some calculations...please help

[uonuav]

I am trying to convert a model plane into a UAV.
However, I find it difficult to select an engine and fuel tank, as I am quite new to this field of interest.

I have asked OS engine for load characteristics information but they have none. Then how do I choose my prop accurately? As I know the engine rpm differs with load (i.e. size of prop etc). Then I can't calculate how much fuel the plane uses, can I?

Any suggestions?
Thanks in advance. :)

[indoruwet]

Need to know which engine and about how much your plane will weigh.

[Lightnin]

Find the following:

Total wing area

Weight of the airframe including any equipment it will carry.

What type of airfoil is it? symetrical, semi-symectrical, flat bottom etc.

What is the sweep of the wings

Then come back and talk to us

also

plan on putting whatever tank you will use as close to the CG as possible.

is it a pusher or a tractor configuration?

[happypappy]

Somehow this question raises the hair on my back.............

[AndyOne]

Somehow this question raises the hair on my back.............

Especially from someone with a post count of 1.

Andy.

[Accu157]

Maybe JBourke still has an IP adress?

Post count of one, yeah, that will stir up concern. Let us make something clear, this is a model aircraft forum, not a UAV forum. There is a UAV section in here, however the people in there are very experienced, and very open about the reasoning. Once a model is self-guided, it's no longer a model.

[Nicetie]

Funny.....no location information for uonuav.

Ken

[Lightnin]

Somehow this question raises the hair on my back.............

Good thing you are paying attention I was asleep at the wheel.

[Crusty]

strange question, they publish prop sizes...no reason to work it out yourself

[uonuav]

Thanks guys. I only wanted to know if it is right that I need the load characteristics of the engine I were to change the prop size (which are not in the manual).

I doing have been doing research on this before asking here. I was on a site giving apparently 'rpm and prop sizes' database. However, the site does not work properly. Anyway, I think I am in a wrong place as newbies do not seem to be welcomed here.

[uonuav]

strange question, they publish prop sizes...no reason to work it out yourself


The reason is, why they publish such sizes?

[uonuav]

Find the following:

Total wing area

Weight of the airframe including any equipment it will carry.

What type of airfoil is it? symetrical, semi-symectrical, flat bottom etc.

What is the sweep of the wings

Then come back and talk to us

also

plan on putting whatever tank you will use as close to the CG as possible.

is it a pusher or a tractor configuration?



Haha! Thank you so much!
I think I put my question incorrectly! Basically I wanna know if I don't know how rpm varies with prop sizes, then would I know the accurate thrust?
I realise I need to do those calculations u listed. Anyway, it was great, thank you very much. ;)

[indoruwet]

Anyway, I think I am in a wrong place as newbies do not seem to be welcomed here.
That is entirely NOT true. If there is one site where "newbies" (your word), are helped out always, then it is this Forum here, unlike some other forums around.

Your initial question was very vague, to say the least, hence all the questions posed.

I find it difficult to select an engine and fuel tank
How would we know what to tell you when we have absolutely no idea what the size/weight of your plane is/will be ?

If you need any more help, pose your question with a lot more information, and we WILL help you.

Read this post to enlighten yourself
http://www.rcgroups.com/forums/showpost.php?p=6290987&postcount=1

If you really think that we are NOT willing to help you, :eek:
then show us how you came in, :confused:
and we will help you out :D

[uonuav]

Thanks indoruwet,

I sincerely apologise for the way I came into this place. I think I was too new on this topic and I don't even know what are to be asked. I am still doing research on more and more of planes, aerodynamics etc... and at the same time, I am trying to read more in this forum and hope I can learn more. The way I came in was not right and I will try my best to fit into this place. :)

I am a Uni student in the UK, developing a model plane into an UAV. The developemnt has only been started 2 weeks ago which it means that I will still be working on model planes most of the time in the coming weeks. But before all that, I need to buy a model plane and again, before buying anything I need to know what to buy.

My main question should have been: What sequence of approach should I go for when I am selecting the engine and propeller?
My thought was to estimate the followings steps by steps:
consider a plane model,
use its dimensions and weight of planes,
shape, duration etc...
find a suggested size engine,
find suitable props,
determine a suitable fuel tank to ahcieve the duration required,
calculate and estimate range.
repeat until required range meet specifications

As I don't know the engine rpm vs load characteristics, would I be able to find the range? I am not sure if I am being too idiotic on this...I'm just hoping to ensure the right way to solve the problem.

Thanks in advance.

S K Wong

[slipstick]

For almost all of us it's a hobby. We don't calculate things to death, we go flying ;). You're asking for information that simply doesn't exist in any codified form. Your best approach is :

1 Decide on a model
2 Read instructions with model to decide a reasonable engine size. All models have recommended engine sizes and you certainly don't know enough to ignore these recommendations.
3. Test model amd engine with various props to see which works best (there will be a limited range of props recommended)

NOW you can measure how long model flies on a known amount of fuel (or even how long motor runs on a test bed). You can even test it at different throttle/power settings. You will now have more information about fuel consumption rates than anyone else has ever worried about, even the engine manufacturers.

Of course it still tells you almost nothing about actual range unless you can guarantee there will never be any wind and that atmospheric conditions (temperature, air density etc) will always be the same as your test conditions :(.

But you simply have to start with some idea of what type of aircraft, payload, speed, range etc. you're going for. E.g. if it's very small you'll be better off with electric power, if it's very large you probably want a gas/petrol engine not standard model 2-stroke.

Steve

[uonuav]

Thank you Slipstick. I total understand what you say. I understand taht, as a hobby, you wouldn't care about the maths about the planes. (that's what I would be anyway) However, as I am a student and also, I have limited budget for my project, I need to know those stuff before I buy. :(

Anyway, thank you very much and I hope I can get a model plane asap. :)

[indoruwet]

Your background does not say anything about your "previous experience" with Remote Controlled Aircraft.

My suggestion first, is to contact some local RC pilots in your neighbourhood. Talk to them about what you like to do and achieve.
From there, you can then decide what kind of a plane you would like to built or have built.
You need to take into account the "space" you need, to install/mount your instrumentation. Some planes have not much room to work with.
Even though your budget is limited, the word limited is relative. Consider the fact also that, the bigger the plane is, the easier it will be to fly her, and the more stable she will fly. Do not look for a "high performance" plane, but look for one that will have an extremely low wing loading, including your instrumentation, so do some comparisons between one model and another. From there, you can then decide what size engine you might need. Once you have that, most of us here have some experience what the performance is of that particular engine at the situation you have.
Then learn to fly her and become proficient in doing so. This may take some time, which in your case may not be in abundance. You could get some experienced pilot to help you in doing the checking/test flight, etc. Then have him help, in setting up the parameters to get the instrumentation you need in correct order.
Hmmm.... I could go on and on, but let's start here.

Do not give up.

[uonuav]

Thanks again!
I am gonna find a local club which I hope I can gain more knowledge on flying.
:)

[Matthew Allen]

Try here:

http://www.bmfa.org/clubs/clist.php

Matthew

[pe reivers]

S K Wong,
As a scholar, you are allowed at least one mistake :) . It is true that a thorough analysis of the application window comes first, before even considering an engine to fill in the power requirements of your contraption. If you have arrived at that stage, find the props the engine of your choice is willing to spin, and at what rpm. There is much information in these fora. Having arrived there, use this calculator I constructed to evaluate thrust-prop-power-speed combinations. http://www.mvvs.nl/prop-power-calculator.xls
It will not provide ready to run engineering charts, but it is nice to play around with parameters, and will give you results very close to real world data.

[uonuav]

Try here:

http://www.bmfa.org/clubs/clist.php

Matthew


Thank you! I actually went on this site before and will get in contact with them soon!

:)

[uonuav]

S K Wong,
As a scholar, you are allowed at least one mistake :) . It is true that a thorough analysis of the application window comes first, before even considering an engine to fill in the power requirements of your contraption. If you have arrived at that stage, find the props the engine of your choice is willing to spin, and at what rpm. There is much information in these fora. Having arrived there, use this calculator I constructed to evaluate thrust-prop-power-speed combinations. http://www.mvvs.nl/prop-power-calculator.xls
It will not provide ready to run engineering charts, but it is nice to play around with parameters, and will give you results very close to real world data.


This is some great stuff u created! Thank you very much!
It's nice to see so many helping hands here!
I will try my best to do my development and will post what I end up later :D

[indoruwet]

I will try my best to do my development and will post what I end up later :D
Please do so, since it is always fun to see how things are done by other people.
If you make a build thread, it even becomes more fun, since most of us are very interested in the progress of a "New Build Project". So please post pics also.
When it comes to engines, Pe Reivers, who is just across the channel from you, will probably be able to really help you there.

[ivanc]

From our experience with different models (size, weight, design) we already know what engine and prop will fly with authority specific planes. Using analogy if your UAV matches some of the RC planes we have flown, we can recommend you an engine, prop and tank size for particular flight duration. We do not use calculations to figure these components out. It's all a "guestimate" based on our experience and it is quite accurate.

As indoruwet once said, if a plane looks right to us, it will fly fine - we are so used to this stuff that just looking at and picking up the plane we can figure it out.

Ivan

[Lightnin]

Who is "we" some of us started electric and do use calculations to figure out what to put in an airplane.

[uonuav]

Thanks Ivan, I am trying to get in touch with an instructor and I hope I can get him to teach me more stuff :)

[ivanc]

Who is "we" some of us started electric and do use calculations to figure out what to put in an airplane.Myself and at least indoruwet. I'd add Sparky Paul and Steve (slipstick) although I'm not absolutely sure ;).

I was referring to glow, but it would apply to electrics too - although I do not have a lot of experience with electrics, I have two really good electric setups which I created using analogy "guestimate" - I did not use any calculations in regards to weight and airframe size. I used some purely electrical calculations to figure out the current at particular power drawn from the battery pack in order to match the motor, ESC and battery. Well, these electrics ended somewhat overpowered :o, but fly great with proper throttle management :rolleyes:.

Ivan

[Sparky Paul]

Electrics are totally baffling! :)
With any 10 motors, 10 ESCs, 10 props, and 10 batteries, there's 10,000 combinations possible. Sifting thru the goods, bads and impossibles takes more time than reading about what other guys use successfully! :D
Worked with glow, and works with electrics... :p

[indoruwet]

Who is "we" some of us started electric and do use calculations to figure out what to put in an airplane.
Not the right place to ask, but here goes anyway.
Short answer please....., If long, PM me.
What kind of calculations does one need to determine what power set-up to use in a specific airplane?

As Ivanc mentioned, I build a plane, look at it and then murmur "hmm... 60 size would be nice, maybe ?" I really do not go through all the required calculations I used to do when I worked in the Aerospace sector. I think, that I usually overpower .. :rolleyes:
Then I look at the range of props, the manufacturer suggests, and do trial and error flying. Usually the same prop ends up to be my favored for a specific size engine.
I do however take into account the total expected weight of the plane and then decide if I have a correct wing loading, But then, what is correct wing loading again ?
If I want speed, I use a certain wing foil that is good for speed, or if I want just something that can do lazy eights, I use another proven wing foil.
So yes, I maybe do make some "calculations", but most of them are just "feel" or "experience" ?

[pe reivers]

This is some great stuff u created! Thank you very much!
It's nice to see so many helping hands here!
I will try my best to do my development and will post what I end up later :D
Thanks,
You might also try to get electro-calc from www.slkelectronics.com/ecalc . This is a nice program where you can calculate the relationship between plane drag, weight and required power for a specific climb angle. It is only for model flight, but data can be extended, and a power/drag/weight/climb angle ratio is quite universal, so is easy to scale up or down.
I even programmed a glow model engine in it.

[Lightnin]

Not the right place to ask, but here goes anyway.
Short answer please....., If long, PM me.
What kind of calculations does one need to determine what power set-up to use in a specific airplane?

As Ivanc mentioned, I build a plane, look at it and then murmur "hmm... 60 size would be nice, maybe ?" I really do not go through all the required calculations I used to do when I worked in the Aerospace sector. I think, that I usually overpower .. :rolleyes:
Then I look at the range of props, the manufacturer suggests, and do trial and error flying. Usually the same prop ends up to be my favored for a specific size engine.
I do however take into account the total expected weight of the plane and then decide if I have a correct wing loading, But then, what is correct wing loading again ?
If I want speed, I use a certain wing foil that is good for speed, or if I want just something that can do lazy eights, I use another proven wing foil.
So yes, I maybe do make some "calculations", but most of them are just "feel" or "experience" ?


No prob short answer.

As pe reivers already said, although I use moto-calc you put in the basic parameters and it calculates everything for you. Much more efficient in the long run (this is not a jab). Some people like tinkering and some people don't, I don't. GIT-R-DONE AND GO FLY