The XPB Stage 1 underway.

[Nobody]

Cool idea with the build method. looks great.

 

I know you are just doing these videos for show but when you go on to build a flying part work on your drilling technique. You will likely have left little dint/nicks on the inside of the far side of the extrusions. This may be a stress concentration in the future. A drill press would help prevent that but be a little bit slower.

 

 

[AussieB1rd]

A drill press would help prevent that but be a little bit slower.

Or a drill stop, they fit onto the drill and tighten with a grub screw, even some tape around the drill and even pressure and slower. Bex is just trying to show how quick it can be done, and I guess it's up to each and every purchaser as to how they go about it. A few extra hours in the build time are nothing if it's done correctly and competently.

 

 

[Marty_d]

I have a question on this method of fuselage construction, I hope you don’t take it the wrong way.

My experience is old and probably out of date, but as a young apprentice AME (mech) for Qantas we were taught that all structural items in an aluminium airframe have no residual stress. I was never a proper “sheety” but I have seen many structural repairs and anywhere we had a longeron, stringer or section of skin repalaced it would be pre-shaped to exactly that required before fitment to the aircraft. For these types of members the material would be formed in the annealed state, and heat treated after forming to ensure no residual stress.

 

For small aircraft, is it common practice to leave residual stress in structural members?

I believe he's using 6061-T6 which is already tempered - correct me if I'm wrong Bex!

 

I'm using the same grade for my build which means that for "formed" parts like wing ribs, you make 2 wooden form blocks, bolt them either side of the material then belt the flange over with a rubber mallet. To allow for curves without creasing you belt relief crimps (is that the word?) into the flange side.

 

I know my old neighbour who used to fix Squirrels for the Navy was surprised at this method, obviously when they built replacement parts it was like you say - use a non-tempered alloy, form it under pressure then temper it.

 

 

[bexrbetter]

Cool idea with the build method. looks great.I know you are just doing these videos for show but when you go on to build a flying part work on your drilling technique. You will likely have left little dint/nicks on the inside of the far side of the extrusions. This may be a stress concentration in the future. A drill press would help prevent that but be a little bit slower.

Ha! I was waiting to see if someone would pick that up. Look above at post #189, last line; "sdblo" - stands for; "shorter drill bit later on"! I am well aware, just lazy while I'm trying to get the pre-production demo together that will never fly, had to many changes and rivets removed and replaced along with a few random and extra holes to be trusted. You can get hand drills with depth stop rods and short, rivet bits also.

 

in his method that mm or 2 mm as he says is a concern as movement can occur at both ends due to the brace not being connected directly to the longeron, also a smaller TEE gusset top and botton would probably be all that is required and further reduce weight and not subtract strength,

 

For the vertical to move at all would need a force totally independent of the longeron approaching 5 TONNES. Concern level is zero.

 

You are the second to say that 'T' gussets would be sufficient, they are not suitable for the gauge being used.

 

For small aircraft, is it common practice to leave residual stress in structural members?

There's a couple I know of, probably more, don't know them all.

 

I appreciate your concern but the stress is of very low value and so well distributed that it's insignificant.

 

.. and yes, it probably would be of more concern on a jetliner the way they are built to the limit.

 

 

[AussieB1rd]

For the vertical to move at all would need a force totally independent of the longeron approaching 5 TONNES. Concern level is zero.

That maybe the case if it's just in one direction, it will not be just going up and down, all airframes will flex, and not just in one direction, torque from the engine will twist it one way, pressure from vert stab and rudder another, landing yet another again and so on, so the weakest point will be on the gusset at just bellow top longeron where the vertical brace starts and just above bottom longeron where the same brace ends, any sideways flexing here may or could fatigue over time regardless of allowable load limits. Just my thoughts.

 

 

[bexrbetter]

Just my thoughts.

 

 

 

[AussieB1rd]

Use the Dahmer drilling technique then lol

 

 

[kasper]

I have a question on this method of fuselage construction, I hope you don’t take it the wrong way.

My experience is old and probably out of date, but as a young apprentice AME (mech) for Qantas we were taught that all structural items in an aluminium airframe have no residual stress. I was never a proper “sheety” but I have seen many structural repairs and anywhere we had a longeron, stringer or section of skin repalaced it would be pre-shaped to exactly that required before fitment to the aircraft. For these types of members the material would be formed in the annealed state, and heat treated after forming to ensure no residual stress.

 

For small aircraft, is it common practice to leave residual stress in structural members?

Short answer is yes.

In ali angle airframes in the light aircraft/ultralight world simply pulling the materials together and securing is common place.

 

Even in the higher end homebuilts using metal it is common to have only semi-formed skins made of already heat treated materials on wings and fuselages eg Long Midget Mustang uses flat sheet for the upper rear and forward upper fuselage that are held to shape on formers by rivets - residual stress low but exisitng but belly skins on rear are pre-formed for the most part.

 

Similar with nearly every homebuilt in ali skins on the wings the skins are not rolled to final but a leading edge is bent in to a reasonably good fit and the rest of the forming is by rivet down to ribs eg RVs, savanahs etc and in all cases the materials are already in final materials state when formed and are not formed in annealed state and then heat/solution treated up to temper

 

 

[bexrbetter]

Been an interesting week. The young guy doing the FEA work for me had his Boss take an interest and they got really stuck into it through the week and made a lot of ground saving over a kilo per side, while maintaining the same strength. Best part is less riveting through the use of 'bandaids' rather than whole plates.

 

So even though I said "locked in" above, I really am locked in now (and to be honest I just don't have the mental energy for another change in this area as I need to move forward) and today did a test run of tying the 'boat' together around the wing spar cross-member ... it was so satisfying I assure you I did a little jig on the spot!

 

 

 

 

 

 

[Kiwi303]

A Jig? Isn't it supposed to be a Jigless build? Isn't a flat table sufficient by itself now?

 

 

 

[rgmwa]

A Jig? Isn't it supposed to be a Jigless build? Isn't a flat table sufficient by itself now?

Sounds like the jig might be optional. Others may prefer a jug.

 

rgmwa

 

 

[Marty_d]

What's the cockpit width Bex?

 

And yes if you give up on it as an aircraft it looks like a damn good tinny...

 

 

[horsefeathers]

Sounds like the jig might be optional. Others may prefer a jug.rgmwa

A jug?

Personally, a cup of tea....

 

Yes, a cup of tea, a bex, and a good lie down....(if you're under sixty, you won't understand)

 

 

[bexrbetter]

A Jig? Isn't it supposed to be a Jigless build? Isn't a flat table sufficient by itself now?

 

What jig? You mean the whipped up booker rod clamps to pull the front together?

 

I actually use ratchet straps but made those booker rod clamps just for the pictures.

 

Or do you mean the rope at the back ..... ok I lied.

 

What's the cockpit width Bex?

Fat Bastards.

 

1065mm inside at shoulders (or 42" for Luddites).

 

 

[AussieB1rd]

tying the 'boat' together

At last some solid transom brackets, lol looking good with that flat bottom should make for a very shallow draft, suit my short leg lol

 

 

[skeptic36]

What jig?

The one you danced, :happy dance:you know, the one that's going to be on page 1139 of the builders manual

 

 

[Kiwi303]

What jig

 

The one you danced, :happy dance:you know, the one that's going to be on page 1139 of the builders manual

Yep, the one on the spot!

 

I'm a hopeless dancer, You better include step-by-step instructions and maybe a music CD or MP4 with a suitable beat!

 

 

[bexrbetter]

Oh that jig!

 

 

[pylon500]

That's looking more like it.

 

Every Kilo you save.......

 

 

[bexrbetter]

Been mainly on the computer designing or tending another personal item the last few days, but did manage to get the diagonals and some horizontal braces in.

 

Also got a test firewall and a test rear floor cut, might get them on tomorrow or the day after.

 

Was whimpering in the corner so I let him outside for a while ...

 

 

 

 

 

 

[Kiwi303]

From the looks it's a plumb square up-and-down firewall rather than slanting rearwards at the bottom to avoid digging the fuselage in after the engine comes off in a crash?

 

 

[bexrbetter]

From the looks it's a plumb square up-and-down firewall rather than slanting rearwards at the bottom to avoid digging the fuselage in after the engine comes off in a crash?

I personally hand file a 1mm radius on the bottom of the firewall to prevent this, nothing but the best for my clients.

 

 

[Marty_d]

From the looks it's a plumb square up-and-down firewall rather than slanting rearwards at the bottom to avoid digging the fuselage in after the engine comes off in a crash?

Didn't know that was a thing. My 701 plans show the firewall actually leans backward at the top providing a lovely sharp edge to dig in, but then again it is a high wing.

 

 

[kasper]

... and if i hit hard enough to remove the engine I think I am not really going to be saved much additional grief by the slope of the firewall at the lower edge ... I'm with Bex on this one, file a 1mm radius if it make you feel better or fit a steel skid but hitting hard enough for the engine to come off is not going to instantly have me going oh dear, wish the firewall was sloped

 

 

[Kiwi303]

Didn't know that was a thing. My 701 plans show the firewall actually leans backward at the top providing a lovely sharp edge to dig in, but then again it is a high wing.

It came up at one point on the HBA forum, I think it may have been the "Design for Safety" thread, anyhow a number of designs were pointed out that had that sort of setup.

 

Even in a less severe crash, the engine on a plane with a Lyc or Cont or similar flat design is usually mounted fairly high up and theres a lot of space below filled with the carb and such, with just a light cowling that is easily pushed up in a crash to expose the much stiffer firewall which can dig in and apparently has caused flips by digging in.

 

Yes, if the crash is that fast and that severe you're likely FUBARed anyway, but it did seem like a reasonable thing to build in if it wasn't dictated otherwise by the geometry of the design. Just loading the dice that few percentage points closer to survival.