Using a Single Launch Lug?

[Swissyhawk]

I'm building a mini Screech (1.6" dia) and I was thinking of using a PML linear launch rail lug instead of rail buttons. The launch lug is 2" long. Do you think it would it be OK to only use one launch lug on this rocket?

 

[fyrfytr310]

I'd be concerned about binding and ultimately lug failure before the rocket gets up to speed.

 

[claytonbirchenough]

I'd use two...

 

[manixFan]

How long and how heavy? I use a single guide like the one you describe on several rockets with no issues. I just make sure it's bonded well and located in the right position. I haven't checked in a while but I would guess most if not all are under one pound and fly on mid power. The biggest issue is to make sure that the rocket is not on the rail at a cross angle to the wind, but that's true for any type of rail guide.

I bet I have several dozen flights without any hang ups or lug failure. But of course others may have had a different outcome.


Tony

 

[markkoelsch]

I think it is too long. If it was under a couple of feet it would likely work.

 

[OverTheTop]

To answer your question, USE TWO. They don't take torque well from my experience.

I used these on my L3 1/2 scale Nike Smoke. They both broke off as we loaded it onto the rail. The ones I had were very brittle for some reason. Ended up flying on standard buttons.

 

[Swissyhawk]

Right now all the parts weight 1.5 lbs, that doesn't include a chute, one harness or the motor; so it will probably be close to 2 lbs on the pad. I think the point about it being too long (it's 43") is a good point.

The main reason I was asking is because I think two rail lugs just looks too big and kind of ugly on a rocket of this size.

On my MDRM I cut the PML rail lug in half and glued each half to the rocket spaced about a foot apart. I may do the same thing with this rocket.

 

[manixFan]

The only way I would use those guides on a larger rocket would be to screw them in. I don't think surface mount guides that are glued on are good for anything other than fairly small lightweight rockets. The longest rocket I have used a single guide on is a min diameter 29mm phenolic about 43" and about 1 pound. It has flown on G80s with no trouble. Most of the other rockets I have used them on are shorter and larger diameter, but all at about 1 lb or less.

Looking at the specs for the Mini-Screech I'd say it's on the edge for a single guide. It's pretty long and the listed weight is 18 oz which always seems to be optimistic. If you mounted it at the CG it will be pretty high up so you'd want a longer rail to compensate.

Since it's a fiberglass rocket you should be able to get a very good bond if you scuff both up pretty well. But since it's not a min diameter you should be able just use regular rail buttons and keep the top button below the top centering ring of the motor mount. I think that would be preferable. I use the glue on ones on rockets that originally had lugs and are made from regular paper tubing and wouldn't support a screw very well.

So, based on my experience I think you could use one and it would be fine. However I don't see any reason not to use regular buttons which I think have several advantages.


Tony

 

[timbucktoo]

I have a LOC-V2 with a 4" lug but it's a pretty short rocket.
Have you considered rail buttons?

 

[OverTheTop]

Have you considered fly-away rail guides? At 1.6" it would be perfect!

 

[Swissyhawk]

I could certainly use rail buttons. I have plenty of those. I could also use a fly-away rail guide. I have one in 54 mm and like it, but I'd have to buy a smaller one for this rocket.

I think there's a good chance a single lug would be sufficient, but when I think about what might happen if the lug failed, I've decided to go with two - whether it be lugs or buttons.

 

[NateLowrie]

I could certainly use rail buttons. I have plenty of those. I could also use a fly-away rail guide. I have one in 54 mm and like it, but I'd have to buy a smaller one for this rocket.

I think there's a good chance a single lug would be sufficient, but when I think about what might happen if the lug failed, I've decided to go with two - whether it be lugs or buttons.

You could use mini rail buttons or even the micro buttons on it and be fine.

 

[markkoelsch]

Right now all the parts weight 1.5 lbs, that doesn't include a chute, one harness or the motor; so it will probably be close to 2 lbs on the pad. I think the point about it being too long (it's 43") is a good point.

The main reason I was asking is because I think two rail lugs just looks too big and kind of ugly on a rocket of this size.

On my MDRM I cut the PML rail lug in half and glued each half to the rocket spaced about a foot apart. I may do the same thing with this rocket.

Use the giant leap conformal guides- they are not as bulky.

 

[manixFan]

Use the giant leap conformal guides- they are not as bulky.

Are those the same as the Acme aluminum guides? I've used those as well with good results. Some folks claim they gall on the aluminum rail but I've never experienced that. I always put a bit of lube on the guide though (and spray the rail with WD-40 if possible).

I have also cut the PML guides in half as well and used them that way. But the shorter guide does increase the chance of binding somewhat. As long as you aren't weathercocking on the rail you should be fine.

But... I think buttons are the way to go. They will screw right into the fiberglass and will hold no problem and can be easily replaced. Plus they don't look bad.

Good luck,


Tony

 

[NateLowrie]

Are those the same as the Acme aluminum guides? I've used those as well with good results. Some folks claim they gall on the aluminum rail but I've never experienced that. I always put a bit of lube on the guide though (and spray the rail with WD-40 if possible).

I have also cut the PML guides in half as well and used them that way. But the shorter guide does increase the chance of binding somewhat. As long as you aren't weathercocking on the rail you should be fine.

But... I think buttons are the way to go. They will screw right into the fiberglass and will hold no problem and can be easily replaced. Plus they don't look bad.

Good luck,


Tony

Apogee sell a 3D printed version of the conformal guides. It holds up great.

 

[Jozef]

Right now all the parts weight 1.5 lbs, that doesn't include a chute, one harness or the motor; so it will probably be close to 2 lbs on the pad. I think the point about it being too long (it's 43") is a good point.

The main reason I was asking is because I think two rail lugs just looks too big and kind of ugly on a rocket of this size.

On my MDRM I cut the PML rail lug in half and glued each half to the rocket spaced about a foot apart. I may do the same thing with this rocket.

Try mini rail buttons from rail buttons.com I use them on my Mini Tomach and Aerotech Arreaux. They work great and look proportioned to smaller airframes. You will need a 20 mm rail, so check with your club... or BYO...

 

[scsager]

I'm building a mini Screech (1.6" dia) and I was thinking of using a PML linear launch rail lug instead of rail buttons. The launch lug is 2" long. Do you think it would it be OK to only use one launch lug on this rocket?

Personally, I would ditch the PML thing altogether and use standard rail buttons.... but that's just me, sometimes I get all crazy and such.

At a club launch, the single PML guide might not even make it past the RSO table.

 

[bobkrech]

Fly-away rail guides will work great. https://cart.amwprox.com/index.php?...mart_product_id=882&virtuemart_category_id=69

No prep work and nothing permanently attached to rocket. The one listed above is specifically sized for thin wall FG tubes.

 

[manixFan]

Fly-away rail guides will work great. https://cart.amwprox.com/index.php?...mart_product_id=882&virtuemart_category_id=69

No prep work and nothing permanently attached to rocket. The one listed above is specifically sized for thin wall FG tubes.

Have you personally used those guides? They are not without their issues and they do require careful prep work and fitting so the body tube cannot slide up inside the guide during launch. If used incorrectly they can have a pretty substantial impact on performance and even safety.

Plus you need to have spares because if they break you are done launching if you are relying on them and you only have one.

All this is based on research I did before using them and my personal experience at BALLS this year (I took guides in 3 sizes - 38, 54, and 75mm). There are several threads that talk about the issues that can occur with the flyaway guides.


Tony