From: "Nat Puffer" Subject: COZY: flutter Date: Sat, 17 Jun 2000 10:27:37 -0500 Builders, We have had the first known case of flutter due to elevators which were not balanced to be nose heavy after painting. Although scarey, it did not result in catastropic failure. Newsletter #70 is at the printers, so we will report on this in Newsletter #71. In the meantime, make sure you heed the warning in the construction manual to check your elevators after painting, and make sure they hang NOSE DOWN!!! Best regards, Nat From: "Nat Puffer" Subject: Re: COZY: flutter Date: Sat, 17 Jun 2000 17:46:00 -0500 Al, The reason flutter occurs when the control surface is out of balance is this: If some turbulence or upset occurs to bend the canard up, the elevator goes up too, but if the trailing edge is heavier than the nose, the trailing edge lags behind, but this causes the canard to generate even more lift and to bend up even higher. The canard reaches its elastic limit on the up-side and starts to come down. But the trailing edge of the elevator is still traveling up. So the elevator ends up trailing edge up as the canard is bending down. So the elevator causes the canard to bend down even lower. The affect of the out-of-balance elevator is to cause the canard to bend up and down more and more until catastropic failure results. Fortunately, the composte construction is so strong that it probably won't fail, but it flutters violently until the pilot is able to slow down enough for it to stop. Regards, Nat > From: alwick@juno.com > To: cozy_builders@canard.com > Subject: Re: COZY: flutter > Date: Saturday, June 17, 2000 1:28 PM > > Appreciate the warning Nat. Only 2 days ago, I determined that I need to > sand off all the paint on my ailerons. One requires 4 oz of lead at mass > area to balance, the other needs 1 oz. Too much paint. > > I don't understand the concept of how mass balance affects flutter. > Anyone care to explain the theory? > > I can see that low total mass might help (less inertia during flutter). > But what does mass balance do? > > -al wick > Canopy Latch System guy. > Artificial intelligence in cockpit, Cozy IV powered by Subaru. > Now assembling. Aug 2000 first flight scheduled > > > On Sat, 17 Jun 2000 10:27:37 -0500 "Nat Puffer" > writes: > > We have had the first known case of flutter due to elevators which > > ________________________________________________________________ > YOU'RE PAYING TOO MUCH FOR THE INTERNET! > Juno now offers FREE Internet Access! > Try it today - there's no risk! For your FREE software, visit: > http://dl.www.juno.com/get/tagj. From: "John Slade" Subject: Re: COZY: flutter Date: Sat, 17 Jun 2000 21:55:03 -0400 Nat, >Fortunately, the composte construction is so strong that it probably won't >fail, but it flutters violently until the pilot is able to slow down enough >for it to stop. Accepting that it should be prevented by correct elevator balance, what is the recommended procedure, should flutter occur? Regards, John Slade From: "Nat Puffer" Subject: Re: COZY: flutter Date: Sat, 17 Jun 2000 19:46:21 -0500 John, Slam on the brakes. As soon as you slow down the speed to approx. 120 kts, it should stop. Slow speed airplanes don't have to worry about flutter, so they don't have to balance their control surfaces. Regards, Nat ---------- > From: John Slade > To: Nat Puffer ; alwick@juno.com; cozy_builders@canard.com > Subject: Re: COZY: flutter > Date: Saturday, June 17, 2000 8:55 PM > > Nat, > >Fortunately, the composte construction is so strong that it probably won't > >fail, but it flutters violently until the pilot is able to slow down enough > >for it to stop. > > Accepting that it should be prevented by correct elevator balance, what is > the recommended procedure, should flutter occur? > Regards, > John Slade > > Date: Sun, 18 Jun 2000 12:41:44 -0400 From: Jim Sower Subject: Re: COZY: flutter Anyone- Given (I intuit) that flutter is a harmonic condition having to do with flexibility of the flying surface (and control surface) and static balance of the control surface, is there any way to make it go away (once it starts) other than slowing down? Will loading the control surface (pull G's for elevator flutter; roll hard for aileron flutter) break the harmonic condition, or is airspeed the only variable that can be influenced in flight? Sounds to me like the procedure would be to pull off power and get the nose up as fast as possible. But loading the surface can be done much more quickly than slowing down, particularly if you encounter the condition in a nose low attitude (which is pretty much the most common place it will happen). Inquiring minds want to know ;-) Jim Sower Nat Puffer wrote: > Al, > The reason flutter occurs when the control surface is out of balance is > this: If some turbulence or upset occurs to bend the canard up, the > elevator goes up too, but if the trailing edge is heavier than the nose, > the trailing edge lags behind, but this causes the canard to generate even > more lift and to bend up even higher. The canard reaches its elastic limit > on the up-side and starts to come down. But the trailing edge of the > elevator is still traveling up. So the elevator ends up trailing edge up as > the canard is bending down. So the elevator causes the canard to bend down > even lower. The affect of the out-of-balance elevator is to cause the > canard to bend up and down more and more until catastropic failure results. > Fortunately, the composte construction is so strong that it probably won't > fail, but it flutters violently until the pilot is able to slow down enough > for it to stop. > Regards, > Nat > > > From: alwick@juno.com > > To: cozy_builders@canard.com > > Subject: Re: COZY: flutter > > Date: Saturday, June 17, 2000 1:28 PM > > > > Appreciate the warning Nat. Only 2 days ago, I determined that I need to > > sand off all the paint on my ailerons. One requires 4 oz of lead at mass > > area to balance, the other needs 1 oz. Too much paint. > > > > I don't understand the concept of how mass balance affects flutter. > > Anyone care to explain the theory? > > > > I can see that low total mass might help (less inertia during flutter). > > But what does mass balance do? > > > > -al wick > > Canopy Latch System guy. > > Artificial intelligence in cockpit, Cozy IV powered by Subaru. > > Now assembling. Aug 2000 first flight scheduled > > > > > > On Sat, 17 Jun 2000 10:27:37 -0500 "Nat Puffer" > > writes: > > > We have had the first known case of flutter due to elevators which > > > > ________________________________________________________________ > > YOU'RE PAYING TOO MUCH FOR THE INTERNET! > > Juno now offers FREE Internet Access! > > Try it today - there's no risk! For your FREE software, visit: > > http://dl.www.juno.com/get/tagj. Date: Sun, 18 Jun 2000 17:55:43 -0500 From: David Domeier Subject: Re: COZY: flutter Re "Obviously pulling back on the stick is the most effective way to slam on the brakes, in addition to chopping power." I agree. The canard flutter I experienced when the prop blade departed stopped almost immediately when the nose was pulled up and the power was cut. That flutter, I believe, was induced by the vibration of the missing blade. (I've had my machine up to 190 knots a couple of times without event) Vibration can be induced by a number of things including a momentary load on the end of the canard in the hangar. It will vibrate for several seconds if it is excited by most anything, but will revert to the calm state when the even that started it is removed. I haven't seen it get going in turbulence, but I'd bet if it was severe enough, there would be moments of flutter caused by it. The insidious thing about elevator induced canard flutter is that it won't go away without slowing below the speed that induced the elevator into motion. When doing your envelope speed expansion, as Mike Melville once said at OSH, do it very carefully. dd Date: Mon, 19 Jun 2000 13:02:14 -0500 From: Mike Pollock Subject: RE: COZY: flutter Early on in the Velocity flight testing, I encountered flutter at 130 knots. Since most of our testing early on was done around 135-140 knots, the flutter was never experienced. Our flutter testing was started at 140 knots IAS up to 210 knots IAS with no hint of any type of flutter. After all testing between 140-210 was completed, I was flying back to my home base. As I slowed to 130 knots IAS, I reached up and tapped the control stick momentaritly to the down position to see how quickly the canard would unload at this speed. What I got was a flutter of about 2-4 Hz with a deflection of the canard tips of about 12". Scared the ?#@1 out of me. I immediately grabbed the stick and retarded the throttle and immediately the flutter stopped. I landed and contacted the Velocity people about the flutter. They informed me that I did not have sufficient torsional strength around the ends of the canard and to add more bid in those areas. Since no other person had experienced this before, I decided to investigate. We balanced our elevators bottom flat per instructions I received from other canard drivers and also from the Velocity factory. Going back to the book, Danny Mayer, the designer of the Velocity says to balance the CHORD of the elevator slightly nose down or level (not the bottom of the elevator). We added extra led to the mass balance weights to balance the CHORD of the elevator slightly nose down. The flutter is now gone at all speeds from stall to 210 knots IAS. Remember, just because someone says to do something a certain way, check to see what the designer says. I feel that I am very lucky..... -- Michael.Pollock@wcom.com Flying Velocity 173RG N173DT Building Cozy MKIV #643