Original Posted By: "Christian Bobka"
Chris,Since the subject of tail volume has come up in the recent e-mails, I thought thatthis might be interesting.When I first started my Piet in '95 using the long fuselage, I was concerned aboutthe small vertical fin and rudder. I then computed both the vertical andhorizontal tail volumes using the formulas quoted by David Thurston in his book"Design for Flying"These calculations showed that the tail volumes of the Pietenpol are woefully shortof modern standards. The Piet vertical tail volume came out to .1389 anda modern standard is .30. The horizontal tail volume was .31389 vs. .55All this adds to the difficulty in increasing the nose moment of a Pietenpol whenmounting a lighter engine such as an A65 or Corvair to the plane to maintainW&B. Since a Model A powered Pietenpol is notoriously known to be slightly tail heavy,I thought it was worth considering using a more powerful engine that is heavierand has more horsepower. This both corrects to tail heavy condition withoutmoving the wing back and also keeps from aggravating the tail volume problem.My solution using the turbocharged Subaru engine seems to have worked to solveboth problems, although the plane doesn't slip as well as one using a lighterengine and longer nose moment.Cordially,John________________________________________________________________________________
Pietenpol-List: Tail Volume
Pietenpol-List: Re: Tail Volume
Original Posted By: John Dilatush
John,You have to remember that the tail volume is necessitated by the pitching momentof the airfoil. As pitching moment increases, tail volume must increase. Ifthere is zero pitching moment, you don't even need a tail, like the flying wings.So the piet's airfoil must fall somewhere between what is common todayand a zero pitching moment airfoil.It flies ok so it must have enough TV.Also, if the tails are bigger, more CG range may be available. This is importantfor a four seater where it has to remain in balance without the use of ballastwhen only a pilot is aboard with full fuel vs. all four seats filled, fullbags, and as much fuel as possible to bring the ship up to gross weight.Chris ----- Original Message -----
John,You have to remember that the tail volume is necessitated by the pitching momentof the airfoil. As pitching moment increases, tail volume must increase. Ifthere is zero pitching moment, you don't even need a tail, like the flying wings.So the piet's airfoil must fall somewhere between what is common todayand a zero pitching moment airfoil.It flies ok so it must have enough TV.Also, if the tails are bigger, more CG range may be available. This is importantfor a four seater where it has to remain in balance without the use of ballastwhen only a pilot is aboard with full fuel vs. all four seats filled, fullbags, and as much fuel as possible to bring the ship up to gross weight.Chris ----- Original Message -----
Tail Volume
Original Posted By: dave rowe
Re: Pietenpol-List: Re: Tail Volume
Original Posted By: "Christian Bobka"
Subject: Re: Pietenpol-List: Re: Tail VolumeIn a message dated 1/24/04 11:22:51 AM Central Standard Time, bobka(at)compuserve.com writes:>The Pietenpol, as well as any undercambered airfoil, has a lot of negative pitching moment (nose down). I believe this is why the Piet is somewhat tolorant of an aft C.G. That's the thing I've always been curious about, is whyPietenpols are more forgiving for an aft C.G. condition. B.H.P called out 1/3(33.3%) of the chord, as the aft limit. I've never seen, or heard of any otherplane with the aft C.G. limit that far back. Most designs call out no more than 30% of the chord for the aft limit, but they are not undercambered. (Tailwind calls out 28% as the aft C.G. limit). I think this is because an undercambered airfoil has such a high negative pitching moment, that it is moreforgiving of an aft C.G. I've tried unsuccessfully to find the aft C.G. limitof planes like the Jenny, but it is a Biplane - difficult to compare. Another design that has an undercambered airfoil is the Ryan Navion. Does anyone havethe C.G. range of the Ryan Navion, or any other plane that has an undercambered airfoil ?Chuck GantzerNX770CG________________________________________________________________________________
Subject: Re: Pietenpol-List: Re: Tail VolumeIn a message dated 1/24/04 11:22:51 AM Central Standard Time, bobka(at)compuserve.com writes:>The Pietenpol, as well as any undercambered airfoil, has a lot of negative pitching moment (nose down). I believe this is why the Piet is somewhat tolorant of an aft C.G. That's the thing I've always been curious about, is whyPietenpols are more forgiving for an aft C.G. condition. B.H.P called out 1/3(33.3%) of the chord, as the aft limit. I've never seen, or heard of any otherplane with the aft C.G. limit that far back. Most designs call out no more than 30% of the chord for the aft limit, but they are not undercambered. (Tailwind calls out 28% as the aft C.G. limit). I think this is because an undercambered airfoil has such a high negative pitching moment, that it is moreforgiving of an aft C.G. I've tried unsuccessfully to find the aft C.G. limitof planes like the Jenny, but it is a Biplane - difficult to compare. Another design that has an undercambered airfoil is the Ryan Navion. Does anyone havethe C.G. range of the Ryan Navion, or any other plane that has an undercambered airfoil ?Chuck GantzerNX770CG________________________________________________________________________________
Re: Pietenpol-List: Re: Tail Volume
Original Posted By:
Chuck,Excellent observation. I have no data on the Navion but will look later.The Type Certificate Data Sheets are available on the FAA website.Chris----- Original Message -----
Chuck,Excellent observation. I have no data on the Navion but will look later.The Type Certificate Data Sheets are available on the FAA website.Chris----- Original Message -----
Re: Pietenpol-List: popsicle sticks and tramelling
Original Posted By: "Michael D Cuy"
Michael,Great info for those of us who have to build the wings. Keep the tipscoming.'Question, on your video tape you mention "dead soft stainless " for thefirewall. I have made inquires with sheet metal men, aircraft mechanics andfellow homebuilders and no one can answer, what it is or where may I get"dead soft stainless". Can you give me a number associated with it? Suchas 2024-T3 is the aluminum in my RV aircraft. The stainless should have adesignator for ordering purpose.Thanks.Alex Sloan----- Original Message -----
Michael,Great info for those of us who have to build the wings. Keep the tipscoming.'Question, on your video tape you mention "dead soft stainless " for thefirewall. I have made inquires with sheet metal men, aircraft mechanics andfellow homebuilders and no one can answer, what it is or where may I get"dead soft stainless". Can you give me a number associated with it? Suchas 2024-T3 is the aluminum in my RV aircraft. The stainless should have adesignator for ordering purpose.Thanks.Alex Sloan----- Original Message -----
Pietenpol-List: popsicle sticks and tramelling
Original Posted By: Clif Dawson
Re: Pietenpol-List: Re: Tail Volume
Original Posted By:
Hi,There was a UK homebuilt with a 16% thick gottingen 535 wing section -heavily undercambered - it's CofG range was 25% - 35% and it needed atailplane incidence of +3 degrees. Didn't go very fast!Phil Humphrey----- Original Message -----
Hi,There was a UK homebuilt with a 16% thick gottingen 535 wing section -heavily undercambered - it's CofG range was 25% - 35% and it needed atailplane incidence of +3 degrees. Didn't go very fast!Phil Humphrey----- Original Message -----
Re: Pietenpol-List: Re: Tail Volume
Original Posted By:
Subject: Re: Pietenpol-List: Re: Tail Volume ----- Original Message -----
Subject: Re: Pietenpol-List: Re: Tail Volume ----- Original Message -----
Re: Pietenpol-List: Re: Tail Volume
Original Posted By: "Christian Bobka"
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Re: Pietenpol-List: Re: Tail Volume
Original Posted By: "John Dilatush"
John,From "Simple Aerodynamics" by Charles Monteith, April 1924, a text book usedat West Point, page 72 says,"When an airfoil is at the angle of attack of zero lift, there is a downloadon the front part of the airfoil and an up load on the rear portion, whichmanifests itself as a negative or diving moment."On the undercambered RAF-15 airfoil, the CP in % of chord plot is asfollows:AOA CP0 492 384 346 318 3010 2912 3014 34This is a very shallow CP plot meaning that there is small shift in the CPwith changes in AOAAs long as the CG is forward of the CP, ignoring a few other unimportant tothis discussion factors, it is obvious that the lifting forces are summedbehind the CG. This would couse the nose to go down "which manifests itselfas a negative or diving moment."The RAF 15 displays the characteristic movement of the CP forward as the ahigher and higher AOA is achieved getting as far forward as 29% of chord at10 degrees AOA.In comparison, the USA-35B, which is used on the J-3 Cub, has the followingCP v AOA plot:AOA CP in % of chord-4 120-3 70-2 600 452 404 366 348 3310 3212 3114 3016 30.5This is a very steep plot at the beginning meaing that as AOA decreases, theCP moves way aft. As a matter of fact the plot I looked at shows the CP tobe 20% behind the wing trailing edge at a -4 degree AOA! That is a negativepitching moment for you!I partially agree with your buddy. The pitching moment appears to be lesstraveled with the undercambered airfoil. But nose down is negative!Chris----- Original Message -----
John,From "Simple Aerodynamics" by Charles Monteith, April 1924, a text book usedat West Point, page 72 says,"When an airfoil is at the angle of attack of zero lift, there is a downloadon the front part of the airfoil and an up load on the rear portion, whichmanifests itself as a negative or diving moment."On the undercambered RAF-15 airfoil, the CP in % of chord plot is asfollows:AOA CP0 492 384 346 318 3010 2912 3014 34This is a very shallow CP plot meaning that there is small shift in the CPwith changes in AOAAs long as the CG is forward of the CP, ignoring a few other unimportant tothis discussion factors, it is obvious that the lifting forces are summedbehind the CG. This would couse the nose to go down "which manifests itselfas a negative or diving moment."The RAF 15 displays the characteristic movement of the CP forward as the ahigher and higher AOA is achieved getting as far forward as 29% of chord at10 degrees AOA.In comparison, the USA-35B, which is used on the J-3 Cub, has the followingCP v AOA plot:AOA CP in % of chord-4 120-3 70-2 600 452 404 366 348 3310 3212 3114 3016 30.5This is a very steep plot at the beginning meaing that as AOA decreases, theCP moves way aft. As a matter of fact the plot I looked at shows the CP tobe 20% behind the wing trailing edge at a -4 degree AOA! That is a negativepitching moment for you!I partially agree with your buddy. The pitching moment appears to be lesstraveled with the undercambered airfoil. But nose down is negative!Chris----- Original Message -----
> > Re: Pietenpol-List: Re: Tail Volume
Original Posted By: Michael D Cuy
Re: Pietenpol-List: Re: Tail Volume
Original Posted By: "Deon Engelmann"
Chris,I just read your post about the need to add more tail volume if you extend theengine forward. A good point, but also consider when you move the wing aftyou do two things... decrease tail moment and increase the distance ahead of theCG. A double edged sword. Moving the engine forward is the lesser of thetwo evils IMO.DJ=This email has been scanned for known viruses and made safe for viewing by Half Price Hosting, a leading email and web hosting provider. For more information on an anti-virus email solution, visit .________________________________________________________________________________
Chris,I just read your post about the need to add more tail volume if you extend theengine forward. A good point, but also consider when you move the wing aftyou do two things... decrease tail moment and increase the distance ahead of theCG. A double edged sword. Moving the engine forward is the lesser of thetwo evils IMO.DJ=This email has been scanned for known viruses and made safe for viewing by Half Price Hosting, a leading email and web hosting provider. For more information on an anti-virus email solution, visit .________________________________________________________________________________
Re: Pietenpol-List: Re: Tail Volume
Original Posted By: "Christian Bobka"
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Re: Pietenpol-List: dead soft stainless and aluminum
Original Posted By: "Michael D Cuy"
Mike,Thanks a lot. I will call mr Vogelsong.Alex Sloan----- Original Message -----
Mike,Thanks a lot. I will call mr Vogelsong.Alex Sloan----- Original Message -----
Re: Pietenpol-List: Re: Tail Volume
Original Posted By: "Deon Engelmann"
Subject: Re: Pietenpol-List: Re: Tail VolumeIn a message dated 1/26/04 11:19:25 AM Central Standard Time, dilatush(at)amigo.net writes:>John et all, I got a lot of my info from a friend that has done lots of research on airfoils, and has all the expensive software to design his own, which he has done. His name is Mike Schuck. He's not a Piet builder, but has lots of interest and experience in evaluating airfoils. He explained to me that a negativepitching moment, is a nose down condition. Let's look at the wing by itself in a wind tunnel. Think about it...at zero degrees angle of attack (AOA) and undercambered airfoil will certainly pitch nose down. Flat bottom airfoil will pitch down some, and a symmetrical airfoil has NO pitching moment. Some laminar flow airfoils, that are somewhatsemi-symmetrical, have the trailing edge reflexed up a little, to counteract the negative pitching moment, therefore using a smaller horizontal stab. I'm still maintaining the opinion that the undercambered airfoil of the Piet is thereason it is somewhat tolerant of an aft C.G. condition.Chuck Gantzer________________________________________________________________________________
Subject: Re: Pietenpol-List: Re: Tail VolumeIn a message dated 1/26/04 11:19:25 AM Central Standard Time, dilatush(at)amigo.net writes:>John et all, I got a lot of my info from a friend that has done lots of research on airfoils, and has all the expensive software to design his own, which he has done. His name is Mike Schuck. He's not a Piet builder, but has lots of interest and experience in evaluating airfoils. He explained to me that a negativepitching moment, is a nose down condition. Let's look at the wing by itself in a wind tunnel. Think about it...at zero degrees angle of attack (AOA) and undercambered airfoil will certainly pitch nose down. Flat bottom airfoil will pitch down some, and a symmetrical airfoil has NO pitching moment. Some laminar flow airfoils, that are somewhatsemi-symmetrical, have the trailing edge reflexed up a little, to counteract the negative pitching moment, therefore using a smaller horizontal stab. I'm still maintaining the opinion that the undercambered airfoil of the Piet is thereason it is somewhat tolerant of an aft C.G. condition.Chuck Gantzer________________________________________________________________________________