The XPB Stage 1 underway.

[bexrbetter]

The XPB, "Extraordinary Plane Build", is termed so because I believe this will lead to a kit manufactured to a price and build speed not seen very often in the world of light aircraft.

 

I will repeat that this is very much work in progress to develop the build system first, the plane itself is of secondary importance at this time but of course that is the ultimate aim. At anytime I reserve the right to run into a dead end, be completely bamboozled, and completely change what you might be seeing in these early days.

 

Here I present the basic theme of stage 1, the frame construction method. Please note that I am actually building this now and as I feel I have proven each step's foundation to myself first, then and only then will I post the results. I would expect to have a freestanding frame complete by this weekend. "Freestanding" means the frame stays together by itself without and fasteners (rivets or bolts etc).

 

During stage 2 you will see my answers and methods for fastening.

 

I currently have everything I need in materials, extrusions, modules, braces and laterals in the factory, just taking longer than expected to set up some tooling and people.

 

 

 

 

[rgmwa]

No diagonal bracing?

 

rgmwa

 

 

[bexrbetter]

No diagonal bracing?rgmwa

Yes, of course, but not during this stage.

 

You might not see it 'til some time down the road either.

 

 

[kasper]

Now I get the need for the rectangular extrusion to have the web creating the '8' shape - elegant solution to the issue of retaining structural strength where cutouts for inserts are to go.

 

Will be interesting to see how much jigging you will need as you move into fixing the joints to retain alignment along then length of the fuselage.

 

 

[bexrbetter]

Now I get the need for the rectangular extrusion to have the web creating the '8' shape - elegant solution to the issue of retaining structural strength where cutouts for inserts are to go.

The cutouts are in the 'anti-buckling' sheaths only and irrelevant as the load paths are bypassed through the surrounding gussets that come later. That's on the top longeron, the floor itself is one huge gusset (with appropriate additional gusseting) in the big picture, i.e. no stress risers.

 

Note this is sample of layout only, not part of actual build ...

 

 

 

.Will be interesting to see how much jigging you will need as you move into fixing the joints to retain alignment along then length of the fuselage.

Will be jigless.

 

Oh you might have to give a push and a shove and check with a tape measure for square before the first couple of rivets are added, but as long as you make sure left and right sides are identical (easily done, just lay your second side on top of the first) then you have a jigless foundation.

 

 

[onetrack]

Woo-Hooo! I just love cheap and fast build designs! Is that Tek screws I can see in the above diagram! If not, why not??

 

 

[bexrbetter]

Well I should have spend the time sorting out a few other things, but being an excitable chap I couldn't wait to see my concept tested ... and as you can see for yourself, it does.

 

There's a couple of little niggly bits I need to sort out, but the main technique is sound.

 

The assembly as you see it here, is completely free of fasteners and only held together by the ratchet strap at the front. It takes less than 5 minutes to assemble this lot

 

 

 

 

[onetrack]

It looks good - but being a picky kind of bloke - aren't the keyway cutouts in the extrusions substantially weakening the strength of the extrusion? - as compared to, say an all-welded design?

 

 

[bexrbetter]

It looks good - but being a picky kind of bloke - aren't the keyway cutouts in the extrusions substantially weakening the strength of the extrusion? - as compared to, say an all-welded design?

Hi onetrack,

 

No, and you might want to read post 5 above in it's entirety where it's not only explained, but visuals as well.

 

Here is a "not to scale" visual approximation of the schedule where the braces meet, there is no weakness but you are the 3rd person to mention it so if that trend continues and it becomes "lore" then I will consider deferring to a couple of backup plans that achieve the same result , but not as elegantly.

 

 

It's of interest to me to understand what people perceive though, correctly or incorrectly, it is part of the process.

 

 

[onetrack]

Ahhh .. O.K., I get the picture now. I did read post #5 in it's entirety, but I couldn't fully grasp the section shape of the extrusions in the diagrams in post #5.

 

The last diagram makes it very clear, and I now understand what you were explaining in the first two sentences of post #5.

 

 

[eightyknots]

Hi onetrack,No, and you might want to read post 5 above in it's entirety where it's not only explained, but visuals as well.

 

Here is a "not to scale" visual approximation of the schedule where the braces meet, there is no weakness but you are the 3rd person to mention it so if that trend continues and it becomes "lore" then I will consider deferring to a couple of backup plans that achieve the same result , but not as elegantly.

 

[ATTACH=full]43014[/ATTACH]

 

It's of interest to me to understand what people perceive though, correctly or incorrectly, it is part of the process.

Nice and clear ...and elegant too. I like it!

 

I hope that you can adapt the same technique for the wings: I expect that the wings are likely to be constant chord, rather than tapered! There are many good constant chord wing aeroplanes so that is not a major issue at all.

 

Next question: is this going to be a low wing plane or a high wing?

 

 

[Kyle Communications]

Low wing by the look of it.......High wing would be better :)

 

 

[Keenaviator]

Low wing, a bit KR2/Joeyish :)

 

 

[Kyle Communications]

The system looks very do-able for almost anyone and would go together quite fast. Alignment would be quite easy too with cnc drilled support plates. What about the extra weight with all the gussets and bracing also I suppose it would depend on the actual tube thickness and associated strength. I like the look of it all so far Bex...good job

 

 

[Downunder]

Ultimately I guess this needs to comform to the 51% rule.

 

It's one thing to make it fast and easy but it must conform to rulings and kit approvals.

 

Something to be mindful of anyway.....

 

There is also a point where the cost of extensive prefabricated parts starts to eat into the cost and value of a kit.....

 

Not trying to put this project down. I really like innovative stuff like this!!!!

 

 

[old man emu]

Ultimately I guess this needs to comform to the 51% rule.

I would imagine that a box of pre-cut assorted lengths of material would not constitute a great proportion of the whole airplane. Just try to tally how much of an airplane the builder actually makes - and make sure you add in all the instruments, electrics, pumps etc.

 

What is the actual wording of the 51% rule, anyway?

 

There is also a point where the cost of extensive prefabricated parts starts to eat into the cost and value of a kit.....

That's probably why it's a goer being made in China.

 

OME

 

 

[bexrbetter]

Low wing, a bit KR2/Joeyish :)

There's a number of craft with this basic foundation, I've reviewed quite a number. Mines better(!) but that's only because others have been refining theirs for the last 100 years and gave me a head start, so credit where credit's due.

 

At the end of the day, it's a just a fancy truss.

 

What about the extra weight

The scales don't lie, at the end of the day that's all that counts.

 

What is the actual wording of the 51% rule, anyway?

Very misunderstood rule, doesn't help the FAA have reviewed it a few times. In simple terms you must prove you are and have performed build items that prove you understand and are capable of holding a Repairman's certificate. This does not mean that you have to physically do 51% of the build, it means you must have a clear understanding, practical hands-on experience and be capable of repairing more than 51% of the planes modules.

 

Example is rivets, the craft may have say 5000 rivets, you don't have to do 2501 of them, you only have to do a nominal amount, lets say 200, to prove that you have the knowledge and capability to repair any one of those 5000 and that you could have done all 5000 yourself. So lets call that 10% of the plane build you are accredited with, and so it goes throughout the plane.

 

This is how the various companies do the 2 week build program where all the staff help you build it, you're not building 51% of the plane, you're being trained hands-on for understanding of, and to be capable of repairing more than 51% of the crafts modules as it's being built.

 

 

[Keenaviator]

I 'built' a Jabiru kit and they're regarded 51%+

 

 

[old man emu]

In simple terms you must prove you have performed build tasks that prove:

1. You have a clear understanding of each process and practical, hands-on experience and,

 

2. You are capable of repairing more than 51% of the plane's modules.

 

This is how the various companies do the 2 week build program. You're not building 51% of the plane. You're being trained, hands-on, for understanding of, and to be capable of repairing more than 51% of the craft's modules.

Hope you don't mind the editing re-write, but I think that clarifies the spirit of the 51% rule.

 

OME

 

 

[Dwilly]

Is there nore info on the tail connection?

 

 

[bexrbetter]

Is there more info on the tail connection?

I'm pretty certain it's up the back somewhere, I think.

 

Everything will come in time in it's order.

 

 

[bexrbetter]

Low wing by the look of it.......High wing would be better :)

Once again, the object in these early days is to sort out the build system.

 

I have some ideas for a high wing that will be undertaken shortly, at least some foundation testing.

 

 

[AllanBendigo]

Hi

 

With this build system how do you indeed to de-burr the holes you drill for the skins, gussets etc inside the extrusion ?

 

 

[bexrbetter]

HiWith this build system how do you intend to de-burr the holes you drill for the skins, gussets etc inside the extrusion ?

Trained mice.

 

I'm not sure you are you even serious with that rudimentary question, are you aware of how many aircraft use rivets in tubes ..... a lot, and there's a plethora of tools available.

 

Personally I use a modified 2.5mm allen key modified to suit, in a cordless drill. The 6 sides of the allen key give great grip in the drill too.

 

 

 

[bexrbetter]

At the outset I said that "this is very much work in progress to develop the build system first, the plane itself is of secondary importance at this time but of course that is the ultimate aim"

 

.. and ..

 

" anytime I reserve the right to run into a dead end, be completely bamboozled, and completely change what you might be seeing in these early days".

 

Well I have changed.

 

Well it's been a long sleepless week and a bit, for me, designing new bits and crash coursing myself in a new 2D CAD to do the laser cutting files for those bits.

 

While being very happy with the first concept in principle, I am not happy with the continuity of supply for material and especially welding to my standards, so felt no choice but to try a modification to the foundation. And here is some proof of what I have tried and discarded ...

 

 

.... so the new system involves having some side plates laser cut to achieve the same result, today test ran the 4th design set (always amazing what seemingly small changes will make) and very happy with the result and will extend this method to the nose and tail through the week as well.

 

Happy days, I might even sleep tonight ...