### How to avoid pitfalls when using taper and twist

Hey guys,

Just put together a quick video to show the effects of taper ratio and twist and how they interact. Turns out using rules of thumb in this area can be detrimental. I have used similar rules of thumb in the past, but thought it was high time to walk through some rigorous calculations to see what's best.

-Doug

https://youtu.be/zy2AoydY3CY

• Doug, great presentation again!

Just wanted to add my nickel to the discussion for people who's just getting into the models design. It is not as straight-forward as designing it on computer and plotter it to the actual thing and enjoy.

Computer program just as good as programmers who wrote it. In reality design may perform quite differently in the air than on a computer screen.

Wing design is a multi-subject work. The same exact wing made of foam or glass may show totally different performance in the air. And so on and on..

Once again, great work! I wish I had the same design tools in my time.

Cheers,

Mark

• @Mostyn: I just uploaded Part 2. Let me know what you think. It was definitely interesting to look at the plots as a function of lift coefficient. You can find the video here:

https://youtu.be/v3BNCc6zdQA

Best,

Doug

• @Justin - Thanks for the comment. You're right that these are very simple concepts. I hear of lots of guys using rules of thumb to design their small drones, and want to point out some of the basic ideas that govern the physics. Hopefully this helps people learn how to do finer-tuned analysis rather than sticking with rules of thumb. If we get into coupling structures, handling qualities, or high-speed aircraft, it gets more technical as you pointed out. But for most of the DIY drone community, I believe basic relationships like this can help improve the aircraft we develop.

• @Mostyn: Good point. I failed to mention that in the video. I'll put together a "part 2" that compares the performance over a range of lift coefficients.

Yes, you can use different airfoils at the wing root and wing tip. MachUp assumes a linear variation betwee the two and linearly interpolates to get the local properties at any point on the wing.

• Doug great video series. May I point out that these are very simple concepts, and as soon as you design a complex wing with more than one foil, much of this becomes a different story. For example, typically a high performance aircraft will have the largest foil change at or near the tips, as well as wing root. The reasoning for the tip is everything from slow speed stall handling, reduced - induced drag, tailored lift distribution, rapid change in ReNos, etc. Reasoning for the root being primarily intersection drag, and pressure management at wing root. (This of course isn't getting into area rule or anything of the sort for high speed full scale aircraft.)

• Another great video Doug, and great explanation of how we can use wingtip incidence to create a more elliptic like lift distribution while also improving wingtip stall qualities.

I suppose that when using wingtip incidence to create elliptic lift, that would only be optimised at one angle of attack. At lower angles of attack the wingtip could be generating negative lift. at higher angles of attack, it will generate significant lift compared to the centre of the wing. On the other hand, a tapered wing will generate an elliptic distribution across a broad range of angle of attack.

Can your program model changing airfoil shape across a cross section?

• Doug, Great presentation!

I enjoy your videos and hope it will help us designing better planes.

Cheers,

Mark