Rogallo Wing Glider

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Aug 13, 2009
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Hi everybody,

I currently live in Germany, and with rather strict explosives laws, I am in fact limited to C engines and one stage designs only.
Still, I am always looking for a small “engineering challenge”. With the C-engine limit, lots of rocketry challenges are excluded from the start (high power, payloads, clustering, staging - you name it!).

What keeps intriguing me, however, are boosted gliders, so I have put some thought into building one (for irrational reasons I prefer rear engined gliders). At first I thought about a glider with rigid balsa wood wings in delta form with a pop pod design, not unlike this Concord semi-scale design.[1] Once I’d have some experience, I might have thought about adding RC capabilities.
The huge problem is the weight: If you want to have anything that looks like a decent glider even from the ground, the balsa wood wings (not to speak of the RC components) would make any design too heavy to be launched on a C engine. Furthermore all rigid wing gliders have to overcome their typical stability problems, but that I estimated surmountable. Still, huge rigid wing areas result in high drag, which doesn’t necessarily help to achieve impressive performances with C engines…

Then I found an old Gemini design, which was to be recovered using a Rogallo Wing.[2] Given the fact that it might be designed to use some fabric that might be used for parachutes as well, this idea seems to have a rather promising wing area o weight ratio.

I thought of a design that does not use a paraglider design (in which case it was just a parachute in the form of a Rogallo wing), but directly attach the wings to the outside of the body tube. The fabric would allow them to be folded together during the launch phase, held back by the very short booster stage (to which also the fins are fitted). The boost stage would only be about 10 cm long to fit the engine and fins. After engine burnout the booster stage would separate with the engine and be recovered with a small streamer. The separation also sets free a spring or elastic band mechanism that unfolds the wings.

I figure that this type of wing would make it harder to trim the glider for the glide phase, but it would most certainly be the lightest type of wing, and thus allow a bigger model under the given limitations.

My problem is concerned with the unfolding of the wings: The overall approach I have in mind is to have the wings under tension when folded. The booster separation would release this tension and the wings would fold up. The main problem is to create the tension. I thought about spanning an elastic band from one wing through the body tube and to the opposite wing. But I am not sure whether this is the technically most elegant solution, and whether this rubber band wouldn’t require too much maintenance or changing.

Another way could be to join both wings with a hinge that has some spring mechanism, although I am not sure yet about its design and where to get the spring.

Do you know of any such design? Do you have any advice concerning the method and design of the various fold/unfold mechanisms?

Any help is very much appreciated!


Welcome to TRF! Actually, there is a lot you can do with motors rated C or less. Are you sure that clustering is out of the question? If it is a matter of total impulse or propellant weight, you could try designing models with 2 or 3 13mm motors using 1/2A3-4T or A3-4T motors. Also, you can fly payloads with a B or C motor just fine as well.

Now, to address some of your questions. Check out Jimz and Ye Old Rocket Shoppe for some interesting rocket plans from a lot of different companies. One that sounds like something you'd like is the Sky Dart - a model that Estes put out in the sixties and seventies. It features a delta wing and an internal boost pod that places extra weight in the nose of the glider and holds the spring-loaded elevator down into the boost position. At ejection, the pod kicks out of the glider body, taking the nose weight with it and letting the elevator flip up into the glide position. The pod comes back by parachute. It is a beautiful design.

As for rogalo (flex wing) designs, you've got a couple of options. You could use rubber bands rigged from the spars to the front of the fuselage to pull them into position at ejection. Another possibility is to use a spring clip bent from piano wire. Do a search in the Archive for flexwing or flex wing - I'm pretty sure there is at least one thread there about flexies that shows how to build a spring bending jig. Both these methods keep the wing spars under tension while in the boost phase, but release and deploy at ejection.

Good luck and keep us apprised of your adventures in rocketry - and don't forget pictures! :D
Actually, there are several ways of doing a flexie type glider.

The most common by far is the standard ejected type from a longish rocket body sans nose cone. These can glide ridiculously well, and tend to get lost way too easily. Normally only seen in contests.

The rarer form of flexie recovery is similar to that of which you described, as in bringing back all or most of the rocket vehicle via flexwing. I myself have done very many of these over the years, including an HPR version with a nine foot span and using H/I motors.

You can just attach a flexwing to a conventional rocket planform by affixing it to the BT by its center spar. In fact, I have also done this with a real delta KITE as well. Bear in mind, though, if you attach a normally free flying flexie to a rocket body it will now have to bear much more weight than it likes, and may therefore collapse if you do not increase the 'stretchiness' of what ever you are using to open the wings.

How do you deploy the wing for glide? Lots of complex ways, and one very easy one. Of course, I am referring to the good old burn string method, where in this case you fold up the wings real nice like and then wrap thread around them and through a pair of holes in the BT, about halfway up the chord of the flexwing, and tied down. This is cool, and even my old HPR sized job used this method.

Caveats though.....if you do this on something smaller than a BT50 you run the risk of having the tube weakened by the ejection charges venting out in such a fashion (but you can double up that area with a coupler) and the possibility of burning/singing the flex material. The latter is not good for glide trim :eyepop::y:

IF you are stuck with C motors and have some experience with normal flexie construction you should try one with like a BT50 size and around two feet long. Of course, you can also make a version that ejects a rear module to deploy both the wings as well as an elevator, which is easier to fly but more difficult to build. The old Estes Soaring Eagle comes to mind here.

Like you also mentioned, just slapping a flexwing onto a rocket body or making it carry a load isnt as easy as it seems. These things are very touchy for glide trim, if you think you have it you probably do not. If you can incorporate an elevator into your model that is better, but once again, youve just traded build complexity for glide complexity.

I have another version of my old standby flexie ready to fly tomorrow. This has a 40" span similar to a kite, mounted onto a triangular Readiboard based body, and also added an elevator system as well. However, this 'hacked' version now requires TWO separate burn strings, one for the main wings and the other for the newly added rudder. It still wants to trim funny though but its going up regardless :eek:

The last version of this looked like it was going to glide nicely but then went into attack mode and landed on Rogers RV (jadebox here on TRF). Wonder how fast Brian can run when I fly this one?? :shock::eyepop:
Thanks a lot for your ideas and comments!

Yes, staging and clustering is out of the question, even when all of the motors' propellant mass is below 20g! I don't get the logic behind this, but that's the way it is. :shock:
I don't live very far from the Netherlands, so I might check out the situation over there.

The Sky Dart is definitely a thing I will look into. Maybe I'll build it first in order to have a benchmark for a "Soaring Eagle" like design, which should have better performance (in terms of height, not necessarily in glide duration - though I hope it does) due to the wings being folded during the ascent phase. Flex Wing designs seem rather complicated, so the Sky Dart is maybe a good first glider to build.

I've finally found some interesting stuff on the internet: the November '68 issue of the Model Rocketry magazine had a Flex Wing article:
Design C3 on p.9 is what I originally had in mind.
It uses a scissor spring for the deployment actuator, but I have no idea where to get one like that, so I will probably use an elastic shock chord to build up the tension.

What makes me wonder though is that he slices something like 80% of the body tube (seems to me it's a BT-20 equivalent) on both sides in order to put the wing inside the tube. Shouldn't that reduce the structural stability quite a lot? I had hoped to only slice it up an inch or so near the top, where the pivot joins both wings and the elastic band passes through, while the flex wing itself is somehow folded on the tube's outside.

From a drag point of view neither option is perfect, but if the folding is done well the whole thing should weigh less than having a sheath plate like that and it should still produce less drag than solid balsa wings such as the Star Dart's.

Unfortunately, the Model Rocket mag design does not give any measures besides optimum wing area (25-35 sq. inches). 35 sq. in. should be about 225 cm², which (unless I got my maths wrong, which is quite possible) gives 2 triangle wings of 15*15 cm. Even if you change the angles a bit, that doesn't seem like a lot to me. What do you guys think?

I guess I'll start with the Star Dart, before combining ideas of the Soaring Eagle, the Model Rocketry Magazine glider and my own ideas into a flex wing rogallo design.

I think I'll start with a boilerplate that lets me figure out the exact wing configuration and lets me test several actuators. I will use that one for trial and error with "drop tests" from a balcony, before working on the actual rocket-propelled model.

Thanks once more!
The scissor spring is very easy to construct using music wire- you just need to loop the wire around a suitable rod or wood dowel and leave enough at the ends to make the arms to attach to the spars.

Also take a look at the plans for the Soaring Eagle kit at