Brodhead Pietenpol Association

Original Posted By: Richard F. Rapp
O.K. Rich...You got me listening! Tell me more...What do you have in mind?Jim-----Original Message-----

Original Posted By: Steve Eldredge
Subject: Pietenpol-List: Re: Big Stick Engine Mods?>Hello Jim,> Well, it occurs to me that a pro is much more effective at lower>rpm where the area of stall speed will only be nearest the tip.>..Hence, a larger, slower prop is superior to a smaller prop attempting>an equivalent amount of thrust by increased RPM.>..Torque is required.>The Model A and the B improvement were the engine of Bernard's choice>because they developed sufficent torque and horsepower at low RPM, even>whe compared with themore advanced engines of today that achieve increases>in both,but at much higher, unuseable RPM.>If a newer production engine could be selectd in the acceptable>weight class. mods could be made so it pproximates the torque band of the>venerable Model A/B.>..Stroker cranks are an expensive mod, big bore kits somewhat less, but>re-ground camshafts are relatively inexpensive.>>One Piet participant noted the VW is employed in a number of designs of a>sleeker profile than the Air Camper, and a smaller prop is used.>It occurs to me he may be correct.>A "big stick" (large diameter prop) may be the most appropriate for the>Air Camper by means of inherent factors beyond mycapability.>..Yet I can see the logic..>>Reduction drives consitute a comumption of hrsepower that may be avoided>if a crank is strong enough to endure the flex that would be induced by a>flange mounted prop.>A long stroke and appropriate cam would generate sufficent torque at low>RPM for the big stick..>>What cams are available for the Subie may be the next question..>I'm sure many high-torque cams are available for VW's.>..and big bore kits and stroker cranks..>I just happens to have a subie engineand would like to work with it.>>Perhaps they use a moe suitable cam in their 4wd or Brat engines?>TTFN, Rich>>________________________________________________________________________________

Original Posted By: Steve Eldredge
Hello Jim, Well, it occurs to me that a pro is much more effective at lowerrpm where the area of stall speed will only be nearest the tip...Hence, a larger, slower prop is superior to a smaller prop attemptingan equivalent amount of thrust by increased RPM...Torque is required.The Model A and the B improvement were the engine of Bernard's choicebecause they developed sufficent torque and horsepower at low RPM, evenwhe compared with themore advanced engines of today that achieve increasesin both,but at much higher, unuseable RPM.If a newer production engine could be selectd in the acceptableweight class. mods could be made so it pproximates the torque band of thevenerable Model A/B...Stroker cranks are an expensive mod, big bore kits somewhat less, butre-ground camshafts are relatively inexpensive.One Piet participant noted the VW is employed in a number of designs of asleeker profile than the Air Camper, and a smaller prop is used.It occurs to me he may be correct.A "big stick" (large diameter prop) may be the most appropriate for theAir Camper by means of inherent factors beyond mycapability...Yet I can see the logic..Reduction drives consitute a comumption of hrsepower that may be avoidedif a crank is strong enough to endure the flex that would be induced by aflange mounted prop.A long stroke and appropriate cam would generate sufficent torque at lowRPM for the big stick..What cams are available for the Subie may be the next question..I'm sure many high-torque cams are available for VW's...and big bore kits and stroker cranks..I just happens to have a subie engineand would like to work with it.Perhaps they use a moe suitable cam in their 4wd or Brat engines?TTFN, Rich________________________________________________________________________________

Original Posted By: Richard F. Rapp
Rich,Rich,Thanks for the info...maybe someone makes the necessary cam for off-road usefor the VW engine.If I we're back home in the U.S. - I would be going the Model A route, but Iam living in Belgium now and neither A's and Corvairs are all that plentifulhere. I'm not necessarily committed to the VW - just looking for a goodinexpensive alternative that can turn a big prop.Jim-----Original Message-----

Original Posted By:> Jim Wright
> From Steve(at)byu.edu Thu Apr 23 11:06:49 1998> Date: Thu, 23 Apr 1998 16:59:05 +0200

Original Posted By: Jim Skinner
The torque produced by the Ford four bangers at low RPM is the key to swinging a big prop, but don't overlook the other advantage of the early Ford engines. They have a three inch long rear main bearing that handles the props gyroscopic procession loads very nicely. John Mc________________________________________________________________________________

Original Posted By: "Warren D. Shoun"
>The torque produced by the Ford four bangers at low RPM is the key to >swinging a big prop, but don't overlook the other advantage of the >early Ford engines. They have a three inch long rear main bearing >that handles the props gyroscopic procession loads very nicely. >>John Mc>>It seems to me that serious modifications to increase the torque of anengine, such as increasing stoke or bore significantly, would hurtreliability. And an unreliable engine in an airplane could ruin your day.As I understand it, the bottom line is cubic inches. If an engine hasadequate displacement then minor modifications (such as the compressionratio increases for the Ford A and cam timing) will give you good torque output.When Continental came out with their A65 they added cubic inches to theirsmaller engine. Lycomming and Franklin wanted to get a 65 Hp engine on themarket quickly to compete (or so I have been told). So they simply ran theengine at higher speed. They may have done other minor mods but the enginesnever had the cubic inches or the torque of the larger Continential and theperformance difference is VERY noticable. A reduction drive works well with the modern, high speed engines because itallows the engines to run at the higher speeds they were optimized for andallows the prop to run at a lower speed where it is more efficient. Inaddition the reduction can be designed to handle the prop thrust andgyroscopic loads. There is some loss in the reduction unit, of course.The BPA homepage has a link to a good explanation of why the VW is not goodfor a Pietenpol (although it would probably work ok with a reduction drive).Find it at: http://members.aol.com/BPANews/vw.htmlJ ... __________