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Old Jan 13, 2015, 02:52 AM
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Build Log
Akaflieg Stuggart FS-26 Moseppl - 2.5m 1:5 scale

This model is a 1:5 (semi)scale version of the FS-26. The plans that I am basing the construction on are by Modellbau Wanitschek. Unfortunately, I don't actually have the construction notes - only 2 pages of the plans. This means that inventive thinking is required along the way!

As I will explain later I am going to stick fairly close to the original plans. However, like all projects I am going to change some things along the way. I have a 3D CAD model for the aircraft, and from this I can CNC cut the parts that I require.

My projects tend to move at an erratic pace, so we will see how this one goes...

Key Statistics - from the modellbau-steinhardt web site
Profile: E-182
Root Chord: approx: 270mm
Wingspan: about: 2.52m

Previous threads
http://www.rcgroups.com/forums/showthread.php?t=1176788 (General info request)
http://www.rcgroups.com/forums/showthread.php?t=1182068 (Re: airfoils in Modeling Science)
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Old Jan 13, 2015, 03:01 AM
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General Notes

Because I have a number of molded fibreglass parts that are already designed to fit E182 I am not proposing to alter the root airfoil. Although there may be many other airfoils that would be as good, or better, I don't really want to modify the glass work. In addition, I did some modeling in XFoil and I think that E182 will work OK.

Although the FS-26 is a sailplane, the model is not going to be the lightest thing in the sky. So we will also take that as a given.

Interesting Challenges

1) Keeping the weight down! At this stage I don't really know what the AUW will be, so I am going to try and keep the weight down as best as I can during construction.

2) Attaching the fins. I have two glass fins that need to connect to the central wing section and the plans do not describe this attachment in any way - so this will require imagination when I get to that part.

3) The CG. In line with keeping the weight down I don't want there to be any lead in the model for the correct CG. Because of the totally unknown nature of this model I am going to construct the wings first and then try and work out the aircraft balance and complete the construction in a manner that gets the correct CG.

Intended Modifications

a) I am going to use direct servo control and separate rudder servos rather than the original bowden cables.

b) I am going to try and construct an all moving tailplane (in line with the original aircraft), rather than the horizontal+elevator shown in the plans. I have decided that this will be more compatible with direct servo linkage, so we will see how this works.

c) The model will be electric. This may well affect the model balance, and thus obtaining correct CG without lead, which is one reason that I want to build the wings and then see how the weights look.

d) The plans have fixed undercarriage (wheel front and rear). I would like to make the rear wheel, which protrudes the most retractable. I have a nylon retract to suit a 2.5m scale model that looks exactly the correct size. So, weight permitting, I am going to build this into the model.

e) Wing joiners will be CF tubes in a glass sleeve. (PBG 95TS 1/2" tube).
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Old Jan 13, 2015, 03:20 AM
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Construction Weights

Parts as delivered:

Body: 182gm, 199gm
Left Fin: 89gm, 90gm
Right Fin: 85gm, 97gm
Rear Deck (solid): 41gm
Rear Deck (openings): 32gm

Power system:
Neu 1110/2.5Y, CC ICE 50, 8x5 prop, spinner: 225gm

Rudders:
Post 10: Each rudder 9gm (uncovered, unsanded)

Central wing section:
Post 11: Ribs and spars, no wing joiners: 64gm
Post 14: Joiner sleeves fitted, including CF joiners: 85gm
Post 16: Mostly sheeted, including CF joiners: 119gm (2xCF joiners are 13gm)

Left wing:
Post 14: Ribs, spars, sub leading edge, joiner sleeve: 57gm
Added D-box sheeting: 81gm
Lower TE sheeting added: 94gm

Right wing:
Ribs, spars, sub leading edge, joiner sleeve: 58gm
Post 16: Added D-box sheeting: 84gm
Lower TE sheeting added: 97gm
Upper TE sheeting added: 115gm
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Old Jan 13, 2015, 03:24 AM
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Obtaining Key Parts

A complete set of glass and carbon/glass parts are available from www.modellbau-steinhardt.de. I decided to purchase these parts (and the plans) as this is the simplest way to get all the required molded parts. See: http://www.modellbau-steinhardt.de/rumpf/fs26.html for details.

Due to the high cost of transport I purchase two sets of parts. Because there were two possible rear deck - one is solid, and the other has holes for access - so I purchased one of each. The canopy is available in various colours, I ordered "smoke" as the canopy colour.

The glass work is good, although the finish is not high gloss like a modern composite model. So I may paint the parts once the model is complete, I have not yet decided.

The parts (except the canopy) are glass & epoxy. The base of the fins is untrimmed - ie. the various parts have a different 'foot print'.

I also ordered the plans, and they arrived as two sheets - no instructions are included. The plans are good, however, not all parts are shown in detail, so you can't really proceed directly from the plans. Also, as is typical of plans from this period, they are not computer drawn and so some of the parts that should be symmetrical are not quite symmetrical.
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Old Jan 28, 2015, 02:53 AM
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Vertical Fins

One of the slightly unknown aspects of the construction is the mechanism used to attach the fins to the centre wing section.

As supplied the fins have quite different trimming around the base. This isn't a problem, however, I will need to trim the two that I use the the same shape once I get a bit closer to determining exactly how this works.

The fins also have a section on the rear that is on the lower surface of the airfoil.

The plans have a dotted line that I am taking as representing the base of the glass/epoxy fin.

At this stage the feeling is that the fin should sit on top of the balsa sheeting for the wing. It looks to me as though the fin should 'hook' over the rear of the airfoil and then is glued to a former that sticks up into the fin. Although I have to admit that I don't quite see how this is going to work.

Additional work that involves the fins:

- build some rudders
- add some fill in balsa at the rudder hinge point
- mount the servos for the rudders and horizontal surface
- make the attachment point/mechanism for the horizontal surface
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Old Jan 28, 2015, 03:05 AM
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Central Wing Section

The wings are in three parts. The central section attaches to the body, and also the fins. This central section is approx 440mm wide, then the outer wing sections are just over 1m each.

The first step is to cut the main spar, then assemble the ribs, sheer webs, fin attachments and the rear spar.

I want to be able to remove the wing from the body so that I can access the retract etc. so I have included 3 location points for 5mm nylon screws to hold the wing to the body.

Also, I have added a rear spar and an extra fin mounting point.
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Old Jan 31, 2015, 01:33 AM
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Power System

As mentioned before this is an electric build.

Some time ago now I selected the power system I was going to use, I have to admit that it was so long ago that the exact reasons for this selection are long gone! I think that the key problem was finding a motor that would fit into the space available in the fibreglass body.

So what I have is:

Neu 1110/2.5Y/S/3.2
CC ICE 50 ESC
Aeronaut 8 x 5 folding prop
40mm spinner to suit (47mm yoke)

This is a pusher model, so I also made a fibreglass piece for the spinner to stop the blades folding too far.

This system is designed to suit a 3S pack. I aim to use my "standard" 3300 pack, however, I may go smaller if weight becomes a serious issue.

I powered this all up and the full throttle input power is just over 400W, with an RPM of 13,500.
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Old Feb 01, 2015, 07:21 AM
Aerotow and sloping Holland
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Hi Tugboat, interesting project.
Is the 8x5 prop the biggest that will fit between the tail booms?
Should there be more space I would go for a setup with a bigger prop and a lower kV.
Now you have a very small prop turning very fast which is not the most efficient setup.
Good luck with your project.
Maarten
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Old Feb 03, 2015, 03:01 AM
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Hi Maarten,

Unfortunately with this model a small prop going fast is about the best that is possible. There is plenty of room between the fins, especially if the rudders don't move in the inward direction.

The limiting factor is the clearance for the prop when the aircraft is on the ground. An 8" prop is the size of the original plans, my 8x5 is really an 8.5" allowing for the 47mm yoke, so there is about 1.5" clearance between the prop and the ground. In theory there has to be enough clearance for the model to rotate on launch.

The plans have a funny bent wire that comes out of the bottom of the model between the rear wheel and the prop to protect the prop from ground strike - I am probably going to delete this bit of wire and solve the launch problem some other way.

Still, I may change my mind when I get closer to completion.

Tim
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Old Feb 03, 2015, 03:12 AM
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Rudders

I have been using some spare time here and there to make the rudders.

I decided to cut a jig to make the rudder construction easier. The jig makes sure that the rudders are symmetrical and also make it easy to sand the bevel on the balsa sheeting for the rear join in the sheeting.

This is probably overkill, however, my past experience of freehand building this sort of part is that I always end up with slight crooked/warped results.

I will leave them unsanded and uncovered until I get closer to the final assembly of the fins and I know exactly what shape is required. Until then they can go into box of almost completed parts.
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Old Feb 03, 2015, 03:18 AM
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A bit more work

I have done a bit of work to complete the wing mounting points. This involves a nylon seat for the bolt, and some bits of balsa to support the sheeting around the bolt holes.

The next step is to glue in the sleeves for the CF joiner.

There has been some work on the left wing. This has reached the stage than I need to attach the beveled rib on the root end of the wing that mates with the centre section. Then I can also complete the top spar.
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Old Feb 03, 2015, 12:30 PM
Lost in the Sky
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Tim,

Here are a couple of pictures I found on the RC-Network.de site ( http://wiki.rc-network.de/index.php/...von_Wanitschek ) along with a data chart.

This is the translated text of the 1978 Wanitschek catalog entry: "The FS 26 Moseppl from Wanitschek is described in the 1978 product range as follows:

A glider or motor glider for electric or internal combustion engine. One of the most interesting designs of the Academic Flying Group Stuttgart, we have created this model of it in 1:5 scale. After years of development, we present the experienced pilot a model that offers exceptional appearance and performance. The specially selected airfoil gives a combination of good climbing performance on the slopes and in thermal flight. This is a model for experienced builders and flyers. It is not recommended for beginners. (like the original)."

I've included a picture I found of the original FS-26, probably in a German museum.

You have to have a logon to do searches on the RC-Network.de site.

Richard
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Old Feb 04, 2015, 01:18 AM
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Thanks Richard,

I have not seen the museum photo before. It clearly shows the mass balances on the elevator.

Also the data chart has the AUW (2kg). This was actually the target weight I was aiming for, so that is also interesting confirmation of a wild guess on my part.

As to whether I am experience enough, only time will tell!


Tim
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Old Feb 11, 2015, 12:41 AM
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More work

The left wing spars and ribs are now complete. The sub leading edge is fitted and the rear rib support as well.

I have glued in place the glass sleeves for the CF joiner, also bonded the sleeve to the spars.

When fitting the angled rib on the root of the wing I used the central section as the template to ensure a correctly angled and aligned rib. I also checked the dihedral (1.8 degrees).

I just need to duplicate this for the right wing and then I can move on to the sheeting and finishing for the left & right wings.
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Old Feb 11, 2015, 02:45 PM
Aerotow and sloping Holland
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Nice project, good luck. Wanitschek made some nice stuff in the past. Good to see another one getting build
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