DBF Q&A #1

This is the first of the 2001 DBF Question and Answer e-mails.  They will be sent periodically to the e-mail address of all participating teams.  They will also be archived on the DBF contest site.  Please continue to send your questions to: greg.page@nrl.navy.mil, and be sure to include "DBF" in the subject line.

I sent an e-mail test out to all the teams last week, and have not received a reply from all the schools yet.  Please make sure you check your contest e-mail frequently.  It is especially important when we get close to the contest dates, as there may be last minute information and this is THE ONLY WAY that teams will be notified in near real time.

If you haven't sent in your e-mail test reply yet, please do as I still want to verify all e-mail addresses.  Missing as of this morning are: West Virginia #1 and #2, Tennessee Tech, Queens University, UCLA, Wichita State, Syracuse, Univ. of Texas at Arlington, State University of New York at Buffalo, and City College of NY #1, #2 and #3.

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There have been several questions asked regarding the use of a "speed loader" for the cargo change out.  For the benefit of new teams who have not seen the speed loaders used in prior contests I'd like to add a little more explanation than is in the rules.  For the benefit of old teams, note that their are new requirements on the loaders this year compared to designs allowed in past years.

Question: Can we store the tennis balls in a tube so as to allow for easy unloading/loading?
Question: How much of the plane is allowed to be changed with each sortie.  For example is the tail allowed to be part of the speed loader and be switched with an identical tail each time?
Question: Is it admissible to have two identical speed loaders, one loaded with tennis balls and one loaded with the steel blocks?
Question: Are we allowed to prepare two boxes with same dimensions, one for tennis balls, and the other for heavy payload so that we can replace the box with tennis balls with the box with heavy payload between the sorties?
Question: Can the speed loader be exposed, as part of the fuselage or must it be entirely enclosed?

Answer: The idea of the speed loader first came about several contests ago, where it was considered a competition sensitive idea.  Since teams from past years have had the opportunity to see the speed loader idea, it seems only fair to new teams to make it a common feature, rather than act as an advantage only to teams who participated in past years.  That is why it was specifically added to the rules for this contest.

For both the heavy and light payload teams may employ a removable container or "speed loader". The container must be the same size and design for both payloads, but may employ different means to secure the payload internal to the container. Containers must be "reusable", meaning that they can be opened/closed multiple times (can not be glued shut) and employ reusable mechanical fasteners to secure the payload inside. Teams may be asked to demonstrate removal of the payload from the container by the judges

The idea of a speed loader is to allow some form of container that contains the payload which can be more quickly installed in the airplane than can the individual payload pieces, for this year either multiple steel blocks or multiple tennis balls.  In it's simplest form it would be either a simple box or tube. 

You may have several loaders, each with a different payload, ready for use on individual laps (sorties) of a given flight period.  For example you can have a loader setup with 10 lbs of steel and another set with 6 lbs, and may select which one to use on any given "heavy" payload flight.  You could also have one loader pre-loaded with 10 tennis balls, and another pre-loaded with 50 balls.  You can take all of the loaders you may want out to the flight line with you and select them based on prevailing weather/wind, state of your batteries, etc.

The speed loader may not be a prime structural part of the airplane (as the airplane must be capable of flying without any payload), so it couldn't be a replacement wing, fuselage, tail boom etc.  It can be a part of the airframe, such as a hatch or store pod. 

The speed loader for each payload is specified to be the same size (and construction) for each payload for this year.  That means that if you wanted to use wing store pods, they would have to be the same size for each payload, so you can't have a small streamlined pod for the steel blocks and a large bulbous pod for the tennis balls.  You also can't fly just one pod for the heavy payload, and several pods for the tennis balls.  Similarly you can't have a flush hatch for the steel payload and a bulged hatch for the tennis balls. 

Also, since the rules state the payload must be internal, you can't have a steel block "bolted" to the outside of the fuselage (the same goes for the tennis balls, though it might have been interesting to see how someone might secure a dozen or so tennis balls to the outside of an airplane and still make it fly :-)  ).  A wing mounted pod, since it must be present for all flights under the rules, is considered part of the structure and can be used to house the payload, not just the fuselage.

Please also note that this years rules require the speed loaders be "reusable", so you can't glue the tennis balls into it, but would have to use a removable lid on the loader to restrain the balls or an internal baffle or net to contain smaller numbers of tennis balls.  You could however have the lid restrain the tennis balls, and have a steel stud in the bottom that contained the steel blocks, and the stud would only need be present in the loader containing the steel.

And finally, although not specifically stated in the rules (though it is alluded to), the payload MUST be restrained in the loader.  The tennis balls (or the steel) can't be just allowed to roll or slide around inside the loader.  For flight safety, the judges reserve the right to tip the loader upside down, on it's end or side, etc to make sure the payload cg can't shift during the flight.

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There have also been several questions (mostly during the summer) regarding the engine REP formula for multiple motors.  I've only included one typical question below.

Question: Could you please clarify the formula for Rated Engine Power given in the rules for the 2001 contest? If a team uses two motors at 500 Watts, does that "cost" the same as using a single motor at 1000 Watts? Also, if a team uses multiple motors, will they also be allowed to use multiple fuses to protect each motor individually?

Answer: The is a fairly detailed answer to this in the FAQ.  I encourage all teams to read the entire FAQ carefully, as it contains information for this contest year, and also items that were raised in past years that new teams might not be aware of.  From the FAQ ....

Question: How is the maximum current limit (40A) applied to multiple motors and battery packs? Is there supposed to be one 40amp fuse for each motor or one fuse for all motors?
Answer: The 40A limit can be considered as a system wide current limit. No motor or battery may see more than a 40A current. Therefore, if you have two separate packs feeding two separate motors, each motor/pack would have a 40A (max) fuse. If there is one pack feeding two motors, there would be one 40A (max) fuse at the pack. Finally if there is one pack feeding one motor, there would be a single 40A (max) fuse at the pack.

Question: In the cost formula the REP equation contains both the number of engines, and the number of cells. How are multiple engine REP's computed?
Answer: The REP is computed for each engine multiplied by the number of cells powering that engine. The individual engine REP's are then summed for the total REP.
For example:
(1) If there are 2 engines connected to a single 20 cell pack, the REP would be
2 engine*40A*1.2V*20 cells = 1920
(2) If there are two engines each connected to a separate 20 cell pack, the REP would be
1 engine*40A*1.2V*20 cells + 1 engine*40A*1.2V*20 cells = 1920
(3) If there are tow engine each connected to a separate 10 cell pack (20 cells total) the REP would be
1 engine*40A*1.2V*10 cells + 1 engine*40A*1.2V*10 cells = 960

-Greg

Gregory S. Page
ITT SES
2560 Huntington Ave
Alexandria VA 22303
202-404-1251
202-767-6194 FAX

email: gregory.s.page@nrl.navy.mil
email: greg.page@itt.com
Contest web page: http://amber.aae.uiuc.edu/~aiaadbf