Flutter Testing the Gee Bee Z - Conclusion! - Leon Tolve - Part Two

oh this is weird it's up here it feels like it goes dead back here now then it goes to back here here here and where back here so it's going like this okay your first p-51 rod here we go [Music] this is an amplifier which generates power to operate the vibration exciters it's a two channel amplifier which can go from a frequency from zero frequency all the way up to very high frequencies this little device on top of the amplifier will control the input to the vibration exciters this is an oscillator which will generate the frequency to run the exciters this can go from a frequency of real low frequency to very high frequencies this is an oscilloscope on which we buy can see the vibrations of the accelerometers which are low are located on the wing and this show you two extensors at any location on the wing at the current time we have eight sensors are located on the wing and this will show you any two of them show the phase relationship between them and shows the amplitude of which the sensors are going by this is a frequency meter which will accurately tell you what the frequency is at any particular time this thing is also controlled by this oscillator here whatever the oscillator is given in frequency is sort of rough and this here will make it more precise these are two air conditioners which will take the output from the accelerometers and put them into this two meters which will give you a velocity output which will give you a relative amplitude of which the various sensors are going this can take any one of the eight sensors that we're employing and will show the relative amplitudes of each sensor at any point on the wing we can always look at two sensors at a time so we have two amplifiers to show two sensors of the eight sensors that we have on the air located on the airplane now leon why is it important to isolate just two of the sensors dude the importance is to determine the phase relationship between any eight points on the airplane and also to determine what the amplitude of those particular points are relative to any other particular amplitude since we don't have an awful lot of equipment we can only isolate two of the time to determine what the total response of the airplane is so with taking two at a time of the eight sensors we can essentially determine what the every part of the airplane is doing we can determine what the wingtips are doing or the inboard portion of the wing we can determine what the fuselage is doing we can determine what the tail is doing relative to the wing so it's because of the limitation of equipment two sensors at any particular time will give us all the added information that we need to determine what the particular vibration mode is of the airplane so we're really using those two to determine whether or not what what their phase relationship is and what their amplitude is with two pickups we can determine the amplitude of any portion of the airplane and at the same time we can determine what the phase relationship is at any point of the airplane at the same time so we go two by two we can determine every portion of the airplane what is doing in the amplitude and what a student-in-phase relationship and it's this uh phase relationship and amplitude that is going to tell us where and what we need to do to fix the problem well the phase and amplitude tells us a number of things it tells us what the important vibration modes are and give us an indication as to what vibration modes are important and what we have to do to make sure that the airplane is a safe airplane to fly [Music] [Music] [Music] [Music] so [Music] so [Music] [Music] i changed we're exciting the wing in the tooth lodge mode this is an anti-symmetric mode it's the wings coupling with the fuselage at a frequency of seven cps you can look at the traces right here and the two traces are opposite each other indicating it's going anti-semitically this is wing coupling with the fuselage side bending and fuselage torsion we're now turning the frequency up to the first wing symmetric bending mode which is that 24 cps so now the curves should be now the curves on the oscilloscope should be in phase with each other so symmetrically now the wings are shaking up and down at the same time now this mode here both wings are going up and down at the same time a few charges going down and each wing tip is going up and this is a wing first bending mode now does this relate to any air speed at all or this is just well this is the mode that the wing will flutter in when it if it goes unstable if the ailerons are not properly balanced it will couple this symmetric mode and cause a flooded condition so this is just the frequency that it'll flutter at not necessarily the speed no it really has nothing to do with the speed except at some speed at this frequency the ailerons will couple and generate unstable aerodynamic forces which will cause the wing to be seriously damaged now right now you've got uh accelerometer one and five set in if we change this relationship will it still stay symmetrical no if i change the relationship it all depends what part of the airplane is on now if i change the relationship let's say to pick up number eight it may change we'll change your pickup number eight and see what happens yeah now you can see that pickup number eight has a small amplitude but it's changed face relationship to an anti-submit to a anti-symmetric condition what it means is that between the wing tip and the inboard end of the fuselage where i have the accelerometer that there's a node line and that no line says the phase relationship between the inboard end of this wing and the outboard wing there's a no line across there so it will change the phase relationship and this one here shows yesterday's change the phase relationship from a positive angle to a to a negative value let me just stop it a little bit you can you can see a little bit better but the amplitude is very low with the inboard end of the wing and very large at the outboard of the wing if you look at it very carefully you can see there is a difference once it's out of phase with the others by a small amount indicating that between the inboard wind of the wing and the outboard end there's a note line and the node line is effectively like if you looked at a teeter totter and if one end went up and the other end went down in the middle where there's no movement that's a node line that's right well there's no motion at all there's a note line so with the accelerometers i can actually determine whether there's no motion by moving the accelerometer inboard or outboard and i come to one point there where there's no motion of the wing that's called a note line and the node line is important to know where it is on the wing in relationship to a balance weight to prevent a flutter situation that's right the note lines are very important because they determine what the aerodynamic forces are on the wing okay hold that for a second i just want to see this so the node lines right about here right here because you can feel it yeah go dead here yeah where it goes dead that's the middle of the teeter-totter yeah it is right here right back here yeah now that's torica yeah and it goes dead up here this is interesting this is interesting yeah yeah oh this is weird it's up here it feels like it goes dead back here now then it goes to back here here here and then where back here so it's going like too dark well it could be back here yeah yeah so it's right in here now this would seem logical here that this would be zero because it's huge it'd have to be essentially zero or centerline oh it's the center line then a lot of the airplanes yeah it has to be yeah where the summation of moments has to be zero so it has to be zero there and it has to be zero out here see those are boundary conditions as you can see it's very long here right of course taylor cross here now the anti-symmetric torsion is almost about the same as the symmetric torsion it won't be much different see we'll get that later but anyway you see the anti-symmetric bending the symmetric bending the no line was way in there by the wheel right and this thing here and it can flutter in any one of those modes okay and you know from experience that the frequencies that these modes happen in will determine kind of relate to air speeds but now this air on can't flutter in this mode here because it goes right across the aileron and you got decoupling your aerodynamic gets picked up see okay it won't have it won't float in anti-semitic okay because this air one section out here is balanced by the other one section okay so metric mode it will see because it's completely because it's on one side yeah it's all on one side completely okay coupled with aerodynamically coupled that's the bad mode okay and that's the mode we get a balance for it and in the torsion mode well you got balance for the torsion mode but generally if we balance the bending mode it will take care of the torsion mode but not always but we just have to do it by analysis but generally you probably will because your torsion mode is up in the order of something 30 35 and your bending motor somebody can order about 20 plates uh but it's possible the analysis will show it now how does the frequency that we're getting these different modes at relate to air speed that the airplane flies at it really has nothing to do with it it doesn't no no in other words the only thing that relates the airplane and flying is the aerodynamic forces if the aerodynamic forces are large enough it will tie in with the frequency now the higher the well it doesn't we the higher the frequency the higher your platters feel everything else being equal if i have plenty of frequencies of 10 cycles per second bending at frequencies at 20 cycles per second my photo speed's gonna be twice as great so that's how it ties in the frequency but the basic one is your basic frequency and here would be about you know put out about 20 25 gps but the only thing is the higher the frequency the more critical the color mode is the more explosive it is so well if i had if i had a frequency of 5 cps it wouldn't be very explosive but when i get up to a frequency of 25 cps they'll be very explosive yeah because of the amount of energy the energy depends upon the air speed and the frequency and if i have the higher frequency the higher the frequency the more explosive the most gonna be because of the uh the location of the weight relative to the yellow line it's pretty good two-dimensionally which is what we were thinking on the stevens the monoplane that jerry got killed in we had a balance we had it 110 balance but we were only thinking two-dimensionally and when leon first came out and started doing the shake and ran his hand over the wing he felt the node line where it was supposed to go the way it was supposed to be behind it it actually went behind the middle line it was sport and it aggravated the situation so the fix was to put weight behind the note line for torsion but for bending you still need it outward so we had a little bit of the tip for the bending consideration but we had to have some further inboard to get it behind the node line for torsion and that was the fix on the steam i think you have a very serious problem here you have an excessive amount of free play in the aileron so i would say with that amount of free of play you probably get into a weather condition just about at any high speed even at low speed you probably get into a flooded condition the only thing that's saving you it looks like is the friction in the system that's getting it from flutter until you get to a fairly high speed so i would advise you not to even fly this airplane probably faster than about 120 miles an hour i know that's just about your takeoff speed but that's about what you shouldn't in other words don't fly the airplane until you get it fixed well i guess we've probably been living on borrowed time here for i would i would essentially say that anytime you even fly this airplane probably you know maybe a hundred less than a at lower speeds or let's say a maximum speed 115 hours 150 miles an hour you're probably living in borrowed time well i think the airplane's only got about probably 12 hours total right well you're very fortunate that you probably in your flight you've been flying you probably don't have hit the right gust condition that would cause the aileron to break the friction loose and allow it to get into a further condition but before you fly the airplane again it needs to be properly balanced so [Music] [Music] i think it's a it's a good thing that we ended up selling the airplane to you and that you have the your because of your past experience with flutter issues and things had the wherewithal to go ahead and see about getting the thing taken care of evaluate it find out what's going on and really solve the problem before there is a problem yeah i think i think if anybody else had bought the airplane they ultimately would have had an accident right now you're basically going to run through the different frequencies take some specific measurements yeah to swap the node lines yeah yeah and then you'll transfer all that to the drawing that i'm going to bring you to come up with some of the various changes yeah yeah he balanced weights in the aileron and and how much balance weight right you understand all this what i've been giving about yeah basically yeah we're following along very interesting the main thing is we got a safe airplane to pull out yeah yeah but how fast do you want to fly the airplane i i think by looking at the numbers to see what it's going to take to even get it within some reasonable parameters and then if we want to go a little more well then maybe that's something we can play with but the first thing is if we have an unsafe airplane to fly right now we've got to make it safe to fly at any speed you know so um because it's a you know it's a very historic airplane it's something people would enjoy seeing flying you know as safe i'm sure you would love to see it continue to fly you know as long as somebody can fly it in a safe manner but uh i don't want to get in it unless it is safe and uh anyway we need to uh make sure it is safe yeah so if you put a balance weight on it which just projects underneath here you really don't see it no you don't i would end up painting a black or something you know and what we're talking about doing leon is possibly developing in a way to where we put the balance weight on it but if we want to take it off for some original still shots or something you know then we can screw it out relatively easy but you know we'll see yeah the fact that we've got a gb that's got a thing and they say that's not original yeah well guess what we got to you can do anything you want we don't have to certify it with the saa no you have to certify it with me and god everyone else is secondary everyone else is secondary that's right let me get the air conditioner going okay [Applause] there we go [Applause] [Applause] [Applause] okay your first p-51 rod here we go [Music] pretty smooth huh smoother than my set to 140. okay we'll do a couple of fly-bys for them [Music] [Applause] [Music] you want to do some aerobatics yeah we'll go out and do a roll or two for you okay just real simple we'll just do an aeron roll okay that just looks straight ahead yeah i can keep it positive so you don't feel like you're going to fall out of the seat there's delay see you know that will be one four point row not bad i have about a half [Music] not a bad landing pretty good for an amateur [Applause] [Music] [Applause] [Music] okay you got it there you go you got it good deal well i enjoyed it kerbet what do you think huh very good well this is the man that did the flutter testing so uh so what do you think of the p-51 now pretty good airplane pretty good airplane well they wouldn't have lasted as long as if you hadn't have uh done uh the proper testing so i hope so yeah thank you for coming [Music] [Music] [Music] [Music] you

Channel: Kermit Weeks Channel - Over 360 Videos to See!

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Id: ZymXOrPL1CQ

Length: 32min 36sec (1956 seconds)

Published: Thu Sep 30 2021