flutter

[Nigel]

I need to determine the effect of adding extra fuel to the wingtips of a Convair 5800 stretch. In particular I need to now how this will affect the flutter characteristics.<br>
<br>
I have the results of a ground vibration test (without the extended fuel tanks)so is the any software out there that will do the aerodynamic analysis? <p>Nigel Waterhouse<br><a href=mailto:nigelw@flightcraf t.ca>nigelw@flightcraf t.ca</a><br><a href=

http://www.flightcraft.ca>Kelowna

Flightcraft</a><br>A licensed aircraft mechanic and a proffessional engineer, who attended university in England and graduated in 1996. Currenty living in British Columbia,Canada and working for Kelowna Flightcraft as a design engineer responsible for aircraft mods and STC

 

[coolbreeze]

The added weight to the tip will probably change the resonant frequency of the wing fully loaded. I would first try to model the wing as a simple damped system subjected to a harmonic forcing function, then try to solve for the natural (resonant) frequency. Another important aspect, that should be considered in relation to the natural frequency at the wing tip is vortex shedding( If it exists). These two frequencies should stay well away from each other, if you ascertain my meaning. With these you should be able to use the frequency ratio with a Transmissibility curve and determine the degree of isolation. If you are adding pylon wing tanks than you have even more to consider due to the increased surface area.<br>
<br>
I am certainly no vibration expert, nor an aerodynamists, but I would like to open a dialog with you because of our similar background and occupation. I am currently working in the defense industry as a mechanical engineer and most of my work is in aircraft structural modification. <br>
<br>
I have a quick question for you. How do you determine multiple support reactions in a statically indeterminate problem. For example, when installing an antenna with 10 screws, how do you determine the support reactions in the fasteners if you apply a static load at CG? Currently I have been using superposition, but that does not give me the accuracy that I would like to have. <br>
<br>
Frank<br>

 

[Nigel]

Are you fitting a large 'blade' type antenna on the top or underside of the aircrft? Tell me a little more about the installation. I have done quite a few antenna installations recently.<br>
<br>
Nigel<br>
<br>
PS where are you working(curious)? <p>Nigel Waterhouse<br><a href=mailto:nigelw@flightcraf t.ca>nigelw@flightcraf t.ca</a><br><a href=

http://www.flightcraft.ca>Kelowna

Flightcraft</a><br>A licensed aircraft mechanic and a proffessional engineer, who attended university in England and graduated in 1996. Currenty living in British Columbia,Canada and working for Kelowna Flightcraft as a design engineer responsible for aircraft mods and STC

 

[coolbreeze]

<br>
I am working under a Lockheed contract but the name of my company is Aerospace Integration Corp.<br>
<br>
Anyway I am sure you are familiar with FAR 23 but if not here’s the link: <br>
<A HREF="

http://dutlls1.lr.tudelft.nl/oshelp/projects/far/23/23subd.html"

TARGET="_new">

http://dutlls1.lr.tudelft.nl/oshelp/projects/far/23/23subd.html</A>

<br>
Just type in the paragraph number 23.629 after you follow the link on flutter and it will give you the spec.<br>
<br>
OK, I am mounting a large blade (VHF-FM) antenna on the bottom of a C-130 aircraft. I have done one other installation of a SATCOM Antenna and I had to make some assumptions that I would rather not have. For example, the support reactions for each screw have given me a fit. The stresses in the doubler plate have also been quite challenging for me. How do you handle these things? I have used deformation theory in solving for the multiple support reactions, but the problem is when the ideterminate order is greater than 2. Determining the moments generated from the support reactions at the doubler attachment points is also killing me. How are you doing these things?<br>
<br>
Frank<br>

 

In response to your question on reactions from the screws, I think it is possible to use the 3 moment method to determine statically indeterminate structures, especially when there are more reactions than loads.

 

[chopin]

Nigel, coolbreeze,

Did you guys bring the discussion offline? I'm interested to know how multiple support reactions can be solved for a statically indeterminate problem e.g. antenna installation.
If there are any other people with similar experience, pls share. Thanks.