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Nodd's Great Planes Spectra

Old 03-16-2014, 12:21 PM
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[QUOTE
PS: I really believe shear webs should have vertical grain to maximize strength.[/QUOTE]

Nodd is correct, the shearing load is diagonal across the web, so vertical or horizontal it doesn't matter.
Old 03-16-2014, 07:18 PM
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Thanks for the info Bo. As I suspected, these old birds, once equipped with modern gear, are really something without having to haul around a pound of NiCads.

That's interesting you enlarged the rudder some. With my extended wing that's something I'll definitely be doing also.

Sheeting the outer wing panels seems to be a smart mod. It's no good to have a nice clean airfoil all along the center panels & then a thinner saggy poor excuse for an airfoil out at the tip. It's no wonder the stock Spectra is known for tip stalling. Hopefully I've addressed that with my half-ribs. Not quite as slick as sheeting but fingers crossed it's a workable alternative.

Appreciate the setup info, thanks again.
Old 03-30-2014, 07:30 PM
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Its been a couple of weeks, have been busy with other projects but I have made some progress...


Wing Rods
When I got this plane the six foot wing was one piece. Now that I've extended it some, there's no way that's going to fit in the family car. So this will be a three piece wing. The outer wing panels will be connected via wing rods. First thing to do was make some end ribs with matching holes...





I'm using a length of brass tube capped at both ends with some epoxy...





This prevents the glue (epoxy mixed with micro-balloons) from entering the tube...





Then on goes the end rib...





Once that's curred I added the outer wing panel. Note the brass tube protruding into the first rib-bay...





Setting up the dihedral...





Some scrap wood to help fill the space around the brass tube...





In goes the epoxy/micro balloons goop...





Added a plywood spar-cap to seal everything up. Note the hacksaw blades positioned between the end-ribs...





The hacksaw blades were there to create a gap just big enough to fit a... well... a hacksaw blade so I could cut the brass tube...





There we go, two perfectly aligned wing-rod tubes...





A short length of carbon-fiber rod & we're in business...





That's starting to look like a wing...


Old 03-31-2014, 11:14 AM
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Hey Chris!
As usual, thanks for write-up. Always love to see how models getting built.
Just one note. I understand it is very easy to do the wing rods the way you do. Although the moment load on a graphite rod is tremendous! Looking at you wingspan and length of the rod - they look inadequate.
All those spars will stay intact while wing at the rod end could fail at a small load (at least the way I feel by looking at it) or, it could fail at rib one. Load is not spread along the spar, it is dropped (or increased) abruptly at rib one.
Do you feel the same way?
Mechanics of the load tells us simple thing - spar could be absolute null at the wingtip and should be appropriately wide and thick at the root of the wing. It saves weight and increase the maneuverability.
Not connecting spar at the root is a trade-off as far as load goes and require good load bearing rod and proper and even load distribution coming out of the rod receptacle (tube in your case).
Just a note.
Regards,
Mark
Old 03-31-2014, 03:52 PM
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I'm using 5.5mm carbon-fiber for the wing rods. Although it's not indestructible I'm confident it's stronger than the spruce spar structure it's attached to. If this was a two piece wing with the joint in the center I'd worry these might be inadequate but positioned where they are, well out along the span, they're not under as much stress. I'm actually far more worried about areas of the center section failing, its been repaired numerous times & not very well at that. This is an old beat up gal, I won't be putting any crazy forces on her & if she does give, oh well. I expect those rods will be fine although I'm considering wrapping the rod-boxes with a little Kevlar to keep the spar from delaminating from the goop.

As far as the load spread, the first bay is solid epoxy pretty much, then from there we have 1/8" plywood sheer-webs either side of the spars running out to the second rib & then from there it's balsa & spruce. So there is some tapering of strength, it's not a totally abrupt change.

Now granted this wing is longer so experiences more stress but bare in mind the stock wing joint in this section consisted of just two dinky pieces of 1/32" plywood dihedral brace. This is a pretty lightweight airframe, not meant for anything more than put-putting around. I think if you held this in your hand & felt how she feels you may not be as concerned. I don't want to jinx myself but I think she's fine, looks & feels good to me. I guess we'll find out though.

Last edited by Nodd; 03-31-2014 at 03:56 PM.
Old 03-31-2014, 05:15 PM
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Sure Chris,
It's hard to judge from pictures. I am sure it'll hold. Looking forward for some flight videos!
Cheers,
Mark
Old 04-03-2014, 08:28 AM
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Great shots. Keep 'em coming!
Old 04-06-2014, 07:48 PM
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Spoilers
I've been using e-spoilers in my giant scale sailplanes for a few years now with good results. I had a couple of extra e-spoilers left over from a review & this seems like the perfect project to try them out in...





For those not familiar with e-spoilers, they're basically your standard blade type spoiler except instead of a linkage that attaches to a servo they come with a built in motor that raises & lowers the blade. The advantage is they're super easy to install as there's no fiddly linkage or external servos to mess with...





I created a frame to mount the e-spoiler into...





Just pop the e-spoiler in, two screws mount it to a pair of hardwood blocks underneath & they're in...





Added a small strip of balsa to the top of the blade & sanded flush...





Deployed position...





Well these spoilers should come in handy next time I'm stuck in a booming thermal...


Old 04-07-2014, 03:10 AM
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How heavy are they? Would seem much heavier than a bit of balsa trailing edge and a servo.
Old 04-07-2014, 04:51 AM
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Originally Posted by aeajr
How heavy are they? Would seem much heavier than a bit of balsa trailing edge and a servo.
~40 grams, but way cooler! Don't worry about the weight, the weight is the motor, the plane has plenty of lift.
Old 04-07-2014, 05:00 AM
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Well, yes, since it probably originally flew at around 55 ounces. With the changeover to brushless and Lipo you probably were able to take 12 ounces out.
Old 04-07-2014, 02:49 PM
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Yeah the added weight is negligible for a sailplane this size. I figure the benefits far outway the cost of a few extra grams. Besides as Rich points out, they're just plane cool :-)

I've been asked where I got these. Here's a couple of examples of e-spoilers...

Hobby King
Glider Spoiler Servoless

Esprit Model
Airplane/Sailplane Electric Spoilers
Old 05-04-2014, 05:11 PM
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BIG HONKIN' Rudder
Okay so I'm sticking an 8 foot wing on a 6 foot glider. According to my nifty sailplane spreadsheet the stock Spectra's vertical stabilizer is now too small, no surprise there. So I drafted a new larger fin...





I always keep the backing from my rolls of UltraCote covering. Unlike wax-paper, whatever that stuff is, it's impervious to CA glue, epoxy & just about every other glue I can think of. Great for keeping the build from sticking to the plans or work-bench...





There's nothing too fancy about this fin. I kept it simple, light & somewhat reminiscent of the stock Spectra tail...





LOL, that's looking pretty darn huge on that dinky little fuselage...





With the wing on there though, it actually looks about right given the short coupled fuselage...





According to my data the stock horizontal stabilizer has just enough area to handle the larger wing however I decided to slap a larger elevator on there which made my spreadsheet much happier. So hopefully we now have enough tail to steer this beast, good stuff...


Old 05-05-2014, 06:09 PM
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A not so BIG HONKIN' Rudder
Having had a chance to step back & look at the assembled airframe I'm finding it's raising alarms in my brain's TLAR (that looks about right) center. Even though it's good on paper (the spreadsheet says it'll fly) I'm not happy with her. So we're making a few minor tweaks. First thing is to trim my giant fin down a little...





Added new top & cross pieces, almost looks like I planned it this way...





The fin is still a lot bigger than the tiny stock fin but this clearly looks & feels much better than the monstrosity I had on there yesterday...





This was a painful decision but I think it's the right one. My new wing is clearly too big for this fuselage so I've removed a length from each end of the wing. The total wing-span is still longer than stock but is now more in keeping with the rest of the airframe...





There that looks somewhat less insane...


Old 05-05-2014, 07:25 PM
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Good choices. That fin-rudder combo was going to give you fits, the new one looks more workable.

If your plane tucks in turns you need either more poly or less vert/rudder.

Last edited by soarrich; 05-06-2014 at 09:19 PM.
Old 05-05-2014, 07:39 PM
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Looking forward to the finished build. Looking good so far.
Old 05-06-2014, 04:37 PM
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Awesome development work.... It takes a clear head and strong will to see and WHACK like you did. And the additional elevator ought to be a good move too. I'd consider putting a longer horn on it. It will use less deflection than the original, and the longer arm gives more leverage and finer control.

Can't wait to see it in the air. Wish CT wasn't in another world.
Old 05-18-2014, 05:26 PM
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This should have been done months ago but you know how these things go once flying season starts. I've already attended two large aerotow events plus a float-fly, flying twice a week on top of that. We're getting there though, made some good progress today...

Balance Test
Before I work on the fuselage further it's time to see how she balances. Here's the electronics...





I placed the electronics roughly where they'll end up. At this stage I need not be all that accurate...





Well look at that, she balances! Granted the covering will affect the CG some but that looks encouraging...





The Nose
Okay first thing is to get rid of this old firewall...





Traced the old firewall onto some nice high quality plywood...





That's looking good...





But you know what? That's one really boxy schnoz, looks about as aerodynamic as a dump-truck...





Lets see if we can make this a little slicker. I crafted a new, smaller firewall...





Split the fuselage along its joints...





Removed some wood, trimmed things down some...





Glued the new smaller firewall on there then used some bands to pull the fuselage back together...





The new slicker nose means I can't use the stock canopy hatch so I'm making a new one from 1/4" balsa...





Clamped the wood while the glue sets...





That sure looks daft...





Queue the banjo music, it's whittling time...





That looking good...





A dowl up front & a couple of rare-earth magnets in back should keep the hatch secure...





Another couple of magnets in the canopy...





Holes
The stock Spectra has lots of wacky holes in the bottom of the fuselage. I understand the need for ventilation but these holes being in the bottom of the fuselage are likely to allow all sorts of crud into the model every time she lands...





Time for a little inlay work to plug these silly holes...





That makes me happier...





I added these ventilation holes, in the side this time...





Installed the motor...





Oh yeah that's looking pretty sweet. That'll do for today, more soon...


Old 05-20-2014, 11:12 AM
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I KNEW you couldn't control yourself from improving things......

But you're right. The model will be better for it. Not only the looks and streamlining but also the way the prop blades fold in tighter and unfold with less nose rubbing.

As always great pictures that show what you're doing very neatly.
Old 05-26-2014, 04:30 PM
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I am trying my hardest to stop changing/modding/improving stuff but it's not easy *grin*

Wingtips
I decided to go with some basic wingtips, nothing too fancy...





Sanded a 20 angle on the underside...





Graphics
Although I've spent a fair amount of time thinking about graphics for this project, I only sketched a few ideas before I found something I liked...





This design is vaguely reminiscent of the stock Spectra graphics, somewhat simplified.


It's covering time!
I'm a big fan of Hangar 9 Ultracote but this is the first time I've tried their Parklite covering. As the name suggests it's quite a bit lighter...





As with any plane I intend to fly high, I like a dark color on the under side of the wing. This black should contrast well against both clear & overcast skies...





I figured this Parklite stuff would be thinner than regular Untracote but I didn't expect it to be this transparent...





Pretty happy with the way this stuff covers even if it is a little see-through. Remind me to cut out the spoilers before plugging them in...





Interesting, this stuff looks better outside. Well that's all I managed to get done today. We're getting there!...


Old 06-03-2014, 01:50 AM
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Interesting mods on your Spectra, your covering job looks first class!
Really like the airbrakes, I never knew you could buy electric ones like that.

I thought I would post two pics of my electrified Gentle Lady I finished last year since you mentioned having one of the birds back yonder in time (I also had a pure gentle lady in my youth, first bungie flight on it was knee-knocking).

The wing root pic shows a very similar brass rod mod to yours, though I extended it through three ribs and re-enforced with some fibreglass tape. Tube is epoxied to the original lite ply central spar doubler. I then have another brass inner tube with a plywood dowel epoxied inside that one which acts as the removable joining spar (I could not get a carbon spar of the right diameter to fit, and here in South Africa materials are very limited). Wing is held on with two front dowels, and two rear nylon bolts. Magnetic hatch.
So far, after about several dozen flights, the wing has not shown any signs of folding or problems with this joiner system. I did a very sharp pull up the other day which put a lot of stress on the airframe (I cringed thinking the wing may break) but all was good. Without the inner dowel for the joiner rod, it bent on the second flight. Since that mod, no bending at all.

I made removable tail feathers which are held on with three tiny nuts. Power is a Eflite Park 480, 2200mAh Lipo under the wing, 40A speed control. AUW is 38 ounces.
Its a little fat compared to a pure sailplane, but man this thing does not want to come down and floats like, well like a Gentle Lady. Wish I had air brakes like yours. Extra weight helps a little in wind though..
Color scheme is nice on the ground, but in hindsight I probably should have gone with something more visible high up.

Good luck on the maiden, I am sure she will be great!

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Last edited by davevh; 06-03-2014 at 01:58 AM.
Old 06-09-2014, 07:06 PM
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That's one beautiful Gentle Lady you have there Dave. I also had an electrified GL, built an extra fuselage with an Astro 05 motor & bloody huge brick of NiCads. Flew like a brick compared to the pure glider version but that was electric flight back then. Things sure have changed, changed for the better... on with the build!...

Covering (continued)
It's time to tackle the fuselage & get that covered. I usually dread using heat-shrink covering on the compound curves of a fuselage, lots of wrinkles but in this case she's a basically a box. Easy-peasy to cover...





That's starting to look kinda sexy...





Finished up the tail, using CA hinges to attach the control surfaces...





The stock Spectra has a reputation for tip-stalling, mostly due to the saggy covering on the tip sections. Even though I've addressed that issue on mine, it's still good practice to twist in a little washout...





Electronics
With the covering done it's time to install the guts.





I noticed the wires were rubbing against the motor housing, not good. So I crafted this simple wooden post to hold them out of the way...





Before you ask, here's what I'm using...








Balancing
Up on the balance stand, lets see how we're doing...





We're just a smidgen tail heavy, nothing a little bird-shot won't fix...





Pretty happy with how little weight it took, worked out well. Mixed the bird-shot lead with a little finishing resin & poured it into the bottom of the nose...





Okay so the all important weigh in...








That's pretty good, five ounces lighter than the stock Spectra. Here's the data...





Project Complete
Woohoo we're ready to fly! Stay tuned for the maiden flight video shortly...





Old 06-09-2014, 08:12 PM
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Cool looking glider!
Looking forward to see some flight videos!
Congratulations!
Old 06-10-2014, 12:29 AM
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Great job Chris!
I really like that you got rid of that triple taper on the leading edge of the outer panels, that was always something that just did not look aesthetically pleasing (kinda like a low polygon version of a rounded edge with sharp vertices) in the Spirit/Spectra to me.

I am curious, what's with the dark gunk inside the fuselage area (post#43) under the wing and in the nose. Looks kinda like moisture rot from old wood left in the rain?

I hear you on the old electrics, my first was a gorgeous Sophisticated Lady (bought brand new pre-built in Johannesburg) back in the early 90's which was outfitted with the old CG Power Pod. Man that thing was heavy, and every landing no matter how smooth resulted in the T-Tail overtaking the nose! If I recall it had an 8 Cell Nicad, no ESC, just an on-off switch. Eventually the T-Tail was lowered Gentle Lady style, a landing gear was added and an OS.09 was put on the nose Airtronics Butterfly style. That's how I learned to fly power. I owe quite a lot to Goldberg as I had several of his aircraft (including a Freedom 20 which was kinda a hotrod for me at the time).
Old 06-10-2014, 10:00 AM
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Low polygon count glider... LOL love it! Yeah this is now a HD Spectra *grin*

Yeap that's some evil black funk inside the fuselage. My Apache balsa DLG spent a night out in the rain (long story), got a little wet. I cut a few holes in the covering & let her air-dry for a few days. Almost immediately I started seeing that same black stuff here & there. I also had a balsa Puddle Master flying boat that got wet all the time. That too had areas of the dreaded black lurg. This Spectra is 20 years old so I'm guessing it's seen its share of moisture over the years. Before working on this project I diluted some bleach & ran a sponge over the scary areas. While it's not very attractive it doesn't seem to harm the structure any. Just one of the joys of working on an old airframe.

Speaking of early electrics, the biggest problem I had with my first e-gliders was the fixed propeller. Folding props were expensive & pretty rare back then so we just bolted on a regular blade & went flying. I recall making low passes, so I could see if the prop stopped in a horizontal position for landing. Broke plenty of props back then LOL.

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