Android Phone App - Center of Gravity Calculator - RC Groups
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Oct 16, 2010, 04:46 AM
Graham Dyer
pardus's Avatar
Cool

Android Phone App - Center of Gravity Calculator


Here is a free Android Phone CGC (Center of Gravity Calculator) for planes (It can prevent a crash!).

You enter your required CG percentage, measure and enter the tip chord, the root chord and the sweep and it will calculate the position of the center of gravity of an airplane measured back from the leading edge at wing root.

It's free, released as donationware, and is now available on the Android Market.

It's pretty intuitive but instructions are behind the 'Instructions' button

Comments and suggestions welcome!

Please try it out and send it to anyone who might be able to use it! (or point them to this post)

Now available on the Android Market:
QR code or http://www.androidzoom.com/android_a...calc_mctb.html



Thanks

Graham Dyer

Last edited by pardus; Oct 25, 2010 at 05:55 AM.
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Oct 16, 2010, 10:35 AM
Sink stinks
Montag DP's Avatar
Looks pretty cool, but if it doesn't at least consider the tail it's not going to be very useful...
Oct 16, 2010, 01:34 PM
Graham Dyer
pardus's Avatar
A more complicated one taking the tail and other parameters into account is a possibility in the future, but you'll have to pay for that one

This is FREE and does a good job, can't ask for much more - try it out...
Oct 16, 2010, 02:22 PM
Sink stinks
Montag DP's Avatar
So, I see what's going on. You basically have to know where you want the CG already as a % of the MAC, and it tells you where on the wing that point is. In that case you don't need to know anything about the tail.
Oct 16, 2010, 02:42 PM
B for Bruce
BMatthews's Avatar
Sorry but it seems like you're only giving folks half a product here.

To find out where the CG should be they need to run the calculations through one of the more overall calculators that are available online. Those calculators use the same root and tip chord as well as the same sweep info ALONG with the tail area and distance info to come up with the location of the CG. And if they put all this info into the calculator then it would already tell them how far back the CG is from the root's leading edge. So there is no need to duplicate the effort to put it into your phone app.

So the only thing this app is good for is if someone off the top of their head says to themselves "I think I want to put my CG at 30%" and ignore the rest of the steps".

Oh, and there are a few equivalent MAC calculators online that do this for free by the way. As well as a couple of fully comprehensive calculators that you input the entire model dimensions into and it tells you where the neutral point is and you can get a CG location given based on how much stability you want. Again these full blown calculators are free to use.

I'm not trying to demean what you have done or will do to make it better in the future but I think you may be missing the reality by a little. This first effort is a nice beginning but it is merely a stepping stone with questionable use since it doesn't actually calculate a SAFE CG location for the whole model. The complete CG calculator would be truly the way to go. But such calculators are available for free online. So unless this app gives further value added I'm not sure if you'd be succesful in actually selling it. After all determining and setting the CG is more of a job to be done in the shop where internet access, and thus access to the online calculators that are free to use, is only steps away.
Oct 16, 2010, 03:36 PM
Graham Dyer
pardus's Avatar
Valid points...

No, it doesn't give the safe CG location for the whole model, it doesn't choose at all, that's for the user to decide based on the guidelines in the instructions (who reads the instructions..). It calculates with a reasonable degree of accuracy the CG position given a user determined percentage. The formulas are sound, not thumb-sucks and have been used extensively (so far personally on about 30 different aircraft from deltas to aerobatic planes, gliders and EDF's). \

The formula's come from here: http://www.nasascale.org/howtos/cg-calculator.htm

If an experienced user wants safe choose a 'safe' CG location then by all means setup the plane using the calculators online on the bench at home and as an experienced modeller you should know what you're doing.

However I've seen a lot people at the field use a 'rule of thumb' of 25% of the MAC line for the first flight of every aircraft they maiden. Generally this results in a successful flight so a calculator is no longer needed.

But at least this will give a beginner an 'idea' and may save an aircraft, for that it's priceless.

By the way: the results from here: http://adamone.rchomepage.com/cg_calc.htm which take the tail into account give almost EXACTLY the same results for non-unusual aircraft as my calculator, it's only when you have unusual sizes, weights or shapes that things differ (and not by that much!)

another ref: http://theknowledgeworld.com/world-o...Gravity-CG.htm
and http://www.rcpowers.com/forum/blog.php?b=98
Oct 16, 2010, 06:30 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by pardus
.........However I've seen a lot people at the field use a 'rule of thumb' of 25% of the MAC line for the first flight of every aircraft they maiden. Generally this results in a successful flight so a calculator is no longer needed....
I have to agree that for such folks that don't stray far from the norm with their models that such assumptions and your app would work well. For those cases where they know that they want to put the CG at 25% of the MAC but the wing shape is odd so they are not sure where that is then your app is just the ticket.

I guess hanging out in the modeling SCIENCE forum has made me more of a stickler for going the whole 9 yards instead of taking shortcuts....
Oct 17, 2010, 04:12 AM
German Engineering.......
HugePanic's Avatar
why use this app on a phone??
i build my planes at home, there i have access to all tools i need.

but what about that:

make an app, that takes a photo from the planes wing&stabilizer.

then it prints lines for LE, TE, fuselage and so on.
the user can then correct them, if necessary.

after this is done, the position of the COG is displayed on the screen, an can be measured...

for this task it would be usefull to do on a plane. without any other tools, i can define the cog for alle configurations. on the field, you could inspect your buddies plane in a minute.....


THAT is something, i really would pay for!
(unless you bring it on blackberry)
Oct 25, 2010, 06:19 AM
Graham Dyer
pardus's Avatar
Quote:
Originally Posted by HugePanic
why use this app on a phone??
i build my planes at home, there i have access to all tools i need.

but what about that:

make an app, that takes a photo from the planes wing&stabilizer.

then it prints lines for LE, TE, fuselage and so on.
the user can then correct them, if necessary.

after this is done, the position of the COG is displayed on the screen, an can be measured...

for this task it would be usefull to do on a plane. without any other tools, i can define the cog for alle configurations. on the field, you could inspect your buddies plane in a minute.....


THAT is something, i really would pay for!
(unless you bring it on blackberry)
You're welcome to build your own application
Last edited by pardus; Oct 25, 2010 at 06:28 AM.
Oct 26, 2010, 06:21 PM
Ascended Master
Sparky Paul's Avatar
For most conventional planes, the tail contribution can be ignored!
The practical c.g.s tend to be between 25% and 35% of the mac, regardless of the tail, as long as the tail isn't way back there or way large/small.
Oct 26, 2010, 06:50 PM
Sink stinks
Montag DP's Avatar
Quote:
Originally Posted by Sparky Paul
For most conventional planes, the tail contribution can be ignored!
The practical c.g.s tend to be between 25% and 35% of the mac, regardless of the tail, as long as the tail isn't way back there or way large/small.
If the tail effects could be ignored, every plane would need the CG at 25% MAC or further forward.

If you really want a good idea of where the CG should be, you need to account for the tail effects. Otherwise you're just guessing and hoping it works out.
Oct 26, 2010, 07:26 PM
Ascended Master
Sparky Paul's Avatar
Conventional layout!
Any plane which resembles another will have the c.g. close to the same point.
Flight testing may refine that point.
But agonizing over the location of the c.g. for a conventional layoutis a waste of time. May be intellectually satisfying, but when the c.g. is found to be -surprise-! at 30% of the m.a.c.......
What worked on -that- airplane will be fine on -this- airplane which looks like -that- airplane.
Oct 26, 2010, 08:52 PM
Ascended Master
Sparky Paul's Avatar
This Wacky Waco had half the horizontal depart in flight! Nothing unusual occurred, and the plane was landed normally.
Adding the Seniorita wing to the Senior as a biplane requires no changes at all in anything, despite the enormous change in wing area.
Things like this remove some of the excitement about worrying about the precise location of the c.g.
Apr 09, 2015, 12:42 PM
IAMCANADIAN
Grejen's Avatar
Quote:
Originally Posted by pardus
You're welcome to build your own application
Quote:
Originally Posted by HugePanic
why use this app on a phone??
i build my planes at home, there i have access to all tools i need.

but what about that:

make an app, that takes a photo from the planes wing&stabilizer.

then it prints lines for LE, TE, fuselage and so on.
the user can then correct them, if necessary.

after this is done, the position of the COG is displayed on the screen, an can be measured...

for this task it would be usefull to do on a plane. without any other tools, i can define the cog for alle configurations. on the field, you could inspect your buddies plane in a minute.....


THAT is something, i really would pay for!
(unless you bring it on blackberry)
Really? How much?


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