The XPB Stage 1 underway.

[facthunter]

While I started with tailwheel and like them for me, A tricycle is the popular choice and likely to stay that way. If a flying school had only one plane it would have to be a tricycle. Probably about the fourth would be a tailwheel, unless doing aeros was a specialty. If the tail sits high like a Savanna sp? on the gound, the plane is not likely to wheelbarrow. Both sets of skills need to be taught properly. Can't blame the plane if the driver doesn't know how to handle it. In limit conditions I would prefer a tailwheel. It's more of a utility vehicle. Nev

 

 

[bexrbetter]

This is a photo-shop to represent somewhat the aprox psychical size and proportions of my craft.

 

The purpose is to understand how I can best achieve a flat wrap canopy for cheapness and ease of replacement at home.

 

Of all the canopies I have tried, I am happy with this representation ....

 

 

 

 

[Marty_d]

This is a photo-shop to represent somewhat the aprox psychical size and proportions of my craft.The purpose is to understand how I can best achieve a flat wrap canopy for cheapness and ease of replacement at home.

 

Of all the canopies I have tried, I am happy with this representation ....

 

[ATTACH=full]47278[/ATTACH]

OMG... an aircraft that's going to tell the pilot his future...

 

 

[Marty_d]

... but seriously - would there be any turbulence issues due to the sharp changes of direction from windscreen/canopy/turtledeck?

 

 

[geoffreywh]

looks great, if a bit Morganish. Canopy looks none too difficult, much better than trying to get one blown. gonna open on hinges or slide back?

 

 

[Litespeed]

The alloy tube welded is interesting. Tell more

 

With the idea of flat wrapped screen, it really grabs me for a number of reasons in all the wrong places. I agree it would be ideal to have a flat pack screen/canopy, but I see ugly and angry to the air.

 

 

[Pilot Pete]

Why ugly? The canopy in the pic looks fine and functional. The idea is cheap, and easy to manufacture by the novice builder

 

 

[bexrbetter]

looks great, if a bit Morganish. Canopy looks none too difficult, much better than trying to get one blown. gonna open on hinges or slide back?

That photoshop started life as a Rand KR2 "for sale" picture. The Morgan is basically a metal'ised and personalised, evolved KR2, and I have taken a few inspirations from both, but nothing is interchangeable physically or dimension'ally.

 

There is a overhead longtudinal central beam that the doors will hinge from. The beam will be great for something to hang onto while getting in and out.

 

but I see ugly and angry to the air.

I have no desire to start "value adding" and ending up just another plane. "Cheap" does necessarily include some "not as great as expensive" features.

 

I am happy to take on any flat wrap suggestions.

 

The alloy tube welded is interesting. Tell more

Since I have been here I have sought quality aluminium welding unsuccessfully, but recently a couple of mobs in China have gotten into stage truss supply and I went and had a look to find some pretty decent stuff including one local agent - and that ties with my "Local supply only" criteria. It's 6061 T6 or 6082 T6, all engineered and certified as it needs to be for various countries work place and safety, so I'm looking into it.

 

I would still rivet gussets over the welded joints for strength and redundancy, but the complete structures make assembly a much easier and accurate time saving task for homebuilders.

 

 

 

 

[bexrbetter]

looks great, if a bit Morganish.

There you go, you can see the differences, again please note it's just a dimensionally close photochop, note the longer tail and nose and different wing location ...

 

 

 

[Nobody]

Since I have been here I have sought quality aluminium welding unsuccessfully, but recently a couple of mobs in China have gotten into stage truss supply and I went and had a look to find some pretty decent stuff including one local agent - and that ties with my "Local supply only" criteria. It's 6061 T6 or 6082 T6, all engineered and certified as it needs to be for various countries work place and safety, so I'm looking into it.

I would still rivet gussets over the welded joints for strength and redundancy, but the complete structures make assembly a much easier and accurate time saving task for homebuilders.

 

 

Just make sure that you get very good engineering advice about the fatigue of the welded aluminium connections. Stage structures are not subjected to the levels of cyclic load that an aircraft structure experiences.

 

 

[djpacro]

There you go ...

Great effort. Just a quick unsolicited comment, just eyeballing it with no calcs done but it seems to me that the vertical tail could be bigger - I've always said that it is better to have a bigger one than smaller.

 

 

[bexrbetter]

Just make sure that you get very good engineering advice about the fatigue of the welded aluminium connections.

The welded joints are not primary structure. It is being fully joint gusseted as if not welded. Joint gussets on the insides and the skin on the outside.

 

It's just a convenience to have the assemblies pre jigged and one piece. It makes everything about the build just so much easier, from transport to pulling it together.

 

it seems to me that the vertical tail could be bigger

Well that's the KR2 tail unmodified and actually because it's further back, it's actually oversized relative (increased leverage)

 

 

[Nobody]

The welded joints are not primary structure. It is being fully joint gusseted as if not welded. Joint gussets on the insides and the skin on the outside.

Anything welded to the primary structure reduces its fatigue life even if the varying load doesnt go through the part welded to the primary structure.

 

This image extract below is from AS1664.1.

 

 

This one most closely matches your detail. The variable loading is horizontal as shown by the double headed arrows. The welded attachment is not loaded but the weld will act as a defect at the edge of the member. A piece of extruded material without the weld is detail category A and this welded one D. The trouble with the curves in the design standards is that they are printed on "log-log" scales. This means that lines that don't look too far apart are very different values.

 

For instance, the stress that causes failure in detail A in 100,000 cycles would cause failure at about 3200 cycles if the element is welded.

 

 

[Head in the clouds]

Anything welded to the primary structure reduces its fatigue life even if the varying load doesnt go through the part welded to the primary structure.This image extract below is from AS1664.1.

 

 

This one most closely matches your detail. The variable loading is horizontal as shown by the double headed arrows. The welded attachment is not loaded but the weld will act as a defect at the edge of the member. A piece of extruded material without the weld is detail category A and this welded one D. The trouble with the curves in the design standards is that they are printed on "log-log" scales. This means that lines that don't look too far apart are very different values.

 

For instance, the stress that causes failure in detail A in 100,000 cycles would cause failure at about 3200 cycles if the element is welded.

Yes ... and the heat affected zone of the 6061 is then no longer T6, it's fully annealed to T0.

 

Depending on the radius of curvature and the wall thickness of the tubing, another thing you may find is that if the longerons are curved when they're welded they'll relax due to the heat from the welding, and adopt a series of facets instead of a smooth curve. It would probably be inconsistent too, some operators would weld hotter than others so the degree of relaxing of the curvature would vary.

 

Welding works OK for marine and transport, but welding of aluminium primary structure really isn't a very good idea for aircraft because the members are so much thinner. That's why welded aircraft structures are usually chromoly tubing. I seem to recall that Grumman tried it with aly way back, I think it might have been for a Goose or Mallard derivative, because it would have made sense to weld flying boats rather than drill and rivet them, but IIRC they had so many fatigue problems in the testing phase that they dropped the idea.

 

 

[facthunter]

Welding is more than neat runs. The filler metal has to be compatible with the metals welded. Chromollysp? can require annealing and stress relieving and subsequent heat treatment. OK for sub assemblies but not major structures due size. Metallurgical knowledge required is extensive. Heat treated aluminium alloys lose some (or most) of their tensile strength. coatings, zinc, Cadmium, lead paints, rust etc can cause weld quality issues. If you want something welded, just mention it's for an aeroplane and they won't want you around. Nev

 

 

[fly_tornado]

You can test all the engineering assumptions inside Solidworks to see how much well it performs.

 

 

[Marty_d]

If you want something welded, just mention it's for an aeroplane and they won't want you around. Nev

Great, who's going to weld my cabin frame??

 

 

[facthunter]

Depends what it's made from. You can get a high grade mild tube and weld it with a Dylan type oxy torch quite well. No annealing needed . Was done that way for years in the USA. Do samples of each joint and destruct them and measure strength/ performance. Keep records. Nev

 

 

[Marty_d]

Depends what it's made from. You can get a high grade mild tube and weld it with a Dylan type oxy torch quite well. No annealing needed . Was done that way for years in the USA. Do samples of each joint and destruct them and measure strength/ performance. Keep records. Nev

No no no no no. I know my limitations and welding (properly) is beyond them. The cabin frame is chrome moly. My intention is to cut everything to size/shape, have it all held together with a wooden frame and say "weld it together please!"

 

Sorry Bex, didn't mean to hijack your thread. Back to the XPB.

 

 

[facthunter]

Just for the record, I think the welding torch is called a Dillon. It's just a fancy oxy torch. Marty, any welding reduces the strength of chrome molly below it's best heat treated condition. It also has to be annealed at the edge of the welds to prevent it being brittle, if the weld cools too quickly. The heat runs from the hot weld area out into the adjacent metal too rapidly sometimes with TIG.. Nev

 

 

[bexrbetter]

Anything welded to the primary structure reduces its fatigue life even if the varying load doesnt go through the part welded to the primary structure.

Got nothing to do with my structure. It wouldn't matter a shite if the welds cracked through, because, again, they are not the primary structure.

 

Here is a Morgan, in some places the braces are up to 20mm gap, more around the 5mm mark. Morgan isn't the only one out there like this successfully flying either, this forum just happens to have lots of Morgan build shots. All I have done is fill up those gaps for the convenient reasons stated above, if they happened to crack through, unlikely, then it does nothing more than revert to the Morgan, and Other's, setup only with a minute gap rather than a large one.

 

And it's because the load paths are what counts, and my load paths, which are broadly distributed, and do not include the welded joints, are just fine thanks.

 

 

The Morgan is even quite scary when you pick up a side with just the small joint gussets holding one side together, comes together just lovely as a complete structure though.

 

Yes ... and the heat affected zone of the 6061 is then no longer T6, it's fully annealed to T0.

adswttn.

In post #575 you will see an acronym at the bottom, "adswttn" - stands for; "and directly, someone with the temper notes".

 

You guys are incorrectly presenting this as a welded aircraft structure per say, not me, and your concerns are not relevant.

 

Of course before when I had gap joints similar to the Others, well that was also wrong, never win.

 

 

[cherk]

Great, who's going to weld my cabin frame??

Hi Marty, No need ..........I can sell you one! Mates rates .

 

 

[Nobody]

My concern isn't the weld failing but that the weld causes a crack to start in the primary member that then propagates. I have tried to show the situation in the sketch below.

 

 

It might be that it is all fine. I don't know the loads and the member sizes. Just get someone who has an engineering background in fatigue assessment to have a proper look at it.

 

 

[Head in the clouds]

.....And it's because the load paths are what counts, and my load paths, which are broadly distributed, and do not include the welded joints, are just fine thanks.

I'm not sure you're right about that. Previously you (like Morgan and others) had your longerons attached to verticals and diagonals with riveted gussets. In terms of the truss your longerons are your top and bottom chords, and your verticals and diagonals are your web members. By necessity your web members are individual but your chords MUST be continuous, or spliced with a moment connection, or else it isn't a truss. When they were riveted your chords were continuous but by adding welds every so often along your longerons/chords, you've effectively broken them up into pieces - or will have once the fatigue sets in - and the additional riveted gusset does not constitute much of a splice. Once the chords start to crack up you won't have a truss, or, effectively, any longerons. So if you're building something where your load paths are as distributed as you claim, why bother to have longerons and/or a truss in the first place? If widely distributed load paths are your design intent why not build a proper monocoque like the RVs? Cheaper, lighter ... and compared to this case, far less prone to fatigue failure.

 

You guys are incorrectly presenting this as a welded aircraft structure per say, not me, and your concerns are not relevant.

....

I think they are relevant. I recall your telling me that you had no intention of flying in small planes and that your sole interest in this field was to produce engines and airframe kits. By benefiting from China's low cost materials and labour, they would be cheaply priced so you would sell lots of them for a handsome profit. There's nothing wrong with profit of course, but the kits people sell don't have to pass any form of testing in regard of whether they will assemble into a safe flyable aircraft. The onus for safety and airworthiness and structural integrity falls on the customer, not the kit producer, as you're aware, and if you're not planning on flying it yourself there might not be quite the same incentive to make sure it's perfectly sound. Nonetheless, for good business reasons as well as the ethical ones, I think it behoves anyone producing a kit to ensure they're employing best practices rather than introducing ones that are known for being unreliable.

 

A while back you said you didn't have any formal engineering qualification. There's nothing wrong with that either, many people with knowledge gained from the internet forums and discussion with their peers have designed and built quite adequate aircraft, but without their having the personal ability to fully analyze every aspect of the loads, stresses and metallurgies involved, we're generally well advised to keep our design parameters within established boundaries, in effect closely emulating structures, member sizing and methods that have been previously formally engineered and proven on similar-sized and loaded designs. That can be quite successfully achieved without 'copying' the design, and also without needing to end up with something that looks significantly similar.

 

If you produce a kit that assembles into something with poor flying characteristics, or which is not structurally sound, those defects will quickly become evident and you won't sell many more kits, so the problem would be self-resolving. However designs with in-built fatigue issues are far more sinister because the failures won't start to show up for quite a while, several years perhaps, by which time there may be many others of them flying and in advanced stages of assembly. People who've invested considerable time and money in buying and assembling their 'baby' don't tend to be willing to trash them without a lot of resistance, consequently they're a ticking time bomb and people die as a result. Some might consider one model of the 601 to be a good example of that, when they started to gain an unenviable reputation for inexplicably shedding wings, apparently some unscrupulous people quickly sold them to unsuspecting buyers who weren't aware of the problem.

 

I imagine someone else will conduct your test flying and every one of your customers will be doing that also. 'Test pilots', and also the vast majority of the people who assemble a kit, rarely have any significant or relevant engineering knowledge themselves, so when they fly the creation they've assembled they're very literally trusting their lives to the person who designed the thing - that person presumably having done so with suitable and relevant knowledge, or where that might be lacking, having sought and heeded appropriate advice.

 

I've largely refrained from commenting on your build because on the two or three occasions where I did your response seemed to be less than appreciative. And your reaction to the considered input provided by several here who are very knowledgeable and experienced builders has been quite dismissive, to the extent where it's noticeable that most have not bothered to contribute any further. Nonetheless, if for no other reason than duty of care, I do feel it necessary to point out things which are clearly wrong, and have been shown by others' previous experience to be so, and which if not corrected could possibly have fatal consequences.

 

 

[rgmwa]

As a structural engineer, I think Nobody and HIC are right to be concerned about the effect of welding and its effect on material properties and fatigue cracking in aluminium. The load paths will inevitably include the welded joints. The structure doesn't know they are not meant to be part of the load resisting system.

 

rgmwa