I wish I knew now what I'm likely to know in a few weeks but learning is half the fun right?
I've been having a great time with a trio of recently built 36" tow line gliders. A larger RC model that could be flown in the same small field, handle light wind and intentionally thermal has some appeal.
The first iteration is being kept light. Rudder and elevator using a receiver with built in linear servos and minimal wing reinforcement. If it works well and demonstrates that it could thermal with more weight I may coat he wings and/or add ailerons. A small motor is also a possibility in future depending on how it launches from a tow. The same receiver will accommodate both. Then again it may end up adorning the ceiling or the trash bin.
The fuselage is shaped, the wing saddle and stabilizer platform have been hot wire cut.
The second image shows the rectangular center block used to attach the wings. The block makes aligning the wings more straightforward.
Current state of the 1:12 Reiher. 70 grams as shown. 62.5" wingspan, 200 square inches of wing area, E392 airfoil with 3 degrees of positive wing incidence at the root and 3 degrees of washout. Tip stall is a concern but it looks like turbulators could help if it does prove to be an issue. The wing stiffness seems marginal at best but I'll try a few test glides before I make any attempt to add weight and stiffness.
That's very neat - 70gms is very light as DLG's of that size are around 200gms. I guess though that is without RC?
I would personally consider using lightweight glass cloth(20gms/sq metre) on a foam wing of this size. If you still have the foam from which it was cut then it could be used as beds to press or vacuum the glass on.
Do a web search for info on weight or vacuum pressing.
John
John,
Yes, the current weight is without RC gear. I'm curious how much that figure will climb once it is installed and ballasted to the proper CG. I hope to stay closer to 100 than 120 but that remains to be seen.
I initially planned to skin the wing but then thought I'll never know how light it could be without at least a few test glides using the wing as is. If, as we both suspect, it flexes too much I'll try to stiffen it. My current plan is to employ one or some combination of these: strapping tape "spars" top and bottom, carbon or balsa spars top and bottom, glass leading and/or trailing edge, cover the wing with film. A full height balsa spar would be pretty easy to do also. If anyone has thoughts on the potential effectiveness (or lack thereof) or other suggestions I'd like to hear them. This is learn as you go for me.
There is a good chance I'll cut another set of cores and fully skin them. One of the many benefits of building with foam is that no single part takes very long to make.
I was actually ready to cut a second set of cores for skinning but decided to wait in case I find something I want to change about the wing, i.e. airfoil, washout, dihedral/anhedral angle etc.
I hope to get the gear and ballast installed tonight so it may be possible to try some test glides in the next day or two. I'm frequently overestimate my ability to get things done so take that with a grain of salt.
I have two other questions.
1) Any suggestions for relatively easy to acquire tubing to run 1mm carbon pushrods through?
2) Is there a guide somewhere to making leading edge "tape" from fiberglass? I thought I had seen some stuff but can't find it now. Just wax paper and spray glue or is there a better way?
Here is a good site on home built DLG's
https://www.rcgroups.com/forums/showthread.php?4699611-Scratch-Built-DLG-on-the-cheap%C2%85-redux
QuoteI initially planned to skin the wing but then thought I'll never know how light it could be without at least a few test glides using the wing as is. If, as we both suspect, it flexes too much I'll try to stiffen it. My current plan is to employ one or some combination of these: strapping tape "spars" top and bottom, carbon or balsa spars top and bottom, glass leading and/or trailing edge, cover the wing with film. A full height balsa spar would be pretty easy to do also. If anyone has thoughts on the potential effectiveness (or lack thereof) or other suggestions I'd like to hear them. This is learn as you go for me.
The answer I feel lies in exactly how you tend to use the glider. Light bungee launches would probably be ok using a simple system of spars to what you have mentioned. Torsional stiffness will probably be the main worry and I feel will need a skin similar to glass reinforced tape.
As a suggestion how about considering a system of chord wise "weblets' - say 3 top and bottom on edge of say 1/4"x 1/8" balsa under the tape - at say 20%, 30% and 50% chord.
These should help with both torsion and bending.
Future wings for heavier DLG launches would need i feel, glass skins and carbon spars.
Quote1) Any suggestions for relatively easy to acquire tubing to run 1mm carbon pushrods through?
2) Is there a guide somewhere to making leading edge "tape" from fiberglass? I thought I had seen some stuff but can't find it now. Just wax paper and spray glue or is there a better way?
I buy this from Hyperlink in the UK but check the site I referenced- it may provide more local sources.
That sounds a reasonable approach but test that the spray glue is compatible with your epoxy first. I have used Hair Spray as a binder for the glass cloth but it is not too strong.
Good luck.
John
John,
Thanks for some excellent suggestions. Skins are probably the ultimate answer but I'll try some of the other techniques first just to test their efficacy.
As expected I made no where near the progress I thought I would. I always forget how long it takes to do the "first one" while you are developing methods for each stage. Subsequent similar builds go much faster once those methods are established.
On the plus side while searching for .020" music wire for control rod ends I found a 60% complete 18" wingspan HE-111 I started from blue foam years ago and completely forgot about. It should probably move up on the to-do list. I also found rolls of 1.5 and 3mil laminating film, a half finished Navy-Wright Racer...the list goes on.
The area for the RX is cut out. I'm going to try working with these grooves. A plastic soda straw fits perfectly in them as a liner.
If you're looking for alternative bonding agents for skinning the foam, take a look at G4 Pond Liner. Many of the outdoor large scale guys use it to glass skin wings and fuselages instead of 2 pack epoxy finising resin. Its lighter, single pack and water clean up. Which also means it can be diluted with water to flow more and for smaller models may be an option depending on what material you use for the skinning instead of glass.
John M
John M,
Interesting, I'll do some reading. After a quick look I'm guessing I'm after G4 Pond Sealer, it appears to be a something like water based polyurethane.
Yes, interesting. Never heard of it before now. Worth playing with IMO.
"Rustins Bonda G4 Pond Sealer is a moisture-cured polyurethane, which forms a non-porous seal on concrete, brick or porous stone. It uses the moisture in the air and substrate to cure or harden. It can be applied onto slightly damp substrates. However, it is important that the substrate is sufficiently dry to be porous so as to enable the first coat to bond and obtain a mechanical grip. It can be applied in poor weather conditions, high humidity and at temperatures down to 0 degrees C. G4 Pond Sealer seals out lime."
Thanks for the lead John M.
Stephen.
That's very interesting John. Thanks for the extra info Stephen.
John
Yes sorry chaps I called it Pond Liner and should have said Pond Sealer. I used it in a 5ft deep concrete lined service pit in my garage which used to sweat profusely and I'd have 6 inches of water in the bottom after each winter. One coat of G4 and it was dry as a bone for several years till I sold the property.
I skinned Wot 4 wing and a Scale Zlin with glass and G4 with the leftover. Not tried it on very lightweight indoor models but worth some experimentation I would think.
John M
Some progress on the RC gear installation. If the wind cooperates I may get a test glide or two in this weekend.
That's a beautiful shape. Keep us updated.
If it was my project, I might inlay strips of thin, unbacked wood veneer top and bottom, at maybe 25 percent of chord. Alternatively, carbon fiber strips or tow. Or glass tow. Or fragments split off from pultruded driveway marker poles, which are very strong but can give you invisible splinters if the color doesn't go all the way through. You won't need much, but I think you'll need some.
If I was going to sheet the wing, I might consider light kraft paper with epoxy. The epoxy should be a SLOW type that cures hard. Relatively low viscosity is probably useful, too. On my project, I painted on the epoxy, let it soak in for a while, scraped off the excess, and then did the other side. I vacuum bagged it onto the wing cores, though perhaps evenly applied pressure would also do. I used 60 lb kraft, which is turned out a little heavy for an RC hlg. 30 or 40 lb might be better. This stuff is as stiff in bending, for its weight, as fiberglass. Not sure about tension or compression. It's easier to work with than fiberglass. I've used kraft paper with thinned Titebond to repair a foamy, which worked quite well. No need for pressure, and it drapes well on curvy surfaces. I think it's probably not quite as stiff or strong, though, and there may be warps. I wonder if fancy linen stationery would be good if used this way or with epoxy.
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Have you tried Highload 60 or Plazamate? Can be wet sanded very smooth, dings less than regular blue foam and is about 2.4 lbs per cubic foot. There are also Highlighted 40 and 100. I think Corning has similar products.
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I think you will need to turbulate that thick airfoil for best performance. Especially with that narrow chord, which makes for low Reynolds numbers. I think the AG03 might work better, especially if you ever have to get back upwind in a breeze. Apogee uses AG03 (https://charlesriverrc.org/articles/on-line-plans/mark-drela-designs/apogee-hlg/) RC gliders benefit from airfoils with a wide speed range, though maybe your glider doesn't need quite as wide as a discus launch would. Maybe slightly more camber would be ok. Slightly thinner might be good, too, but in either case you will lose the convenience of the flat bottom. You could keep it if you reduce the camber while thinning, which I guess is like thinning about the chord line instead of the camber line. If you lose the flat bottom, you might as well start with the AG04.
--------
It's hard to find a lower aspect ratio sailplane that's as pretty as the Reiher, but some of them still look good. The DFS Habicht is one. DFS Habicht (https://www.j2mcl-planeurs.net/dbj2mcl/planeurs-machines/planeur-fiche_0int.php?code=487) Note that there were even stubbier versions of the Habicht. You can find some other attractive gliders with modest aspect ratios by selecting "voltige" in the "fonction" window here: https://www.j2mcl-planeurs.net/ (https://www.j2mcl-planeurs.net/). The Castel-Mauboussin Jalon is one of my favorites: https://www.j2mcl-planeurs.net/dbj2mcl/planeurs-machines/planeur-fiche_0int.php?code=2757 (https://www.j2mcl-planeurs.net/dbj2mcl/planeurs-machines/planeur-fiche_0int.php?code=2757)
A modest aspect ratio is structurally and aerodynamicly superior in small models. Look how low the aspect ratio of Drela's Apogee is.
Unless you are already an experienced RC glider pilot, your Reiher may be better for practicing repairing than flying.
On my way out the door so this will be a quick note. I was able to do some test glides today. Here is the short version, I'll add more detail and respond to the comments above later. I do want to say thank you for the excellent information though.
1) It did fly and if I could leave it as is the wings would be stiff enough for careful towline launches and the very floaty glide it provides.
2) I don't have enough roll control. If everything goes well it is flyable but if it gets a gust from the side it won't turn back even with full opposite rudder.
All up weight as flown today was 87 grams.
Would a wing without anhedral, like the Nemere, give more roll control with rudder only?
I plan to add ailerons to the existing wing. The process of adding them will also add some stiffness.
Even with ailerons I would try and increase the dihedral of the outer wing panels to around 3 - 4 degrees to help with roll stability.
The scale small fin/rudder area and short tail moment is also not helping recovery from gusts in roll and pitch probably.
Mixing some aileron into the rudder may also be necessary to control adverse yaw.
Good luck with it.
John
If this flies slowly enough, that rudder can be added by the left thumb*. Another possibility is aileron differential. I'm assuming mode 2.
*I try to use thumb and forefinger, actually. Not sure I actually do that on the left stick, though.
That model is looking very nicely finished. Would you mind sharing how you did such a neat job cutting out the wings?
The replies with suggestions of others. materials and techniques is appreciated.
Let me know if I'm not answering the question you are asking. ;-)
The wings are cut using a gravity feed hotwire cutter. I purchased a used commercial unit ages ago but there are several sites with instructions to make your own.
I cut a new set of blanks for a fuselage and wings last night. I'll cut cores and shape the fuselage today. The wings will be glassed, equipped with ailerons and the front half of the fuse will be glassed.
lincoln,
Knowing this glider won't see the kind of speed range that a DLG would is the AG04 still a good choice? I considering something slightly thicker like the AG24 for the root and the AG26 for the tip.
I think that with such a light model - the original suggestion by lincoln of AG04 would still be the best selection.
A quick look(on XFOIL) at Ago4,AG24 and AG26 for a low operating Reynold's Number of around 50,000 shows AG04 having an advantage - lower drag over most of it's speed range.
Generally as the flying speed and thus Re No reduces - thinner airfoils will be best.
John
Here are some shots of the new cores and fuselage cut this afternoon. The cores are Ag24 root, Ag26 tip, they look so thin compared to the E392. I'll need some time to adjust before going even thinner with AG04. ;-)
I'll weigh the everything before and after glassing for reference.
Can ypu please post a photo of your gravity wing hotwire setup?
I built and have used for years the drop arm device described in Radio Control Soaring Digest back in 2008. I works well, if you read, remember and apply all the little tips and tricks therein.
https://redirect.viglink.com/?format=go&jsonp=vglnk_177192117058111&key=5e5e6e04e939b9674c384ca8b03117f4&libId=mm0bvjv4010248ul000ULbyxn75vl&loc=https%3A%2F%2Fwww.rcgroups.com%2Fforums%2Fshowthread.php%3F1779705-Gravity-Drop-Arm-Foam-Cutter&gdprConsent=CQgE_UAQgE_UAAKA1AENCTFsAP_gAEPgAAQAMBtR_G__bWlr-bb3aftkeYxP9_hr7sQxBgbJk24FzLvW7JwXx2E5NAzatqIKmRIAu3TBIQNlHIDURUCgKIgFryDMaE2U4TNKJ6BkiFMZA2tYCFxvm4tjWQCY4vr_9lc1mB-t7dr82dzyy6hHn3a5_2S1UJCdIYetDfv8ZBOT-9IEd_x8v4v4_EbpEm-eS1n_pGtp4jd6YnM_dBmxt-Tyff7Pn__rl_e7X_ve_n3zv84XH77v____fv-7___2b_-___aDAQAJhoVAEZZEAAQKBhBAgAUFYQAUCAIAAEgaICAEwYEOQMAF1hIgBACgAGCAEAAIMAAQAACQAIRABAAQCAACAQKAAMACAICABgYAAwAWAgEAAIDoGKYEEAgWACRGRQaYEoACQQEtlQgkAQIK4QhFngEACImCgAABAAKAAAAeCwEJJASsSCALiCaAAAgAACCAAgRSFmAIIAzRaCsCTgMjTAMHzBMkpgGQBEEJGQZEJvwiAAAAAAAIEAQAAAAAAAQAABAA.YAAAAAAAAAAA&ccpaConsent=1NNY&gdprApplies=true&v=1&opt=true&out=http%3A%2F%2Fwww.rcsoaringdigest.com%2Fpdfs%2FRCSD-2008%2FRCSD-2008-11.pdf&ref=https%3A%2F%2Fwww.google.com%2F&title=Gravity%20Drop%20Arm%20Foam%20Cutter%20-%20RC%20Groups&txt=http%3A%2F%2Fwww.rcsoaringdigest.com%2Fpdfs%2F...SD-2008-11.pdf
Sorry its a large link but article starts on page 103
John M
Here is a picture of the same unit I have. The concept is brilliant in its simplicity. Many people have built their own from wood or other items. A commercial unit is not required.
Quote from: bcarter1234 on Feb 22, 2026, 10:05 PMLet me know if I'm not answering the question you are asking. ;-)
The wings are cut using a gravity feed hotwire cutter. I purchased a used commercial unit ages ago but there are several sites with instructions to make your own.
I cut a new set of blanks for a fuselage and wings last night. I'll cut cores and shape the fuselage today. The wings will be glassed, equipped with ailerons and the front half of the fuse will be glassed.
lincoln,
Knowing this glider won't see the kind of speed range that a DLG would is the AG04 still a good choice? I considering something slightly thicker like the AG24 for the root and the AG26 for the tip.
First of all, keep in mind that I'm not an expert. I've read quite a bit about this stuff, and I have some engineering background, and I've messed around with model airplanes. That's it. Anyway, if at one point I figured out the Reynolds numbers for your model, I've forgotten. As I mentioned before, a little thinner than the AG04, and maybe a bit more camber. Thinner, percentage wise, as the chord gets narrower.
Speaking of gravity feed hotwires, I wonder if anyone has used a gearmotor, rotary damper,clockwork, etc. to give them a constant speed. I know a guy with an NC cutter he concocted. He controls the speed so that it cuts without actually touching the foam. That way, the wire remains straight.
lincoln,
Do you have any idea if he is cutting with a higher wire temp to achieve the cut without the wire touching? Typically my wire moves through the foam at about 2 inches per minute or so but it is in contact with the foam.
Thanks gents for the photo, explanation and links. I might have to build one when I next cut a wing.
QuoteAs I mentioned before, a little thinner than the AG04, and maybe a bit more camber. Thinner, percentage wise, as the chord gets narrower.
I believe Lincoln is correct. I'm also not an expert but model aerodynamics is a large part of my hobby and my experience supports this comment by Lincoln.
At the tip I would suggest reducing the thickness below that of the main section , and reducing the camber.I also try to improve the airfoil near the tip by moving the thickness high point forward, but this needs access to XFOIl to see the benefits or lack of.
QuoteTypically my wire moves through the foam at about 2 inches per minute or so but it is in contact with the foam.
This is around the speed that I have seen used successfully. The wire melts the foam and then moves through the liquid melt. The slower you can cut the more accurate the wing aerofoil will be as the drag of the wire moving through the liquid increases with the square of the speed. Thus the lower the speed the lower the drag and thus for a given tension - the lower the bow in the wire.
I saved that same link John M years ago - it's about time I built it!
John
OZPAF, John yes it makes a good manual set up.
Regarding speed of cut to reduce wire drag - that's all well and good, but you do have to play with the wire temperatures as well. Because if you cut too slowly to avoid drag, the hot wire melts more of the foam to a larger radius around the wire diameter, so you have to account for the bigger kerf when making the root and tip templates to end up with the correct aerofoil section and thickness once cut.
Ends up being an iterative process where many trials on offcuts are made before the final process is arrived at. (Certainly for me it was). Then write it down so you can set up the next cut 6 months later correctly without wasting foam or time practicing!
John M
QuoteBecause if you cut too slowly to avoid drag, the hot wire melts more of the foam to a larger radius around the wire diameter, so you have to account for the bigger kerf when making the root and tip templates to end up with the correct aerofoil section and thickness once cut.
That's true unless you have a variable DC supply , and this is a major help. There were many approaches to achieve this - from Variac's to using light dimmers.
John
Finally an opportunity to use some rock hard balsa I've had for decades. The grooves are sanded in the top of the wing. The spars are 1/16" deep, 1/8" wide. I'll glue the top spars in and then sand the grooves for the lower.
The cap strips were bonded into the top and bottom of the wing. Glidden Gripper provided a better bond than PVA/white glue in a quick test using scraps. For an additional 9 grams the wing is noticeably stiffer. The current weight ballasted with battery is 96 grams.
Inboard ailerons are next. If the ready to fly weight is 110 grams that would work out to 2.8oz/sq ft or 8.5grams/sq decimeter. The 36" free-flight tow line Reiher is at 1.6oz/sq ft, 4.9grams/sq decimeter.
Quote from: OZPAF on Feb 27, 2026, 02:04 AMQuoteBecause if you cut too slowly to avoid drag, the hot wire melts more of the foam to a larger radius around the wire diameter, so you have to account for the bigger kerf when making the root and tip templates to end up with the correct aerofoil section and thickness once cut.
That's true unless you have a variable DC supply , and this is a major help. There were many approaches to achieve this - from Variac's to using light dimmers.
John
I have a light dimmer in my setup. However, measuring the current is probably a good idea.
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I doubt if it would be necessary to turn up the heat on the wire for cutting without touching. Just cut more slowly. Foam is a good insulator. I think it's probably a good idea to make a bunch of cuts to get the kerf figured out before making airfoil templates. As I recall, one way to reduce the problem with the kerf is to make the lower cut first and let the core drop down after the cut. The kerf will be thicker at the tip than the root of a tapered wing.
I should admit that I haven't done much cutting with my gravity feed setup. Long ago, I did a bit of cutting with someone else's user-unfriendly NC cutter.
I think a really long bow might be good for cutting a really flat foam top for a less than perfect workbench. I haven't figured out the catenary curve, though. Maybe it becomes unreasonable.
The inboard ailerons are installed. I don't have differential programmed correctly yet but I hope to get that sorted through OpenTx soon. It has been about six years since I last messed with it, I've forgotten almost everything. Ready to fly at 101 grams, a 14 gram increase for ailerons and cap strips.
This morning's test flight was a success in terms of gathering information, not so much from a desired outcome aspect.
The internal ailerons added a very small amount of influence over the roll axis but not nearly enough. Back to the drawing board! ;-)
Are you using rudder with ailerons? Adverse yaw is a major issue on long glider wings.
John
John,
An excellent question. As I was trying to get the first test glide to roll I realized I wasn't adding rudder. Adding rudder gave the tiny amount of roll response that was available. It seems ailerons on the inner panel, before the anhedral break, don't have enough influence even with rudder added. I'm going to add rudder to the aileron input on the TX.
I'll try up only ailerons on the outer panel next. Spoilers are tempting. Any thoughts on which is likely to provide the greatest roll control with the least adverse yaw? If I did use spoilers they would probably be the flip up type so like an up only aileron near the spar instead of on the trailing edge.
The weather was amazing this evening so I got several flights on the 36" towline free-flight Reiher. It flew along as stable as you could wish. If I can just get the larger RC version to do the same...
I'm not sure how effective "flip up" spoilers would be at your low RE no's. I tend to think that you may lose too much lift and that the best solution is to use rudder.
don't be afraid to use a fair amount mixed in with the ailerons. Try increasing the mix to see if it will provide good roll control.
I have used coupled aileron/rudder for years on all my RC gliders from F3B to F5J and now DLG - it makes a large difference.
Good luck
John
Step 1 of switching to outboard up only ailerons was bonding the inboard ailerons back to the wing. Once the Glidden Gripper dries I'll cut the outboard ailerons.
The outboard ailerons are cut and hinged. The pull lines are routed. Only one servo will be needed for this installation. Boring the holes for the pull lines was an interesting project.
Ready for a calm morning to test the new ailerons.
Flew about a dozen test glides yesterday without incident. I now have roll control as long as rudder and aileron are both used. It is not what I would consider authoritative but I think it will suffice for the way this model is intended to fly. My biggest concern is if it will be sufficient when on tow.
I did program the Taranis to have switchable 100/50/25% rudder added to ailerons so I can see what is preferred.
Any pointers for tow hook location? I will need to use a high start rather than towline for this one as flying and using the reel both take two hands. ;-)
For best height on a high start with RC - the CG can go back till under the CG. However I would suggest that you make the position adjustable and start with a position that is 15deg ahead of the CG.
An easy way to have an adjustable hook is to use a small screw hook(1/16" wire) - 90 deg bend, screwed into a small section of ply - then adjustment only requires drilling a few more holes.I used this approach on a 1.5m glider launched on a heavy duty HiStart
John
John,
Thanks for the pointers on hook location. I assumed more forward would be good since I can always add some up elevator.
With a split foam fuse moving the tow hook is simple. The hook is bent to look like a T-pin with an inch wide T at the top. The vertical portion of the T is given about an 80 degree bend 1/4" below the T to form the hook. The actual degree of bend is whatever is needed to make sure the rear of the hook diverges from the wing's horizontal centerline. Having the hook parallel on some of the towline gliders turned out not to be a great idea.
The horizontal T part goes in the groove between the two halves. Tape is put in front and behind the vertical portion of the lower loop. Moving it is just a matter of removing and re-taping in the new location. I'm finding foam an excellent medium for experimenting.
That's a clever solution for your launch loads.
John
Another eight or nine test glides were flown on Friday morning. With the coupled rudder it has what might best be described as sluggish roll control. The glide however is beautiful to watch. Distances ranged from 250 to 320 feet with roughly 20 foot of drop.
A rotary servo will replace the linear servo in order to add a bit more aileron deflection. I'm considering a very small amount of elevator coupling as it seems to track better if a little down elevator is added when aileron is applied.
It feels like it has a tendency to weathervane in a crosswind. Any suggestions for that?
I feel that the primary problem may be lack of rudder authority - possibly stemming from the small scale size of the fin/rudder and accentuated by the low flying speed due to the very low wing loading.
The corresponding low roll rate would also make it more susceptible to gusts as you have noticed.
I would suggest that you try adding extensions to your fin and rudder.
As a last resort it may be necessary to add some ballast to the model.
many years ago our club had a contest to see who could make the slowest flying RC glider. The limiting factor was the wing loading - flying slow was not the problem - lack of control was the limiting factor!
John
John,
Thanks for the helpful observations. I'll add temporary extensions to the fin and rudder. If that works making larger replacements won't take long. I'll also make a pocket for ballast to see how much higher glide speed helps.
Your comments are echoed in the 99 year old technical document that contained the La Pruvo drawings I'm using for the next 36" towline glider.
"N.A.C.A. Technical Memorandum No. 471
Performances and Properties of School and Training Gliders
Despite their simple construction, the school and training
gliders made very good flight records. Long soaring flights
were made by the more skillful pilots with the school glider,
even at wind velocities of less than 6m (19.7ft.) per second.
Gliders of both classes showed a marked superiority as regards
maneuverability, over many earlier performance gliders. This
is all the more noteworthy, because satisfactory rudder effect
has always been difficult to obtain at the low speeds attained
by the lightly loaded gliders of this class."
It's interesting and almost strange to think that the fin/rudder area can cause problems - as it rarely appears.
One of the most surprising issues I had was with a small semi scale jet catapult catapult glider. On launching it was OK at speed but on slowing it started spinning around the CG on the yaw axis. Completely puzzled I tried extra dihedral, CG shifts - all to no avail.
Finally out of desperation I extended the fin and the problem was solved. I was more than a little amazed.!
Good luck with the alterations.
John
1/12 Scale Reiher Sailplane foam
Hi bcarter1234. Tues March 31 2026
Thanks for the builds. You have me interested .... I am considering building another high start towline glider for my next model. The tow hook was/is, a big deal for me to get right.
I am interested in that tow hook that you and John are talking about? Would you please post a pic, or even better, a pic of your sketch, of your tow hook? Thanks for your help.
And also some help from John on this: " the CG can go back till under the CG. (?) However I would suggest that you make the position adjustable " and a nice hand drawn diagram from John too. Oh, and a pic of the adjustable tow hook please. Thanks.
My apologies for the newbie questions ...
Lastwoodsman
Richard
Richard,
Your questions are welcome, nothing I have would fly if people hadn't answered a lot of questions for me.
Keep in mind my fuselages are foam so adding and moving a tow hook is simply a matter of cutting a thin slot in the bottom of the fuselage and inserting the hook shown below into it. The hook is held in place with two strips of tape in front and behind the vertical leg of the hook. Tape is sufficient for my application because the loads om these light planes is very low. Once I find the best location I may glue them in. The hooks are bent from a paper clip.
The hook is placed somewhere between 15 and 45 degrees in front of the CG location at the bottom of the wing. Make sure the rear of the hook diverges from the bottom of the wing a little bit. Otherwise the tow line may not release when you want it to.
I think a lot of these control issues can be traced to what the fin area (aft of the CG) is actually doing. I like to think of what the fin is doing when it comes to directional control and spiral instability. These are often at odds with each other. I like to keep in mind that as we slow down the aerodynamic forces from our control surfaces drops by the square of the speed. But the mass stays the same. Generally, the slower I design a model to fly the larger I make the aft vertical area.
This is the type of straight tow hook I have used on every thing from Tow Line FF models to F3B winch launched models.
The hook is a screw in "L" shaped or straightened cup hook. It is screwed into a piece of ply (section of glass fibre on F3B models) and adjustment just requires drilling and tapping new holes.
The hook shown is 1.5mm dia and the F36B models used 3mm or slightly more.
John
1/12 Scale Reiher Sailplane foam
Hi bcarter1234 and John : Tues March 31 2026
I was always wondering how to move the tow hook to a new position, after you glued it in place. Thanks for the pics and tips John and bcarter. Now I understand them.
I only had three types of tow hooks, Pics 1 to 3, and I only had flying sucess with the 20" Osprey from Vintage Model Co. The cheap store bought 'ready to throw' foamy glider, and the balsa builtup Mystery Man "Vulture Glider", were both 37". I never got the foamy to fly, and the Vulture Glider broke right up upon hitting earth, for reasons I do not yet know why - it was flimsy, I suspect, because of the cheap double covering I used, of cheap, present-wrapping tissue ?
Anyways, those are good ideas for the tow hook - I can see your threaded screw into a plate, John, and I can see your tape-it-in-place "sandwich" slot also, bcarter1234. Which ones to use depends on if my next model glider will have a flat fuse bottom, or a skid on the fuse bottom ....
Pic #1 2212
Pic #2 2212 expanded snip
Pic #3 2213
Lastwoodsman
Richard
QuoteI like to keep in mind that as we slow down the aerodynamic forces from our control surfaces drops by the square of the speed. But the mass stays the same. Generally, the slower I design a model to fly the larger I make the aft vertical area.
Yes I agree. The large old rudder/elevator floaters such as the Paragon and Drifter with 100" wing spans and low wing loadings had large fin/rudders with a lot of movement compared to current models.
John