Why do you have a separate reciever pack on the Chrysalis E where most go BEC off of one pack?
From : Don Stackhouse
It's a safety issue, important for sport flying, less of an issue for contest work. I have flown it with a single battery powering everything, and Joe is flying his that way at the moment, but there is a risk involved.
The motor is capable of draining the battery in a couple minutes or so. This equates to many minutes of radio power from that same battery. As soon as you have long flights and multiple motor runs of varying throttle settings and run times, it becomes nearly impossible to figure out how much battery life is left to run the radio. For example, say you had a climb to altitude, didn't find any lift but managed to drift way downwind looking for it, motored back at part throttle, went to full throttle to climb up for another try, shut down, and then managed to find a real "boomer", got to speck height, cruised around for a while power-off doing aerobatics, got low, had a little trouble finding lift again so you powered up to climb back up to a good thermal-search altitude, shut down, found some more weak-but-usable lift, then spent the next 20 minutes slowly working back up to altitude. By now you're about 45 minutes into a really satisfying flight, at speck height again and half a mile downwind. The question is, exactly how many minutes of radio life do you still have? You're half a mile downwind - if you stumble into some bad sink or a sudden bad headwind (such as the ones that downwind thermals can generate) coming back, can you fire up the motor without draining whatever juice is left in your single battery, thereby killing the radio? Many models have been lost under exactly these sorts of circumstances.
By using a separate battery to run the radio, you can predict with a fair degree of accuracy how much flight time your radio will give you, regardless of what you do or don't do with the motor.
Yes, if you have the self-discipline to limit and keep track how many seconds you use the motor, always use either full throttle or none at all so you use the same current for all of those seconds, then throw a huge safety factor on your estimates of how much radio time that all leaves you with (at which point the weight from the extra battery needed for this safety factor probably would pay for a separate radio battery anyway), you can make it work. However, that's an awful lot of "if's", especially when what's at stake is the survival of your airplane.
Also, wouldn't generally the battery pack go right behind the motor? IS it so tail light one doesn't need the weight ahead of the wing?
The plane was originally designed as a sailplane, and balances reasonably well with just the radio battery, receiver and servos in the nose. On the electric version, even after shortening the nose 3.5", that heavy motor up front takes care of C/G issues. Also, especially with the old nicads that were the only option back when we first started on the electric version, there were options for different motor batteries. For example, for a contest situation where you only had one climb to altitude, only a ten minute or so task window, and wanted the plane as light as possible for soaring on light air, a 7-cell 500AR pack might work. OTOH, for an afternoon of sport flying, with longer flights and possibly multiple "relights" during the course of one flight, an RC2006 pack might be more desirable. On windy days, you might also want the bigger battery just for the ballast.
To facilitate that, I designed it to have the variable-sized motor battery located on or near the C/G, so you could put anything in there and not have to worry about balance.
Don Stackhouse
DJ Aerotech
|
May 17, 2008
