---------------------------------------------------------- Pietenpol-List Digest Archive --- Total Messages Posted Thu 02/18/16: 7 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 09:12 AM - Re: weight & balance (Jim Boyer) 2. 09:14 AM - Re: weight & balance (Jim Boyer) 3. 09:57 AM - Re: weight & balance (Ray Krause) 4. 10:04 AM - W&B S/S -- remarks re Oscar's post (Timothy Willis) 5. 10:30 AM - Re: W&B S/S -- remarks re Oscar's post (Ray Krause) 6. 08:08 PM - Re: weight & balance (taildrags) 7. 08:14 PM - Re: weight & balance (taildrags) ________________________________ Message 1 _____________________________________ Time: 09:12:47 AM PST US From: Jim Boyer Subject: Re: Pietenpol-List: weight & balance Sounds like you are getting very close though Ray. Have you had your final inspection by a DAR yet? Cheers, Jim ________________________________ Message 2 _____________________________________ Time: 09:14:04 AM PST US From: Jim Boyer Subject: Re: Pietenpol-List: weight & balance Hi Oscar, Will you send me a copy of your Piet weigh and balance sheet? Thanks, Jim B. ________________________________ Message 3 _____________________________________ Time: 09:57:20 AM PST US From: Ray Krause Subject: Re: Pietenpol-List: weight & balance Jim, No inspection, yet. Have to put the wings on, do final rigging W/B and a lot of other little stuff. Ray Sent from my iPad > On Feb 18, 2016, at 9:12 AM, Jim Boyer wrote: > > Sounds like you are getting very close though Ray. Have you had your final inspection by a DAR yet? > Cheers, > Jim ________________________________ Message 4 _____________________________________ Time: 10:04:20 AM PST US Subject: Pietenpol-List: W&B S/S -- remarks re Oscar's post From: Timothy Willis =8B Oscar is certainly right to recommend a pre-build spreadsheet for W&B, in order to plan well and to save iterations-- Plan B,C,D.... Years ago I wrote a fab pre-build W&B spreadsheet. Unfortunately that was a PC crash and several PCs ago, and I no longer have it. However I will share a feature and some findings. I had a "what if" feature in the Excel model so that I could move a battery fore or aft to improve balance. Of course moving it away from the firewall also adds longer heavy wiring. Thus IMO this partial solution falls among the category of "desperate corrective measures." Slanting the wings aft obviously is a very effective way to alter CG to within bounds. My major concern as a fat boy has been my nearly 100 lbs. over the 170-pound "FAA pilot." I discovered that every *25 pounds *of added pilot weight required a movement of the wing back* one inch*. My setup features an A-65, and while I did also test for a Corvair instead, I do not recall those comparative data. I did not run versions with a Model A engine, radiator, etc. My setup also features an 18 gallon fuselage tank, which accentuates W&B considerations... about 100 lbs. (16 gals) difference between full and empty-useable. In this regard a *wing *tank empty/full and a passenger yes/no made almost no difference. I added a "thousand pound passenger" as a test, and it moved the resultant CG nearly nil, under an inch, since both are right at the CG. I have concluded that I will slant my cabanes aft 6 inches. If in actual practice that is not enough, I will develop a close relationship with Jenny Craig, a virtuous step in its own right. Tim in Central TX ================= >> Okay, so really, builders don't need to be waiting till their aircraft are almost finished before thinking about W&B. In fact, the earlier you start to think about it and start getting numbers in your head, the more confident you'll be about it when it comes time to do the final, actual W&B and fill in the forms that you'll show at the end. Once you have the bare fuselage -covered or not- on the gear, you're ready to start measuring and weighing. At that point you can start plugging some numbers into a W&B spreadsheet and it will be even easier if you don't have the wings or engine on the bare fuselage because you can move it around the shop or hangar very easily. Not only that but if you don't have the cabanes and centersection mounted yet, it will be even easier to get your helper to climb into that front cockpit to do the weighing to get the passenger moment arm calculated. >> >> With the fuselage on the gear (as long as the geometry is locked in and the gear mounting brackets are actually bolted to the fuselage or at least pinned in place in final locations), you can determine the various moment arms for the main gear and tailwheel, as well as the moment arms for pilot and passenger. If you're using a nose tank you can also determine the moment arm for it if you have the tank fabricated and can set it temporarily in place in the forward fuselage. All of this can be done with nothing more than masking tape, markers, a string and plumb bob or fishing weight, and a couple of simple bathroom scales since the accuracy of the scales doesn't matter too much at that point. They just need to be reasonably accurate and the readings repeatable, and the actual weights won't matter much in order to determine moment arms. >> >> As a starting point I can offer the Excel spreadsheet that I've used for the W&B on 41CC, and I can probably also cook up a simple spreadsheet for com ing up with the passenger and pilot moment arms after you've taken some simple readings on a rainy workshop day when you and a helper are able to make some measurements slowly, carefully, and thoughtfully. If you do it right the first time, you'll never have to do it again. The upside to all of this is that if you start the process early, you can make adjustments as you go along and not get surprised at the very end when you find out your airplane has a heavy tail and you have to find a way to offset or move it. >> -------- >> Oscar Zuniga >> Medford, OR >> Air Camper NX41CC "Scout" >> A75 power ________________________________ Message 5 _____________________________________ Time: 10:30:43 AM PST US From: Ray Krause Subject: Re: Pietenpol-List: W&B S/S -- remarks re Oscar's post Tim, Very interesting comments and well written, thanks. Ray Krause Sent from my iPad > On Feb 18, 2016, at 10:03 AM, Timothy Willis wrote : > > =8B > Oscar is certainly right to recommend a pre-build spreadsheet for W&B, in o rder to plan well and to save iterations-- Plan B,C,D.... Years ago I wrot e a fab pre-build W&B spreadsheet. Unfortunately that was a PC crash and se veral PCs ago, and I no longer have it. However I will share a feature and s ome findings. > > I had a "what if" feature in the Excel model so that I could move a batter y fore or aft to improve balance. Of course moving it away from the firewal l also adds longer heavy wiring. Thus IMO this partial solution falls among the category of "desperate corrective measures." > > Slanting the wings aft obviously is a very effective way to alter CG to wi thin bounds. My major concern as a fat boy has been my nearly 100 lbs. over the 170-pound "FAA pilot." I discovered that every 25 pounds of added pilo t weight required a movement of the wing back one inch. My setup features a n A-65, and while I did also test for a Corvair instead, I do not recall tho se comparative data. I did not run versions with a Model A engine, radiator , etc. > > My setup also features an 18 gallon fuselage tank, which accentuates W&B c onsiderations... about 100 lbs. (16 gals) difference between full and empty- useable. In this regard a wing tank empty/full and a passenger yes/no made a lmost no difference. I added a "thousand pound passenger" as a test, and it moved the resultant CG nearly nil, under an inch, since both are right at t he CG. > > I have concluded that I will slant my cabanes aft 6 inches. If in actual p ractice that is not enough, I will develop a close relationship with Jenny C raig, a virtuous step in its own right. > > Tim in Central TX > ================= > > >> Okay, so really, builders don't need to be waiting till their aircraft a re almost finished before thinking about W&B. In fact, the earlier you star t to think about it and start getting numbers in your head, the more confide nt you'll be about it when it comes time to do the final, actual W&B and fil l in the forms that you'll show at the end. Once you have the bare fuselage -covered or not- on the gear, you're ready to start measuring and weighing. At that point you can start plugging some numbers into a W&B spreadsheet a nd it will be even easier if you don't have the wings or engine on the bare f uselage because you can move it around the shop or hangar very easily. Not o nly that but if you don't have the cabanes and centersection mounted yet, it will be even easier to get your helper to climb into that front cockpit to d o the weighing to get the passenger moment arm calculated. > >> > >> With the fuselage on the gear (as long as the geometry is locked in and the gear mounting brackets are actually bolted to the fuselage or at least p inned in place in final locations), you can determine the various moment arm s for the main gear and tailwheel, as well as the moment arms for pilot and p assenger. If you're using a nose tank you can also determine the moment arm for it if you have the tank fabricated and can set it temporarily in place i n the forward fuselage. All of this can be done with nothing more than mask ing tape, markers, a string and plumb bob or fishing weight, and a couple of simple bathroom scales since the accuracy of the scales doesn't matter too m uch at that point. They just need to be reasonably accurate and the reading s repeatable, and the actual weights won't matter much in order to determine moment arms. > >> > >> As a starting point I can offer the Excel spreadsheet that I've used fo r the W&B on 41CC, and I can probably also cook up a simple spreadsheet for c om ing up with the passenger and pilot moment arms after you've taken some s imple readings on a rainy workshop day when you and a helper are able to mak e some measurements slowly, carefully, and thoughtfully. If you do it right the first time, you'll never have to do it again. The upside to all of thi s is that if you start the process early, you can make adjustments as you go along and not get surprised at the very end when you find out your airplane has a heavy tail and you have to find a way to offset or move it. > >> -------- > >> Oscar Zuniga > >> Medford, OR > >> Air Camper NX41CC "Scout" > >> A75 power ________________________________ Message 6 _____________________________________ Time: 08:08:46 PM PST US Subject: Pietenpol-List: Re: weight & balance From: "taildrags" For all those who asked, I've uploaded my W&B spreadsheet to the forum but if you're unable to get it that way, email me privately and I'll send it to you. The usual caveats apply, especially "the numbers in this spreadsheet are for NX41CC ONLY!" Do not use them for your airplane except as a starting point so you can check to see if your numbers are reasonable. The other thing I'd like to mention is that I did not author this spreadsheet. It was generously shared with me and it is in that spirit that I share it with others. Like Tim, I also added another tab so that I would have a "what-if sandbox" to play in without messing up the REAL sheet with the real numbers. In fact, I would suggest that once you enter your final numbers into the real sheet, that you lock those cells so you can't inadvertently change the numbers that shouldn't change. Ray: the spreadsheet doesn't care if you have a one-holer, two-holer, or twelve-holer... you can either leave the numbers for passenger weight and moment arm as "zero", or else eliminate those cells to streamline the spreadsheet. And if you're building a 3-cockpit Air Camper, just add rows for another cockpit and passenger ;o) As I mentioned, you don't need to have a complete airplane to start entering values into the sheet. For sure you can add the basic information at the top, but then as you measure the moment arms relative to the datum that you choose, you can start entering those values into the sheet and begin playing what-ifs. If the datum that you choose is going to be the wing leading edge and you don't have the centersection mounted yet, you'll have to enter values relative to the firewall and then later adjust those numbers when the distance from leading edge to firewall is determined. I have set the precision of weights and moment arms to one decimal place (roughly to the nearest 2 oz and 1/8"). I've played with it by increasing the precision of them one at a time and then both together, but I decided that I do not have eyes or tools that can measure closer than that. I've tried decreasing the precision to whole pounds and inches only, but that is unsatisfactory. If I were going to simplify one of the two, I would use whole pounds but keep tenths of an inch of length. You may argue about the acceptable range of 15 to 20" aft of wing leading edge for the CG and you may argue about the allowable maximum gross weight of 1,088 lbs. You just won't be arguing them with me ;o) Anyway, here is the spreadsheet. -------- Oscar Zuniga Medford, OR Air Camper NX41CC "Scout" A75 power Read this topic online here: http://forums.matronics.com/viewtopic.php?p=452991#452991 Attachments: http://forums.matronics.com//files/nx41ccw_b_2014_117.xls ________________________________ Message 7 _____________________________________ Time: 08:14:05 PM PST US Subject: Pietenpol-List: Re: weight & balance From: "taildrags" ...oh, and also- my empty weight includes 3 quarts of oil in the engine, which is the minimum amount recommended by Continental. You can argue about whether minimum oil should be included in the aircraft's empty weight, but I won't fly the airplane without it. You can make it whatever you want it to be when you weigh your airplane and edit the notes in those cells appropriately. -------- Oscar Zuniga Medford, OR Air Camper NX41CC "Scout" A75 power Read this topic online here: http://forums.matronics.com/viewtopic.php?p=452992#452992 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message pietenpol-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Pietenpol-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/pietenpol-list Browse Digests http://www.matronics.com/digest/pietenpol-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.