Brodhead Pietenpol Association

Original Posted By: "Jack Phillips"
Corky,I wish the wing were back a little but maybe we can do the old "bolt thelead to the motor mount like Frank Pavliga" trick. This would be to allowthe aircraft to "live" more toward the center of the expected allowable CGrange.I did a bunch of looking around trying to find a high wing monoplane with anundercambered airfoil where known CG limits were in place per the TypeCertificate Data Sheets. Unfortunately, any that I found were too old toeven have an allowable CG range posted on their TCDS. The best I could comeup with was the 10.6" to 22.7" allowable range on a J3C-65 Cub. Thattranslates to 16.8% to 36% of it's 63" chord allowable CG range with a rearseat solo near the aft limit. this is close to your situation although witha different airfoil and different tail surfaces.The Piet has a chord of 60". Your EW CG numbers look correct at 631 lbs and7170 in-lbs moment with a 11.36" EWCG or 18.93% of chord. Assuming theworst aft CG case with a 220 lb pilot and 220 lb passenger and empty of fuelwith 6 pounds of gloves in the glove box, we have 631 + 220 + 220 + 6 = 1077lbs. Moments are {7170 + (220)(21) + (220)(53) + (6)(66)}/1077 = 22.14" or22.14/60 = 36.90% of chord. A tad more aft than the Cub.We can back off the totally empty fuel and say there is 1 gallon of fuelunuseable. This would add a (6)(-6) = -36 moment to change the CG to23810/1083 = 21.98" or 36.64%. Still not enough. In addition, let us trythe old "bolt the lead to the motor mount like Frank Pavliga" trick. Add 10lbs to the motor mount support tube 6" aft of the oil sump (add atstation -18). (10)(-18) = -180 moment so the CG would change to(23810-180)/(1083+10)= 23630/1093 = 21.62" or 36.0%.Looks like we can show the fedman that it can be done.As the passenger actually sits behind the CG the worst forward CG case isfull fuel, 100 lb pilot, no passenger, and empty glove box. So: (7170 +(96)(-6) + (100)(53))/(631 + 96 + 100) = 14.38" or 24.O% of chord.You can see that the cub allows the front limit to be 16.8% of chord and wereally at the mid point of the range even with the worst case forwardloading. This is why a repostion of the wing would be better. To figure itout fairly closely, I would need to know the weight of the wing as it isright now with the cover and paint and a weight for the wing struts andseparate weights for the cabane struts would be helpful as well.Look at the bright side, if you hand prop the airplane and don't jump insidefast enough and the thing takes off without you with the 6 pounds of glovesin the glovebox, then you have: 631 + 96 + 6 = 733 lbs and moments of 7170+ (96)(-6) + (6)(66) = 6990 inch-lbs. 6990/733 = 9.5" or 15.9% of chord.Compare this to the Cub's 16.8%. Pretty close. Maybe a little nose heavybut it should fly by itself ok as long as it does a wheel landing!!chris________________________________________________________________________________

Original Posted By: Isablcorky(at)aol.com
HI Chris, Corky,As an ignorant bystander who will be doing the same thing in a few months, Iwould just like to say I am really enjoying following these discussions onW&B.I have tried to anticipate such problems by keping a running spreadsheet ofweights and moments as I have worked on the project. I estimated what Ithought components would weigh and put them into the spreadsheet with theirproper moment (I used the firewall as a datum since I expected to have tomove the wing). As each component has been completed I weighed it to seehow it compared with my estimate and updated the spreadsheet with the actualweight. Based on these numbers, I made my motor mount 2" longer than theplans call for (I built the long fuselage), and shifted the wing aft 3" fromvertical. According to the spreadsheet, my empty weight should come in at633 lbs, and my worst case aft CG (full fuel in centersection tank, 200 lb,passenger, 200 lb. Pilot, nothing in the nose baggage compartment and 4 lbsof stuff in the helmet box) should come at 34.2% of wing chord. It'll beinteresting to see what the final numbers look like.Good luck, Corky!Jack________________________________________________________________________________

Original Posted By: "taildrags"
Gardiner;I think many of the other smokers are burning baby oil, and I agree that the smokefrom it tends to be a little whiter and thinner. I did some research on theCanopus oil that Mikee (and aerobatic performers) like to use. It's also usedas a form release agent for concrete forms, obviously is not harmful to theenvironment since it washes off the form boards onto the ground, and is a food-grademineral oil. Shell has a comparable product.Some people have mentioned using spent or dirty automatic transmission fluid (ATF),and it will indeed make nice smoke, but it's not as innocuous as the mineraloil because you're burning a hydrocarbon, but not burning it completely. I wouldn't do it.The Stearman chat site has a discussion about this subject and one guy said hefound a reasonable alternative... soybean cooking oil from Costco. $20 for 5gallons. Food grade, good smoke, didn't make a mess on the airplane, but he saidthat smelling it made him want to go eat at McDonald's. Worth pursuing.--------Oscar ZunigaMedford, ORAir Camper NX41CC "Scout"A75 powerRead this topic online here:http://forums.matronics.com/viewtopic.p ... ___Subject: Pietenpol-List: CG calculations

Original Posted By: "Mike McGowan"
Pietenfolk;In preparation for the annual on my airplane, I updated the W&B sheet to reflectthe change to the tail weight with the slightly lighter Matco. In doing so,I ran some what-ifs to examine both normal configurations and extreme loadings.What I found with my airplane, and I'd like to see if anyone else with theirW&B on an Excel sheet wants to play with this, is that the passenger weightdoes not shift the CG at all. I tried passenger weights from zero to 2000 lbs(yes, one ton)- and the CG does not budge. I tried negative passenger weightsand the CG moves, but those aren't reasonable or rational numbers. The pointis, and it's been mentioned before, if a passenger can physically get intothe front cockpit and the gross weight isn't exceeded, the CG will not be affected.If it was within range with pilot and fuel and everything else, it willremain within range with any passenger you can stuff in the front cockpit aslong as gross isn't exceeded.I would welcome anyone else's experiences with this phenomenon to see if it's ageneral condition for most Air Campers or if it's specific to mine.--------Oscar ZunigaMedford, ORAir Camper NX41CC "Scout"A75 powerRead this topic online here:http://forums.matronics.com/viewtopic.p ... __________

Original Posted By: taildrags
Just look at the aircraft from the side and you can see the front seat is right under the cg point on the wing so the arm is 0 so the moment is 0 so there is no change in cg.Mike McGowan-----Original Message-----

Original Posted By: Steven Dortch
Hi all I made a smoke system for a friend long ago using anti freeze and a windshieldsquirter pump ... Great clouds of "smoke" good hang time(ran us out of his hangarin seconds.) his wife was really pissed.worked well in the air too.Sent from my iPhone> On May 8, 2014, at 8:45 PM, "taildrags" wrote:> > > Gardiner;> > I think many of the other smokers are burning baby oil, and I agree that thesmoke from it tends to be a little whiter and thinner. I did some research onthe Canopus oil that Mikee (and aerobatic performers) like to use. It's alsoused as a form release agent for concrete forms, obviously is not harmful tothe environment since it washes off the form boards onto the ground, and is afood-grade mineral oil. Shell has a comparable product.> > Some people have mentioned using spent or dirty automatic transmission fluid(ATF), and it will indeed make nice smoke, but it's not as innocuous as the mineraloil because you're burning a hydrocarbon, but not burning it completely.I wouldn't do it.> > The Stearman chat site has a discussion about this subject and one guy said hefound a reasonable alternative... soybean cooking oil from Costco. $20 for5 gallons. Food grade, good smoke, didn't make a mess on the airplane, but hesaid that smelling it made him want to go eat at McDonald's. Worth pursuing.> > --------> Oscar Zuniga> Medford, OR> Air Camper NX41CC "Scout"> A75 power> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 037#423037> > > > > > > > > > ________________________________________________________________________________Date: Fri, 9 May 2014 07:27:49 -0500Subject: Re: Pietenpol-List: Re: elevator stops and smoke oil !!!