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Dec 16, 2019, 08:52 AM
AndyKunz's Avatar
Wow, if you can't make those fly you've got problems! All three fly well if you follow the instructions.

Andy
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Dec 16, 2019, 02:10 PM
B for Bruce
BMatthews's Avatar
Other than the fins being missing on two of them why do you think they are display only? Those should fly just fine with a little trimming. Keep in mind that with free flight like this you still need to "pilot" the models. It's just that you do all the piloting as small trim and balance changes before you launch them. They seldom fly well right off the bat.

The friction fits rapidly wear loose. So some trimming then glue the parts together aids with their longivity and consistent flying.
Dec 16, 2019, 11:21 PM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
Thread OP
I'm confused... Perhaps due to my own posts (the three models were removed from floorboards and trunks of vehicles, after kid's/my interest was lost...of silly store bought planes)

I posted a picture to mock the current unflyable Jetfire and what used to be called a Jetstream, which were bought for over $30 at a non-hobby-store with non-restrained, non-hobby kids pawing the packages.... Not to mention the rubber was old and cracked and didn't even stand up to 150 turns.

I saw a Youtube video from Indonesia showing pre-sanded airfoils and I stopped there and ordered 12 for under the price of 3 flat-sheet-balsa garbage, so...
Dec 17, 2019, 12:42 AM
B for Bruce
BMatthews's Avatar
Well OK... With THAT story yeah, they were junk. And you got taken to the cleaners on them by your enthused progeny... But hey, at least they were enthused about them.

I hope the wood in the dozen pack is decent stuff. I've seen small gliders like this built from balsa wood so heavy that could be used for framing a house. The gliders didn't fly worth a hoot as a result. So I'm keeping my fingers crossed in hope for you and the young'uns.

If the wood is even half way suitable it'll still be a great bargain.

And in anticipation here's a write up I did some time back for the folks in the free flight section on how to get contest performance from their cheap and easy catapult gliders. Maybe make a set of one each to start and try modifying one with the instructions below to "twist" the things around to make them trim out for a more contest like performance. Just don't complain when they hook a passing thermal and go away...

_____________________________
Building and Trimming Free Flight Hand and Catapult Launched Gliders - Bruce Matthews

The flight trimming for hand launch FF gliders starts on the building board.

If you're right handed you want the model to circle to the left in the glide. To achieve that with only adjustments to the fin means that there will be much too much turn in the launch. To get around this it's normal to use some stabilizer tilt to provide some left turn. This means you want the left side stab tip to be about 1/4 inch high compared to the center line. Reverse everything if you're left handed and will be going for right hand circles.

To aid in smoother recoveries from stalls you want a little bit of washin on the left hand wing tip. I used to warp some into the wood but now I "toe in" the outer dihedral break on the left side by 3/32 inch over a 4 inch chord. Tapered wings with smaller chords at the tip break would be angled appropriately less. I know this sounds odd since the washin at the tip is fighting the rudder. But trust me. Having the model set up so the turn fights the washin is what aids in avoiding those frustrating never ending series of stalls that never seem to damp out. Models set up with a touch of washout will settle back down a lot nicer and with a more rearward CG than "straight" models. If the wings are simple V dihedral then make the center line joint skew to the right at the leading edge by 1/16 inch over 4 inches of chord, or some scaled down amount for smaller chords, so you can glue the wing on straight across but still have a touch of washin on the left side and a touch of washout on the right.

Now to the flying field.

To avoid the looping over and hitting your self in the back of the head or having it gyrate around uselessly and stalling a few times before settling into a glide you need to trim the model to find the most rearward CG location that will still give you just a little bit of pitch stability. I know it seems odd but the best way to avoid these typical problems is to trim the model so that it is LESS strongly pitch stable. To fly their best and trim out the most easily it's pretty common that free flight models need to be set up with their balance point really far back and on the edge of being almost but not quite being unstable. Models set up this way handle the dynamics of the powered or climb portions of their flight with more control, a smoother overall climb pattern, gain more altitude and have a smoother transition to the glide..

To test this you're going to do two types of test gliding. The first is to adjust the stab warps by breathing on the balsa and curling it slightly to achieve a nice slow and floaty glide with no signs of any stalling. The second is a "pitch stability" test toss where you push it slightly faster and slightly down towards a point about 25 to 30 feet ahead. This faster test glide should show a mild but still noticeable pitch up to a mild stall. Don't worry that it won't recover to a glide from such a test glide. You're just looking to be sure that it's still stable. Keep moving the CG back a bit at a time and retrim for a nice stable glide then do the stability test. When it won't raise the nose up to a mild stall before it hits the ground when aimed about 25 feet away you know you went too far. So move the balance back forward to the last test point and retrim the stab warping to get a nice slow and stable glide. You should also be looking for signs that the model is turning to the left during this test gliding. It won't turn much but you should see definite signs of it beginning to come around to the left. Add some left fin warp to where you're seeing that it's beginning to set up for such a turn.

Now it's time for the launching tests. Start with a fairly shallow angle and half power throws or catapult releases. For these you'll want more of an over the shoulder toss or a level wings release since it's not going to go far enough "under power" to really arc around. So more of a level wings and nose up at around 30 degrees is suitable. What you're looking for during this is that the rudder isn't so effective that it's over rolling the nose and making the model roll too far in the climb. Ideally you want the model to roll and turn in the climb about a third to quarter turn and be left hanging with the left wing low and almost no airspeed. The glider should then roll down into the glide and continue away. Play with the fin warping until you get this. In the longer glide that comes from this higher launch watch for signs of stalling or for the turn to get too tight and want to spiral in with a "death spiral". The glide turn should be roughly 30 to 50 feet in size. I like to aim for around 30 to 40 myself but remember that you're playing off the stab tilt and fin where the fin adjustment is used for the climb. And the climb takes priority in the fin adjustments.

If you're getting promising results from the low power testing then it's time to wind up more. You'll need to play with just where you and the model want to hold your arm by altering where the throw occurs between the "over the shoulder" and "sidearm" throwing. For a catapult model you're looking at full on side arm pull to stretch the rubber the most and you want to angle and bank the model to around 45 degrees up and roughly 45 degrees bank. Alter this as needed to where the model runs out of inertia up top with the correct attitude for the transition. Models with a strong rolling action in the climb can be thrown or released banked strongly to the "sidearm" position. Others with less rolling action in the climb will need something up more towards "over the shoulder". Some minor tweaking of the fin can add to or take away some of the rolling/turning in the climb. A little goes a LONG way so go easy.

When it's all working well you'll see the model arc up in an S curve to the right then roll over to the left. The model will end up somewhere overhead and over to the left having performed somewhere around a 120 to 200 degree turn during the climb. Ideally it'll end up slightly nose high and strongly banked with left wing low. As the speed bleeds off it should transition smoothly into the glide with little or no stalling by rolling down into the low wing and leveling up and just go into a nice glide circle.

From there if you did your job right and found it some buoyant air the model will begin circling upwards. When you get a little better at picking the air you'll understand why so many folks are adding DT systems to chuck gliders.
Dec 17, 2019, 06:03 AM
Registered User
rchopper56's Avatar

Boomerang


Just sent this one to OZ
Wing span: 20"
Wing span with dihedral: 19"
Stick and tissue wing construction.
Has dethermalizer.
Dec 17, 2019, 02:22 PM
B for Bruce
BMatthews's Avatar
I built one of those Boomerangs back when I was a pimply faced teen! At the time I knew so little about thermals that I didn't bother with the DT.

Phil Hainer must have later moved up to the Seattle area at some point in the 60's. He was a regular flyer at the FF contests in the Seattle area before I went to eastern Canada in 1980 and was still flying there when I came back in the late 80's. As was his son.
Jan 14, 2020, 10:21 PM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
Thread OP
All in all, these are decent kits, except for the ridiculous skewer sticks for the fuselage. Grocery store skewers are straighter!
A scrap piece of carbon fiber is perfectly straight and can be reused after wrecking the rest.

But included is 1oz of fast cure CA!
The airfoil is primitive, but sanding is clearly an option.


$20 for 12 kits, plus $20 shipping from Indonesia
Last edited by cityevader; Jan 14, 2020 at 10:32 PM.
Jan 14, 2020, 11:59 PM
B for Bruce
BMatthews's Avatar
You did well to swap the bamboo for carbon.

Looking at the full size close up of the first picture I can suggest that you'd save a heap of weight by being more aggressive with the wing airfoil shaping. You can go a lot thinner and remove wood further back on the leading edge and go really crazy on the trailing edge. I tend to aim for removing about 35 to 40% of the wood even if the wing is only made from 1/8 sheet. I take the leading edges down to around 1/32 to 3/64 thick then lightly round them and the arc off this small diameter nose extends back about 5/8 to 3/4 inch. And for the trailing edge I remove wood over about 1 1/4 to 1 1/2" and take the trailing edge down to about 1/64" or roughly the thickness of a business card.

When we remove the wood this aggressively it'll start to curl and go wavy if we use too much pressure. So good fresh free cutting sandpaper is a must and use light pressure letting the grit rip the wood away. I start with a razor plane. But if you don't have one of those go with fresh 80 grit paper and get the bulk removed. Then switch to 100 or 120 and fine tune and work down close to the final shaping. Then 220 to 240 to finish and smoothen. Through all of this sanding keep the pressure on the block quite low. If you do so the wings will stay flat. But start pressing too hard and the thin edges start to curl or go wavy.

You can also sand a slight lifting airfoil into the stabilizer. It'll save weight again as well as it'll aid in limiting the looping effect during the high speed of the launch. the fin can also get given an airfoil shape. If you're launching right handed sand the camber into the right hand side for a left turn. If launching to the right switch that.

It's almost impossible to have too much dihedral on these things. You don't need it for the launch or the glide. But it plays an important part during the transition from launch to glide. So what I see looks just fine.

For the next one you can start to gild the lily. These models fly in a fixed manner. So it's OK and even wise to build in some offsets. Namely for a right hand launch and left hand glide circle you want to toe in the left hand wing tip dihedral joint by about 1/16 to 3/32" so the left hand tip has a touch of washin given to it by the angled joint and dihedral combination. At the same time you don't want all the left turn to come from fin warping. That would be too much and it would mess up the launch. So you want to tilt the stabilizer mounting so the left tip is about 3/16 to 1/4" higher than the center joint.

Do this and get the launch trim dialed in for good launches with nice transitions to a stall free glide and then you'll really get to know what these things can do. And don't be surprised when one or two of then hook thermals and fly away on you.
Jan 15, 2020, 10:37 AM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
Thread OP
Everything is pre-shaped. At first, they are un-modified aside from the skewer... I'll sand the next one.

The center wing comes as one piece... The first one was built flat with only wingtips up at the (low) existing angle. Even with issues, it flew better than those silly Jet Fires.

Then i found instructions in the box and built the above #2, yet to be flown.

Each later version will get better.
Jan 15, 2020, 12:14 PM
B for Bruce
BMatthews's Avatar
Quote:
….Each later version will get better.
And that's certainly part of the fun!

Given the materials (bamboo stick for fuselage boom) and cost I suspect that these kit bundles were produced by some ma and pa outfit that likely hires the local kids. The pre shaping I see in your picture isn't much more than dubbing off the corners. Weight is very important on these small catapult launch gliders. The less they are the better. And the biggest part is the wing. So the better it is shaped with more airfoil shaping to remove the excess weight the better they will fly. Likely when you start removing the excess for the first one or two to get this extra shaping when you think you went too far likely it'll be just right...
Jan 19, 2020, 09:46 PM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
Thread OP
While i haven't flight-balanced the CF boom plane yet, it required 50% more nose weight, so of course i made another.

This one had a really straight (and lighter than CF) skewer boom, and with sanding of the wing to a more airfoil shape, and more taper/thinning of the tail feathers (and a bit of an airfoil to the stab) it is 13.5g vs the CF boom at 19.7g.

This new one has left wingtip toe-in, the stab is tilted, and a tiny bit of left rudder (which was a mistake while gluing, but hopefully not too detrimental.)

I've never looked forward to tossing up a woodie free flight until now.
Jan 20, 2020, 02:08 PM
B for Bruce
BMatthews's Avatar
Zooming in on the big version of the first picture shows a really nice job of shaping the airfoil. You likely got the lion's share of your weight loss right there. And at a bit under 14 grams I'd say you're getting down to a pretty good "fighting weight". I would not be at all unhappy with that design at that weight for my own contest flying. With a bit of trimming that should certainly be thermal worthy.

On the other hand the first one at 19.7 is going to have a fairly fast and determined glide. It won't fall out of the air but it won't have the same light and buoyant look in the glide to your second one. I'm sure this will show up once you get to fly the two side by side.

Fair warning on the fin angle of the second pic. When launched with the rubber band catapult it's liable to be enough to do a barrel roll during the launch. But try it before you consider cutting it off and aligning it differently. It doesn't take much to kick them around in the launch due to the extra speed. On the other hand it might be just fine with hand tossing it around the yard or local playground. Or with lighter rubber band size "arm saver" rubber catapults.

If the tail surfaces are made from 1/16 as I suspect from the pictures don't be shy about sanding them down to save a little at the tail. For the fin you can easily get by with 1/32 and for the stab go for a upward lifting airfoil shape but taper it heavily towards 1/32 at the tips. A quarter gram of lightness at the tail will mean 3/4 of a gram less needed on the nose.

If you have a table saw or someone you know has one shop around the local suppliers for a piece of nice tight grained pine. Something with at least 16 growth rings per inch when looking at the end grain. They are rare but with a bit of patience they do turn up if you shop around. The board can be ripped down to 3/4 tall by 3/16 wide strips and those strips used to make your own fuselages. The result can be a lot stiffer than the bamboo and only a touch heavier. Not as stiff but then not as heavy either as the carbon. Something to keep in mind for later on. But if you keep your eyes open for suitable wood now you'll be ready later.

That same board can also serve well as spar stock in place of spruce for a lot of uses. Or as longeron stock on some really big built up old timer.
Jan 20, 2020, 09:18 PM
IT'S NOSE HEAVY!!!!
cityevader's Avatar
Thread OP
That fin angle should be taken with a grain of salt, as the bamboo skewer isn't perfect either.
When sighted down the length of the plane, it is aimed at about 1/4" out from the point of the nose.
I imagine a heat gun and mild pressure might get it more inline?

I guarantee that my boy will prefer a barrel rolling plane anyhow, haha.
Oh, and these are hand launched, not catapult.

I got my boy a dartboard for Christmas, because i constantly tell him to toss something "like a dart" and not like a baseball..... He now throws darts like a baseball. Sigh...
Jan 21, 2020, 01:45 AM
B for Bruce
BMatthews's Avatar
If it's a young lad that would get fun out of the launch time antics then you might try the Backyard Jet in my blog. I've flown the one shown outside one time and it does tend to flt around in corkscrew paths and loops depending on settings warped into the wing and fin. Two or three #32 rubber bands threaded through each other to link them into one long catapult launcher works like a charm.

https://www.rcgroups.com/forums/show...Garden-Gliders
Jan 21, 2020, 09:21 AM
Registered User
Nice tutorial here, Bruce, and I like the Garden Glider too.

Jim


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