Pietenpol-List: PhD dissertation on axle placement among the different

[matronics]

Original Posted By: walt evans
Walt,The following is related to your issue and I hope becomes a classic posting thatis referenced by many for years to come. I wrote it 5 years ago almost to theday in response to a question posed by Greg Cardinal. It was about 5 hoursof research and headscratching. Of course, it will prompt some controversy.Since the fisherman is gone, we haven't had much. This was supposed to havebeen published in MacLaren's BPA newsletter. I sent it to him but he never cameout with the next edition (and took everybody's money - but he did a good job).I think I will send it to Doc Mosher to put in To Fly!It appears that the 1932 fuselage has the wood gear axle about 13.5 inches aftof the firewall. The 1933 Improved Air Camper has the axle 17 inches aft of thefirewall. The weight and balance sheet I have from Don Pietenpol shows theaxle on the "1937 Air Camper with Corvair engine" (metal split axle gear on a163 inch fuselage) at 16.5 inches aft of the firewall. The question Dale isasking is how far aft of the firewall should the axle be on the Pavliga long fuselagefor which we have no help from the drawings?The 1932 fuselage (Hoopman drawings and 1932 Flying and Glider Manual) is 161 incheslong. The 1933 Improved Air Camper fuselage is 163 inches long. The Pavligalong fuselage is 172.375 inches long. This is the one I understand youhave built.It appears that the intersection of the first truss verticals with the lower longeronon the 1932 fuselage is 8.375 or 8.5 inches aft of the firewall, dependingon which set of plans you look at. On the 1933 Improved fuselage, it is 10inches, and on the Pavliga long fuselage, it is 12 inches. This would meanthat the wood gear, unmodified from the 1932 plans and as mounted on the Pavligalong fuselage, would put the axle 12-8.5 or 3.5 inches farther aft on the longfuselage than on the 1932 fuselage. It would be at 13.5 (see paragraph 1sentence 1) + 3.5 or 17 inches aft of the firewall. Is this a good place forit? Frank P. said it was too far forward at 17 inches aft of the firewall sohe moved it aft when he did the engine switch.A better indicator of proper gear position is comparing it to the rear seat backposition in the particular fuselage since this indicates the shift aft of theCG position as the fuselages have been stretched. The rear seat back (at thetop longeron) in the 1932 fuselage is 70.5 inches aft of the firewall. Therear seat back in the 1933 Improved fuselage is 72.25 inches aft of the firewall.The rear seat back of the Pavliga long fuselage is 76.25 inches aft of thefirewall. This is a substantial shift aft in the position of the CG versusthe axle position as the fuselage is stretched.Therefore, the axle on the 1932 fuselage is 70.5 -13.5 or 57 inches forward ofthe rear seat back. The axle on the 1933 Improved is 72.25 -17 or 55.25 inchesforward of the rear seat back. Let us ignore the value from the 1932 fuselagefor reasons to be discussed later. Using the number from 1933 and applyingthis to the Pavliga long fuselage, we should have the axle at 76.25 - 55.25 or21 inches aft of the firewall. Two paragraphs ago we determined that it willactually wind up at 17 inches aft of the firewall with the wood gear, unmodified,and Frank P. says this is too far forward. Therefore, it appears that weneed to redesign the gear so that the axle will sit farther aft in the V to thetune of about 21 -17 or 4 inches.As we noted above, if you look at the sweep of the V in the 1932 plans, you willnote that the front attach of the V is at 8.5 inches aft of the firewall. Weknow that the axle is about 13.5 inches aft of the firewall. Therefore, thesweep is 13.5 - 8.5 or 5 inches for the wood gear. Doing the same analysis forthe 1933 Improved Air Camper, we know the front attach of the V is at 10 inchesaft of the firewall and the axle is at 17 inches aft of the firewall. Thereforethe sweep is 17 -10 or 7 inches for the split axle gear. The next sentenceis important. If you put the 1932 wood gear on a 1933 Improved fuselage, youwould have an axle that will be 7 - 5 or 2 inches forward of where it wouldhave been if you had used the split axle gear!!!! So the gears are not necessarilyinterchangeable!!! Logic says that it does not matter which style gearyou use. The axle should always be in the same relative position. I see thisas an admission by BP that the original 1932 axle was too far forward by 2 inches.And now we know what Frank P. was talking about!!!!It is obvious that BP saw fit, when designing the 1933 Improved Air Camper, thatif he lengthened the fuselage from 161 to 163 inches and moved the pilot's rearseat back aft by 1.75 inches, then he must move the axle aft by 17 -13.5 -2 or 1.5 inches. (Consider 2 of the 3.5 inch difference between 17 and 13.5as a design correction and the remaining 1.5 of the 3.5 inches to be an adjustmentfor the new fuselage length and movement aft of the rear seat back.) Sowhat would BP do if he made the fuselage 172.375 inches long (a whopping 9.375inches longer) and moved the rear seat back aft yet another 76.25 -72.25 or 4inches?As mentioned before, I propose a redesign of the V to allow the axle to sit 4 inchesfurther aft of where it sits in the 1932 V. This makes sense. As justdiscussed, the original sweep was 5 inches. The new proposed sweep is 5 + 4 or9 inches. This is reasonable compared to BP's increase of sweep in the splitaxle gear to 7 inches for a slightly longer fuselage with a repositioned pilot.Adding even more length for the Pavliga long fuselage and moving the pilotan astounding 4 more inches aft over the 1933 fuselage and 5.75 more inches aftover the 1932 fuselage definitely calls for an adjustment in the sweep of thewood V.As I see it, after BP's design correction is factored in, if you want to use awood straight axle gear in the short 161 inch long 1932 fuselage, then the axleshould be at 13.5+2 (the 2 inch correction) or 15.5 inches aft of the firewall(the V has a 7 inch sweep). If you want to use a wood straight axle gear inthe 163 inch long Improved Air Camper fuselage, then the axle should be at thesame location as in the split axle gear, 17 inches aft of the firewall (theV has a 7 inch sweep). If you want to use a wood straight axle gear in the 172.375inch long Pavliga long fuselage, then the axle should be 21 inches aftof the firewall (the V should have a 9 inch sweep).Frank P. started with 5 inch sweep and ended up with 7 inch sweep after his engineswap and gear modification. I propose that a 9 inch sweep is optimal but youcould probably get by just fine with the 7 inch sweep. Either way, I wouldnot use the 1932 gear as it is on the drawings. Does this help? I rest my caseand am going to bed.Chris Bobka ----- Original Message -----

[matronics]

Original Posted By: "Christian Bobka"
different fu...Subject: Re: Pietenpol-List: PhD dissertation on axle placement among the differentfu...Chris,Thanks for a GREAT article ref. the 172 inch fuse builders out here. Your research and experience helps for those of us, me, who are just getting startedand learning as we go.Greg MenocheDelaware ________________________________________________________________________________