Reko

Inspiring as always Alex. Thank you for sharing! I'm definitely curious to hear what weight your wings will come out at.

Forgive me if this question is already asked, but are you doing all this work for yourself or will you start production/sales of this aircraft?

Alex Voicu

Thanks Reko. The target weight is ~400g/ wing panel which is the usual weight for composite wings these days, but this first set of wings will be significantly heavier. Since it's our first attempt at composite wings, we didn't know how heavy and how strong the internal structure will be until we actually built it, so it's a bit overdone at the moment. I wanted to test the model and validate the aerodynamic concept as soon as possible, so we decided to build this first set of wings even if it comes out heavier.

If there's interest in the model, sure, we can manufacture some kits on demand. But first it's important to make sure we have a good quality model that flies well.

Alex Voicu

Well, the stabs came out at 104g which is a pretty good weight for composite construction. As expected, wings are quite heavy (~496g) but i can use them for flight testing and we have plenty of ideas where we can save weight, so i'm sure we can achieve the target weight with the next pair of wings. The elevator is already cut and the peel-ply hinge seems very good.

David Kyjovsky

Alex, this is great work. I am looking forward to see more work in progress. Do you consider painting the color scheme in the mold?

Alex Voicu

Thanks David. Painting in the mold would save a lot of weight, but i don't have enough experience with painting. I will probably take all the parts to a professional painter when the model is finished.

David Kyjovsky

Fair enough. If you start mass production though, painting in the mold is the way to go... and I am sure you would find someone to help you with that, at least at the beginning..

drac1

My Feedback: (4)

Just be careful who you get to paint it. If you use a auto paint shop, they tend to paint heavy.

Alex Voicu

We have a few great builders around, but i intend to oversee the painting process to avoid this situation, and maybe learn a few tricks while i'm there.

Anyway, since this pair of wings is quite heavy it's not worth painting them, so the plan is to test fly the model as it is, in overall white color, and paint it later when i'll have the new, lighter wings.

I will probably design and build a balsa structure wing over the winter, the light weight compared to the composite wing is very attractive.

David, mass production is too much to say, unless of course there's a model factory willing to produce it But i'm sure we can produce some kits on demand for those who are interested.

drac1

My Feedback: (4)

Have you decided on a spinner yet?

Alex Voicu

I haven't even decided on the motor yet It would look great with a contra spinner at the front, but i'm a little low on budget for that.

I do have this electric contra-rotating motor though, but i'm not sure how reliable it is:



If i decide to go with a single propeller setup, i will use a Himax 210 pro with a Mejzlik or Marquet 82mm spinner.

apereira

Alex,

It reeeeally looks good, beautiful shape, I hope it performs very well.

Best regards

Alejandro

Alex Voicu

Thanks Alejandro, i'm glad you like it.

I attached a few images showing the rudder construction. The internal structure is positioned using a cardboard template. I plan to paint the plane later, after the maiden flight so i have to make the rudder removable. I will use Robart hinges, with a removable carbon rod going through them.

Alex Voicu

The composite fuselage extracted from the mold is just an empty shell, so i had to add some internal parts for equipment installation and structural strength.

I started with the landing gear support structure; the vertical frames were cut from 2mm plywood and the gear support plate is made of 4mm plywood, all carbon laminated. I added the M3 blind nuts for each gear leg and in the end the structure was assembled and epoxied inside the fuselage.

highfly3D

Awesome...

Alex Voicu

Thank you Highfly3D.

The tail structure was added next. The shape for the formers was taken from the CAD model, printed at 1:1 scale. First i made a cardboard template, adjusted it a little here and there and used it for tracing the formers on a balsa sheet. I noticed that even fairly thick balsa can easily buckle under lateral loads, so i added a few pieces of balsa with the fibers going at 90 degrees relative to the formers. These weigh almost nothing but add a lot of strength to the structure.

The location of the tail structure was traced on the outer surface of the fuselage. Using a light source on the inside, i aligned the formers with the markings and attached them with epoxy and microbaloons.

Alex Voicu

I added a piece of 4mm plywood for the tail wheel support and worked on a few more structural elements. A vertical balsa frame will be attached behind the cockpit and a horizontal depron crutch with balsa reinforcements will be fitted between the frame and the tail structure.
I also put the landing gear on just to take a quick look at the model.

Alex Voicu

I also made a balsa tube for the elevator servo extensions to run through. I attached it to the horizontal depron former and in the end all the parts were glued inside the fuselage.

Alex Voicu

The rudder servo tray was added next. The receiver and digiswitch will also be installed on this tray. As usual, i started with a cardboard template to make sure it will fit perfectly, then cut the final part from nomex honeycomb.

The canopy latches seem way to large and heavy, so after some trimming and sanding here and there i managed to save about 7g. The metal pins are also much longer than needed, so i will save more weight later when i will figure out the exact length.

drac1

My Feedback: (4)

Looking good Alex.

How do you attach the pins in the canopy? Photos?

Alex Voicu

Thanks. I will cover this in the next update here, but you can already see the photos for the pin attachment in my Facebook album here: https://www.facebook.com/alexandru.v...0541866&type=1

drac1

My Feedback: (4)

Thanks. I didn't realise that you had photos there as well.

Scott

Alex Voicu

To attach the locking pins to the canopy, first i created a cross-member using a few pieces of plywood and balsa. I used a regular screw to create the threads in the plywood parts. The plywood ends with the pins attached were placed on the fuselage and a piece of balsa was used to join them. This way i was sure the distance between the pins is the same as the distance between the holes in the fuselage.

A few pieces of balsa were used to create some sort of spring that would keep the cross-member pressed against the canopy flange. This way i was able to move the canopy around a little bit to fit the fuselage properly while the cross-member was held in place by the locking mechanism. When i was happy with the position of the canopy, i added some tape to keep it still while the epoxy was curing.

serious power

' A few pieces of balsa were used to create some sort of spring that would keep the cross-member pressed against the canopy flange. This way i was able to move the canopy around a little bit to fit the fuselage properly while the cross-member was held in place by the locking mechanism.'

Alex,
Very clever and well done.

Brian

Alex Voicu

Thanks Brian. Sometimes everything goes according to plan, but sometimes i make some mistakes too. I initially planned to go with 2 carbon pins at the back of the canopy and the locking mechanism at the front. As you can see in some of the images below, i attached the 2 carbon pins but found out this combination is not going to work. With the 2 carbon pins inserted in their slots at the back, it's not possible to make the 2 metal pins at the front to engage the locking mechanism. I had to cut the 2 carbon pins and use a canopy latch instead. Will have to pay more attention to this in the future.

Alex Voicu

It's been a while since the last update; in the meantime there has been a "slight" change of plans but work never stopped. My friend at the composite workshop is busy molding a jet, so i didn't want to bother him with another set of composite wings. Anyway, instead of sitting around doing nothing over the winter i decided to start working on a new set of built-up wings and stabs for Audax. If you read the initial post in the this thread, i've been thinking about the balsa structure from the start, so this was a good moment to do it. I also designed a built-up rudder because the composite one was a bit heavy.

The 3D design took about 3 weeks to complete, working every day for a few hours in the evening and maybe a bit more during weekends. The basic concept of the structure was borrowed from Radiance, which proved to be very strong, but decided to add a second spar around the carbon tube to help distributing the loads on a larger surface of the skin panels. I was a bit worried about bending the balsa around the compound curves at the tip of the wings and stabs, so the ribs were positioned closer together in this area. I added some secondary spars to the rudder structure, also to help the balsa sheets bend around the compound curves.

The balsa sheets available here are not very light, so i'm pretty sure i won't be setting any records with my final weights. For example, the lightest 2.5mm (~3/32) balsa sheets i can find here weigh around 25g, while other projects i've seen here on the forum use 16g sheets. Since my balsa sheets are heavier, they are also probably denser and stronger, so i will use 2mm instead of 2.5mm balsa for sheeting the wings. It's still heavier, but other than that there's not much i can do.

I attached a few images of the 3D structure, building images will follow.