Aircraft Design Tutorial: Back of Envelope Calculations for Aircraft Design
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- Опубліковано 18 жов 2024
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The video shows how to implement simple, yet practical "back-of-the-envelope" calculations in aircraft design. Seven selected examples are presented. These use methods from my book "General Aviation Aircraft Design: Applied Methods and Procedures."
NOTE:
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HELPFUL POINTERS:
0:31 Introduction
2:23 The Engineer's Conundrum
3:26 Defining "Ballpark Number"
5:43 Topic 1: The Lift Equation
9:06 Topic 2: The Thrust-to-Weight Ratio
11:45 Topic 3: Required Engine Power
18:53 Topic 4: The Drag Equation
20:32 Topic 5: The Total and Minimum Drag Coefficients
23:36 Topic 6: Basic Wing Geometry
25:53 Topic 7: Initial Wing Load Assessment
The video uses excerpts from Dr. Gudmundsson's textbook, "General Aviation Aircraft Design - Applied Methods and Procedures," published by Elsevier in 2013 (Edition 1) and 2021 (Edition 2).
The book is available from multiple outlets. Among those are:
www.amazon.com...
and
www.elsevier.c...
Great teaching... Best regards to Prof. Dr. Gudmundsson. I am among the wrong brothers. Any one can be wright ( = Right ) brothers after learning aircraft design from your book and video. I hope one day I would be right (= Wright) Bother. Thank you for helping me.
@maharshisubhash1193 Thank you for the kind words. I appreciate them! :-)
Good day prof. Gudmundsson,thanks for all your support and help am very grateful sir. Concerning determination of Oswald efficiency "e" in the first edition of general aviation aircraft design textbook, can "Equation(9-89) on page 363 be used in finding Oswald efficiency for wings with AR(aspect ratio) of upto 20? When i used it, i got a value of 0.506 which seems unrealistic for an aspect ratio of 21 since Oswald efficiency should increase with increasing AR if am right. If eqn 9-89 isn't acceptable for aspect ratio of up to 20 and above, what is the best and most reliable equation that can be used in accurately finding Oswald efficiency for aspect ratios of upto 20
I have used that equation up to 16. However, I did it with a healthy doze of skepticism. I extracted the CDmin and e of several sailplanes using their POH and the method of Section 15.6.2, which helped me assess its accuracy. I recommend you do the same. By the way, I get 0.527 for AR=20.
@@dr.gudmundssonaircraftdesign ok, I'll try it out. thank you sir.
@@dr.gudmundssonaircraftdesign i used equation 9-126 and it yielded a more realistic result, for AR of 21 e=0.596 and for AR of 20 e= 0.601. taking into account that P= K*CDo
and using CDo=0.025.
Any known back-of-envelope methods to estimating eta-p?
I've seen clever nomograms to get to a ballpark efficiency but a smart bit of cleverness would be nice.
@Peilin Stephen Thank you for your excellent question! Yes, I do know a back-of-the-env method for eta-p, both for fixed and constant speed (CSP) propellers. I developed both of these methods and have used them with great success for a long time. Both are in my book, 1st and 2nd editions.
For fixed pitch props use Method 1 of Section 14.4.2 (in Ed1) or 15.4.3 (in Ed2). For CSP use Method 3 of Section 14.4.2 (in Ed1) or 15.4.4 (in Ed2). For CSP, I recommend the method of 15.4.4 (in Ed2). It directly returns eta-p (the others return thrust) AND my students make less mistakes when using it.
For any of these methods that return thrust, you can calculate eta-p from the relation: eta-p = T∙V/(k∙P), where T=thrust (lbf or N), V=airspeed (ft/s or m/s), P=power (hp or kW), and k=conversion factor (550 if P is in hp, and 1000 if P is in kW). Example: If T=175 lbf, P=75 bhp, V=169 ft/s => eta-p=T*V/(550*P)=0.717. Conversely, if T=778 N, P=55.9 kW, V=51.5 m/s => eta-p=T*V/(1000*P)=0.717. Hope this helps. Have fun designing!
Time line 22:56, When you plug and chug, there appears to be an error with the two equation given in this frame. " + OR - ".
@keithharris4970 Greetings. Please be more specific. I don't understand what you mean.
@@dr.gudmundssonaircraftdesign My bad! Re-watched the topic and understand now. One another note, do you have another book coming our way? MOSIAC should be approved this year. Will be a boost in innovation, well past due! LSA's will get faster, and 54 knots VS1.
@@keithharris4970 No problem. Elsevier has not yet asked me to work on a 3rd edition but I expect them in 3-4 years or so. I am also thrilled about MOSAIC and the prospects of the progress it should bring. Best wishes.