Estes BT-80 Body Tube?

[Conan4480]

Can Estes BT-80 handle a G engine?

I am building a 1.6X Big Bertha up scale and I have a Balsa Machining BB nose cone. It should fit the Estes tubing just fine. If I use LOC Precision tubing the tubing will extend beyond the NC. I want to put a 29MM motor mount in as well.

 

[skip_dye]

I've flown my Estes Phoenix AIM-54C on G's several times. I've even put it up on a H128 before. It's built stock except for the 29mm MMT, plywood centering rings, and recovery harness.

Here's a pix on the H128 https://tinyurl.com/cdfqob

If you want a little extra insurance, pick up a full length coupler from BMS or Totally Tubular and insert it inside the BT-80. Just remember to cut it a little short, so the nose cone will fit.

Alan

 

[dwmzmm]

Shouldn't have any problems if the model is built ruggedly. I rebuilt my Estes
Maxi-Alpha a while back (also BT-80) to accommodate two D12's and two E9's
(actually, it could handle any properly combined four 24 mm cluster configuration). Flew it twice with excellent results (only to lose it during recovery on the last flight ). Liftoff shot below taken at NSL - 2006 in
McGregor, TX, photo by Tim Sapp. It was on this flight I lost it.

 

[luke strawwalker]

Why is it every time we lose a rocket, it's on it's last flight??

Sorry Dave couldn't resist... LOL

Later! OL JR

 

[dwmzmm]

Why is it every time we lose a rocket, it's on it's last flight??

Sorry Dave couldn't resist... LOL

Later! OL JR

No real sweat, Jeff. I have the parts on hand to build another Maxi-AlphaX4,
hope to get around to building it sometimes this year . Oh yes, it'll be a
four engine (24 mm) cluster again!!

 

[georgegassaway]

It depends on what the G engine is and what the BT-80 rocket is.

So, what G engine, and what is the rest of the BT-80 rocket design you have in mind?

A G80 will put roughly FOUR times as much aerodynamic stress on a model as a G40 would.

N-sec doesn't kill rockets, excess speed caused by thrust curve overcoming the rocket's strength is what kills rockets. And building a rocket like a tank to survive an overkill engine, instead of using a milder engine that could give similar altitude, is not good rocket science.

I am not thrilled that the "lower thrust" G choice is a G40 or G38 (well, there is the G33 reload but that is technically HPR).

It is SUCH a shame that Aerotech never came up with a low-cost alternative to the old great G25 engine (which IIRC was about 120 N-sec). The labor and other costs involved with the original G25 design made it price itself out of the market. So, I am not talking about reviving the original G25 but some sort of G twenty-something engine that would make models fly about the same on it as they did on G25's. It is screwy that there are ten different G engines ranging from 53 N to 80 N avg thrust, while there is no model rocket G engine with an average thrust between the G12 and G38.

So, let me suggest this. Build what you have in mind out of BT-80. And fly it with an F25. Because if you build it strong enough to hold up to an Aerotech G40, you will almost certainly increase the weight by more than 21.25%. That is the percentage of the N-sec difference between the G25 (80) an G40 now (97).

So if your rocket weighs more than 21.25% to hold up to an Aerotech G40, than it would have weighed to hold up to an F25, your rocket will fly LOWER on a G40 than it would on an F25. I’ve seen that happen for real, when NCR made a “thick wall” G powered version of an F powered version of mine. Theirs weighed at least 50% more than my original, so my original flew higher on an 80 N-sec F than theirs did on a 120 N-sec G (and mine cost significantly less to fly....the cost of the F vs. the cost of the G).

Now if the answer is "I do not care how well it flies, I want it to fly on a G", then there's no more advice I can give on this.

- George Gassaway

 

[Conan4480]

Thanks for the info. I do want this rocket to fly well. I think I had a little wonder lust when I first started designing this rocket. Its kinda like a car, I want the biggest and baddest engine I can get in it. Which is fine. However, putting a 29mm motor mount in this thing maybe isn't the right idea. But I already have a standard size Big Bertha with a 24mm mount in it. So to me it makes sense to put the 29mm motor mount in it.

As far as motor selection goes. I have some G64s on hand that are screaming to be launched. So that is what I had in mind. Will the Estes BT80 hold up?

I had already planned on putting at least a LOC coupler at the joint. It is 6" long and stronger than the Estes coupler.

 

[shreadvector]

Look at the thrust curves on the NAR website and you can answer your own questions about each and every possible motor and how it compares to the original D12. The G64 will deliver a serious kick.

You will want a lower average thrust motor. And you probably do not need to go with 29mm to get more oomph. Why not use a 24mm motor mount and simply use the readily available Aerotech 24mm motors, such as the single use E15 or E30 or the new F32? And then there are all of the reloadable 24mm motors.

 

[peter_stanley]

I launched a rocket made entirely of BT-70 tubing on a G-38 and H-97 without any problems. Here's the onboard video of the H powered flight.

Peter

 

[Handeman]

Make it a 29mm MMT. Just because it has the 29mm doesn't mean you have to fly it on G80s. You can adapt down and use the 24mm.

When you get to a launch early and if the RSO lets you launch it on the G80 as a "heads up" flight from the HPR pads before a lot of people show up, you'll know if it will hold up. If it shreds, the debris field should be safely away at the HPR pads, kind of like the extra distances required for EX.

I think it will hold up fine. Just keep an eye on the BT. If you get any kinks or wrinkles, fix it.

 

[rrobe99999]

You are building a Super Big Bertha (SBB). I built my SBB clone W/ BT-80, 29mm MM and some weight in a plastic NC. It has sucsessfully flown on an F26-6 and an F22-5. I chose low thrust motors because Berthas should have a slow liftoff. The scientific arguments make sense too.

 

[Johnly]

Can Estes BT-80 handle a G engine?

I am building a 1.6X Big Bertha up scale and I have a Balsa Machining BB nose cone. It should fit the Estes tubing just fine. If I use LOC Precision tubing the tubing will extend beyond the NC. I want to put a 29MM motor mount in as well.

I've flown a modified Launch Pad Kit AMRAAM kit that was built using standard BT-80 on a H238 with out a problem. The downside is that if a long length of BT-80 tubing gets a kink or dent in it, the airframe might not survive a high thrust flight.

John

 

[hardinlw]

If you are worried, glass it. I came up with a pretty easy way to glass some BT-55 so that it could take a G. We have not actually flown it yet, but the glassed tube is really strong. Basically, you use two layers of 0.6 ounce cloth with West Systems or equivalent resin rolled on with a small foam paint roller. Then, warp it with peel ply. This will not hold up to vacuum bagging, so I used the old Hobby-Poxy balloon method. Get a long "airship" balloon and blow it up. The peel ply needs to be folded over into the inside of the tube. Start pushing the balloon onto the tube while letting the air escape. With practice, you can get it entirely onto the 18" tube; although, you might need to slide the neck down over the rest of the balloon. Practice doing this with just a bare body tube until you get the technique down. If it doesn't work for you, you may need a larger balloon. Tubes glassed in this way will be a little rough which is good for bonding on the fins. Light sanding and some automotive primer will smooth things out.

 

[Sandy H.]

Here is one I built a while back. Smallest motor so far was an E23 and the largest the new full G80. It has flown on G64's the most, but last weekend was an F40 and a G40 the previous month.

It is an Estes PNC80, 2 18" BT80's, ply fins, TTW and a 29mm heavy motor mount. I also put in a plain baffle, but there's nothing magic there. The shock cord is long kevlar (10ft-ish) but it does zipper easy if the delay is short. I have recovered it on a 15" or 18" nylon chute most often, but on a 6"x60" streamer on a soft field.

The attached picture has been modified in the Gimp to change the background and add the lettering. I have no idea why I chose "Search Problems" for the name, because it really is the Gee-Whiz. I made the decal, but never put it on.

I guess that's plenty of information, but the bottom line is that wood glue and Estes components can make a fully functional full mid-power rocket. If you added a bunch of nose weight or really lengthened the design, you'd start to run into problems. This one is simple and flies well, nothing more to it.

Sandy.

View attachment gee whiz.pdf

 

[snaquin]

Can Estes BT-80 handle a G engine?

I am building a 1.6X Big Bertha up scale and I have a Balsa Machining BB nose cone. It should fit the Estes tubing just fine. If I use LOC Precision tubing the tubing will extend beyond the NC. I want to put a 29MM motor mount in as well.

Have you considered the T80H tubing and BBH cone? Save the BT-80 for another build.

.041 wall thickness compared to the .021 wall thickness you have now.

I'm cloning an OOP kit with this same heavy walled tubing that I bought from Madcow Rocketry and it's nice stuff to work with.

BT-80 may work just fine but this will make for a more durable build.

.

 

[Balsa Bob]

I built a SBB modified only for dual deploy, and it loved the AT F40W.
https://www.youtube.com/watch?v=Xts6HgSLQIk
Once I put it up on one of the old G33Js, but it suffered separation.

 

[Sandy H.]

Nice video (on the F40?)! I have a G33J left, so should I be concerned with the pic in the post? [edit] I see it was a seperation, so it shouldn't be a deal breaker, I think. [edit]
Sandy.

 

[Balsa Bob]

The G33J provided an impressive boost.
I should have replaced the shock cord a few flights earlier.
Instead, my procrastination turned and bit me hard.