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Author Topic: Zweibox HLG  (Read 1293 times)
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dosco
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« Reply #25 on: September 01, 2020, 04:25:53 PM »

It flies!!

Decided to play hooky for an hour this afternoon ... the day started drearily but at 2:30PM or so the sun peeked out and the ground was reasonably dry.

At the local soccer pitch, a few hand tosses and it looked OK for a higher powered launch. I went with maybe a 50% launch and on several tries (maybe 5) it just would not "get over the top" and would stall and zoom to the ground. On the upside, the dirt was moist so it just lawn darted. I decided to go for it and really heaved the hell out of it. Success! Pic attached is on flight #2. On flight #3 I hooked a small thermal and I was convinced it would fly away. It landed just shy of a tree and I was able to continue the fun. She is sensitive to launch conditions, if she's off kilter by a little she will veer steeply to the right and not really gain any altitude. If I launch it basically straight ahead and up, she climbs gracefully and "flips" at the top to a nice glide. She circles to the left, as designed, in about 50 foot circles.

Sweet!

-Dave

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dosco
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« Reply #26 on: September 01, 2020, 05:32:26 PM »

Here's a cropped shot, for fun!

-Dave
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philly
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« Reply #27 on: November 21, 2020, 03:24:02 PM »

Disgusted. New to forum and just made a long post. Gone. Into the ether, shudda put a DT on it?
Short this time case I loose it again!
Foam wing Zweibox.
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Jez Wilkins
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« Reply #28 on: November 21, 2020, 10:06:15 PM »

Disgusted. New to forum and just made a long post. Gone. Into the ether, shudda put a DT on it?
Short this time case I lose it again!

Hi philly.  Don't you just love it when that happens Roll Eyes Grin.  Did you log in 'forever', or for just for a limited time?  If it was the latter, then the site may have 'logged you off', before you hit the 'Post' button.  Hitting the 'Preview' button occasionally sometimes helps. The best thing though, if you know at the start that you are going to do a long post, is to draft it 'off site', using your favo(u)rite word processing software and then 'copy' and 'paste' it onto the site.  Wiser to use 'copy' than 'cut' as your original text is still there, if you have problems. Grin


Cheers,

Jez Wilkins    

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dosco
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« Reply #29 on: November 22, 2020, 12:51:00 PM »

Philly:
Very nice. How does she fly?

Did you apply any sort of finish to the foam?

Cheers-
Dave
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philly
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« Reply #30 on: November 22, 2020, 05:30:20 PM »

No finish on the balsa or foam. Was concerned foam may not have the strength for a catapult launch but so far so good.
I am pretty new to this, this is my 3rd glider. I was blown away how she flys! Maiden flight, a little too windy and not sure what its gonna do, so crouched down and gave the LIGHTEST toss into the wind from~3 foot height. Flew nearly across the yard! Could see it getting little whiffs of lift keeping it going. Think it will thermal over a mouse fart.  Have a notch under the nose to catapult launch it, tried that today. Discovered if I launch flat/level it flys amazing. Several 360's before landing from a 20 foot(?) pattern. Great flight times but little launch height this way though. Experimenting with higher launch angles though...not so good. Played with CG, nada. Stalls and comes down like a lawn dart no matter where I set it.. Much more experimenting and I find if I launch maybe 40 degrees up and with a LEFT bank put into it, getting some good launches now.Suspect flying better with this technique only because its not stalling at the top. That being said, when it is gliding I can see the longitudinal pitch stability is spot on. Nose gets knocked down by a gust and it responds with a pitch up and right back to a stable glide. I've see the opposite too. Nose gets pitched up and it noses down into a beautiful glide. Dihedral gives it great stability too, yeah, it was a little windy today. Not sure what to make of the un recoverable stall I was seeing with high launch angles? My other two gliders like a steep launch and 45-90 degrees of right roll at launch. Somebody gotta be an oddball I guess.
I had been thinking of building this glider someday. This post/thread inspired me to get-er done, and join Hippockets to let you know how she flies for me. Thank you Dosco.
« Last Edit: November 22, 2020, 06:29:38 PM by philly » Logged
dosco
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« Reply #31 on: November 22, 2020, 08:12:07 PM »

philly:
Wow. I'm glad my build helped you decide to build one.

I will say the as-designed CG is too nose-forward for calm air, so for windy air it should be (I think) OK (hard to say because I removed about 2/3s of the called for noseweight). It's designed for a right-left pattern, so she should be banked to the right when you launch. Also, I did notice she was heavy enough that she really needed a strong heave to "get over the top." Finally, she does need a touch of "up elevator." Assuming you have the warp in the left wing, stab tilt, etc., she should "flip" at the top and transition from launch to glide.

The last time I flew her was about 3 weeks ago on a visit to a close friend in Upstate NY. It was pretty windy and nasty ... with the previous CG and adjustments she wasn't consistent. About half of the launches ended with a rapid return to earth. The other half would result in a suitable glide, and I did hook a small thermal that caused her to traverse the field to the tune of ~200 yards.

Keep at it!

(post some flight pics?)

Cheers-
Dave

P.S. ... I just unpacked a few things from my storage unit (moved recently) and parts for Zweibox #2 are now in my house. Need to get her together soon!

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philly
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« Reply #32 on: November 23, 2020, 05:15:37 PM »

It's designed for a right-left pattern, so she should be banked to the right when you launch.

        I was thinking about that last night. As is it must be wanting to launch left. Next outing I should try to make it launch right. Is that a rudder tweak?
Maybe not as the rudder has a airfoil shape to push nose left....for the left glide?

Also, I did notice she was heavy enough that she really needed a strong heave to "get over the top." Assuming you have the warp in the left wing, stab tilt, etc., she should "flip" at the top and transition from launch to glide.

         I have no warp in the left wing. I do not see it on the plans. Buried in the article text perhaps? Do have the stab tilt. What exactly is the "flip" at top? Goes from a steep right bank, to a steep left bank?
                 "getting over the top", was thinking about that too. I was just using your typical home/office type rubber band for launch and was wondering if a stronger rubber might be a benefit. Selected some new ones from Office Depot today to play with before making any changes. But...does it not transition when the airspeed declines to some point? And wont it transition from a hard launch or soft launch at that same speed regardless?
                  Will try to get a pic or viseo.
       



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philly
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« Reply #33 on: November 23, 2020, 06:41:19 PM »

Well after poking and searching around a bit for trimming instructions said to myself, hey, wasnt there trim advice in the Zweibox thread? Lets go back  and re read from post one. Phil ur a genius LOL
Answered most of my questions regarding trimming but if you have any comments regarding "the flip" or "getting over the top" that I had inquired about that would be cool.
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dosco
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« Reply #34 on: November 23, 2020, 07:29:24 PM »

Well after poking and searching around a bit for trimming instructions said to myself, hey, wasnt there trim advice in the Zweibox thread? Lets go back  and re read from post one. Phil ur a genius LOL
Answered most of my questions regarding trimming but if you have any comments regarding "the flip" or "getting over the top" that I had inquired about that would be cool.

The flip at the top ... I think someone posted a video link, I'll have to look. It's hard to describe, other than to say it will be almost upside down at the top, then she should roll to wings level. It's actually amazing to watch if you've never seen it before (hell, it amazes me every time I see it, because I can't believe that it just "does it").

"Over the top" ... it has enough energy to transition from launch to glide without stalling. I was giving her 1/2 and 3/4 power launches, worried that a full-powered throw would end badly. Instead, the half power throw caused her to go up, tailslide, stall, and nose in. After several of those, I just threw her as hard as I could, which worked perfectly.

-Dave

PS: Did you find the piece about the washin warp on the left wing? It's in the article.

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OZPAF
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« Reply #35 on: November 24, 2020, 02:56:21 AM »

Re the transition from the climb to the glide - here is a classical "S" style transition.

If you watch this launch video at 1/4 speed, you can see the model slowly rolling left out of the right banked launch till the wings are level when the glider slows to its gliding speed at the top of the climb.

https://www.youtube.com/watch?v=NjQezD1iDsw

The timing of the roll is established for a given launch stretch, launch angle and bank. I regard changing the launch and bank angles as the final stages of trim - useful for say an increase in launch tension.

John
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philly
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« Reply #36 on: November 24, 2020, 05:15:12 PM »

Since I can get a fair ( but not great) flight by doing a left launch, and I'm right handed so you know what that like, I thought to myself, how can I get a right launch? I thought there might be too much left turning from the fin. Cut off the airfoil shaped fin and replaced with a "flat" fin. Still have a bit of left rudder due to the tapered fuselage side. As much as I wanted to test today it was gusting to 20mph.  About sunset it settled down some.  I've lost the nice left circling glide so I'll be putting on an air foiled fin tonight.
But it raises a question in my mind. If the rudder is more effective at high speeds, does it not make the plane turn left at launch when we want right?
Yes but the right roll I put in at lunch counters it?
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dosco
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« Reply #37 on: November 24, 2020, 06:06:25 PM »

Since I can get a fair ( but not great) flight by doing a left launch, and I'm right handed so you know what that like, I thought to myself, how can I get a right launch? I thought there might be too much left turning from the fin. Cut off the airfoil shaped fin and replaced with a "flat" fin. Still have a bit of left rudder due to the tapered fuselage side. As much as I wanted to test today it was gusting to 20mph.  About sunset it settled down some.  I've lost the nice left circling glide so I'll be putting on an air foiled fin tonight.
But it raises a question in my mind. If the rudder is more effective at high speeds, does it not make the plane turn left at launch when we want right?
Yes but the right roll I put in at lunch counters it?


Philly:
The Zweibox is "cross controlled" which means it has left rudder (airfoil + glued to tapered side), stab tilt (for left turn in the glide), and right roll (from the washin on the left wing). It's supposed to be launched with a right roll, which will then transition into a left circling turn.

The purpose of the cross-control setup is to have a stable left hand turn without getting into the unstable part of the yaw-roll couple (which would result in a spiral death dive).

The dihedral plays into this as well.

So ... throw her hard and to the right. It takes some practice, and I've noticed she's sensitive to the launch conditions. There is "not enough" and "too much" ... you'll know when you get to "just right."

Oh ... keep the airfoiled fin, but maybe glue it to the not-tapered side of the fuselage stick. I think the taper and airfoil might be too much (although you could probably compensate with more left wing washin).

-Dave
« Last Edit: November 24, 2020, 06:21:19 PM by dosco » Logged
OZPAF
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« Reply #38 on: November 24, 2020, 07:09:53 PM »

Quote
But it raises a question in my mind. If the rudder is more effective at high speeds, does it not make the plane turn left at launch when we want right?
Yes but the right roll I put in at lunch counters it?

Yes the rudder is more effective at high speeds as are all the surface deflections, gurney strips etc. To achieve a reliable launch and transition the rudder induced left turn is balanced against the launch bank angle. As Dosco has mentioned - this is cross trimming - the basis of most FF trimming. How much rudder is required depends on high fast - ie hard, the glider is launched. The faster it is launched - the less that will be needed with the right bank angle varying to match the effect of the rudder. The aim is to have the right rudder only just enough to roll the glider to the left by the time it has slowed to it's gliding speed.

If the glide turn is too wide - the rudder should not be used to increase the turn as this upsets the balance on the climb - where the extra rudder deflection is not needed. Trim the glide circle with either tail tilt - add more if necessary or add some tip weight on the left wing tip. These adjustments do not have much effect on the climb but do on the glide.

It is best to trim the climb first after you have a safe glide - then fine tune the glide - without changing the climb settings.

Have you added the "wash in" on the left wing? Apart from providing spin in protection on the glide - it helps the balance on the climb - slowing the roll to the left. You shouldn't have needed to change the plan rudder setting. Also check the wing dihedral - if it is more than on the plan - it could be making your rudder too powerful.

Anyway good luck.

John


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philly
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« Reply #39 on: November 24, 2020, 07:33:26 PM »

Oz,Dosco, thanks for reply's. I have been thinking obsessively on my question and I think I understand it now. Without going into a long message as to why, I actually think I am not getting enough left turn from the rudder. Forecast/guess is for light winds tomorrow. Will report on my success, or lack of tomorrow.
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philly
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« Reply #40 on: November 26, 2020, 01:56:08 PM »

Fail. Last post mentioned I feel Im not getting enough left rudder? Why was I thinking that? Biggest complaint is I can not get it to climb right.
No, I do not have any washin in the left panel and that is likely the problem. The foam wing is too springy. Give it a little bend and it goes back to its original position. Experimented by taping on a aileron in the down position to left wing. Somewhat better? Little more down and - ooo, look at the neat 360 roll. Take some out.  Can not maintain precision adjustments with the jurry rigged set up I had. Next thing I know its gliding to fast and would not slow down. Give it some up elevator and now stalls at slow speed glide. Chasing my tail.

Used a 7 X 1/8 rubber band and seemed pretty energetic. Maybe a little weak? Tried two 7X1/8 and now must have enough energy to get over the top? But sometimes it does stall at the top before transitioning to a glide. Could that be a tuning adjustment? Launch technique? Or do I need more power?All the above?
What size band are you guys finding effective?
Did get some video and will see if I can get it posted. Ever notice the best flights are when the camera is not running?
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philly
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« Reply #41 on: November 26, 2020, 02:28:20 PM »

https://vimeo.com/484176869
The good,bad, and the ugly
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OZPAF
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« Reply #42 on: November 26, 2020, 06:45:46 PM »

Nice glide Phil and I think the glide circle is good, you have the basis of a good glider there.

Definitely needs more power on the launch - it is running out of steam too early. That looks like 20-30' on your right banked launches?  I would be aiming for around 60' at least. I use a 9' approx. loop of old 1/4 FAI rubber. I would recommend you use the standard AMA catapult rubber spec as attached.

Also it should definitely have wash in on the left wing as otherwise as you have found the rudder as you have found is too sensitive - cross controlling gives you a chance to balance the rudder and enables fine adjustment.

I think your best approach here is to use a wash in wedge as shown on the attachment - however you will be using it on the left wing about 2/3 of the semi span. The gliders shown use a different climb/glide trim - the exact opposite of yours actually.

Also I would check that the wing/tail bottom surfaces are parallel to each other - ie you have a 0 - 0 degrees incidence difference between them, and that as per plan the CG is close to 60% of the root chord.

You may have to retrim the elevator after you add the wash in wedge - by adding a bit more down elevator. It is best to try and keep the CG where shown on the plan to help the climb.

Good luck.

John


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dosco
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« Reply #43 on: November 28, 2020, 09:57:01 AM »

Phil:
Thanks for posting that.

Agree with John on needing more "oomph" on the launch ... that's what I meant when I said "enough energy to get over the top." Several of your launches didn't have enough energy to "get over the top" and she stalled. You really need to crank her hard.

You also need to launch her "to the right" a bit more. Most of the launches look like "wings level" and really when you let her go she should be banked to the right (as she climbes she will roll out to the left).

Hopefully you're considering installing a wedge on the left wing?

I love how the design looks while flying along. So graceful.

-Dave
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philly
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« Reply #44 on: November 28, 2020, 04:16:30 PM »

Yes they were weak launches. Was holding a single 1/8" rubber band between thumb and forefinger (no stick), band wrapping up over top of camera(you see it in a couple shots),glider in right hand. Very difficult and could not draw back to full power. Other flights with camera off were with two 7X1/8 rubber bands. Better that way but might need more power still. I cant see ordering a 1/4 lb of FAI rubber when I only need one piece...but it might come down to that.
Yes they were wing level launches. As I said before it wont fly/climb to the right. Ends quite baldly. Will only get a decent flight with wings level launch, or a left bank. 40 degrees elevation max.
Got the wash-in wedge installed per the formula Dosco posted. Have some extra made up to add if it needs more.
Anxious to try it out today even though I knew it was too windy. Somewhat better. Looks promising with more tweaking and less wind. Called it quits before breaking or loosing it.
Currently I can give it a bunch-o-right bank at release and a steep launch angle (45 deg + ). Quickly rolls wings level in climb for a straight out departure, then goes into the left glide. No climbing right turn, but getting better height. Its a start.
Gonna try some up elevator and/or some more left wing wash-in.
Confirmed dihedral, declage, balance laterally. CG at 60%.
I made a repair to the tail and the weight is coming on shockingly fast! Extra tail weight plus added lead up front. Now at 1 ounce flying weight. Grrr.
What are your Zweiboxes weighing?

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« Reply #45 on: November 28, 2020, 05:26:25 PM »

Thanks for the report

I would suggest lengthening the wash in wedge a small amount before touching the elevator. The wash in is also increasing the decalage so may need an adjustment to the CG.

I did some early flying on my CLG's with a catapult using 3 rubber bands(about 3" long x 1/4" wide) daisy chained together and that worked ok for a start. The model aircraft rubber is much better though.

Your rudder seems very powerful and if you are able to warp the top(only about 1/4") a small amount to the right - it will help to maintain the right bank in the climb longer and give you better height.

However the climb trim will become dependent on the launch power - so I think you should make a AMA style or similar catapult, first.

Good luck.

John
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dosco
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« Reply #46 on: November 28, 2020, 06:23:30 PM »

Phil:
I had posted in one of the very early posts, she was weighing in at 37g with the "per plan" noseweight (most of which I removed). Oddly, the repairs probably removed mass (a chunk came out of the wing root, I sanded off most of the paint on the wing, I sanded the aft portion of the wing to thin it down, and I sanded the elevator to thin it out ... ... ) ... so let's be generous and assume she's weighing in at 35g ... or 1.3oz.

Ugh. I just took a look at the article, Oldenkamp's apparent "average weight" was 22g. I don't think I'll ever hit that, ever. Damn. (with that said, I *am* having a lot of fun with mine, so I'm not all that worried ... plus it's really about picking good air and launching into it ...)

If you're at 1 oz, your Zweibox is certainly lighter than mine.

I wouldn't worry, the design is good. Mine flies well, she has certainly snagged some small bubbles of lift, so I've no worries that she's too heavy. Yet.

Once you get her sorted, she'll hook a thermal and bid you farewell(!).

Not sure if you read my Lunchbox thread, but I lost one about a month ago in a big thermal. I can envision the same for the Zweibox.

Cheers-
Dave
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« Reply #47 on: November 29, 2020, 05:25:22 PM »

Ozpaf, good point regarding getting some proper rubber and handle before getting too carried away trimming. I took another look at the FAI website for rubber and I don't have to buy a 1/4 lb, they have a 16 ft (?) package for $2.50. Went to check out and was shocked to see 10 plus dollars for priority shipping! Didn't order. Sent an email asking about cheaper shipping options.
Dosco, I think 22 grams average weight was for his 16" models so that gives us a little.
The Zweibox article in regards to fuselage stock selection says" moderate springiness and harness", or something like that.
In balsa speak mod hard, and hard, relate to weight and not literally hard right?
I have a piece to make a new fuselage but it is 6 lb balsa. Would love to use it but would it be too weak?
Yes, new fuselage.  Added some more wedge to the left wing and anxious to try it out.  Wing broke on first launch. Unknown if it failed due to acceleration at launch, or from nosing in. The foam wing was an experiment to save weight and actually was holding up very well. Had I got this flying better, sooner, it would  not have experienced as much trauma and been a good idea.
Zweibox Rev-B will be foam with one layer 3/4 glass cloth.
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« Reply #48 on: November 29, 2020, 06:21:42 PM »

Quote
In balsa speak mod hard, and hard, relate to weight and not literally hard right?
That's right. It's a sample of nontechnical modeller's jargon Smiley Like semi semi symmetrical airfoils for example Smiley

I wouldn't use the 6lb for a fuselage - I doubt whether it will be strong enough. The "springiness" that Oldenkamp refers to is more a  property of the grain of the balsa. So my interpretation of his balsa fuselage spec would be 9-10lb balsa with nice long grain - ie "A" cut balsa.

Actually I use a spruce/balsa fuselage - mainly spruce with a balsa wing seat. On my 12" gliders it is only 1/8 spruce and balsa and I have only broken the wing off the wing seat and cannot remember ever breaking the spruce!

These 12" versions weigh around 8-9gms ready to fly and I use the same fuselage construction on my 18" version and only modify it slightly for my 22" version.

John
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« Reply #49 on: November 29, 2020, 07:44:33 PM »

I wouldn't use the 6lb for a fuselage - I doubt whether it will be strong enough. The "springiness" that Oldenkamp refers to is more a  property of the grain of the balsa. So my interpretation of his balsa fuselage spec would be 9-10lb balsa with nice long grain - ie "A" cut balsa.


John:
I was fairly happy that on this build I'd used "the correct balsa." Am questioning that now, haha.

The fuse on mine is made of "C" grain ... I have a nice sheet and I put a bright light against it and used the darker stuff. Thus far it has survived numerous nose-in impacts that have destroyed other HLGs I've built.

Phil:
Sorry to hear your wing failed.

Maybe you should try some paper with white glue. There are some threads along those lines "Mambo in Foam" is one that I posted on recently, about foam and paper.

-Dave


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