6G Ultimate load test - Sort of an LE wing...

[Rodgerthefish]

Hi Everybody,

Apologies if I offend anyone by inadvertently saying the wrong thing or not following the forum etiquette; I haven't posted on a forum before.
1stly I would like to say thank you everyone for the inspiring pictures and words! It sure helps you psychologically when you can see what other people are doing and saying!

There's a bit of a back story to this whole load test thing. It's not a Legal Eagle wing any more for a few reasons, and I'm using a wood closer to Douglas fir than sitka spruce, but you might find my results interesting if not completely relevant.

I started building a pair of LE XL's with a friend. I'm based in Australia and here the rules are slightly different. You can't fly anything unregistered and the lightest, least GA category has an upper limit of 300kg all up weight (660 lb) so we probably have a little more leeway in terms of what we are constrained to than in the states. We do want to build a light aircraft but we won't cry if it goes over our goal weight either.

I really like the design of the LE, but one of the things we couldn't see was any evidence of doing a static load test. There was talk of a test to 4G but without seeing it, I wanted to make sure that the wing would support the weight I needed it to.
 
I figure I want to be able to do something by accident and not be killed by my escape manoeuvre, so a 4G limit would be handy. 
I know people have an awful lot of opinions about this but we have decided that sticking as close as possible to the FAR 23 standard makes sense. There is over 100 years of experience contained in those pages. A sensible safety margin of 1.5 has been drilled in to me from an early age, so if I want 4G I am going to have to make sure the structure stands up to 6. This safety margin is there to take care of unexpected gusts, bad glue joints or faults in the wood I haven't seen whilst building.

But then it's awfully confronting to risk that much work. so I spent the last year semi committed to doing a static load test but then thinking I would probably chicken out and just fly the thing. 

OK, so how is this wing different from a standard LE XL wing?

1. Australia is the back end of XXXX XXXX when it comes to getting aviation material. Sitka spruce is not grown here and getting it from the states or Canada is just remarkably expensive. You might pay $200 for wood and then pay $800 in shipping. 

We decided to use local Hoop pine. This is an indigenous wood approved in WW2 for aircraft. It's about the same weight as Douglas Fir but about 10% stronger than spruce - it's an acceptable if slightly heavier wood. The ply is also hoop pine ply. It's made to an Australian standard for marine ply, and though not as light as gaboon or mahogany, it's very tough. Glues used on the wings are mostly T-88 (though it's over 100$ A a pint here) and a locally made thing called Bote Cote. I've come to the conclusion that Bote Cote is probably a very good glue. It's also a thinner-free epoxy system. It's much cheaper but also a lot more runny. If you want to be assured that the glue is staying where it is, T-88 is slightly better, but if you want to seal something well, then Bote Cote is good. The Bote Cote guys do a super thick version called EPOX-E-GLUE and this I have found really good for where my wood working skills need to be disguised. It's very strong and fills gaps perfectly. All the sample glue joints I've broken have had a wood fracture. 

2. I used the original drawings for the ribs, as directed. Traced carefully onto a build table. Pretty soon (shut up Jim) I had the 52 ribs I needed and was feeling pretty pleased with myself. I'm fairly sure everyone reading this would know what that meant. When I made the spars to plan I got a nasty shock. I had spars that had large gaps between the top of the spar and the rib. So. What I did was I shamelessly stole a thicknesser, used T-88 to glue a 1/4 inch piece of Hoop to the top and the bottom of the spar to beef it up in each direction and then planed it down to fit the wing with the thicknesser. This meant that I also had the opportunity to plane the rear spar to be flush with the gaps in the rear rib cutouts. 

Now after all this we realised that we didn't really have LE wings any more. Adding material to the top and bottom of the spar might have been a silly idea if not glued perfectly as the first thing to go under load would be the thin material. And then there was the different wood - does it grow the same still? was I even getting real hoop pine? and I was also using a non aviation folklore glue. 

Oh and I wanted to see how flaperons worked. So I altered it with some of those too.

I really had to do that test.

So. This is not really a stock wing. One more thing. The strut attach and the wing attach straps are made of 4130. I just don't like aluminum where I'm not going to see it all the time.

So I've put the loading plan in, along with the result. 900kg (6G load) passed! If anything the load profile is a little conservative so I am quite happy it will take over 6G. No ominous creaks and groans and it stayed loaded up for a fair while as I contemplated the effort of carrying all those bricks again.

I am impressed with this wing. We thought we would have to break out the matches and have a bonfire but it's back hanging up in the garage again and I'm continuing to build the rest of it.

[Rodgerthefish]

Something I haven't mentioned - is a huge thanks to my friend who is doing this project with me who so far has lent me:

Time
Beer
Bricks
A Router
A router table
Welding services
A thicknesser
Band Saw
Glue
Steel
Bolts
Aluminum
Time
Space
Put up a new post and made the test rig

So far I'm just the glue covered idiot that can't read a plan

Thanks man!

[Tom XL-7]

Great report,  Keep them coming.
A question I had was how much do the wing panels weigh?
also interested in your flaperons,
When you get there shows us the operation.
Thanks, it's always great to hear new progress.
Tom XL-7

[Dave Stroud]

Very nice report on a very nice build, Roger. Thanks for that. Good common sense and resourcefulness. I've used Doug Fir while building up box spars for a Farichild 51 project a while back. Just a few questions and comments please. What size and material are your strut attach straps on the wing ? Same at the root end of each spar ?

I always find it interesting to look past the main subject in photos submitted and thus imagine more of the overall situation. So, in one pic I see a WW1 type fuselage and in the lower left of another pic I see what may be a Subaru engine. We'll need to hear about those when you have a chance.  :-)

[Tom H]

Great info.  Seems I saw a report on the original LEU wing being tested in the past, but not sure where.

What weight is the 6G based on?

[Rodgerthefish]

Tom H, the 6G was based on an all up weight of 300kg. It's the maximum for this class of aircraft here in Oz. 
I didn't take anything off for the wings, so this test is pessimistic.

All I did was take the weight (300kg) multiplied by 6 (1800kg) 
and assume the weight is distributed evenly between two wings (pin jointed structure - no spar carry through to consider)
So divide by 2 wings = 900kg (1980lbs)

It didn't really creak or groan or do anything strange and it reverted to it's original shape as it was uloaded. 

By the way, total deflection at the tip was 5cm (under 2 inches), and slightly less than an inch mid way between the root and the strut. 

The loading assumed a high angle of attack so 1/2 the weight centred in the 1st 1/4 chord and the other half centred in the last 3/4 chord.

Something I didn't do was do a tilted wing test. 
Mainly because it's very difficult to do without introducing an unrealistic twist with the rig we were able to make.
The weight is distributed correctly (as far as I can tell), but it doesn't really represent the anti drag loading that will occur. 
There is a large component of the lift force that acts forwards, and the diagonals on this wing design are configured to counter drag (backwards).

What I think I might do is apply gussets to the bottom of the diagonals to give me another shear connection between the diagionals and the spars.
I don't really like relying on epoxy in tension.

Dave Stroud, the straps are all 100 thou 4130, same dimensions otherwise as the plans. 

The test was conducted at my friend's house he put in another post in his shed and welded up the test struts - it's his Graham Lee N11 you see in the background - I'm looking forward to seeing that fly soon too!

The engine is a subaru but it's also not mine

Tom XL, the Flaperons I will try and take pics of / describe. They are a total experiment and entirely my fault. 
I'm embarrassed to say I haven't weighed the wings. I will post the weight when I've found some scales. I was going to put fuel tanks in and then weigh them.
Not much though.

Thanks for the feedback, all comments welcome! 
I'm just working this all out as I go and I would rather someone point out any flaws on the ground before I discover them in the air!

[Dan_]

Rodger,

Have you seen this on loading schedule..?  Schrenk approximation.pdf

Were the ailerons free to move..?

Thanks for sharing your work.  

[Rodgerthefish]

Hi Dan, 

I used that document and others to validate and calculate my span-wise-loading plan.
When I say I had a more harsh loading plan, that's what I am comparing to.

The ailerons were free to move and tested throughout - they maintained full free movement (which was actually a surprise to me - I had backup plans for them)

Thanks!

[macca]

Great to see that test mate Ive sent you a message Im Macca from the hunter valley NSW welcome to the forum

[MrG]

MR Fish
nothing personal but ive built two planes here in australia and been involved with 23 others at least 5 first of type at this airport 

you can buy what you want, may not be here in the country,  but get it just as quick as local, i ordered spruce from AC Spruce and was at my house with in 7 days, 
 Quicker than Australia post and im in the bush. we have over 30 planes at this airport that have been home built.
 
Now we have had experimental in for some 12 years and you can build what you want - technically there is no weight class, RAA has - but GA sort of don't, and you can build a plane from scratch with one inspection at the end and fly it. 

its a great place to build a plan  (no ill get off the horse)

[Rodgerthefish]

Hello Mr G!

Hey I am certainly not slanging the ability to get things quick from the states, it's actually obscene how fast things arrive compared to 100km away in Oz.

But... if you've found a way to get things cheaply I really want to know about it!

I know there's no real restrictions with GA flying but this thing is going to be RAAUS registered. I would like to build a primary glider next but that's a while down the track given current progress

how did you find the quality of the spruce you ordered? Was it all good? I've had to do a number of scarf joints on this hoop and have had to reject a bit.

Gads that's a point.

All my spar webs are cut 45degrees to the grain and scarf jointed to get the highest strength, I'm not sure I mentioned that in the original post.

I would love to see your DE, how long have you had it?

[ParQld]

Sent you a PM Mr Fish !

cheers Paul

[MrG]

Hey Mr Fish
i have nearly 70 hrs up on my DE and im at Temora Airport NSW - Always welcome we have some great airshows here with the Aviation Museum
I was extremely happy with the spruce form AC Spruce, would buy from them again - as you useing hoop i guess you in Qld?
RAA reg is just as easy as experimental and Darren is the one to talk to there and is good,  now we have one flying makes it easy for the next one
happy to show you my paperwork to make it easier when you get that far 
I know there is a cut of with old rules to new you need to talk to him asap, ok to say you were talk to me, there is one in Melb not far of flying  (LE)
As for getting things cheaply - my job did get me some good deals at the time i bought some of my stuff as i was working for Performance Metals

[Rodgerthefish]

Hi MrG,

Apologies for the delay replying, I've been having computeriser issues. Yep I'm up in Brisbane  
RAA is probably the way I shall go, thanks for the offer of seeing the paperwork! I reckon I'll need to lean on you for advice as I get closer to finishing this thing!

R

[Flyguyeddy]

Can we get some pictures of the ends of the ailerons?