BobDaly
Well-Known Member
attached is a spreadsheet that calculates wing loads for the Minimax airplane.
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lake_harley
Well-Known Member
- Joined
- Jan 4, 2007
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Bob.....I don't have the appropriate program on my computer to open the attachment you posted. I have a copy of the October 1991 Structural Analysis that was done by an engineer, W. J. Collie, for TEAM. Is the analysis you posted similar, or ??
Thanks
Lynn
Thanks
Lynn
That's very cool!
It appears to be similar. The final numbers are very close.
BobDaly
Well-Known Member
It's my attempt to do the calculations behind the numbers quoted in the TEAM report. It's incomplete as it only examines symmetric loading and points A and D of the flight envelope. The calculations are found in the highly accessible "Design of Light Aircraft" by Richard Hiscocks.
Heliano
Well-Known Member
Nice job, BobDaly! There are two things that called my attention, though: 1) Angle of attack: you used 24 degrees. Unless I am not foreseeing something, it seems a little excessive - but I suspect that you have an explanation for that; 2) Load factor of 4.4: Is that the maximum operational load factor? I would suggest, as you are very good at setting up a spreadsheet calculation, that you set up a spreadsheet to build the V-n diagram, to verify what is more critical, maneuvering or gust load factors. Once you do it, there are two strengths one has to check: permanent deformations (comparing stresses with the material yeld stress) and failure (comparing stresses with the material ultimate stress). To check for failure, one has to add 50% to the V-n diagram load factors.
Thanks for posting the spreadsheet. My computer has a "read only" program for Excel spreadsheets, Is it possible someone could change a couple of parameters and provide the resulting change to one loading?
If so here is what I need.
Line21 change from +4.4 to-3.0
Line 34 change H from 47 to 84
Line 34 change V from 29 to 46
Interested in change to line 27 and 28 THANKS
If so here is what I need.
Line21 change from +4.4 to-3.0
Line 34 change H from 47 to 84
Line 34 change V from 29 to 46
Interested in change to line 27 and 28 THANKS
BobDaly
Well-Known Member
Thank you and sorry for not replying sooner. The angle of attack is one of the inputs to the calculations. The Minimax airfoil is supposed to have a maximum lift coefficient of 1.5 unflapped and 2.0 with the flaps fully deployed. If the lift curve slope is 0.1/° then the 2 dimensional alphas would be 15° and 20°. But the calculation includes 3d effects so the angle of attack is somewhat higher. So, the 24° angle of attack is the full-flap angle of attack.
The 4.4 load factor is the design limit load factor for a utility category airplane and used for the Minimax. It is an input, so can be adjusted.
Because the Minimax is an ultralight with an arbitrary speed limit lower than the design maneuvering speed, I did not include any gust load analysis. I believe the spreadsheet can be used to examine the other corners of the flight envelope.
BobDaly
Well-Known Member
What are you trying to accomplish? You would probably be better served finding a beam calculator. This spreadsheet is specific to the Minimax. That's not to say it couldn't be used for most two-spar, fabric covered, strut braced monoplanes with some modification but one cannot simply change a couple parameters and expect useable results.
Understand exactly what you are saying , the Minimax wing and the Legal Eagle wing are almost twins. I was looking for changes in loading on the struts and once I opened the spreadsheet with Explorer rather than Firefox got what I needed.
This file has an error in it..
at L=W-P and L=nW-p (this formula has circular references error means L is calculated by P and P is calculated by L)
the designer took airfoil's value directly like maximum camber and location of it also some coefficients, you have to change all the airfoil parameters as per your airfoil in all the necessary formulas.
i will change it to workable manner, if anyone share (Design of Light Aircraft, 1995, Richard D. Hiscocks ) pdf ..
searching for this book to read necessary but dint get yet...
at L=W-P and L=nW-p (this formula has circular references error means L is calculated by P and P is calculated by L)
the designer took airfoil's value directly like maximum camber and location of it also some coefficients, you have to change all the airfoil parameters as per your airfoil in all the necessary formulas.
i will change it to workable manner, if anyone share (Design of Light Aircraft, 1995, Richard D. Hiscocks ) pdf ..
searching for this book to read necessary but dint get yet...
So are you saying that if the airfoils are identical on both the MiniMax and Legal Eagle (they are, also identical in chord) that the spreadsheet values are valid? I have decided to do a test to destruction (compression) of a couple of struts using a strain gauge, faster and easier (also has more validity) than refreshing 60 yr old math skills that I most likely got a "C" in anyway. JohnB
BobDaly
Well-Known Member
The spreadsheet does have a circular reference in the balance equation section where the lift calculation and the tail force calculation reference each other. The spreadsheet program (Excel) must be set to allow circular reference and the number of iterative calculations is specified, a hundred is plenty.
BobDaly
Well-Known Member
Iteration is a common numerical method of obtaining an ever more accurate approximation of a set of values that satisfy a series of equations . In this case, we have a guess for lift and in the first iteration the tail force is assumed to be zero. This results in an approximation of the balancing tail force. Then subsequent iterations produce values that converge on the true values. They never get there but once the difference between iterations becomes small enough, in this case a pound is close enough, we can stop. Probably 10 iterations is sufficient in this case.
Really I retired from the Army after twenty years in 1990! I think I've got you beaten!
