# thrust to weight calculator Android app

Discussion in 'Rocketry Electronics and Software' started by jackman, Jun 11, 2013.

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1. Jun 11, 2013

### jackman

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Does anybody have an app to perform the T:W calc for Android? I've searched and can't find one anywhere. I get tired of always doing the mental gymnastics or using pencil and paper. It would be especially useful if doing RSO duty.

2. Jun 11, 2013

### bobkrech

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Not required. T/W = 4.45 pounds/Newton x Average Thrust in Newton divided by rocket weight in pounds.

3. Jun 11, 2013

### Sully

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Dimensional analysis is hard to show on here without fancy fonts, but I think the lbs/Newtons here is either backwards or I'm reading it wrong.

1 lb-force = 4.45 Newtons.

So divide your motor's average thrust by 4.45 to get the thrust in lbs. Then divide this by 5 to get the MAXIMUM recommended liftoff weight of your rocket. (Or, divide by your rocket's weight in lbs to get the ratio)

So an N5800 exerts about 1300 lbs-force, and therefore could lift 1300/5= 260 lbs. (approximately 1 snowmobile).

OR, if you use your N5800 to launch an Estes Alpha, which weighs around 0.05 lbs, your T/W ratio is about 26,000:1, which is more than adequate, even on a short launch rod. Of course T:W may not be the only thing to think about here. :wink:

I think this is right.....

So if you were an RSO in a hurry, aside from slowing down, you could divide the motor's average thrust by 25 to get in the ballpark of a maximum safe liftoff weight and to decide if you needed to look more closely at the rocket/motor specs. But really, slow down.

Last edited: Jun 11, 2013
4. Jun 11, 2013

### Dave A

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Easier formula:
Average thrust in Newtons /22.5= weight of loaded rocket in lbs. cannot exceed this value.
Preferably slightly less
When you cut this value too close, rocket tends to get lazy and layover slightly

Last edited: Jun 11, 2013
5. Jun 12, 2013

### Sully

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Yes, this is the accurate short way. I suggested 25 because its an easier number to divide by, and it errs on the side of caution. Cutting it closer to 5:1, and certainly with less, requires a closer look at the rocket, motor, and weather, rather than relying on rules of thumb.

6. Jun 13, 2013

### bobkrech

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Doh! You're correct. A senior moment. I've Had my head up a broken laser for the past 5, now 6 days. Should not post when thinking about something else.

7. Jun 13, 2013

### jackman

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Given all the discussion I still think it would be nice to have just a simple little app. You enter the average motor thrust and your rocket weight and it computes the ratio. If you leave out the rocket weight it computes the max liftoff weight. Unfortunately my programming skills were left behind with FORTRAN and BASIC :blush:

8. Jun 13, 2013

### niels popping

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You dont have to be an professional in computer programming
There are apps, you can use exel for mobile
I dont know at the time what the app is called like,
But when i got home, I will look up the name of the app for you

9. Jun 13, 2013

### dgreger

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Ok, so if I am doing this right a G80 should lift a max. of 3.59lbs?
80/4.45=17.97, 17.97/5=3.59. My MDRM weighs 2.5lbs, should give it a good ride!

10. Jun 13, 2013

### Sully

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For iOS, both RocketCalc and SmartLaunch will calculate T:W ratios (and lots more). Very handy at home and the field. Not sure whats available for other platforms.

11. Jun 13, 2013

### jackman

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Yeah, I've seen RocketCalc. It almost makes me want to buy some iStuff, LOL!

12. Jun 14, 2013

### brianc

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Here's your app! Works on all smartphones (iPhone, Android, etc) with a photo viewing capability.

Store these two pictures and refer when you want to verify the T:W ratio. Be sure you choose the correct one (LPR/HPR) for the rocket in question.

13. Jun 14, 2013

### Area66

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I was ready to post these charts ...... Madcow as a nice tool for Iphone, Ipod and Ipad, you enter the weight and the diameter, and it give you choice of motors and give you info about the launch , they use to have one for Android but it don't work with the new Android and I guess it was not popular enough to worth an upgrade. Since my son get is Android phone he don't use is iPod, so I use it for the Madcow software.

14. Jun 15, 2013

### MGRC

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I've been needing an excuse/idea to start writing Android apps, so I thought a simple thrust to weight calculator would be a good starting point. I uploaded it to the market yesterday, it takes a weight (g, kg, oz or lb) and an average thrust in newtons and displays the thrust to weight. As it's my first app, if anyone would like to see something added or changed, I'll try my best to do it.

15. Jun 16, 2013

### jackman

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That works thanks so much. Any chance you can modify it so that if there's no rocket weight entered it simply computes the max weight allowed using the 5:1 rule.

16. Jun 16, 2013

### Area66

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I install it, nice little apps, thanks

17. Jun 16, 2013

### MGRC

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I would like to keep the option to enter the weight, but I may have it so if you leave the weight blank, it will calculated max allowable weight instead.

>> I changed the app so now when you leave the weight blank, it will automatically calculate the max allowable weight. The new version is already on the market.

Last edited: Jun 17, 2013
18. Jun 17, 2013

### jackman

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I just got the update and it's exactly what I wanted. Thank you so much.

19. Jun 17, 2013

### Jimmy F.

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That's a sweet app
no i stuff required

20. Jun 18, 2013

### accpool

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works great, thanks

21. Jun 19, 2013

### cwbullet

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22. Feb 11, 2020

### Collan Fraser

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what happpend to this app anyone got a copy?

23. Feb 11, 2020

### tollyman

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The app I use on Android is TTWcalculator. Does what it's supposed to

24. Feb 11, 2020

### Collan Fraser

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yip thats the one, can't find it anywhere got the apk file? if so please zip it and put it up here cheers

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