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  #1  
Old 07-14-2010, 10:55 AM
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dhall_polo dhall_polo is offline
 
Join Date: Nov 2006
Location: Cumming, GA
Posts: 610
Default (free) gps2tas iphone app

GPS2TAS:
http://itunes.apple.com/us/app/gps2tas/id381224165?mt=8

I was inspired by some recent threads from brantel and others to do some additional checks of my airspeed indication. I wasn't quite hitting vans numbers, and I was so sure I'd built a clean plane. After doing the calcs, it looks like my indicators are low, and I'm right on vans numbers. Now my next step is to fiddle with my safeair static port to see if I can increase accuracy. Anyway, there's a lot of great info in the forums about computing TAS from GPS track information, and I was able to find spreadsheets and online tools that can do the computations for you. I guess I'm impatient and didn't want to wait until I landed to get the TAS results, so what the heck, I decided to write iphone app number cajillion and one.

If you want to see how accurate your airspeed indicators are, just download this app (free) and bring it with you. It works just like the spreadsheets and online tools, requiring you to fly three legs and input your heading and groundspeeds. Once it has valid vectors, it computes TAS on the fly. It currently requires an iphone with the new v4 os. I'll upload a version that supports the older 3.x os when I can.

In putting the app together, all credit for the math goes to fellow RV'er, Doug Gray. I was able to reference algorithms published by Doug more than a dozen years ago, located here: http://www.kilohotel.com/rv8/rvlinks...y/TAS_FNL4.pdf. Additional references are available on the NTPS site here, which also leverages Doug's work as the base. Here's a post that sums it the general topic of computing TAS from GPS data. Most of the links in that post are now invalid, but it's a start. If you have any issues, questions, or comments, please feel free to PM me.
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Don Hall
N517DG - RV7 - Flying!
Ticked Van's Hobbes meter at #6110, 3/7/09

Last edited by dhall_polo : 07-14-2010 at 09:09 PM.
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  #2  
Old 07-14-2010, 12:18 PM
jerryab jerryab is offline
 
Join Date: Dec 2008
Location: Northwest Arkansas
Posts: 40
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Thanks, that should remove any doubt and help me find a problem, if there is one. Great App.
jerry
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  #3  
Old 07-14-2010, 03:49 PM
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Ironflight Ironflight is offline
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I happened to have a little "free aviating" time this afternoon, so I downloaded this and took it along - works great! Both the TAS and computed winds compared very well to those same values computed on my EFIS. It must be a great App - it told me that my airspeed error is still less than 1 knot.
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  #4  
Old 07-14-2010, 03:58 PM
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N8RV N8RV is offline
 
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OK, this app had better be worth the effort, guys. I just spent the last few hours downloading iOS4 for my 3GS, just so I could try this app! If it's no good, then I'M NOT PAYING!
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  #5  
Old 07-14-2010, 07:25 PM
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dhall_polo dhall_polo is offline
 
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Default ios4

The app works better than the iphone4os.
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N517DG - RV7 - Flying!
Ticked Van's Hobbes meter at #6110, 3/7/09
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  #6  
Old 07-14-2010, 07:27 PM
Sid Lambert Sid Lambert is offline
 
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Location: North Atlanta
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Yeah, iOS4 on my 3G iPhone is so slow I feel like bouncing it off the pavement.

I did download your app and plan on using it soon. Thanks for contributing to the community.
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  #7  
Old 07-14-2010, 07:38 PM
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RV6_flyer RV6_flyer is offline
 
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Went to download the App to try it out on my way to AirVenture. I have not updated to OS4 and refuse to do so till after AirVenture. The App requires OS4 so looks like I will have to wait till after I get home from AirVenture to be able to download and try it.

I updated to the latest Apple iPhone OS last year before going to OSH. My phone kept crashing and needed to reboot to get it working again. I do not want this happening again so will not be doing any UPDATES to my iPhone till at least the next month. After hearing so many people say how OS4 is slow, I am not sure I even want to try it. I have the 2nd generation iPhone or the first model to have 3G service that is not the 3GS model.
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  #8  
Old 07-14-2010, 08:27 PM
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apkp777 apkp777 is offline
 
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What about for Droid? Any similar apps?
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  #9  
Old 07-14-2010, 09:57 PM
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dhall_polo dhall_polo is offline
 
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Location: Cumming, GA
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Default references on gps2tas

I was asked a question or two about the calculations. Most of the links in the post I referenced initially are bad now. Here's some detail.

Credit for the math goes to a fellow RV'er, Doug Gray, from down under. He published an article back in 1998. See:
http://www.kilohotel.com/rv8/rvlinks...y/TAS_FNL4.pdf

Another good source is this one. They have some additional formulas and information on calculating TAS with more than 3 legs. This site also references Doug's original work.
http://www.cockpitgps.com/other_arti...and_calcul.htm

Finally, it's not surprising that Ken has a detailed reference on the subject:
http://go.phpwebhosting.com/~khorton...ex.php?&PID=49

That ought to be enough to get someone going on a droid app. Isn't "droid" just some sort of code word for "I wish I had an iphone."?

Good Luck!
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N517DG - RV7 - Flying!
Ticked Van's Hobbes meter at #6110, 3/7/09
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  #10  
Old 07-14-2010, 10:44 PM
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apkp777 apkp777 is offline
 
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Quote:
Originally Posted by dhall_polo View Post
Isn't "droid" just some sort of code word for "I wish I had an iphone."?

Good Luck!
LOL!...Hey I'll have you know that I owed one of the first PDA's ever. It was an Apple circa 1991 or so. I forget what they called it. I know what I called it... a piece of... Then I went to a IIci and onto a Powerbook. At the time peripherals were 3 or 4 times more expensive. So I switched to PC's. Hated computers ever since, boy they sure are cheap though

Yeah, I am not a fan of Droid much either, but I am just a slave to Sprint.
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