Original Posted By: owner-pietenpol-list-server(at)matronics.com
Jon,For an experimental, it is whatever you want it to be. Believe it or not.You set the rules. No kidding.Chris Bobka-----Original Message-----
Pietenpol-List: Question about Gross Weight
Pietenpol-List: Question about Gross Weight
Original Posted By: "Christian Bobka"
Can someone on this list tell me how the Gross Weight is calculated for an aircraft?Jon Botsford________________________________________________________________________________
Can someone on this list tell me how the Gross Weight is calculated for an aircraft?Jon Botsford________________________________________________________________________________
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Jon,Chris is right, up to a point. The gross weight is basically set by somestructural parameter in the aircraft, usually the wing spar or the landinggear. You hear of a plane being stressed to +/- 10 G's, well that meansthe structure can handle a certain limit load, and depending on how many G'sthe designer wants the plane to be good for, he divides the limit load bythat number of G's and voila - the gross weight pops out!When I was a young engineer just out of college and was working for GeneralDynamics on the F-16 initial design (sad that a plane designed in 1975 isstill one of our front line fighters), the initial gross weight of the planewas 23,000 lbs. (which meant it could go supersonic straight up with its25,000 lb. thrust engine). Later, some mods to the landing gear enabled itto takeoff with more fuel on board in external tanks and the takeoff grossweight was increased to 37,000 lbs, but its maneuvering gross weight wasstill 23,000.In other words, the gross weight is somewhat arbitrary. However, be awarethat stall speed is a variable and goes up with gross weight. It is quitepossible with a robust structured airplane to have a gross weight that isstructurally safe but simply can't fly because the stall speed is too high.For my Pietenpol, I've figured on a gross weight of around 1100 lbs.Jack -----Original Message-----
Jon,Chris is right, up to a point. The gross weight is basically set by somestructural parameter in the aircraft, usually the wing spar or the landinggear. You hear of a plane being stressed to +/- 10 G's, well that meansthe structure can handle a certain limit load, and depending on how many G'sthe designer wants the plane to be good for, he divides the limit load bythat number of G's and voila - the gross weight pops out!When I was a young engineer just out of college and was working for GeneralDynamics on the F-16 initial design (sad that a plane designed in 1975 isstill one of our front line fighters), the initial gross weight of the planewas 23,000 lbs. (which meant it could go supersonic straight up with its25,000 lb. thrust engine). Later, some mods to the landing gear enabled itto takeoff with more fuel on board in external tanks and the takeoff grossweight was increased to 37,000 lbs, but its maneuvering gross weight wasstill 23,000.In other words, the gross weight is somewhat arbitrary. However, be awarethat stall speed is a variable and goes up with gross weight. It is quitepossible with a robust structured airplane to have a gross weight that isstructurally safe but simply can't fly because the stall speed is too high.For my Pietenpol, I've figured on a gross weight of around 1100 lbs.Jack -----Original Message-----
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: "clif"
To all,Thanks for you insight on gross weight. It is very helpful.jon b----- Original Message -----
To all,Thanks for you insight on gross weight. It is very helpful.jon b----- Original Message -----
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: "clif"
Clif,I've often wondered those things too.But just to add.......was in a hanger and saw an Aeronca (don't know which model) wing with thefabric ripped off. It's amazing to see, the wing had 3/4" wood spars. Theylook like a skinny piece of book shelf. Since then I've pulled some "G's"in one doing steep turns. That memory always pops in my head at thosetimes.walt----- Original Message -----
Clif,I've often wondered those things too.But just to add.......was in a hanger and saw an Aeronca (don't know which model) wing with thefabric ripped off. It's amazing to see, the wing had 3/4" wood spars. Theylook like a skinny piece of book shelf. Since then I've pulled some "G's"in one doing steep turns. That memory always pops in my head at thosetimes.walt----- Original Message -----
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Citabrias also have 3/4" spars, as do Pitts Specials and many otheraerobatic planes. 1" is overkill, which is why BHP routed them down. Iused 3/4" spars fore and aft in my Piet.Jack -----Original Message-----
Citabrias also have 3/4" spars, as do Pitts Specials and many otheraerobatic planes. 1" is overkill, which is why BHP routed them down. Iused 3/4" spars fore and aft in my Piet.Jack -----Original Message-----
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: Michael D Cuy
OK, I should know better than to make blanket statements like "1" isoverkill". Good points, Mike. Citabria spars are (I believe) six inches inheight, but they are also several feet longer than Pietenpol spars. I wasresponding to the remark that some Aeroncas used 3/4" spars. I think 3/4"is a much more common thickness than 1".Before deciding on 3/4" spars for my bird, I ran a quick stress analysis,with a number of assumptions: 3/4" sparsGross weight 1050 lbs 65% of load carried by front spar, 35% by rear spar ultimate tensile stress for Sitka Spruce is 9400 psi no load carried by centersection (actually a pretty fair assumption, itturns out) even lift distribution over entire spar lengthThe result was that with the lift strut fittings as designed by BHP (notin-line with the struts as modern ones are) the wing is good for about 4.9G's. If a more modern lift strut attach point is used, which doesn't impartits own bending moment to the spar, the wing is only good for 3.92 G'sThese are ultimate loads, and I wouldn't expect the wing to survive too longat these loads. This was enough to convince me that Pietenpols have nobusiness doing aerobatics, but are plenty strong for normal fun flying.Jack -----Original Message-----Bernie routed down the center portions of his spars to save weight butdidn't rout thespar caps. The material in the center of a beam (spar) in bending does verylittleother than carry shear loads. This is why there are many spars with the"beef"located at the top and bottom with only a plywood shear web between thecaps.A much more important measurement than the spar thickness is the spar'swidth, fromtop to bottom. Before we go writing off Bernie's spars as overkill onthickness, letsdo a real comparison with these other famously strong wings that includesspar width,length of the wing in actual bending (the Piet wing inboard of the strutattach pointssees less bending load than the outboard portion), comparable flight loads,etc. Ablanket statement that 1" is overkill because something like a Pitts hasthinner sparsis not really supportable.The experiences of a very large number of builders who have successfully andsafelyflown 3/4" spars is certainly more reliable than comparing apples andoranges, but I'mnot sure anyone has any idea how much safety margin is left over whenpullingsignificant flight loads on spars thinner than designed.Mike________________________________________________________________________________Date: Wed, 05 Feb 2003 08:22:23 -0500
OK, I should know better than to make blanket statements like "1" isoverkill". Good points, Mike. Citabria spars are (I believe) six inches inheight, but they are also several feet longer than Pietenpol spars. I wasresponding to the remark that some Aeroncas used 3/4" spars. I think 3/4"is a much more common thickness than 1".Before deciding on 3/4" spars for my bird, I ran a quick stress analysis,with a number of assumptions: 3/4" sparsGross weight 1050 lbs 65% of load carried by front spar, 35% by rear spar ultimate tensile stress for Sitka Spruce is 9400 psi no load carried by centersection (actually a pretty fair assumption, itturns out) even lift distribution over entire spar lengthThe result was that with the lift strut fittings as designed by BHP (notin-line with the struts as modern ones are) the wing is good for about 4.9G's. If a more modern lift strut attach point is used, which doesn't impartits own bending moment to the spar, the wing is only good for 3.92 G'sThese are ultimate loads, and I wouldn't expect the wing to survive too longat these loads. This was enough to convince me that Pietenpols have nobusiness doing aerobatics, but are plenty strong for normal fun flying.Jack -----Original Message-----Bernie routed down the center portions of his spars to save weight butdidn't rout thespar caps. The material in the center of a beam (spar) in bending does verylittleother than carry shear loads. This is why there are many spars with the"beef"located at the top and bottom with only a plywood shear web between thecaps.A much more important measurement than the spar thickness is the spar'swidth, fromtop to bottom. Before we go writing off Bernie's spars as overkill onthickness, letsdo a real comparison with these other famously strong wings that includesspar width,length of the wing in actual bending (the Piet wing inboard of the strutattach pointssees less bending load than the outboard portion), comparable flight loads,etc. Ablanket statement that 1" is overkill because something like a Pitts hasthinner sparsis not really supportable.The experiences of a very large number of builders who have successfully andsafelyflown 3/4" spars is certainly more reliable than comparing apples andoranges, but I'mnot sure anyone has any idea how much safety margin is left over whenpullingsignificant flight loads on spars thinner than designed.Mike________________________________________________________________________________Date: Wed, 05 Feb 2003 08:22:23 -0500
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: "John Dilatush"
Subject: Re: Pietenpol-List: Question about Gross WeightJack,My curiosity compels to ask you, " give me an estimate of G's on a Piet wing (with 1 1/2 degree DIhedral) in a steep turn of 60 to 90 degrees,cruise speed "? ThanksCorky in La________________________________________________________________________________
Subject: Re: Pietenpol-List: Question about Gross WeightJack,My curiosity compels to ask you, " give me an estimate of G's on a Piet wing (with 1 1/2 degree DIhedral) in a steep turn of 60 to 90 degrees,cruise speed "? ThanksCorky in La________________________________________________________________________________
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: "Jack Phillips"
----- Original Message -----
----- Original Message -----
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: "Greg Cardinal"
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: Michael D Cuy
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: Mike [mailto:bike.mike(at)verizon.net]
Mike,Remember also that the "builder's manual" suggests using 3/4" spars and theca. 1960 wing center section supplemental drawing shows 3/4 inch. On thatbasis, it's hard to say that 3/4" is "thinner than designed".Gene-----Original Message-----
Mike,Remember also that the "builder's manual" suggests using 3/4" spars and theca. 1960 wing center section supplemental drawing shows 3/4 inch. On thatbasis, it's hard to say that 3/4" is "thinner than designed".Gene-----Original Message-----
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: Mike
Subject: Re: Pietenpol-List: Question about Gross Weight
Subject: Re: Pietenpol-List: Question about Gross Weight
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: owner-pietenpol-list-server(at)matronics.com
In any plane, with or without dihedral, regardless of cruise speed, a sixtydegree bank will require a 2 G load on the wing, assuming you are neitherclimbing or losing altitude. It has nothing to do with the design of theplane, it's just simple trigonometry. The load on the wing equals theweight of the aircraft divided by the cosine of the bank angle. The cosineof 60 degrees is .5000, so the load is the weight of the plane divided by.5, which is the same as the weight of the plane multiplied by 2. In a 90degree bank, assuming all the lift forces come from the wing, the load onthe wing approaches infinity since the cosine of 90 degrees is zero.Sufficiently confused? Me too.Jack -----Original Message-----
In any plane, with or without dihedral, regardless of cruise speed, a sixtydegree bank will require a 2 G load on the wing, assuming you are neitherclimbing or losing altitude. It has nothing to do with the design of theplane, it's just simple trigonometry. The load on the wing equals theweight of the aircraft divided by the cosine of the bank angle. The cosineof 60 degrees is .5000, so the load is the weight of the plane divided by.5, which is the same as the weight of the plane multiplied by 2. In a 90degree bank, assuming all the lift forces come from the wing, the load onthe wing approaches infinity since the cosine of 90 degrees is zero.Sufficiently confused? Me too.Jack -----Original Message-----
RE: Pietenpol-List: Question about Gross Weight
Original Posted By: owner-pietenpol-list-server(at)matronics.com
You're right Mike, the published "G" loading for an airplane includes a 150%safety factor. That's why I stressed that these were ultimate loads. Thisis a 3 G airplane and should not be used for aerobatics. By the way, when Icontinued with the simple stress analysis I did, I found that without Jurystruts, the lift struts could buckle under as little as 1.0 negative G's,which can be produced by strong turbulence. Jury struts are absolutelynecessary.Jack -----Original Message-----
You're right Mike, the published "G" loading for an airplane includes a 150%safety factor. That's why I stressed that these were ultimate loads. Thisis a 3 G airplane and should not be used for aerobatics. By the way, when Icontinued with the simple stress analysis I did, I found that without Jurystruts, the lift struts could buckle under as little as 1.0 negative G's,which can be produced by strong turbulence. Jury struts are absolutelynecessary.Jack -----Original Message-----
Re: Pietenpol-List: Question about Gross Weight
Original Posted By: "Ken & Lisa Rickards"
Subject: Re: Pietenpol-List: Question about Gross WeightJack,I absolutely agree about the jury struts, and had mentioned this earlier. I realize now were I went wrong on saying build per plans. It seems all the Piets I have seen, including the Last Original have jury struts, so I guessed they were on the plans. Someone corrected me on this oversight, and asked me if I were to follow the plans which do not show the jury struts, then would I also follow the plans by using #7 screws to hold the stabilizer on. Of course not, AN hardware is the way to go, and I would certainly not leave jury struts off either. I think the hole debate had been over some UK Piets having only one jury strut, one is better than none, but for the price I would rather have both.Dan ________________________________________________________________________________
Subject: Re: Pietenpol-List: Question about Gross WeightJack,I absolutely agree about the jury struts, and had mentioned this earlier. I realize now were I went wrong on saying build per plans. It seems all the Piets I have seen, including the Last Original have jury struts, so I guessed they were on the plans. Someone corrected me on this oversight, and asked me if I were to follow the plans which do not show the jury struts, then would I also follow the plans by using #7 screws to hold the stabilizer on. Of course not, AN hardware is the way to go, and I would certainly not leave jury struts off either. I think the hole debate had been over some UK Piets having only one jury strut, one is better than none, but for the price I would rather have both.Dan ________________________________________________________________________________
Re: Pietenpol-List: Airfoil
Original Posted By:
It's the same basic airfoil as the Piet, a Clark "Y", uses 1"spars, front &rear.KenGN1 2992----- Original Message -----
It's the same basic airfoil as the Piet, a Clark "Y", uses 1"spars, front &rear.KenGN1 2992----- Original Message -----