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Is the Mantis launch pad rated for G motors?

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Zeus-cat

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A friend of mine received the Aerotech Intiator/Mantis launch pad starter kit as a present. He worked his way up launching the Initiator on E's and F's and finally went to G's. He then stretched the Intiator by adding an electronics bay and a MAWD altimeter. This is where he started having problems.

On his first MAWD launch on a G64-10 he broke a clip on one of the legs on his Mantis pad. He also ripped the lower launch lug off the rocket as it whipped the launch rod rather violently. He launched it in the MAWD configuration for the second time yesterday and this time broke the clips on two more of the legs and again ripped the lower launch lug off. We decided one thing he needed to do was upgrade the 1/4 inch aluminum launch rod to steel to prevent the wild flexing and whipping. But the pad now has three broken legs. This doesn't seem right to us.

I thought the Mantis pad could handle an Intiator on a G64. What are other people's experiences with the Mantis pad?
 

MarkII

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Don't know, never had one. But one thing is apparent: your friend wasn't launching an Initiator when the pad's legs broke. You said that he had launched his Initiator on E's, F's and G's. So there's your answer - his Mantis pad provided a stable support during the launches of his Initiator on G motors. Then he modified his rocket by increasing its mass and adding length to it by installing a payload bay and an altimeter. At that point it was no longer a stock Initiator. The Mantis pad broke during his launches of that enlarged model, but it had held up fine when he launched his stock, unmodified version. If the two launches - the one of unmodified Initiator and the launches of the enlarged model - had occurred on the same day, at the same launch event, then one could perhaps infer that the leg breakage was somehow related to launching the larger version of the rocket. You don't mention how much mass and length his mods added to the Initiator, so it's hard to say if either change could have played any role in the structural failure of the pad supports. But presumably the launches of the modified Initiator occurred at some other time subsequent to the launches of the stock model. During that interval any number of things could have happened to the pad, things that might or might not have contributed to the weakening of the legs. In any event, one cannot immediately conclude that the thrust of a G motor produced the failure of the pad's legs, because, according to your account, he had previously launched rockets with G motors from it with no reported problems. It is therefore reasonable to surmise that other factors or events probably played a role in the failure of three of the pad's legs.

MarkII
 

Initiator001

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If a stock built AeroTech kit is flown off a Mantis pad using the motors listed for the specific AeroTech kit, then the pad will be fine.

I glue the leg holders/clips to the body of the Mantis pad for additional strength.
 

Chrisn

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Ive seen large H motors launch off a mantis and the pad is still in service
 

Donaldsrockets

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A friend of mine and I use a Mantis pad and it's always worked great for us.

The one exception was when I launched my AT G-Force off it on a G71R. At ignition, the pad was thrown backwards and the rocket flew off at about a 45 degree angle and was nearly horizontal at motor burnout. Luckily it got enough altitude to deploy the chute without incident and was recovered safely and both launch lugs were still firmly attached.

Since then, I have used bricks to secure the pad to the ground and all flights, including several more G-Force flights, even on the thrusty G76G have been perfect.

For the smaller AT kits and other MPR kits, securing the pad to the ground might be necessary but for large rockets like the G-Force, securing the pad is a MUST!!!;)
 

JoeG

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It's been many years since I have used a mantis pad but i did have one in the early nineties. I remember having to assemble mine. Is this still the case? If so what glue did you use?

I have launched the entire Aerotech line of rockets that was available then which included the Astrobee D, which is significantly heavier and longer than the Initiator, on a G80 and the Phoenix rocket glider. No problems.

The only weak point on the launcher at that time was those plastic clips that held the T shaped adjuster. I promptly broke those off, being clumsy, and ended up wiring it together and used it until I went to rails for mid power. Great pad. Lightweight and handles well the rockets it was intended for.

Not sure why your friend is having a problem.
 

Zeus-cat

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Eyeballing it I would say he stretched it by about 8 inches by adding the altimeter bay. He said the launch weight was about two pounds. I can ask him for specific details when he gets back to work on Tuesday.
 

RoyAtl

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I've seen the Mantis handle up to small H motors, and I've seen one handle a US Rockets CCV-1, a 10' long 4" diameter rocket (though on a longer rod).

I wouldn't call it heavy duty by a long shot, but I wouldn't hesitate to fly my Phantom 4000 on a G80 from it. The previous suggestion about bricks on the legs is probably a good one, though.
 

El Cheapo

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The bottom piece that is attached to the base where the legs slide in is a definite weak point. I broke one before I even used my mantis pad for the first time just removing the legs. To correct this problem, I permanently screwed the legs in by using two screws through the bottom of each leg and one through the top between the two bottom screws. It's not quite as portable or stowable but it's definitely more stable and has held up just fine on several launches w/G motors in taller heavier rockets than your friend's stretched Initiator.
 

hardinlw

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I've used my Mantis for G's but I drilled holes through the ends of the legs so I can skewer them to the ground with 1/4" aluminum tent pegs. I had an Estes rocket hang on the launch rod and tip over the Estes launcher and the thought of something G-powered going horizontal just did not appeal to me. The whipping sounds like one of the launch lugs is dragging on the rod which is exactly what made my Estes rocket tip over the pad back in the dim past.
 

Zeus-cat

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Thanks for all the replies. My friend has done a SpaceCad simulation of his rocket and it shows the CG 9 inches ahead of the CP. That says the rocket is stable.

The lower launch lug has been ripped off in both of the last two launches on a G64. See photos below from the last launch.

I shot high definition video of the launch. Watching it in slow motion the rocket starts leaning into the launch rod almost immediately; within the 2 or 3 inches of lifting off. Maximum deflection is maybe 15 to 20 degrees and the rotation happens all the way up the rod. It seems to stop once the rocket leaves the rod.

I recommend that he uses a steel launch rod to reduce the whip, but I am not sure what else to tell him.

IMG_2665mod.jpg


IMG_2666mod.jpg
 

kelltym88

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A Mantis pad should be fine. Stake the legs down into the ground and use a 5' launch rod.
 

JoeG

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My guess is it's not the rod but the lugs. Actually it's not the lugs either but the placement of them.

You moved the cg forward significantly but not the location of the lugs according to your photos. Pick the rocket up ready to fly. Hold it horizontally at the forward lug. I'll bet it is still way nose heavy in relation to the lug. Hold it by the forward lug. Now pull down on the aft lug. Note the amount of force needed to keep it horizontal. Now suspend the rocket at the cg and notice the change in the amount of force needed to keep it horizontal. Same thing happens on the rod in the vertical plane at lift off.

If you attach the forward lug nearer the cg I'll bet the whip problem goes away and the lugs stay on. You could probably use a 3/16" rod with no problems. Not that i would recomment it.

It's not the pad or the rod. It's the setup.
 

Zeus-cat

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Thanks for the info JoeG. My friend says the forward lug is 2 1/2 inches in front of the CG. Hmmm...
 

JoeG

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As I said in my post my thoughts were a guess. Somehow I don't think we have all the info.

You said,
Thanks for all the replies. My friend has done a SpaceCad simulation of his rocket and it shows the CG 9 inches ahead of the CP. That says the rocket is stable.
Then you said,
Thanks for the info JoeG. My friend says the forward lug is 2 1/2 inches in front of the CG. Hmmm...
The lugs I see in the photos are at the standard place on the Initiator. This means they are approximately 9 1/2 inches apart. If the c/g is 9 inches ahead of the c/p and the forward lug is 2 1/2 inches ahead of that point that puts the c/p about a half inch behind the aft end of the motor tube. Hmmm...

I think your friend might want to do his calculations over.

Folks here are trying to help but the info keeps changing. The initiator works great on the Mantis. The lugs are in the correct location. It looks like you have at least doubled the length of the rocket. Adding length to a rocket makes it more stable. That means it not only moves the c/g forward but increases the distance between the c/g and c/p.

My "guess" was that the lugs needed moved. I came to that conclusion through the information you have given and the photos posted. If this info is wrong then those who are trying to help have no basis for understanding the problem.

I hope your "friend" figures out what is wrong with his rocket because it is the rocket and not the pad. I have flown my Astrobee D from a Mantis many times.
 

Zeus-cat

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My friend made minor repairs to his rocket. He returned it to the same configuration he used on the flight with the violent whipping action he had when launching it from the Mantis launch pad.

He had today off and took the opportunity to launch his rocket. The only change he made from the last launch was to replace the Mantis launch pad with one he made out of 2X4’s with a six foot steel launch rod. He reported that it was a perfect launch with the rocket going straight up. There was no deflection during launch and no damage to the rocket.

on_pad.jpg


Flash 3.jpg
 

drain_bamage

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I want to thank everyone, especially Zeus_cat for posting this question and Joe-G for the input. The one missing detail is that I also have a launch lug on the upper body tube which can't be seen in the photos.

I will probably fix the Mantis and use it for my smaller rockets. Watching the video of the pad bending down and away from the exhaust flames just confirmed that using it with this rocket again isn't a good idea.

The new pad, while not the best looking, is cheap, very sturdy, easy to break down and transport, and should be usable with even larger rockets.
 
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