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A-Bird

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Want to announce and introduce my design project:
A-Bird, affordable advanced aerobatic aircraft...

a-bird.jimdo.com
 

BJC

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Interesting. Since you posted here, I'm assuming that you want some comments.

I like the concept of a new, easy to build aerobatic airplane.

Most aerobatic peole will find a way to build a single piece wing if necessary, so if your intention is to sell plans, you might be able to simplify and lighten the design with a continuous spar wing.

Dimensions are difficult to surmise in the drawings, but I am curious about room for feet and rudder pedals above or behind the spar carry-through.

Another deminsional question: Is the rudder power adequate? It looks really close to the CG.

What engine?

Using a LG similar to the Wolf Pitts will be lighter, more streamlined, and easier to build.

Where will the fuel tank(s) be?

The ailerons will either need huge spades, which can also serve as the counterweights, but they increase drag significantly. Consider using an aft hinge line and a cove / aileron LE design per the Wolf Pitts, plus a square TE. That will give good feel, low forces, as well as centering forces. Counterweights still will be required, but they can be much more streamlind than the spades.

Have you estimated the empty weight?

My compliments to you for taking on such an ambitious project.


BJC
 

wsimpso1

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You seem to have covered a most of the design issues.

I too am curious about fuel tanks.

I would caution you on designing a new concept inverted oil system. The systems out there are pretty simple. Remember that they have to swap both the oil feed and vent lines when g's swap signs.

What g-levels are you designing?

Have you checked you tail volumes yet? I saw no mention of how the tail sizes and fuselage length was sized.

With the large ailerons needed for competitive aerobatics, I too suggest putting the hinge line aft into the aileron in order to make the control forces adequately low.

Now that you have the basics arranged, you have to design the details of all of these structures and check them for safety. Main spar needs detail sizing to keep its mass down, then checks on skin torsion flow, and checks on wing and tail bay sizing, and fuselage elements need sizing. It is a massive job - please do not underestimate it. At least you are working in aluminum, which allows closed form stress analysis.

Billski
 

TFF

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Looking at the specs, it will not be a head to head with a One Design; more like a RANS. 80 hp sounds like you are going after the Rotax 912 as engine, and a much lighter gross. Most of these planes are designed to hit a aerobatic class for competition. At what level do you tend for this plane to reach? G loads might be a little low for aerobatic competition; monoplane guys pull more than minimum certified, in comps if going to higher classes. Lower classes should be OK.
 

Jay Kempf

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Going for an affordable build makes you go for an affordable engine. So that is going to drive the design process like it does for all powered planes. If you want affordable and adequate to great performance on lowish HP you are going to have to build an airframe out of very readily available materials and use them miserly to get high Gs. Nothing can be wasted. A one piece wing is the first thing to look at. Aluminum built up sheet and extrusion is going to probably be the lightest thing you can do other than an out of the box composite design which wouldn't be affordable. To reduce build complexity you are going to have to think very hard about the joinery in the structure and reduce the fastener count.

Reproducing the original Extra 230 say even if you ever so slightly scaled is down due to lower gross and lower weight engine would be a good starting point aerodynamically. The structural side is going to be tough. Think joinery like the Cri Cri but somehow simpler. That is a VERY light structure of aluminum but not simple to build by any measure. A spreadsheet with weight budgets is your first friend.
 

A-Bird

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First of all - thanks for the replies. I don't have answers for all the questions yet. It's the development phase and I try to get as much input as possible. The No.1 goal is to keep A-Bird affordable, my guess is that this will be the biggest issue for a lot of the interested people.
-affordable
-ease of construction
-common (certified) material (Alu 6061T6)
-strong, small, robust
-smart look
-beginner friendly
I know thats a lot, maybe not possible. I have to make some compromises!

BJC the fueltank is planed to be in the fuselage behind the firewall in front of the spar. Putting weight to the wing seems to be not a good idea, also its easier to maintain.
I will keep the wing as a two piece part to ease the handling, save some shop space, transportation aso.
Jay you are right 'affordable engine' this is what Barry Smith states on his website (search 'acroadvanced'). I hope the Revmaster (Turbo?), or a Jabiru will be an option (I don't like the Rotax..)
I've made a small PDF with some preliminary design figures.
Last but not least every design has some precursors. I've stated that on the A-Bird website. If there is a good idea, why not keep it and use it..? But I think also the A-Bird is not a copy its unique because of its design goals.
If we could take all the designs: Corby Starlet/Kestrel, Mehari cea309, Snap, Panther, Sonex, Thatcher...put them in a mixer and save the essence and it looks a bit like the A-Bird - I would be happy...;-)
 

addicted2climbing

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The wing has no dihedral and will still fit an a standard garage for the build, so I see no reason why you would not take the weight and simplicity savings and make it one piece. Weight is going to be your biggest issue and by making it one piece you loose all the added fasteners and any additional structure in the fuselage to distribute the G loads from 2 joined wing panels. Is one of the requirements to be trailered or stored in a small space making removable wings a design feature?

On another note, I like it. Any chance it will fit a tall 6'4" pilot that weighs 230lbs?

Marc
 

BJC

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I missed the design g factors earlier. I recommend +9 and -6, with adequate strength to snap roll both ways at high enough speed to continue a 45 degree up line after the snap.


BJC
 

A-Bird

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Ok, to say it clear - the A-Bird will be not a competitor to the Extra, Xtreme or Edge! This is out of reach and that is ok.
If you increase the design loads to +9/-6 it will increase the costs and the weight and the needed power and and and... It will throw the idea out of a realistic range definitely. 6 G's are a lot, especially -3 or -4! You can do a lot of aerobatic manoevers within this range up to advanced aerobatics. The A-Bird is planed as a rigid, neat fun machine not more...not less, but affordable!

My flying skills are ok so far, the try to improve is always a good idea. By the way,most of the designers are'nt even once pilots...

(I apologize my bad english)
 

A-Bird

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Wow Marc you are tall (1,93m) you should play basketball instead of flying ;-)
21inches will be the approximate shoulder width. The weight should be no problem. For the taller guys maybe the canopy height could be expanded a bit - it will be a homebuilt...
 

mcrae0104

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6 G's are a lot, especially -3 or -4!
I would imagine BJC was suggesting +9/-6 ultimate, which would correspond (roughly) to a typical aerobatic +6/-3 limit load (with a little extra negative thrown in).

Of course, if it's a very serious competition machine, maybe the higher limit load is appropriate, but I'm not one of those guys. BJC?
 

BJC

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I would imagine BJC was suggesting +9/-6 ultimate, which would correspond (roughly) to a typical aerobatic +6/-3 limit load (with a little extra negative thrown in).

Of course, if it's a very serious competition machine, maybe the higher limit load is appropriate, but I'm not one of those guys. BJC?
My thought is that anyone buying plans or a kit for an aerobatic airplane would want a design load of at least +9 and -6. Certainly routines can be flown at lower g, but there is a degree of comfort in having some margin in g capability without bending anything. Keep in mind that the really good pilots won't be building a limited perfomance homebuilt. They will be flying an MX, an Edge, a Suhkoi, or something similar. Most aerobatic people will be leery of aluminium construction anyway, so some margin will be comforting. Not talking science here; talking emotion and bias.

For historical perspective Kermit Weeks won the 4 minute free program at a World Aerobatic Contest in the 1980's (not certain of the date) in a Weeks Super Solution, which was, essentially, a super light Pitts S-1S with a 540 lycoming. It had a design g limit of +5 / -4, IIRC.


BJC
 

A-Bird

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My thought is that anyone buying plans or a kit for an aerobatic airplane ..
BJC
BJC the A-Bird is planed to be 'open source' and the plans (when finally available) 'free of ccharge'. This is the first step if an aircraft design has the major claim to be affordable. I currently working with an AutoCAD format (.dwg/.dxf) and still have to learn a lot. I also work with a 3D Software to check the items if they will work and how it looks like (a good part, if it is looking good, WILL work..). It all stays a hobby! I don't want to have time limits to finish - only want to see a 'learning curve'.

Kind regards
 

BJC

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BJC the A-Bird is planed to be 'open source' and the plans (when finally available) 'free of ccharge'. This is the first step if an aircraft design has the major claim to be affordable. I currently working with an AutoCAD format (.dwg/.dxf) and still have to learn a lot. I also work with a 3D Software to check the items if they will work and how it looks like (a good part, if it is looking good, WILL work..). It all stays a hobby! I don't want to have time limits to finish - only want to see a 'learning curve'.

Kind regards
Understand. That is a different market from what I had thought that it was intended for.

Like the concept.


BJC
 

mcrae0104

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When I open the DXFs in ACAD, there is nothing there.
 

Jay Kempf

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Jay you are right 'affordable engine' this is what Barry Smith states on his website (search 'acroadvanced'). I hope the Revmaster (Turbo?)
A light weight low capacity engine with a heavy large prop and a turbo may not have the throttle response to be a true aerobatic machine. That is more of a FL10 cruise configuration.

VW is probably the right way to go. Bolt on large pistons and some sort of heads that have enough cooling capacity for short blasts of WOT would be the way to go. If you could keep it real light and simple and get as close to 100HP as you could and keep the airframe LIGHT you would have a fun plane that could do all but brute power moves. That would be a good beginner machine because you would have to be very efficient with the momentum to do a real routine. You are going to be looking at fabric covering as much as you possibly can. Riveted/bolted aluminum tubing and extrusions with gussets everywhere you can to save weight.
 

A-Bird

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When I open the DXFs in ACAD, there is nothing there.
Sorry mcrea, I've checked all 4 by downloading them - it works. I upload a .dwg and you may try this...




Jay, advanced aerobatics in an alu design is not that special. Saving weight will be certainly important. If you have the Sonex, the CriCri, the Corby Kestrel, the Panther aso. in mind -they all have proper capabilities to do some aerobatics. This realizing should be a solid basis for the development of the A-Bird.
 

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