Brodhead Pietenpol Association

Original Posted By: "bike.mike"
Folks,I'm finishing my Grega Aircamper and attempting to estimate the c.g. with the understanding that if built to the plans, there is a tendency toward aft c.g. problems. If any GN-1 builders or owners on the list can help me with this I would appreciate it. The example weight and balance included in my CAD plans were done for N4705G on 9/17/65. The computations in the plans are in error, but using the weights and arms I ran the numbers. The empty c.g. is 31% aft (leading edge). Most forward 38% and most aft 41%. I saw a picture of this plane in flight??? My question is what has been done to all the flying GN-1's to correct this situation. I have a J3 motormount per the plans with a C-85. Looks to me like I'll need a longer mount. Any thoughts?(N4705G -- Left 326, Right 323, Tail 50, Leading edge datum, 7.5" arm to main wheels, 169" arm to tail wheel, oil arm -23", fuel arm -1.5", pilot arm 53", passenger arm 24")Regards,Tom BernieGloucester MA978-281-8892________________________________________________________________________________

Original Posted By: Thomas Bernie
Tom,I have read that the new CAD drawings for the GN-1 have quite a few errors.This is likely one of them.MAYBE this one is simply a "5" where a "3" should be (i.e. maybe the numberfor the ailwheel should be 30 instead of 50).Perhaps you could do the calculations using 30 in place of the 50, and seewhat you get.It's a lucky thing that you're smart enough to see that something isn'tright, and are doing something about it. Maybe this is one of the reasonswhy the plans are no longer available for sale.Bill C.________________________________________________________________________________

Original Posted By:> "Thomas Bernie"
Mike,I haven't done mine yet. The numbers on my post were presented as an example weight & balance by the designer and printed on page 4 of the CAD plans I purchased from the Grega website. They are obviously bogus. I'm wondering what the other GN-1 builders/owners have experienced. I don't see my plane flying, as designed.TomOn Jul 1, 2008, at 12:12 PM, bike.mike wrote:> >>> Tom,> Was your fuselage absolutely level (at the top longeron) when you > weighed> it?> A CG at 41% MAC just seems horribly far back.> Mike Hardaway>> ----- Original Message -----

Original Posted By: H RULE

Original Posted By: "Thomas Bernie"
Tom,Was your fuselage absolutely level (at the top longeron) when you weighedit?A CG at 41% MAC just seems horribly far back.Mike Hardaway----- Original Message -----

Original Posted By: "Thomas Bernie"
Tom. I can't speak for the Grega Aircamper but for the Piet you can move the wings back to correct for C.G. problems.Gene (just back from my motorcycle trip to the West Coast and still working on my wife to let me go to Broadhead)----- Original Message -----

Original Posted By: "Gene Rambo"
Tom; I plugged your numbers into the spreadsheet that I used for the W&B on 41CC(thanks, Bert and Corky!) and you're right... your Grega doesn't pencil out.I guessed at a whole bunch of things, like your design gross (I used 1,088 asin 41CC), fuel capacity (I used 16 gal., also like 41CC), and some other thingslike pilot and passenger weight- but the one number that jumped out immediatelywhile I was plugging in numbers was the weight on your tailwheel. 41CChad 29 lbs. on the tailwheel when empty, whereas 05G has 50. There's your problem.Twenty more pounds on the tailwheel. Oh, and BTW- I sent the Excel spreadsheetto Matt Dralle for posting on the file share, so it should be availablelater today if you want it to do some what-ifs. You'll have to check all thenumbers and info in each cell or you'll get bad info out of it though.That twenty extra pounds at a moment arm of 169" yields 3380 in-lbs. of moment.Your C-85 weighs about 220 lbs. so you'd have to move the engine forward by15" to offset that moment... which I don't think you would want to do. Time tolook at some other options for bringing it into balance. Think about heavystuff that you can move forward.Oscar ZunigaAir Camper NX41CCSan Antonio, TXmailto: taildrags(at)hotmail.comwebsite at http://www.flysquirrel.net________________________________________________________________________________

Original Posted By: "Gene Rambo"
You are never going to win taking FedEx to court. Always, ALWAYS, pay the extra for insurance whenever shipping something valuable.Gene________________________________________________________________________________

Original Posted By: "Bill Church"
Oscar,The weight and balance example from the plans has to be disregarded. The plans do however, specify a c.g. range of 18.1 to 20.7 (30.2% to 34.5%). I weighed my wing panels with scales at the strut attach points and added the appropriate weight to my fuselage and did a weight and balance. It came out 31% fwd and 34% aft. It's not exact by any means, but it did end up close to the design numbers. I expect the GN-1's built to plans are all operating at the back of the c.g. envelope. I guess I'll have to make a new, longer, motor mount. I have no intention of operating in the plans specified c.g. range. I've got nothing to move but the engine. Thanks for posting the spreadsheet that will come in handy. Over the last few days I have generated a huge pile of paper and worn out my calculator, so the spreadsheet will be useful for working out the mount. My plane has 30# on the tailwheel and an empty c.g. of 13.9. I need to move that fwd a couple of inches. Thanks for the help.Regards,TomOn Jul 2, 2008, at 8:51 AM, Oscar Zuniga wrote:> >>>> Tom; I plugged your numbers into the spreadsheet that I used for the > W&B on 41CC (thanks, Bert and Corky!) and you're right... your Grega > doesn't pencil out. I guessed at a whole bunch of things, like your > design gross (I used 1,088 as in 41CC), fuel capacity (I used 16 > gal., also like 41CC), and some other things like pilot and > passenger weight- but the one number that jumped out immediately > while I was plugging in numbers was the weight on your tailwheel. > 41CC had 29 lbs. on the tailwheel when empty, whereas 05G has 50. > There's your problem. Twenty more pounds on the tailwheel. Oh, and > BTW- I sent the Excel spreadsheet to Matt Dralle for posting on the > file share, so it should be available later today if you want it to > do some what-ifs. You'll have to check all the numbers and info in > each cell or you'll get bad info out of it though.>> That twenty extra pounds at a moment arm of 169" yields 3380 in-lbs. > of moment. Your C-85 weighs about 220 lbs. so you'd have to move > the engine forward by 15" to offset that moment... which I don't > think you would want to do. Time to look at some other options for > bringing it into balance. Think about heavy stuff that you can move > forward.>> Oscar Zuniga> Air Camper NX41CC> San Antonio, TX> mailto: taildrags(at)hotmail.com> website at http://www.flysquirrel.net>>Thomas Bernietsbe________________________________________________________________________________

Original Posted By:> "Oscar Zuniga"
Mike,I can't explain how such bogus information could end up in a set of plans. The specified center of gravity range on the plans could not possibly have been achieved on N4705G.However, my GN-1 looks like it will be close to the specified range of 30.2% to 34.5% -- the problem is, I don't want such a far aft c.g. range.TomOn Jul 2, 2008, at 11:13 AM, bike.mike wrote:> >>> Oscar,> My puzzlement is the same as Tom's; N4705G is/was a flying airplane, > which I> don't think it would have been with a CG at 41%. Where did these > numbers> really come from, and what was done to 05G to make it flyable?> It almost looks like those numbers either came before engine > installation or> the airplane was weighed while tail-down.> Mike Hardaway>> ----- Original Message -----

Original Posted By: "Oscar Zuniga"
Oscar,My puzzlement is the same as Tom's; N4705G is/was a flying airplane, which Idon't think it would have been with a CG at 41%. Where did these numbersreally come from, and what was done to 05G to make it flyable?It almost looks like those numbers either came before engine installation orthe airplane was weighed while tail-down.Mike Hardaway----- Original Message -----

Original Posted By: "Rick Holland"

Original Posted By: "Rick Holland"
Speaking of typos, I just saw that my post refers to the "ailwheel". Doh!Maybe if it weighs 50 pounds, that's actually the right name.We all make mistakes. But I would think a set of plans for an airplane wouldbe proofread many times over before being sent to the printshop.Bill C.________________________________________________________________________________Date: Wed, 2 Jul 2008 10:55:47 -0600

Original Posted By:> Bill Church
Al,You are absolutely right, this has certainly been a learning experience for me. If Grega had kept selling and correcting the plans, as well as making the drawings from the old plans available, we would have a great GN-1 builder community. When I pointed out the orientation of the vertical pieces in the aft fuselage were incorrect he just disagreed with me? If you are ever coming to Gloucester, give me a call and you can see my plane.Regards,Tom Bernie978-281-8892On Jul 2, 2008, at 12:26 PM, ALAN LYSCARS wrote:> Tom,>> I've been working with a set of the "CAD" Grega plans for about four > years.>> I've offered, over that time, queries and suggestions concerning > questionable detail found in those drawings. At one time-I think > about three or four summers ago- Bob Grega was very responsive to > those of us on the list with these observations. Bob issued > corrections to the plans to all registered plans owners as he became > aware of them from us and when there was technical consensus for the > change. Most of these suggestions were minor in detail: one such, > I remember, was a mislabled turnbuckle assembly.>> At some point Bob Grega, who was only reproducing plans for those > who wanted to buy them, stopped cold. I never found the reason why > but, considering all of the armchair quarterbacks and litigators > instant in our society today he may have, rightfully, gotten scared > of being sued.>> It's really a crying shame, too, for with the withdrawl of these > plans sets from the market a whole generation, or generations, of > builders will never come to be: at least with this design.>> I always try to remind myself that as an experimental builder it is > my charge to myself to try to know or learn as much as I can about > what I'm doing. The fact that a few errors have been caught and > corrected in these plans is a real testament to our willingness to > "get it right" to the best of our collective ability.>> After all, even young boys can put together a kit plane.>> Sincerely,> Al Lyscars> Manchester, NH>> ----- Original Message -----

Original Posted By: "ALAN LYSCARS"

Original Posted By:> Thomas Bernie
Harvey,Thanks for the numbers -- very helpful for me to see what c.g.'s flying GN-1's have.Best Regards,Tom BernieGloucester Mass978-281-8892On Jul 2, 2008, at 5:43 PM, H RULE wrote:> I fly aGN-1 aircamper and here are my figures:CofG=D+(RxL)>> W>> where Cof G =distance from datumto center of gravity of the aircraft > =14.6 in.>> W =the weight of the aircraft at the time of > weighing =777 lbs (right wheel = 365lbs,left wheel =379 lbs and tail > wheel =33lbs>> D =horizontal distance from datum to main weighing > point =7.6 in.>> L =horizontal distance from main wheel weighing > point to nose or tail weighing point =167 in.>> R =the weight at the tail weighing point =33 lbs>>> 7.6+(33x167)>> 777 =Cof G of 14.6>>> ----- Original Message ----

Original Posted By: Oscar Zuniga
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