1/16" plywood fin flutter at mach 1.7

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You need to go to a better hobby store :). What I believe Chris was reporting about (and I've talked to him in person several times at launches and seen what he's using in his rockets) is something like "Micro-Cut Aircraft Grade (Birch) Thin Plywood Sheets" from Midwest Products Company (https://www.hobbylinc.com/htm/mid/mid5244.htm), not the crummier stuff one sees at places like Michael's. But my point is that once you get as thin as the 1/16th the OP was talking about, you are looking at a major loss of strength, both absolute and directional, even for the best grades of plywood available.

Bought a lot of plywood--Midwest is especially bad. Yes, have aircraft grade with birch veneer, but beyond that lite-ply poplar. Really weak stuff.
 
I agree with that. I have it and have run some sims but I'm not so certain that the materials I'm using match the approximations in the program. I've been told "it's easy" to input the
data from different materials but I have yet to see someone state how the mathematical constructs are input. Kurt

The properties of aircraft plywood available directly in FinSim are representative of aircraft plywood used in the aircraft industry. The values for modulus of elasticity (E), shear modulus of elasticity (G) and material density determine the torsion mode of flutter for a fin and do not vary greatly between various types of industrial grade aircraft plywood. Major departure from the properties of aircraft plywood occur when the designer laminates the fin with alternating layers of resin and fiberglass cloth or carbon cloth material. For a laminated fin the properties "hardwired" in FinSim should be replaced by material properties computed using a supplemental method like the Rule of Mixtures as shown in the FinSim instructions and available as a free download as Composite Material Properties.xlsx or a program like The Laminator, both are equally accurate if used correctly. But, if the designer is using a fin fabricated using aircraft plywood the results computed by FinSim will be determined by the engineering skill and creativity of the FinSim user and the proper use of the program. For those individuals who feel uncomfortable using FinSim an Exel spreadsheet call NACA_TN_4197 is available as a free download. To see the material values selected in FinSim simply click Additional Results to display the values of E, G, etc used in the program. Finally, user defined materials are easy to input using the User Defined Material pull down menu.


Thank you, AeroCFD
 
The properties of aircraft plywood available directly in FinSim are representative of aircraft plywood used in the aircraft industry. The values for modulus of elasticity (E), shear modulus of elasticity (G) and material density determine the torsion mode of flutter for a fin and do not vary greatly between various types of industrial grade aircraft plywood. Major departure from the properties of aircraft plywood occur when the designer laminates the fin with alternating layers of resin and fiberglass cloth or carbon cloth material. For a laminated fin the properties "hardwired" in FinSim should be replaced by material properties computed using a supplemental method like the Rule of Mixtures as shown in the FinSim instructions and available as a free download as Composite Material Properties.xlsx or a program like The Laminator, both are equally accurate if used correctly. But, if the designer is using a fin fabricated using aircraft plywood the results computed by FinSim will be determined by the engineering skill and creativity of the FinSim user and the proper use of the program. For those individuals who feel uncomfortable using FinSim an Exel spreadsheet call NACA_TN_4197 is available as a free download. To see the material values selected in FinSim simply click Additional Results to display the values of E, G, etc used in the program. Finally, user defined materials are easy to input using the User Defined Material pull down menu.


Thank you, AeroCFD

Note the OP is from Canada and your fin sim software is not available here.
I have sent you a couple inquiry emails about this using your website contact email and have received no response:sigh:

Greg
 
The properties of aircraft plywood available directly in FinSim are representative of aircraft plywood used in the aircraft industry. The values for modulus of elasticity (E), shear modulus of elasticity (G) and material density determine the torsion mode of flutter for a fin and do not vary greatly between various types of industrial grade aircraft plywood. Major departure from the properties of aircraft plywood occur when the designer laminates the fin with alternating layers of resin and fiberglass cloth or carbon cloth material. For a laminated fin the properties "hardwired" in FinSim should be replaced by material properties computed using a supplemental method like the Rule of Mixtures as shown in the FinSim instructions and available as a free download as Composite Material Properties.xlsx or a program like The Laminator, both are equally accurate if used correctly. But, if the designer is using a fin fabricated using aircraft plywood the results computed by FinSim will be determined by the engineering skill and creativity of the FinSim user and the proper use of the program. For those individuals who feel uncomfortable using FinSim an Exel spreadsheet call NACA_TN_4197 is available as a free download. To see the material values selected in FinSim simply click Additional Results to display the values of E, G, etc used in the program. Finally, user defined materials are easy to input using the User Defined Material pull down menu.


Thank you, AeroCFD
I did want to use finsim but i cant.
 
FinSim result in post #12. With the geometries and material (true birch ply), you are just OK at 1.7 Mach.
Yeah but i also would like finsim for my other MD builds to find out when they will flutter. Because i cant ask all the time for other people to do it for me.
 
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