High Aspect Foils, whats the hype?
Author: Jon Mann
What is a high aspect foil? Why should I (or shouldn’t I) get a high aspect foil? With people chasing the endless glide, especially with the rise in downwind foiling, the term high aspect rears comes up a lot in all the marketing campaigns. But what does the term high aspect actually mean?
In this post I’ll try to explain what Aspect Ratio (AR) is, how it’s applicable in the foil world, and how you choose what foil is best suited to you.
What is Aspect Ratio?
Let’s start with the basics and anser the fundamental question of what aspect ratio is. Its very simple. As per the definition from this NASA site:
“Aspect ratio is a measure of how long and slender a wing is from tip to tip. The Aspect Ratio of a wing is defined to be the square of the span divided by the wing area and is given the symbol AR.”
In laymans term it is how wide the span is of your foil relative to the chord of your foil (span divided by chord).
A higher aspect foil is shaped more like a glider with a high span and smaller chord and a lower aspect foil has a smaller span and a bigger chord.
What makes a foil ‘high aspect’?
A common misconception in foiling is that a foil with a large span is a high aspect foil. Often this happens to be the case but there are also large foils with large spans and large chords which means these are not ‘high aspect’.
Looking at the current trend a higher aspect foil is a foil with an AR of around 9 or higher. An important thing to note is that glider aeroplanes have wings with aspect ratios over 30, which makes ‘high aspect’ hydrofoils then look like they have low ARs. The important thing to conclude is that AR is really a relative scale. Hence why I often refer to them as higher aspect rather than high aspect.
Some brands include references to AR in their foil names. Ignore this! It doesn’t really mean much and is relative within their range. Some brands have (or had in the past) HA foils with lower AR’s than other brands’ surfier foils. When comparing foils, it is best to ignore the name and compare numbers (primarily AR or span, area, volume, thickness, just to name a few).
What makes higher aspect foils so great?
Higher aspect foils tend to be more efficient and have improved glide.
Another common misconception is that high aspect foils are fast. This is not the case! That stereotype has come about due to the fact that the majority of foil manufacturers made high aspect foils with thin foil sections meaning that they had very little drag allowing them to go fast. However as proven by some of the larger area and higher aspect dock start foils that are out there, high aspect foils can also go slow. These foils (for example the Axis PNG 1310) have thick foil sections which allow them to also have great low ends as well as good glide characteristics.
Why would I want to buy a higher aspect foil?
Higher aspect foils are great to have in your quiver, especially if you want something with more glide that will allow you to learn and practice manoeuvres, pump and connect waves or bumps and particularly for downwinding.
The more glide you have, the more time you have to make corrections or decisions. In addition the efficiency means that when you pump a high aspect foil you get more bang for your buck than a lower aspect foil (typically) – meaning more metres covered per pump.
Are higher aspect foils surfy?
Surfiness is largely dependent on the shape of a foil, whether it has anhedral plays a big part, but of course one of the main components leading to how well a foil turns in the span.
Generally (rule of thumb), the smaller the span the better the turning. The biggest downside then of a higher aspect foil with a smaller span, is that you then have a smaller foil. What does this mean? Typically this means you have a foil with a higher low end and a higher stall speed. Is this a problem? That depends on your conditions. With enough wind or swell to get going it’s not really a problem as so long as you can get above the foil’s minimum speed (as with all foils, but especially with higher aspect foils), you can reap the benefits of the higher aspect foil (pump, glide, general efficiency) whilst also reaping the benefits of the lower span (see Zane ripping on his HA90 from Lift foils below).