Astron Invader 2.5x upscale R/C

[iter]

This is my ~2.5x upscale of the classic Estes kit, Astron Invader.

Plans of the original are available from JimZ's site: https://www.spacemodeling.org/jimz/estes/k-19.pdf

Mine uses foamboard as main construction material and has R/C with elevon control. Foamboard (the kind with paper on each side) is a new material for me and aside from how heavy it is, is a pleasant surprise in sturdiness. I use a single piece of 20"x30" red-and-yellow for this build. Foamboard comes in many colors. I use polyurethane glue on all joints, and all joints and all surfaces hold through some wild flights (description below). I do notice some delamination around the edges. I wrap masking tape around sharper corners to prevent further delamination.

An unusual feature in this model (a departure from original plans) is using ACME conformal rail guides on the bottom of fuselage. This lets me have the top of the model facing the flightline and me. This is an advantageous camera angle, and makes it easier for me to keep orientation of the plane as it flies away from me.

First flight was past Saturday at the LUNAR launch at Moffett.

Ari.

 

[iter]

First flight, on an E15, did something I'd never seen before: it got stuck on the Black Sky rail.

(Sam Fineberg photos)

 

[iter]

For second flight, I swapped sectional Black Sky rail for one-piece 80/20 1010 rail. The model left the rail, but soon started looping wildly.

It appears that I had too much up trim. At first, off-axis thrust created a nose-down moment. Then, as airspeed grew and elevator became more effective, nose-up trim took over. I got the looping under control eventually. By the time -4 delay fired, the model was gliding in a controllable path. (I removed the ejection charge, but you can still see a puff of smoke as the delay grain burns out in the one-before-last photo). The landing was reasonably soft, if a little closer to spectators than I prefer. Being that the Invader spent most of the burn looping, I had relatively little altitude to maneuver from for landing. Incidentally, my toolbox and another glider are visible in the background on the right in the last image. I have no idea who the boys are. Some people just like to get too close to other people's stuff.

I've re-programmed my transmitter to avoid this trim issue. I'm planning to fly the Invader again this Saturday, hopefully with a more stable boost.

Ari.

 

[TheAviator]

Very cool. I hope you have a better next flight!

I've been experimenting with foam board lately, and it is heavy. It is, however, very cheap and relatively durable.

 

[aerostadt]

I had the original Estes kit about 45 years ago. I flew it once or twice and gave up. It did not fly well. I think I might have modified it and then it only fluttered like a leaf to the ground like a leaf during the supposed glider phase.

 

[AstronMike]

Welll......

About time someone else does this!! I first made a 20" Invader around 30 years ago, but modified for better boost and glide transistions, as this was free flight. I'm sure Jeff Gortatowsky can chime in here about those kits of this I made 17 years ago.....

As far as foamboard being 'heavy', as you and another poster here have said, why? Compared to what? I'd bet that if you made similar sized and larger gliders using 1/4" balsa or such it would be LOTS heavier, not to mention the $$$$ factor as well. It appears you are using standard colored board here, which is of the heavier type. Strange aside to this - the black stuff, with black core, is actually a bit *stiffer* and *lighter*. Not by much, mind you, but once you're throwing up into HPR that does come into play.

As far as even cheaper and MUCH lighter goes....try the Adams Readiboard variety. This is *only* found in either Dollar Tree or DEAL$, and is only a buck for a 20x30 sheet. This stuff, if you get *straight unwarpy boards* RULES THE WORLD for free flight midpower gliders. Drawback - this stuff is NOT as sturdy as conventional foamboard, but it does not have to be, if you plan and pick your intended motors correctly. You can do a search both here and on the old TRF archive, not to mention YORF, for pics of some of the stuff made with this, usually deltas and other low aspect goodies.

One other maddening thing about foamboard based gliders, if larger: Warpage. No matter how well you store them, after some time you get inherent warpage, which can totally dork up subsequent flights. This can actually be planned for and work to your advantage, if you preselect a warpy board to have the curvature act as dihedral, and any subsequent warpage is usually in the same direction. Typically, it's along the long axis of the sheets you get, the 30" span.

Ari, I'll bet this will be one of the cooler gliders you fly, as not many people get to see a disc up there alone!! BTW, one of the most powerful gliders I ever made was based upon this very design - a 52" disc flew well on a J350 back in '96, right after that reload came out. Required over 4lbs of ballast to be ejected to transition to glide, and the disc returned in a very slight stall and landed nice. This was made with half inch Gatorfoam or similar, and had some reinforcing. It, along with the rest of my old HPR glider fleet, was destroyed in storage as the 2004 hurricanes flooded where they were stored.

You oughta look up my 'Marauder' design and do an RC version of that too. BT70 and a 32" span would do rather nicely..

 

[AstronMike]

Very cool. I hope you have a better next flight!

I've been experimenting with foam board lately, and it is heavy. It is, however, very cheap and relatively durable.

Ok, I was wondering why you were saying this until I figured that you're a BTC, to whom *everything* is heavy! :flyingpig:

Foamboard type stuff is great for low aspect larger gliders, usually 24mm powered. What are you planning to make?

 

[AstronMike]

I had the original Estes kit about 45 years ago. I flew it once or twice and gave up. It did not fly well. I think I might have modified it and then it only fluttered like a leaf to the ground like a leaf during the supposed glider phase.

Yes, the problem with this config is the necessary boost CG needs to be near the LE of the disc, while the glide CG is typically around 25 to 28% aft of LE. The original pylon setup doesn't really allow for the former, and dialing in a consistent glide trim on something this small with no elevator tends to be hit and miss. Hence, I went my own way, and even made kits using the now outdated Artcor material around twenty years ago.

Since you're the guy who did the awesome Double Trouble Shuttle, you should make two 20" discs and parasite them off like a long BT80 rocket. Or, do four discs that size like I did 24 years ago, and all four glided four different ways. Only got one back :blush:

 

[aerostadt]

Since you're the guy who did the awesome Double Trouble Shuttle, you should make two 20" discs and parasite them off like a long BT80 rocket. Or, do four discs that size like I did 24 years ago, and all four glided four different ways. Only got one back :blush:

Mike, thanks for the good words! I am a novice compared to you and Ari. I am sorry to hear about the loss of your models in the 2004 flood. I'm keeping pretty busy with the Trouble Shuttles. I don't think I can handle anymore trouble. Hopefully, you can go back and re-build some of your favorite HPR gliders.

 

[BABAR]

For second flight, I swapped sectional Black Sky rail for one-piece 80/20 1010 rail. The model left the rail, but soon started looping wildly.

Ari.

That's sort of how the original (non-RC) version flew, IIRC :wink:

 

[iter]

That's sort of how the original (non-RC) version flew, IIRC :wink:

Do you remember which way it looped?

Ari.

 

[Mr Rocket]

Very cool project and great pix! Thanks for posting.

I have been thinking about doing a clone of the invader, but the only experience I have with gliders is the Estes Space Shuttle back in the 80's. I don't ever remember a fully successful launch, but I still have it so you never know:wink:

 

[AstronMike]

Very cool project and great pix! Thanks for posting.

I have been thinking about doing a clone of the invader:wink:

The best way to make a good boosting standard sized Invader is to replace the two strakes and motor tube/NC with ONE long strake and place the motor tube/NC atop it. Make the single long strake out of 1/4" by 1/2" balsa, about 7 to 8 inches long (best if you start long and shorten as needed). The motor tube with NC goes onto the end of this, with NO standoff. To allow motor ejection clearance, you just sand behind where the tube is, at least two inches, a little bit.

Real important here: Coat the *top and sides* of this single long strake piece right behind the motor tube, preferably with wood glue, and after it dries, do a second hit to the top. That's going to be charred over time anyways, and when that occurs, you just add another glue layer. Epoxy might be too heavy for this, and not heat resistant enough.

Other big deal: The nose cone. You want the *smallest and lightest* one you can get! The one I have has no more than a little button looking one, and the one from a Yankee would also do. If you want to be real cheap, use an acorn. Seriously, I can't count the gliders of this type I've used 'natural partz' on.

Now for the tricky part: Balancing for glide. By now, you've gotten the motortube/NC glued on one end, with the strake having been coated with a good slathering of wood glue or such, and perhaps a second run over the top side. Hope you sanded the top first, to allow ejecting motor clearance....

Discs like this require a glide CG just over 25% aft of the leading top edge. Usually, it's around 27-28%, and no more than that. Take your completed strake assembly and TAPE it onto your already made dihedralled disc. Start with 2" of strake overlapping the front of the disc first, that's where mine is now, and proved well enough. Test toss it several times until you are sure what it's doing. If you haven't hit the exact glide point, then UNTAPE the strake and SLIGHTLY move it a tad fore or aft until you find a consistent 'looks like it might actually NOT crash' point. Then, glue the strake on at that point.

You may find that after the first flight, it may need a tad of noseweight for trim. Since you've already glued on the strake, what you do is tape something onto the small motor tube or strake upfront. I tend to use paperclips, small or large if need be. Mine, which glides almost too well, has a single large clip taped in this fashion.

Now, what about that confounding boost CG issue, so inherent in the original?? That is NO concern, as the single long strake version has the motor tube much more forward, and the addition of a live motor more than stabilizes things. I suggest B4-2s mainly, as this version is a tad heavier and draggier, and an A8-3 does not go very high and ejects nose down, driving the glider hard downward.

You can find a picture of this version on Chris Michealsson's blog site, from several years ago, I forgot which month though. You ought to build this version, and enjoy it immensely!

 

[iter]

You can find a picture of this version on Chris Michealsson's blog site, from several years ago, I forgot which month though. You ought to build this version, and enjoy it immensely!

Found it! https://modelrocketbuilding.blogspo...launch-february-19-2011.html#SPELLING_ERROR_8

Ari.

 

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As long as I'm Chris's blog looking at your gliders, can you tell us about the materials in this glider: https://modelrocketbuilding.blogspot.com/2012/03/tampa-ttra-launch-march-17-2012.html

Ari.

 

[iter]

Invader crashed today. Last time it did a couple of inside loops with the slight up trim I had in it. Today I dialed neutral trim and it did a half outside loop straight into the ground--off-axis thrust creates a nose-down moment. Motor was still burning when it hit.

I think I'm going to try a different planform configuration on my next glider. I understand Mike's idea of putting the motor further out front. On my R/C gliders, I like to keep the motor win the glider (especially if it's reloadable), which limits rearward CG shift. I might try something wedge-shape like Jet-Freak, where CG is closer to 50% root chord rather than 25% in a disk, which means I can keep everything closer together.

I do like my experience with foamboard. It's surprising to me how much of it survives a crash like this. All of the glue lines held (except dihedral). Servos are still in their bays, elevons are still on their hinges and fins are still on. I'm looking forward to new foamboard gliders.

Ari.

 

[rokitflite]

I might try something wedge-shape like Jet-Freak, where CG is closer to 50% root chord rather than 25% in a disk, which means I can keep everything closer together.

Ari.

Funny, you are doing all the ones I did in the same order :grin:

 

[iter]

What did you end up with?

Ari.

 

[AstronMike]

As long as I'm Chris's blog looking at your gliders, can you tell us about the materials in this glider: https://modelrocketbuilding.blogspot.com/2012/03/tampa-ttra-launch-march-17-2012.html

Ari.

Since the only glider Chris got on his blog from that day was the Maxi Astron SST, I'm guessing *that's* the one you are referring to.

Besides the standard LOC 4" tubing and NC, the wings/tail are made of standard *black* foamboard, two plys, with a coating of thin epoxy on the top surface for a bit of added stiffness. Like I mentioned earlier, two ply standard foamboard is quite sturdy, and the glider you see there in that pic later flew very well on an I284 without a hint of flutter at all and glided *majestically*. Kind of wished that was RC like you do....

How much can that sort of construction really take for boost? Well, back in '94 I flew the original Excelsior, which was about this very size and made from the same stuff, on bigger motors, and soon thereafter on a J415. Yes, a full J, and it held together, although *that flight* fluttered madly. Thing is, though, that glide was made from standard white board, and the main gluing was only wood glue, and the top layer slathering was nothing more than polyester resin with no cloth! That's why it's called *research*, I suppose....

 

[AstronMike]

Invader crashed today. Last time it did a couple of inside loops with the slight up trim I had in it. Today I dialed neutral trim and it did a half outside loop straight into the ground--off-axis thrust creates a nose-down moment. Motor was still burning when it hit.

I think I'm going to try a different planform configuration on my next glider. I understand Mike's idea of putting the motor further out front. On my R/C gliders, I like to keep the motor win the glider (especially if it's reloadable), which limits rearward CG shift. I might try something wedge-shape like Jet-Freak, where CG is closer to 50% root chord rather than 25% in a disk, which means I can keep everything closer together.

I do like my experience with foamboard. It's surprising to me how much of it survives a crash like this. All of the glue lines held (except dihedral). Servos are still in their bays, elevons are still on their hinges and fins are still on. I'm looking forward to new foamboard gliders.

Ari.

Ari, I'm very sorry this happened!! In my old research (there's that term again, for 'AstronMike has NO idea what's gonna happen) with this design, I trod the same path you just did, with the same results, sans RC of course :y: Yea, before I 'figgered out' the boost CG stuff, I nearly took out a 300lb lady some distance away with an F powered version!! Man, did NOT think someone THAT SIZE could move *THAT FAST*!!

Even though this is probably against your grain somewhat, you *could* try to redo this 'sorta' the way I did when I sold kits long ago. Since you want to retain the motor casing onboard, but obviously need the CG assistance, here's what you do:

Keep the motor tube and pylons like you have them now, but make the MMT have an ejecting nose section, replete with needed mass for boost stability, and just let the motor's ejection charge kick that off, leaving you with an open MMT but the CG now rearward. Not sure where your electronics are stored, but you'd have to relocate them to be ondisc instead of inside the MMT.

Even with the added drag of the opened MMT, this still glides well, and if you locate the glide CG at 25% or a *tad forward*, you'd be able to sustain a nice glide with minimal up elevator throughout the glide.

As far as foamboards crash resilience, welllllllll, I *might* have a *bit* of experience with that :blush:

Definitely want to see you have this working, especially with RC.

 

[iter]

Besides the standard LOC 4" tubing and NC, the wings/tail are made of standard *black* foamboard, two plys, with a coating of thin epoxy on the top surface for a bit of added stiffness. Like I mentioned earlier, two ply standard foamboard is quite sturdy, and the glider you see there in that pic later flew very well on an I284 without a hint of flutter at all and glided *majestically*. Kind of wished that was RC like you do....

This is amazing Mike. I keep trying to engineer these gliders for dealing with drag, but your designs remind me that I haven't seen one come apart from aerodynamic forces yet.

Now when you say "two-ply board," do you mean that you take two 1/4" boards and glue them one on top of the other?

Ari.

 

[AstronMike]

This is amazing Mike. I keep trying to engineer these gliders for dealing with drag, but your designs remind me that I haven't seen one come apart from aerodynamic forces yet.

Now when you say "two-ply board," do you mean that you take two 1/4" boards and glue them one on top of the other?

Ari.

Yes, two ply refers to two 3/16" thick sheets glued together, with lots of weight to press them well overnight. That results in a pretty stuff structure.

Good thing you mentioned 'engineering for drag reduction', because that's good thinking, and something I did not do well 20 years ago. That J415 powered Excelsior only had the wing leading edges taped over, leaving them pretty squared, and that is a TON of drag!! Now, you can see that I've chrome-taped rounders over those edges, reducing drag.

I don't go too crazy with such detailing, but yes, if you can reduce drag easily, you've got to do that.

 

[iter]

I realize my sentence is ambiguous. What I mean is that I fret a lot about what might happen to a glider if it gets going too fast; if the drag force is going to tear it apart.

Thank you for clarifying the material note. It's pretty amazing to me that this foam can take these levels of thrust.

Ari.

 

[iter]

I'm growing to like foam board. I like how polyurethane glue, if you mask it right, creates fillets on surface mount joints as it foams. I'm curious to test the limits of foam board construction. I went and built a Baron/Flying Jenny type glider, about the size of my Mega Baron. Shockingly, it weighs 90g comparing to the Baron's 200g (including ~35g R/C gear, so 165g for free flight). One aspect is my use of MD fuselage, omitting CRs, larger nose cone, etc., but that accounts for only part of the weight difference.

I think I'm not going to bother with R/C on this one. I'm pretty sure I know how Barons glide :=) I'm curious what size motor this construction can withstand.

Ari.

 

[AstronMike]

I'm growing to like foam board. I like how polyurethane glue, if you mask it right, creates fillets on surface mount joints as it foams. I'm curious to test the limits of foam board construction. I went and built a Baron/Flying Jenny type glider, about the size of my Mega Baron. Shockingly, it weighs 90g comparing to the Baron's 200g (including ~35g R/C gear, so 165g for free flight). One aspect is my use of MD fuselage, omitting CRs, larger nose cone, etc., but that accounts for only part of the weight difference.

I think I'm not going to bother with R/C on this one. I'm pretty sure I know how Barons glide :=) I'm curious what size motor this construction can withstand.

Ari.

Ok, this is a horse of a different color here. This is not a delta or disc planform, and therefor will NOT be a strong. If you tape and round the LE's of all the wings and stuff you can get by with more speed. One other note: Burnage. Did I neglect to tell you that foamboard products REALLY burn EASILY? If any of the sparks from the motor catch it just right, you recreate the Hindenburg, sans helium of course.

Funny you should make a Jenny type glider. About six years ago, I did likewise, except mine used Readiboard instead (half the weight) and had a 30" span. Called this "Huge Butt Lady". Also, it had a totally different motortube setup with ejectable forward mass section. Flew on the *old* AT E15's okay enough, but was tough to dial in the glide trim, despite getting fabulous test throws. At that size, I think inherent warpages were the culprit, hence, I don't really recommend long span stuff using such material.

Since you're doing the standard 20" span you are fine, and in fact, would do better with Readiboard if you get your grubby mitts on any. I'm still considering an 18mm powered Depron 20" version, since that is ridiculously light, but fragile as well.

 

[iter]

Biplane boxes are inherently very strong. The obvious advantage of a biplane is lower induced drag since wings have lower chord for the same span and area. A more subtle advantage is lower mass per area since the wings act like flanges on a huge I-beam. The disadvantage is higher frontal area and associating parasite drag.

I'm coming to the conclusions that most damage I see in rockets occurs on landing rather than on boost. I have had an M flight come apart on the way up from fin flutter at M.8. I have seen rockets with fins loose from hard landings lose fins on the way up. But mostly I see rockets come apart on hard landings, deployment failures and such. I'm curious about making an MD 29mm rocket and surface-mounting foam-board fins on it. I doubt they would survive a parachute landing, but in my current enthusiasm I'm thinking they are going to stay on just fine as long as I stay subsonic.

Ari.

 

[iter]

Just for kicks, I'm trying to see what a Van Halen-style pattern might look like in foamboard :=) Here, I'm testing on a scrap panel.

 

[iter]

So this happened (on E15)

Glider broke up about 30' off the ground. In the second photo, motor is still going up. You can see the breakup point in the smoke trail--just above the falling debris, it goes from straight to spiral.

Failure mode is interesting and contrary to my expectations. I'm too tired now to photograph the remains, but I learned something about foam board today and want to share with the forum after I get some sleep.

Ari.

 

[AstronMike]

So this happened (on E15)

Glider broke up about 30' off the ground. In the second photo, motor is still going up. You can see the breakup point in the smoke trail--just above the falling debris, it goes from straight to spiral.

Failure mode is interesting and contrary to my expectations. I'm too tired now to photograph the remains, but I learned something about foam board today and want to share with the forum after I get some sleep.

Ari.

Im guessing that it fluttered and failed first along the two 'diagonal' side pieces first. Foamboard has one annoying tendency. If it flutters to a point where it creases, then a foldover/shred is pretty likely. Even if the craft 'holds' through this, I have found that subsequent flights on lower thrust motors still flutter uncomfortably when compared to before hand. Building a Jenny type craft with this stuff is OK for the bi-wing box structure itself, but likely not so much for those critical support sections connecting these to the MMT/NC section. Unless....

YOu said 'E15'. Is this *really* an old *real* E15, or one of the so-called 'relabels' from VR? As you know, those are really E20's, (actually more liek E22), and those kick HARD compared to the original 'softer' E15 which I loved (save for the prices thereof). Note of comparison: I have a Readiboard based Marauder that I flew plenty of times without a hint of flutter on these old motors, no problemo. Once VR then shipping the relabels, that changed mighty fast, as the first one of these I put into the Marauder went up *way faster*, and nearly fluttered itself to death. EVen though it held, it creased too much, and will never fly again. NOt only this, but I built another of the same glider, and even added a bit of reinforcement, and flew this on the 'new E15'. Yep, you guessed it, fluttered like mad and ripped off one panel. Still glided back though, but that was evidence enough. AeroTech is out to get me, since I'm onto 'em for HPR, they sneak in these to catch me off guard :blush:

Now, what you should likely do is remake this, but with Readiboard. Yes, it's weaker yet, but with the massive weight reduction, you'd be able to fly this on a D12 and likely keep it together. Perhaps line the LE of the supports with doweling too. Heck, I might do one too. I'm guessing this the 20" span.

I'm sorry I forgot to point out about this sort of hidden 'gotcha' with foamy products before when I first saw your Jenny pic. I was afraid there'd be an issue with a thrusty AP motor with those support sections.

 

[K'Tesh]

I'm wondering if this idea may help resolve the delaminating issue. Make the leading edge out of balsa (or a light ply), and glue the foam to it.