NARAM-51

Event Tips Pages (draft)

For NARAM-51, the Dual Egg Duration event is D engine class

Dual Eggloft Duration combines the challenge of flying a model containing and recovering TWO Grade A Large eggs intact, with trying to stay in the air as long as possible. Sometimes doing too well, staying up so long that the model flies away, unrecoverable, or landing in an inaccessible spot (or tree).

The model must stay together, nothing can separate from it other than wadding. It cannot be staged. If the eggs are not both returned or one is damaged (cracked, broken, etc.), the flight is disqualified. You can NOT catch the egglofter, it must be allowed to land naturally.

For the full rules for this event, please see the Dual Eggloft Duration Rules on the NAR web page.

Scoring - For Eggloft Duration only, the scoring is best SINGLE qualified flight time, returned, of two flights allowed.

Design considerations - Balancing ability to store and reliably deploy a large parachute, with low model weight. An all-18mm body with a capsule on top as used for Eggloft altitude is not a good choice here since parachute storage space is very limited.

An egglofter with a long tapered conical shroud is a good way to go for lower powered single Eggloft Duration, as it has a significant amount of parachute storage space. The Two Minute Egg plan is such a model, and both ASP and QCR have similar contest oriented kits.

A straight body tube with a larger diameter, such as 1.3" to 1.65" diameter (BT-55, 35mm, BT-60) can be used. The model will be draggier and usually heavier, of course, and therefore at a competitive disadvantage. The Quest "Courier" egglofter kit can be used for D Eggloft. Some regular models you might already have can be adapted to fly as an eggloft duration model by replacing the nose cone with a capsule. But they cannot be too heavy or they just will not fly safely enough with the added weight of an egg.

A list of plans and kits is included further down on this page.

Egg Capsule - Pratt Hobbies makes an excellent vac-formed egg capsule (the old CMR capsule). Some companies like Aerospace Specialty Products (ASP) and QCR carry that capsule. Apogee also has their own vac-formed egg capsule. Pratt Hobbies also makes a Dual Egg Capsule. It is nice, but the two eggs cannot be totally isolated from each other with a bulkhead, as can be done when using an extension tube with a bulkhead. A good way to use the Pratt Hobbies Dual Egg Capsule would be with a SHORT extension, that had a bulkhead glued into it.

Another capsule sometimes used is a plastic Easter Egg, of a size that is just a little bigger than an egg. Using two "long halves" from two 1.75" diameter Easter eggs, rather than one plastic egg due to the short half with a flange sticking out, as the flange limits the inside diameter too much. Easter Egg capsules that small can be hard for the eggs to fit in and be safely cushioned, however. "Grade A Large" eggs tend to vary significantly in diameters, so Easter Egg capsules are somewhat risky, unless you have an Easter Egg that is 2" or so in diameter. Since this is for duration, it's best not to risk using a too-cramped capsule.

Dual Egg Extension - A lot of people like to convert single egg capsules to carry two eggs by using an extension tube. This serves two purposes. One, of course, is to simply be able to convert a single egg capsule. But there is another reason. By gluing in a bulkhead in the middle, the two eggs can be isolated from each other. Too often, eggs get broken at liftoff, or landing, because of the forces of one egg being transferred into the other egg. By using an extension with a bulkhead in the middle, the eggs can be packed so they are isolated, one egg cannot apply force to break the other egg. Padding - Use foam or some other flexible material to try to cushion the egg so it will not get cracked. My favorite basic cushioning is to get hold of a foam egg carton and cut out the four corner "cups", as they fit the egg pretty well. I add other thin foam padding as well. The egg needs to be padded enough that it can't rattle, but don't pack it so tight that it's under pressure loaded in the capsule. If you are using a plastic capsule, don't bother with putting the egg inside of a plastic bag....if the egg breaks you can just clean the capsule with water, without any damage.

click on thumbnail

Special Design Considerations - Successfully flying two eggs and getting them back safely is a lot trickier than for one. And things get harder with D power, compared to B or C power. I would recommend converting an Estes Big Bertha, or even building your own scratch-male model using an Estes BT-60 body tube. If scratch-built, then a 24" main body would be better than the 18" or so of the Big Bertha (or add 18" to a Baby Bertha!). The reason for this suggestion is to make use of the large volume of chute storage space that is available that way, which is more than would be available from a 2-minute egg type conical body. Since this is not altitude, then engine performance is not quite as critical. You may be better off using a D12-3 than using a D10 or D13. At right (first photo) is a model that is a bit more advanced, in that its body is a custom made 40mm FAI type fiberglass body tube, with built-in tailcone. But, forget about the fiberglass part. The 40mm body is a little under the diameter of a BT-60. So, the reason it is shown is to get across the idea of a BT-60 bodied model. And this one was flown simply on a D12 engine. And indeed, in the 3rd photo, far right, is a similar model by Jim Stum, which used a BT-60 main body.

Parachute - The chute needs to be relatively big so it can get good duration, though hopefully not so big that the model drifts away. Very big chutes of 48" diameter or more are good for D Dual Eggloft duration, as long as it can be deployed RELIABLY. But, a model could drift too far away on even a 36" chute if there is a lot of wind or it hits a big thermal. It is best to have a number of chutes at different sizes, and select what seems most suitable for the conditions. Andy Jackson of ASP (Aerospace Specialty Products) has written a great article on considering what size or type of parachutes to use in egglofting competition, whether for duration or altitude. It also has tips on chute packing. Commercial chutes as sold by big manufacturers such as Estes can be used, of course. But such chutes are limited in size, are pretty thick, and are pretty inefficient due to only 6 shroud lines. Homemade chutes are better, you can have a larger diameter, use 8, 12, even 16 shroud lines, and use a thin material that packs well in limited space. Some people like to use 1/4 mil mylar, some prefer to use colored dry cleaner bags or other pre-colored very thin plastic, and some prefer to use 1/4 mil "dropcloth" plastic with color added by use of a large black or red magic marker. Another plastic chute material source, not as thin as 1/4 mil dropcloth but pre-colored, is an inexpensive emergency poncho. The chute at right seems to have been made from a poncho or similar material. ASP has a line of "Over Easy" Parachutes intended for eggloft duration, in sizes from 18 to 36". However, for a really good competitive D Dual Eggloft model , you may want to have more than 36" chutes. Such as 48", or even more. At some point it comes down to how large of a chute you can pack into the model, which can be reliably ejected out and deploy. This again is why a model with 24" or so of BT-60 is recommended over a model with a smaller or shorter body, as there is a lot more room to store and deploy a chute from. Normally 24" of BT-60 would be too heavy for an event like say B single Eggloft Duration, but D Power opens the door to this design consideration. A good shroud line source for homemade eggloft chutes is "button and carpet thread", which is what most manufacturers use. To avoid the lines pulling loose from the parachute under stress, the shroud lines can be attached to run over the top of the chute as shown at right. Cut-up band-aid pieces can make for very sticky yet flexible shroud line tabs. Sometimes a chute can be too big to get to deploy reliably, some people do better than others due to more experience and technique at packing. So, use parachute duration type packing methods. Practice packing chutes and try to work up a folding method that allows the chute to unfurl quickly and reliably.

click on thumbnail 2-Minute Egg type egglofter with a partly tangled chute         click on thumbnail

Shock Cords - It is useful to use a shock cord that can actually absorb the shock of deployment , given the weight involved with egglofters. 1/8" elastic works very well for that purpose, but is not ideal to attach directly to the body tube. Many competitors prefer to use a length of 100 pound grade Kevlar cord to attach to the body tube (especially for mounting inside), then tie the elastic shock cord to the other end of the Kevlar cord. The 2-Minute Egg plan mentions using wire cable in a similar way to link elastic to the model, that was a method used before Kevlar came into use for contest models, so 100 pound Kevlar can be used rather than wire cable for the 2-Minute Egg.

WARNING - Kevlar Shock cords can eaisly be burned through by the heat of the ejection charge of a D12 engine, and may suffer the same from a D10 or D13 ejeciton. Therefore, it is better to attach a 100 pound Kevlar cord to the outside. Such as a loop around the base of the engine mount tube, and run up the side of the body tube.

Model Plans & Kits

Designer

Notes

2-Minute Egg Plans (NAR website)  

Plan by George Gassaway

18mm engine model, would need a dual egg extension tube.

ASP - Egglofter Kits (various) & Pratt Egg Capsules

ASP (Aerospace Specialty Products), Andy Jackson

Good competitive kits, may need dual egg extension tube.

QCR - Egglofter Kits using "Easter Egg" & "Pratt " capsules for 18mm engines.

QCR - Qualified Competition Rockets, Ken Brown

Good competitive kits, may need dual egg extension tube.

QUEST - "Courier" sport egglofter kit

QUEST - Model Aerospace Company

Fly D10 or D13 reload, or convert to a 24mm mount for D12-3 power. Available from Quest dealers, including Red Arrow and Apogee. Needs dual egg extension tube.

Estes - Big Bertha

ESTES

Add Dual Egg Capsule, fly on D10 or D13, or convert to 24mm mount for D12-3 or D12-5

TIPS - Selecting Parachutes for Egglofting

by Andy Jackson, on the ASP website

Great article on considering what size or type of parachutes to use in egglofting competition, whether for duration or altitude. Also tips on chute packing.