much. Looks okay to me.

Attachment 187522

I have glued 3 mm thick balsa strips along each wing, but only on top of the wing.
I will do the same on the bottom wing as well. I don't feel any significant increase of weight due to the balsa strips.

aaindthu 06-16-2019 02:58 PM

4 Attachment(s)
Attachment 187529Attachment 187524Attachment 187525


tried to make a clear plastic canopy out of coke bottle, but didn't work.
So, I'm making a foam canopy. I'll put some paper mache over the canopy and around the edges and cover it with black tape, that should look good.:)

I've also elongated the nose to get the CG right.
Almost complete.

quorneng 06-17-2019 01:05 AM

aaindthu
Your wing load test looks quite adequate to me and should allow gentle aerobatics.
There is nothing wrong with "adjusting" the length of the fuselage, within reason, to get a suitable CofG position.

aaindthu 06-23-2019 01:18 PM

1 Attachment(s)
Phew !! So this is what the glider looks like now.
Attachment 187538

I had to shorten the nose back to the original length. The elongated nose messed up the proportions of the glider and it looked very odd, like half glider and half private jet :Q

To bring the CG forward, I reduced the weight in the tail section by narrowing the fuselage and by reducing the distance between the tail-plane and the wings itself.
But still, the CG is somewhere around 40-50 percent of the chord.
I have no choice but to add ballast, just a little bit.
I have also increased the wingspan by 30 centimeters on each side of the wing, just have to glue the balsa strips in the same fashion and
conduct that load test again. :)

Also, the flaperons are no longer full length and it should reduce the roll sensitivity and improve the stall characteristics when deploying flaps.

quorneng 06-24-2019 01:26 AM

aaingthu
That looks quite impressive.
Adding wing span and reducing the fuselage tail length at the same time can lead to handling issues. How significant will rather depend on how much 'reserve' stability there was in the first place.

Careful doing a load test. As the wing root is unchanged the ultimate strength of the wing will be reduced directly in proportion to the increase in span.

Whilst the stall characteristics are important so is how it recovers from a stall, particularly when the plane is close to the ground! ;)
The safest combination is normally outboard ailerons and separate inboard flaps. This layout means the inboard wing is likely to stall first and the ailerons still remain effective.

aaindthu 06-25-2019 02:15 AM

3 Attachment(s)
Yes, the wings flexed a lot.. even the aluminium rods were bending. So, I glued one more aluminium rod in between the already glued 2 rods. Now, there are three aluminium rods.
Attachment 187542 Attachment 187543

Load test :-

Attachment 187544

aaindthu 06-30-2019 08:35 AM

3 Attachment(s)
The glider is ready for maiden flight.
Attachment 187550

Here are the specs:-

Wingspan ------------------------ 2500 mm
A.U.W ----------------------------- 1240 grams (or) 43.74 oz (yes it's heavy)
Wing loading -------------------- 0.255 gram/sq.cm (or) 8.378 oz/sq.ft.

And I got the CG right without any ballast by making a "special" room for the battery which is very forward into the fuse.
Attachment 187551 Attachment 187552

And yes, 1.24 kg is heavy. But, compare it's wing loading with that of a proven design, like the E-flite, Mystique.
Wing loading of Mystique ---> 10.9 oz/sq. ft https://www.horizonhobby.com/mystique-29m-arf-efl4905
So, the wing loading of our glider is less and I could really see the difference when I did the "glide test".
My glider (with a slight camber) glides really nice and slow. I could even use the word "floater" to describe the way it glided.

So, I am all set to make the maiden flight. (next weekend :()

aaindthu 07-08-2019 05:50 AM

I launched it. crashed it. fixed it. launched it again. crashed it again. Now I am fixing it again. LOL.

I gave it too much angle of incidence. So much that I first thought that it was tail heavy. Now I am fixing it again.

I will launch it again. Hopefully this cycle ends there.

Panther 07-09-2019 12:00 AM

You certainly are determined mate. Good luck. Keep the spirits up.

quorneng 07-09-2019 01:54 AM

aaindthu
Are you sure what is happening is just down to the angle of incidence?
Could also be related to the position of the centre of gravity.
Or even some unwanted flexibility some where.

Perhaps you are discovering some of the issues in building your own design.
The important bit is learn what is 'poor' so next time it can be 'better'.

aaindthu 07-09-2019 06:39 PM


Originally Posted by quorneng (Post 1019684)
aaindthu
Are you sure what is happening is just down to the angle of incidence?
Could also be related to the position of the centre of gravity.

Quorneng,

Yes, I am certain.
I did not measure the exact angle of incidence though. But, I could easily see that angle with a simple method, by standing at a distance from the glider with a ruler in hand so that the glider appears smaller in size and within the length of the ruler. I aligned one end of the ruler with the chord line of Horizontal stabilizer and saw the other end of the ruler intersecting the chord line of the wing. The angle was obviously too much.

But I fixed it again, just waiting for the weekend. :)

quorneng 07-10-2019 12:38 PM

aaindthu
You may well be right.

Within certain limits the incidence of the wing to the airflow determines the speed at which the wing generates sufficient lift to carry the weight of the plane.
However the centre of lift generated by the wing changes with its incidence so the position of the CofG has to be changed to maintain a constant flight speed.
So within limits either too much incidence and/or a CofG too far back will generate exactly the same flight path as you describe.

Just be careful you don't remove too much of the incidence between the wing and tail or it will not fly at all!

aaindthu 07-15-2019 05:47 AM

The glider glides very nicely. But the moment I give some throttle, it spins out of the sky and falls. I think there is an issue with thrust line.

But I am done doing repairs on this model. I'd rather build a new one. This time, a high wing, conventional tail (no T-tail), and a one-piece wing that will be attached with screws.
Conventional in-board flaps and outboard ailerons.

I will post again with my new glider.

quorneng 07-15-2019 11:45 AM

1 Attachment(s)
aaindthu
If it becomes uncontrollable as soon as thrust is applied I would suspect wing flexing coupled with motor torque is the problem. To do this just because of a thrust line issue it would have to be a long way out.

A one piece wing sounds a good idea. I would also suggest you keep the wing span to wing chord (its aspect ratio) to about 6:1.
Broader wings may be a bit less efficient but are much less prone to flexing issues and are considerably stronger for their weight.

This may not look much like a high performance glider, high wing and a pusher, but it is nevertheless pretty efficient.
Attachment 187572
Its relatively broad wing is strong and light.
It glides nicely and thermals well too (I don't have access to any slopes!)
It also carries a pretty big battery so can stay up under power for a longer than I ever want to fly!

aaindthu 07-15-2019 12:26 PM

Quorneng,

As you have mentioned, the problem could be motor torque because I remember now, I noticed that the prop spinner was heavy for my 2212 motor. It's a 11 inch prop.
So, I will give this glider one last shot with a smaller prop. I almost hacked this glider to rip off the electronics from it. Thank you for saving this glider.
I am also working on a R/C Trainer 2.0. (with better foam than the previous one and definitely better looking), will post it too, when finished.

Thanks,
Aaindthu

quorneng 07-16-2019 02:05 PM

1 Attachment(s)
aaindthu
You will have to decide if your glider is worth saving.
What is the kV of your 2212 motor?
The lowest kV version I can find is 1000kV and an 11 inch (is it 11x6?) prop is rather too big for even that one . It is likely over loading the motor and of course will also create more torque.
A 10x4.7 is recommended..
The weight of the folding prop is not necessarily a problem if you need the weight up front anyway although unless well balanced its weight can cause motor vibration issues.

If you can manage the reduction in weight I would go for a fixed 10x4.7 just to get it to fly. It you close the throttle before it lands the chances are it wont break.
This one, with a prop adaptor, weighs just 16.3 g (0.6 oz),
Attachment 187573
If there is a question about the plane's stability, launch without power and then add it gradually.seeing what happens before adding any more. If it glides as well as you say it should be able to maintain height on just part throttle.

CHELLIE 07-16-2019 11:35 PM


Originally Posted by aaindthu (Post 1019777)
Quorneng,

As you have mentioned, the problem could be motor torque because I remember now, I noticed that the prop spinner was heavy for my 2212 motor. It's a 11 inch prop.
So, I will give this glider one last shot with a smaller prop. I almost hacked this glider to rip off the electronics from it. Thank you for saving this glider.
I am also working on a R/C Trainer 2.0. (with better foam than the previous one and definitely better looking), will post it too, when finished.

Thanks,
Aaindthu

Hi :) You dont need a 11" prop for a 2 meter glider, thats way way to big, when i was flying 2 meter gliders, I would use a COX 049 engine with a 6x4 prop to get the glider in the air, when the fuel ran out, I would just catch thermals and fly for quite a while, I had the engine on a power pod strapped to the top of the wing, it worked great, that was my Rc Trainer, Also make the rudder wider, gliders need a big rudder as they fly slow, use a 7x6 prop on your glider, that will be more than enough, Take care and have fun, Chellie

since you like to build, here are a few of my Plans
https://www.wattflyer.com/forums/showthread.php?t=55444

aaindthu 07-22-2019 10:11 AM

1 Attachment(s)
My new glider, the basic structure. It's a pretty simple design. This time, I am not going to install the rudder and elevator servos onto the tailplane. I am going to use pushrods and the servos will be installed into the fuselage just behind the wings. So, I don't have to worry about adding any ballast, to the nose. And I made a bigger rudder, as suggested by Chellie.
I am keeping the design as simple as possible so that it flies in the first attempt itself.

Attachment 187577

I tried to cut the wing with 8:1 aspect ratio (2m span and .25m chord) but due to my poorly built foam cutter, 4cm of trailing edge was lost :oops: and finally, the wing has a chord of 21cm. so the aspect ratio is roughly 10:1.
And this is a very high density foam. So I was able to make the tail section of the fuselage more slender without weakening it.

quorneng 07-22-2019 10:36 AM

That looks very "professional".
With no servos or electrics how much does it weigh ?
High density foam may be stiffer/stronger but with the extra weight it will also crash a bit harder too!

.

aaindthu 07-22-2019 07:14 PM


Originally Posted by quorneng (Post 1019866)
With no servos or electrics how much does it weigh ?
.

It weighs 397 grams (wings+fuse+tail fins)


quorneng 07-23-2019 10:42 AM

1 Attachment(s)
aaindthu
That sounds reasonable for a 2.1M span glider.
Will reinforcement to the wing be required?
The success of your design is going to depend on how well you can add strength to the critical areas for the minimum increase in weight.

There are advantages in placing the rudder and elevator servo close to the wing but do consider the weight of long push rods that are stiff enough to move the control surface under load.

A very light alternative is to use pull/pull cables if you can find some suitable fine line.
Like this it is all external so it can be easily adjusted/replaced as required.
Attachment 187584
This set up using mono filament nylon fishing line has been in place untouched for several years and was last flown just a week ago!

aaindthu 07-23-2019 11:24 AM


Originally Posted by quorneng (Post 1019882)
aaindthu
That sounds reasonable for a 2.1M span glider.
Will reinforcement to the wing be required?

Quorneng,

Reinforcement will be required. For minimal strength - I think tape should be enough. But to be able to do loops, I feel that just one strip of balsa sheet should be more than enough. I can always do that load test to make sure the wing is light and strong.

I always had the idea of pull-pull cables.

I like this design very much. But, I noticed that the model in your picture has a stiff tail boom. My glider is foam, so it's not stiff. When the glider lands, for instance, the tail section will shake/vibrate a bit upon impact. I am concerned that this shaking might disturb the taut cables and could possibly cut them too?

Please do tell us what you think. I really want to use this technique.

Aaindthu

quorneng 07-23-2019 04:12 PM

aaindthu
The tail, and the rest of the plane!, is indeed foam - actually Depron.
It has no under carriage so is always belly landed.
Note the tail plane is fixed to the top of the fuselage so the lower "pull" cable does not touch the ground.
Never had a cable catch on anything but even if it did being external it would not be difficult to replace.
It uses mono filament nylon line with a 10 lb breaking strain which is over twice what that particular servo can deliver.
The significant stretch in the nylon line is actually used to 'tension' the cables slightly so there is no free slop between the servo and the elevator.
As long as the nylon line is not stretched too far it behaves like a true spring and does not loose the tension.over time.

For light weight foam planes I prefer to place the servo close to its control surface but where the servo has to be far away my next preference is pull/pull.
A snake is only used where it is impossible to place the servo in a direct line with its control surface..

aaindthu 07-23-2019 07:36 PM


Originally Posted by quorneng (Post 1019887)
A snake is only used where it is impossible to place the servo in a direct line with its control surface..

Quorneng,

​​​​​I am sorry but do you mean to say that the servo must be in a direct line with its control surface when using the pull pull cable? Because I was planning to run the cables through a small plastic tube buried into the foam.

Maybe I did not mention my concern clearly before. My concern was whether the fuselage has to be stronger than usual, especially between the servo and the control surface because the tension in the cables will exist as long as the fuselage is strong enough to resist the pulling force of the cables.

I am really considering to use this technique because I already have a clear nylon fishing line. But I am just worried that the fuselage will have to bear the extra forces from the cables.

​​​​​​Please advise. And thank you so much. If this technique works out, I will probably build every plane with pull pull cable.:rolleyes:
aaindthu


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