Delay

No, I have not given up on this project.

However life sometimes throws a curveball.

I intend to restart this project in a few weeks… until then.

Engines and work table

The engines arrived a couple of weeks ago, in fact just after the previous update was posted. They look really good and give a solid impression:

engines

I especially like how they can be ‘reverse mounted’, which makes construction of the nacelles easier and lighter.

But that is not all I have done since then, the wood was ordered and has arrived. I was not too happy about the packaging of the wood, but everything is at least usable, and only 1 piece does have a really annoying ‘ding’. The quality looks good.

I also had a piece of stainless steel cut into pieces of 2x2x4cm. These are nice heavy (and have right-angles) blocks that I can use to fix things into place while the glue cures/dries. This instead of having to use needles like I have done in previous projects. I quite dislike needles and hope that the steel blocks will make a difference.

rvs

One more thing I did was building a new work-table. The old one was too small, and not perfectly flat. The new one is big enough to build the main wing in 1 piece and has an excellent “flatness”. What I did was taking a big sheet of plywood of 2.44x1.22m and 18mm thickness. I had the shop saw off several small stripes from the side and used these to reinforce the bottom such that it does not flex. Btw the whole things is glued, no screws or nails. And as the reflection shows, the top is painted as well. Really smooth…

table

I put a Turmeric on top for scale, the Turmeric has a span of 1.5m. The table is now 2.44x0.6m. I also made it much higher than usual (ca 95cm), so most of the work can be done without having to bend over. Very convenient. The bottom reinforcements can be seen (looking like dual-jet exhausts) as well as the wheels that I put on one end. The table is quite heavy, so it is not possible to lift and manipulate it on my own. The wheels allow me to lift one end, remove a strut and put it on the wheels. Then I can lift the other end off the remaining strut, and wheel the table to another place and repeat the process in reverse.

The table itself rests on 3 points, so there are no torsion forces on it. There is only little space between the table and the struts to minimize the possibility of tipping.

Next up is finishing my current build (a Thermy-3). The structural work is done, but I need to finish it up on the servo’s, engine and the covering. Given that I have other stuff to do as well, it may take another month or so before I can report on the first cut for the CL-415.

Parts

Having a plan is one thing, its quite another to translate the plan into a list of items to be purchased. That took longer than expected, but I finally have a pdf parts list. Some of the plan is still TBD (to be defined) those parts I will have to make up as I go along. Most of these are due to changes I want to make upon the original plan. Like flaps, rudder, or attaching the nacelles to the wing permanently. I am also still unsure of the wing/fuselage coupling. There is no clear indication how this is done.

Btw: The pdf document will be updated continuously as the build progresses.

With the parts list in hand a map was created that maps each part onto a standard item that can be purchased.

This looks as follows:

map

(Click the image for a larger version)

The ordered items itself can be seen in the PDF parts list. In the present version there are two alternatives one with prices from the Balsabar shop and one from Balsabaum (both in germany).

However care should be taken when comparing prices. While the Balsabaum is slightly cheaper, this does not factor in the dimensional and quality differences. Still, prices were generally a bit lower in the Balsabaum shop. But the dimensions of the items in the Balsabar shop did match the dimensions of the plan better, making for less work when creating the parts. So in the end it’s a toss imo. (I went for less work…)

The order has been placed, and should arrive next week.

Flaps final (?)

Of course one should always be carefull when saying ‘final’, but I like following flap design:

flaps

The flap is a little smaller than the previous one, and the top is rounder (the hump is gone). While I do not have any numerical data the design seems similar to both the real one and to the visuals in the videos that were referenced in the previous flaps post.

Here are the pictures that show how the flaps will look like when extended:

flaps-15

Flaps at 15 degrees

flaps-30

Flaps at 30 degrees

flaps-45

Flaps at 45 degrees

The hinge point is closer to the wing to prevent the slot from becoming unreasonably big.

The thickness of the wing at the point of the flaps is approximately 26mm, which is big enough to mount the control rods internally.

The intention is to hinge the flaps at 4 points like the real one. But it is not sure yet if they will be distributed like the real one. This because of the placing of the ribs. Keeping the same spacing as on the real one would require extra ribs (or parts of the ribs). In the motor/prop calculations that were made it was checked what would happen if the weight comes out a little high, and that was not too bad. So there is at least the option of mounting them realistically.

Motor selection

One thing that I have experienced so far when building planes is that the motor you want, is just out of stock. So this time I want to avoid that and have selected and ordered a motor (2 of them) up front. Props, ESC and battery will have to wait, but they are much less critical to the actual design. Of course selecting a motor also means choosing the prop and battery, its just that there is some leeway in changing these components at the last possible moment (or even after the build). Not so with the motor. Dimensions and mounting holes need to be part of the design.

With that in mind, my first visit was to the Hacker website were they have a nice list for motor selection. From that list it was simple to select an engine/prop combination: select sport/scale, then weight 4500gr/2 = 2250gr yields two choices: A30-10XL (prop 14x7, 3s1p) and A30-12XL (14x7, 4s1p).

That was not hard at all! well, maybe not so fast… this engine costs €95, that is quite a lot of money…

Turnigy engines are usually much cheaper, so I used the ‘specs’ of the A30 to select a corresponding Turnigy engine. Initially my choice was the Aerodrive 3542. And I posted this choice to the RCGroups forum. I quickly learned that simply comparing sizes & power is not enough ;-)

In the thread you can see my initial ignorance in this matter. After some more searching I found two resources, one the Electric Motor Handbook and the other ecalc an online calculator for motor/prop calculations. I read the handbook and bought a subscription to the calculator website. I did need some more pointers which I got from users scirocco and Ron on RCGroups. Then things started to come together and was able to narrow down my selection.

My final try was another motor, the Turnigy 4240-740 and with a very nice 4 blade prop (scale!) that has an adjustable pitch. The results from that can be seen in the following screen shots:

(for full size: right-click -> show image in new tab or window)

ecalc

ecalc

ecalc

What is not visible in the screenshots is that this battery/motor combination can support a wider range of propellors than the other motor’s I tried. And since the Ramoser 4-blade is pitch-adjustable that should give me plenty to experiment with. Btw: a plain-old 12x9 2 blade prop can be expected to perform even better that the 4 blade. But the 4-blade is more scale like.

The blue lines warns that the prop is operating in ‘stall’ mode at stand and low speeds. But at only 4km/h this effect is gone. And since flying is always at higher speeds, this is no concern at all. It does reduce the trust at stand-still a little, but quite likely not enough to be of concern. So why do this? that is for better throttle-response in flight. The air when leaving the prop is at higher speeds this way. This means that changes in throttle have more (air)mass to work with, resulting in a better behaviour of the model. Especially at higher speeds.

The motor(s) are ordered now, and should arrive in a few weeks (at most).