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Old 02-07-2009, 01:48 AM
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blackshire blackshire is offline
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Default "Boost-Glider Blues" (overcoming them)

Hello All,

I have read several postings on this forum by people who have had great difficulties with getting boost-gliders to fly properly. The common front-motor boost-glider, regardless of whether it ejects only its spent motor or jettisons an entire streamer-recovered (or parachute-recovered) pop-pod, is really nothing more than a conventional HLG (Hand-Launched Glider, also called a "chuck" glider) that is boosted to altitude under rocket power.

For those who have been struggling with boost-gliders: Before trying another one, why not first develop proficiency in building and flying "glued-together" balsa chuck gliders? These most humble of aeromodels can, if built carefully and flown skillfully, fly for miles and climb thousands of feet into the sky with the help of thermals. For many decades, Free Flight (F/F) aeromodelers have held chuck glider competitions that range from informal local affairs to national meets sponsored by national aeromodeling organizations to large international contests that are officially sanctioned by the FAI (Federation Aeronautique Internationale). This British chuck glider web site (see: http://www.f4bscale.worldonline.co.uk/hand.htm ) contains a wealth of information and links about building and flying chuck gliders, including tips for detecting thermals and pointers on effective hand-launching techniques.

As a first step, try a simple and inexpensive "glued-together" balsa chuck glider kit that is similar in size and layout to a typical front-motor boost-glider. The most common such kit is Guillow's 4101 "Goldwing" HLG (see: http://www.guillow.com/GuillowDetai...d=28&FamilyId=1 ). This decades-old classic kit includes clay for trimming the glider, and it often even comes with a tube of balsa-wood model airplane glue. (I use aliphatic resin glue [yellow wood glue, that is] for building chuck gliders [even though it is a little heavier] because it produces stronger balsa-to-balsa bonds than the tube-type balsa model airplane glue. Also, unlike balsa model airplane glue, yellow wood glue has no fumes!) The Goldwing glider is available much more cheaply from many vendors than it is when bought directly from Guillow's, and here are links to just a few:

http://www.alliedhobbies.com/catalo...&showprevnext=1
http://www.rudystoys.com/category.aspx?categoryID=116
http://www.acsupplyco.com/aerospace...wer/gui4101.htm
http://www.hobbypeople.net/gallery/848375.asp

In addition to being a great way to build skill and expertise prior to tackling boost-gliders, building and flying balsa chuck gliders is a lot of fun to do in and of itself!

I hope this information will be helpful.
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Old 02-07-2009, 10:52 AM
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Very helpful! Thanks for posting the links!
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Old 02-07-2009, 12:17 PM
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I modified a Campbell (sp) hand launched glider to fly as a boost glider. Really nice material in the kit. Just have to modify the rudder so it's not in the exhaust plume and added pylon hooks from Apogee. Hand tossing got it pretty well trimmed. But, you never know how well trimmed they are till you actually put one up under boost. Not wanting to loose it, I put it up on a 1/2A....the glider has a large wing span so with the drag I wasn't expecting much altitude. And it didn't. Separation occurred at maybe 50 feet. Started snapping pictures but noticed the glider seemed to be getting smaller. Last I so of it, it was perhaps 1000 feet and down range 1/4 to half a mile. I couldn't climb the fence to keep after it but I figured at the rate it was going, it would land in Arkansas somewhere.......

Here's a link to the vendor and kit.......

http://www.pennvalleyhobbycenter.co...m312maxwell.htm

Of course, they have lots of hand launched gliders that would make great boost gliders.
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Old 02-07-2009, 01:28 PM
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HLG technology has seriously advanced with the "discus" style of launch.

Way back when, you could build your very own simple all-balsa HLG for the price of a sheet of balsa and some nitrate dope (optional, really). The modern kits are significantly more expensive, much larger, fly better, and dethermalize reliably.

For a glimpse into my world, check out Sting Aero Products HLG and DLG . Scroll down to the middle of the page for the Discus Launch kits.

Yes, those kits have up to a 42 inch (!) wingspan and can cost as much as $87.50! But they're made from a bunch of composites and carbon fiber, feature lightweight timers to trigger the dethermalizer, and such.

Back in the day, I used to campaign a 26" HLG with some success. I placed second two years running at the Free Flight Champs in the Dawn HLG Mass Launch. Then the young kids start kicking my butt. Now with the Discus launch, I'm competitive again!

I throw the discus in Masters Track and Field!

PS. Don, I'm still working on the "care package" for you. I'm trying to get up to speed on boost gliders so I can send you "the right stuff".
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Old 02-07-2009, 06:54 PM
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blackshire blackshire is offline
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You all are most welcome! I have seen both the Campbell and Sting Aero Products HLGs (Hand Launched Gliders) online, and that thought (that they could make fine boost-gliders) had crossed my mind as well. When I first heard of the discus HLG launch method some time ago, I thought it was some kind of F/F (Free Flight) aeromodelers' "in-joke"--until I saw photographs of it being done.

Also, this morning I found these downloadable balsa chuck glider plans on the Tom Martin Radio Control (TMRC) web site: www.tmrcsailplanes.com/plans-and-patterns.html

These are classic Jasco, Jetco, and Frank Zaic designs (they're near the bottom of the "screen-page" on the TMRC web site) that people have built and flown for years. Tom Martin also has laser-cut kits of some of these available. The Jetco Thermic 18 and Jetco Thermic B are just like pop-pod front-motor boost-gliders. In fact, you could easily convert these to boost-gliders by adding pop-pod attachment points at their front ends and by moving their vertical stabilizers to the bottom side of their fuselage booms.

Speaking of Frank Zaic, G. Harry Stine made extensive use of the information in Mr. Zaic's book "Circular Airflow and Model Aircraft" (Northridge, California: Model Aeronautical Publications, 1964) to develop his "Stine's Basic Boost-Glider Design Rules" in his "Handbook of Model Rocketry," and Mr. Zaic's book is listed in its bibliography section. In fact, Stine even wrote that "These Design Rules will also produce a very fine chuck glider for hand launching." Stine designed the MPC (now Quest) "Flat Cat" boost-glider kit using these rules.

One thing in particular from Stine's rules that I found very interesting is that (to quote him):

"And it isn't really necessary to use the classic model airplane airfoil that's curved on top and flat on the bottom. A symmetrical airfoil, such as used on [rocket] fins, will glide just as well (and perhaps better since its CP [Center of Pressure] remains at or near the 25 percent chord point [back from the wing's leading edge], whereas the CP of a flat-bottomed or *cambered* classic airfoil moves *forward* with increasing angle of attack, introducing another variable into an already complex system)."

The wings of aerobatic airplanes (both full-scale and models) use symmetrical airfoils because they work just as well when flying inverted (upside-down) as they do when flying rightside-up. Using just a degree or two of nose-up trim with either a fixed horizontal stabilizer or movable elevators is all that is necessary to make a symmetrical airfoil generate lift.

Stine also wrote that both the wings and the horizontal stabilizer of a boost-glider can have zero incidence (having them mounted on the fuselage boom at zero degrees angle of attack, that is) *if* the horizontal stabilizer is located both behind *and* below the wing. This places the horizontal stabilizer in the downwash from the wings (which "fools" the horizontal stabilizer into "thinking" that it is flying at a slightly negative angle of attack). This prevents the boost-glider (in glider mode, after the pop-pod has been jettisoned) from pitching down into the upward-angled relative airflow and diving into the ground, as an ordinary non-gliding model rocket would.
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Last edited by blackshire : 02-07-2009 at 08:43 PM.
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Old 02-07-2009, 08:32 PM
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georgegassaway georgegassaway is offline
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I highly recommend this:

Estes Boost Glider Technical Report, written by Tom Beach (PDF file from Estes Educator website). An excellent article with many illustrations, that cover a wide range of areas involving Boost Gliders and Rocket Gliders, including trimming.

Link to PDF file:
http://www.esteseducator.com/Pdf_files/2266.pdf

G. Harry Stine knew a LOT of great stuff about rockets. Gliders, well, there some good stuff there, but not all 100% accurate.

A zero-zero incidence is something only the best Free-Flight glider fliers are able to pull off. It is way too finicky for the average rocketeer to try to perfect. Heck, I never do zero-zero, I always use a degree or so of incidence. See “Pitch Trim and Stability” on pages 6 thru 8 of the Technical Report by Tom Beach.

And for no airfoil, it can make someone feel good about not going to the trouble, but a glider really needs to at the least have the leading and trailing edges rounded and not left square. If a person wants the glider to perform better, and even have some better pitch stability, then give it something of an airfoil, flat on bottom, rounded near the leading edge, tapered in the back. I do not mean one has to try to achieve a fully curved half-teardrop type of airfoil shape, anything that goes beyond just rounding is better, and rounding is always better than nothing.

Now a few gliders can be left square and at least fly stably anyway (just not as well as they otherwise could fly). Like some of the Edmonds gliders, and the old Centuri Mini-Dactyls and Stine’s Delta-Katt. Note that they all pretty much use some significant incidence, and usually incidence with canards.

Take note that what Zaic was writing about was Free Flight Gliders WITH AIRFOILS, mostly flat bottom Airfoils, which was partly or perhaps totally invalidated by H arry Stine using that to also apply to wings that were symmetrical, and even worse squared off. But even with an ideal flat bottom airfoil, zero-zero is too finicky for less -than-experts to mess around with.

Stine’s Flat Cat, and Renger’s “Falcon” for Estes, both had zero incidence and both were a PITA to trim. My Falcon never did glide down, it glided FINE in hand throws but always death-dived after boost (on the second flight, the death dive was into hard ground and it shattered, game over). The Falcon was my first B/G kit, IIRC, and I did not know enough about gliders then to realize what the problem was. It was because it was zero-zero. And I ran into the same thing with the Flat Cat, but I had learned enough by then to warp the back of the stab up to get some incidence. And the first B/G I designed that flew successfully, it had incidence in the stab too. Maybe one of these days I will get around to cloning a Falcon and THIS time give it the incidence it needs (though just a bit so as not to make it loop on boost).

- George Gassaway

Last edited by georgegassaway : 02-08-2009 at 04:12 PM.
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Old 02-07-2009, 08:59 PM
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blackshire blackshire is offline
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Quote:
Originally Posted by georgegassaway
I highly recommend this:

Estes Boost Glider Technical Report, written by Tom Beach (PDF file from Estes Educator website). An excellent article with many illustrations, that cover a wide range of areas involving Boost Gliders and Rocket Gliders, including trimming.

Link to PDF file:
http://www.esteseducator.com/Pdf_files/2266.pdf

G. Harry Stine knew a LOT of great stuff about rockets. Gliders, well, there some good stuff there, but not all 100% accurate.

A zero-zero incidence is something only the best Free-Flight glider fliers are able to pull off. It is way to finicky for the average rocketeer to try to perfect. Heck, I never do zero-zero, I always use a degree or so of incidence. See “Pitch Trim and Stability” on pages 6 thru 8 of the Technical Report by Tom Beach.

And for no airfoil, it can make someone feel good about not going to the trouble, but a glider really needs to at the least have the leading and trailing edges rounded and not left square. If a person wants the glider to perform better, and even have some better pitch stability, then give it something of an airfoil, flat on bottom, rounded near the leading edge, tapered in the back. I do not mean one has to try to achieve a fully curved half-teardrop type of airfoil shape, anything that goes beyond just rounding is better, and rounding is always better than nothing.

Now a few gliders can be left square and at least fly stably anyway (just not as well as they otherwise could fly). Like some of the Edmonds gliders, and the old Centuri Mini-Dactyls and Stine’s Delta-Katt. Note that they all pretty much use some significant incidence, and usually incidence with canards.

Take note that what Zaic was writing about was Free Flight Gliders WITH AIRFOILS, mostly flat bottom Airfoils, which was partly or perhaps totally invalidated by using wings that were symmetrical, and even worse squared. But even with an ideal flat bottom airfoil, zero-zero is too finicky for less -than-experts to mess around with.

Stine’s Flat Cat, and Renger’s “Falcon” for Estes, both had zero incidence and both were a PITA to trim. My Falcon never did glide down, it glided FINE in hand throws but always death-dived after boost (on the second flight, the death dive was into hard ground and it shattered, game over). The Falcon my first B/G kit, IIRC, and I did not know enough about gliders then to realize what the problem was. It was because it was zero-zero. And I ran into the same thing with the Flat Cat, but I had learned enough by then to warp the back of the stab up to get some incidence. And the first B/G I designed that flew successfully, it had incidence in the stab too. Maybe one of these days I will get around to cloning a Falcon and THIS time give it the positive incidence it needs (though just a bit so as not to make it loop on boost).

- George Gassaway


Thank you for the link! I don't do "zero-zero" either. When my father built the first boost-glider I ever saw fly in person (also an Estes Falcon), he--acting on a hunch--added a thin sheet balsa shim under the rear of the horizontal stabilizer to give it a slight negative incidence. It certainly did the trick, as the Falcon always quickly attained glide attitude after ejection and came down slowly in huge, ~1/8 mile-wide circles.
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Old 02-07-2009, 11:21 PM
shockwaveriderz shockwaveriderz is offline
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The original Larry Renger SkySlash had a pop-elevator that provided negative incidence in the stab. ,The later Estes published SkySlash II, which was the basis for the later Astron Falcon, both were 0-0 negative incidence gliders.

The pop-stab was determined to be too advanced for typical model rocketeers of the time, so it was removed leaving a glider with 0-0 incidence.


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Old 02-13-2009, 05:57 PM
Jeff Walther Jeff Walther is offline
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Quote:
Originally Posted by georgegassaway
Maybe one of these days I will get around to cloning a Falcon and THIS time give it the incidence it needs (though just a bit so as not to make it loop on boost).


Semroc's Hawk is an adaptation--almost a clone--of the Falcon. IIRC, it has a slightly thicker boom.

Alternatively, they sell a laser cut fin set for the Falcon. Either option would make cloning it wildly faster.

Of course, if you enjoy using templates and cutting your own balsa, those options are less attractive.
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Old 02-13-2009, 08:16 PM
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Quote:
Originally Posted by Jeff Walther
Semroc's Hawk is an adaptation--almost a clone--of the Falcon. IIRC, it has a slightly thicker boom.

Alternatively, they sell a laser cut fin set for the Falcon. Either option would make cloning it wildly faster.

Of course, if you enjoy using templates and cutting your own balsa, those options are less attractive.


Semroc's Hawk boost-glider kit is actually a reproduction of the AMROCS Hawk kit. It is very similar to the Estes Falcon, though. The most noticeable difference between the two kits is that the Hawk's motor tube pylon is swept foward rather than rearward as in the Falcon kit.
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