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vgstol(at)bigpond.net.au
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 Posted: Wed Mar 03, 2010 11:55 pm Post subject: Substituting 020 for 016 |
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Increasing the skin thickness by 25% does not increase the strength of an aircraft like the 701 by 25%, it's just dead weight. Many years ago I knew a 701 built with .020, along with a few other 'strengthening' mods considered essential by the amateur builder, and a heavy Subaru engine. The flying performance was a complete disappointment to the builder - it was the classic 'lead sled' just as Bolding predicts....
That short 701 wing was originally designed for a much lighter 701, with a 2-stroke engine. Since then it's gained a lot of weight, with no more wing. [b]Beware of adding any more weight at all to this aircraft.......
[/b]
I have experience in rebuilding three very bent 701's that had come to grief on perilous short strips. In no instance would .020 been an advantage to the result. The wings and fuselage on the 701 are excellent at crumpling in just the right places to absorb the impact energy, and so protect the occupants and the rest of the aircraft from damage.
The oil canning issue is easily fixed. Just add .016 angle in the rear fuselage, and intermediate foam ribs in the wings. Both stuck in with Sikkaflex or similar polyurethane adhesive. Using the adhesive instead of rivets is easier, and leaves a more fair surface. This adhesive needs to have a thick bead to cure properly, so cut the ribs 2-3mm smaller. When the wing is ready to close, put a good bead of adhesive on the underside of the foam ribs and set them in place and let the adhesive cure. Check with a straight edge to see that the upper edges of the foam ribs are just below the aluminum ribs. Then put a thick bead of adhesive on the top edges, and rivet the top skins in place. The adhesive will take up any gap and adapt to the contour of the skin. When it's cured it will hold the skin in place even better than rivets. Using 10mm (3/8") close-cell polyurethane foam (same as used by the fiberglass industry), the weight is probably only 1 lb for the whole aircraft, and very effective.
Once again - If you want good STOL performance, beware of adding any extra weight to the 701........
JG
On Thu, Mar 4, 2010 at 2:36 PM, Joe Spencer <jpspencer(at)cableone.net (jpspencer(at)cableone.net)> wrote:
[quote] I did not use a 1 X 4 which is a great idea but did find near the end of
| Quote: | the building process that rolling up the .016 skin each time it was
taken off the aircraft made the process go a lot easier. After rolling
it up I used bungee cords to keep it rolled up. The result was no more
smilies and a lot fewer bad words.
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| Quote: | I like your reported 579# and 97 mph cruise with VG's. My estimate for
N701VG on weight and cruise is about the same with the VG's.
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Right, Stan...there must be all sorts of ways to handle the 016 skins w/o damage besides resorting to 020.
Further thoughts on the thicker skins solution suggested by some here...the reference to the 020 on the 750 probably is probably hardly relevant to the 701; that's a larger plane with higher gross weight. Zenith I feel sure went to the thicker skins because of a load requirement which doesn't apply to our smaller, lighter plane. Some mentioned the 020 would make it stronger...we already have a +4G/+6G (yield) design; why would we possibly need more strength...we're mostly just a bunch of old farts motoring around and landing in cow pastures and beaches and such. If we were in a fast mover trying to dodge SAMs over Hanoi or Bagdad or somewhere well maybe yeah...Zenith has already designed the thing for our typical mission; why add needless weight? I work my butt off trying to save a pound or two here and there. To add 30 needless pounds is unthinkable to me. I realize that to some the building process is more important than the finished product; me, I want a light good perfor!
ming machine and realize that minimum weight and least drag are all important...Bolding and JG got it right
Best
Joe
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rockiedog2
Joined: 03 Mar 2010
Posts: 19
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| Posted: Thu Mar 04, 2010 3:40 am Post subject: Substituting 020 for 016 |
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hmmm...
Sorry for the double post; the list sent my reply back as rejected/returned mail so I sent it again. Now I see it decided to post both. Technology. Or maybe pilot error? Admin please delete one.
Thanks
Joe
[quote][b]
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stepinwolf
Joined: 21 Jan 2008
Posts: 133
Location: Canada
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| Posted: Thu Mar 04, 2010 5:38 am Post subject: Substituting 020 for 016 |
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Joe, Stan, JG, and others,
I think it might be time to bring this thread to an end, since we have reached the point where it sounds like we are just beating a dead horse. As I previously mentioned, we all know that when it's comes to aircraft " light is right ", however, when I first responded to the original post, I gave my personal opinion ( "hello" if memory serves me correctly, this still is an experimental ) and not the road, or the option, that everyone should choose.
Personally I live in the boondock's, and I could not have purchased any 6061 T6 in .016 if my life had depended on it, since none of it is available locally, and on disability, there was no way I could afford to have it shipped to me from afar. Secondly since I have slightly increased the wingspan, my 701 actually has a lower wing loading then most of you, and lastly, I did not paint the airplane, so I got my 30 lbs back.
I completely understand, and appreciate the fact that most of you have chosen to follow the building instructions to the letter, and for that I commend you, ( we will not address those who have chosen to remove the slats and use VG's ) but by the same token, that same consideration should be given to those who have deviated from the normal building procedure.
Fly safe fellows,,,
Robert
The 701 & 750 scratch
[quote] ---
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_________________
Long wing + vga's, = lo & slo
Last edited by stepinwolf on Thu Mar 04, 2010 6:45 am; edited 1 time in total |
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John Bolding
Joined: 23 May 2006
Posts: 281
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| Posted: Thu Mar 04, 2010 6:42 am Post subject: Substituting 020 for 016 |
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Robert,
You are ABSOLUTELY correct that this is "experimental" aircraft and we have a lot of latitude to change as we see fit.
You are certainly free to do as you wish, I'm just trying to point out the downsides of your approach to those that might not know how muddy the swamp is.
I also gave my thoughts on weight because I've witnessed a BUNCH of builders that put in thousands of hours building a beautiful airplane but it was waaay overweight and the builder was disappointed in the flying qualities. As Spencer says you might be looking for something that looks good in the hangar and not care if it is a pig to fly, your choice.
I remember a Spezio TwoHoler that became a OneHoler because of the weight. Couldn't even take his 110# wife.
Award winning aircraft but it was a DOG in the air.
When I was building my Glasair I was putting in a Ford V6 with Blanton redrive, Jeff Ackland (of Turbine Legend fame) was doing the same combo, (Jeff works a LOT faster than I do) he called one Sat. morning after test flights and yelled "STOP THE PRESSES" the extra weight of the Ford KILLED the performance of the Glasair. He installed an 0-360, I put in an 0-320. He saved me a yr of work .
Going the other way I know a guy that had a good flying Teenie Two with 1600cc VW, he took out the VW and put in a 084 4 cyl.generator engine, 35# lighter but only 3/4 the HP. Guess what, performance stayed the SAME except for fuel burn which was 20% less.
As far as ending the thread I don't think so, I have not run into many newbies that do much homework before asking questions, hence in the next few days we'll have a couple of new guys ask about slats Vs VG's.
We'll go thru this again I'm sure.
LO&SLO John
[quote] ---
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river1
Joined: 07 Sep 2007
Posts: 28
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| Posted: Fri Mar 05, 2010 8:56 am Post subject: Re: Substituting 020 for 016 |
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"That short 701 wing was originally designed for a much lighter 701, with a 2-stroke engine".
Amen!
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mcjon77
Joined: 17 May 2008
Posts: 55
Location: Chicago
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| Posted: Tue Mar 09, 2010 12:37 am Post subject: Re: Substituting 020 for 016 |
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Great info, as always guys. Thanks a lot.
It seems that the number one issue in favor of such a mod is ease of handling during construction, and the number one detriment is obviously the 30lbs+ of additional weight.
I brought this up after seeing some 701 wings with waves/wrinkles in them. An example can be seen in this pic on the Zenithair website.
http://zenithair.com/stolch701/pic2000/e-soule6.jpg
I know the 701 is structurally sound. It has proved that all over the world. I just hat the looks of those wrinkles (I have heard that the factory demo plane has the same wrinkles, but can't confirm it).
Have current/former owners noticed these types of waves/wrinkles in their wings? Would the false ribs eliminate the wrinkles seen here?
Thanks again.
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Jon McDonald
Building Sonex #1287
Next up CH 701  |
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vgstol(at)bigpond.net.au
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| Posted: Tue Mar 09, 2010 1:59 am Post subject: Substituting 020 for 016 |
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Yes, those waves/wrinkles can be easily and effectively eliminated, with very little weight penalty.
Intermediate foam ribs, stuck in with Sikkaflex or similar polyurethane adhesive. This adhesive needs a thick bead to cure properly, and then it's still slightly flexible and pretty much indestructible. So cut the ribs 2-3mm inside the profile of the aluminum ones. Also cut a couple of holes in the foam ribs to allow air circulation. The foam is the closed-cell polyurethane foam used by fibreglassers, 10mm (3/8") thick. When the wing is ready to close, and the the skin remains fair when the pinned down with clecos, open the top skin, and stick the intermediate foam ribs onto the bottom skin with a thick bead of adhesive. Check with a straight edge to see that all foam ribs are 2-3mm below the Al ribs. Place a tick bead of adhesive on the top surface of the foam ribs, and rivet down the top skin. The adhesive bead will adjust to any variations to keep from stressing the skin, then remain exactly in that position when the adhesive is cured. The foam ribs are plenty strong enough to hold the thin skin in place, and prevent waves and oil-canning. If you want a really 'solid' feeling wing, then place two intermediates. It all adds up to only 1-2 lbs extra weight, for a really effective solution, and a very satisfying result. Tried and proven several times, with excellent results.
JG
On Tue, Mar 9, 2010 at 6:37 PM, mcjon77 <mcjon77(at)yahoo.com (mcjon77(at)yahoo.com)> wrote:
[quote] --> Zenith701801-List message posted by: "mcjon77" <mcjon77(at)yahoo.com (mcjon77(at)yahoo.com)>
Great info, as always guys. Thanks a lot.
It seems that the number one issue in favor of such a mod is ease of handling during construction, and the number one detriment is obviously the 30lbs+ of additional weight.
I brought this up after seeing some 701 wings with waves/wrinkles in them. An example can be seen in this pic on the Zenithair website.
I know the 701 is structurally sound. It has proved that all over the world. I just hat the looks of those wrinkles (I have heard that the factory demo plane has the same wrinkles, but can't confirm it).
Have current/former owners noticed these types of waves/wrinkles in their wings? Would the false ribs eliminate the wrinkles seen here?
Thanks again.
--------
Jon McDonald
Building Sonex #1287
Next up CH 701
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=289755#289755
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mcjon77
Joined: 17 May 2008
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