Performance glider scratch-build: delta wing or traditional/swept wing planform?

[Rktman]

Eric,

Looks great !

QUESTION : What is the Grain Direction on your Xerclod ?
In the pic, it looks parallel to the Fuselage . . . Might be prone to breaking during Boost ?

Dave F.

Yeah, realized the goof after I already glued it on so I soaked it in CA. Best I could manage since there's no room to reinforce it with carbon strip.

 

[Ez2cDave]

Eric.

Here's a thought . . . Use toothpicks for reinforcement !

Drill a small hole or holes through the Xerclod, into the Fuselage . . . Use the "center section" of the toothpick(s), coat it with glue and slide it into position . . . After it is dry / set / cured ( depending on what glue you use ), sand it down flush . . . PRESTO !

Dave F.

 

[Rktman]

Eric.

Here's a thought . . . Use toothpicks for reinforcement !

Drill a small hole or holes through the Xerclod, into the Fuselage . . . Use the "center section" of the toothpick(s), coat it with glue and slide it into position . . . After it is dry / set ( depending on what glue you use ), sand it down flush . . . PRESTO !

Dave F.

That would work. Or a piece of music wire, whichever is lighter.

 

[Rktman]

Drilled down through the Piece X into the fuselage with a pin vise, then inserted a sewing needle to reinforce it.

 

[Rktman]

Oh bother...
They say bad news comes in threes. Well, if the snapped rudder was the first and the wrong piece X grain direction was number 2, this should be the last one. The final incidence on the stab ended up being waaay too much. I must’ve been asleep at the wheel because I was aiming for 1°, but it’s closer to 4°. But heck, what’s a scratch build without something not going as planned? I’ll have to tear off the existing stab and rudder and fabricate new ones.

 

[Rktman]

Got lucky and was able to remove both stab and rudder in one piece with minimal damage. Just need to patch up the tissue areas and reattach the unit very carefully at a much shallower angle.

Not sure why this pic strikes me as somewhat disturbing…disturbing like coming across a severed foot while walking in the woods…

 

[Rktman]

Just thought of something: I want to put in a little stab tilt to get the glider to circle.

Does anyone know whether it circles toward the lower stabilizer or the higher?

 

[Ez2cDave]

Just thought of something: I want to put in a little stab tilt to get the glider to circle.

Does anyone know whether it circles toward the lower stabilizer or the higher?

Hi, Eric,

The glider will turn towards the "high side" . . . ( use about 10 degrees +/- )

https://www.nar.org/kevin-mckious-glider-trimming-tips

https://www.rcgroups.com/forums/showthread.php?2356767-Free-Flight-stab-tilt-how-does-it-work

Dave F.

 

[Rktman]

Thanks Dave, much obliged!

 

[georgegassaway]

Drilled down through the Piece X into the fuselage with a pin vise, then inserted a sewing needle to reinforce it.
View attachment 438664

Had not seen this thread till now. I learned ages ago, to make the hook's wood grain to be parallel to the leading edge (front edge) of the hook, never parallel to the fuselage or pod. Same reason you do not cut balsa fins with the grain parallel to the root since they snap off too easily, but have the fin's grain swept with the LE (or possibly TE, or possibly straight out at 90 degrees, depending on fin shape).

 

[Rktman]

Thanks Dave, much obliged!

Hi, Eric,

The glider will turn towards the "high side" . . . ( use about 10 degrees +/- )

https://www.nar.org/kevin-mckious-glider-trimming-tips

https://www.rcgroups.com/forums/showthread.php?2356767-Free-Flight-stab-tilt-how-does-it-work

Dave F.

Had not seen this thread till now. I learned ages ago, to make the hook's wood grain to be parallel to the leading edge (front edge) of the hook, never parallel to the fuselage or pod. Same reason you do not cut balsa fins with the grain parallel to the root since they snap off too easily, but have the fin's grain swept with the LE (or possibly TE, or possibly straight out at 90 degrees, depending on fin shape).

First time using one, I've been using Apogee's universal hook until now. Guess I was in a hurry and didn't realize till too late that the grain direction was wrong.

 

[Rktman]

Reattached the stab and rudder and went outside to do some trimming. 30 minutes of fine-tuning it for a nice flat glide with a slight stall when first tossed meant adding 2 grams of nose weight. I didn’t expect that (or the hand-numbing 34° temp. I wonder if the temperature had something to do with it)?
I suppose I may have gotten carried away with the thick CA when reattaching the stab and rudder.

Final hand trimming will need to be in a much larger area than my yard. Like its maiden flight, it’s going to have to wait till things are safer outside (as in post-vaccine).

Final weight: 12.69 grams (0.45 oz.), final CG: 1 3/16” (1.1875”) from the wing leading edge. That comes within a hair of what @TheAviator estimated. Whatever formula you’re using to calculate predicted CG is a good one.

 

[Rktman]

Musings
This started out as a what-if thought experiment along the lines of: "what would I build if I were going to enter a NARAM BG competition?" and to experience getting way outside my comfort zone building for duration instead of durability.

What've I discovered? First up, I couldn't bring myself to go "all out" on weight reduction. Many contestants go bare-balsa and with flight surface airfoils sanded so extreme (especially at the tissue-thin trailing edges) that they invariably shred on launch. If I'm going to be DQd on something I'd like it to be for an uncontrollable mishap like a "Red Baron". At the very least I wouldn't go crazy with the sanding trying to reduce every micro gram of weight and would lightly dope my flight surfaces to guard against balsa disintegration. I know I won’t win any contest without taking the risks, but watching all my efforts “exceed the speed of balsa” isn’t my idea of fun; but just participating is.

2nd, I wouldn't enter a kit build as many contestants seem to be doing these days. They're not optimized for competition IMHO and I'd likely be competing against some of the same kit models, so the only major advantage would be luck and being good at picking thermals. (Well, okay, maybe better craftsmanship to a degree). Bottom line is I'd rather design my own glider optimized for competition the best I could.

3rd, I'd trim and test fly the heck out of my glider, then build another to see what I could do to tweak more performance out of it. If I couldn't I'd at least have a backup, always a good idea in a competition should you lose the first to a thermal.

So no, I'll probably never enter a NARAM due to physical and air travel limitations but I’m sure it would be a high just to participate in and experience the excitement (and anguish) of their BG duration event. That said, I've enjoyed this build a whole lot and will continue to feed my glider addiction with scratch builds — but now with more of a mind to focus on maximizing duration/efficiency without the penalty of weight.

 

[GuyNoir]

Does anyone know whether it circles toward the lower stabilizer or the higher?

The glider will turn to the high side of the stab tilt.

 

[georgegassaway]

If I'm going to be DQd on something I'd like it to be for an uncontrollable mishap like a "Red Baron".

Epoxy can be cured, and Red Barons can be almost eliminated.

Spooler Pop-Pod.

There is no shock cord to hang up on anything. A streamer for the main pod, that is not unfurled until after the ejection has kicked the pod backwards from the glider (the nose section keeps the streamer spooled inside until ejection. The nose section tumbles down, and only rarely is a nose section not found eventually (write your name on it. and usually the nose is some distance downwind of where the main pod lands as the nose lands later). With cast "L-Hooks" adding consistency of attachment and release, the Spooler pod system has been 99%+ reliable. For now the cast hooks are not available but I hope to make them again by spring.

Made them for various size models. Even a BT-55 pod for a 24m powered R/C B/G.

A minus, and a plus, is that the Spooler pod does add a bit more weight than a non-spooler pod. So a bit lower boost due to mass. But then a more forward CG which helps the boost to be straighter, so it can help offset that. I think it's worth the trade-off for the reliability.

More info, more images, and link to entire R&D project:

Spooler Pod & L Hook R&D

 

[Aeronerd]

Finished assembling. Now for some trim tosses as soon as the weather decides to cooperate.
View attachment 438525


This is the smallest, lightest bird I’ve ever built. It tips the scales at only 10.69 grams (0.38 oz.)
View attachment 438526

Nice build. Congrats!

 

[Rktman]

Postscript
Did a follow up trim session today. Turns out it didn’t need 2 grams of nose weight, only 0.62 grams. Nice! That drops the weight to 11.31 grams (0.39oz). When I previously trimmed it, there was a 5 – 7mph breeze blowing that kept forcing the glider to go nose-up before it would try to recover in a series of stalls. Turns out it really doesn’t have the weight or mass to punch through much of breeze, unlike my usual heftier B - C gliders. Flies beautifully when it’s relatively calm, and the stab tilt gives it a nice, gradual right turn. No biggie, I prefer calm flying conditions anyway, as my days of sprinting after a wayward glider or long recovery hikes for a rocket are not easily accomplished anymore.

 

[Ez2cDave]

When I previously trimmed it, there was a 5 – 7mph breeze blowing that kept forcing the glider to go nose-up before it would try to recover in a series of stalls. Turns out it really doesn’t have the weight or mass to punch through much of breeze, unlike my usual heftier B - C gliders. Flies beautifully when it’s relatively calm, and the stab tilt gives it a nice, gradual right turn.

Eric,

That "twitchy" behavior may be caused by the CG location . . . The further Aft the CG is, the less Stable the glider becomes.

Alternatively, the Decalage of the Stabilizer may still be too much. Higher Decalage can offset a more forward CG location, while too much can reduce Glide Speed, flirting with Stall Speed.

I'm also curious how that unusual Wing Planform "behaves" in a Stall, due to the straight Leading Edge and forward-swept Wing-Tip Trailing Edges.

Dave F.

 

[Rktman]

Eric,

That "twitchy" behavior may be caused by the CG location . . . The further Aft the CG is, the less Stable the glider becomes.

Alternatively, the Decalage of the Stabilizer may still be too much. Higher Decalage can offset a more forward CG location, while too much can reduce Glide Speed, flirting with Stall Speed.

I'm also curious how that unusual Wing Planform "behaves" in a Stall, due to the straight Leading Edge and forward-swept Wing-Tip Trailing Edges.

Dave F.

That could very well be, especially the latter. I’ll probably build another after its first couple of flights, keeping a more careful eye on stab incidence.

 

[Ez2cDave]

That could very well be, especially the latter. I’ll probably build another after its first couple of flights, keeping a more careful eye on stab incidence.

Eric,

An interesting comparison might be to build another glider, but reverse the Wing Planform, so that the Leading Edge is tapered and the Trailing Edge is straight, to see how the Wing "behaves" . . . Thoughts ?

BTW - Don't forget that the Stabilizer can also Stall.

Dave F.

 

[Rktman]

Eric,

An interesting comparison might be to build another glider, but reverse the Wing Planform, so that the Leading Edge is tapered and the Trailing Edge is straight, to see how the Wing "behaves" . . . Thoughts ?

BTW - Don't forget that the Stabilizer can also Stall.

Dave F.

Reversing the wing might be an interesting experiment on down the road. For now I'd like to perfect this design. It gets easier after building the first.

 

[Rktman]

Couldn't resist tweaking the glider a bit more. Since the stab's incidence ended up being possibly a tiny bit too much at 1.5 degrees, I heated the trailing edge and was able to bend a minuscule amount of downward angle into it to try to compensate. Also set the CG a few mm back to where it was. Glides every bit as beautifully but now it handles breezes a whole lot better (no nose-up attitude when tossed into the wind).

 

[Ez2cDave]

Couldn't resist tweaking the glider a bit more. Since the stab's incidence ended up being 1.5 degrees I was able to heat the trailing edge and bend a minuscule amount of downward angle into it to try to compensate. Also set the CG a few mm back to where it was. Glides every bit as beautifully but now it handles breezes a whole lot better (no nose-up attitude when tossed into the wind).

Eric,

Excellent . . . That design seems to be a bit "temperamental" . . . LOL !
( I suspect that the CG location contributes to those tendencies )

Dave F.

 

[Aeronerd]

Looks great. How much does i t weigh?

 

[Rktman]

After a last trim and some tweaks, it picked up 0.04 oz of weight and is now 13.27g (0.47 oz.). I feel that compares favorably to the OOP 13mm motor Estes Tercel (0.78oz) or their foam 18mm motor Eagle (3.4 oz.). Admittedly those were a bit larger and were aimed at the consumer market, not something aimed at sport/competition like in my Icarus experiment.