Siebel Si 201. Not only obscure but as ugly as sin - perfect! - RC Groups
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Oct 03, 2009, 08:21 AM
Single-task at best...
tim hooper's Avatar

Siebel Si 201. Not only obscure but as ugly as sin - perfect!

I blame the RAFster for this.

He really shouldn't have sent me this link;

Anyway looks like the seed has been planted in what's left of my mind, so a quick trawl over the net unearthed a sketchy little 3-view and brief description;

"The Siebel Si 201 was designed to meet a specification calling for an air observation post and army co-operation aircraft placing emphasis on STOL and slow-flying performance and all-round visibility. The specification was issued early in 1937, by which time the Luftwaffe was already evaluating the Fieseler Fi 156 Storch, and the Bayerische Flugzeugwerke produced a competitive design, the Bf 163, which, built by the "Weser" Flugzeugbau, flew in 1938 as did also the Si 201. Whereas the Bf 163 closely followed the Fi 156 concept, the Si 201 was unorthodox in that its Argus As 10 eight-cylinder inverted-vee aircooled engine was mounted above the wing as a pusher, driving a four-bladed fixed-pitch airscrew which rotated above a slim, circular-section tailboom. High-lift devices included full-span automatic leading-edge slots, a fixed slot at one-third chord on the outboard wing sections, and four-section Fowlertype flaps which occupied almost the entire trailing edges, the outboard sections serving as ailerons.
The fuselage was of welded steel-tube construction with metal skinning and the plywood-covered wing was of wood. The pilot and observer were seated in tandem in the extensively-glazed forward fuselage, the observer being positioned ahead of the pilot with his seat offset to starboard. The first of two prototypes of the Si 201 flew during the early summer of 1938, revealed excellent short take-off and landing characteristics, and was found to possess acceptable slow-flying characteristics closely comparable with those of the Storch, but at the upper end of the speed scale tail flutter proved troublesome. Considerable effort was expended in damping out oscillation in the tailboom which developed under certain flight conditions, and the second prototype, which featured some simplification of the high-lift devices, was flown with a somewhat sturdier tailboom. The most serious shortcoming of the Si 201 proved to be the extremely limited cg travel permitted by its configuration, and when Siebel was ordered to abandon further development of the aircraft the problem of tail flutter remained largely unsolved.
General characteristics
Crew: 2 (pilot, observer)
Length: 10.4 m (34 ft 1 in)
Wingspan: 14.0 m (45 ft 11 in)
Height: 3.4 m (11 ft 1 in)
Empty weight: 1120 kg (2469 lb)
Gross weight: 1440 kg (3175 lb)
Powerplant: 1 Argus As 10C eight-cylinder inverted-vee air-cooled piston engine., 179 kW (240 hp)
Maximum speed: 185 km/h (115 mph)
Cruising speed: 150 km/h (94 mph)
Range: 450 km (280 miles)
Service ceiling: 5500 m (18,040 ft)

Gotta be a winner, right?

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Oct 03, 2009, 08:50 AM
Single-task at best...
tim hooper's Avatar
Now, the tiny little 3-view that I found on the net really was too small to work from, so I've sketched an 'intermediate' drawing, so I can get a better grasp of the Siebels proportions (and they're not pretty, believe me).

So most of this design is pure guesswork so far. If anyone has any other information at all, then please pass it on!

I'm intending that the model should work out at 1/12 scale, with a span of 44" and AUW of maybe 30oz. 150 watts should give more than ample power for some STOL manoeuvres.

I'd like to fit some working flaps (driven by a single servo, via torque rods), although the LE slats will be a no-no. So that's 5 servos in all.

The swept back wing allows for a seemingly rearward CG position (28% MAC as per my usual practice), and I guess this was also in the mind of the designer of the full-sized abomination too. The sweep back also must have aided the visibility of the crew considerably.

That quirky tailboom means that I'll be limited to an 8" propellor - preferably multi-bladed. Construction of the tailboom itself calls for a bit of lateral thinking, so I think I'll have a bash at rolling it from 1/64" plywood around a disposable mandrel. To this end I've drawn it with an ID of 40mm - co-incidentally exactly the diameter of a piece of plastic piping I happen to have knocking around the shed!

I think it's a given that the intended 3S 1800 cell-pack will have to live in the nose, so I want the entire glazed area of the cockpit to detach as a hatch.

Anybody got any thoughts on the high thrustline?

Oct 03, 2009, 08:58 AM
Sloping off....
leccyflyer's Avatar
Works for the Wingo Tim

Oct 03, 2009, 09:28 AM
Registered User
portablevcb's Avatar

Welcome back to the weird stuff!

This one bears a striking resemblance to a motor glider that Mike Roach led me to. My 72" version is close to being finished.

At your scale it will make a very nice flying plane.

Looking forward to watching more of your work.

Oct 03, 2009, 09:34 AM
Registered User
vintage1's Avatar
Originally Posted by tim hooper
Anybody got any thoughts on the high thrustline?

Looks remarkably similar to my Pushy cat adaptation. Which still suffers from lateral instability at high airspeed and power. I have guessed at too much fin being blanked by the Slipstream. Put ailerons ion, just in case.

You will be happy that the Pushy needs no sidethrust or downthrust tho. No ladybirdesque props hanging out of the side like a fagend out of a Nora Batties mouth..
Oct 03, 2009, 09:59 AM
Suspended Account
WTFLYR's Avatar
The Farman Jabiru was worse than that. In fact, it was horrible.
I may have to look at this subject more closely. I'm burned out on "popular" planes.
Can't be any more difficult than a non-plan, 3-view Stosser scratch build was, a few months ago.

BTW Tim, if you don't shrink the covering 100% tight on the rudder, it's ok. They didn't either.
More thoughts: Now I know where Spencer got the idea for the Seabee.
Could be a FW189, if you broke it into a twin-boom structure.
Better than a Waco glider, since it can stay in the air.

On the high thrustline:
I finally flew a high thrustline 32" M33 a few weeks ago. The first hand launch under full 150W power, with a good 3-deg upthrust, slammed straight down into the water. Unscathed, other than a broken motor mount flange (only added right thrust under power anyways, so we'll be fine, right?) I went for another toss. Using less than full throttle allowed me to get control of things just before it touched the water, and go off for a nice flight. The plane now has added upthrust closer to 4 or 5 deg, after actually measuring, (eyeball and protractor) rather than a flat out guess. Speaking of, I should be at a seaplane meet today, where I could try it again with the added upthrust. Oh well, maybe it will be better yet tomorrow, as it is still going on then. Irregardless, it's possible that the thrust angle needs to be exaggerated on models, compared with the full scale planes.

As for cg, I have found the sweep on models to not move the cg rearward as calculatioins would entail. At that low of a sweep angle, I'd start more conservatively forward. This has proven to be a general trend with 4 or 5 ME262s, FW250, Flitzer, and maybe more I've missed.
Last edited by WTFLYR; Oct 03, 2009 at 01:44 PM.
Oct 03, 2009, 10:37 AM
I eat glue
Yup, it's ugly alright. But there is a little bit of dihedral there. Should look real odd in the air.
Oct 03, 2009, 10:42 AM
Suspended Account
WTFLYR's Avatar
Originally Posted by baldguy
Yup, it's ugly alright. But there is a little bit of dihedral there. Should look real odd in the air.
Gotta look at the right pic. The sweep makes it look as if there is dihedral. In Tim's last pic, you can clearly see that it is really like the 3-view, without dihedral. The sweep will give dihedral effect in flight though, which is why they can omit it, and have good stability.
Oct 03, 2009, 11:03 AM
I eat glue
By gosh yer right! Forgot about the sweepback.
Oct 03, 2009, 11:11 AM
Registered User
Tim, thanks for returning to the builds of "only planes Tim Hooper could love..."

Looking forward to seeing how she does...she was a STOL aircraft so she shouldn't be a fast one...otherwise all manner of other ugliness might happen...

You are legendary Tim, and I couldn't resist feeding the obsession you have with these birds...

Thanks for the ray of sun in a rainy day...

Oct 03, 2009, 02:42 PM
Senile Member
Lnagel's Avatar
Tim, I've seen photos of Mrs. Hooper so I know that you weren't always attracted to ugly. Maybe it's a mid-life crisis. You definitely need help my man.

Will be watching the build. Are you going to incorporate the high speed tail boom flutter also?

Oct 03, 2009, 03:36 PM
Single-task at best...
tim hooper's Avatar
So the mickey-taking has stated already, has it? I do wish you blokes would take my art more seriously!

Now, I usually get the wings out of the way first when I do an OD model, but on the Siebel pretty much everything depends on the success of the tailboom, so I thought we'd start there first.

I wrapped my waste-pipe mandrel in clingfilm (to avoid stiction), and then wrapped it in pre-wetted 1/64" ply, chamfering the edges in the overlap area to avoid the formation of any unsightly lumps and bumps. PVA glue is the bonding agent. The length of dowel you can see is purely to add a little localised pressure to the edge of the overlap. Now, let's just hope I can get the pipe back out in the morning - we can't use the bathroom until it's back in its usual place......

The fuselage is beinng built from the ground up, as it were. The floor is made from 2mm Liteply, as is the roof, and is embellished by 1/16ply reinforcement for the undercart and wing mount. 3/16 'longerons' complete the components.

The rectangular item is, of course, the ubiquitous F1 - as beloved by traditional aeromodellers the world over..........

Oct 03, 2009, 04:12 PM
The Junk Man
Just looking at the three-view makes it appear that the tube was slightly tapered. No?

Oct 03, 2009, 04:32 PM
Single-task at best...
tim hooper's Avatar
Originally Posted by T_om
Just looking at the three-view makes it appear that the tube was slightly tapered. No?

I'm wondering just how accurate the 3-view is, given that the photos seem to indicate a parallel-sided item.

I must confess that I did contemplate a tapered tube initially, but for commercial reasons I want this tube to be easily duplicated by other modellers, so a straight tube it's going to be!

The model doesn't pretend to be anything other than 'sport-scale'- my euphemism for over-simplifying the airframe to the point of caricature if need be - and as data appears to be very scant I reckon I can get away with it!

I'm only aware of one other model of the 201, and that's a static construction kit as produced by Kora, and they've mocked-up some imaginative box art.


Oct 03, 2009, 04:51 PM
Heli Bouncer
Looooeeee!'s Avatar
I'm a bit concerned about the "fluttering tail" thingy they mentioned as it's reason for not being accepted to the Luftwaffe. I hope this problem doesn't scale down,

Tim, you've let Maltone take the ball away from you concerning ugly and weird, I for one am glad to see you back in the saddle, FWIW.

Now when are you going to do A.V. Roe's triplane?

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