Over-building

[Kirk G]

Can we get a definition for what it means to "over-build"?

When I am attaching balsa wood fins, and laying on an additional bead of glue for a smooth fillet, I am always concerned that I might be adding too much weight.

Is there an actual definition for being "over-built", and is it possible that this might disqualify one from a competition or have a range safety officer reject your rocket?

Comments?

 

[TopRamen]

:w: op:

 

[blackbrandt]

I am what one would call an overbuilder. My darkstar jr (2 inch by 5.5 foot fiberglass) weighs almost a pound more than the kit parts, and that is dry weight. Of course, I never have failures due to weaknesses... except for that #$%^&* motor adapter, but that is a different story.

 

[GregGleason]

"No".

Unless the rocket is so over-built (i.e., the launch mass is so great) that the intended motor(s) cannot safely launch it.

Greg

 

[samb]

Can we get a definition for what it means to "over-build"?

I suspect you will get alot of them ! Like asking for the definition of pornography ("I know it when I see it.") or 'common' sense.

Is there an actual definition for being "over-built", and is it possible that this might disqualify one from a competition or have a range safety officer reject your rocket?

The range safety officer is or should be concerned with the safety of the people and equipment on the range, not judging the build methodology. Thrust to weight ratio, evidence of stable flight with a given motor, and appropriate robustness of the recovery system are what the RSO should be looking at IMO.


Why do you ask ? Have you seen some evidence of questionable enforcement ?

 

[SCrocketfan]

I probably overbuild a bit. There's no real definition, and adding extra glue really can't hurt until you run into weight problems. For example, LOC says the Mini Magg should weigh 40-50 oz built and mine's somewhere around 70 oz now. A combination of thicker fins (1/4, it's a newer kit so it has stronger fins), 9 oz of nose weight, bolts, quicklinks, and a bigger chute contributed to it weighing a lot more than some. However, I really don't mind as it's super stable and flies great.

In general, overbuilding is fine when you want a tough rocket. Just make sure you have enough thrust to handle the weight of said rocket.

 

[o1d_dude]

You people say "overbuild" like it's a bad thing.

If it's worth building, it's worth overbuilding.

 

[Bat-mite]

All a matter of opinion. I think overbuilt is a catch phrase that means, "I probably used a little more adhesive than I needed," or, "I probably didn't need to glass those fins, but I did anyway." I think that if two guys build the same kit, and one builds it stock, and it flies safely and successfully for five years, and another builds it with extra-reinforced everything, and it still flies safely and successfully for five years, you might say that the second one was overbuilt. But in the same scenario, if the first one breaks off a fin or sheds a MMT on its first flight, you might say it was underbuilt. Or maybe you just had bad luck.

 

[les]

For LPR/MPR, so long as the rocket will be stable with the selected engine, there should not be a reason for an RSO to block a flight for an "overbuilt" rocket.
Unless you try to use depleted Uranium for a nose cone to make it bullet proof I think would require a motor that gets you out of the LPR range :wink:

Other may disagree about being overbuilt creates a safety issue if the rocket comes in ballistic, but if we are talking LPR/MPR it is still going to be lightweight enough to not be an issue (well, maybe the high end of MPR could)
Per your original post, it sounds like you are just making a bigger fillet - definitely no issue there
Some people have posted about not doing TTW for LPR as over-building. I personally see no issue with doing TTW, especially if you have large fins or pods on the ends of the fins.

For HPR, I think it may be harder to define. On the one hand the rocket needs to be assembled in a manner that will survive the flight. At HPR launches I'm sure most people have seen some rocket shred or "re-kit" itself. Those rockets were under built for the motor they selected.
Conversely, I'm also sure most people have seen a ballistic hit due to failure of the recovery system. Having a heavier than necessary rocket because it was overbuilt would only make matters worse if the rocket was to hit someone/something. But I'm not sure if it would make a big difference. Getting hit by a 50 pound ballistic inbound or getting hit by a 60 pound overbuilt ballistic inbound is going to hurt (and many of these HPR are way over 50 pounds - like hundreds of pounds)

 

[slipperyfrog]

Overbuilding is where the fun is.

 

[astronwolf]

Is there an actual definition for being "over-built".....

I say no. It's mostly subjective, but after attempting to fly the rocket, it can get objective.

I can build a Big Bertha with TTW fins. To do so, I'd slot the tube for the four fins, and include fin tabs on the root edge of the fins. The fin tabs would be something like 7/16" x 3.25" x 1/8" of balsa, i.e. four little extra strips of balsa. Big Bertha crawls off the pad on an A8-3, but so has any Big Bertha on an A8-3. It flies great on B's and C's.

Did I over build the Big Bertha?

OK, so I decide I want to beef this model up. I reinforce the fins with paper, replace the shock cord with 100-lb. test kevlar line, and add a 15" rip-stop nylon 'chute. It doesn't fly too well on an A8-3 anymore, mostly because of the heavy chute. A8-3s in a Big Bertha suck anyways, so I'm going to stick with B's and C's from now on.

Over-built yet?

One of the fins somehow breaks. So I replace the fin, and apply 3-oz. fiberglass and epoxy to all the fins. That ought to work. Still flies nicely on B's and C's.

Over-built yet?

I finally want to paint the Big Bertha, and I want to make it look all over as nice as the glossy, slick fins do. So add some beefier, more rounded, fin fillets with epoxy. I fill all the body tube spirals with Bondo. I apply about 8 coats of automotive primer, wet-sanding between each coat, followed by about 3 coats of gloss enamel. Takes forever for the paint to dry. Somehow, it feels heavier. I definitely prefer flying it with C's, but it works best with C6-3s.

Over built yet?

I want to move up a step and send Big Bertha into orbit. So I rip out the motor mount and replace it with a 24-mm motor mount with paper centering rings and fly it with an E30-7. Motor flies through the Big Bertha, blowing out the parachute, which brings the model down so the parachute snags on the end of the launch rod. Dang. I replace the motor mount with 24mm heavy tube and plywood centering rings. Now it flies great!

Over-built yet?

I can continue to evolve this model until I am flying a carbon/kevlar wrapped Big Bertha with G10 fins and 38mm high power motors at Mach 2. At what point is it over-built? I don't know. Maybe if I still expected to fly such a thing with B6-4's, it's over-built. But that would be kinda dumb, wouldn't it?

 

[Kirk G]

Why do you ask ? Have you seen some evidence of questionable enforcement ?

No, none at all.
The range I fly at is somewhat relaxed, but always with an eye toward safety.
There are any number of older, more experienced rocketeers at hand who are always willing to lend an eye, a tool or an adapter and an opinion of "how do to it". So, NO, I have no complaint at all.

I was just thinking of a situation where "over-built" might come back to haunt you.

 

[samb]

No, none at all.
The range I fly at is somewhat relaxed, but always with an eye toward safety.
There are any number of older, more experienced rocketeers at hand who are always willing to lend an eye, a tool or an adapter and an opinion of "how do to it". So, NO, I have no complaint at all.

I was just thinking of a situation where "over-built" might come back to haunt you.

Sounds like a well run range. I think over-built has a weight added connotation that raises an alarm with some folks. Certainly, the more mass you put in the air could have a larger negative impact if the flight goes "south". In most competition scenarios, overbuilding (and the assumed added weight) is the enemy.

I think that in Stine's conception of model rocketry, in a contest between a wayward rocket and most anything that it could contact, the rocket would lose badly. Some overbuilding kinda gets away from that idea.

 

[SCP]

By my interpretation of the meaning of "overbuilt" - I took this perspective - if it was "underbuilt" it would fail with 100% certainty. If it was "built on target - built", it would....hmm...fly once?.......What are the design parameters?

We overbuild everything, to a certain extent it is the only sensible practice. We design with a safety factor for many reasons right? Human safety of course, as well as the safety or life of the product being designed.

So we overbuild to buy some leeway on the life of the rocket, safety of the people around....

But wait, its now no longer considered "OVER built, as we designed and built it to a new set of parameters to include safety , robustness and reliability. So, it was built to that target and NOT overbuilt. Now we go round and round........

Maybe its not so much overbuilt, but more that some factors in a design phase are UNDER defined or not 100% understood.

This will be very interesting to follow.

 

[dward]

I was going to say that I have seen more safety issues from underbuilding, which mostly comes with inexperience, than overbuilding, and then I remembered a cmass launch in which a gaggle of college students all tried for their level 1 certifications. They were all identical rockets with carbon fiber boattails. There was skywriting all over the place (margin of stability issue). Don't get me wrong, I like boattails and I like carbon fiber, and I usually like overbuilding, but this was over the top for should have been a 1000 gram rocket.

 

[Jesse]

From an engineering perspective, and by technical definition, a design can be said to have been "overbuilt" if it has a FOS (factor of safety) greater than 1.0.

So for example, if you require a structure to support a 1000lb load, but you design/build it to take 2000lb, than it can be said to have a FOS of 2.0. Whereas if you design/build that same structure to support exactly 1000lb and it is loaded as such, you have zero margin for error. There are obviously tradeoffs that will need to be considered during design. :wink:

 

[Gary Byrum]

OK, I'll weigh in. I'm a LPR to MPR builder. Kits in both areas. But mostly designs I created. That being said, I think the MPR kits are over designed and have expectations of being over built. I give you the Madcow DX 3. My first MPR build. I bought this to learn how MPR rockets were constructed. After that, I bought a PML MR-1, and built that. These two models define what being over designed and built are to me. Granted, MR-1 was for both Mid and HPR flying, but in the MPR way of thinking, both of these rockets do not require being this over designed. Hence, they get over built. In short, I could build both of them with LPR parts and fly them with BOTH, with LPR and MPR motors. The only reason I see these two as being MPR models is because they weigh a lot. I give you the Arapahoe F. The true test that a MPR model, that can be built with LPR parts, and launched with an F-32. Next to it's cousin the Arapaho E.

 

[Gary Byrum]

Do you think we could get an opinion from the Angry Launch Lug?
I'm sure he's got a scathing comment or two...

He would say what I just said. But with an attitude. My point of view, is that, because it is designed as a MPR rocket, doesn't mean it has to be.

 

[Gary Byrum]

Let's take, for instance, I build a facsimile of the DX 3 using LPR parts. I may not find the exact parts in LPR availability, But with enough tenacity I could create a model that would weigh 1/2 what it does. The DX 3 is such a simple design. I could put that in a way higher altitude, on something like an F 32, VS something more expensive. And get successful flights. The DX 3 is nothing more that a heavier rocket than it needs to be.

 

[Cl(VII)]

Overbuilding is case specific, and sometimes what you thought was overbuilt ends up just right. For instance I built an upscale Cherokee to fly on pretty common H and I motors which it does with ease. It is in fact overbuilt for this purpose, heavy internal fillets with basswood strips imbedded in them, fiber glassed fins, blue tube...it is admittedly a 3.5 lb anti-tank round. Recently I have developed a love for Warp-9 motors, and have flown it on an H669 and H999. The later puts out peak thrust of 384 lbs, which is about 100:1 thrust to weight. This rocket is NOT overbuilt for this motor. In the end I "overbuild" for two reasons; 1) maximum flexibility of motor choices on the high end (at the sacrifice of low and slow which I do not really enjoy as much for high power flights), 2) because I love to build rockets, and HATE to repair rockets (the Cherokee could take a landing with a tangled main or similar non-ballistic mishap and likely be fine).

As far as safety is concerned, at least with larger rockets. Having seen a 7 lb cardboard and wood glue rocket come in ballistic I am confident the result of a direct hit by that, or a fiberglass rocket of the same weight would be quite similar.

 

[JohnCoker]

From an engineering perspective, and by technical definition, a design can be said to have been "overbuilt" if it has a FOS (factor of safety) greater than 1.0.

That is the issue; we're working with many different materials for which we don't know the properties so there is no way to know what's sufficient except empirical testing. This ends up coming down to a matter of experience.

If a rocket flies correctly, we have no idea what the margin of safety was, just that it worked in that particular instance. I suspect most of us "overbuild" rockets by many times as progressive overcompensation for lack of information about our materials and structures.

Mostly this isn't bad, except in terms of adding weight. More mass means more momentum, which puts more stress on those parts. Another thing we don't know is what those "stress caused by extra mass" and "strength added by overbuilding" curves look like.

It could be that fiberglass HPR rockets are less overbuilt than stock model rockets because the extra mass causes so much more stress. This seems to match reality; for example boy scouts launching poorly-built Estes models dozens of times while we slowly prep and carefully fly a large and complex HPR.

We need more "real engineering" in this hobby.

 

[Binder Design]

Build for expected flight loads plus safety margin. So if you are flying an H motor, but eventually plan on flying a K in the same rocket, yes, it will be overbuilt for the H. So the flight performance will be handicapped on the H due to extra weight.

It is silly to see some new to HPR folks showing up with 4" diameter all glass birds with a couple extra wraps of CF "just in case" to fly on small 38mm motors. First flight goes like 600' while little kids are flying Estes rockets off the LPR pads going double that, lol.

And then on the other end of the spectrum, I have customers that fly our stock 4" paper kits assembled with wood glue on L's.

 

[mikec]

We need more "real engineering" in this hobby.

I agree, while acknowledging that some people aren't in the hobby to do engineering and that's fine as long as we all fly safely.

Having said that, despite the efforts of you, John, and others, there isn't a lot of useful data about the material properties of common rocket materials. For example, you can find good data about the axial strength of tubes, but not the bending strength, which may matter more. Fin material strength is even less certain, as are fin flutter calculation methods.

I have an article in an upcoming SPORT ROCKETRY about a couple of attempts to fly lightweight HPR rockets past 2000 MPH (I haven't been successful yet.) I enjoy finding the limits of building "just right", but this isn't everyone's cup of tea and doesn't have to be.

 

[Micromeister]

A year or so ago there was an article published in Sport Rocketry "Bullet Proofing the Estes Guardian" or something like that.
That is the absolute defination of "Over building". It is the incorporation of HPR building techniques into LPR models that are not intended to be bullet proof that cause the Safety issue.

Our "Model Rockets" are intended to absorb kinetic energy Not transfer it to what is being impacted.

ps: Instead of Overbuilding we should be stressing building As LIGHT Weight as Possible. I disagree with John C. concerning the need for more engineering in the hobby. There is more then enough engineering date available if the builder takes the time to learn about the materials, adhesives and fasteners being used.

 

[astronwolf]

A year or so ago there was an article published in Sport Rocketry "Bullet Proofing the Estes Guardian" or something like that.

Which spawned this thread (2010):
https://www.rocketryforum.com/showthread.php?10186-Overbuilding

 

[Handeman]

By my interpretation of the meaning of "overbuilt" - I took this perspective - if it was "underbuilt" it would fail with 100% certainty. If it was "built on target - built", it would....hmm...fly once?.......What are the design parameters?

We overbuild everything, to a certain extent it is the only sensible practice. We design with a safety factor for many reasons right? Human safety of course, as well as the safety or life of the product being designed.

So we overbuild to buy some leeway on the life of the rocket, safety of the people around....

But wait, its now no longer considered "OVER built, as we designed and built it to a new set of parameters to include safety , robustness and reliability. So, it was built to that target and NOT overbuilt. Now we go round and round........

Maybe its not so much overbuilt, but more that some factors in a design phase are UNDER defined or not 100% understood.

This will be very interesting to follow.

I have to assume that the kit manufactures sell kits that will meet the minimum requirements for safety. If you build it according to instructions, or acceptable standards, then it should reasonably fly without incidence. Using additional methods or practices that strengthen the rocket above and beyond the manufacturers instructions is "overbuilt".

Is being overbuilt a good thing or a bad thing? That depends on how much you trust the manufactures assembly methods and what they have determined is a proper build.

With LPR, I think that varying from manufacturer instructions is overbuilding.
With MPR, varying from manufacturer instructions can be a matter of risk avoidance, is probably overbuilding, but....
With HPR, varying from manufacturer instructions, if there even are any, may be a matter of getting the rocket to survive more then a couple of flights with the motors you intend to fly and is a personnel decision.

Overbuilding becomes much more gray as the motor size increases.

 

[Meatball 1]

The following is a link to thoughts on rocket construction that John Pursley posted a few years ago that I think are relevant here. Even if you ultimately disagree with his ideas, I think it's worth listening to his point of view:

Just What Is Safe Recovery? Model Construction

 

[CZ Brat]

I believe that "overbuilding" is not an issue. Building a rocket that will fly safely, and repetitively IS important. Take this comparative scenario:

Rocket A is a 4 lb PPP Kit (Plastic, Paper, Plywood), but the builder adds an extra 1 lb in "overbuilding" it. It comes in ballistic. Imagine the harm it could do if it hits someone/something.

Rocket B is a 10 lb Fiberglass Kit, and the builder does not add "extra" weight because he does not "overbuild" it. It too comes in ballistic. Imagine the harm it could do if it hits someone/something.

The only negative thing I hear about "overbuilding" is that the rocket is a greater hazard if something fails than if it were built "stock". But there is always someone flying something bigger and heavier. Obviously, in my scenario above, the "stock" built rocket B is the greater hazard. Assuming the 2 rockets come in at the same speed, B has twice the kinetic energy of A. B is also made of stronger materials that will give less when they impact something. Either case, I don't want to be around when they come in ballistic, but if I had to choose one, it would be the overbuilt rocket that weighs 5 lbs.

 

[Space Oddity]

As far as the term "over building" is concerned, in my work the term is "over engineering". It is not necessarily a bad thing as long as everything works. The real impact, in the commercial world is cost. Over engineering adds cost and reduces competitiveness of product or service, reduced margins.

I guess this does apply to manufacturers in the model rocketry world. For example, if a company were planning a model rocket kit to sell to us, would they include an aluminium retainer that costs $30 or would they include a plastic one that costs $5?
The weights are similar but I suppose the plastic retainer might do five flights compared to the aluminium one doing say, twenty flights. If you are on a tight budget what would you buy? You are the market that the manufacturers are selling to.

I have personal experience of this having been sold an aluminium retainer for £28, then having discovered (with more understanding of what I was buying) I could buy a plastic Estes retainer, in the UK for around £2. If the plastic one burns out earlier so be it. I can use 14 of them before they equate price wise to the aluminium one. That's over engineering on a cost base and performance.

Getting back to the original question, what is wrong with over building/engineering?
As long as the design is sound then surely it is only cost that counts?
As far as the weight of adhesive is concerned, my best investment was in a digital scale (+/- 0.5 gram from eBay). On low and medium power rockets there's not really a big weight impact. If using a simulation (I use OR which is great) you can adjust for the minimal increase that the adhesive adds to weight and still get the design right.

I'm only aspiring for level 1 qualification and appreciate I've lots to learn before going beyond. But in my level 1 design I'm not interested in under building. I want weight, drag, and low altitude. In April in the UK it tends to be windy. The last thing I want is my attempt going up beyond 2000 ft and disappearing forever. I've overbuilt the design and brought it down to a theoretical 1500 ft. Providing the design works and it doesn't go ballistic, isn't that the sensible thing to do? I want my attempt to be unremarkable, reliable and recoverable. Above all I want the experience to move on beyond to level 2.

Finally and with regard to John's comment that we need more engineering. As an engineer and working in the aerospace industry, in principle I agree. But we are talking about model rockets (low/medium power) and not the processes of safety and airworthiness applied to aircraft, let alone space. I agree we need controls in the hobby but the safety factors that apply (certainly in the UK) are quite restrictive and stringent.
Yes we need more engineering but don't let's turn off newcomers to the hobby, many of which I'm sure, are not from an engineering background.
As a beginner, I've found information very hard to come by. John, your videos are great, they really helped. Thrust curve is fantastic and above all, OR. But don't we need to make it more understandable and certainly not introduce too much "engineering" in a prohibitive way.

In conclusion; understand the dangers, measures to launch safely, construction techniques, sound construction even if it is overbuilt. Make sure the design matches the build. Promote the hobby and take away the mystery.

I'll let you know how our level 1 attempt goes. If badly I'll eat humble pie.

Best regards.

SO.

 

[JohnCoker]

But don't we need to make it more understandable and certainly not introduce too much "engineering" in a prohibitive way.

Sure, that's why we tend to offer personal experience and rules of thumb. However, if those rules of thumb are based on incorrect information, we should modify them. It's not that everyone needs to be an expert, but the answers we give should be right, so the conventional wisdom must be validated.

You are right that the original question talked about balsa fins, implying model rockets, and I jumped to over-building in HPR.