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Author Topic: Zweibox HLG  (Read 1942 times)
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dosco
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« on: July 21, 2020, 05:05:39 PM »

The fun with the Lunchbox convinced me to build a Zweibox.

Here she is, not totally done yet (the incomplete paint is obvious), but she's close, posing with parts for another.

No D/T ... if Hung takes her, I'll be happy.

Cheers-
Dave
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Zweibox HLG
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dosco
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« Reply #1 on: July 22, 2020, 10:12:39 AM »

Zweibox #1 is shaping up to be about 37g with noseweight.

No sheet lead to be had, and I improvised by cutting a piece of scrap 1-5/8" OD copper pipe and fashioning a piece of "copper sheet" (by bending the piece into a flat of sorts). I'm in the process of gluing it on now, and will use plasticine for final trim at the field.

Still working on the red stripes, almost done there.

Fun!

-Dave
 
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dosco
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« Reply #2 on: July 22, 2020, 02:47:11 PM »

Here she is.

Now for some trim flights...

-Dave
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Re: Zweibox HLG
Re: Zweibox HLG
Re: Zweibox HLG
Re: Zweibox HLG
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dosco
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« Reply #3 on: July 27, 2020, 09:40:52 AM »

Took her out yesterday afternoon for some trim flights.

She has a tendency to spiral dive to the left. I chose not to put a warp in the port wing, instead I added a Gurney flap ... it's not large enough in terms of 1) how far it extends into the airstream, and 2) its length in terms of wingspan. I've removed it and will install a taller and longer one.

I think the CG is incorrect ... slightly nose heavy. I noticed this with the Lunchbox design. As I mentioned I took a piece of copper pipe and flattened a piece ... it was not lost on me, as I glued it on, that it may have been to heavy. I'd rather have "not enough" copper and trim the CG with plasticine. I plan on removing about 30% of the copper.

-Dave
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dosco
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« Reply #4 on: July 28, 2020, 12:30:37 PM »

I made some modifications...

1) I removed the copper sheet noseweight from the fuselage, and cut off about 1/3 of the material. I will use plasticine to make fine adjustments, and at a later date consider adding another, small, piece of copper to the nose.

2) I removed and replaced the Gurney Flap. The Zweibox article states that the left wing washin should be 1/3 of the wingspan of the aircraft. I cut a piece of 1/64th plywood, 5 3/8" long and about 3/16" wide.

I haven't had a chance to perform any test flights. The wife and I are putting the house on the market, and the "staging" work is a PITA.

-Dave
 
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dosco
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« Reply #5 on: July 29, 2020, 06:52:14 PM »

Forecast for the next few days is bad, then I have a trip to NY ... so I scooted off to the local school field to chuck the Zweibox around.

It really wants to turn left ... even after adding a much larger Gurney Flap. The Gurney Flap is 5.5" long, made of 1/64" ply, and extends 1/8" below the lower wing surface. There is "built in left rudder" (by virtue of tapering the fuselage where the fin is mounted) as well as stab tilt. I attempted to warp in some left wing washin and right rudder. Still was gently (but firmly) spinning in to the left. I added a small blob of plasticine to the right wing, and that seemed to tame the left turn.

After a few more throws, I added a small blob of plasticine just ahead of the fin (to move the CG aft). At some point in the near future I will again remove the copper sheet from the nose and remove some of it (I will measure the mass of the plasticine and remove the equivalent from the copper sheet).

Of note, it would appear the 60% CG position may or may not be the right location. It's reasonable to assume each airplane has slightly different "as-built" wing/stab airfoils (differing from the plan), which means the actual CG position may (or may not) need to be the same as on the plan. The Zweibox plan calls for 6g of sheet lead applied to the nose ... the piece of copper I applied to the nose was 3g, and I've removed about 1/3 of it, and need to remove more. Not the end of the world. Also interestingly, with the Lunchboxes I started with no noseweight, and added a bit of clay for each flight (or series of flights) until the CG was too far forward (with the Zweibox I unintentionally reversed the process).

The last few flights before I left were quite satisfying ... I caught a few bubbles of evening lift. Interestingly, it seems I can launch the smaller Lunchboxes higher than the Zweibox (at least that is what it looks like ... not lost on me that it could be an optical illusion). Will be interesting to see if Zweibox #2 flies a bit differently with the differences I articulated below.

Also on the upside the fuselage stick seems quite robust, which is pleasing (I have memories of HLGs past where the fuselage was prone to failure after nosing in).

So, for Zweibox #2:
1. I will sand the TE of the wing much thinner (I left it a bit thick, definitely thicker than the plan).
2. I will warp in a boatload of washin. I may even cut an aileron and glue it into the "down" position.
3. The fin is cracking because of my attempts to warp in adjustment at the field; I will sand the next one thinner.
4. The horizontal stab may be a bit heavy (and I did try to warp in a bit of "up elevator" ... and there was some cracking); I'll sand the next one thinner as well.

-Dave



EDIT: added some comments about the Gurney Flap (and wing warp) as well as CG position.
« Last Edit: July 29, 2020, 07:35:10 PM by dosco » Logged
OZPAF
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« Reply #6 on: July 29, 2020, 08:18:10 PM »

What a pretty looking glider Dosco.

I have had that strong turn tendency on a couple of my gliders - even with wing panels close in weight. Invariably if the rudder offset wasn't too much, it was caused by a the wings being slightly skewed on the fuse! It doesn't take much. To my eyes this could be your problem looking at the plan view of your build.

It will take a lot of inboard wing washin to control this - as you are discovering. Perhaps a better solution would be to remove the fin and replace it with much reduced or even no, left rudder offset.

Happy flying.

John
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dosco
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« Reply #7 on: July 29, 2020, 08:26:52 PM »

What a pretty looking glider Dosco.

I have had that strong turn tendency on a couple of my gliders - even with wing panels close in weight. Invariably if the rudder offset wasn't too much, it was caused by a the wings being slightly skewed on the fuse! It doesn't take much. To my eyes this could be your problem looking at the plan view of your build.

It will take a lot of inboard wing washin to control this - as you are discovering. Perhaps a better solution would be to remove the fin and replace it with much reduced or even no, left rudder offset.

Happy flying.

John

John:
Thank you very much for the kind words.

I agree, I did notice some wing asymmetry after I assembled her (drat! I was hoping to get away with it ... lol!) ... I think the panels are slightly different in shape by virtue of aggressive sanding of the dihedral joint, but I'm not 100% certain. When I made the wing blanks, I made them separately and then glued them together at the root. Instead of using acetone to separate them (which probably would've been the smart thing to do), I used my Zona saw. The wing blank for #2 is a single (spanwise) piece.

I'll continue to fly #1 (I think I'll name her "Stripey" and the next one will have stars painted on the wings). I like the idea of altering the fin. One option would be to mount it on the port side of the fuselage stick (the fin is mounted to the starboard side, and the taper is sanded into the starboard side). Other option is make and mount a smaller fin in the location specified by the plan (starboard side).

John, how much smaller would you think? 20%?

Cheers-
Dave

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OZPAF
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« Reply #8 on: July 29, 2020, 08:44:45 PM »

I use a couple of small pieces of double sided tape to hold the separate wing panel blanks together while shaping the outline to ensure they are very close. I also use jigs to sand the dihedral and poly joints which help to give stronger joints and more accuracy. I started down the jig road as i was working with kids and wanted to ensure that they had a decent chance of flying.

If you reduce the fin height - I would suggest that you just shave say 1-1.5mm and radius it and then reshape the fin leaving the width the same at the root. Take small steps. Moving it to the other side of the fuse may be a good idea.

I use a very small fin which I arrived at many years ago by this sort of trial and error. Have a look at the Jikah AL300 CLG in the plans gallery.

Hope some of this helps Dave and good luck with the move.

John
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dosco
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« Reply #9 on: July 29, 2020, 08:57:33 PM »

I use a couple of small pieces of double sided tape to hold the separate wing panel blanks together while shaping the outline to ensure they are very close. I also use jigs to sand the dihedral and poly joints which help to give stronger joints and more accuracy. I started down the jig road as i was working with kids and wanted to ensure that they had a decent chance of flying.

If you reduce the fin height - I would suggest that you just shave say 1-1.5mm and radius it and then reshape the fin leaving the width the same at the root. Take small steps. Moving it to the other side of the fuse may be a good idea.

I use a very small fin which I arrived at many years ago by this sort of trial and error. Have a look at the Jikah AL300 CLG in the plans gallery.

Hope some of this helps Dave and good luck with the move.

John

John:
Thank you for the advice. Will start there and after making alterations to the noseweight I'll make some test flights.

Also, thanks for the good word on the move. The house is ready, and we'll have a showing tomorrow at lunchtime. We'll see what happens, the market is very tight right now (not many houses for sale, and surprisingly strong demand). The upside is that we may be able to sell quickly. Downside is that houses are getting snapped up very, very quickly. We have a place in mind in Annapolis, which has many benefits (one is a full basement with a suitable "work area" (i.e. "model building area")), but it could get bought at any moment.

These things always work out ... so only time will tell!

Regards-
Dave
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Jasco
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« Reply #10 on: August 13, 2020, 07:27:31 PM »

I enjoyed reading your trials getting this plane built and flying. I too am trying to get chuck gliders to fly and I have some questions, if you don't mind allowing me to pick your brain.

About your wing: I see you are basically carving a straight line from the L.E. to the high point and another straight line to the T.E. creating a triangular airfoil with a sharp LE.  Is that how all of these gliders are designed? Many plans show only an outline and a high point...is this the intended standard airfoil shape? None of the gliders I build have survived long enough for me to draw conclusions based on performance.

Question 2: What in the world is the proper way to attach the wing to the fuselage? There is  a 1/8" fuselage stick with the wing sitting on top. Should I sand a groove in the wing mount area? Just glop on the epoxy and hope for the best?

Q3: Your wing is nicely finished. (shiny!) I assume this is for drag reduction. I gotta try that.

4: How are you setting the incidences? Whenever I use anything other than 0-0, I get a loop-the-loop toy, and of course 0-0 tends to fly like a lawn dart and never pulls out of any dive.

My dad taught me to build stick and tissue models, but I seem to have missed some building lessons on balsa gliders.

I realized I have a box with no fewer than 5 hlgs I attempted to build and fly over the years. They are all patched up and dinged and none have flown as expected.

In the interest of full disclosure, I can't actually throw anything. I have to use a catapult, but that should give me more consistency. I don't fly in competition so I don't really care about rules. I just want to fly.

Since I'm in the mood to ask questions, one of my gliders built from a Zaic Yearbook  calls for " 4" Jasco wing stock". Does anyone know what that is? My username is of no help. Grin
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OZPAF
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« Reply #11 on: August 13, 2020, 08:18:11 PM »

I hope you are successful with that place Dave - I well understand the hassle and stress as I had to do the same thing almost 3 years ago.

Quote
About your wing: I see you are basically carving a straight line from the L.E. to the high point and another straight line to the T.E. creating a triangular airfoil with a sharp LE.  Is that how all of these gliders are designed? Many plans show only an outline and a high point...is this the intended standard airfoil shape? None of the gliders I build have survived long enough for me to draw conclusions based on performance.

Yes that is the way it is meant to be on this design.
Quote
This sort of airfoil has been used by many over the years and appears to work well. I personally use a curved shape to the high point and then a straight line to the TE.

Quote
Question 2: What in the world is the proper way to attach the wing to the fuselage? There is  a 1/8" fuselage stick with the wing sitting on top. Should I sand a groove in the wing mount area? Just glop on the epoxy and hope for the best?

sanding a groove will work but up to 21" WS have never found it necessary. I sand a flat on the bottom of the centre section of the wing - carefully making sure that it will not change the incidence of the wing and glue that to the top of the fuse with CA. A thin fillet of 30 min epoxy is then wiped along the join and in front (to form a fairing). If the epoxy is warmed - place the mixing container in hot water, it will flow very easily for a few minutes using a wet finger.

Quote
Q3: Your wing is nicely finished. (shiny!) I assume this is for drag reduction. I gotta try that.
I'm not sure how Dosco achieved at his shiny finish however a light very smooth finish can be obtained by using a polyurethene varnish. The trick is to wipe it on with a tissue and then use another dry tissue to immediately wipe of the excess and let it dry. When it is dry - and not tacky, sand it gently with 400 grit and it will produce a very smooth finish which is reasonably water proof. however don't leave ant dew, water on the surfaces when flying - wipe them dry straight away. More coats will give a more glossy finish but add weight. the above finish adds about a gram to my 12" CLG.

Quote
4: How are you setting the incidences? Whenever I use anything other than 0-0, I get a loop-the-loop toy, and of course 0-0 tends to fly like a lawn dart and never pulls out of any dive.

I find that starting at 0-0 is the secret to getting a decent trim on HLG or CLG's. I balance the glider to start and then do a few hand glides to check that it is close - it is only necessary to ensure that the glider is gliding relatively flat without any strong turns. I also add some wash in on the left inside panel at this point.

if the HLG goes straight up and then dives in - great - all it now should need is a bit of up elevator. You will or should not need much. I warp up the tip of the right elevator till it starts to pull out of the dive on launch. Once it pulls out of the dive it may become necessary to trim the glide turn. I have attached a doc with more detailed trimming comments. One thing to keep in mind during this trimming is that the launch angles and throw need to be consistent - particular how hard it is thrown. The harder the throw - the finer the trim adjustments.

This is how I trim my CLG - HLG's are similar.

Try some gentle glides. It will most likely need a small amount of up elevator added.

I usually warp the right tip section of the stab TE up by the time humored method of breathing on it and tweaking. Right tip only.

Also add around 0.8mm of washin around the midpoint of the left inner panel.

These two tweaks should start to produce a flat glide with a slight turn to the left.

If the turn is not noticeable in the glide then check that the left wing is slightly heavier than the right. If not reduce the weight of the right until there is a slight bias towards the left.

When the glide is flat with a slight left turn, try some slightly harder level launches. These should produce a slight climb settling down into a flat glide. If it tends to stall too easily then the glider may have too much decalage with a CG too far forward.

Retrim slightly further aft and reduce the up elevator warp.

Try a catapult launch – pull back around 250mm on a 250mm loop of 6mm rubber.

Hold the glider with 60 deg or more of right bank and launch to around 70 deg slightly left or directly into the wind.

If the glider flies through around 1/4 to 3/8 of a turn to the right before turning left then the decalage is close to correct.

The glider may travel almost vertical and then dive straight back down to the ground. That’s good – that means it doesn’t have much decalage. Tweak in a bit more up elevator and retry until it slows and transitions smoothly to a left turn.

It may roll very strongly to the left in the climb. This is usually caused by too much built in left rudder. Warp the very end of the fin very slightly to the right. Use small amounts and only use the end of the fin.

At the same time the glide should be in fairly flat left turns.

If the glide is spiraling in too steeply to the left – check the left wing washin and add more if it persists. This will most likely require a little less up elevator.

If the glider stalls at transition before turning to the left when only flying around a quarter to a half turn to the right in the climb – then check that there is not too much right rudder tweak an reduce if necessary. Check that there is not too much washin on the left inner panel and lastly check again that the wing has a weight bias to the left.

When correct the pattern will be a fast climb of a bit more than a quarter turn to the right while rolling to the left and slowing down into a smooth left gliding turn without stalling.

The glide can now be optimized by tiny backwards movements of the cg until it starts to rock on the glide(onset of Dutch roll). This is the desired result for still conditions – the CG should be a little bit further forward for windy turbulent conditions (lower AOA and a bit more stability).

If it glides with too much left bank and or starts to spiral inwards – add more washin to the left inner panel an readjust the decalage if necessary for the climb. If this follows a strong roll to the left during the climb then it has too much left rudder. Only a tiny amount of left rudder is needed for the climb and it is best to use the tail tilt as the primary glide control on the glide.

Good luck

John

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Jasco
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« Reply #12 on: August 14, 2020, 08:35:45 AM »

 Cheesy Thanks, OZPAF...those are pretty comprehensive trimming gudelines.  Much better thought out than my usual procedure.  I think when I get to the flying field I go through some kind of time warp where I turn back into a 10-year-old and all common sense leaves me. I keep shooting planes into the air blindly until they either fly or break. Usually break.

So the dive into the ground is "close"? I'm "close" a lot.

One design that has me really vexed is "Fritz" It looks like it should fly, and according to the designer, it does. Mine flew like an elevator.

https://aerofred.com/details.php?image_id=101453

So frustrating when the rtf models fly better than anything I make... Angry

Fortunately, I liked running across big fields like an idiot when I was 10, I guess that hasn't changed.
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dosco
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« Reply #13 on: August 14, 2020, 04:37:32 PM »

Just saw these replies.

OZPAF: thanks for the kind words wrt the move. We have an offer for our current home, and have made an offer on a townhome in Annapolis, MD (about 15 miles from where we are now). Downsizing a bit since the kids are older, and also trying to cheapen up the mortgage payment (and save some $$). Maybe save enough sometime soon to get a small boat or a small place on the beach (Ocean City isn't that far from us).

I sprayed the wing with several coats of Deft spray lacquer. Then lightly sprayed with white and the red trim (both spray paint). Mostly to seal it up a bit and look neat. For this project "good enough" was good enough and I did not obsess over surface finish. I did obsess a little bit on picking the balsa properly, and I did pay attention to the sanding method (although I did deviate on the wing section, more below).

I built the incidence as close as I could to the plan, which appears to be zero-zero.

I used Beacon to glue the wing to the fuselage stick ... plan call for epoxy but I don't have any handy and didn't want to spend any money on this project (the balsa was all stuff I had on hand).

The wing airfoil is triangular because I chose to build it that way, the plan calls for a more reasonable section ... a slight Phillips entry on the "chin" of the LE, a curved section to the high point, then straight to the TE. At these Reynolds Numbers I'm not sure how much it matters, and frankly I think the primary variable is air picking (assuming the glider is "close enough").

Regards-
Dave

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« Reply #14 on: August 14, 2020, 06:36:31 PM »

[quoteAt these Reynolds Numbers I'm not sure how much it matters,/quote]

I went through my "professor" phase prior to computers being invented ( Tongue) when I would slavishly plot every rib from its polar coordinates by hand. Loads of time-wasting fun, but alas, you are probably right.

Off to the field this evening. Wish me luck!
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« Reply #15 on: August 14, 2020, 08:38:30 PM »

Quote
At these Reynolds Numbers I'm not sure how much it matters, and frankly I think the primary variable is air picking (assuming the glider is "close enough").

What low Re No FF models(indoor rubber and glider) have indicated is that thin airfoils work better and this is the starting point for me. Also most modern HLG airfoils have a relatively sharp nose radius. My root airfoil is around 6% thick - using 1/8 sheet on a 2" chord for a 12" WS CLG. The Nose radius would be around 0.25mm. I also use a thin TE of around 1/32" - and left square - not rounded!

The High point was to me not quite as important as long as it was close to 30% - i do use templates to mark this out though. The straight line from the high point to the TE is to help to maintain airflow over the wing by using the sharpish break in the curvature to form a separation bubble. Anyway that's the theory and it is also used in more extreme forms by some of the top HLG, CLG fliers such as Buddenbohm and Tony Mathews.

I also thin the wing span wise pretty dramatically. The tips are only around 1/32" thick with a linear taper from the root. This benefits the even lower Re no's at the tip but possibly even more important - reduces rolling inertia at the tip, which helps the transition from the climb to the glide. however I still feel it helps to keep the tips flying as I do not use washout at the tips and have not needed it.

Anyway while I feel all the above helps - accurate construction is possibly the most important item, followed then by good trimming(which needs accurate construction) and then practrice, practice, practice Smiley

So good luck to both of you fellows and stay safe.

The Fritz you linked Jasco looks ok but one aspect that may not help is the large tail planes on some of these older designs. It makes trimming the transition much harder and more knife edge.

John

 
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« Reply #16 on: August 26, 2020, 01:24:39 PM »

A beautiful day today, so I broke free for about an hour to fly the Zweibox and Lunchboxes.

It was a bit breezy at the field, probably a steady 2-5 knots with sharper breezes as thermals broke free and infilled.

The Zweibox flew horribly. It would simply not fly, it would tightly spiral to the right without gaining altitude, followed by nose-dives (either straight in, or left-handed death spiral).

I cut of bits of the fin which did not help. I attempted to warp the TE on the port panel, but it cracked. I also tried additional clay on the starboard wing. Nothing worked Evenutally got to the point where I removed the fin, mostly to see what would happen. It still would not coorperate.

So, rather than crunching it (the thought occurred to me), I will follow my initial plan to fix.

1. Remove wing and sand the aft portion per the plan (it's a bit thick now).

2. Make sure wing panels are symmetric.

3. Make a new fin, sand it much more thinly, and mount on the opposite side of the fuselage to take out the "built in left turn."

4. Thin out the stabilizer.

5. When I re-mount the wing, make sure there is no skew.

Not sure if I will tackle this soon considering the impending move to Annapolis.

The Lunchboxes flew swimmingly. Almost lost #2, as it hooked a thermal and traversed the field, only to land in a small tree. Was able to find and retrieve it.

Interestingly the Lunchboxes launch very high. Much more so than the Zweibox, which is counterintuitive. Hopefully this will change as I make mitigating fixes.

I'm not sure why the Lunchboxes flew off the board compared to the Zweibox. I'd say "got lucky" but I made 3 and they all fly pretty well. I'm guessing the Zweibox has building mistakes (wing panels may not be symmetric, wing skew when I glued it to the fuse, etc.) that are enough to really negatively impact its flying characteristics.

Anyhow, live and learn. And it's been a very long time since I've built and flown anything. So the re-education is ... necessary.

(In the back of my mind, I'd like to build a 2x Zweibox and put a teeny R/C system onboard ...)

-Dave


-Dave


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« Reply #17 on: August 26, 2020, 04:48:00 PM »

Update:
I've cut off the wing and split the joint at the wing root/centerline. I've glued the cracks/split and will start sanding tomorrow.

I've thinned the horizontal stabilizer quite a bit ... it's ready for some Deft spray.

-Dave

PS: OZPAF, we backed out of the townhouse, and found a small Cape Cod styled home (with a decent sized addition (it also has a nice basement)) not far from the Naval Academy stadium. It's really neat. Fingers crossed.

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« Reply #18 on: August 26, 2020, 08:20:17 PM »

Quote
PS: OZPAF, we backed out of the townhouse, and found a small Cape Cod styled home (with a decent sized addition (it also has a nice basement)) not far from the Naval Academy stadium. It's really neat. Fingers crossed.

That's good news and best of luck with it. Would I be right in thinking that the new place will have more room? Townhouses here in OZ are generally not much bigger than flats! You may also have a indoor possibility in the Naval Academy?

John
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« Reply #19 on: August 27, 2020, 07:23:47 AM »

John:
Hrm, hard to say about the space difference ... the newer 3-story townhomes around here are fairly large, we lived in one prior to the place we're in now (that we're leaving). That townhouse had a garage and was something like 2,400 square feet. The one we were considering had a garage and was similarly sized. We backed out after the inspection, as we found many, many issues that were not obvious to the casual observer (the sellers had been using it as a rental property).

More importantly, my wife was having a lot of second thoughts about it ... she didn't love the place. She very very much loves the Cape Cod styled place that we're buying.

The house we're in now, she hated it when we moved in. She has a great sense of style, so with her vision we were able to turn it around into something much nicer. With that said, were we to stay here it would require a significant investment for me to feel happy ... new roof, remove all siding and replace 1960s sheathing with plywood and Tyvek, new windows (with proper installation (current windows are newer but were poorly installed)), remove all engineered flooring in the lower floor, demolish kitchen to studs and floor joists, install a nice porch ... (I think that's it, probably a cool $200K investment).

Indoor at the Naval Academy? Interesting thought. In the mid 1990s I used to host indoor sessions at the C-5 hangar at Travis AFB. I was also able to get a session at the dirigible hangar at Moffett Field, which kicked off a few years of indoor flying there until the "lead problem" shut the place down. I've taken a walking tour of the Academy, but I'm not 100% familiar with the possibilities there. A friend's son is a Plebe there, perhaps he can be my "inside man" there, lol. Unfortunately in today's day and age, arranging sessions there may be too Byzantine ... we'll see, though. I'd not considered it, and it might be worthwhile.

-Dave

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« Reply #20 on: August 28, 2020, 04:16:10 AM »

Our present 3 BR house would not be any bigger than the townhouses you mention Dave, and it could do with a fair bit of work - but there is no money for that! Anyway thanks for the trip off track and keep your fingers and toes crossed!

cheers
John
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« Reply #21 on: August 31, 2020, 10:18:49 AM »

The preparation for the move continues, seems like we're making reasonably good progress. The last 2 moves were not good, and I'm a bit concerned I'm fooling myself into thinking "things are good."

As far as the Zweibox, I cut her up and did some work ...

1. Remove wing and sand the aft portion per the plan (it's a bit thick now). Complete. Inadvertently cracked the TE of the port wing - the repair included putting a skin of cement on over the crack, which induced a washin warp. I will claim this as a victory (it needed some washin there anyways, so it's better to be lucky than good).

2. Make sure wing panels are symmetric. Complete. Turns out, unsurprisingly, the wings were asymmetric at the root. One panel had a bit more material which resulted in an angle (effectively put a wedge in the root). A picture would probably be clearer, sorry. After sanding the joint between the sheets (I glued 2 sheets together to form a blank with the proper dimensions), I was able to see the joint and draw a line at 90 degrees. I ended up cuttin off about 3/8 inch from each wing and was able to ensure the blanks were matching/correct.

3. Make a new fin, sand it much more thinly, and mount on the opposite side of the fuselage to take out the "built in left turn." Done.

4. Thin out the stabilizer. Done.

5. When I re-mount the wing, make sure there is no skew. In work. Last night I re-sanded the dihedral into the root of each panel and glued them together. This morning I applied some Beacon to the bottom surface in preparation for gluing the fuselage (I'm double-gluing the joint).

Since the wings were asymmetric, I'm guessing the angle of one panel at the root (thereby introducing skew) was the root cause of the left-handed spiral death dive. I won't make that mistake again.

I'm going to apply some Deft to the sanded balsa ... not sure I'm going to paint the wings prior to test flights. We'll see.

-Dave
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« Reply #22 on: August 31, 2020, 02:08:23 PM »


5. When I re-mount the wing, make sure there is no skew. Complete. Wing is on the fuselage. I measured the distance from each wingtip to the fin. The measurements were - as far as I can tell - within 1/16".

Still have to glue on the triangular reinforcement for the "throwing peg" (not sure what it's called).

I'll mix some West System 403 Microfibers into a puddle of Beacon and apply a bead/fillet to the opposite side of the fuselage (from the throwing peg thingus) for reinforcement.

-Dave

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« Reply #23 on: August 31, 2020, 05:08:44 PM »

Updated pics.

I forgot to mention that I sanded the wing LE to achieve a sharp point, previously I'd attempted to round it but upon closer inspection it was flat (the LE is a lamination of basswood I cut a strip from a sheet of 1/16" bass). It is evident where the paint has been removed (perhaps more striking when assessing the underside view).

You can see the port wing TE, where it cracked and my not-so-neat repair. I will say that I think I should've used softer balsa, less prone to cracking. Ah well. Hopefully the needed warp will work in my favor. The wing blank for #2 is partially sanded, so maybe #3 (when I get around to building it) will have a hard front half and a soft rear half.

You may be able to see on the underside view, the fillet made of Beacon and West System 403.

I've sprayed the wing with Deft, so it's mostly ready for some test flying. If I'm lucky it will be nice tomorrow and I can toss it around a bit.

-Dave
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« Reply #24 on: August 31, 2020, 08:42:59 PM »

Hope that all pays off for you Dave!

John
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