ATEC Zephyr for sale

[aro]

11 hours ago, Blueadventures said:

This report explains and questions to some extent the method of fitting the fabric

Very interesting. The fabric attachment doesn't sound like it meets the commonly accepted standards. Also interesting that they think the 10 year life limit is too long, since the failure occurred after 10 years 6 months.

[skippydiesel]

9 hours ago, aro said:

Very interesting. The fabric attachment doesn't sound like it meets the commonly accepted standards. Also interesting that they think the 10 year life limit is too long, since the failure occurred after 10 years 6 months.

Try not to make illinformed statements - where humans are directly involved in manufacturing/construction/fabrication, there can/will always be failures. We don't l hear much about it these days but there was a time when people referred to Monday morning/Friday afternoon cars - a bad purchase. This did not condemn the whole brand/model - people understood, as you don't, that humans are fallible.

 

The fabric attachment system is excellent.  It relies on advanced adhesives (that have continued to evolve) and heat shrunk fabric - does not use stitching and doesn't need to.

 

The ATEC Zephyr has a very good safety record - was until production ceased, in I think 2022, after about 24 years, used mainly in the Eu , as a training, glider tug, personal transport aircraft. Also found in USA, Australia (about 12 aircraft) NZ. The Zephyr was replaced by the Faeta (2 models)

[aro]

52 minutes ago, skippydiesel said:

Try not to make illinformed statements - where humans are directly involved in manufacturing/construction/fabrication, there can/will always be failures.

All I said was it didn't seem to meet commonly accepted standards. Can you point to a commonly accepted fabric covering standard that allows a 50mm bond area, with the edge into the slipstream?

 

I have covered an aircraft so I have some knowledge of the usual practices, but I'm prepared to be educated. The usual processes generally have a large margin to allow for error, this type of failure is not expected.

[skippydiesel]

Aro - I take it from your comments that your experience is the "traditional stitching/lacing" & doping system. This is a system that has been around since the dawn of aviation - nothing actually wrong with it, other than the time to do it & the exposure to some very nasty substances.

 

The new system (not so new anymore) is to glue the fabric in place. No lacing./ stitching and heat shrink the fabric to make a tight membrane - eg the certified  Stewart System https://stewartsystems.aero/. (mainly waterborne solutions) As with any new technology there is a learning phase. From distant memory, I think the original fabric leading edge of 30mm worked just fine, until there was some human installation error. As a result (I think it was one incident) the width was increased to 50mm accommodate this error.

 

FYI: I am no expert however it seems to me, that the area that is under most aerodynamic (lifting) stress is the trailing edge, of the upper skin ie not the leading edge at all.

[FlyBoy1960]

NO, the area of the most lifting is the CENTER of PRESSURE and this moves with the angle of attack and is usally above and foreard of the C of G.

 

Your ignorance and denial is concerning to say the least.

 

I dont want to be rude but your a danger to yourself, and others who fly with you, and people on the ground.

Edited Monday at 11:30 AM by FlyBoy1960
Spelling

[turboplanner]

Would one of you experts like to post the Bernoulli Theorem?

[skippydiesel]

"...............under most aerodynamic (lifting) stress is the trailing edge"

 

This is about the potential for fabric separation from the underlying frame - not about wing lift. I will apologise only IF a genuinely knowledgeable person correct me on this.

Edited Monday at 08:53 PM by skippydiesel

[FlyBoy1960]

My good friend, let's correct you again (I really do hate being the bad cop in this thread)

The claim that the trailing edge of a fabric-covered wing is under the most aerodynamic (lifting) stress is not correct. Here's why:

Stress Distribution in an Airfoil:

1. Lift Generation:

   • Lift is primarily generated by the pressure differential between the upper and lower surfaces of the wing. The maximum aerodynamic stress occurs near the forward third of the wing, typically around the leading edge to the quarter-chord point, due to the high-pressure gradients and airflow acceleration over the surface.
   • This region is where the airfoil experiences the highest bending and torsional loads due to lift forces.

2. Trailing Edge:

   • The trailing edge plays a crucial role in defining the airflow's exit path and reducing drag by allowing a smooth flow separation. However, it experiences much lower aerodynamic loads compared to the leading edge or the main body of the wing.
   • Structurally, the trailing edge is usually designed to withstand tension from the fabric but not the primary lifting stresses.

3. Fabric-Covered Wings:

   • In fabric-covered wings, the fabric itself handles aerodynamic pressures, but the internal spar and rib structure bears the majority of the load.
   • The trailing edge of such wings often incorporates a thin and flexible structure (like wire or wood) that holds the fabric taut but isn't designed for significant load-bearing.

Structural Stress:

From a structural engineering perspective, most load-induced stresses on a wing occur at:

• The spars (especially the main spar near the leading edge).
• The rib connections, which maintain the airfoil's shape.

The trailing edge is structurally important but not under "most stress" during lift generation.

Conclusion:

The statement that the trailing edge is under the most aerodynamic stress is incorrect. The leading edge and the forward part of the wing's chord experience the highest aerodynamic and structural stresses.

 

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

 

Let me follow this up with some references which may allow you to learn more about your aircraft, its design and performance.

 

Here are a few authoritative references to support stress distribution in wings and the role of different parts of an airfoil:

---

Aerodynamics and Stress Distribution:

1. "Fundamentals of Aerodynamics" by John D. Anderson

   • This textbook explains the physics of lift and pressure distribution over an airfoil. It specifically describes how maximum lift-related stress occurs near the leading edge and quarter-chord point, not the trailing edge.
   • Relevant Section: Pressure distribution and aerodynamic loads on an airfoil.

2. "Aircraft Structures" by David J. Peery

   • A classic reference on how aerodynamic forces are distributed across wing structures and the role of spars, ribs, and trailing edges.
   • Relevant Topic: Stress distribution in wings and structural design for load-bearing.

3. NASA Glenn Research Center - Airfoil Pressure Distribution

   • NASA provides detailed resources on airfoil aerodynamics, including pressure distribution diagrams that show how lift-related stresses are concentrated towards the leading edge.
   • Website: NASA Aerodynamics Resources

4. "Theory of Wing Sections" by Ira H. Abbott and Albert E. Von Doenhoff

   • Another key text in aerodynamics that details how aerodynamic stresses vary across an airfoil and provides pressure distribution graphs for different airfoil designs.
   • Relevant Sections: Airfoil pressure distribution and structural implications.

---

Fabric-Covered Wing Design:

5. Federal Aviation Administration (FAA) Advisory Circular AC 43.13-1B

   • This document contains guidelines for the construction and maintenance of fabric-covered wings, discussing how spars and ribs bear the main structural loads, while the trailing edge provides shape and minimal structural support.
   • Website: FAA AC 43.13-1B

6. "Structural and Stress Analysis" by T.H.G. Megson

   • Provides a comprehensive look at structural stress distribution in aerospace structures, including how loads are transmitted through spars and ribs in traditional and fabric-covered wings.
   • Relevant Sections: Structural analysis of airframes.

7. The National Soaring Museum - Sailplane Wing Design

   • Articles on vintage and fabric-covered sailplane wings that explain the structural role of the trailing edge compared to spars and leading edges.
   • Website: National Soaring Museum

---

Citation:

• "According to John D. Anderson in Fundamentals of Aerodynamics, the highest aerodynamic stresses occur near the leading edge and quarter-chord point of a wing due to pressure differentials, not at the trailing edge."
• "The FAA's Advisory Circular AC 43.13-1B explains that in fabric-covered wings, the primary load is borne by the spars and ribs, while the trailing edge provides shape and minimal load-bearing support."

 

 

Let me know if you'd like more information ?    I rest my case.

Edited Monday at 09:45 PM by FlyBoy1960

[FlyBoy1960]

4 hours ago, turboplanner said:

Would one of you experts like to post the Bernoulli Theorem?

Sure, I am just copying and pasting from my aviation reference material so I don't pretend to be an expert just somebody who understands more than I should and has easy reference to it.

 

The Bernoulli Principle in Aviation

When you think about how an airplane stays in the sky, the Bernoulli principle is a big part of the answer. Named after Daniel Bernoulli, who figured this out way back in the 1700s, it’s a concept about how air (or any fluid) moves and creates pressure.

 

Here’s how it all works:

 

Faster-moving air creates lower pressure.

In aviation, this comes into play with the shape of the airplane’s wings, or the airfoil. Wings are designed so that the top surface is curved more than the bottom. When the airplane moves forward, the air traveling over the top of the wing has to move faster to "catch up" with the air traveling below. Since the air on top is moving faster, it creates less pressure compared to the slower air underneath the wing.

This difference in pressure is what gives you lift. The higher pressure under the wing literally pushes the wing (and the plane) upward. The wing essentially "floats" on this pressure difference, like how a beach ball can sit on a stream of water from a hose.

---

How This Works in Real Life

Pilots don’t need to do a lot of math to understand Bernoulli; you see it every time you take off. When you add power and the plane accelerates down the runway, the air starts moving faster over the wings. At a certain speed (called the stall speed), the pressure difference becomes strong enough to lift the plane into the air.

It’s also why an airplane’s angle of attack (the angle the wing makes with the oncoming air) is so important. The more you tilt the wing, the bigger the pressure difference—up to a point. If you tilt too much, the airflow can’t stay smooth over the wing, and you lose lift (that’s called a stall).

---

A Quick Reality Check

The Bernoulli principle isn’t the only thing creating lift. There’s also something called Newton’s third law: for every action, there’s an equal and opposite reaction. That plays a part too—air gets deflected downward by the wing, and the reaction pushes the wing up. So, lift is really a combination of Bernoulli and Newton working together.

But when it comes to explaining why wings work in a simple way, Bernoulli gives you the big picture: fast air = low pressure, slow air = high pressure, and the difference lifts the plane.

---

This is why proper wing design and airflow are such a big deal in aviation. It’s also why things like frost or damage on a wing are dangerous—they mess up the airflow and ruin the lift that Bernoulli and Newton worked so hard to give us!

[facthunter]

Best to reinforce the end of the fabric at the TE  by going around it and overlapping,  It tends to lift at the edge. the tension of the tight fabric pulls a weak TE IN between the ribs and it looks terrible. There's nitrocellulose dope. Butyl Dope and heat shrink which has to be fairly tight to  start with as it only shrinks about 10%. Faster Planes in  the early days tended to be stitched and use stronger fabric.

   Nitrocellulose dope often used silver ( fine al particles) incorporated in the dope for  lightness hence the Popularity of silver for many parts other than engine cowls etc.  IF thick paint forms cracks the fabric will crack also under it.  Nev

[aro]

11 hours ago, skippydiesel said:

Aro - I take it from your comments that your experience is the "traditional stitching/lacing" & doping system. This is a system that has been around since the dawn of aviation - nothing actually wrong with it, other than the time to do it & the exposure to some very nasty substances.

 

The new system (not so new anymore) is to glue the fabric in place. No lacing./ stitching and heat shrink the fabric to make a tight membrane - eg the certified  Stewart System https://stewartsystems.aero/.

I used Polyfiber, which is glued and heat shrunk. I had a read of the Stewart System and it is a pretty similar process. The Stewart System does require rib stitching (there are various methods e.g rivets, screws - not only thread.)

 

Neither system seems to have a specification for a fabric edge joined to the structure. The fabric-fabric join is the strong joint, and they have specifications for the overlap required at the leading edge etc. The theory is that the fabric envelopes the whole wing, and the load is carried by the fabric joints. The fabric to structure joint is not a strong joint and needs reinforcement e.g. stitching.

 

That's not to say you couldn't find an adhesive that gave you a good fabric to structure join. But I don't think the usual adhesives in these systems qualify, and it wouldn't be a standard practice.

[skippydiesel]

"The Stewart System does require rib stitching" 

 

It is some years since I used this system (adhesive/fabric/paints) however I do not recall any requirement for stiching and I did not do so. It is likly that Stewart say to stitch were stitching required and not where not.

 

The Zephyr has relativly wide caps, on each rib and trailing edges to facilitate gluing - this may not be the case for a stitched system. In effect this makes every rib to rib, an almost self contained fabric over wood cell.

 

"The fabric-fabric join is the strong joint, and they have specifications for the overlap required at the leading edge etc"

 

Only the fabric covered control surfaces (later models had some/all? composite) were wrapped ie had an overlap, however the wings & horizontal stabiliser were not.

 

"The theory is that the fabric envelopes the whole wing, and the load is carried by the fabric joints. "

 

May be so for some aircraft, however the Zephyr had about half of the wing chord covered in plywood (later models may have had carbon fiber) and a large portion of the inner wing also fully covered in ply. This left an upper/lower  wing "patch" in fiber.

 

The Zephyr was/is not the only aircraft to use this (no stitch) system - I recall seeing an aircraft at a NSW air show with the same concept (unfortunately forget the name)

 

"That's not to say you couldn't find an adhesive that gave you a good fabric to structure join. But I don't think the usual adhesives in these systems qualify, and it wouldn't be a standard practice."

 

I used the Stewart System (certified) which include their adhesives - what is this ".... standard practice"??

 

 

.😈

Edited Tuesday at 12:02 AM by skippydiesel

[aro]

9 hours ago, skippydiesel said:

It is some years since I used this system (adhesive/fabric/paints) however I do not recall any requirement for stiching and I did not do so. It is likly that Stewart say to stitch were stitching required and not where not.

 

The Zephyr has relativly wide caps, on each rib and trailing edges to facilitate gluing - this may not be the case for a stitched system. In effect this makes every rib to rib, an almost self contained fabric over wood cell.

...

the Zephyr had about half of the wing chord covered in plywood (later models may have had carbon fiber) and a large portion of the inner wing also fully covered in ply. This left an upper/lower  wing "patch" in fiber.

...

I used the Stewart System (certified) which include their adhesives - what is this ".... standard practice"??

You linked to the Stewart Systems page, it has the documentation on how to do it. From that document:

 

"Fabric is attached to cap strips in many ways: rib lacing, screws with fabric washers, rivets and wire clips. All of these methods require the use of reinforcing tape under the attaching device. Do not rely on cement to hold fabric to cap strips."

 

It is very common for wings to have e.g. the leading edge covered in wood or metal. The fabric goes over the plywood - not just as a patch over the open areas.

 

You used the Stewart Systems products, but not the Stewart System if you didn't follow the instructions for using it.

 

"Cemented overlap seams at wing leading edge shall be a minimum of 3”. This seam shall them be covered with a minimum of 4” wide finish tape, centered on outer edge of overlap seam... The trailing edge shall be glued with a minimum of a 2” glued seam. This seam shall be covered with a 3” or wider finish tape."

 

You are describing zero overlap. If you didn't have the required overlap, you didn't have the strength designed into the system, and didn't meet the airworthiness standards it was designed to provide.

[skippydiesel]

You are a troll !

 

The Stewart System does not override the ATEC system - I used a combination, as any sensible person would, IN CONSULTATION WITH BOTH ATEC & STEWART, using each as and where appropriate,  to achieve an excellent outcome.

 

That's it I'm done with your ill-informed, selective out of context quoting, unfounded accusations, negative & destructive commentary. 

 

😈

 

 

[FlyBoy1960]

People here are trying to help you but instead you get all defensive and start throwing back abuse.

 

I have reluctantly corrected your misinformation several times including going to great lengths to pull out information which I have forwarded that completely negates what you have said. I don't do it to belittle you, I don't even know you, I do it to try and keep other aviators safe.

 

ARO went to the trouble of looking at the covering system website, that took a lot of time and effort to reply to you. What information he found directly from the website is different to what you have been saying and he has pointed it out. There is no need to go ballistic at him.

 

If a product is made by a manufacturer and it has installation instructions then you are required to follow those instructions for your aircraft to remain airworthy. You as an individual do not have the skills or experience to decide otherwise.

 

If the manufacturer declares a 10 year inspection then you have to comply with those instructions for your aircraft to remain airworthy.

 

All of your excuses in different directions do nothing for your credibility as an aviator, in fact they do the opposite and show just how inexperienced and lacking knowledge about aviation really is.

 

I was studying yesterday for my beyond visual line of sight drone course and I must pull up the notes that came from the human factors. There were 4 types of conditions that would affect pilots and you are definitely number one. 

 

That was the pilot who said they knew everything, they had survived so far, they were better than everybody else, they didn't need anybody telling them what to do, and the rules don't apply.

 

When we were going through the human factors training it made me directly think of you at the time.  Just saying.

[pmccarthy]

This exchange reminds me of several cases some years back when a valuable forum member was driven to leave the forum by repeated attacks. We were all the losers each time that happened. I have learned a lot from Skippy's posts over the years and I hope this exchange is over and he doesn't take it to heart.

[Methusala]

Moderators please!

 

[skippydiesel]

8 hours ago, pmccarthy said:

This exchange reminds me of several cases some years back when a valuable forum member was driven to leave the forum by repeated attacks. We were all the losers each time that happened. I have learned a lot from Skippy's posts over the years and I hope this exchange is over and he doesn't take it to heart.

My thanks Pmccarthy.  I will survive .

 

The Forum is a truly wonderful resource, that I feel privileged to part of. I am on several forums, non as congenial and informative as this one.😈

 

 

[dlegg]

On 17/12/2024 at 7:56 AM, FlyBoy1960 said:

Sure, I am just copying and pasting from my aviation reference material so I don't pretend to be an expert just somebody who understands more than I should and has easy reference to it.

 

The Bernoulli Principle in Aviation

When you think about how an airplane stays in the sky, the Bernoulli principle is a big part of the answer. Named after Daniel Bernoulli, who figured this out way back in the 1700s, it’s a concept about how air (or any fluid) moves and creates pressure.

 

Here’s how it all works:

 

Faster-moving air creates lower pressure.

In aviation, this comes into play with the shape of the airplane’s wings, or the airfoil. Wings are designed so that the top surface is curved more than the bottom. When the airplane moves forward, the air traveling over the top of the wing has to move faster to "catch up" with the air traveling below. Since the air on top is moving faster, it creates less pressure compared to the slower air underneath the wing.

This difference in pressure is what gives you lift. The higher pressure under the wing literally pushes the wing (and the plane) upward. The wing essentially "floats" on this pressure difference, like how a beach ball can sit on a stream of water from a hose.

---

How This Works in Real Life

Pilots don’t need to do a lot of math to understand Bernoulli; you see it every time you take off. When you add power and the plane accelerates down the runway, the air starts moving faster over the wings. At a certain speed (called the stall speed), the pressure difference becomes strong enough to lift the plane into the air.

It’s also why an airplane’s angle of attack (the angle the wing makes with the oncoming air) is so important. The more you tilt the wing, the bigger the pressure difference—up to a point. If you tilt too much, the airflow can’t stay smooth over the wing, and you lose lift (that’s called a stall).

---

A Quick Reality Check

The Bernoulli principle isn’t the only thing creating lift. There’s also something called Newton’s third law: for every action, there’s an equal and opposite reaction. That plays a part too—air gets deflected downward by the wing, and the reaction pushes the wing up. So, lift is really a combination of Bernoulli and Newton working together.

But when it comes to explaining why wings work in a simple way, Bernoulli gives you the big picture: fast air = low pressure, slow air = high pressure, and the difference lifts the plane.

---

This is why proper wing design and airflow are such a big deal in aviation. It’s also why things like frost or damage on a wing are dangerous—they mess up the airflow and ruin the lift that Bernoulli and Newton worked so hard to give us!

I really appreciate Bernoulli but surely if you got a BBQ plate moving fast enough and increased AOA it would fly. Lots of aircraft have wings with identical profiles each side of the centreline, so does the Bernoulli effect simply enhance a wings behaviour..?

[FlyBoy1960]

58 minutes ago, dlegg said:

I really appreciate Bernoulli but surely if you got a BBQ plate moving fast enough and increased AOA it would fly.

Thats called a fighter jet.

[turboplanner]

7 hours ago, dlegg said:

I really appreciate Bernoulli but surely if you got a BBQ plate moving fast enough and increased AOA it would fly. Lots of aircraft have wings with identical profiles each side of the centreline, so does the Bernoulli effect simply enhance a wings behaviour..?

Yes, about 1/3. The other 2/3 comes from downward deflection of the wing.

For the 1/3 to kick in the fllow over the top surface has to be laminar, hence it doesn't suck fabric off the ribs as we found out if we used dope on the fabric of model aircraft.

 

With enough power to weight ratio you can fly an aircraft with just deflection.

Most control line and RC aircraft are in this catergory.

 

As someone mentioned, supersonic forces are very different requiring a different form of wing. A lot more complicated.

 

[aro]

Posting details from the Stewart Systems manual is hardly trolling. All the information I posted is in investigation report someone else posted earlier. I didn't know anything about this before reading that, but it's scathing.

 

On 17/12/2024 at 7:52 AM, skippydiesel said:

This is about the potential for fabric separation from the underlying frame - not about wing lift.

 

Wing lift is what is trying to separate the fabric from the frame. Air pressure acts on the fabric, which transfers the lift force to the ribs and structure. You can see the fabric bulging between ribs, or even the aluminiun skins on some metal aircraft.

 

Let's run some numbers...

 

If the aircraft G limit is 4G, it must be able to handle 6G without failure. So for a 544 MTOW the wings need to handle over 3000kg lift force.

 

That's 1500kg per wing. If the top surface produces 2/3 of the lift that's 1000kg force. Lets say the fabric covers 40% of the wing area, that's 400kg force trying to suck the fabric off the structure.

 

To picture it, imagine turning the wing upside down, removing the bottom skin and stacking 400kg of sandbags on the inside surface of the fabric. That's what it has to be able to handle. Is a 35mm (or 50mm) glued joint enough? Personally, I prefer the standard method - wrapping and overlapping the fabric around the leading and trailing edges.

[aro]

12 hours ago, dlegg said:

I really appreciate Bernoulli but surely if you got a BBQ plate moving fast enough and increased AOA it would fly.

Bernoulli is a bit of a red herring. It is generally used incorrectly trying to explain lift.

 

A flat plate at an angle of attack produces lift. At subsonic speeds there is a pressure wave ahead of and below the plate that changes the flow of air ahead of the plate. If you see the stream lines (e.g. smoke trail) you can see the air flows around the plate in a similar way to a conventional airfoil.

 

The airfoil is just a way to improve the airflow, to make something that works better than a flat plate. If we make the leading edge more curved, we can get a smoother flow for less drag and keep the flow attached at a higher angle of attack. If we adjust the curve on top, we can change where the centre of pressure occurs, and how it moves at different angles of attack. If we change the curve on the bottom, we can reduce the drag at high speed... and many other factors.

 

If you look at the airfoils used on the very early aircraft, they are often very similar shape to the air flow you get around a flat plate. The very start of refining the airflow around the wing...

[facthunter]

The Fabric on the top of the Lower wing  of a tiger Moth can be observed to visibly Bulge up above the wing ribs in flight. Bernoulli s theory is not that helpful to explain what is going on. All aerofoils have a zero lift angle of attack. The whole wing deflects the air, Top and lower surfaces. The reaction to the displacement of the air provides the lift force.  Nev

[turboplanner]

21 minutes ago, aro said:

Posting details from the Stewart Systems manual is hardly trolling.  I didn't know anything about this before reading that, but it's scathing.

 

Wing lift is what is trying to separate the fabric from the frame. Air pressure acts on the fabric, which transfers the lift force to the ribs and structure. 

 

There's no sucking.