My god, this type of tutorial is a treasure. A concise aerospace engineering lecture/tutorial is very hard to find compared to computer science/engineering
Thank you so much, Dr. Gudmundsson, for this outstanding video. Well organised, clear explanation and easy approach by following your book. Your passion and all the depth and applications you go into with the topics in every video and lectures makes a difference. Besides that, it includes an important lesson: “Your work becomes a mirror to your professionalism.”
I have watched several of your videos in a row now so this may be slightly off topic for this video, but I am wondering, can you reverse engineer certain coefficients if you already know aircraft performance? For instance, I know the various speeds of an aircraft (cruise, take off, etc.) with an engine with four different propeller configurations, as well as other engine / propeller combinations. Using that real world data, I should be able to calculate a real world drag coefficient right? Oh yeah, and edit to add, I have purchased your book and will be going through it soon. Your youtube content alone was supremely helpful for someone who has an engineering background but nothing to do with aircraft.
@cbbbbbbbbbbbb Excellent question. The answer is a resounding yes. In fact, I do this very frequently. To extract the minimum drag coefficient, CDmin, it is best to use the cruise speed (e.g. from the POH) as it is an equilibrium speed that yields better quality results. Section 16.5, Special Topic Involving Drag treats this issue. Check out Example 16-24 in the 2nd edition. Make sure you use proper propeller efficiencies (e.g. 0.75 for fixed pitch cruise prop and 0.85 for constant speed props). Best wishes.
Thank you for this video. I ordered the second edition of the book from Elsevier. I wonder how a two lifting surfaces configuration (tandem, large canard) would be represented in this excel. How would you define both wings and their aspec ratio. Would you consider calculating an equivalent wing of both wings? How would the down-wash from the canard affect the Cl of the main wing (rear wing)?
Hi Christos. Thank you for your message and for purchasing my book. With respect to your question, fundamentally, you don't have to treat unconventional aircraft differently from a conventional one. The spreadsheet does not "know" the shape of the airplane that is being analyzed. It presumes the drag model you use (CD) is appropriate for the configuration. Downwash from the canard has significant impact on the wing lift (see Figure 11-36 in the book). This must be treated in the stability and control evaluation. This, in part, gives you the drag contributions that are unique to the canard (e.g. trim drag) and must be present in the drag model. This serves as an indirect representation of the configuration. This is all that is needed to treat canards (or other unconventional aircraft) in the spreadsheet. I hope this helps. Have fun designing!
@@dr.gudmundssonaircraftdesign Thank you for your response. Btw I just received the eBook this morning (waiting for the hardcover as well), it is a masterpiece! an aviation bible!
Having done my ATPL exams and not being particularly mathematically gifted, it is interesting to see how those graphs are actually made, though it sticks out to me as a chicken and egg situation, how do you know what the weight or fuel capacity will be, if you do not know the materials used? would you then need to come back and redo the analysis after the aircraft is built and weighed? Also does this take into account wing plan forms? being more oriented in this case to LSA aircraft I suspect not, however I wonder how accurate an analysis of this kind would be for a light aircraft hoping to achieve high speeds, such as that in air racing. If one were to attempt to design an aircraft, which of your books would you recommend purchasing to learn how to analyse, select materials and then test the theory?
@barnstormingbandit2611 Good questions. The aircraft design process is actually a well defined process that, unfortunately, is too involved to describe here. However, I'd like to think it is clearly described in Chapter 1 of my book "General Aviation Aircraft Design" 1st and 2nd editions. So, I'd recommend the 2nd edition, as it is updated to discuss 14 CFR Part 23 with 64th amendment. While the book is laden with mathematics (which you may not like), it is a good reference for pilots wanting to know more about aircraft design. Best wishes.
Question about estimating Prop efficiency (Eta). At an early stage in the design process we know almost nothing about the propeller characteristics, we certainly do not have clever quadratic equations based upon the advance ratio (J). In my case a wee little homebuilt with a Gross Weight = approx 250kg, with a wooden fixed pitch prop. Annoyingly most texts make an assumption that Eta (cruise) = 0.75 across all airspeeds, which, in my view, is not the best engineering. Raymer's big book tries to fix this this with a correction factor based upon J/J(design). In your book (1st edition) section 14.4.2 Method 2 you make use of a cubic spline method but again start with the Eta =0.75 assumption at design point. At very early design stages I feel an urge to reduce the number of variable at play, at least until I get a basic understanding of the performance characteristics. What would you propose for a simplified method as a starting point? Stephen
Hi Stephen. That is a great comment. First, like you say, using 0.75 across all speeds is not just poor engineering, it is altogether incorrect. Eta is 0 when the airplane is at rest, because it depends on airspeed. Thus, fixed pitch propellers reach a maximum value at only one combination of airspeed and RPM. And like you know, constant speed propellers (CSP) achieve their large efficiency over a wide range of airspeeds. The quadratic spline method should be used for fixed pitch props and the cubic spline for constant speed props. This will definitely reduce the number of variables. I make this more clear in the second edition of my book. Second, I specify in the discussion for the quadratic spline method that because we don't know the final efficiency early in the design phase, we have to make the assumption that a properly manufactured propeller has a likely maximum efficiency of 0.75 if fixed and 0.85 if CSP. The manufacturer will most likely sell us a propeller for which the max eta is achieved at a combination of airspeed and RPM that is reasonable for our airplane (e.g. the target cruise speed and, say, 2500 RPM). Once this is established, the thrust splines take care of the rest. The reason I use 0.75 as a maximum value for fixed pitch propellers (I use 0.85 for constant speed props) is because it is a conservative value that a hair below what typical fixed pitch props may achieve in practice. Yes, many props achieve a higher value (the expression in the video achieves 0.82), but that value is typically obtained using Blade Element Momentum Theory. It assumes perfect surfaces qualities and geometry. In my experience, I don't usually get the efficiency predicted by the computer in practice. Best wishes.
Dr. Gudmundsson, I would really like to use your book for developing my aerobatic and gliders RC models but the prices of electronic or harcore book are prohibitive for me. It's sad. Let see is it going to survive the censor? 🙂
Hello, professor. I am working on my undergraduate thesis on aircraft performance calculations, and I am using your General Aviation book as a reference. I find it quite challenging to comprehend the example given in TABLE 18-5, which involves ground run analysis using the numerical integration method. Would it be possible for you to create a detailed video explanation for this example?
@@NejlaTomrisYelmen While your suggestion is good, I cannot produce a video about the topic any time soon. Contact me on LinkedIn if you can and describe the bottleneck.
Thank you for your interest, Gabriel, but I'm sorry, I don't want to risk the worksheet in the public domain because some of my future students might get hold of it someday and "pretend" they wrote it (for class credit). I hope you understand. Thank you regardless and best wishes.
@@dr.gudmundssonaircraftdesign Hi Dr Dudmudsson I totally understand. I have already ordered the second edition of your book and will use it to develop the spreadsheet. I work for a UAV company and we are trying to develop something like this for our future products. It will have to be tailored to introduce VTOL capabilities and other parameters but it is a great starting point for us! Thank you for the material!
@@gabrielkierulff Thank you for your purchase, Gabriel. I wish I could help you more and appreciate your understanding. You will find more sophisticated methods for drag and thrust modeling in the book, which will improve the accuracy of the spreadsheet predictions. I wish your design project all the best.
My god, this type of tutorial is a treasure. A concise aerospace engineering lecture/tutorial is very hard to find compared to computer science/engineering
Thank you for your kind words, micko. Best wishes.
He's the greatest author on this subject Dr. Gudmundsson!
@chafaon Thank you for the kind words. Best wishes.
I bought the first edition and thought enough of it that I bought both the printed and PDF second editions. Buy it, you'll be glad you did.
Thank you for your kind words and purchase, Jay. I appreciate it. :-)
Thank you Dr. Gudmundsson for the excellent tutorial.
You're welcome. Best wishes. :-)
He's back !!!
Love the book.
LOL. I like your comment! :-)
Thank you so much, Dr. Gudmundsson, for this outstanding video. Well organised, clear explanation and easy approach by following your book. Your passion and all the depth and applications you go into with the topics in every video and lectures makes a difference. Besides that, it includes an important lesson:
“Your work becomes a mirror to your professionalism.”
Thank you for your very nice comment, Daniel. I appreciate it. :-)
Thank you for sharing a vital impetus to aero design and analysis... using microsoft excel!
Thank you for your response, Alexander. I appreciate your opinion. Best wishes.
That’s a great tutorial. Thank you for sharing.
You’re welcome 😊
I have watched several of your videos in a row now so this may be slightly off topic for this video, but I am wondering, can you reverse engineer certain coefficients if you already know aircraft performance? For instance, I know the various speeds of an aircraft (cruise, take off, etc.) with an engine with four different propeller configurations, as well as other engine / propeller combinations. Using that real world data, I should be able to calculate a real world drag coefficient right?
Oh yeah, and edit to add, I have purchased your book and will be going through it soon. Your youtube content alone was supremely helpful for someone who has an engineering background but nothing to do with aircraft.
@cbbbbbbbbbbbb Excellent question. The answer is a resounding yes. In fact, I do this very frequently. To extract the minimum drag coefficient, CDmin, it is best to use the cruise speed (e.g. from the POH) as it is an equilibrium speed that yields better quality results. Section 16.5, Special Topic Involving Drag treats this issue. Check out Example 16-24 in the 2nd edition. Make sure you use proper propeller efficiencies (e.g. 0.75 for fixed pitch cruise prop and 0.85 for constant speed props). Best wishes.
Thank you for this video. I ordered the second edition of the book from Elsevier. I wonder how a two lifting surfaces configuration (tandem, large canard) would be represented in this excel. How would you define both wings and their aspec ratio. Would you consider calculating an equivalent wing of both wings? How would the down-wash from the canard affect the Cl of the main wing (rear wing)?
Hi Christos. Thank you for your message and for purchasing my book. With respect to your question, fundamentally, you don't have to treat unconventional aircraft differently from a conventional one. The spreadsheet does not "know" the shape of the airplane that is being analyzed. It presumes the drag model you use (CD) is appropriate for the configuration. Downwash from the canard has significant impact on the wing lift (see Figure 11-36 in the book). This must be treated in the stability and control evaluation. This, in part, gives you the drag contributions that are unique to the canard (e.g. trim drag) and must be present in the drag model. This serves as an indirect representation of the configuration. This is all that is needed to treat canards (or other unconventional aircraft) in the spreadsheet. I hope this helps. Have fun designing!
@@dr.gudmundssonaircraftdesign Thank you for your response. Btw I just received the eBook this morning (waiting for the hardcover as well), it is a masterpiece! an aviation bible!
Having done my ATPL exams and not being particularly mathematically gifted, it is interesting to see how those graphs are actually made, though it sticks out to me as a chicken and egg situation, how do you know what the weight or fuel capacity will be, if you do not know the materials used? would you then need to come back and redo the analysis after the aircraft is built and weighed? Also does this take into account wing plan forms? being more oriented in this case to LSA aircraft I suspect not, however I wonder how accurate an analysis of this kind would be for a light aircraft hoping to achieve high speeds, such as that in air racing.
If one were to attempt to design an aircraft, which of your books would you recommend purchasing to learn how to analyse, select materials and then test the theory?
@barnstormingbandit2611 Good questions. The aircraft design process is actually a well defined process that, unfortunately, is too involved to describe here. However, I'd like to think it is clearly described in Chapter 1 of my book "General Aviation Aircraft Design" 1st and 2nd editions. So, I'd recommend the 2nd edition, as it is updated to discuss 14 CFR Part 23 with 64th amendment. While the book is laden with mathematics (which you may not like), it is a good reference for pilots wanting to know more about aircraft design. Best wishes.
Question about estimating Prop efficiency (Eta). At an early stage in the design process we know almost nothing about the propeller characteristics, we certainly do not have clever quadratic equations based upon the advance ratio (J). In my case a wee little homebuilt with a Gross Weight = approx 250kg, with a wooden fixed pitch prop. Annoyingly most texts make an assumption that Eta (cruise) = 0.75 across all airspeeds, which, in my view, is not the best engineering. Raymer's big book tries to fix this this with a correction factor based upon J/J(design). In your book (1st edition) section 14.4.2 Method 2 you make use of a cubic spline method but again start with the Eta =0.75 assumption at design point. At very early design stages I feel an urge to reduce the number of variable at play, at least until I get a basic understanding of the performance characteristics. What would you propose for a simplified method as a starting point? Stephen
Hi Stephen. That is a great comment. First, like you say, using 0.75 across all speeds is not just poor engineering, it is altogether incorrect. Eta is 0 when the airplane is at rest, because it depends on airspeed. Thus, fixed pitch propellers reach a maximum value at only one combination of airspeed and RPM. And like you know, constant speed propellers (CSP) achieve their large efficiency over a wide range of airspeeds. The quadratic spline method should be used for fixed pitch props and the cubic spline for constant speed props. This will definitely reduce the number of variables. I make this more clear in the second edition of my book.
Second, I specify in the discussion for the quadratic spline method that because we don't know the final efficiency early in the design phase, we have to make the assumption that a properly manufactured propeller has a likely maximum efficiency of 0.75 if fixed and 0.85 if CSP. The manufacturer will most likely sell us a propeller for which the max eta is achieved at a combination of airspeed and RPM that is reasonable for our airplane (e.g. the target cruise speed and, say, 2500 RPM). Once this is established, the thrust splines take care of the rest.
The reason I use 0.75 as a maximum value for fixed pitch propellers (I use 0.85 for constant speed props) is because it is a conservative value that a hair below what typical fixed pitch props may achieve in practice. Yes, many props achieve a higher value (the expression in the video achieves 0.82), but that value is typically obtained using Blade Element Momentum Theory. It assumes perfect surfaces qualities and geometry. In my experience, I don't usually get the efficiency predicted by the computer in practice. Best wishes.
Dr. Gudmundsson, I would really like to use your book for developing my aerobatic and gliders RC models but the prices of electronic or harcore book are prohibitive for me. It's sad.
Let see is it going to survive the censor? 🙂
@cristiansandor4435 Not sure what your last sentence means. Please elaborate.
@@dr.gudmundssonaircraftdesign I was refering to your NOTE2 🙂
@@cristian-scd Oh, I get it. The head-censor is perfectly fine with your comment. Can't offend anyone. You're good. 🙂
Hello, professor. I am working on my undergraduate thesis on aircraft performance calculations, and I am using your General Aviation book as a reference. I find it quite challenging to comprehend the example given in TABLE 18-5, which involves ground run analysis using the numerical integration method. Would it be possible for you to create a detailed video explanation for this example?
Which edition of the book are you referring to? First or second?
second edition
@@dr.gudmundssonaircraftdesign
second edition
@@dr.gudmundssonaircraftdesign
@@NejlaTomrisYelmen While your suggestion is good, I cannot produce a video about the topic any time soon. Contact me on LinkedIn if you can and describe the bottleneck.
i need the excel sheet please
Hi! is it possible to get this excel or maybe buy it?
Thank you for your interest, Gabriel, but I'm sorry, I don't want to risk the worksheet in the public domain because some of my future students might get hold of it someday and "pretend" they wrote it (for class credit). I hope you understand. Thank you regardless and best wishes.
@@dr.gudmundssonaircraftdesign
Hi Dr Dudmudsson I totally understand. I have already ordered the second edition of your book and will use it to develop the spreadsheet. I work for a UAV company and we are trying to develop something like this for our future products. It will have to be tailored to introduce VTOL capabilities and other parameters but it is a great starting point for us! Thank you for the material!
@@gabrielkierulff Thank you for your purchase, Gabriel. I wish I could help you more and appreciate your understanding. You will find more sophisticated methods for drag and thrust modeling in the book, which will improve the accuracy of the spreadsheet predictions. I wish your design project all the best.