Sailplane Design Spreadsheet

[SoarNeck]

Hi folks,

I thought I'd create this thread to answer any questions anyone might have while using my Sailplane Design Spreadsheet. I eventually plan to write a full set of articles for LIftZone describing its use, but that isn't likely to happen anytime soon. Hence this thread.

First off, the sheet can be downloaded off of this page:

http://www.soarcalgary.com/Extras/Articles/Sailplane%20Design%20Spreadsheet/

[SoarNeck]

First set of questions I received:

>1. How you calculate design AoA and Turn AoA ?

You don't actually calculate design AoA and Turn AoA, the spreadsheet does. The AoA is a function of the weight of the model and the operating Cl.

First, specify the parameters of the model. That would be all the geometric data, plus the polar data for the various airfoils across the wing.

Geometric data goes on the "Main Input Sheet", where polar data goes on the "Polar Data" page. Use the tabs at the bottom of the spreadsheet to navigate through the pages, and please read the instructions at the top of the pages (hopefully they're clear).

Next, specify the total weight of the model (in ounces) under the "Structural Parameters" section. Don't worry about filling out the fuselage weight entry unless you're trying to do the turn analysis or a spar design.

Lastly, go over to the "Operational Parameters" section, and find the blue boxes marked "Wing Root Cl" and "Design Speed".

Pick a design speed (in mph) that represents the condition you want to use (thermal, distance, speed etc). Note that this speed also affects other calculations on the sheet, so it's a good one to set early.

Next, adjust the wing root Cl until the "Level Flight Force Imbalance" number is zero. This represents a measure of how hard the wing is working to maintain level flight at the design speed. The sheet will lookup the corresponding values of Cd, Cm and Alpha (angle of attack) at that Cl value, and will do the same for the other stations of the wing (which are a function
of the root angle of attack to varying degrees).


>2. Local Cl and lift distribution diagram look strange - maybe I put wrong parameters ?

First, check the "Geometric Twist" entries under "Wing Dimensions" on the Main input Sheet to make sure you don't have any twist you didn't mean to add.

Next, make sure that the twist you did mean to add is correctly entered - washout is specified as a negative value.

Last, check to make sure that the polar data was added at the correct Reynold's number. The sheet accounts for the fact that the zero-lift angle of an airfoil changes with Reynold's Number. As a result, a constant airfoil used across the span of an average sailplane planform will usually require some washout to manage the effective aerodynamic wash-in, or a transitional
airfoil series must be developed.

If you look at the data which is loaded into the default spreadsheet, you'll see this effect. I just loaded data for a constant 7037 airfoil into the sheet, and you'll notice that that particular planform requires about a degree of washout out to the tip to prevent the local cl from being too far outboard (tipstall). I didn't try to do anything fancy, I just adjusted the "Twist Sum" to zero (that being the sum of aerodynamic and geometric twist...here geometric washout balances aerodynamic wash-in).

>3. If I have diff. airfolis across span - which polar I use ?

The airfoils can now be specified at each chord break in the wing. Just enter the data that is appropriate to each airfoil on the "Polar Data" sheet (see tab at bottom of spreadsheet). This data should be collected from Profili2 using its export function (cut and paste from the window that will pop up).

How the airfoils interact will be a function of their particular characteristics, and will be shown by the sheet. I'll leave it up to you to figure that part out :)

Note that you can also enter airfoil data for the horizontal and vertical tailfins as well. This airfoil data will be used to calculate the stab angle and required size, among other things.

Let me know if screenshots would be helpful, but I think everything should be reasonably easy to find.

Cheers,
Adam

[championliu]

Hello Adam,

I cannt download the doc from your URL,pls indicate if you have new place to

down?

Thanks

Championliu

Hawk dexun model

Shanghai China
Email:championliu@126.com

[SoarNeck]

Don't know why it doesn't work for you...works okay here.

Anyway, I sent it to you by email.

Cheers,
Adam

[Lazy]

Great job, Adam.
Now I use this sheet as addition to Nurflugel programm. :)

[SoarNeck]

Thanks very much, hope it proves useful. Please post photos of your models when they're done :)

[Lazy]

Hi Adam
As I promise you...

[SoarNeck]

Very nice - how does it fly?

[Lazy]

Predictable :D No tip stall tendency, nice glide...
With 10x1950 FAUP and AXI2814/12 - 10+ min of fly without special power management.
V.