Baudis Fosa F3B/F3F - RC Groups
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Oct 05, 2010, 11:24 PM
Eagle Butte User
PDX Slope Pilot's Avatar
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Baudis Fosa F3B/F3F

Is this model intended to replace the Cyril? The elliptical plan form and high aspect ratio look great.

Any more info out there on this model?
Last edited by PDX Slope Pilot; Sep 23, 2012 at 01:06 PM.
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Oct 06, 2010, 06:50 AM
Registered User
Dont tease us with this thread !
Need some photo's and a nice video of it doing the 14.8 second B speed task in the hands of Mr Baudis
Oct 06, 2010, 07:48 AM
Registered User
That's just cruel man!
Oct 06, 2010, 07:52 AM
F3B and F3K
RetoF3X's Avatar
Hi there

It is a cat like animal on Madagaskar!( )

The Fosa was tested this season by several F3B pilots including Andreas Boehlen. It already has one Eurotour win (Dresden). On one of its first contests Jiri flew a 13.8s speed run in Kirchheim ( )

Some pictures can be found in my Oktoberfest Report.

It was noted by Mark Drela and many others that an F3B ship would benefit from higher aspect ratio (less induced drag in high lift like launch and turns, more legs in distance).
The disadvantages are higher demands on the airframe structure (e.g. torsional stiffness) and less straight line speed than lower AR plane and higher inertia in the turns.

The Fosa has an aspect ratio above 18 and is really stiff. That is 3.2m wingspan and a wing area of a Freestyler! Launching in wind seems to outzoom most other F3B planes and it did not show any visible wing flex (under quite some tension).

I was pleased that Jiri and Dirk Pflug tried something new.

I am not so sure if the Fosa is suited for F3F. Again, the high aspect ratio helps most in the winch launch (lifting ballast for distance and speed). From what I have seen it is really the launch were the Fosa excells and it has to compensate with extra launch height for the speed task (lower AR presumably faster).

Last edited by RetoF3X; Oct 06, 2010 at 08:04 AM.
Oct 06, 2010, 10:39 AM
Registered User
Bro's Avatar


I heard from a "good source" that there was a prototype from Bob's long time friend Jiri coming into LAX next week..

Latest blog entry: 2015
Oct 06, 2010, 10:51 AM
Woodstock 1's Avatar
Well, at least it's a (slightly) better name than "Cyril"...
Oct 06, 2010, 11:55 AM
Registered User
Avaldes's Avatar
Very cool looking model The Herrigs showed with the Schocker/Radical/Freestyler that smaller and thinner airfoils can do amazing things in speed. There also seems to be an advantage launching these models in lite to moderate conditions. I think the larger models have an advantage in more wind, due to the higher CL capabilities that overcome the higher flying weight.

But as Reto alluded to above, minimum drag coefficient is king in speed.
Oct 06, 2010, 12:13 PM
F3B and F3K
RetoF3X's Avatar
Hi Aaron

My observation and also talking to people there is that the Fosa really shines in moderate to strong winds, then it launches like crazy. With the extra height it is quite a hard opponent in distance (Jiri won his flights with quite a lead in Munich).

Speed run is a different story. Despite the early success with the plane, it still has to prove if it works. In the marginal air in Munich, the Freestylers and Radicals seemed a bit happier than the Fosa.

Check also the one to one results of the Speed knock out in Luenen under (scroll to "20.09.2010 Speed Knock Out Lünen 2010").

In short, it is quite an experiment and I am glad that someone tried it. Time will tell if it will prevail against the lower AR (14-15) F3B planes.

Also a big plus: the plane looks quite different in flight. I have one picture in the Oktoberfestpokal report. It really stands out of the crowd and there should be no confusion in a distance group. The plane also looks much bigger in flight due to its slender wings.

Last edited by RetoF3X; Oct 06, 2010 at 12:19 PM. Reason: more info
Oct 06, 2010, 03:22 PM
In F3J size does matter!
roydor's Avatar
I wonder how it might do as a windy weather F3J, it could probably launch well and range well with good penetration. Could be an interesting experiment if it can be built strong enough for F3J at a weight of around 1.9 to 2 kg and with a bit more dihedral, it should be interesting.
Oct 06, 2010, 04:18 PM
Registered User
Originally Posted by RetoF3X

Speed run is a different story. Despite the early success with the plane, it still has to prove if it works. In the marginal air in Munich, the Freestylers and Radicals seemed a bit happier than the Fosa.
I wonder if this is a case of figuring out the correct amount of ballast for lighter conditions. I would expect the lower induced drag to give the high aspect ratio wing a noticeable advantage in speed. . .

Oct 06, 2010, 05:05 PM
F3B and F3K
RetoF3X's Avatar
Hi Tom
Please correct me:
In speed you fly close to cl=0 (except in the turns) so induced drag is not high in that flight regime ( induced drag scales to the power of two to the lift and reciprocally to AR). Thus a high AR plane has no advantage in straight line speed but has a higher form drag.
The lower induced drag makes the biggest effect when you fly at high cl like the launch.

So my assumption is that a high AR plane is slowed down more in straight line speed, but it can make up for these loses if it can launch higher and carry more ballast. Where this cross over point lies (more launch potential vs less straight line speed) is an open question and Fosa might give us another clue.
I assume that building technology and thickness of servos prohibited the use of higher AR in F3B designs so far and they settled at moderate AR's of 14-15.

Given its early development status, the success by Jiri and Andreas Boehlen is promising.

Last edited by RetoF3X; Oct 06, 2010 at 05:27 PM. Reason: typo
Oct 06, 2010, 05:27 PM
Team JR Air
tewatson's Avatar


Originally Posted by Bro
I heard from a "good source" that there was a prototype from Bob's long time friend Jiri coming into LAX next week..
I call dibs for the first time Bob hands the TX to someone!

Oct 06, 2010, 06:38 PM
Daryl Perkins's Avatar
Reto - over half the energy lost in a speed run is lost in the turns... so lower induced drag pays an advantage here...

I would suspect that the model's performance opportunities are not being taken advantage of just yet... with the launch advantage and lower induced drag, you can turn the model tighter, or fly heavier...

Every F3B model has pros and cons - me? I'll take launch advantage every time...
Oct 06, 2010, 07:04 PM
F3B and F3K
RetoF3X's Avatar
Hi Daryl

I agree on the turns, but I was not aware that so much energy is being dissipated in the three turns.
How much the hit in straight line speed really is might also strongly depend how thin they could make the wing/airfoil while keeping it stiff and enabling a clean servo install (which they did). Where the crossover point in the speed task lies (with todays building technology) will be seen by the results in the future (and thanks to the Fosa we might get a clue if it is more to higher AR).

The plane did deliver in the launch department! In speed it did not yet show an advantage. But it is correct, maybe one has to use its launch potential to carry more ballast, maybe one should bang the turns harder (they were pretty hard though).

But don't get my post wrong, that bit that might have lacked in speed is not that much (and it is also just an impression and not a long term observation). Jiri's sub 14s and a Eurotour contest win are already promising.

Cool that there is again something going on in F3b designs!

Last edited by RetoF3X; Oct 07, 2010 at 05:00 AM. Reason: typo and bad english
Oct 06, 2010, 11:06 PM
Eagle Butte User
PDX Slope Pilot's Avatar
Thanks for the great information Reto! Appreciate it.

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