# Tools advised for Windfoil basic understanding ?

Discussion in 'Hydrodynamics and Aerodynamics' started by jmf11, Oct 28, 2019.

Tags:
1. Joined: Oct 2019
Posts: 33
Likes: 1, Points: 8
Location: Aix en provence - france

### jmf11Junior Member

Hello,

I have started windfoil this year and really enjoy the practice. I look at better understand how windfoils work, and how different designs compare. I learned a lot from:
http://mauiultrafins.com/technology-2/hydrofoil-mechanics/

I'm looking for a tool to simulate the "basic behaviour" of the foil, compare behind different models/geometries.

I would like to get some grasp about:
- minimum foiling speed,
- minimum sail surface (thrust) for take-off
- pitch stability understanding (effect of elevator angle on stability, is Static margin a useful concept for windfoil...)
- "best" flying domain of a windfoil geometry
-...

Having a RC glider backgroud, I'm having a first look using XFLR5. I also identified AVL a candidate to study.

They look OK to study the main wing but don't seem to address the equilbrium of moments with Thrust not at CG level. The fact that the analysis should be done with a fixed elevator angle and a moving CG to achieve balance.

Any advice to a beginner about free tools and/or workflow to analyse (and get some understanding about) those things ?

In parallel, any formula / excel sheet / tool to get some sail thrust from sail surface / wind speed / wind angle ?

Best regards,

JMF

2. Joined: Feb 2002
Posts: 2,319
Likes: 303, Points: 83, Legacy Rep: 1673
Location: Port Gamble, Washington, USA

### tspeerSenior Member

I would go with AVL. It can handle the wing, tail, and fuselage, and provide all of the stability derivatives. You can also specify a linear free surface condition (infinite Froude number approximation). You can get profile drag from XFOIL.

3. Joined: Oct 2019
Posts: 33
Likes: 1, Points: 8
Location: Aix en provence - france

### jmf11Junior Member

Thanks for the advice Tom.

Up t now,I played with XFLR5 which helped me get a first understanding (I had already used XFLR5, so it was easier). I should now dig into AVL.

I apologize in advance for what may be a dumb question (but I don't have an aerdynamics/hydrodynamics background): I understand that AVL does not computes the viscous drag. And drag is key in the Windfoil balance of moments. Would AVL results still have some relevance ?

And is there a wy to inject Xfoil (or XFLR5) drag into AVL (or is it two separate things) ?

JMF

4. Joined: Feb 2002
Posts: 2,319
Likes: 303, Points: 83, Legacy Rep: 1673
Location: Port Gamble, Washington, USA

### tspeerSenior Member

AVL and Xfoil are two different things. AVL will calculate the induced drag, and you need to add the viscous drag to it. AVL does have a viscous drag coefficient as an input so it will give you a number for the total drag. But it doesn't calculate the viscous drag itself.

What you need to do is set up a system for drag bookkeeping. There are a lot of contributions to drag and different methods of estimating them. You can get some from AVL and some from Xfoil. Others you may have to estimate using empirical handbook methods like you'll find in Hoerner's Fluid Dynamic Drag. If you could find a tool that would calculate them all, you probably couldn't afford to run it.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.