So, doing some more research on this.
The Vought V-173 is an example of a very radical high chord, super low aspect ratio experimental plane. Radical enough that it made a lot of people who knew what real aircraft looked like, deeply uneasy about it's shape.
There's a good discussion of it here:https://oldmachinepress.com/2017/01/20/ ... s-skimmer/
Including mention of the initial test plane being under powered and financial woes affecting the successor version, including a decision that a test flight needed to be made far away but that it would be too difficult to transport it there. Then a wrecking ball came along...
The V-173 exhibited very short take off requirements and potential for high speed. Slightly skewing matters for us, the props effectively increased apparent wind and lift by working over a large proportion of the aircraft's body.
Apparently even at 45 degrees it wouldn't stall
! Landing, it would experience a ground-effect further back than the free-flight centre of lift and take a dive. Control requirements were hugely underestimated because in-flight the high chord presented massive stability
that required huge effort to overcome for steering and roll. (You don't want to be that test pilot!
Take a moment to reflect on the Airforce's likely automatic reaction to the test pilot's underwear-staining
experience in a profoundly unusual looking plane. All the armed forces primarily recruit Myers Briggs S(sensing), J(judging) types, people stronger in observation, judging and conservatism than in intuition, perceiving and change adaption.
Now lets take a look back at aeronautical reasons to avoid Deltas
despite their known superior lift/weight characteristics: and there's a biggie!
Airports the world over work on the basis of runways with a lot of length and short width.
A plane with high aspect ratio can easily control it's roll with ailerons. Approaching a runway with high cross winds, a pilot can compensate for cross wind by keeping the plane flat under aileron control and straight (with rudder)relative to the runway/cross winds(it's a compromise that starts with centre of mass and ends with skidding and paralleling the fuselage with the runway)
A delta plane uses elevons for a combination of pitch and roll control, it doesn't have yaw control
but looking from a bird's eye view, yaw is provided by oposing left/right elevon input until the aircraft is partially rolled and then elevator control of pitch(both elevons in the same direction) so that the off-horizontal axis from the roll moment converts the pitch moment to yaw as seen from a bird's eye view. All this works much easier than it sounds but the end result is that yaw changes are done in 3 dimensions for a delta
, while for conventional fuselage planes, yaw motions can be done while the plane is still flying in a 2D-plane
. This means that for a delta plane, runways approached in high cross winds are very dangerous, a rudder on a delta doesn't get enough leverage and is pretty much a waste of time. I'm mentioning this because the single biggest reason Aviation doesn't use deltas is a safety reason that simply has zero affect in our hydrofoiling use-cases.
None of the above dissuades me from trying my latest design out. As I said, it's intended as a learner unifoil with high pitch stability due to the long chord. The low aspect ratio improves roll control allowing for tighter turns. My gull-wing modification is primarily done for ease of manufacturing but the downward pointing tips should improve wingtip lift performance to my untrained
perception by diverting water flow closer in to the longer trapped path. As for aspect ratio and eficiency, it's only part of the picture. I've flown RC gliders including deltas, jets and more traditional glider shapes. Deltas can be very high performance. A swing-wing jet can actively change from a high aspect traditional shape for low speed high lift, to low resistance, high speed delta shape. Note that a longer surface will experience more drag than a shorter surface for the same width but this is not what we are doing, Drag is more about total area, thickness, thickness profile and surface interaction. In a wing with longer chord, fluid molecules close to the wing actually have more distance to speed up, I'm thinking that means a longer chord for the same area has better
speed potential. Remember we aren't trying to get ultimate lift at high speed, we want control, glide and LOW
speed lift. At high speed lift is more than we need.
Here's the next consideration- a high mass uncompressible fluid vs air. All those of you who've flown a kite in a loop, felt the apparent wind. Wind surfing, you know that feeling of power you get when the sali is no longer stalled but slicing through into new air that hasn't had a chance to slow and stall, it's that new, not yet slowed air mass that is dumping it's moving energy into your attached surfaces. In the air, a high aspect wing, a tall but narrow sail only develops it's power at higher speeds. A lower aspect kite, a shorter but higher chord sail have better low down power. So think about what you want under your feet... do you want max lift at highest speeds?? Imagine that surface cutting through not air, but water. That mass is around 800 x more dense than air. Your required lift comes off a much smaller area, span. Do you really want that "lift
optimised for high speed" foil under your feet?