Valley Engineering's new ultralight

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BBerson

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Thanks Bruce, for the link. Topaz, If you look close (post 39)you can see a large (1 1/4" or so) cross tube that prevented cockpit intrusion.
Sure, as George said in post 39, the landing gear held and the fuselage collapsed.
Ultralight designers are not required to test drop the design like part 23 requires.

George said look at the breaks at the welds and claims that is proof the weld zone is weak. So.
Everybody knows this. So does drilling bolt or rivet holes in the tube weaken it so it breaks at the hole.

In any case, the latest version is different, with a much larger tube. It still won't meet your approval, I suppose, because it isn't your approved rigid truss exactly.
But consider a 250 pound pilot in the seat. In an ultralight the pilot is the largest load to handle. This structure is built for that.

Further, the new larger tube now has a much smaller heat affected zone. I could see the heat affected zone in the weld, might not be visible here.

PT said the gear was weak or unhinged or something. On the other hand, George said the gear was too strong.... Can't win.

I would rather crash this than a wood Sky Pup.
 

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Topaz

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Topaz, If you look close (post 39)you can see a large (1 1/4" or so) cross tube that prevented cockpit intrusion....
I don't see anything of the kind. Are you talking about the forward lip of the seat? The deformation most definitely intruded into the cockpit. The lower longeron is bent upwards at the rear "gusset tube" (you can see the crushing where it attaches), and the entire lower longeron - previously straight - is pushing up into the volume that would've been under the pilot's legs. If this had deflected any more, his legs would've been crushed between the upwards-bending fuselage bottom and the lower edge of the instrument panel.

Sure, as George said in post 39, the landing gear held and the fuselage collapsed.
Which is exactly my point. I'm failing to see the difference of opinion here. Having the fuselage collapse and the gear "hold" is exactly the opposite of what you want.

Ultralight designers are not required to test drop the design like part 23 requires.
I'm not sure what you're getting at here. Whether or not they are required to test against a standard has no bearing at all in how "safe" any given part of the structure might be in service.

...In any case, the latest version is different, with a much larger tube. It still won't meet your approval, I suppose, because it isn't your approved rigid truss exactly...
"My" rigid truss? I just said that I'd like to see the drag strut not attach in the middle of a largely unsupported tube span. No more, no less. If the picture you're showing is "the latest version", that must be a tri-gear derivative or something - the gear is moved considerably further aft than the one we were looking at earlier. Now they've got the compression strut - the main load-bearing member - as the smaller diameter tube, with a larger diameter tube in tension as the drag strut. Which, again, is the exact opposite of what you'd want to do. And just as before, the drag strut attaches to the longeron in the middle of a span supported only by the bent tube that fixes the front edge of the seat pan.

They haven't fixed the problem, they've just moved it around. I'll grant you one thing - in exactly the same accident, this gear would pull the lower longeron down instead of pushing it up into the cockpit. I "guess" that's better, but you're still failing the structure around the pilot, seemingly deliberately. I'm certainly no expert, but everything I've read about crashworthiness design says that's a really bad thing to do.

Look, I don't have any particular beef with Valley Engineering. I may well end up buying one of their motors. I'm just saying that this part of this design is something that I personally don't like, and would do differently.

PT said the gear was weak or unhinged or something. On the other hand, George said the gear was too strong.... Can't win.
Win? What's the competition here? I don't see it in those terms. Win/lose? Huh?

I would rather crash this than a wood Sky Pup.
And I'd rather not crash at all. You don't like the SkyPup for crashworthiness and I don't particularly like this particular aspect of this particular model of Backyard Flyer. Opinions duly and clearly noted. You act as if I'm saying the whole airplane is worthless, when I've said nothing of the kind.
 

kennyrayandersen

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Nor have I. we are merely saying this particular 'feature' sould been redesigned. That is all! It's wouldn't take that much, just some engineering. It's is true -- people cannot take criticism!
 

BBerson

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Nor have I. we are merely saying this particular 'feature' sould been redesigned. That is all! It's wouldn't take that much, just some engineering. It's is true -- people cannot take criticism!
Was your calling this design a "death-trap" as you did in post 140 and other posts considered as "constructive criticism"?
 

kennyrayandersen

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if you would have acknowledged the condition rather than merely being an apologist, the language wouldn't have become quite so emotive. Still, in it's current condition death-trap isn't so far from reality!
 

PTAirco

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One. More. Time:

Take a look at the landing gear in this picture. This is the airplane I saw in person and what my initial comments were based on. It NOT hinged. "Not" as in NOT. It it welded rigidly to the longerons. It still uses that weird curved tube as some kind of spring. So the general idea seemed to have been to let the leg flex around the welded joint, no? But since it's an ultralight, that's ok, right?? And let's not even talk about triangulation - apparently ultralights don't need any of that fancy stuff.

The collapsed version had hinges. It still collapsed.

Why should calling something bad design when it clearly is bad design cause such controversy? Any first year engineering student can see the fatal flaws in any of these airplanes. But because they ultralights it's ok....



When any of you stand next to my airplane design and see some glaring fault, please tell me about, would you? If I do something stupid, I'd like to know about it and fix it before I fly it. Seems some people don't.







 

kennyrayandersen

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Truss nodes are meant to take axial loads. If your introduce large bending loads it's will pretty much act like a hinge anyway. Again, the baffling thing to me is it's relatively easy to fix, but it's been this way for years. If someone really wants tom build one PM me and I'll give your some tips on how to mod it.
 

zaitcev

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Take a look at the landing gear in this picture. This is the airplane I saw in person and what my initial comments were based on. It NOT hinged. "Not" as in NOT. It it welded rigidly to the longerons.
LOL, of course it's not welded to the longerons, and it's actually pretty obvious at the picture. The langing legs are welded to a short piece of a thicker tube, which works as a slieve over the longeron. In fact anyone who's not invested heavily into the "welded to longerons" nonsense can see the dark lines where slieve ends. The metal of the slieve tube is also somewhat different color than the metal of the longeron, although not by much.
 

Jrees

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I have been, and still am, considering buying a BYF even after all of the negative comments posted here. I would really like to speak to someone that owns or has flown one. PM me if you would like, just to keep the negative comments down. I have several questions for the owner/flyer of a BYF. Thanks in advance.
 

zaitcev

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A legal ultralight crashing into the same house at it's normal cruising speed will most likely not hurt anybody in the house, will cause little property damage, and the pilot will most likely survive.
Sorry if this comes across as nit-picking, I'm afraid this is not quite true. While an ultralight is much, much safer to the people or property on the ground (just as you outlined), it is still plenty dangerous for the pilot. My local ultralight association lose about one member every 7 to 10 years just to stalling for no good reason and falling on the ground. A smack into a house at cruise speed is not going to be surivable. What really helps us is our low stall speed, which makes an off-airport landing more survivable despite comparative lack of structure. Also, our low speeds and weights make ballistic recovery chute feasible, which helps our odds. But you absolutely do not want to cruise into a house in an ultralight!
 

danmoser

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Sorry if this comes across as nit-picking, I'm afraid this is not quite true. While an ultralight is much, much safer to the people or property on the ground (just as you outlined), it is still plenty dangerous for the pilot. My local ultralight association lose about one member every 7 to 10 years just to stalling for no good reason and falling on the ground. A smack into a house at cruise speed is not going to be surivable. What really helps us is our low stall speed, which makes an off-airport landing more survivable despite comparative lack of structure. Also, our low speeds and weights make ballistic recovery chute feasible, which helps our odds. But you absolutely do not want to cruise into a house in an ultralight!
I agree that you can die in an ultralight crash .. but that wasn't really my point.
The context is that the FAA largely ignores ultralights because they present little risk to hurting people & damaging things on the ground.. not that they are inherently safe for the pilot.
As to stall-spin accidents, yes they happen and that is highly regrettable.. but also not my point.
I was comparing the kinetic energy (destructive potential) of an ultralight vs. a GA aircraft.. KE proportional to m*v^2 .. mass times velocity squared.. GA aircraft are obviously capable of inflicting much greater damage than an ultralight.

PS: I did witness a pilot crash his ultralight into the side of a metal hanger at ~30mph.. he had only cuts & bruises.. perhaps lucky it was a front-mounted engine .. good thing he wasn't flying a Cessna 172 ;)
 
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JohnG

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I do hold to the opinion that drilled & bolted joints are far better than welding, where aluminum tubing is used..
Experience would tell me otherwise.

I once modified a Spectrum Beaver 550 (originally a pusher) into a twin-engine push/pull. Had to do heaps of modification to move the landing gear for new CofG, support the new forward engine mount, and build in lots of pilot protection. Lots of MIG-welded aluminum, lots of it looking very coarse and rough, as basic MIG without pulse control gives. When trying to land on a country road I hooked the landing gear in a power line, and crashed very hard vertical nose down onto a paved road. Thanks to the built in pilot protection, and good 6-point seat belts I only got a broken ankle. The gearbox on the front engine was shattered into pieces by the impact, and the airframe was totally mangled.

NOT ONE of those welded joints broke, but EVERY bolted joint broke!
That welded aluminum saved my bacon....

Just my real life experience with MIG-welded aluminum....

JG
 

kennyrayandersen

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Experience would tell me otherwise.

I once modified a Spectrum Beaver 550 (originally a pusher) into a twin-engine push/pull. Had to do heaps of modification to move the landing gear for new CofG, support the new forward engine mount, and build in lots of pilot protection. Lots of MIG-welded aluminum, lots of it looking very coarse and rough, as basic MIG without pulse control gives. When trying to land on a country road I hooked the landing gear in a power line, and crashed very hard vertical nose down onto a paved road. Thanks to the built in pilot protection, and good 6-point seat belts I only got a broken ankle. The gearbox on the front engine was shattered into pieces by the impact, and the airframe was totally mangled.

NOT ONE of those welded joints broke, but EVERY bolted joint broke!
That welded aluminum saved my bacon....

Just my real life experience with MIG-welded aluminum....

JG
The example you have given is for a static failure whereas generally the problem with welding aluminum is that it causes hardening just outside the weld zone which causes a fatigue problem. So, it's not the static strength that is at issue here but rather fatigue; so, even if the welded joint is statically stronger it may have a short fatigue life.

Subsequently, there are only a couple of weldable aluminum alloy that are used. 6061 and 5052 can be welded, but neither are high-strength. Additionally, the heat treat is lost in the weld zone so you have to either re-heat-treat or live with the loss in properties. So generally we see very little welding in modern aircraft structure.

Also, if joint is well-designed it can be stronger than the bass material. Unfortunately, it is not the case that joints are well-designed or even analyzed.
 

BBerson

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Welding on 6061-T6 tube doesn't make it harder, it makes it softer, much softer. The weld zone will be somewhat stronger than annealed, but not very much. Probably 11-18k, or about half the original 35k.
The advantage of welding is no drilled holes.
A drilled tube tends to snap off at the drilled hole.
A welded tube will just bend (yield) more before it cracks.
 

kennyrayandersen

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Welding on 6061-T6 tube doesn't make it harder, it makes it softer, much softer. The weld zone will be somewhat stronger than annealed, but not very much. Probably 11-18k, or about half the original 35k.
The advantage of welding is no drilled holes.
A drilled tube tends to snap off at the drilled hole.
A welded tube will just bend (yield) more before it cracks.
Of course there are exceptions to the local hardening and 6061 [as well as 5052] is [are] one of them. Still, compared to most 'structural' aluminums 6061 is at the bottom of the heap. I think I saw it used one time many years ago, but we rarely use is in commercial, or military aircraft. I think it does show up in some home-built ultralights and whatnot, but it's about 1/2 the strength of 7000 series aluminums, and even when stuff is welded (mostly titanium) the processes are very tightly controlled and frankly these days when you consider labor, it's simply not cost-effective -- the same goes for bent parts! By the time you get the process, the inspections and the labor figured out, it's cheaper just to machine it out of a billet! A well-designed joint shouldn't snap off in the joint -- this would be an indication that it wasn't well-designed! A simple net-section check should tell you whether you have enough material in the joint, and a fastener shear check confirms that. Unfortunately, there is frequently not enough actual engineering that goes into some home-builts. Unfortunately, if the weld is not done just right, or there is a poor material choice, the welded part can easily crack in fatigue -- just like a poorly designed joint! Either CAN work, but either can have problems as well -- it has to be done right! Note: it's probably been 25+ years since I've seen anything welded on an aircraft that I worked on, and that was titanium!
 

Dana

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...compared to most 'structural' aluminums 6061 is at the bottom of the heap. I think I saw it used one time many years ago, but we rarely use is in commercial, or military aircraft. I think it does show up in some home-built ultralights and whatnot, but it's about 1/2 the strength of 7000 series aluminums...
A lot more than "some"... 6061 is still probably the most common aluminum alloy used for aircraft aluminm tube structures. Sheet structures can take advantage of 2024's higher strength (and corrosion resistance in the Alclad form), but for tube structures column buckling is usually the limiting factor. Since column buckling is a function of elastic modulus, not tensile strength, the higher strength alloys have no advantage there, so 6061's lower strength gives it the advantage.

The 7000 series alloys are much stronger, but are subject to stress corrosion cracking, making them unsuitable for riveted and other prestressed joints.

Dana

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Matt G.

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The 7000 series alloys are much stronger, but are subject to stress corrosion cracking, making them unsuitable for riveted and other prestressed joints.
I disagree, and so would Boeing and Airbus. Commercial airplanes are full of 7000 series alloy parts.
 

kennyrayandersen

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A lot more than "some"... 6061 is still probably the most common aluminum alloy used for aircraft aluminm tube structures. Sheet structures can take advantage of 2024's higher strength (and corrosion resistance in the Alclad form), but for tube structures column buckling is usually the limiting factor. Since column buckling is a function of elastic modulus, not tensile strength, the higher strength alloys have no advantage there, so 6061's lower strength gives it the advantage.

The 7000 series alloys are much stronger, but are subject to stress corrosion cracking, making them unsuitable for riveted and other prestressed joints.

Dana
I work mostly for the big companies, so I see very little tube, and none of it 6061 -- it's just not that good and would add too much weight, and weight is money. You need to get out a Mil-HDBK-XX and read some (replaces by MMPDS0X). Years ago (maybe 25+) some early 7075-T6 alloys had some corrosion issues, but even 7075 comes in alloys that don't have corrosion issues (I believe 7075-T76 is widely used at Boeing). 7050 is about as common an alloy as you can find on an airplane these days for machined parts (and there are very few bent parts on commercial aircraft being designed now), and AFAIK there are NO corrosion issues whatsoever. It's used in home-built aircraft as it is cheap.


I disagree, and so would Boeing and Airbus. Commercial airplanes are full of 7000 series alloy parts.
Exactly
 

Dana

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OK. The stress corrosion cracking issues I recall were on Navy ground support equipment about 30 years ago, so it's not surprising that the metallurgy has improved. Still, I haven't seen 7075 readily available in tubing form (can it even be extruded?). But as I said, when buckling (either column buckling or local crippling due to bending) is the primary failure mode, the higher strength gives no advantage, so even 2024 tubing (which is available, though not in as many sizes) isn't used as much as 6061, which is considerably less expensive.

Dana

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