Yeah, my first one was pretty impressive until I got greedy and painted it. The next flight was a power-prang that I swear never cleared 12 feet. Literally made balsa shards out of the two engine tube pylons. I sanded thapaint off and fixed the pylons and it flew fine until it caught a power line up in Akron. (The only wire on the field.)

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Bill Eichelberger
NAR 79563

http://wallyum.blogspot.com/

I miss being SAM 0058

Build floor: Estes - Low Boom SST Semroc - Marauder, Shrike, SST Shuttle

In paint: Canaroc - Starfighter Scorpion Centuri - Mini Dactyl Estes - F-22 Air Superiority Fighter, Multi-Roc, Solar Sailer II, Xarconian Cruiser Semroc - Cyber III

Ready to fly: Estes - Solar Sailer II Semroc - Earmark

My problem was definitely a pitch forward and not a back flip.

It made a half circle and buried itself in the ground with the bottom of the saucer pointed directly at the launch rod.

If it had been a back flip, the top of the saucer would have been pointed at the rod.

Since the pod broke loose, I guess I can experiment with changing the thrust angle.

Well here's my little Sunday post-flight report - or post-mortem, actually.

After all my ponderous lecturing yesterday, it was time to put my theorizing to the test.

Let's just say the my Invader #2 found every way it could to get to the ground fast while under power.

After three flights today, the final score was: 2 back flips and 1 forward prang. With the starting degree of difficulty, that definitely put me in the gold (fool's gold, that is). Oh, and another destroyed Invader to add to my collection.

I don't need to go into every last detail - you all know how these flights go - so I'll just hit the highlights. First flight was on a B4-2. It was the first time I ever tried to fly an Invader on a B. But last weekend's flights were so low and sluggish that I thought I'd give it a try. Off a vertical launch rod, it back flipped and buried it's nose into the soft ground as far as it could. The motor pylon stopped it from boring its way any further into the ground, otherwise the next time I might have seen it would have been tonight on TV, as it burst through the midfield in the Bird's Nest Stadium.

Hmmm - too much motor, I thought.

Second flight was on an A8-3. Last weekend, the Invader struggled to get up to about 60 feet in altitude off a vertical rod on this motor, before nosing over and flying horizontally for a short ways, and finishing with what will turn out to be the only decent glide I will ever get out of this particular build (about 6-8 secs. duration). Not this time, though. With the launch rod angled a few degrees into the very light wind, it did another back flip into the ground.

Prior to each of these flights, I had done some hand tosses to adjust the clay blob under the tail. When I tossed it around it in preparation for its last flight, I noticed that it was making a funny sound when it hit the ground. It turned out that the motor mount had developed a small break along the glue seam where the right pylon was glued to the wing. Still, the mount seemed to be secure, and besides, I didn't have any CA with me. So against my better judgment, I decided to try to put it up one more time.

I loaded it with another A8-3 (I hadn't brought any 1/2A's with me to the field), and leaned the launch rod heavily into the wind. Thiis time, it did a forward prang. When I dug the Invader out of the ground, I could see that the motor mount was now just barely hanging on. When I jiggled it a little to see how much of the two pylons' seams were still bonded to the wing, the mount simply broke away, taking a bit of the wing with it.

I really thought that I had finally figured this thing out, but obviously I had not. I had built it with an inclined motor, as Craig advised. I had given it MANY test tosses in order to nail the trim balance. I had carefully watched it during dozens of test tosses and had finally identified a secondary source of imbalance, which I thought that I had remedied. And finally last weekend, on a day that was much windier than today, I had actually gotten two non-prang flights, one of which could even arguably have been called a glide. But in the end, I had exactly the same results as I had with my first Invader last year, which was built much heavier and much more crudely.

I'm still not giving up on the idea that the Invader needs a little bit of tail weight in addition to the nose weight, but I have to admit that I still really have no idea what it is going to take to get this design to boost and then glide.

Very, very discouraged.

Mark \\.

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SAM # 0011

Back when I used to fly stuff this small, I made a number of balsa based Invaders similar to the old kit. I did however make some important mods that made it boost and glide MUCH more reliably.

First, I did make a bit more dihedral while keeping the pylon height the same. This meant that the two pylon supports were now spread a bit more than the standard 90 degrees.

Second, I made some versions using a single rudder mounted on the aft centerline. Even though I did get some good stuff out of the standard two strake types I felt this was more reliable to trim and glide without it attempting to glide inverted.

Third, and most important, was that I made the two motor tube pylons at least TWICE as long and therefore had the BT/NC more forward. This pretty much cut down on the needed nose weight that the standards needed (arent most of you ending up adding seemingly a lot?).

Well, if you make those balsa pylons longer, that also weakens them. I got around that by just coating them with thin epoxy or an overall slathering of wood glue. You do end up charring the upper edge of those over time but they hold just fine.

The main reason this helps the boost so well is that with the motor more forward, it has a greater ballast effect (moment arm) and brings the boost CG up, which this design BADLY NEEDS. A glider that has very low stability in the pitch axis will do just that, pitch on boost, usually DOWN. With the CG correct, these boost straight and coast well.

Finally, do NOT do any finishing on that disk in terms of sealing/paint. Do rub down some glue and spread it out where the motor exhaust will hit (which isnt much on the disk if you use the longer strakes above). Weight on THIS design at such a small size is a KILLER, and since anything adding weight on the disk drags the CG back, that is doubly bad.

Glide trim is a bit touchy in terms of hand tosses. Usually, if it looks good itll probably stall or worse in flight. Trim it for a tad nose down test tossing until NO stall is evident. Then fly it a few times to dial it in.

Even though I basically quit small balsa based gliders, I may have to revisit this as it was a consistent pleaser, and I even quit using a lug, just slid the thing over a 1/4" rod and had at it.

Personally, the only way that I can see a standard Invader working correctly is if you either had very light wood or quite a bit of nose weight since the MT/NC is not forward enough.

BTW one of my last HPR gliders back in 97 was a disk type but with the MT kept and a heavy section above it ejected. This worked well on a J motor, returning back with just a touch of stall into the wind. Test tossing THAT was NO picnic!!

What is it about the Astron Invader? Despite its sketchy history as a kit, and with so many other BG designs to choose from, why do so many people, including me, spend so much time and effort, and burn so much balsa and brain tissue, trying to make this one design fly? Maybe it is the look; the Invader's profile, with its twin large top-mounted rudders and its hood ornament-style motor mount, just screams 1959 Cadillac. It's a look that still stirs the souls of many of us who are of a certain age; it was Vern Estes channelling Harley Earl. And that's another reason: it was designed by Vern Estes himself, and it came with the label of "Astron," both of which signify quality to us old BARs. For those of us who got their start in model rocketry with the early- and mid-1960's Estes Industries catalogs, this was one of the very first boost glider designs that we ever saw, and therefore, it is iconic. The design also dovetailed nicely with a couple of cultural phenomena from that time: the late '50's-early '60's UFO craze, and the 1960's emergence of that enduring pop icon, the Frisbee flying disk. Even though the Frisbee flies on an entirely different aerodynamic principle, the fact that the Invader has a disk shape means that, to at least some of us, it just has to be able to fly, somehow, right? Finally, the fact that it is one of the simplest boost glider designs to build, with no moving parts and no airfoils to laboriously sand in, means that we can just keep making prototype after prototype in search of that elusive goal of "getting it right."

Thanks, Astron Mike, for your very helpful tips. Your advice, along with that from Craig McGraw and Bill E., has given me new hope that one day I will actually see one of these gliders actually glide. Maybe even with Invader #3. Anyway, I've often thought about upscaling the Invader, once I've gotten one to actually fly, of course. But you flew one on a J?!?!?! How honking big was that?

Mark \\.

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SAM # 0011

Mark:

Reading your post-mortem, one thing kind of leaps to mind, based on my extensive adventures in flying PMC jets in interesting winds. You mentioned you angled the rod into the wind--bad idea. For anything that wants to fly like a plan, not a rocket, you want to angle down wind with the rod, and in particular, you want to make sure the "cockpit" or top of the glider is catching all the wind, and the bottom/underside is sheltered from the wind. This will help manage the natural tendency to pitch up and tends to promote a more vertical boost.

I do like Astron Mike's suggestion of longer pod legs, though in my case I think I'll simply move the motor tube about 1/4-1/2" forward and add the 1-2 degrees of incidence so I can take away some of that nose weght and maybe get back down under an ounce. I'm at 1.14 ounces now (without motor).

Another bit of historical significance: the Invader was the first Estes kit to ever be "discontinued", in the 1970 catalog (the first one with the Damon logo).

Chan -

In the two back flips, my Invader arced downwind; that is, the bottom of the glider faced the wind as it left the rod each time, and it arced over backwards and impacted downwind from the launcher. In the first launch, I set the rod to vertical, and in the second, I inclined it very slightly into the wind (no more than 5 degrees). There were only some very light and intermittent breezes out on the field on Sunday (3-5 mph, barely rustling the leaves). They were mild and infrequent enough that I didn't have to hold the countdown to wait for a lull. That's one of the ironies; when I launched it on the previous weekend, it flew much better (well, it actually flew, anyway) in two launches despite having to fly in much gustier conditions (5 to 10 mph steady, and closer to 10 most of the time, with 15 to 20 mph gusts). I did wait for lulls before launching on that day, of course. But I see your point about how the very slight wind could have helped to flip the Invader upside down as it left the rod, and I realize now that if I had angled it away from the wind, the light breeze might have actually helped to keep it flying. I'm kicking myself now about making such a stupid mistake, which I chalk up to inexperience with flying gliders (I've only flown the two Invaders and one other glider).

On the third prang, I angled the launch rod well into the breeze, but my intention was to "angle the arc" so that the glider would pull out of it and fly level before impacting the ground. Writing this now, I cannot for the life of me imagine why I thought that it could possibly work out that way. Maybe if I was launching it on a 1/4A, but I'm not sure even then. When I prep for my next trip to the launch field, I'll have to remember to check my range box to make sure I packed my brain.

BTW, Bob, I think the Astron Invader was canceled after only one year. It only appeared in the "1965" (released in 1966*) Estes catalog. I did see it in sale flyers from Estes when I got started in model rocketry in 1967 and for a couple of years afterwards, though.

Mark \\.


*To my fellow YORF members: SEE!?! Estes has released the catalog late BEFORE!!!

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SAM # 0011

Mark,

Any rocket prone to weather cocking should be launched with the wind if you are looking for a high, straight launch and don't mind a long walk (assuming a rocket with some umph). Launching into the wind will provide a lower launch and maybe even a prang. Not to mention some excitement

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Don
NAR 53455
"Carpe Diem"

Mine was oriented the same way and pitched over forward. There was very little wind that day and I don't remember if the rod was angled any.

If you try and launch it with the top side facing the wind, the force of the wind on the saucer will cause the launch lug to bind. Hmmm, I wonder how I know that. I intend to add a small piece of launch lug further down in the vee of the saucer to correct that problem.