> Pietenpol-List: Re: Speaking of outdated stuff? Center section f

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> Pietenpol-List: Re: Speaking of outdated stuff? Center section f

Post by matronics »

Original Posted By:> jarheadpilot82(at)hotmail.com
Sorry I think you are making the wrong conclusion. Your weight has nothing to do with it. You simply don't fly if there is an aft CG and having the fuel in the wing just makes the problem worse.Running out of fuel (or nearly running out of fuel) in a nose tank versus the same in a wing tank (or nearly running out of fuel) cannot make the situation worse. If the fuel is gone it is gone. The difference that in a nose tank is that any fuel moves the CG forward at everything but empty. Since no one can fly on empty it is always better in the nose than in the wing and the amount of weight added to the nose=2C the length of the engine mount or the amount the wing is moved back is less and on average the cg is more forward. There is also the 15lbs or more of the tank weight itself that is helping the aft cg problem all they time. The 10 lbs (or whatever you consider that to be) of reserve fuel that no one ever uses is also helping. If you weigh more and it is your airplane then it is more important that the fuel is forward.> Subject: Pietenpol-List: Re: Speaking of outdated stuff? Center section fuel tanks vs. n
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> Pietenpol-List: Re: Speaking of outdated stuff? Center section f

Post by matronics »

Original Posted By:> jarheadpilot82(at)hotmail.com
sorry I wasn't clear so if you didn't follow my logic maybe I can try again. Of course the weight of a pilot matters and you must compensate for it.I was responding to the concept that if a heavier pilot is in an airplane and the fuel burns off in a front tank that the CG moves behind the aft limit. That is not necessarily so.While that could occur the idea is to move the adjust the aircraft CG so as the fuel burns off it does not move to behind an aft CG limit and therefore the weight of the pilot doesn't matter if you do that. That was my point.When you complete an airplane you make sure by calculation that the aircraft stays in the CG range with a certain pilot weight. If you design it for you and you are 200 lbs then you adjust the aircraft to fly safely by three of the methods I mentioned. I weigh over 200 and this in not a problem in my aircraft. So to my original point. You have a moveable object in the aircraft=2C that for argument sake=2C weighs 25 lbs (in this case - tank plus reserve fuel) and you move it forward the CG moves forward. Add another 75 lbs of fuel and it has even a bigger effect. Yes a tank directly on the CG it has less effect on trim=2C but if you have an AFT CG problem then moving it forward helps this problem. Likewise if you had a forward GC problem you would want to shift weight back.Pietenpol`s with A65 continentals typically have this problem that requires a long engine mount and moving the wing back or both. Both changes reduces the directional stability of the airplane. Add a heavy center section wing tank and the problem gets bigger.I have seen three Piets with this problem. These are extreme examples. Two of them moved the pilot to the front seat and made a two seater into a one seater. The third had a about 25 lbs bolted to the engine. Then there was the guy that was flying at 22.2 ins behind the leading edge - he sold it because he knew he was going to kill himself! The new buyer fixed the problem by moving the wing. > Subject: Pietenpol-List: Re: Speaking of outdated stuff? Center section fuel tanks vs. n
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> Pietenpol-List: Re: Speaking of outdated stuff? Center section f

Post by matronics »

Original Posted By:> tkreiner(at)gmail.com
Tom being similarly educated I have thought about this too. Yes you could conclude that the horizontal stabilizer is not at the correct angle however here is some more to think aboutI think in reality the more correct assumption is that angle of incident of the wing is incorrect - this is important - wait for it - because these aircraft are flying too fast. The Air Camper was designed for an engine that produced less power than most of the ones flying. If you reduce the power the trim changes and the elevator position changes and this slightly down elevator position changes from slightly down to level and if you are slow enough to up. When I first built my aircraft it had an engine problem and it was producing an estimated 40 to 45 horsepower. I needed a fixed trim to give the elevators an up position to adjust the nose down trim. While this a true observation it creates another mystery? Why does flying faster not do the opposite? Asymmetrical airfoils have a negative pitching coefficient. What this means is that the air coming off the tailing edge is at a downward angle and this is behind both the center of pressure and center of gravity so there is a torque created that wants to rotate the wing nose down. If you have every thrown a model wing without a tail you will observe that the wing just dives. The amount of this torque increases the faster you fly. In many aircraft the tail or elevator trim has to be adjusted to increase the negative tail lift or to say it another way to increase the down force on the tail. So flying faster should mean the opposite to what is observed in reality with an Air Camper.Here is why I think the Air Camper is different. The wing is higher than the tail. As the wing downwash exits the trailing edge it hits the horizontal tail and automatically compensates for the increasing negative pitching moment. This is not a feature of just the Pietenpol but many high wing aircraft. The faster I fly the more I have to push the elevator down (stick forward)- totally counter intuitive. The correction to this problem is if you are going to fly faster you need to reduce the lift on the wing at the higher speed and that means you need to reduce ever so slightly the wing incidence. Here is another way to look at it and it demonstrates why this is the fix if you want to fly faster. If you use more power the angle of the wing to the horizon changes. This is because the lift is increasing with speed. You can get this wing "up on the step"=2C as some people call it=2C so far the bottom of the wing is on a negative angle to the horizon. That means the by that point the fuselage is pointing down quite significantly. So at that speed the wing is lifting and the fuselage is diving. So you are really starting to increase the drag and aerodynamically the airplane trying to separate the wing from the fuselage. So decreasing the angle of incidence would reduce the negative angle at that speed and reduce the drag for that speed and allow the aircraft to fly even faster. In reality everything is just fine if the elevator is pointing down slightly and the aircraft is completely stable and safe. The mystery of the Air Camper continues - why is it so good? > Subject: Pietenpol-List: Re: Speaking of outdated stuff? Center section fuel tanks vs. n
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> Pietenpol-List: Re: Speaking of outdated stuff? Center section f

Post by matronics »

Original Posted By:> curtdm(at)gmail.com
It is not an illusion but it requires two things to be happening for it to happen and to be obvious The aircraft need to be lightly loaded and the airplane needs to be flying fairly fast. If the CG is forward it is less likely to happen as well. > Subject: Pietenpol-List: Re: Speaking of outdated stuff? Center section fuel tanks vs. n
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Post by matronics »

Original Posted By: "Cuy, Michael D. (GRC-RXD0)[Vantage Partners, LLC]"
> To: pietenpol-list(at)matronics.com> tmail.com>> > Oscar=2C> > Thanks for the input. Your clear explanation was the reason for my question. It sounds like running your nose tank low puts the non-standard weighing guy like me in an aft CG condition that may put the aircraft beyond the recommended aft CG limit. I also get it that you have flown in that regime with little to no consequence. > > But my question still boils down to risk management. Are we trading one risk (fuel in the center section=2C a potential risk in the event of a crash which one hopes never happens) for another risk (nose tank which has the capacity to affect every flight=2C but definitely affects longer flights with greater fuel burn). That is not an area that in which I would want to fly on a regular basis.> > The nice thing about your long=2C clear explanation is that a beginning builder can write in and post this same question a year from now and someone can answer back=2C "Look it up. It is in the archives" [Wink]> > --------> Semper Fi=2C> > Terry Hand> Athens=2C GA> > USMC=2C USMCR=2C ATP> BVD DVD PDQ BBQ> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 974#420974> > > > > > > ============================================> > > ________________________________________________________________________________
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Post by matronics »

Original Posted By: Michael Perez
> To: pietenpol-list(at)matronics.com> tmail.com>> > Brian=2C> > I am not getting your logic-> > "Your weight has nothing to do with it. You simply don't fly if there is an aft CG and having the fuel in the wing just makes the problem worse."> > Fuel in the wing makes it worse? How is that? Fuel in the wing sits closer to the CG than fuel in the nose=2C and the burn off affects CG less=2C not more the closer it is to the aircraft's CG.> > "Running out of fuel (or nearly running out of fuel) in a nose tank versus the same in a wing tank (or nearly running out of fuel) cannot make the situation worse. If the fuel is gone it is gone. The difference that in a nose tank is that any fuel moves the CG forward at everything but empty. Since no one can fly on empty it is always better in the nose than in the wing and the amount of weight added to the nose=2C the length of the engine mount or the amount the wing is moved back is less and on average the cg is more forward. There is also the 15lbs or more of the tank weight itself that is helpingthe aft cg problem all they time. The 10 lbs (or whatever you consider that to be) of reserve fuel that no one ever uses is also helping. "> > Brian=2C I am not worried about the fuel that is left in the nose tank. I am worried about the fuel that burned off that was=2C at one time=2C forward of the CG that was balancing against my fat butt sitting behind the CG. Once that fuel has burned off=2C there is less weight to counteract my fat butt=2C so the CG moves aft. Check your aerodynamics and design books. I just don't want to move it so far aft=2C that the airplane is aft of the safe aft CG. That can be mitigated in the construction phase by adjustment of the wing location=2C and all I am saying is that that issue should be dealt with in the build. Nobody should fly an airplane outside of the CG range. Will the airplane fly? Yes. Are your options lessened when you do? Absolutely. > > "If you weigh more and it is your airplane then it is more important that the fuel is forward."> > It is most important that the CG is balanced=2C and the aircraft is flown in the proper CG range.> > --------> Semper Fi=2C> > Terry Hand> Athens=2C GA> > USMC=2C USMCR=2C ATP> BVD DVD PDQ BBQ> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 985#420985> > > > > > > ============================================> > > ________________________________________________________________________________Date: Tue, 25 Mar 2014 08:14:07 -0700 (PDT)
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Post by matronics »

Original Posted By: Brian Kenney
> To: pietenpol-list(at)matronics.com> > > Cliff=2C> > In response to your question=2C "Doesn't everything below it act like a > pendulum? > > The short answer is NO=2C that said=2C some explanation is required...> > In a properly designed and built airplane - the designer sets the CG so that the plane is slightly nose heavy=2C which=2C in flight=2C requires an equal and opposite tail down force. Now on the surface this may appear to be a pendulum=2C but in fact=2C its quite different. > > The purpose of nose heavy=2C coupled with tail down force is what gives us pitch stability. In other words=2C the plane will tend to stabilize itself in flight when you take your hands off the stick - and return to whatever pitch it's trimmed for=2C assuming=2C of course=2C that you've trimmed the plane for a given pitch attitude=2C i.e.=2C climb=2C cruise=2C descent.> > What is somewhat bothersome is that many on the list have indicated that the elevator on a Piet "droops" during cruise flight=2C when in fact=2C the elevator should be slightly up=2C in order to provide the tail down force.> > Perhaps the horizontal stabilizer on the Piet is - HERESY COMING - improperly designed=2C but satisfactory. If the angle of incidence of the stab were changed somewhat=2C this condition might be corrected...> > Personally=2C I'd like for Jack Phillips and a few of the others to comment on the drooping issue=2C as I'd like to make sure the plane I build is flying "correctly."> > I KNOW=2C I KNOW=2C I KNOW=2C BUILD IT PER THE PLANS=2C AND IT WILL FLY.... that still doesn't satisfy the Mechanical Engineer I am.... just sayin.> > --------> Tom Kreiner> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 126#421126> > > > > > > ============================================> > > ________________________________________________________________________________
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Post by matronics »

Original Posted By: "Gary Boothe"
> To: pietenpol-list(at)matronics.com> .com>> > My theory of the elevator droop is it could be an optical illusion. The outboard line from the elevator and horizontal stabilizer is bent because of the leading edge of the horizontal stabilizer not having the same span as the rest of the tail. > > I had this discussion and wanted to do some testing at Brodhead last year=2C but because of lack of time I was unable. > > I propose those who could=2C prior to Brodhead=2C set=2C their elevators in a faired (neutral) position and and somehow temporarily make a mark on their torque tube and the cable just above. > Then go fly and compare in cruise flight if the marks are aligned yet. If not=2C make another mark to show the difference. > > Also while the tail is faired neutral on the ground=2C sit in the cockpit and look over your shoulder and look or take a picture of the tail and let us know what it looks like. Take pictures in slightly up and down elevator position. > > This is a great exercise not only to prove my theory right/wrong=2C but also like Tom said=2C the tail should always be creating downforce while flying and if elevators are drooping=2C the horizontal stab might need some shimming and re-rigging. > > My planes not flying and I'm definitely not an Opthamolagist=2C he'll I don't even think I can spell.> > --------> Curt Merdan> Flower Mound=2C TX> > > > > Read this topic online here:> > http://forums.matronics.com/viewtopic.p ... 132#421132> > > > > Attachments: > > http://forums.matronics.com//files/image_545.jpg> > > > ============================================> > > ________________________________________________________________________________
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