The Tale of Tails

[PonoBill]

With all the testing and development KD has done with tails I feel fairly comfortable starting with designs he considers his most advanced rather than asking him to make me something custom. I'm even more comfortable knowing that he is not a lightweight--he's probably about 190kg--his development efforts are relevant to me though the size of his typical main wings seems impossible to me--some of them look more like my larger Axis tail wings.

It's also pretty clear that he's capable of paying attention to design parameters while testing. I'm generally fully focused on simply staying up on foil. Here's Randy Royce's video from yesterday of KD and Gabi finishing up at the harbor after a 10-mile Maliko run. KD is the first to enter. Note that he's staring at his phone and possibly even texting while riding bumps. I'm not convinced the kid is human.

I also note that someone posted recently that they'd heard Maui wasn't going to have much wind for the rest of the winter. Ponohouse is well shielded from trades with a huge mock orange hedge. Despite that, the howling and window shaking woke me up at 3:00 am, as it has for the last four days. The Maui 10-meter wind forecast shows I won't be sleeping late for the foreseeable future.

[Admin]

Good stuff. I'm determined to do downwinders without a wing, even if I have to cheat to do it. So yeah, a motor. But more importantly, increasing the efficiency of high-lift wing/fuselage/tail combinations. This project with Admin to screw around with designing something that works better with our limited capabilities might yield some results. I've been playing with tails this year on Maui and mine are getting smaller and thinner. I going to pick up a few from KD, but I've also ordered some G10 sheets to experiment with my own ideas.

After spending time with a slightly re-profiled Axis 400/60 tail (I made it thinner) I rode my 999 with a 340 tail that previously felt really good. I came in after one pass thinking I had something stuck on the tail.

I'm also going to try 3D printing some tails. I got some polycarbonate filament which should hold up long enough to test some ideas.

We are going have some fun.  We can print 375's or down in one piece (maybe larger with some creativity).  Either way we can do the same tail with 3, 4, 5 subtle variations (or big ones) laminate and bake them all at once.  So many things to try.  The oven came yesterday.  I got it set up with extra shelves and kit for two bags at once so we should be ready to jam.  Check this out: https://www.standupzone.com/forum/index.php?topic=38297.msg438537#msg438537

[PonoBill]

If we're going to laminate them we can print two pieces and join them. It would be a good idea to play with lots of tails before we do many wings.

[jondrums]

@Beasho - I don't understand why you are adding the tail area to the front wing area?  I believe a much more appropriate formula would be:

Read up the first half of this article first

A better formula to track with would be ratio of total area to tail area.  So for 300P tail on a 999 front wing:

999 has area of 1038cm2
300P has area of 148cm2  (300 wide, aspect ratio 6.07)

(1038 + 148) / 148 = 8:1 ratio of total area to tail area

-------------

But what you're really after is Static Margin which tells you how stable the system will be.  And for this you need to know the fuselage length.  This is all just a bit complex, but with these formulas, you could equate different tail areas to various fuselage lengths.  I'm going to do this math for 250P-350P and Crazy-Short to Standard fuselages and post it up when I have the time.  Should be fun!

[Beasho]

@Beasho - I don't understand why you are adding the tail area to the front wing area? 

The Lift from the Front Wing has to Carry:

Person + Board + Downforce of the Tail

In the Example = 200 + 25 + 35 = 260 lbs. 

But there is an added DRAG Penalty from the 35 lbs of Downforce from the Tail.  Therefore the FRONT Wing load produces DRAG based upon 260 lbs of LIFT and the TAIL produces DRAG from 35 lbs of "Lift". 

The NET DRAG producing LIFT is therefore 295 lbs.

Take away the tail and the ONLY "LIFT" necessary is 225 lbs.  295 / 225 = 1.31 representing a 31% increase in DRAG vs. a NO Tail scenario.

Click on Graphic Below to see Animation

[Beasho]

But what you're really after is Static Margin which tells you how stable the system will be.  And for this you need to know the fuselage length.  This is all just a bit complex, but with these formulas, you could equate different tail areas to various fuselage lengths.  I'm going to do this math for 250P-350P and Crazy-Short to Standard fuselages and post it up when I have the time.  Should be fun!

YES!

Fuselage Length is Required to determine how the See-Saw works.  It was in all my calculations.  I will include the spreadsheet below (NO DICE on Attaching Spreadsheet).

[Beasho]

NOTE:    Nothing we are trying to figure out here is NEW to the Universe.  When Airplanes were invented 119 years ago this Saturday Dec 17th (vs. 1903) there were near infinite resources that went into optimizing flight because enterprising individuals could make money and/or kill people better.

I found a great write up on Tail Design. This publication refers to a Horizontal Tail Volume Coefficient roughly defined as:  Volume Tail / Volume Main Wing

This ratio is similar to my Area Tail / Area Front Wing.

FULL PDF Attached Below -->

[Beasho]

 The Flight Mode we most represent is in Figure 6.2

With Center of Gravity FORWARD of the Center of Pressure from Front Wing, relying on Tail Downforce for Stability.

[Hdip]

The Flight Mode we most represent is in Figure 6.2

With Center of Gravity FORWARD of the Center of Pressure from Front Wing, relying on Tail Downforce for Stability.

So why not balance up the board and foil and body position so that the center of gravity is in line with the center of lift?

[Beasho]

The Flight Mode we most represent is in Figure 6.2

With Center of Gravity FORWARD of the Center of Pressure from Front Wing, relying on Tail Downforce for Stability.

So why not balance up the board and foil and body position so that the center of gravity is in line with the center of lift?

This is Exactly what a No-Tail solution would do. 

Otherwise (almost) all Stable Aircraft designs are shown as figure 6.2.  There are some caveats but in steady state flight mode Tail Downforce permits us to glide 'comfortably.'  First generation GoFoil tails were cambered upside down (e.g. flat section up) to enhance down force.  As we get better tails are becoming more symmetric but that is where the discussion is headed. 

Clifford Coetzer said it succinctly in his interview with Erik Antonsen on the Progression Project podcast

"An airplane with CG forward flies poorly but an airplane with a CG behind (aft) flies once."

[Beasho]

But what you're really after is Static Margin which tells you how stable the system will be.  And for this you need to know the fuselage length.  This is all just a bit complex, but with these formulas, you could equate different tail areas to various fuselage lengths.  I'm going to do this math for 250P-350P and Crazy-Short to Standard fuselages and post it up when I have the time.  Should be fun!

Jon:  See this articulation on Tail Design and some comparative metrics for standard aircraft:

I love the assumption:

It is presumed that the horizontal tail designer is familiar with the flight dynamics principles and is capable of deriving the complete set of longitudinal trim equations based on the aircraft configuration.

[Beasho]

On the Airfoil Shape of the Tail wing:  Generally downforce, but when changing angle of attack aka pumping things can get weird

This .. necessitates the tailplane to behave similar in both positive and negative angles of attack. For this reason, a symmetric airfoil section is a suitable candidate for horizontal tail.

[Beasho]

So this is all theoretical.  Its got my brain tied in a knot.

The theory has to meet with reality.  Think Jack Ridley Aeronautic Engineer and Chuck Yeager Test Pilot.

"Well, ... Hoover and I were definitely not flight test engineers! We could fly airplanes and we had an instinct for aerodynamics ... but Jack Ridley ... was a brain! Jack Ridley knew everything there was to know about aerodynamics and he was practical. And, besides, he was a good pilot ... and he fit right in with us. He spoke our language. Bob was a Tennessean and I was a West Virginian and, being an Okie, Jack spoke real good language for us." - Chuck Yeager

Meanwhile here is a picture of James Casey with his latest tail.  Extremely HIGH Aspect but NOT disappearing to Nothing.

[sflinux]

Meanwhile here is a picture of James Casey with his latest tail.  Extremely HIGH Aspect but NOT disappearing to Nothing.

Do you reckon James Casey is using the new Axis 400 Flat Speed Carbon Rear Wing?

WINGSPAN: 400 mm / 15.75 in
CHORD: 60 mm / 2.36 in
ASPECT RATIO: 8.22
ACTUAL AREA : 196.24 cm² / 30.42 IN²
PROJECTED AREA: 194.66 cm² / 30.17 IN²
VOLUME: 70.77 cm³ / 4.32 IN³
https://axisfoils.com/collections/rear-wings/products/400-flat-speed-carbon-rear-wing

Your Axis 999 + 400 Flat speed (195) = 1205 total projected area, versus 1223 that you currently ride.  Should be an easy drop in replacement with respect to lift, but with a much faster ride, looks sweet.
And with Jondom's calculation the 400 tail wing with a 999 front has a total area to tail ratio of 6.29:1 [(1038+ 196)/196]
versus your current tail (375) wing total area to tail ratio of 5.41:1 [1038+ 235)/235]

[Admin]

I have posted something similar before but this is pretty critical.  This NASA calculator is awesome.  It will simulate a straight wing generated from any foil section.  Be sure to change it to water and leave depth at zero.  The results below are from the default symmetrical wing (but you can input any wing section) set up as a tail wing at both -2 degrees and -1.5 degrees.  Each are then changed from (common for tails) 9 % thickness to 10%.  This is run twice.  First near takeoff speed at 6.5 MPH and then again at 20 MPH.

Very informative when considering the relative result of changing tail incidence by only a half degree vs tail thickness by a full percent, especially because with most tail mount designs you can accidentally miss by a full degree and not even know that it has occurred.

I just varied thickness vs angle for this but also play with scale and aspect ratio (although those things will not likely change by accident ).

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/foilsimstudent/

6.5 MPH

Joukowski Airfoil
Camber = 0 % chord, Thickness = 9 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -2 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 6.5 mph
Lift = -2060 lbs
Drag = 132 lbs

Joukowski Airfoil
Camber = 0 % chord, Thickness = 9 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -1.5 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 6.5 mph
Lift = -1553 lbs
Drag = 117 lbs

Joukowski Airfoil
Camber = 0 % chord, Thickness = 10 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -2 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 6.5 mph
 Lift = -2077 lbs
Drag = 133 lbs

Joukowski Airfoil
Camber = 0 % chord, Thickness = 10 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -1.5 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 6.5 mph 
Lift = -1565 lbs
Drag = 119 lbs

20 MPH

Joukowski Airfoil
Camber = 0 % chord, Thickness = 9 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -2 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 20 mph
Lift = -19506 lbs
Drag = 1158 lbs

Joukowski Airfoil
Camber = 0 % chord, Thickness = 9 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -1.5 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 20 mph
Lift = -14699 lbs
Drag = 1005 lbs

Joukowski Airfoil
Camber = 0 % chord, Thickness = 10 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -2 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 20 mph
Lift = -19666 lbs
Drag = 1160 lbs

Joukowski Airfoil
Camber = 0 % chord, Thickness = 10 % chord
Chord = 5 ft span 20 ft
Surface Area = 100.00 sq ft
Angle of attack = -1.5 degrees
Under Water
Altitude = 0 ft , Density = 1.940 slug / cu ft
Pressure = 14.694 lb/ sq in , Temperature = 60 F
Speed = 20 mph
Lift = -14820 lbs
Drag = 1021 lbs