What’s the best angle to maximize distance of a rocket boosted glider?

[RGClark]

The lift/drag (L/D) ratio can approach 60 for a modern sailplane:

An ASH 31 glider with very high aspect ratio (AR=33.5) lift-to-drag ratio (L/D 56)
https://en.m.wikipedia.org/wiki/Aspect_ratio_(aeronautics)

The L/D ratio is equal to the glide ratio, which is the ratio of the horizontal length traveled for the vertical drop of a glider. Then by just getting a glider with a 60 L/D ratio to 100 meters, it would be able to glide 6,000 meters, 6 km, horizontal distance.

My idea about how to get a small glider with this high L/D ratio to 100 meters would have the wings first folded up, swung back, and retracted into the fuselage. The fuselage would be given a minimal drag cross-section, such as a tear drop or airfoil shape:

Using the airless approximation, i.e., operating only by gravity, you need about 45 m/s, 160 km/hr, 100 mph, vertical launch speed to reach 100 m altitude. You would need somewhat more than this speed under drag to reach the 100 m height, but the airfoil shape should mean the required speed is still well within the capabilities of a small motor.

After the glider reaches the 100 m altitude, the wings are deployed and the up to 6 km glide range is reached.

Still, I wonder if we can arrange an even larger glide range simply by keeping the glider in its usual configuration and launching at an angle from the ground so you get both altitude and distance from the beginning. The issue though is that eventhough you have high L/D, this will also be accompanied by high drag, when the wings are fully deployed.

So it’s not certain you can get increased range this way. But what would be the optimal angle to maximize distance?

Bob Clark

 

[Maxout]

I don't see any way you're going to get 60:1 out of any small model, no matter how carefully you design it. Air molecules don't scale.

Swing wings are great if you're looking for a wingloading reduction. They are not good if you're looking for L/D, unless you're willing to resort to some serious composite voodoo.

If you're only looking to boost to 100 meters, stick a long burn G motor on the back of a Maxa or Explorer 4. They're big, light, and efficient.Better yet, do it with Plus: https://www.kennedycomposites.com/plus.htm

This is probably the ultimate swing wing (not available in stores): https://www.thebuildingboard.com/2012/02/vladimir-sychovs-folder.html

A commercially available F1C folder would probably handle F-G long burn launch speeds just fine. The Free Flight For Sale group on facebook sometimes has those up for grabs.

 

[RGClark]

I don't see any way you're going to get 60:1 out of any small model, no matter how carefully you design it. Air molecules don't scale.
Swing wings are great if you're looking for a wingloading reduction. They are not good if you're looking for L/D, unless you're willing to resort to some serious composite voodoo.
If you're only looking to boost to 100 meters, stick a long burn G motor on the back of a Maxa or Explorer 4. They're big, light, and efficient.Better yet, do it with Plus: https://www.kennedycomposites.com/plus.htm
...

The gliders on that Kennedycomposites page have quite high aspect ratio. As discussed in the first post this is related to high glide ratio. I’d like to see what it is for these gliders.

It doesn’t have to be at the very highest range of 60 to 1 to be useful.

Bob Clark

 

[Alan15578]

Bob,

It is not clear why you want to maximize horizontal range from only 100m altitude, but it is an interesting problem. Model rocket launch angles are limited to 30 degrees from vertical. That will get you downrange the farthest, and you can adjust other parameters to get your 100m altitude. You can also make use of the "gravity turn" and accentuate it a bit by shortening the launch guide length, with a minimum velocity constraint off the rail.

I have a lot of contest experience flying Groundhogs. This is a constant chord, aspect ratio 24 swing wing rocket glider for NAR duration contests. The AR is really too high for duration, and better for distance. Most swing wings share a common problem; They can lose a lot of altitude in the transition from boost to glide after the wings deploy. What you actually want to do is launch at an angle into the wind so that the model arcs over, right side up, before the wings deploy. This will minimize altitude loss in the transition. It is not uncommon for a swing wing to deploy the wings from vertical flight and then pull a 270 degree turn to near glide attitude, losing perhaps half of its peak altitude. Similarly, if the model arcs over but is upside down at deployment, it then pulls a half loop to transition into a proper glide orientation. Swing wings just don't transition as quickly as their stout stubby brethren. The Groundhog has enough dihedral with wings folded that it will usually follow the boost and coast arc right side up and deploy the wings to transition into glide with minimal loss of altitude. Of course you can always force it to roll on boost as I did once with an E5 motor. The deliberate non vertical boost can be used just to fly up wind, but it can also be used to try and hit thermals that may be off the side. You are going tn need to find some lift if you want to achieve a 60:1 glide ratio! If you fold back your wings and stuff then into a tube, you will be cursed with random deployment attitudes, and the associated transition losses. Similarly, if you use a swing/flop design and rely on only tip panel dihedral, you will have difficulty getting good reliable optimal deployment attitudes.

I'm still puzzled by the problem that you set up, but good luck!

Alan

 

[RGClark]

Bob,

It is not clear why you want to maximize horizontal range from only 100m altitude, but it is an interesting problem. Model rocket launch angles are limited to 30 degrees from vertical. That will get you downrange the farthest, and you can adjust other parameters to get your 100m altitude. You can also make use of the "gravity turn" and accentuate it a bit by shortening the launch guide length, with a minimum velocity constraint off the rail.
...
Alan

Thanks for the informative response. The actual impetus of my question was a real world application. But I would think in amateur competitions there would be interest in records for glide range of a boosted glider just as there is for altitude and duration time.

By the way, if my real world application pans out there may be useful contributions amateurs can make in regards to getting aerodynamic shapes to maximize glide ratio for small scale gliders. And also methods to stabilize flight passively to maintain stability and straight flight path under the effects of wind.

Bob Clark

 

[Alan15578]

Thanks for the informative response. The actual impetus of my question was a real world application. But I would think in amateur competitions there would be interest in records for glide range of a boosted glider just as there is for altitude and duration time.

By the way, if my real world application pans out there may be useful contributions amateurs can make in regards to getting aerodynamic shapes to maximize glide ratio for small scale gliders. And also methods to stabilize flight passively to maintain stability and flight straight path under the effects of wind.

Bob Clark

You would think wrong. Ideally, we want our contest models to be recovered with near zero net range, even when from extreme altitude or duration.

You should know that many, probably most, of the participants on this forum are experienced professionals. But yes, amateurs can make contributions, and even develop skills beyond that of some professionals. Small glider models will never match the L/D glide performance of full size aircraft. It is a Reynolds number thing. If you discover any methods to passively maintain straight flight paths under the effects of wind, be sure to share them with us!

Alan

 

[burkefj]

To clarify if you are flying an RC rocket glider you may go to 45 degrees if controllable during boost and pointed away from spectators.

1. Launch Angle. An R/C RBG may be launched at angles of 30 to 45 degrees from vertical provided that it is capable of having its flight path controlled safely during rocket boost and provided that the launcher is pointed away from specified spectator areas. Otherwise the R/C RBG may not be launched at an angle exceeding 30 degrees from vertical.

Bob,

Model rocket launch angles are limited to 30 degrees from vertical. That will get you downrange the farthest, and you can adjust other parameters to get your 100m altitude. You can also make use of the "gravity turn" and accentuate it a bit by shortening the launch guide length, with a minimum velocity constraint off the rail.