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A tiny wing - the Bachem Ba349 Natter

quorneng

Active member
#1
After I built the Depron ducted prop Skyray I wanted to take the 'big but light' concept some what further.
In terms of wing span the Bachem Natter is just about as extreme as a manned plane could get.
BA349_3viewB.jpg
Amazingly it was built of wood.
As I don't have a scale Walter rocket engine or Schmidding boosters it was going to use a pusher prop hence I have put this thread in 'Warbirds' rather than EDF. ;)
The objective was to see if I could get a true scale version to fly so no cheating with extra span or anything!

I selected a span of just 26" but even so the fuselage was going to enormous, 8" deep, 6" wide and 39" long.
FusePlan.JPG
There certainly wasn't going to be a space problem inside!
The original fuselage was built in 3 sections. I copied this as it makes each a bit more manageable.
First the fuselage formers. Only the first and last are 'solid' all the rest are just 'rings'.
Formers1.JPG
Rather unusually each fuselage section is built vertically.
Fusecentre2.JPG
Very 'wobbly' to start with! The planks are added symmetrically to each side to keep it true and square.
The completed centre section.
Fusecentre4.JPG
Not much inside, in fact you can get you whole arm in, very useful when fitting it out!
Fusecentre3.JPG
Amazingly rigid and light it weighs just 1/2oz.
 
#6
yea, this is pretty cool but I wanna see your P-nuts scale planes. I KNOW you've got some somewhere and they probably look 10 times better then mine.
 

quorneng

Active member
#7
Thanks for the comments.
The fuselage nose and tail sections were built the same way but with slower to do with sharply tapered planks.
The nose
Fusenose1.JPG
The tail
Fusetail1.JPG
The whole cockpit area was left open to obtain the correct battery position.
Fusenose2.JPG
The tail is just as big and empty.
Miniformer.JPG
By comparison the wings are very simple.
The balsa/Depron/balsa sandwich wing spar.
WingSpar.JPG
Each wing has 5 ribs - just like the full size!
LHwingA.JPG
A completed wing skinned in 2mm Depron.
2mmSkin.JPG
With a scale fully symmetrical section.
1mmLedge.JPG
The wings added to the centre section. The spars are joined in the middle with 1mm balsa 'flitch' plates glued on top and bottom.
Centrewings.JPG
A much easier operation when you can get you whole hand inside!

So far so good but will it fly? or would I ever pluck up the courage to even try?
 

earthsciteach

Moderator
Moderator
#8
You simply need enough power and it will fly. Now whether you will be to control it, we'll...

What is your anticipated wing loading?
 

quorneng

Active member
#9
The conventional wing area is almost exactly 1 sqft, but then the fuselage plan area more than doubles it!
I hope it will weigh a good bit less than 1lb.
My biggest concern is the elevons as they have a very small lever arm. It may have been adequate for a torque less rocket but with a prop?
 

earthsciteach

Moderator
Moderator
#10
Quarneg-at some point, would you consider starting a thread or writing an article on your development of plans, and your techniques for building your planes?
 

quorneng

Active member
#12
My techniques? I will have to think about that but in the meantime on with the Natter!

The tailplane is built the same way as the wing but in one piece.
Tailplane3.JPG
It uses the same balsa/Depron/balsa type of spar.
A 3.7g micro servo is built in for each elevon.
Elevonsrvos.JPG
The fin spar goes right through the fuselage.
Finspar.JPG
The complete tail assembly.
Tailassycmplt.JPG
Like the wings being able to get you hand inside makes it much easier to assemble.
The motor mounted on the rear bulkhead and it is still Depron!
Mtrmntfront.JPG
The motor mount is extended to pick up the fins spar to provide rigidity to the motor.
With the rear and centre fuselage sections glued together the motor and servo cables can be installed.
Cableruns.JPG
The nose section can then be added along with the radio, ESC and battery.
Finally the cockpit canopy is built on.
Hatchnose.JPG
The fact the canopy is not glazed is correct as most of the unmanned flights were done like this.

With a 1000mAh 3s in the nose the CofG is at 25% wing chord. It weighs 310g (11oz). The Blue Wonder motor has a 7x4 prop and gives close to 280g (10oz) thrust.

The maiden did not go well!
Tail heavy, full down elevator did not control the pitch up and with full down elevator there was no roll control to counter the motor torque so the power had to be cut after a couple of seconds.
2 very short 'flights' ended with a crumpled nose!

It was going to need a heavier battery mounted as far forward as possible.
I just have to hope that once the speed has built up there will be sufficient roll authority.
 
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earthsciteach

Moderator
Moderator
#15
1) Go to the Flite Test Home Page - not the forum page, but the one with all of the articles and videos.

2) Click on "My Account" in the upper right hand corner.

3) On the left-hand side you will see a spot for a profile photo and below that a menu that two boxes outlined in what looks like chalk that say "Private Messages" and "Create an Article." Click on the create an article and you're off and running! You first have to choose a category for the article, then you have a series of additional info to click on.

Thank you for considering posting an article. I've seen your posts on Wattflyer. That site has amazing build threads. I don't want to take anything away from that great forum, but I would really like to see more complex builders on FT. There are many people on here who build sheet planes and simpler stuff using foam board. With builds like yours, I hope they will be inspired to progress in their scratch build modeling!
 

quorneng

Active member
#16
The battery box enlarged for the bigger heavier 1500mAh 3s and repositioned further forward.
1500mAhbat.JPG
It was painted yellow overall.
Yellow.JPG
Not a scale finish but it is lightweight and stands out quite well!
After a couple of short low powered glides I got my son to video a 'proper' flight. Big mistake!
[video=vimeo;43032580]https://vimeo.com/43032580[/video]
The damage was quite severe. The nose was crushed (again) and the trailing edge of the right wing cut into the fuselage like a knife!
Crash2side.JPG
It was tricky to do but repairable.
RBside3.JPG

However I was a little puzzled by its behaviour.
Although it performed reasonably in a low power 'glide' when under full power it not only pitched up but continued to do so long after the aerodynamic stall.
The thrust line was almost exactly on both the CofG and the centre of drag. Something else was having an effect, but what?
 

Foam Addict

Squirrel member
#17
Hmm, I had a pusher that did that, and the only way to fix that was to add severe down thrust and move the cg to the 10% of the chord and even that didn't cure it entirely.
My guess is, the incidence of the wing or horizontal stab may need to be changed, so that the whole tail assemble is giving slight down incidence at all times.
I hope this helps.
Foam Addict.
 

quorneng

Active member
#18
Whilst considering possible solutions to the pitch up problem I also needed to address its lack of roll control.
The simplest but non scale solution would be to add ailerons.
Of course the Natter had upper and lower rudders so I wondered if I could use them as additional ailerons - rudderons?
First cut the rudders out of the fins.
Rudders1.JPG
The rudders are moved by torque rods and bell cranks.
Torquerod1.JPG
Rudroncranks.JPG
And seperate pull/pull cables to a servo in the nose.
Rudronservo.JPG
By crossing over the cables to one bell crank the action is reversed.
[video=vimeo;43317939]https://vimeo.com/43317939[/video]
Comical but it works and adds very little weight.

The additional servo in the nose helps move the CofG a bit further forward but I still have not come up with an answer to the power on pitch up.
 
#19
Cracking build! Totally impressed with the skills! Surely the pitch problem is just down to CG? It was looking quite tail heavy from launch.
 

earthsciteach

Moderator
Moderator
#20
You are definitely going to have roll authority now. Watching the video of the crash, I'm not so sure its completely a cg issue. This plane could simply have beastly stall characteristics. It stalled, tumbled, then appeared to not have the airspeed over the elevator to pull the nose up.

Here's what I'm thinking... The plane is pretty light, so the motor has enough power to keep it in the air simply due to the air being deflected downward off of the fuselage and wings similar to how a nutball or other flat airfoil plane flies - high angle of attack.

Once you stalled, the nose dropped. Since the nose was pointed downward, the high angle of attack was lost. At the low speed, the elevator did not have enough authority to pull the nose up and the wings are not large enough to produce adequate lift. Therefore, an uncontrolled landing occurred.

That's my analysis. I've been know to be completely wrong in the past, though.:p