Need advice on how to check stabitliy on Sunward Gravity Rider

[Fox Flyers Rocketry]

Greetings! I have recently finished a Sunward Gravity Rider kit. I tried giving it a swing test and it wouldn't track straight even after adding 1 oz of weight to the forward nose cone. It's CG is currently located 1" forward of the top angle cut tube with engines installed. I would greatly appreciate any advice on how to proceed to confirm this model is stable.

 

[Fishhead]

I'm assuming that yours is the dual 18mm design. I was the photographer for Chan Stevens' flight several years back. That was probably the review that made them go with the 2x18mm cluster. https://www.rocketreviews.com/sunward-aerospace-gravity-rider--by-chan-stevens.html
https://www.rocketreviews.com/sunward-aerospace-gravity-rider--by-preston-hoover.html
https://www.rocketreviews.com/sunward-aerospace-gravity-rider-224-les-bradshaw.html
You might want to give these a read. Good info in all of them. I packed mine with a good load of epoxy and bbs and it still wasn't enough.:wink: But I build 'em FAT.

 

[boomtube]

Two of the reviews have this rocket built with a combination of BT-56 and BT-50 tubes while one of the reviews as well as my own example of this kit was built with BT-50 and BT-20 tubes.

I have yet to fly mine and it is difficult to “Swing test” not because it is inherently unstable but because you can’t get it swinging fast enough quick enough and once it starts to tumble nothing you can do is going to get it to stop.

On the other hand my stock build Estes “Alpha” won’t pass a swing test and neither will my Semroc “Astron” both of which fly fine. And don’t get me started on some of my two stage rockets.

Sooner or later you just have to put a couple of motors in it and let-er-rip. This is one of the nice things about BP motors and balsa/paper tube models. Little damage can be done if it does go wonky.

 

[Fox Flyers Rocketry]

Thanks for the links to the reviews Fishhead. I read through them all. Those were some great photos! Yes my Gravity Rider is set up for a 2 motor cluster. From what I read in the reviews I'm glad I built it that way. Thanks for the input on the swing test boomtube. I've flown lots of rockets but this will be my first cluster model. I also built this one with epoxy so I was a little concerned with having too much weight on the rear end of the model from all of the fins and tubes and fillets. Guess I'll have to give it a try and see what happens. Thanks again.

 

[Fishhead]

Thanks for the links to the reviews Fishhead. I read through them all. Those were some great photos! Yes my Gravity Rider is set up for a 2 motor cluster. From what I read in the reviews I'm glad I built it that way. Thanks for the input on the swing test boomtube. I've flown lots of rockets but this will be my first cluster model. I also built this one with epoxy so I was a little concerned with having too much weight on the rear end of the model from all of the fins and tubes and fillets. Guess I'll have to give it a try and see what happens. Thanks again.

I dragged mine out after I reread the reviews the other night. I think I'm going to give it a go at B6-4 Field sometime in the next couple of days. (I have vacation after tonight.) I flew it on a 2xC6-5 combination a couple of years ago, and the altitude was just about perfect. Besides, my nephew will love it.

 

[mjennings]

I'll vouch for that it is not swing testable. I put a ton of weight in the nose to get it to swing test and it cleared the launch rod by about 4 feet. that was on a single C6. Need to rebuild mine as a cluster. Where did you put the recovery gear? I was think of venting mine to the forward tube.

Mine is the older version with the cockpit nose cones.

 

[worldofglenn]

I do miss my Gravity rider - Antares Class! I built it as close to the instructions as I could fathom. It was very forgiving. My forward fins instead of being angled/aligned with the rear fins were instead level/parallel to the dual body tubes. Also, it was the model of redundancy, as it was dual engined, it was also dual parachuted! This was my first rocket that I build a baffle for (only on one side). She was one of the fastest rockets I've ever seen off the pad! I flew her on B's and C's, fast and straight up!

However, the dual parachute designed didn't work great. At start of descent they looked great, but invariably would find a way to wrap around each other. That being said, they were still filled enough to gently lower her to the grass.

Alas, I lost her in one of the most hated ways possible, a tragic accident in the garage involving some piled too high and heavy packing boxes. Her snapped fins and mangled body tubes await salvage in a forlorn corner now. I figure I'll take out the chutes and the baffle and one day build another one.

If you stayed close to the instructions, she'll fly beautifully for you. Let us know.....

 

[mjennings]

Another flaw in mine was it was my first build in a while, and I over filleted the tube joints and she was on the heavy side too.

Live Learn and Rebuild

 

[boomtube]

Here’s the problem IMO you encounter with the “Gravity Rider” and the swing test.

You can find the “Center of gravity” along its length, for and aft; the problem is the “Gravity Rider” is a non-symmetrical rocket. It has those two big fins on the “Port” side and two smaller fins on the “Starboard” now; how do you find a center of gravity along the centerline?

You can’t and when you try and swing the rocket those two heavier fins on the port side are going to try and move outward which will cause the rocket to tumble. This is a result of the centripetal force of the rocket going round and round and won’t show-up if the rocket is going straight up.

You’ll get this effect with a lot of those non-symmetrical rocket designs.

On the other hand; the Estes “Alpha” won’t pass the swing test and they fly fine.

 

[Fox Flyers Rocketry]

Mjennings I put my recovery device in the right side motor mount. Unfortunately I didn't think about the venting option or I probably would have opted for that instead. I think I may have gone a little heavy on the fillets on my Gravity Rider as well. I used epoxy so I'm sure that put it on the heavy side.

 

[Fox Flyers Rocketry]

I do miss my Gravity rider - Antares Class! I built it as close to the instructions as I could fathom. It was very forgiving. My forward fins instead of being angled/aligned with the rear fins were instead level/parallel to the dual body tubes. Also, it was the model of redundancy, as it was dual engined, it was also dual parachuted! This was my first rocket that I build a baffle for (only on one side). She was one of the fastest rockets I've ever seen off the pad! I flew her on B's and C's, fast and straight up!

However, the dual parachute designed didn't work great. At start of descent they looked great, but invariably would find a way to wrap around each other. That being said, they were still filled enough to gently lower her to the grass.

Alas, I lost her in one of the most hated ways possible, a tragic accident in the garage involving some piled too high and heavy packing boxes. Her snapped fins and mangled body tubes await salvage in a forlorn corner now. I figure I'll take out the chutes and the baffle and one day build another one.

If you stayed close to the instructions, she'll fly beautifully for you. Let us know.....

Thanks for the reassurance that this design is forgiveng. I did follow the instructions closely. I'm eagerly awaiting launching it. I'll let everyone know how it turns out, and I'll post launch pics.

 

[Fox Flyers Rocketry]

Here’s the problem IMO you encounter with the “Gravity Rider” and the swing test.

You can find the “Center of gravity” along its length, for and aft; the problem is the “Gravity Rider” is a non-symmetrical rocket. It has those two big fins on the “Port” side and two smaller fins on the “Starboard” now; how do you find a center of gravity along the centerline?

You can’t and when you try and swing the rocket those two heavier fins on the port side are going to try and move outward which will cause the rocket to tumble. This is a result of the centripetal force of the rocket going round and round and won’t show-up if the rocket is going straight up.

You’ll get this effect with a lot of those non-symmetrical rocket designs.

On the other hand; the Estes “Alpha” won’t pass the swing test and they fly fine.

Thanks for the input. Thats a good point about the non-symmetrical design. That was also why I was concerned about stability. I thought that the smaller forward fins on the starboard side may have been added to compensate for the large fins on the port side, but rocket designer I am not.

 

[boomtube]

The small forward fins may indeed compensate for the additional drag the larger fins produce but they won’t compensate for the additional lateral off center weight.

 

[Fox Flyers Rocketry]

A good point. Thanks for pointing that out boomtube. I should be launching sometime next week. I'll let everyone know how it turns out. I'll try to get some good pictures too. Thanks again.

 

[Fox Flyers Rocketry]

Greetings! I recently launched my Gravity Rider. It had a near perfect flight on 2 C6-3s. It rolled slightly clockwise during boost and drifted down range a ways on recovery. I got a couple of pics of it leaving the pad. 1 pic is from the spectators, the other is from a camera I had mounted under the launch pad. Thanks again to everyone who encouraged me to go for it after my rocket failed the swing test.

 

[Fishhead]

Greetings! I recently launched my Gravity Rider. It had a near perfect flight on 2 C6-3s. It rolled slightly clockwise during boost and drifted down range a ways on recovery. I got a couple of pics of it leaving the pad. 1 pic is from the spectators, the other is from a camera I had mounted under the launch pad. Thanks again to everyone who encouraged me to go for it after my rocket failed the swing test.

What kind of altitude did you get with the C6-3s?

 

[mjennings]

nice pictures!

 

[Fox Flyers Rocketry]

Thanks for the compliment on the pictures mjennings. My sister and her husband took most of the pictures. I'm not sure how high the rocket flew on 2 C6-3s Fishhead. Unfortunately I didn't have any altitude tracking equipment on hand. I would guess 700-800 feet. Here are some pictures of it on the way down.