RC DeltaGliderIV project

RisingFury

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Finally held together by glue and not string or tape! I only have to sand 4 pieces and glue them on and plywood skeleton will be finished. The thing is like a tank.

Also, turns out that the old spring scale I've been using is giving me somewhat false weight at low numbers... so I weighed the scale down and weighed the plane again and it is right now at 470g. That means when the body is done, it will be around 700g. Still 100g more then desired, but more then 100g less then what I thought it would be.

On Monday I'm starting work on the wings. The airfoil I'm using isn't exactly usual. It's a little bit nose heavy - which I want, because most of the weight will be in the back and I don't wanna stall out when landing.

I've been able to estimate the wing area at 39 dm^2 and the frontal surface area at around 8 dm^2. I'm guessing the drag coefficient to be around 0.15. Don't know what the lift and drag with respect to AOA is, so I can't do any detailed calculations, but I do think that the plane will handle very well at low speeds - at least as good as my trainer.

More pics next week :)
 

Arrowstar

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Looks good! I'm curious to know how you estimated the drag coefficient, since I'm in the high powered rocketry game and that's always the big question.
 

RisingFury

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It's just a guess..........

An airfoil has a drag coefficient around 0.1. There are two vertical stabilizers and not exactly an aerodynamically perfect body, which push the coefficient higher. The propeller is in the back, so the turbulent air won't drag all over the plane, which helps to keep the drag down.

For a rocket, you could look at a drag coefficient of a shell or a bullet and add a little bit to it to account for stabilizers.
 

Arrowstar

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Drag coefficients for rockets I typically construct are usually in the 0.3 range, though of course that's a flight average I basically back out mathematically. Still, sounds good, best of luck with the project!
 

RisingFury

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Thanks and according to Wiki, a bullet at subsonic speeds has a coefficient around 0.3, so that's a fair guess for a rocket :)
 

RisingFury

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Well, she's getting there:

DSC06208.JPG

DSC06209.JPG



The basic frame of the right wing is finished, but it still needs some support structure so it doesn't break off.

I built my previous foam by cutting styrofoam and sandwiching it between wood... I thought this time I would do "classic build" by cutting out airfoils and gluing them together... I think I gained nothing. If anything, I lost some structural integrity.

At least the weight of the wings isn't in excess... like the body. I've been getting two readings when weighing the body frame... one around 600 g and one around 400 g. I thought the spring is bad, so I weighed down the scale to see if it'll make a difference... it did... but yesterday I realized that I could figure out if the scale was correct, but putting 1 kg pack of sugar on it. Turns out that the scale is quite correct... and the weight of the body when fully built will be around 1 kg, which is around 400 g more then I had hoped for.

I can probably lose like 50 - 100 g on the body and I'm hoping that I can lose at least 50 g per wing. That would bring the total weight to right around 2.5 kg... which is exactly as much thrust as I expect...

I did find out the reason why my early estimates proved to be wrong...
I ordered 4 mm thick wood. I got sent 5 mm thick. So instead of around 900 g of frame weight, the weight is now 1100 g. Also, because I did not get the 2 mm balsa that I ordered, but got 1.5 mm, I had to make some changes to the frame on the fly to make sure the 1.5 mm balsa wouldn't break... that added at least 200 g to the plane.

We'll see what the end weight will be. If I blow the weight budget, I will put steerable landing gear on the plane.

Also........ all RC planes eventually crash and break to the point where you can't fix them. At that time, I will build a new version of the DeltaGlider, making it look far more like the real one (not rounding up the vertex locations from 1.4 to 1.5 and so on) and also using more DG like wings - thick inside, thin outside. I will also take into account the lessons learned from this build.
 

jinglesassy

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nice and video tape the first flight of it? that would be cool and dont crash it get atleast 10 flights out of it!(thats more then i can get out of a store bought plane)
 

dansteph

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I'm amazed by your project, I fly myself RC and have constructed somes, I would love to see a 'real' DGIV flying :)

With LIPO and brushless you can make almost anything fly so I don't think such model would cause any problem. (you only have to be carrefull about CG)

As said don't forget to make some videos.

WOOT !!!

Dan
 

RisingFury

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I'm amazed by your project, I fly myself RC and have constructed somes, I would love to see a 'real' DGIV flying :)

With LIPO and brushless you can make almost anything fly so I don't think such model would cause any problem. (you only have to be carrefull about CG)

As said don't forget to make some videos.

WOOT !!!

Dan


Thank you!

Well, the thing will have plenty of thrust and lift. I've used an airfoil that acts nose heavy (you know what they say - nose heavy plane flies poorly, tail heavy flies once) and I'll try to move some electronics into the nose.

I'm gonna use a 3S, 2600 mAh, 25 C LiPo, with a 1100 kV brushless with a 13x6 prop. I'll try to make the plane light enough to fly vertically. If the thrust comes up short, I can still try with a 14x6 prop.



nice and video tape the first flight of it? that would be cool and dont crash it get atleast 10 flights out of it!(thats more then i can get out of a store bought plane)

Thanks! I will video it and post to YouTube. Link will be posted either here or in the other RC thread I started.

Everyone crashes... it's part of the hobby. Though I think that if you build your plane instead of buying it, you'll have far more respect for it and will fly it more carefuly.

I've had over 120 hours in the simularor so far and I'm able to fly planes without crashing them due to error... and I'm able to pull tricks off without crashing them. But when flying for real, I fly really high and don't go for tricks. Granted, my 15 minutes of flight time for real so far has been somewhat above the average starter level... but I have crashed due to having inverted ailerons once.
 

RisingFury

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Alright! The wings are finally glued onto the body and I must say, she looks good!

DSC06211.JPG


And to give you a sense of scale of the size of this thing (and a sense of one very happy me):

DSC06213.JPG



Ok, so that was the good news. Here comes the bad:

It's *way* too heavy. I think I blew the weight budget on the wings as well, so now the weight will definitely exceed the thrust provided by the motor....... so, I'm going for a bigger one!

Instead of being powered by a 1100kV motor at 11.1V, spinning a 13x6 inch prop, I'm now gonna put on a 500 kV motor at 14.8 V, spinning a 17x12 propeller! The thrust will increase from 2.5 kg to 4 kg :cheers:

Now... with the new thrust, I can afford to put some more stuff on the thing, like a landing gear with a front gear being steerable and LED lights on the wings and body for some added coolness. I'm now estimating the end weight to be around 3 kg. That will make the wing loading at around 75 g/dm^2, which is... not bad. My trainer's loading is 60 g/dm^2 and an Extra 300 does around 120 g/dm^2... so no worries there.

The new motor also means that the DG will shoot up into the sky as if it really was rocket powered.

Also, the new motor (ironically) runs on a lower current then the previous one. The peak is at around 47 A, compared to 54 A and the current load once in flight will also be around 35 A and not 40 A... so the 3300 mAh battery I'm putting on will last LONGER then it would on the previous motor. Also, the cost of the new batteries and motor aren't *that* much higher then of the previous stuff. Only a couple of bucks per piece... so for the same price, I can get a bigger motor AND more flight time. For the 300€ I have allocated to the electronics, I will be able to get the motor, the LiPo charger, 3 60 Ncm torque servos and 4 4S 3300 mAh 20C batteries, which will provide at least 20 minutes of flight time.

The speed of the DG will now also increase, compared to the old motor, as will the climb rate. I now have no doubt that I will be able to take off vertically.

Also, I was a bit worried about the structure of the wings... if they would be able to survive a high G maneuver, so I strengthened them a little bit. I now feel more then confident that they will.

The plywood structure is now done. Now I need to start putting on the balsa skin and finish up the leading and trailing edges of the wings, do the vertical stabilizers on wing tips, make the elevons and rudders, run the wires for the LED lights,... and once the wood is done, I have to put the foil over the wood and make it look like a real DG. After that, I need to mount the electronics and get it flying! :)
I'm hoping the first flight will be at the end of August or around that time.


So............... some good news.

I'll be away for the weekend so I won't be able to work on her. Also I need to slow down a bit and think about how to wire a couple of things... like control wires for the elevons and rudders and so on... don't wanna put the skin on before I wire it up cos I need the access.
 

spcefrk

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It's looking really good!

If you don't mind I'd like to pass on a few tips: There's really only a few places that need to be structurally beefed up on the fuselage: the gear mounting, the wing carrythrough, and the motor mount. Everything else is carrying air loads which balsa stick and some 1/32 ply skin can handle

I looks to me like you've seriously overbuilt the fuselage (it looks like a tank!) and seriously underbuilt the wings. The wings will need to carry the entire weight of the aircraft, so I think having such a beefy fuselage is going to hurt you even more in the wings. (The spars just look scrawny to have to carry that fuselage packed in with a LiPo and a motor.

Balsa and 1/32 ply can make a really amazingly stiff structure and if designed right, with plenty of strength -- on par with composites at this scale. You've got so much done I think you ought to go ahead and give it this one a shot -- I'm really excited (1) to hear someone finally was going to try this and (2) that you've made such a great representation of the DG-IV! I can't wait to see the first flight.

If you do decide to make a second one, I think you could cut the weight drastically. Try going with an all balsa structure and only using denser woods to make shared load paths -- one bulkhead to carry the gear and wing carrythrough and a second bulkead to carry the motor mount loads. Covering the thing with 1/32 ply will not only give you a really smooth surface to paint or cover, it will also add a lot more stiffness than balsa skin.

Remember stiffness increases with the cube of the material height. Using a dense wood isn't effectively taking advantage of that. Using balsa and putting your stiffest material furthest from the neutral axis will maximize that.

EDIT:
but I do think that the plane will handle very well at low speeds - at least as good as my trainer.

Don't go expecting a short span delta-wing to fly at all like a trainer. You can tame the thing to make it feel more like a trainer, but it's not going to be fundamentally the same. Some interesting tidbits:

(1) Unless your wing loading is low, you will have to fly faster to maintain level flight than the aircraft with straight wings. At high speeds (more than you'll see) the drag increment is reduced from an aircraft with straight wings so they're beneficial at high mach numbers.

(2) You will not have the wide span and comparatively high AR of a trainer in this configuration. That means that you may have more induced drag and you will not have the natural roll damping of your trainer for two reasons -- First, the loss of span means the loss of wing area to resist roll. Second, you are flying a low wing. A high wing will give you some inherent dihedral effect because the CG is below the wing. The higher above the wing the CG is the less roll-stable you become. So, when you go to do mixing, be prepared to set the aileron travel pretty low unless you're feeling aerobatic.
 

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According to the comparison of you and the rc DG, it might be 3 ft (at the bottom of the wing and 3 ft (at the middle)
 

RisingFury

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Thanks for the advice! :)

Yea, the original plan was to use 4 mm plywood and 2 mm balsa, but I got sent 5 mm plywood and 1.5 mm balsa, so I had to improvise on the fly. For one, the extra thickness of the plywood added some weight and the weakness of the balsa meant I needed to add extra plywood supports where I did not intend to...

The second version will use 3 mm plywood for the supports and 3 mm balsa for the skin. Surprisingly, even 2 mm balsa is quite stiff along it's length and won't bend much. I've crashed my trainer twice now, which I expected to be a broken body, but surprisingly, it didn't even crack.

The wings aren't done yet. They're missing the front edge, which will be 2 cm thick balsa and a couple of supports on the body, as well as 2 cm thick balsa on the back. I estimated that each wing in a high-G turn would have to hold up around 10 kg, so I tested them. They do bend a bit at high loads, but I haven't noticed any damage. The outer part would have to withstand around 3 kg of force and even though it doesn't bend much, I've decided to strengthen it the same way I did the first 3 ribs. That will prevent any bending.

Oh and about handing at low speed, sorry, I expressed myself poorly...
What I meant was that I'm not expecting it to be stall prone. Granted, wing loading is larger then on my trainer and I'm expecting a lower lift coefficient then on the trainer, but it's higher mass means that the deceleration will be slower. Also, delta wings create a nice vortex above the wing at high speeds, which kinda works like a KF airfoil and prevents stall.

All very true about the induced drag though and that's what I'm worried about most - especially the last moments before gear touchdown, when the plane has to pitch up.


And yes, it's 1 m wing span and 1 m in length.
 

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This is really AWESOME, can`t wait to see it flying.

My recommendation is for first test flights find some large field with long thick grass or small brush to reduce chances of fatal damage in case of crash.
And be careful with reentries;)
 

RisingFury

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Hahaha! Yea, the dreaded reentries! :lol:

First off will be some taxiing so I can straighten out the gears - make the plane taxi in a straight line.

The first flight will be tricky. If the plane survives the first flight, there's a high chance that it will fly well. I'm most worried about the landings because at 3 kg, the thing won't exactly stop. I'm expecting a couple of aborted landings before I get it right.

After that, I need to get confident at dead-stick landings - LiPo batteries die if they get below a certain voltage... I mean die... no charging will revive them, which means the electronics in the speed control will cut off the power when the voltage gets critical. That will preserve the battery, but it will give me only one shot at landing.

So far I've managed one dead-strick landing with my trainer, when I run out of fuel. I was way high and quite close in, but far enough that I didn't dare circle around... so I went into a nosedive and then leveled off around 10 m high, dropping down slowly. The plane flew towards me and my friends and over us. It must have had around 70 km/h when it passed us. It was really exciting when we heard the sound it created when it passed (the best "wooooshhh" I've ever heard). It landed some 100 - 150 m downrange...

Anyways... after I get confident that I can land the thing at any time, I'll start doing some tricks. Rolls and loops will come first, knife-edge will test the rudders and so on...
I'm most worried about diving and pulling up. That's where the load of the wings will be the highest, because of highest speed and having to fight weight as well as centrifugal force. If the wings break, that's when it'll happen.

You mean 1 yard, 3 ft = 1 yard 1 meter = 3.2 ft I said 3 ft not 3.2 ft (maybe you don;t understand US units because you are not in USA)

No, I mean the wing span is 98 cm and length is as well... and when the stabilizers come on the tips, the width will be right around 1m.

The length will be just over that, depending on how long big I decide to make the nose cone.
 

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Yea, we all want to it flying :)
 

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So far I've managed one dead-strick landing with my trainer, when I run out of fuel. I was way high and quite close in, but far enough that I didn't dare circle around... so I went into a nosedive and then leveled off around 10 m high, dropping down slowly. The plane flew towards me and my friends and over us. It must have had around 70 km/h when it passed us. It was really exciting when we heard the sound it created when it passed (the best "wooooshhh" I've ever heard). It landed some 100 - 150 m downrange...

Should practice spot landings. Its one of the things that makes a better pilot. Just bring the throttle to idle at a random time during a flight and try to touch down right in front of you (passing left to right or vice versa of course). After some practice you'll be able to bring the plane down in front of you no matter where the engine quits.
 

RisingFury

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Should practice spot landings. Its one of the things that makes a better pilot. Just bring the throttle to idle at a random time during a flight and try to touch down right in front of you (passing left to right or vice versa of course). After some practice you'll be able to bring the plane down in front of you no matter where the engine quits.


I did a lot of that in the sim... but once it comes to the real thing, I'm not as confident anymore. That is something I must work on as well...
 
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