### Short Course on Mission-Specific Aircraft Design

Hey guys,

Sam Weiss and I have put together a short, 30 minute course on designing aircraft for specific missions. Would you mind watching these three 10-minute videos and leaving some feedback? We're looking specifically for comments and suggestions of what areas within aircraft design are not well understood or are the most frustrating so that we can cover those topics in a longer course we are developing.

Part 1:

Thanks!

• Good job guys, regardless of who your audiences are keep doing great stuff and don't pay attention to trolls.

• Hey Guys, Thanks for your comments.

We put this video together for people who don't have much experience designing - just to give them some basic places to start. You are all obviously more experienced and have great comments on how to improve the spreadsheet. Thanks for your thoughts.

We've addressed the fuselage drag and max CL issues in an updated version which we'll be posting shortly. We also realize it's difficult to get a firm grasp on the equations by looking at the spreadsheet. We'll consider adding a list of equations at some point to make the math easier to follow. Finally, we've added notes in several cells to explain more fully what those values represent and reorganized the sheet as well. We think this next version will be a noticeable improvement and be easier to follow.

Thanks again, and let me know if you have any other questions. I'll post a link shortly to the new sheet.

• looking at the spreadsheet the overall drag is just the zero lift drag ( considering that it is a coefficient for the full airframe with the wing area as a reference area?? ) plus the induced drag. I do not know how the zero lift coefficient is computed but for me it is a friction drag and I am used to use the total wetted area as a reference, as a rule of thumb the total wetted area is about 4 times the wing area so the value here seems extremely low. you also seem not to consider the increase of friction drag with CL?

• @frederic

the predicted flight time in the table is calculated from payload power, and drag introduced motor power, which calculated from wing drag. so there's no other consumption sources in the calculation. i think it is a very naive prediction so you need to guess a good efficiency here.

• @jerry I dont get your comment about efficiency?? the 40% is supposed to be what is left in mechanical energy from the electric energy straight out of the battery: battery restitution, cables, ESC, motor, propeller represent 60% loss

• @frederic that's why 40% efficiency ... i think

the spread sheet link is on the youtube comment of video 1

• hi, I watched the videos then I created an account on Blucraft but cannot find that spreadsheet. there are few minor things on the videos but I have more comments on the numbers. for example you consider that minimum speed is based on your max CL for the Clark Y. if you adjust for reynolds number and aspect ratio the stall CL is 1.15. you cannot  use the stall CL for the minimum speed as it is obviously too dangerous so a max CL of 1 seems already optimistic as you have then to correct for washout... also I am curious to understand how you evaluate drag. I made a back of the envelop calculation ( literally. I use an envelop! ) the power seems to be 22w on cruise, with an induced drag coefficient of 0.0088 we find the wetted area drag coefficient to be 0.0069!! the best full scale airplane (think racers) have one of 0.0035 at RE numbers in tens of millions so that number seems very optimistic to me. but I of course can be wrong so I would like to understand how you evaluate your drag. in video 3 you design the actual airplane and with a fuselage shape that will generate a lot of drag at the jonction with the boom the wetted area CD becomes 0.004!! you add a washout ( good for safety of course ) so your wing lift should decrease, yet your min speed do not change...

• Hi Doug,

First off, thank you for making these videos and that spreadsheet. They are very nice tools, and as you outline in your videos, they are very useful for the initial sizing and conceptual model of a UAV.

One thing that would recommend (coming from an aero background) is for a rough outline of how you arrive at these numbers-- I was looking through your equations in the spreadsheet and was unsure about some of your calculations.

• Moderator

Sorry, but...You tell about nothing.

• the spread sheet looks like a eclac in excel, is that functional by connecting to blucraft or just for demostration.

really like your product, but spending 600 to buy a AC calculator is too much for me. i thing most scratch builder will be motivated to build and test actual model in MachUp if AC is provided by free. if you have ecalc equivalent and better nurbs model export i would consider buying one pro license.

current i am building aircraft by FMD 3D printing in PLA. after hundreds of hour now i can build a 1m span fix wing in 50g/dm load. i want to try build fly wings and more variance on my designs but had no good tools to test AC before froze a aerodynamic design. if AC function is free i would try to print many designs after building it in MachUp.

Maybe you could consider a version, if one would like to use AC function for free, his model is for free to others.

thanks.

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