Launch Lug Opinion Request

[RCBrust]

Guys,

I'm wrapping up the design of a rocket for the grandkids and was wondering what you guys think of the current launch lug configuration. The launch lug is part of the fin can (3D printed) and is 4 inches long. The overall length of the model is 21 inches. Do you think I can get away without a top launch lug on the body tube?

Thanks,
Randy

 

[lakeroadster]

Guys,

I'm wrapping up the design of a rocket for the grandkids and was wondering what you guys think of the current launch lug configuration. The launch lug is part of the fin can (3D printed) and is 4 inches long. The overall length of the model is 21 inches. Do you think I can get away without a top launch lug on the body tube?

Thanks,
Randy

View attachment 636524

That'll work. Ideally a bit higher. Where's the cg?​

 

[RCBrust]

It will be about 1 to 2 inches ahead of the top of the fin can.

Randy

 

[SolarYellow]

The Enerjet/Centuri/Estes BT-56 fin can did it that way and it was only around for like 50 years, so it'll probably never work.

 

[BEC]

The Enerjet/Centuri/Estes BT-56 fin can did it that way and it was only around for like 50 years, so it'll probably never work.

Oddly, the instructions for the Estes Eliminator (which uses that fin can) say to NOT use the built in lug in the fin can. The last time I built an Eliminator I put a short length of 3/16 launch lug up near the top of the body in line with the fin can's launch lug. That works nicely.

Many Centuri designs have a launch lug very low on the body like this.

 

[Art Upton]

Oddly, the instructions for the Estes Eliminator (which uses that fin can) say to NOT use the built in lug in the fin can. The last time I built an Eliminator I put a short length of 3/16 launch lug up near the top of the body in line with the fin can's launch lug. That works nicely.

Many Centuri designs have a launch lug very low on the body like this.

I've put regular Rail buttons on my many Eliminators. I also put 29mm motor mounts in them at times also, sometimes they get lost, sometimes someone finds them and brings them back

Edit: I have one I need to finish upstairs for this flying season still. Needs 29mm motor mount installed , recovery attached to that, and buttons put on.

 

[BEC]

I've put regular Rail buttons on my many Eliminators. I also put 29mm motor mounts in them at times also, sometimes they get lost, sometimes someone finds them and brings them back

Edit: I have one I need to finish upstairs for this flying season still. Needs 29mm motor mount installed , recovery attached to that, and buttons put on.

Yeah, an Eliminator with a 29mm mount is a good start on an Enerjet 1340 clone. I need to get up the nerve to fly mine on a 29mm motor someday...

 

[kjhambrick]

@RCBrust --

The built-in fin-can launch lug worked fine on the Estes Maniacs I flew in the olden days, even on 24mm AT G55W motors

HTH

-- kjh

p.s. I miss the Maniac !

The Eliminator looks much the same !

Is it still in production ?

Thanks, @Art Upton and @BEC !

EDIT: shucks, never mind ... I see that the Eliminator is out of production too ...

 

[Art Upton]

@RCBrust -

EDIT: shucks, never mind ... I see that the Eliminator is out of production too ...

I bought a huge box of them at Hobby Lobby when they went on clearance when going out of production even though I had been buying them [and breaking or loosing them] for as long as they were made. I think I had 8 of them in that box. I don't have that many left now.

I did get one back flying on an Ellis Mountain H50 motor twice. One I walked to for a long time and found. The one at LDRS 23 in Geneseo upstate NY I found in the Kid's Lost and Found Box the next day.

I saw a yellow nose cone on a the edge of a purple body tube. I walked over and there was my rocket back.

 

[kjhambrick]

... I did get one back flying on an Ellis Mountain H50 motor twice ...

It has been a long time but I only recall finding my Maniac + G55 once.

It was a rare dead-calm day in Ocotillo and it landed over a slight ridge, right on the road -- 'Coyote Wells #2' -- is that the right name @CoyoteNumber2 ?

I think I lost five -or- six other Maniacs, including one at Fiesta Island in Mission Bay on a 'measley' D12

-- kjh

 

[CoyoteNumber2]

It was a rare dead-calm day in Ocotillo and it landed over a slight ridge, right on the road -- 'Coyote Wells #2' -- is that the right name @CoyoteNumber2 ?

Home Sweet Home.

 

[SolarYellow]

I bought a huge box of them at Hobby Lobby when they went on clearance when going out of production even though I had been buying them [and breaking or loosing them] for as long as they were made. I think I had 8 of them in that box. I don't have that many left now.

OK, I guess I'm buying all the HFXLs I can find now.

 

[RCBrust]

The built-in fin-can launch lug worked fine on the Estes Maniacs I flew in the olden days, even on 24mm AT G55W motors

I thought of the Maniac when I posted this. I had one years ago. I was thinking that it only used the fin can lug but when I looked up the manual online, it showed an upper lug mounted to the body tube. I'll try the new model with just the lower lug and see how it works.

Randy

 

[lakeroadster]

Sorry... Nevermind... Wrong Thread...

 

[PDawg]

OK, I guess I'm buying all the HFXLs I can find now.

That's what I did, Lol. I like mid split rockets and it's easy with that kit.

 

[BABAR]

Most of my scratch built standard rockets have the lug set in the fin/body root (so very near the tail) and they fly just fine.

Not optimal for high winds, but you probly shouldn’t be flying in high winds anyway.

Not sure it applies with one piece 3D printed models, but my biggest concern with lugs far posterior to CG is the wind tipping the rocket and breaking off the lug if it sits on the pad for a while (think club batch launches.)

Second concern is lug drag on the rod during launch due to winds, but yours is a pretty long lug so this should be minimal..

Straight Trails!

 

[RCBrust]

Good data point. About how long are your lugs typically?

Randy

 

[BABAR]

Good data point. About how long are your lugs typically?

Randy

I use paper straws, as I build a lot of rockets scratch and am too cheap to buy “real” lugs. Mine probably average 1 3/4 to 2 inches.

FWIW, the lug on your model eyeballs pretty well on my MindSim, your rocket is not extremely long, so the moment arm between the CG and the lug doesn’t seem extreme.

Launch lug position might be more critical if you were building a rocket for competition or other extreme performance, but in those cases usually you’d be launching from a tower with NO lugs.

Not sure it matters for your design, all my scratch builds tuck the lug into the body/fin joint. I figure it strengthens BOTH the rocket fin joint AND the rocket lug joint. Also, assuming the fin is straight, the lug is gonna be straight automatically. As for drag, dunno if it helps or hurts versus a free standing independent lug, probably a wash.

 

[cwbullet]

Guys,

I'm wrapping up the design of a rocket for the grandkids and was wondering what you guys think of the current launch lug configuration. The launch lug is part of the fin can (3D printed) and is 4 inches long. The overall length of the model is 21 inches. Do you think I can get away without a top launch lug on the body tube?

Thanks,
Randy

View attachment 636524

One that long will be fine - no need to move it.