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I built a Glider Launcher to help me calculate Glide Ratio (among other things)

NighthawkGliders

Enjoy Flight & Enjoy Life
#1
To be honest, I wasn't certain I could build one that could launch a balsa glider with any consistency, but I may have lucked out here and made something that works fairly well. Just sharing my results here.


I just searched around my house and found just the right combination of materials to make one:
Shoe-box, 2 Dowel rods, PVC Pipe, 2 Clothes Pins, 1/4" Balsa Wood, Rubber Bands, Caps from Old Crayola Fat Tip Markers, and some Duct Tape (always handy).

I slopped together something that (gently) chucks my Sandpiper gliders.
(I may have to make video showing how I made this) if anyone is interested.

Details about my Sandpiper Glider:
Wing span: 12"
Wing area: 21 sq in
Weight: 4.5 grams

I was able to get some measurements (to the best of my ability), averaged over a number of flights, and calculated:

Here are the measurements:
Launcher to Wall: 20.5 ft
Launcher Height: 47 in
Air Density: 0.002378 slug/cuft (a number I used, not real measurement that day)
Sink Distance: 27 in
Flight Time: 1.48 s

Here are the calculations:
Air Speed: 9.5 mph (15.29 kph)
Sink Speed: 1.52 ft/s (46.33cm/s)
Lift: 4.47 grams
Drag: 0.49 grams
Glide Angle: 6.26 deg
Glide Ratio (also L/D Ratio): 9.11
Lift Coefficient: 0.292902812
Drag Coefficient: 0.03214787

So, in the end... I think the results turned out decent... but, I wanted to check in with the FT Community...

Given a Balsa Glider of these dimensions, does a 9.11 Glide Ratio seem about right? I was wondering if I should have expected a higher number.

There are a few things I'd like to change about this launcher, especially to make it more customizable. (Things like Launch Speed and Launch Angle come to mind). I had limited space, but I think one of my biggest challenges with this was launching the glider as close to its glide speed and glide angle as possible. In other words, I want it to be settled into its glide right off the gate for more accurate measurements. (My video shows the slow-mo of quite a few launches-- so, they are not perfect by far.)

I'm a noob at this stuff, so your thoughts and comments are welcomed!
 

PsyBorg

Wake up! Time to fly!
Mentor
#2
You YOU you brought maths here!! sir I will have you know this is a family forum!!

That was a great edit mate. Green screening in an alter ego +1 for that.

Are you familiar with bow hunting and the release techniques by chance? The whole key to that is the have an extremely repeatable release of the arrow. Same as you letting the glider fly. Maybe add some form of "trigger" mechanical release to that system so it is more consistent? I noticed that the two dowels holding the Glider are prone to a twisting effect that shows an obvious non symmetrical release compared to others. I think you can cure that and get a tighter control with a mechanical set up instead of just by hand.

Cool project so far and I am sure specially the FAI guys here might be interested in something like this.
 

NighthawkGliders

Enjoy Flight & Enjoy Life
#3
You YOU you brought maths here!! sir I will have you know this is a family forum!!

That was a great edit mate. Green screening in an alter ego +1 for that.

Are you familiar with bow hunting and the release techniques by chance? The whole key to that is the have an extremely repeatable release of the arrow. Same as you letting the glider fly. Maybe add some form of "trigger" mechanical release to that system so it is more consistent? I noticed that the two dowels holding the Glider are prone to a twisting effect that shows an obvious non symmetrical release compared to others. I think you can cure that and get a tighter control with a mechanical set up instead of just by hand.

Cool project so far and I am sure specially the FAI guys here might be interested in something like this.
Yes, PsyBorg, yes I did bring up that 4 letter word (MATH)-- oops! sorry to offend anyone!

I must admit, I was able to calculate a number of these things all by myself (yay me!)
But I need to give due credit to Gary Hinze who posted a spreadsheet that helped calculate the stuff I didn't know.
Here is a link to the webpage where he did some glide testing:
http://www.endlesslift.com/glide-test-spreadsheet/

I did pull both arms all the way back as far as they could go to hit the very back of the box-- this helped ensure I always had each arm pulled back at same power and distance. To release them, i just had to ensure both my fingers let go of both arms simultaneously. Each arm is bound to the pvc pipe as a pivot point, so they work together (mostly) but there is, indeed a wee bit of wiggle.

I totally agree with you on installing some trigger mechanism. So, I wondered if shorter and/or stiffer dowel rods would help. I wondered if I can reinforce the dowel rods in a way that they are always in alignment with each other. And, I also wondered how I might be able to push a trigger (so to speak) to release both the arms. Some problems I'll have to ponder how to solve. Great thought and good eye for noticing that!

I also have a concern that if I try to launch a glider with a traditional or inverted empennage it could clip my launcher arms... I think that is a strong possibility, so I'll have to test that to confirm. Also, I'd rather see if I can have the arms continue thru the wedge much further and fall completely down and away from the glider w/o hitting an immediate stop. That seems more ideal to me.

Oh, and thanks for the +1 for alter ego-- such a goofy thing to do, I know... but I'll take that extra credit point.
In this video, I was going to do a 3rd part with my alter ego, but it was quite a technical editing challenge that was harder than I thought and took up a bunch of my time to get it reasonably right.
 

FAI-F1D

Free Flight Indoorist
#4
Whoa. Psyborg contacted me privately about this and I've just now gotten around to seeing it. Don't know why I didn't see it before. This is seriously cool stuff.

So a few thoughts:
1. I think that you're running into a problem of the launcher imparting to much rotational momentum onto the glider. This is a function of the short radius of the launching arm relative to the size of the glider. There are several ways to address this:
-Go to a linear launcher (not hard, but does involve a total redesign)
-Increase the radius of the arm (makes it bulkier and whippier)
-Set the arm to release prior to reaching full vertical (may or may not mitigate the overall effect; hard to say until you try it, and even then the size of the glider may impact the results)
2. The release may need some work to get perfect consistency. If had to guess, I'd say some of the uncertainty in you glide patterns is a function of friction from the release wedge and slop in the arm's bearings. This is just a wild guess...I could be wrong. Also, you do need perfectly still air, and to make matters even harder, hitting the wall can jar a model out of trim. Lots of little variables to track...
3. I'm seeing the need for a stopwatch linked to the release so that you can start timing the glide from that point and then manually stop it with a remote stop switch.
4. Get yourself a combination of elevation and distance that will let you avoid hitting the wall so you can get exact measurements. You'll also need to attach a landing skeg to the glider so that it won't skid along the floor. You want to to stop as soon as it touches so you can get an exact measurement without having to look for the exact point of impact.
5. Your glider holder needs to be calibrated in some way to guarantee the glider is fitted exactly the same way every time. Something that doesn't require you do do a lot of checking to make sure. We can talk about that this weekend. ;)
6. Your editing skills are absolutely awesome. This is the best video you've ever made, and seriously, this is quality. Really, really good quality. We need to find a way to boost your view count.
 

NighthawkGliders

Enjoy Flight & Enjoy Life
#5
Whoa. Psyborg contacted me privately about this and I've just now gotten around to seeing it. Don't know why I didn't see it before. This is seriously cool stuff.

So a few thoughts:
1. I think that you're running into a problem of the launcher imparting to much rotational momentum onto the glider. This is a function of the short radius of the launching arm relative to the size of the glider. There are several ways to address this:
-Go to a linear launcher (not hard, but does involve a total redesign)
-Increase the radius of the arm (makes it bulkier and whippier)
-Set the arm to release prior to reaching full vertical (may or may not mitigate the overall effect; hard to say until you try it, and even then the size of the glider may impact the results)
Imparting too much rotational moment on the the glider? Yes, it may also be possible that when the arms hit the wedge, they continue to bend forward a bit tipping the holding pads forward and causing the backside of the pads to push up on the TE of the wing.

Go to a linear launcher?
Yes, I’m sure I will try this down the road… I have an idea in mind.
Most likely, i’ll try out a number of launchers and see which design is best.

My goals with any one of these are to:
1) Keep design as simple as possible so that anyone could make one,
2) Remove as many variables as possible for consistent data (although, this could preclude #1 above)
3) Make a robust enough design to fit a number of glider models (possibly precluding #1 & #2 above)
So, yeah... I guess that's why we call these projects a "challenge!"

Increase the radius of the arm (make it bulkier and whippier)?
Certainly an option. A longer and more massive lever arm will require more forces to swing it (and more forces to stop it).

Set the arm to release prior to reaching full vertical?
I was adjusting the wedge position forward and back to achieve best result upon launch. It was near vertical.
But, again, slop in construction… wedge was not firmly staying in place. So, yeah...

2. The release may need some work to get perfect consistency. If had to guess, I'd say some of the uncertainty in you glide patterns is a function of friction from the release wedge and slop in the arm's bearings. This is just a wild guess...I could be wrong. Also, you do need perfectly still air, and to make matters even harder, hitting the wall can jar a model out of trim. Lots of little variables to track...
Yes, release does need work. I’m thinking of trying something where arms fall onto a long thin wedge— eventually, they pull apart at a slower rate due to the friction, but it should lessen any bouncing and it should also keep the arms well clear and underneath the glider for clean release.

Air turbulence?
Yes, tried to eliminate most of it. I did this indoors and launched when central heating was NOT blowing.
Also, when I retrieved my glider, I quickly noticed I did leave a turbulent wake behind me. Launching into that certainly made flights unpredictable. So, after every retrieval, I gave a minute to let air settle before next launch.

Hitting wall knocks my glider out of trim?
These gliders are fairly rigid, so I wasn’t too concerned about that. I would adjust the clay and re-mold the smashed dent after every launch. Occasionally, I hit a table leg, or some other obstacle. Minor dings on LE of wings since I don’t have any hard wood on my LE.

3. I'm seeing the need for a stopwatch linked to the release so that you can start timing the glide from that point and then manually stop it with a remote stop switch.
I like the idea of showing the flight time (as on a stop watch) in the video itself. Good idea.
When I calculated my glider’s speed, I reviewed dozens of my flights from launch to wall hit and used a stopwatch to average results.

4. Get yourself a combination of elevation and distance that will let you avoid hitting the wall so you can get exact measurements. You'll also need to attach a landing skeg to the glider so that it won't skid along the floor. You want to to stop as soon as it touches so you can get an exact measurement without having to look for the exact point of impact.
Yeah, In a weird way I kind of liked it hitting the wall. If I had a second back-wall camera, I suppose I could have some lines of measurements on the wall and I could record more accurately where it hits.

Certainly, I could have lowered launch platform and/or backed it up so that the glider ends on the ground. But, like you said, difficult to tell where it hits exactly when it skids. I was only one making this video so I didn’t have second set of eyes. Also, I didn’t want to alter anything about the glider just for testing purposes. I could have a long paper runner, I suppose, and some way to have nose leave a mark on the paper. (e.g. damp paint dabbed on the nose clay).
Plus, I wondered if a shortened flight time would not allow the glider time to glide. Also, what about ground-effect? Probably ground-effect is small relative to many other possible variables that have more impact.

5. Your glider holder needs to be calibrated in some way to guarantee the glider is fitted exactly the same way every time. Something that doesn't require you do do a lot of checking to make sure. We can talk about that this weekend. ;)
Agreed! I did my best to load the glider on the arm pads same way every time and level the glider, but… yeah, lots of wiggle room.

6. Your editing skills are absolutely awesome. This is the best video you've ever made, and seriously, this is quality. Really, really good quality. We need to find a way to boost your view count.
Thanks, Josh, I appreciate that! This one was a beast to record and edit… took me about 3 days. Still trying to learn new technical skills in the video making/editing realm— a work in progress and something I enjoy doing! :D
 

PsyBorg

Wake up! Time to fly!
Mentor
#6
AAhh I knew I went to the right person for this.. Was funny when Josh told me you know each other already hehe. I agree your sub count and views should be a lot higher for that effort. I had to check and see if I was logged in and subbed myself. I was .. just forgot to thumbs up it while I was replying the first time. So I just did.

I will chalk this up for my good deed for the month as we all know no good deed goes unpunished and I have had my Bills Law moment for this month already.
 

Tench745

Active member
#7
I had a great day with my Simple Soarer the other day and ever since have been excited to play with gliders more As such, I really enjoyed your video on the glider launcher.
It reminded me of the care and quality in videos by Wesley Treat, Maker of Things.
 

NighthawkGliders

Enjoy Flight & Enjoy Life
#8
AAhh I knew I went to the right person for this.. Was funny when Josh told me you know each other already hehe. I agree your sub count and views should be a lot higher for that effort. I had to check and see if I was logged in and subbed myself. I was .. just forgot to thumbs up it while I was replying the first time. So I just did.

I will chalk this up for my good deed for the month as we all know no good deed goes unpunished and I have had my Bills Law moment for this month already.
Thanks, PsyBorg... I appreciate you reaching out to Josh. Also appreciate your viewership!
 

NighthawkGliders

Enjoy Flight & Enjoy Life
#9
I had a great day with my Simple Soarer the other day and ever since have been excited to play with gliders more As such, I really enjoyed your video on the glider launcher.
It reminded me of the care and quality in videos by Wesley Treat, Maker of Things.
Glad you had a great day with your Simple Soarer! Also glad you enjoyed my video.

I haven't heard of Wesley Treat, so I had to look him up...
Ok, I like his channel and his style... he builds some really cool stuff and has a good sense of humor.

Thanks for commenting!
 

Mid7night

Jetman
Mentor
#10
This is awesome! I love bringing some maths into the hobby, makes it more fun (for some). ;)

I'll let Joshua handle the nitty-gritty when it comes to glider and launcher construction (which he's already weighed in on quite well), but I would like to speak to your question about expected L/D.

One additional calculation that is helpful is the wing Aspect Ratio, which is (Span^2)/(Wing Area). For your model as reported, the AR is 6.86, relatively low for most cases. Now, a few things and how they affect L/D:

1) Higher AR's enable higher L/D
2) Small slow models have a lower Reynolds Number, which generally means lower L/D

There are, of course, many many other factors that can affect L/D, but given those two generalities I'd say an L/D of 9-ish is not bad for your model.

Without changing the physical layout of anything, you could play around with the amount of nose weight you have, and observe how much (or little) your model porpoises in its flight path. Once you have a consistently-level launch, and you have a consistently straight-declining flight path, you know you have matched what we in industry would call a "trimmed cruise" condition and CG location. With that condition found, you're likely at your Max L/D.
 

NighthawkGliders

Enjoy Flight & Enjoy Life
#11
One additional calculation that is helpful is the wing Aspect Ratio, which is (Span^2)/(Wing Area). For your model as reported, the AR is 6.86, relatively low for most cases. Now, a few things and how they affect L/D:

1) Higher AR's enable higher L/D
2) Small slow models have a lower Reynolds Number, which generally means lower L/D

There are, of course, many many other factors that can affect L/D, but given those two generalities I'd say an L/D of 9-ish is not bad for your model.
Yeah, It has a 2-inch root chord and 1.5 inch tip chord-- which I thought was more narrow than typical.
I figured it would have less drag but would have to fly a bit faster as well.

Without changing the physical layout of anything, you could play around with the amount of nose weight you have, and observe how much (or little) your model porpoises in its flight path. Once you have a consistently-level launch, and you have a consistently straight-declining flight path, you know you have matched what we in industry would call a "trimmed cruise" condition and CG location. With that condition found, you're likely at your Max L/D.
Yeah, I believe I have the glider trimmed pretty well-- but, I think my biggest challenge is with a perfectly-consistent launch.

Thanks for your feedback!
 

desla

New member
#12
To be honest, I wasn't certain I could build one that could launch a balsa glider with any consistency, but I may have lucked out here and made something that works fairly well. Just sharing my results here.


I just searched around my house and found just the right combination of materials to make one:
Shoe-box, 2 Dowel rods, PVC Pipe, 2 Clothes Pins, 1/4" Balsa Wood, Rubber Bands, Caps from Old Crayola Fat Tip Markers, and some Duct Tape (always handy).

I slopped together something that (gently) chucks my Sandpiper gliders.
(I may have to make video showing how I made this) if anyone is interested.

Details about my Sandpiper Glider:
Wing span: 12"
Wing area: 21 sq in
Weight: 4.5 grams

I was able to get some measurements (to the best of my ability), averaged over a number of flights, and calculated:

Here are the measurements:
Launcher to Wall: 20.5 ft
Launcher Height: 47 in
Air Density: 0.002378 slug/cuft (a number I used, not real measurement that day)
Sink Distance: 27 in
Flight Time: 1.48 s

Here are the calculations:
Air Speed: 9.5 mph (15.29 kph)
Sink Speed: 1.52 ft/s (46.33cm/s)
Lift: 4.47 grams
Drag: 0.49 grams
Glide Angle: 6.26 deg
Glide Ratio (also L/D Ratio): 9.11
Lift Coefficient: 0.292902812
Drag Coefficient: 0.03214787

So, in the end... I think the results turned out decent... but, I wanted to check in with the FT Community...

Given a Balsa Glider of these dimensions, does a 9.11 Glide Ratio seem about right? I was wondering if I should have expected a higher number.

There are a few things I'd like to change about this launcher, especially to make it more customizable. (Things like Launch Speed and Launch Angle come to mind). I had limited space, but I think one of my biggest challenges with this was launching the glider as close to its glide speed and glide angle as possible. In other words, I want it to be settled into its glide right off the gate for more accurate measurements. (My video shows the slow-mo of quite a few launches-- so, they are not perfect by far.)

I'm a noob at this stuff, so your thoughts and comments are welcomed!
Hello! I am trying to assemble a launcher, and I really like your model. May I ask you please if you can share the drawings or enlarged photos of your launcher? Thanks in advance:)