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Author Topic: UAV help  (Read 3726 times)

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Offline bendex

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Re: UAV help
« Reply #30 on: August 09, 2010, 04:31:11 AM »

and about the air compressed cylinder, do you think that it's a good idea to get it off the ground for a instant?

I'm a noob to robotics, but compressed gas is part of my job, you can get small cylinders from a bicycle shop, they use it for quick puncture repair, normally about 8 bar. It'll give you the thrust you looking for but not the accuracy. In other words it lift your craft, just not in the direction you want it to go.

Keen on building my own UAV in the near future, like to see your working model.

Best of luck

Offline ballbreaker

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Re: UAV help
« Reply #31 on: August 09, 2010, 04:52:35 AM »
you will make it jump because the air will run out but you can point it at the back for a quick take off
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Offline Razor Concepts

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Re: UAV help
« Reply #32 on: August 09, 2010, 06:19:25 AM »
Not particularly good for RC aircraft, the weight of the CO2 cylinders is a lot compared to the amount of thrust, and for the short amount of time it does produce thrust.

However I have seen some JATO type RC airplanes before using model rocket engines, its not very practical but very fun to watch  ;D

Offline Bas_E

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Re: UAV help
« Reply #33 on: August 09, 2010, 03:07:55 PM »
Hello,

English is not my native language, so I hope that I can make myself clear.

When your planning on becoming an aircraft engineer you probably know this.
Its some years ago since I had this in school so correct my when I make a mistake.

How an aircraft flies is easy on paper:
L=1/2ρ*V2*CL*A

That’s all. If you stick to this rule/law your fine and your aircraft will take off.

That means:
lift = half the air density*velocity to the power of 2* lift coefficient*surface size

To get your plane off the ground all these components play there role. Its a bit difficult to alter the density of the air your trying to fly in, so you have the other components left to influence. As you can see speed is a very important factor because its to the power of 2. Not enough speed will cause a low speed stall. But to much speed gets you a high speed stall.

The lift coefficient is a bit of a though one. Its your design that determines it. The profile of your wing. Just check the difference of wing design on a glider compared to an F16. The difference is the speed that it is supposed to fly. (And an F16 can go above the speed of sound, that changes the rule of lift, but that’s an other topic.)

 The surface is how much effective wing you have. To small wings will not work, to big wings will give you extra resistance in the air and a heavier construction. You need more lift than the weight of your plane off course.

The propeller works exactly like a wing. So the rpm of the propeller is important, because it  to to get enough lift/trust to get your plane moving. But to much rpm results in a high speed stall, and your lift/thrust is gone again. So just throw “some rpm” at a propeller and hope it “goes flying magically” is not going to work I am afraid. To much rpm is as bad as to less. High speed stall will take away your lift/trust too. And you have to keep in mind that when you plane is standing still, the airspeed is (how to say this in English) from the side of you propeller. When your plan gains speed the vector changes because you get airspeed from the front. Its something to keep in mind. The risk is loosing trust again because the angle of attack changes. Its like when you take off with your plane and you would directly pull it on his tail it will crash because of this stall.

I have not read the whole threat but my advice would be, get a good design. That profile of the wings is very important. You probably get result by trail and error but that is kind of risky because you have no idea what it does at what speed. So you can end up with a high speed stall just after take off and crash. So when your going for the trail and error approach, don’t expect to take off your first try and more important, make sure you don’t kill people in case you crash!

Same with propellers, to get optimal performance you need the optimal airspeed as its “to the power of 2“ important. And the airspeed get more high to the tips of the propeller. So the lift coefficient changes from the axle to the tip of the propeller.

More weight means you need more lift to get off the ground. During operation you can only change the speed, so it means you need more speed to get of the runway. That means you need more fuel. More fuel == more weight, etc.  that is why those airlines are nagging so much about weight.

Turbine engines is an interesting topic too, but you have to understand propellers very good first. The compressor and turbine are like propellers in theory.

Hope this helps.
« Last Edit: August 09, 2010, 03:23:25 PM by Bas_E »

Offline Razor Concepts

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Re: UAV help
« Reply #34 on: August 09, 2010, 03:40:45 PM »
Of course with todays technology you can mash something together and it will still fly:

 ;D

Offline @EricTopic starter

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Re: UAV help
« Reply #35 on: October 02, 2010, 12:18:17 PM »
all right. thanks for everybody
It helps a lot,
and I still have some questions, like:
I'll buy an RC controller:
     TTX404 - TACJ2404
Includes:
Digital* Trims and Servo Reversing on all Channels
Wireless Trainer System
V-tail and Elevon Mixing
Programmable Fail-Safe
Compact, Lightweight TR624 Receiver
Power LED and Low-Voltage Alarm
Built-In Charge Jack
Adjustable Stick Lengths
4-cell “AA” Battery Holder, Adjustable Neck Strap, On/Off Switch Harness with Charge

all right, i think it's good, for a beginner. but, Can I use lipo batteries in stead of NiCD or NiMH, like in the specifications? or it's gonna make some damage?

 


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