Quantcast

First time boost-glider needs advice

The Rocketry Forum

Help Support The Rocketry Forum:

kruland

Well-Known Member
Joined
Aug 20, 2009
Messages
1,230
Reaction score
1
Hi all,

I'm a BAR who decided to build a boost glider on my first summer back to the sport. I built up the QCR Never Loop I 13mm. I trimmed it out the best I could but it still stalled a little tiny bit. It seemed to be adequate so I loaded it with Estes 1/2A3-4T and hoped for the best!

Well, the flight wasn't all that pretty as I'll describe. The rocket pitched radically into the wind and ended up doing a loop under power. It almost seemed that it was under power as it was flying back to earth. At about 3 feet from certain death, the ejection charge went off, the booster separated and the little glider came squirting out horizontally clipping the tops of the grass! Honestly, I don't know how the glider got off but it did.

The booster boom was stuck into the ground with no damage, any by excited boy ran all of 50' to recover the glider.

All recovered, no damage, all fingers accounted for - must have been a good flight.

So, I really want advice on what went wrong and how to correct it on the next flight.

Looking forward to flying it right next time!

kruland
________
Vaporizer Questions
 
Last edited:

bcanino

Well-Known Member
Joined
Mar 4, 2009
Messages
203
Reaction score
0
Hard to say what caused it without seeing the flight or the glider.

Did it loop in around the wings or did it pitch over on it side?
Did you add a much weight to trim? Where did you attach it?
Did you tilt the launcher about 10 degrees into the wind?

Some things to check:

Make sure the pop pod is tight and no slop in it. You should be able to hold the glider with the pod on it and not have the pod fall off. The pod should be able to come off with the slight push down on the nose.

Is the pod straight in line with the glider bode and is the motor pod parallel with the glider body?

Sight down the body, is the rudder straight in line with the body?

Are the wings and elevator parallel and not slanted?

Here is a link to some instructions for another glider, but it had good information about trim for flight. http://plans.rocketshoppe.com/apogee/Maxima/apoMaxima.htm
 

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,547
Reaction score
390
For a 1/2A Glider you need a 2 second delay.

Of course the time delay would not explain why the flight looped, so something else was off. But it would have ejected 2 seconds earlier and not been that close to the ground at ejection.

You said regardless of the trimming, it always stalled a bit. Makes me wonder if it had a lot more incidence angle in the stabilizer than it needed.

- George Gassaway
 

kruland

Well-Known Member
Joined
Aug 20, 2009
Messages
1,230
Reaction score
1
The glider pitched straight over the wings with no roll.

In order to trim it, I had to shave the boom at the stabilizer. I also added a lot of nose weight. I couldn't trim it with clay alone so I cheated and attached a loop of copper wire in front of the nose. Even after doing this, I still had to wrap it with masking tape 3 or 4 times.

I think this indicates the stab had too much -- oh what's it called -- up force.

The instructions for the kit had me put a shim of balsa (probably 1/16" thick) at the leading edge of the stab. Is this the source of all my troubles.

I did not angle the launcher into the wind. Wind was 5-7mph. My buddy at the launch thought the wind gusted just as it was taking off. He also had a video camera but I don't know if there's any video of it.
________
NO2 VAPORIZER
 
Last edited:

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,547
Reaction score
390
For most gliders, I prefer just a tiny bit of incidence angle in the stabilizer. That is, if one did nothing, the wing and stab would be parallel to each other when glued to a fuselage if the fuselage was rectangular, then the back of the stabilizer would be made to be a little bit higher up than he front of the stabilizer.

Reading that the FRONT of the stab was shimmed about 1/16” under the leading edge, that sounds like way too much.

And, from all that noseweight, you mentioned adding, that was WAY more than a model with a normal amount of incidence angle in the stab should ever need.


I would suggest this: remove the stab. Re-prep the rear of the aft fuselage where the stabilizer is glued, so that the stabilizer will be at almost zero angle to it. But that the rear part of the stabilizer will be just a tiny bit higher than the leading edge of the stabilizer,

If you were building it brand-new, I might even suggest just gluing the stab on flat, then score the last 1/2” of the stab and bend it up about 1/32” of an inch, and add a little bit of glue (like CA) where it is bent to help old that angle.

One other thing I was not clear on. Did the model take off and loop “up” (or on its back) first? If so, then all the above makes total sense and the only issue should be reducing the incidence angle (stab angle to the wing).

But, if it pitched DOWN very badly first, and then once it got some speed it started to pitch UP the other way and do the loop, then something else also was going on. If it did pitch down first, then that could be the wind. Or it could be the pod-to-glider pylon was too tall, or something else.

BTW - there are some tips for Boost Gliders here. Written for “A” sized Boost gliders, but a lot of it applies to other gliders, especially the external links to other sources.

http://homepage.mac.com/georgegassaway/GRP/AOL/GCGassaway/contest/boost_glide.htm

That one was written in 2004 for NARAM-46. It was modified for tips for “D” sized gliders in 2008 (NARAM-50), what is more relevant in your case if there are busted external generic links in the 2004 A Gliders page, the 2008 page for D Gliders may have more up to date links:
http://homepage.mac.com/georgegassaway/GRP/CONTEST/TIPS/N-50/boost_glide.htm

As Bruce Canino indicated, the "Maxima" glider instructions (written by Ed Lacroix when it was an Apogee kit) may be useful, and those are among the links on the glider tips pages above.

Also, very useful for the big picture of all gliders is Tom Beach’s Glider Technical Report on the Estes website, also linked on the above glider tips pages. Well, here is a direct link for Tom's report, you should absolutely download and devour every word and illustration of it so you can get a much better understanding of Rocket Boosted Gliders.

http://www.esteseducator.com/Pdf_files/2266.pdf

If we ever create a permanent "Sticky" for glider resources, THAT should be item # 1 on the list.....

- George Gassaway
 
Last edited:

kruland

Well-Known Member
Joined
Aug 20, 2009
Messages
1,230
Reaction score
1
George, those links are great!

At the advice of others, I cut the stab/rudder from the body and removed the shim. I sanded body and stab and glued it back on. At this time, I can't say if the angle of incidence is any different from the wing.

However, I pulled off quite a bit of nose weight and gave it a toss. It was a beautiful glide all the way across my yard. It did seem to pitch down at the end so it's probably still a little nose heavy.

I'll takes some photos and try to launch it again this weekend.

Kevin
________
AZ-OFFROAD
 
Last edited:

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,547
Reaction score
390
At the advice of others, I cut the stab/rudder from the body and removed the shim. I sanded body and stab and glued it back on. At this time, I can't say if the angle of incidence is any different from the wing.

However, I pulled off quite a bit of nose weight and gave it a toss. It was a beautiful glide all the way across my yard. It did seem to pitch down at the end so it's probably still a little nose heavy.
If you can not see any difference between the angle of the stab and the wing, that might be trouble. If they were perfectly parallel (zero-zero) , then there will be pitch stability issues you will chase but may never pin down.

Indeed the fact the glider seemed good when you threw it and then only at the end did it pitch down, makes me a bit concerned. Although, if you do have the right amount of the incidence that it needs (slightly up elevator effect, instead of zero), then yes, it probably just still had too much noseweight left on it.

Try removing noseweight bit by bit until it stalls too easily ,then put a bit back on. And you might have to put more back on. The idea is to try to get it to settle into a steady glide. Of course the way you throw it will have a great effect on what you see happen, so try to make a straight-ahead level throw at about the speed the glider wants to glide at. Three different not-good throws could show you three different results, so part of the learning game is to figure out how much of what you see is due to the glider trim, and what is due to a poor throw. In other words, a too-fast throw or a throw that is pointed slightly up will make it stall, but that does not necessarily mean it needs more noseweight, but perhaps a better throw.

- George Gassaway
 
Last edited:

powderburner

Well-Known Member
Joined
Jan 18, 2009
Messages
7,356
Reaction score
4
kruland,

What these guys are telling you is true. The glider must be built carefully, and trimmed to glide properly from a hand launch.

And even more fundamental, you must follow the build instructions exactly. If the plans say to use a wedge between the wing root and the body, you have to do exactly as instructed. Ditto for mounting horizontal tails. These alignments are critical to proper boost trim (and to avoid those powered loops), and later in the flight, to proper glide operation.

Same general comment goes for checking wing (and tail) panels for warps. Balsa is good at warping sometimes, other times you can pull a model out of a lake and it's still fine. Select a flat sheet of balsa, cut out parts, and odds are that the parts will warp (well, sometimes it feels that way). Wing alignment must be "true" or you will have problems.

For a straighter launch, you could try a longer/larger boost pod. You may need to build a "trainer" version of the glider with wingtips clipped off (outer 25%?) and with slightly enlarged tail surfaces. It will not glide as well, but it sounds like the "baby step" that is called for in this case is to achieve any sort of glide at all, even a high-sink-rate glide.

If you are just learning about boost-gliders, you might want to back up and try some classics. They might not be competition winners but most of them work reliably, trim easily, and glide decently. I would suggest that you try the old FlatCat design, or the old Estes Falcon, or even the Flying Jenny. These all perform fairly well, even for beginners. From there, you can move on to more aggressive designs.
 

TheAviator

Well-Known Member
Joined
Jan 18, 2009
Messages
829
Reaction score
16
In other words, a too-fast throw or a throw that is pointed slightly up will make it stall, but that does not necessarily mean it needs more noseweight, but perhaps a better throw.

- George Gassaway
George, correct me if I'm wrong, but I find the best way to final trim gliders (after I've got the big balancing work done) is to trim to turn opposite one's handedness (for me, a righty, I trim gliders for a left-hand turn.) Then you give the glider a nice heave with your dominant hand with a 45ish degree bank in the wing and at about a 20 degree up angle. It'll do a large on-handed turn while climbing, and once it stops climbing, it'll settle into a glide with a turn in the off-hand direction, assuming everything is trimmed correctly. This gives you plenty of altitude to determine what needs to be done to the trim and is a readily repeatable toss.
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,212
Reaction score
9
In the only flight so far of my Astron Falcon clone, which I built exactly as instructed, at motor ejection it looked for a second like it had transitioned into a nice flat glide, but then it suddenly dove straight down into the ground. It buried the nose in right up to the joint with the pylon and I had to give it a bit of a tug to extract it. In hand tosses it glides with no additional nose weight needed (when it glides), and depending I guess on how I toss it, it will either pitch up and stall, glide level for about 15-20 feet, or pitch right down into the ground. There is no consistency with that, which I attribute to my hand-tossing technique being not quite up to snuff. I have not trimmed it to make any turn during the glide. I used a lot of care when I sanded the airfoils into the wings when I was building it, and I was rather proud of the fact that when I placed the two wings together at their flat undersides, the airfoils appeared to be perfect mirror images.

Even though I am a huge fan of this type of rocket, I have had very little success myself in building boost gliders that boost and then glide. Either they don't boost or, in the case of my Falcon, they don't glide. I am truly in awe of people who appear to have gotten any kind of handle on this black art. The only success that I have has has been with my Amrocs Wombat clone, which recovers via a steep Space Shuttle-type glide. At least my Wombat seems to travel a little bit farther than it would if it simply followed a ballistic path. That's real progress for me.

MarkII
 

georgegassaway

Lifetime Supporter
TRF Lifetime Supporter
Joined
Jan 18, 2009
Messages
4,547
Reaction score
390
George, correct me if I'm wrong, but I find the best way to final trim gliders (after I've got the big balancing work done) is to trim to turn opposite one's handedness (for me, a righty, I trim gliders for a left-hand turn.) Then you give the glider a nice heave with your dominant hand with a 45ish degree bank in the wing and at about a 20 degree up angle. It'll do a large on-handed turn while climbing, and once it stops climbing, it'll settle into a glide with a turn in the off-hand direction, assuming everything is trimmed correctly. This gives you plenty of altitude to determine what needs to be done to the trim and is a readily repeatable toss.
You are correct. But remember I was talking to a person totally new at this. Need to know how to learn to walk before running, kind of thing.

For a side-arm angled type of hard throw, yes, if you are right handed, meaning it is thrown banked to the right then the glider needs to be trimmed to glide to the left so it will begin to lose that right bank angle and transition into a left glide. And vice-versa for left handed fliers, trim for a right glide. But if a person does not yet know what they are doing with such hard throws, they will likely have it make a very hard crash into the ground and perhaps break, so again I did not want to say anything beyond a gentle level throw.

In the only flight so far of my Astron Falcon clone, which I built exactly as instructed, at motor ejection it looked for a second like it had transitioned into a nice flat glide, but then it suddenly dove straight down into the ground. It buried the nose in right up to the joint with the pylon and I had to give it a bit of a tug to extract it. In hand tosses it glides with no additional nose weight needed (when it glides), and depending I guess on how I toss it, it will either pitch up and stall, glide level for about 15-20 feet, or pitch right down into the ground. There is no consistency with that, which I attribute to my hand-tossing technique being not quite up to snuff. I have not trimmed it to make any turn during the glide. I used a lot of care when I sanded the airfoils into the wings when I was building it, and I was rather proud of the fact that when I placed the two wings together at their flat undersides, the airfoils appeared to be perfect mirror images.
My one and only Falcon, on its one and only flight, about 1970 or so, did that. Although the ground based glide throws seemed OK. But when it flew, after engine ejection, it went into a vertical dive into the ground, and shattered everything. Totaled.

I realized later, once I knew more about gliders, that the stab must have been at zero-zero to the wing. And that is bad-bad. So, warp the trailing edge of the stab up some, does not need to be a lot, but enough to know it is no longer zero. And then you will probably need to add a little bit of noseweight, do so. Then try it. Since the Falcon does not have a pop-pod, so s not as nose-heavy on boost as a pop-pod model, it may pitch up some on the boost that it did not do when you flew it before, but that in part of what you need to do to tame it for glide.

Actually, if indeed it is going to pitch up some on boost, you could try to alleviate that by re-gluing the engine pod on crooked, in the sideways (yaw) axis, by about 3 degrees, maybe even 5 degrees. What that will do is tend to make the engine side-thrust from that 5 degrees to push the nose to one side, which will make the model roll during the boost, and that roll will help to even out any pitching on the boost. Or, simply aim the launch rod into the wind so that the model is nose-down say 20 degrees from vertical when it takes off (belly into the wind), so it will have that extra 20 degrees to pitch upwards. Though that rod angle idea may backfire if the model rolls as it leaves the rod.

Oh, and try it on a small engine first, then if that boosts OK, work your way up to the next engine. And always use a short delay.

- George Gassaway
 
Last edited:

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,212
Reaction score
9
Thank you very much for your advice, George. The field was so soaked from recent rains that my Falcon suffered no damage at all from its death dive. I forgot to mention that I had launched it on a 1/2A3-2T (that I had adapted with a lot of tape so that it fit into the BT-20 pod) because I was trying to get a qualified flight during a little post-NARAM sectional meet that we were having. Much to my great surprise, it did boost straight up, to maybe 80-90 feet. I'm not sure that I can get any warp into the stab because it is pretty stiff, but I'll try.

I'm surprised that Larry Renger didn't put any negative incidence into the stabilizer when he designed the Falcon. But then, maybe he did, but it was a little bit too subtle for a novice like me to notice. :rolleyes:

MarkII
 

TheAviator

Well-Known Member
Joined
Jan 18, 2009
Messages
829
Reaction score
16
I'm not sure that I can get any warp into the stab because it is pretty stiff, but I'll try.

MarkII
If you need to bend really stiff balsa, just wet your finger on a damp cloth or your tongue and rub that into the side that you are bending TOWARDS. Not only will the balsa be slightly softer, the SMALL amount of moisture will warp the wood ever so slightly. Go sparingly on the amount of moisture used.
 

kjohnson

mox nix
Joined
Jan 19, 2009
Messages
1,297
Reaction score
4
I'm surprised that Larry Renger didn't put any negative incidence into the stabilizer when he designed the Falcon. But then, maybe he did, but it was a little bit too subtle for a novice like me to notice.
It's possible he did- but it takes making a good symmetrical airfoil on the stab to get it. It's been a while since I've built one (and yes- my first one did the exact same thing yours and George's heh) but with the stab glued directly to the boom if you just round the leading and trailing edges you end up with a flat mounting. If instead a symmetrical airfoil was used, there would be some built in incedence.

kj
 
Last edited:

kruland

Well-Known Member
Joined
Aug 20, 2009
Messages
1,230
Reaction score
1
What these guys are telling you is true. The glider must be built carefully, and trimmed to glide properly from a hand launch.

And even more fundamental, you must follow the build instructions exactly. If the plans say to use a wedge between the wing root and the body, you have to do exactly as instructed. Ditto for mounting horizontal tails. These alignments are critical to proper boost trim (and to avoid those powered loops), and later in the flight, to proper glide operation.
I hear what you're saying. Perhaps I was too quick to remove the wedge and made a different mistake during construction which required all the nose weight.

At this point I'm happy to launch it, break it, loose it, learn from it, then build some more.

Other than stab incidence, what other construction problems would lead to requiring excessive nose weight?

Having the wing too far forward makes sense. For my build, the wing was as far back as possible because the top of the body is carved away at the tail.

I guess "excessive" is a judgement I'm not fit to make yet either. I believed the weight in my case was excessive because it required all the clay provided in the kit.

What behavior will the glider exhibit when there's no stab incidence (parallel to wing). It's something with pitch stability, but what would I see -- diving out of control? Unable to recover from loop? Bad boost behavior?

Granted QCR kits contain limited instructions so perhaps this is the wrong first kit. So, lets pick out my second kit! The Flat Cat looks nice, but it seems rather large for my field. Is there a good "beginner" boost glider which flies on 1/2A or A (13 or 18mm, I don't care)?

Again, thanks for the advice.
________
No2 Vaporizer
 
Last edited:

kjohnson

mox nix
Joined
Jan 19, 2009
Messages
1,297
Reaction score
4
I think most of the gliders out there in the form of kits aren't the best for learning the basics. The exceptions might be the Flat Cat, Semroc's version of the Swift BG, and the Edmonds/Contest Craft IVEE2g (my personal favorite glider kit).

You can get the IVEE2g from Balsa Machining Service fro $9.99 and a larger version suited to B motors for $20.00.

I built a lot of my first gliders from plans, then started from there and built my own. A good deal of info about building and trimming catapult gliders can translate into boost gliders directly.

kj
 

TheAviator

Well-Known Member
Joined
Jan 18, 2009
Messages
829
Reaction score
16
I hear what you're saying. Perhaps I was too quick to remove the wedge and made a different mistake during construction which required all the nose weight.

At this point I'm happy to launch it, break it, loose it, learn from it, then build some more.

Other than stab incidence, what other construction problems would lead to requiring excessive nose weight?

Having the wing too far forward makes sense. For my build, the wing was as far back as possible because the top of the body is carved away at the tail.

I guess "excessive" is a judgement I'm not fit to make yet either. I believed the weight in my case was excessive because it required all the clay provided in the kit.

What behavior will the glider exhibit when there's no stab incidence (parallel to wing). It's something with pitch stability, but what would I see -- diving out of control? Unable to recover from loop? Bad boost behavior?

Granted QCR kits contain limited instructions so perhaps this is the wrong first kit. So, lets pick out my second kit! The Flat Cat looks nice, but it seems rather large for my field. Is there a good "beginner" boost glider which flies on 1/2A or A (13 or 18mm, I don't care)?

Again, thanks for the advice.
My first BG experience was two QCR Never Loops (whatever the 1/2A and A version is). I did find that they were indeed very tail heavy.

No stab incidence could cause the glider to have very poor "pull out" characteristics. With a small glider like the A-sized Never Loop, it could take as little as a 1/64" Ply shim to get the proper incidence. Theoretically, though zero-zero would give you good boost characteristics.

One final thing that I would try (if you don't get success other ways) is to get a piece of tube and add it to your pop-pod. This will bring the boost CG farther forward without affecting the glider characteristics.

If you don't have anybody at your local launches that has experience, ask the local hobby shop owner if there are any "free flight" guys in the area. They won't be able to help you with the boost portion, but they can most certainly help you with the gliding portion. And certainly a good arm toss is a lot cheaper than a rocket motor!
 

MarkII

Well-Known Member
Joined
Jan 18, 2009
Messages
8,212
Reaction score
9
It's possible he did- but it takes making a good symmetrical airfoil on the stab to get it. It's been a while since I've built one (and yes- my first one did the exact same thing yours and George's heh) but with the stab glued directly to the boom if you just round the leading and trailing edges you end up with a flat mounting. If instead a symmetrical airfoil was used, there would be some built in incedence.

kj
I didn't put any airfoil into the stab because there was nothing in the Falcon's instructions that told me to do so. In order to get the trailing edge of the stab to warp upward. I had to take a razor saw and cut ~0.25" slots in the seams on either side of where it was glued to the fuselage and to each of the winglets. I cut at each seam, going forward from the trailing edge. The stab was too well reinforced and stiffened by being attached at those points to bend otherwise. After I did that, I attampted to bend the now-freed trailing edges upward, and managed to crack the balsa on each side of the fuselage. So I cut chord-length lateral slits on the bottom of the stab with my X-Acto knife at the points where I wanted the trailing edges to bend, then bent the edges and applied CA to them in order to affix them in the desired position. I bent them up far enough for the trailing edges to be even with the top bar of the fuselage instead of being beneath it. It isn't elegant or pretty (and certainly not smooth anymore), but I hope it is effective. I gave the Falcon one quick toss out in the backyard immediately before I had to leave to go out of town for the day. (I just returned home not too long ago.) It pitched up and stalled, so I may now need to add some weight to the nose. One small wood screw turned into the base of the nose cone might be enough for that, I hope. Gee it would be great if the thing could consistently go into a glide now when I hand-tossed it. I am cautiously hopeful.

This was a pretty glider before I started messing with the stab. Not anymore, though. But at least now maybe it will be able to pull out of death dives. Unless I totally screwed up what had previously been a nice piece of handiwork.

MarkII
 
Last edited:

Zack Lau

Well-Known Member
Joined
Feb 13, 2009
Messages
538
Reaction score
0
The Ivee2g has great instructions for learning about building and trimming gliders. Sticking with 1/2A3-2Ts is a good idea--a smaller glider takes significantly less time to sand a good airfoil than a bigger one. You might even consider buying a couple of kits and a digital scale that goes down to 0.01g--this will let you sort out the wood--you want to group the light pieces of wood together for the last one you build and start off with heavy wood that won't glide as well, no matter what you do. You can even mismatch wing section weights to automatically put in a turn.

At first, you should learn the basics of trimming a glider, and not worry about what it looks like or how much it weighs. If it needs lots of nose weight thats the way it is--add the weight! Only once you have gotten the hang of it should you try to build that contest glider that will glide forever...
 
Top