I will continue the Mubu stuff in another thread in the High Performance section from now on.
Seems more appropriate to me.
So, Jojo, Mr. Merzhäuser and all the others, follow this link.

biber

We had so much fun at the (clocked) official training session.

Paul did a 104 with the Multibumm, even with four years old NiMHs!

Best clocked time of the training was Oliver Mahr's 102 seconds, perfectly flown with a tailed model.

In Limited there is none below-hundred-seconds-flight officially clocked yet.
But it will happen soon, either this or that way, that's for sure.

biber

We are well prepaired for the training tomorow.

biber

I launched it in a quite lousy way, with little power, lots of bank and some spin.
The absence of any wind adding to that made a not so easy recovery for Paul on the sticks.
But it went well though.

Now, with the decreased whashout, it tracks straight ahead with all control surfaces neutral.

It's rather noisy during highspeed runs, wich may be caused by the 1-2mm gap between pod and wing (very prototypish, you know...).
We hope, with an improved fit of the pod, it will stop screaming all the way round.

The CG seems to be a bit noseheavy, it was impossible to stall the wing.
A more aft CG will require less elevator throw for turning, wich should give even better turning performance.

And sorry for the lack of pics in this entry, but we tried to video the flight and failed.
I always wondered why on many pylon videos there is hardly a model to be seen.
Now I think I know.
A Gentle Lady might be better suited for a video coverage...

biber

Multibumm #2 is now covered and ready to fly.

We checked the CG and it came out at exactly the position we had tested
on the first proto, but now we didn't need any nose lead.
This and an about 40g lighter fuselage pod gives us an AUW of 802g
wich is just 2g more than the contest rules require as minimum weight.

Seems like the new shape of the pod is a big improvement to the whole flyer.

The Winglets are again slightly decreased in size, now they are really tiny.

...Continue Reading

Right now Paul is ironing the skin onto the 2nd Multibumm prototype.

Later this evening I'm going add some pics of it.

Seems we'll have a new maiden flight tomorow.

We will try to get a stock Turn Left into the air at the same time along with the Multibumm.
That should give us a rough speed reference,
since just a fast look doesn't say all that much.
Only drawback then will be, that I won't be able to operate the video camera and the Turn Left at a time.

biber

After the first Mubu prototype showed some pitching up tendencies
we decided to build another one with less washout (wich means close to zero).
Also a new fuselage pod should allow to shove the guts a bit forward
and avoid the neccessity of any nose lead.

Things are going quite well since then.

On sunday Paul prepared the RDS linkages for the new flyer,
shaped a new pod plug from polystyrene and built a pod on it.

I cut a set of new wingblanks with the new washout
and we sheeted them the same day.

Now the thing is at a point, where both winghalfs has to be
glued together with the root rib and the GF joint.

This is going to be done today.
A rather quick setting brand of laminating resin combined with the finally warm
summerlike weather should make it possible to cover it by this evening.

Tomorrow we should be able to maiden the #2.

And if it's allright, it will be with us on the training
session in Erftstadt (near Cologne) this weekend.

We would love to see some perplexed faces there,
since in German forums noone should have seen anything of this project yet.
And I doupt, that anybody from over there would find this here.

biber

Forgot to mention it in the last entry.

We decreased the winglet size by about 20% and there seem to be no problem with that.
We will try even smaller WL sizes and as long as they keep the ship on track we'll be fine.
That means more speed by less wetted surface.

biber

During the second powered testflight we suddenly got an idea
of why it would have been wise to attach the fuselage pod more thoroughly to the wing.
It went of in flight and we are lucky to have only little damage on wing, pod and the gear.
Since only minor disintegration of the model occured, we came to the conclusion that,
except for the pod attachment, it's a tough model.

However, there was still this mysterious pitching up, with all controls neutral.
We already made some airfoil gauges to check, if the airfoil came out as accurate as we wanted.
And it seems quite ok.
That means, we didn't sand an unwanted reflex into the TE for example
wich could otherwise have lead to a pitching up moment... *sound of scraping his head*

So we will have to measure the exact washout too,
in order to find out why that thing has still this pitch up attitude.

Note, that it has only 1.2 degrees washout and an airfoil with negative pitching moment.
Normally that'd make anyone think, it should want to pich down.

Another thing we will try, is to get the thrust line a bit higher and tilt it,
so that any pitching up moment it could generate would be decreased or eliminated.

Finally one could blame an insufficient torsional rigity of the wing.
I don't really want to do stuff like areo-elastic tayloring on a model, but...
If the cm of the airfoil is indeed negativ (as calculated),
its torque may increase the washout in flight and lead to the...Continue Reading

Pics of the CG measurement campaign to exactely locate the CG that seemed to handle well in the glide tests.
After that, all the electric gear had to go into the ship's belly.

biber

Ok, now there should be the following two small videos downloadable:
One toss
And another one


The first powered flight,
one day after the videos have been taken,
was quite a success too.

It handled well and was fast, even with only a 4.5" pitch APC.
Only thing that was not quite as calculated seems to be the pitching moment of the airfoil.
It seems to be more positiv in reality than in the computer.
Maybe we can even decrease the amount of whashout and get even more speed performance.

biber

Multibumm is maidened.
Only a few tosses, but it flew!
Paul and I did some glide tests with slightly different CGs.
From what I have measured afterwards, about 10% static margin seems to be
the most tailheavy (or what should I call it?) CG that handles well.
Glide is straight and nicely stretched.
Elevator response seems ok.

I made two small videos with Paul tossing and flying it.
I don't know how to get videos uploaded on this board or even if it is possible without paying for webspace.
Maybe I can host it on some other domain, we will see.
Well I'm completely newb' for that matter.
Anyway, I'm posting this from a terminal in the University.
So the vids and pics will have to wait until tonight,
since I don't see a way to get them from the memory card into this computer.


Now we are installing electric power to make a first powered flight tomorow.

biber

When Paul yesterday said to me, that it was day he would iron the oracover on,
because something has to finished, I thought he was kidding...
Nope, he was not.
He has quite some skills in covering and did a great job on the wing, even though he hates ironing,
while I took the winglets and was close to desperation in the atempt to cover them by myself.
CG of the wing itself (without any batteries and motor) is almost the supposed CG to fly.
Today we have scheduled to maiden it as a glider.
Will weigh about 370g or so, less than half as much as the powered version.
Less chance to damage it during the first flights, as we hope.
Another reason is of course our impatience.

biber

Yesterday we epoxied the RDS pockets and Servos into the wing.
Only the Pockets of the ailerons seem to extend the surface at about half a mm or so, still way nicer than any control lever could be .
This is going to be an overal sleek flyer .
The wing halfs are now glued together with some three degrees anhedral each side.
That should counteract the effective dihedral of the sweep and winglets.
Taped and waxed the PS core of the fuselage pod, then made the layup.
Maybe, if the shape of the prototype's pod works out ok, we will make a mold of it.
But for now it's just made for getting this thing airborn.

biber

We had a great fun building yesterday.
All controls are cut out and moving now.
Servo holes are also cut including the wiring chanels.
A piece of PS foam is shaped to become a fuselage pod.
The Servos are prepared for the RDS.
The RDS pockets are built as a strip of about 1' length
to cut of one when needed.
Paul made a quick and dirty mold of the wing connector, as we don't want to sand every single next one out of a piece of plywood in the future.

...Continue Reading

Im doing this Multibumm thing not alone.
Such a project is much more fun when it's done together with a buddy.
So may I introduce to you Paul Schreiber who's the buddy in this case,
to help this thing to become a fun build and a winning plane.
While I'm a total newbee to F5D Limited (wich is btw a very interesting low cost alternative to the 'real' F5D), he has already lots of experience in this class, as he happens to be the current German Champion...

For further info on the F5D Limited class, I'd recommend a visit at www.F5D.org.
The only problem may be that it's not available in english language (yet).

The non german speakers may have a look at the following thread on this board:
https://www.rcgroups.com/forums/show...+limited+rules

Another thread is on the 'Turn Left', the standard model for this application:
https://www.rcgroups.com/forums/show...ht=f5d+limited

biber

In my last entry I mentioned a F5D Limited Wing.
That thing will be named 'Multibumm'.
And it's going to look like pictured below.
The other pics show what it looks like about now.

The special gimmick in this design is its distribution and management of control surfaces.
It won't use a common elevon mix like most wings do.
The outer control surfaces are supposed to act as ailerons only and the more little inboard ones as elevator only.

That means e.g., to pull up the inboard controls are lowered some degrees.
On most common swept wing designs up elevator means that 50% or more of the airfoil's TE
is seriously reflexed during turns and pullups wich does not really match the increased lift situation.
The rest of the TE remains unchanged.
That is different with the Multibumm.
It will have 75% of the TE unchanged, 25% slightly cambered in the same situation.
No reflex to pull up.
That is possible due to the high sweep of 30 degrees combined with the quite high aspect ratio of 9.3 (without the winglets).

Hm, have to continue this tomorow, it's now late over here in Germany.

biber

My first entry in my own Blog, wow.

The two attached pics are exemplary showing myself doing the stuff I like most.
Knowing both worlds, fullsize gliding aswell as modeling,
I think I can say that none of both can fully replace the other's experiances.
OTOH, the very thing attracting me to it is basicaly the same for both, aswell.
Hard to put into words without sliding into philosophic mumbo jumbo.
Well, it's the Idea of Flying.
For me that is not connected to wether it is rc, freeflight, or fullsize.
But this is a place for the modeling part of it all. And so it be.
And to get that one thing clear: I don't like glow stuff, Helis, ARF,...
I do like Slope stuff, Soaring, Micro thingies, reall Wings, fast models, electric powered...

The following entries will show the ongoing development of a swept F5D Limited Wing.
As that particular competition class is national, flown only in Germany,
there is not much risk of other competitors seeing this here .

Another reason to put this into my blog is,
that it's hard to decide wich forum would be best suited for it.
Wings?
No, only Zagi style wings in there, how boring. It would get lost in there anyway.
High performance?
Well, perhaps, but the fact, that it's actually a wing,
is the main thing about it and I think it deserves a special place therefore.
The best possible audience for it would be the Slope forum,
but this isn't going to be a slope glider in the first place
(maybe later on there will be an unpowered version), so no again.

For people who want to know about the current state of the projct
this will be the place to check it anytime.

*waveing Mr. Merzhäuser*

Ok then, stay tuned for more...

biber