# Helicopter Equations?

#### Cog

Hey,

Recently I have decided to attempt to create a helicopter on the cheap, just to see if I can make one and if it can fly "well". I have a friend who is going to help me with this, so I'm not alone, even though he's not helping with working out equations/the theory side of it.

So far, the main problem is that I don't know many equations that can help with building a helicopter - I know what I need to work out, just not how.

I've done this mostly in metric, as I find it easier to work with than imperial measurements.

So far I know the Lift Equation (L=1/2*Ad*V^2*Sref*Cl), and so far I have this:

L=1/2*1.2*3.125*9.8*188.4=2884.875 Newtons
2884.875/4.5=641lb

(4.5 Newtons is the amount of force needed to keep a pound hovering constantly)

I'm planning on having the circumfrence of the rotors as 6.2m, and the axle (or shaft, whatever floats your boat) it's attached to as 0.05m in circumfrence, so as I thought that the aircraft velocity was just the rotors for a helicopter (as that's the only thing moving to make it fly), so I added them together and halved it (I didn't multiply it by the time it would travel round, as I am expecting it to travel the whole circumference in one second) for the aircraft velocity - Is this the correct way to do it? I was guessing at this, as I couldn't find anything to help me on Aircraft Velocity.

Also, this is with the angle of attack at 30degrees. I think this should be the max angle it can go up to, as I am thinking of somehow making the angle of attack adjustable.

So I have 641 pounds to work with, if my calculations are correct.

I'm not entirely sure on this... I mean, I need to know the dimensions of the rotors as well, don't I? That should affect flight I would think.

So does anyone have any equations that I need to help work out what I need? I don't know what engine I'm going to be using (I'm expecting around 70-100hp) and also I don't know how much.

So thanks for looking, If I haven't explained anything very well please tell me and I'll try to re-explain ;)

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#### Cyrus

I appreciate your enthusiasm for helicopters, but you have no idea what you're trying to do here. It just isn't going to work, sorry. You *Could* try building an airplane. That might work, and will probably kill you (that's not a joke). But a helicopter is wasting your time.

I would recommend you some books, but you wouldn't be able to go past the first chapter due to your limited knowledge of physics. Essentially, all your calculations above are wrong - very wrong.

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#### Cog

OK, well thanks for pointing out that my equation's are wrong, but where am I wrong and how? I mean, it's all very well and good saying I'm wrong, but I'd appreciate some help.

And I know it would be easier to make an airplane, but I don't have anywhere nearby large enough to take off/land with it, whereas a helicopter can move straight up.

Also, I like a challenge - Yeah, sure, making anything that will fly is a challenge, but it's not like I can't look up things I don't know when I'm researching the information.

And anyway, if Igor Sikorsky said "Hey, I wont try and improve those previous attempts at flight with large spinning rotors, I'll just make an airplane" That wouldn't have gotten anyone anywhere.

#### Cyrus

OK, well thanks for pointing out that my equation's are wrong, but where am I wrong and how? I mean, it's all very well and good saying I'm wrong, but I'd appreciate some help.

And I know it would be easier to make an airplane, but I don't have anywhere nearby large enough to take off/land with it, whereas a helicopter can move straight up.

Also, I like a challenge - Yeah, sure, making anything that will fly is a challenge, but it's not like I can't look up things I don't know when I'm researching the information.

And anyway, if Igor Sikorsky said "Hey, I wont try and improve those previous attempts at flight with large spinning rotors, I'll just make an airplane" That wouldn't have gotten anyone anywhere.
Im not going to teach you helicopter aerodynamics, but you can try here:

I'm not going to explain these equations though, nor do I expect you to be able to follow them.

You should read the review on amazon.com for Wayne Johnsons book by one of the professors here, it will serve you well:

https://www.amazon.com/dp/0486682307/?tag=pfamazon01-20

Looking for information on how to fly a helicopter? Look elsewhere. Trying to design and build your own helicopter? Yeah, right, how about performing a quadruple bypass on your own heart? But if you are an aerospace engineer interested in helicopters, or if you are studying to become one (an engineer, not a helicopter), this is a must-have book.
This *is* an advanced textbook, which will take you from the fundamentals of helicopter aerodynamics, dynamics, and flight dynamics, all the way to the advanced topics. The book came out in 1980, and helicopter engineering has made a lot of progress since then. However, much of what is in the book remains current. The extensive bibliography gives a comprehensive picture of the state of the art until 1980.

Want some bedtime reading? Get Patricia Cornwell. Want to read stories about airplanes and military hi-tech? Read Dale Brown or Tom Clancy. Serious about learning helicopter engineering? Get this book.
I would advise you to build a car or model airplane or model helicopter.

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#### Cog

Ok - Thanks for these links - I've already looked through them and they seem quite helpful :)

#### Mech_Engineer

Gold Member

I would say the general consensus for building a home-made helicopter is:
1. Buy a kit. Building a helicopter from scratch is tough enough for anyone with some real experience and engineering training, let alone a home tinkerer with no education in the subject.
2. Don't expect it to be "cheap." Even the simplest kits can easily surpass \$20k when you take into account thinkgs like engine, transmission, avionics, etc.
3. It's very dangerous and you can easily kill yourself. Don't take anyone else with you if and when you do.

#### FredGarvin

Oh yeah. I remember that thread. Good times. I wonder if "icabuildit" has killed himself yet...

#### Cog

But I'm trying not to build it the "conventional" way - Yeah, I know it would be a good place to start and I should modify it from there, BUT I don't have enough money to buy a kit and then tinker around with it - If my ideas of working the steering and changing rotor angle of attack etc. work, then I could easily build it without (m)any electrical components. Yes, that just increases the danger, but it wont be flying high, as obviously the higher it will be going the more dangerous it will be.

And also, as you say, helicopters aren't cheap - But this is only going to be a small, 1 man helicopter, that wont have many extras. Sure, it will be dangerous, but everything is dangerous in one way or another (I mean, pencils seem the perfect size to stick up your nostril and get lodged in your brain).

#### Danger

Gold Member
Cog, you are way over your head. I'm going to go out on a limb of hubris here and say that I'm pretty damned good at designing and building things. I'm also pretty damned good at flying things. I would not go up in a chopper that I built myself.
I'd trust my life, in a back alley, to a sub-machine gun that I built from my wife's muffin pan and a couple of mousetraps, but helicopters are in league all of their own.

Oh yeah. I remember that thread. Good times. I wonder if "icabuildit" has killed himself yet...
Well, we haven't heard from him recently...

#### mgb_phys

Homework Helper
in a back alley, to a sub-machine gun that I built from my wife's muffin pan and a couple of mousetraps,
You know a computer at the NSA just went

#### Cyrus

But I'm trying not to build it the "conventional" way - Yeah, I know it would be a good place to start and I should modify it from there, BUT I don't have enough money to buy a kit and then tinker around with it - If my ideas of working the steering and changing rotor angle of attack etc. work, then I could easily build it without (m)any electrical components. Yes, that just increases the danger, but it wont be flying high, as obviously the higher it will be going the more dangerous it will be.

And also, as you say, helicopters aren't cheap - But this is only going to be a small, 1 man helicopter, that wont have many extras. Sure, it will be dangerous, but everything is dangerous in one way or another (I mean, pencils seem the perfect size to stick up your nostril and get lodged in your brain).
I'm going to seriously ask that you stop such nonsensical posts. I'm not even going to entertain this stuff at this point -its absurd. Please stop, or im going to have this entire thread delted or locked.

#### xxChrisxx

I think this is a case of: If you have to ask, you probably shouldn't be doing it.

You clearly dont have to knowledge or experience to even remotely attempt to build one. My suggestion would be to build several models first, if you can build a recent working model (like an RC helecopter) then thats a start. RC and real life are two worlds apart though.

#### rbeale98

But I'm trying not to build it the "conventional" way - Yeah, I know it would be a good place to start and I should modify it from there, BUT I don't have enough money to buy a kit and then tinker around with it - If my ideas of working the steering and changing rotor angle of attack etc. work, then I could easily build it...

Do you even understand what the "conventional" way is? Do you understand how "conventional" helicopters change pitch? do you understand how they steer? if you understood these things you might begin to realize the complexity of this problem.

#### Danger

Gold Member
You know a computer at the NSA just went
I love messing with those Yankee ***holes. They have no authority over me.

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#### russ_watters

Mentor
Good advice given. No point in continuing.

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