Using BIGGER engines

[KevinP]

Hi all,

I kind of scratched at this question in another thread, but here it is in earnest.

If I want to use a bigger engine in one of my rockets:

Do I buy another kit and build it with a larger mount or can I disassemble the rocket somehow and install the bigger mount?

I know very little (actually nothing) about engines bigger than E. What precautions should I consider?

I assume more thrust means more stress on the parts (particularly fins and engine mount). What can be done to strengthen these parts?

Finally, these engines are available in single use or reusable. Are there any considerations besides price when deciding on which way to go? In addition, Estes builds in the delay from thrust to recovery deployment. How is that accomplished when one "loads" an engine?

Thanks.

[STRMan]

I strongly recommend you buy a rocket that has been designed to use mid power engines for your introduction into this segment of the hobby. I have yet to build a mid power rocket, but I have been studying them. Fins will start to change from balsa to plywood. Elmer's will change to CA and epoxy. I'm sure an experienced mid-power rocketeer could convert a low power rocket to mid power, but I wouldn't experiment with engines this powerful without a proven design.

[Doug Sams]

Do I buy another kit and build it with a larger mount or can I disassemble the rocket somehow and install the bigger mount?

I know very little (actually nothing) about engines bigger than E. What precautions should I consider?

I assume more thrust means more stress on the parts (particularly fins and engine mount). What can be done to strengthen these parts?

Finally, these engines are available in single use or reusable. Are there any considerations besides price when deciding on which way to go? In addition, Estes builds in the delay from thrust to recovery deployment. How is that accomplished when one "loads" an engine?.At first I was gonna second STRMan's advice - it sounds solid as a rock. But then I reflected on my own introduction to mid-power and realized I started by hot-rodding LPR kits. (In fact, I've never built a mid-power kit to this day, and only one HPR kit. All my other M/HPR stuff has been scratch built or hot rodded in the case of some mid-powers.)

My first E and F motors were an Aerotech E30 and an F23, flown in my 29mm Big Daddy and my stretched 29mm Fat Boy. The Fat Boy used uni-rings from Totally Tubular (BMS also carries them) and a 29mm motor mount. The stock thru-the-wall balsa fins were laminated with 1/64" birch ply. HPR style motor retention was added to the aft centering ring. And a hearty recovery harness with kevlar leader was connected to the nylon chute.

The Big Daddy was similarly upgraded. I used a flycutter for the 29mm centering rings for the non-standard tube, and laminated the fins with card stock IIRC. The chute and shock cord got treatment comparable to the Fat Boy.

Neither rocket got fiberglass, but the Fat Boy did suffer a small zipper. While the Big Daddy body tube was up to snuff for mid-power, the thinner walled BT-80 of the Fat Boy really needed a bit of glass. One wrap of 1.5 ounce cloth around the forward 3" of airframe is good protection against chute-jerk

So, yeah, go ahead and beef up a large MR for mid-power. Besides the Big Daddy, the Executioner is a popular 29mm upgrade.

Doug


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[Arley Davis]

You can take a Larger Low power rocket and modify it to a Mid power rocket as Long as the rocket is 29MM or larger in diameter. Balsa as Long as the fillets are large can withstand the trust of an F or low power G motor, put its best to either replace them or strengthen them. To make them stronger you can sandwich them between light cardstock and press the fins together. Or you can lay down some wax paper then smear on a light layer of Epoxy on both sides of the fins, next lay down another sheet of wax paper then press them together tall the epoxy has dryad. The best way is to make up some Balsa Ply; it’s light and much stronger than just Balsa.
You also have the option of using Plywood or G10 fiberglass fins that are lighter than Plywood and a lot stronger.
One note the added weight to the fin area will make the rocket unstable so you need to add weight to the nose cone so the Center of Gravity on the rocket dose not move back.

To strengthen the body tube you can take Finish Cure Epoxy and using a epoxy Brush attached to a small dowel you can smear the Epoxy on the inside of the tubing, from above the motor mount up to about 2 “ from the mouth of the rocket. To strengthen any rocket at the mouth you can use CA (Super glue). First be sure to wear rubber gloves because CA bonds to skin, next place in some CA, then very quickly smear the CA around the Mouth before it has time to dry. Once it is dry then sand the inside of the mouth until the nose cone fits correctly. This will strengthen the mouth and help to prevent any Zippers.

There are several ways to attach the shock cords so the best way is to join a Rocket Club and you can learn a lot from just asking for help. Put do not use the rubber bands the Estes uses, The best Shock cord is in my opinion is Tubular Kavlar it comes in many sizes, from ¼” up, The ¼” can cost $2.57 a yard. The ¼” works great in The larger Low Power rockets such as the Mean Machine. You will need a different Motor retainer; I recommend T-nuts, There cheep and work will. You will also what to use a Nylon parachute.
This may help, http://www.giantleaprocketry.com/hpdefault.asp

To your last question, If you plan on doing a lot of mid power flights its more economical to use reloadable engines. Put be sure you get help building your first one. As for the delay, The Reloadable engines have three different delay elements that can be purchased with the engine. Short, Medium and long. If memory serves me the short has a 6-second delay, I thank the Medium is 10-seconds, and the Long has a 16-second delay element. If your flying a Big rocket with a smaller motor you what a Short Delay, if your flying a smaller rocket with a large and powerful motor you want a Long delay.

The T-nuts on the back end of the LOK Nomad.
My Modified 29 MM Estes Shadow, built as described above.

[Royatl]

"Hot-rodding" larger low power models is a good way to get started, but don't get carried away.

Some people underestimate the forces on a rocket, but at the same time, it is easy to "over-build" a rocket.

For instance, some people replace the paper centering rings in their rockets with model aircraft plywood. That's fine, but it adds weight. Instead, simply adding gussets made from the leftover cardboard the original rings came from (triangular pieces that are glued like internal fins to both the centering rings and the body/motor tubes) will increase strength tremendously without adding so much weight.

For fins, you can get by with balsa for a long time as Arley suggests, sometimes simply by adding a tab to the root of the fins and inserting this into a slot on the body. You can even kill two birds with one stone by making the tab long enough to reach the motor tube and essentially make the fin tab the centering ring gusset! Of course, this means you may have to cut your own fins, if the kit you choose has die- or laser-cut fins.

Surface mount can still be done successfully, however. I have a nearly 20 year old rocket that has flown mostly on G motors that has surface mounted plywood fins, and I finally had a fin pull off on landing on its last flight a few months ago. Good alignment and 30 minute epoxy (and occasional maintenance of small cracks with thin CA!) are the key.

Parachutes and shock cords are the first things that should be considered when beefing up a rocket for mid power. The Estes plastic chutes and their attachments are not sufficient. A number of manufacturers make nylon parachutes from 18" on up. I like the Top Flite chutes, especially when you're starting out.

For the shock cord and mount, I prefer nylon coated steel fishing leader, wrapped around the motor mount tube and threaded through a hole in the upper centering ring (the original North Coast "Gorilla" mount. Look up some NCR instructions here for examples), with elastic tied to the top of it . Others like 300 or 1000 pound test Kevlar rope mounted the same way. Or you can take a short section of that Kevlar, tie a loop in it, and epoxy the non loop end right to the inside of the body tube. Works find for many smaller rockets.

While low power tubes seem light (and they are thinner walled than usual MPR and HPR tubing), they can still take a lot in flight. I wouldn't worry about glassing or anything like that. There *is* a point where tubing can buckle, but unless your rocket is long and skinny (an H motor in an Estes Mean Machine!) you shouldn't have a problem.

The last bit about overbuilding is that overbuilt rockets survive crashes. In the interest of safety, you DON'T want that to happen. The whole idea of light airframe rockets is that the airframe absorbs impact energy. Yet, there are lots of HPR flyers who take it as a point of pride when their rocket "digs a post hole", and most of the rocket survives. I cringe when I see that happen.
-------

Now, the best beginner 4" MPR/HPR kit to get is no longer made (the Phantom 4000 by North Coast! :-) ) but similar kits can be had from LOC/Precision -- the Graduator is a good 2.6" kit -- and Aerotech makes the Initiator with fancy-schmancy parts you won't find anywhere else!

[Mark II]

I was going to jump in with my own list of Do's and Don'ts, but Roy has already said what I was going to say.

The main things that I would say to do are:



upgrade and strengthen the recovery system as Roy described
strengthen the fins by laminating them. A suggestion would be to use cardstock for the laminations- you don't need anything stronger than that
an alternative fin material to balsa is basswood, which is denser and tougher than balsa but not as heavy as plywood
Important: use stronger adhesive than you would for a rocket that flies on A-C motors. Carpenter's glue and epoxy are good choices.
Even more important: re-check the stability of your rocket with the larger motors. You may have to add a little bit of nose weight if the larger motors are heavier than those that the rocket was designed for.
To address another part of your question: adapting an existing kit to larger diameter motors requires building your own larger diameter motor mount for it, as Doug described. You can also "adapt" a rocket built for 18mm A-C motors to fly on more powerful motors by simply switching from using black powder Estes or Quest motors to using composite propellant 18mm diameter "D" motors from Aerotech or Apogee. They are exactly the same size as the Estes and Quest motors. Instant upgrade! You will need a 12 volt system to fire them, though. And be prepared for the fact that your A-C rockets will go MUCH higher.

Almost the same holds true for "adapting" rockets designed to take 24mm Estes D and E motors; you can simply substitute same-sized composite propellant motors from Aerotech and Apogee. But you will need to beef up the rocket and check its stability as previously described for these motors, because many of them (especially the Aerotech motors) put out much higher peak thrust than the same-sized black powder D's and E's, and some may weigh more, too.

One final thing is that you will almost definitely need to fly your rockets with these motors in a good-sized field, certainly one that is bigger in size than what you need to fly with low-power motors. And be forwarned: these motors are loud! (But that's a good thing, right? :D )

Mark

[KevinP]

Thanks for all this great input. I have my eye on a couple of mid-power kits and, with the information on the difference between the Estes engines and the composite engines. That is cool info. I have a couple of rockets that use D/E engines that I would be willing to apply just such a technique. I just have to work on the beefing up of the recovery and fin systems. One other question: Would they be okay to launch from the standard launch pad that is required for the rocket in un-modified conditions?

[jj94]

In my opinon, the conversion can be done very easily. A kit can be bought and the motor mount can be switched up for use with larger motors (in fact, I'm building a Big Bertha for use with 24mm reloads, a Fat Boy for use with 29mm reloads, and am planning on building a Big Daddy for 29mm reloads and possible 18mm outboards for clusters, and a 24mm Fat Boy with 18mm outboards). Also, not much more has to be done to strengthen parts. I tend to build relatively strong on even LPR builds, so I don't know how much more stronger you have to build, but for MPR, wood glue would be just fine to use. Usually, it will still be much more strength than necessary. For fin fillets, I build up the fillets in thin layers, usally 3-5 for MPR rockets. The fillet gets very strong, but still light. I build the motor mount with wood glue too; I use medium thick fillets on these though, with an average of two layers. For installing the motor mount, I layer the fillets in about 2-3 thin layers, though thicker than the layers used for the fins. The fin material for smaller MPR rockets don't require plywood at all. That's just complete overkill. Balsa will be completely fine, but basswood will be fine too. For MPR rockets with balsa fins, I usually soak the outer edges with CA for a little more durability. One thing that should be considered is launch lugs; for me, anything that has a 24mm mount has atleast a 3/16 inch lug and a 29mm mount has atleast 1/4 inch lugs or rail buttons. Also, make sure you upgrade your shockcord. Use the elastic embedded fabric instead of the Estes 'rubberband' type shockcords. Rubberbands snap easily; so do Estes' shockcords. For your parachute, I'd recommend getting a nylon parachute instead of using plastic parachutes. The plastic chutes can rip easily and the shroud lines can shred off with little force. Nylon parachutes are much much stronger and will last a longer time.

If you plan on flying a lot of mid power motors, I suggest getting an RMS case. Cases have more motor choices available and can save big money after heavy use. For APCP motors, the delay starts burning at the point of ignition and continues through out the motor's entire burn(unless the motor is an endburner, like the Apogee motors, or the Aerotech G69). After burn out of the motor, the delay continues to burn, and from then on, the motor's burn is the same as it would be with any other motor. The delay burns out and the ejection charge is activated.

As for launching from certain launch pads, it depends on what you're launching. If you're launching from an Estes pad (not the E one, just the normal Porta Pad), I'd launch things that are less than 10 ounces. I'd be uncomfortable with launching anything heavier than that with Estes pads. For anything over 10 ounces, I'd recommend getting the Estes E pad for things below 18 ounces. Custom built PVC launch pads is an even better choice. It can be cheaper and yet much more sturdier. If you don't want to build your own, you can go to http://members.buckeye-express.com/turbopig/products.htm. Their Tri-pad and POD launch controller combo would be a good start. You would need a good launch controller with longer leads to get the reloads burning. The normal Estes stuff won't cut it. You need a launch controller that can handle a lot of power. A car battery or motorcycle battery would be a power source.

[Mark II]

I'll second what Josh has said, and add that the decision of what pad to use can also be affected by the thrust of the motor that you are using, especially the initial thrust spike just after ignition. Motors that put out a big initial thrust spike (and most motors from B to G do, although the actual force of that spike is relative and is usually commensurate with the impulse class of the motor - the initial thrust spike of a B will certainly be substantially less than that of an E, for example.) That initial spike delivers a hit to the blast deflector and launch pad, and the bigger and more powerful the motor, the harder it wallops the pad underneath it. If you ever want to see an extreme example of this, check out some videos of some big high power launches; in some of them where the pad wasn't sufficiently anchored and weighted down, at ignition the pad visibly jumps around - and these were pads made out of beefy steel girders that weighed several hundred pounds before being anchored and weighted down!

So as you use higher thrust motors, you will need to use a sturdier pad. A lightweight pad like the Estes Porta-Pad II is plenty strong enough for motors up to C, but if you tried to launch a rocket with an F motor on it, you would most certainly see one or more of the legs sag and even break under the load exerted by the motor's initial thrust, and it would throw your rocket off on a dangerous trajectory. So heed Josh's advice about getting a more beefy pad. An Estes Porta-Pad E would be a good choice for D, E and even some small F motors; if you see one in the store, you will notice right away how much larger and thicker the legs are, and that the blast deflector is dramatically larger than the one on the PP-II. But many, if not most, rocketeers home build their own pads, often out of PVC pipe, when they want to fly mid-power motors.

The other reason to get a bigger pad is that you will need a thicker and stiffer launch rod, for all of the same reasons that you need a sturdier pad. A Porta-Pad II will suffice for launching A-C rockets using 18mm D motors if you swap out the 1/8" diameter launch rod for a 3/16" Maxi-Rod. You can get an inexpensive version at just about any hardware or home improvement store. A 3/16" cold-rolled steel round bar or rod (don't get hot-rolled) will work just fine, but may leave some black marks on your rocket; because of that, I always get, and would recommend, a plated steel rod, which you will find in the same section as the other types. If you can find one, a stainless steel rod is actually the best choice. Don't bother with brass or aluminum rods, because at the diameters and lengths that you need, they are just not stiff enough. Get a 4 foot long rod, because the extra length may come in handy with some rocket and motor combinations and with larger and longer rockets. When you move up to large E's, F's and G's, you should also move up to using a 1/4" diameter rod. Obviously, you will need to equip your rockets with larger launch lugs, too. You can get them from vendors that sell model rocket parts and components. Good luck!

Mark