Skinveen Posted November 12, 2009 Report Share Posted November 12, 2009 Can anyone show me to a numerical formula for Hover Ceilings vs. Gross Weight. I know I can use performance charts to get the information, but for what I'm working on, I need a formula. I would make one myself, but my head would probably explode. Thanks for any leads, Scott Quote Link to comment Share on other sites More sharing options...
Gomer Pylot Posted November 12, 2009 Report Share Posted November 12, 2009 There is none. It varies by model, by temperature, and a lot more. It's not a linear formula. Quote Link to comment Share on other sites More sharing options...
kodoz Posted November 12, 2009 Report Share Posted November 12, 2009 Can anyone show me to a numerical formula for Hover Ceilings vs. Gross Weight. I know I can use performance charts to get the information, but for what I'm working on, I need a formula. I would make one myself, but my head would probably explode. Thanks for any leads, Scott If you have the charts and a formula can be derived from the data, you can use Microsoft Excel to figure out the formula. This is from memory, but I think you plot a few representative points, add a trend line, then show the formula. You'll need to do this for every line (or part thereof) that has a different slope. Quote Link to comment Share on other sites More sharing options...
Tom22 Posted November 12, 2009 Report Share Posted November 12, 2009 If you are looking for mathematical models of helicopter performance get a copy of Principles of Helicopter Aerodynamics by Leishman. Quote Link to comment Share on other sites More sharing options...
Skinveen Posted November 12, 2009 Author Report Share Posted November 12, 2009 Yes Gomer there is a formula that will work.Sorry should have been clearer. I am looking for info for a R22 (R44 too if you have it). Seems like temperature could be left out if Density Alt. was used instead of Pressure Alt. (just to make it easier for Gomer). Kodoz - I'm trying, but I think I've gone way past my Excel limits. Thanks again, Scott Quote Link to comment Share on other sites More sharing options...
Tom22 Posted November 12, 2009 Report Share Posted November 12, 2009 Give Frank Robinson a call. Out of curiosity, why do you need to derive this formula? Quote Link to comment Share on other sites More sharing options...
Skinveen Posted November 12, 2009 Author Report Share Posted November 12, 2009 I have a weight & balance spread sheet that I am expanding with performance information. I would much rather input the latest ASOS info and get back a yea or nae to OGE/IGE than to rely on me making a mistake with a performance chart. Quote Link to comment Share on other sites More sharing options...
kodoz Posted November 12, 2009 Report Share Posted November 12, 2009 How good are you at algebra? And, have you seen this W&B calculator [link]? I didn't include performance data (I knew it'd be complicated, but now I fully understand why). Quote Link to comment Share on other sites More sharing options...
kodoz Posted November 12, 2009 Report Share Posted November 12, 2009 Here's how you get the equations in Excel: Figure out at least 2 x and y coordinates for each lineplot the data on a scatter plot (data points only)add a trendline and check "display equation on chart"Here's why I think what you're trying to do is not a good idea [link] Don't get me wrong: I see exactly where you're coming from with the idea. This ties back to the Power Check threads that keep coming up, but my thoughts are that we shouldn't be operating so close to the limits of the aircraft's performance that we need this level of precision, at least not in the flight training environment. (I'd be interested to see what the guys in Arizona and SLC do in the summer though.) None of this stopped me from taking a crack at trying to figure this out--it's an intellectually interesting question--but.... Here's why I don't think you can do what you're trying to do...there's a non-linear relationship in performance at different temps. It's probably worse for the HOGE data, and there are fewer data points to derive the equations from (=worse data). Any one equation might work for a given temp, but trying to determine the performance in the in-between temps would give you some serious grief. And you'd end up with a loss of precision, which is what you were trying to avoid in the first place. And, FWIW, these are your equations (based on very sloppy estimates): @-20: y=-17.7x+34626@-10: y=-17.4x+33689@+0: y=-18.1x+34057@10: y=-19.0x+34703@20: y=-19.2x+34403@30: y=-19.2+33953@40: y=-20x+34500 Maybe by spending more time working off the graphs you could get more accurate slopes for these lines, but seeing the trend going up in temp suggests that it actually varies. You can also see the differences in slopes pretty easily if you look at the R22 Beta HOGE chart. Quote Link to comment Share on other sites More sharing options...
lelebebbel Posted November 12, 2009 Report Share Posted November 12, 2009 (edited) You can enter the OGE and IGE graphs into excel (don't need the formula for this, just a few data points taken from the POH charts, which are then connected by a line), and then have it plot a line in the same graph for the current conditions and weight that shows you where your ceiling is. Be careful though, most R22s actually perform nowhere near as good as the charts say they should, at least in my experience. Also, the charts in the POH are based on 0% humidity. Higher humidity does have a effect on DA. Edited November 12, 2009 by lelebebbel Quote Link to comment Share on other sites More sharing options...
Skinveen Posted November 12, 2009 Author Report Share Posted November 12, 2009 Kodoz and lelebebbel thank you both for your intelligent thoughts. My plan isn't any different than using a POH. I'm not looking for a more accurate formula, only a easier way for me to get the info. For me that is inputting in a spreadsheet and possibly getting a red flag. lelebebbel, i will try your method, the problem is I am teaching myself Excel charts through this process...fun, but time consuming. Thanks again and don't be afraid to chime back with any more ideas...they all help. Scott Quote Link to comment Share on other sites More sharing options...
kodoz Posted November 12, 2009 Report Share Posted November 12, 2009 Kodoz and lelebebbel thank you both for your intelligent thoughts. My plan isn't any different than using a POH. I'm not looking for a more accurate formula, only a easier way for me to get the info. For me that is inputting in a spreadsheet and possibly getting a red flag. lelebebbel, i will try your method, the problem is I am teaching myself Excel charts through this process...fun, but time consuming. Thanks again and don't be afraid to chime back with any more ideas...they all help. Scott Sheet 2 shows you how to do Lele's method (the actual data could be refined probably). Change the file extension from pdf to xls or xlsx and you should be able to open it. You can plot a line up from your GW, but getting that temp to automatically plot involves some fudging. I guess my point is that the difference in your performance at 22C and 24C is negligible--if you can't land there at 24C, you gotta ask if you have the performance to try it at 22C, or maybe even 20C. A difference of 10C maybe gives you a margin of 500 feet. I guess I'd say "It's 25C out, so I'm taking my performance as if it's 30C." That builds in a margin that helps account for reality (eg, uncertain elevation of LZ if it's off airport, exact temp unknown at planned LZ, variability in fuel burn).HIGE.pdf Quote Link to comment Share on other sites More sharing options...
Skinveen Posted November 14, 2009 Author Report Share Posted November 14, 2009 (edited) Yippee! Success and my head didn't even explode! Thanks for the ideas lelebebbel And Kodoz. Edited November 14, 2009 by Skinveen Quote Link to comment Share on other sites More sharing options...
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