cliffy Posted July 7 Report Posted July 7 I ran across some notes about Mooneys and one repeating something Bill Wheat (preeminent Mooney test pilot) said about flutter on Monneys. The note said- Wheat said flutter is not possible in an Mooney. He observed that the control surface hinge-lines are not 90-degrees to the longitudinal axis making flutter impossible I'm trying to get my head wrapped around this statement. I presume he was referring to the stabilizer/elevator and the rudder hinge lines as both "cant' forward from their inboard position and I can just visualize maybe what he was referring to but my "schooling " in aerodynamics wasn't as deep as this postulation goes. Can any aerodynamic engineer around here expound on this specific subject? Quote
N201MKTurbo Posted July 7 Report Posted July 7 This statement is true as far as the hing lines are concerned with regard to the ailerons, but not the elevator or rudder. Quote
cliffy Posted July 7 Author Report Posted July 7 So, he was referring to the ailerons and not the tail feathers- OK Would you be willing to expand and educate me on the subject or point me to information I can find on the subject? I am very interested to fully understand the concept. Quote
Pinecone Posted July 7 Report Posted July 7 It will be interesting to see what an expert says. But many aircraft have hinge lines that are not 90 degrees to airflow. And they can have control surface flutter. If it was that easy to prevent, why would any aircraft have 90 degree hinge lines. This video shows surfaces on a swept wing exhibiting flutter - https://www.instagram.com/uwaeroastro/reel/DHRJAHTvWw4/ 1 Quote
MikeOH Posted July 7 Report Posted July 7 Not an AE, but the 90 degree thing sounds suspicious to me (as an EE). IF it was true, then at what angle off 90 is sufficient to prevent flutter? Is 85 good? Or?? Seems to me the onset of flutter is waaay more complicated than just hinge angle (which, I'm sure, plays a part). 1 Quote
KSMooniac Posted July 7 Report Posted July 7 That is not an aerodynamically accurate statement by Mr. Wheat. It is quite possible that a Mooney flutter speed is dramatically higher than anything the airframe can achieve, but the angle of the control surface hinge line relative to the longitudinal axis has very little to do with it. (degreed Aerospace Engineer but not a practicing aerodynamic engineer. I did take an upper-level Aeroelasticity course long ago, and have stayed at Holiday Inns, though.) 3 Quote
CCAS Posted July 7 Report Posted July 7 (not an aerospace engineer but...) I always thought aerodynamic flutter could affect any lifting or control surface and wasn't limited to hinged components. Several videos online show flutter on a variety of aircraft. My favorite is the Twin Comanche classic: 2 Quote
KSMooniac Posted July 7 Report Posted July 7 Flutter in its simplest terms relates to the interaction in a lifting force and the structural response of the vehicle. There are a LOT of potential flutter modes from simple wing bending (think bird wing flapping) to twisting, or bending + twisting, or a single control surface flapping, or a combo of control surface + wing (or empennage). Then there are modes associated with engines mounted on wings or tails, or fuselage bending & twisting, etc. The first and easiest failure to visualize is called "divergence" where the aero load simply exceeds the capability of the structure and something breaks in a single load application because of the deflection causing an increased aero load. Flutter is what can happen without a simple divergent failure, as it is a dynamic condition where there are tons of variables, and the modes are driven by the aerodynamic input, the structural response (think deflections) as well as the level of damping inherent in the structure. An un-damped structure can cause the structural response/deflection to increase with each oscillation until there is a failure. Think about a car on a bumpy road with no shock absorbers... it will get so bouncy that it likely will hop right out of control. It is a very complex topic, and quite fascinating. Quote
MikeOH Posted July 7 Report Posted July 7 1 hour ago, CCAS said: (not an aerospace engineer but...) I always thought aerodynamic flutter could affect any lifting or control surface and wasn't limited to hinged components. Several videos online show flutter on a variety of aircraft. My favorite is the Twin Comanche classic: YIKES! I wonder how difficult it would have been to bail out of that Commanche had the tail said, "see ya later"! I suspect the Martin-Baker exit was not an option Quote
GeeBee Posted July 7 Report Posted July 7 Take your Mooney up and stall it. Look back at the stab and see what happens during the stall. Quote
cliffy Posted July 7 Author Report Posted July 7 That's why I offered the question as even though he was the preeminent test pilot I had cause to winder why IF it was impossible WHY did we have counter weights on the control surfaces? In my almost 70 years with airplanes I've never heard that theory of impossibility to flutter Anyone else want to chime in? Please! 1 Quote
EricJ Posted July 7 Report Posted July 7 My understanding has always been that flutter is just another example of resonance. Many mechanical systems have resonance. The Tacoma Narrows bridge collapse was an example, too. The last time I was teaching engineering I used this video to show how mechanical resonance can be destructive, so pay attention to it. Helicopter peeps know all about ground resonance. Flutter is bad mojo for these reasons. Quote
GeeBee Posted July 8 Report Posted July 8 The Hansa jet had forward swept wings and they had a lot of flutter problems. Quote
Hank Posted July 8 Report Posted July 8 1 hour ago, GeeBee said: The Hansa jet had forward swept wings and they had a lot of flutter problems. I understood the point to have been the angle of the controk surface hinge rather than the angle of the wing. The trailing edges of our wings and stabilizers angle forward nicely behind the perpendicular leading edges; most airliners' wings are significantly swept, but flap hinges are not . . . Does a swept hingeline make a control surface flutter proof? No idea, I studied basic aerodynamics and many propulsion systems with emphasis on turbojets many, many moons ago. Flutter is not a basic calculation. Quote
Pinecone Posted July 8 Report Posted July 8 15 hours ago, GeeBee said: Take your Mooney up and stall it. Look back at the stab and see what happens during the stall. Or to get really scared, find a Piper Tomahawk and spin it. In the spin, look back at the tail. Some things are best not noticed. I remember my first formation flight in the T-38. First was how much that short wing (25 foot span) bent at 4G. And second was how much the horizontal stab shook and flopped around when on final. 1 Quote
cliffy Posted July 8 Author Report Posted July 8 11 hours ago, GeeBee said: The Hansa jet had forward swept wings and they had a lot of flutter problems. Who the h&ll would even remember the Hansa Jet but real old farts like us? BTW it had real old tech very heavy rotary inverters for AC power. Real old school. 1 Quote
cliffy Posted July 8 Author Report Posted July 8 @N201MKTurbo Would like to read the attachment but it won't download for me Quote
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