Article 3 - November 2005

Article Guidelines- Please submit articles in Word .doc or text formats as ATTACHMENTS to your e-mail.  Photos should be resized to approx 3x4” and 130 kb to reduce download time.  Please indicate what contact info you want published, if any.  If you don’t tell me, I won’t put any!  Articles are updated the first of each odd month - Jan, Mar, May,etc.  Mark your subject with “DEAF”. 

I will acknowledge all submissions-  ron214(at)att.net


Article 3 - November 2005 Contents


  • Take it to The Ultimate (Mini) by Frank Korman



As I age I seem to become less sensible.  How else to explain untold hours invested in assembling sometimes fragile sticks of balsa to formers, wrestling with stick-to-itself Nelson covering, fitting and refitting pieces of acetate to a windshield frame, etc. when for less money, time, and occasional bother I could buy an ARF, one that if crashed would, unlike a handmade plane, cost very little emotional capital?

So, insensibly I was attracted to a Mini Ultimate Bipe, designed by Pat Tritle, and featured in a recent Model Airplane News construction article (go to the article HERE) written by him.  To be honest I would probably not have built the Mini if a semi-kit, available from Pat (email Pat at Patscustommodels@aol.com) was not available.  The semi-kit includes laser cut balsa of all curved, or otherwise shaped wood, and a nice set of plans (each wing, full-span, presented separately).  The builder supplies, stick wood, wheels, etc.  The laser cutting was the finest I’ve seen.  Parts not only depart the wood cleanly, but there is very little, if any, edge burn to sand off.  I do wish shaped wing trailing edges had been supplied.

Any building questions or problems, (and most of these were due to my perceptuallimitations), are quickly resolved via emails (see above) to Pat.

Now for some numbers:

  • Wing span = 21.5”
  • Wing area = 175sqs.
  • Weight = 5.8ozs.
  • Loading = 4.8ozs/sq. in.
  • Motor = GWS IPS w/4.14:1 gear ratio
  • Prop = GWS 8x4 to 8x6
  • Battery = Kokam 340ma, 7.2v Lipo
  • Controller = GWS 5 amp
  • Receiver = GWS 4 ch.
  • Servos (R&E) = Hitec 55’s
  • Rudder and elevator use pull-pull (Kevlar)
  • Power = about 15 watts (2 amps x 7+ volts)
Flying is fairly easy, but this is a small plane, that even at partial throttle, can get to the edge of visibility quickly.  It slows down nicely, does a loop from a shallow dive, and can handle winds up to about 5mph.  It is very responsive to controls, especially elevator.

All in all a very satisfying little ship with loads of personality. (See photo) Now if I can just keep it in one piece ARFS will remain a sensible, but unattractive alternative.

Frank Korman, FSKorman (at) aol.com, 214-327-8411

 


Bob Aberle's Response to Questions Asked by Frank Korman 11/05

1.  Years ago almost everyone, including me used a fuse in the motor/battery circuit.  This is not the case now.  What are your observations?

(1)- I haven't seen anyone use a fuse in years. Most modern ESC's have overload protection such as a thermal cut-off that will turn off the motor in the event excessive current is being drawn. The most likely scenario to an overload is when you go nose up on a landing, the prop hits the ground and you still have some throttle applied. Most of us gave up on fuses because of the extra voltage drop that results from the fuse itself.

As far as where to put the fuse, I think the best place would be at the motor to play safe. This is esecially true if you are using a BEC. If you were to have the fuse close to the battery and it blew out you lose all power, to the motor AND TO THE RC SYSTEM -- end of story!

2.  How important is idle current when choosing a servo used in a plane that also uses a BEC?

(2)- Idle current should not be of any concern. Most sevos idle at something like 20 - 60 mA and when you take three or four servos the total idle current doesn't come close to the usual 1 amp or so rating of the BEC regulator.

But servo current under load can be a critical item. The average servo might go to 300-400 mA when moving and when control rod/control surface loads are placed on it. Of course a stalled servo can go out of sight! For this reason you must be concerned with how much current your BEC can tolerate. Some tell you no more than three small or micro servos. Some others may be able to take 1.5-2.0 amps and that is much better. But you must check the spec on both sides, the servos and the BEC.

An alternate solution, when you need more current than your BEC can supply, is to get an add-on BEC often called a "UBEC". This device employs a switching circuit to obtain a regulated 5 or 6 volts. I've seen some of these that can take 35 to 40 volts and supply up to 2 to 3.5 amps to the servos. Look up the Medusa Research website for more info on this. In fact I just released a review of their BEC's for MA. Attached is a draft copy, but please don't re-print it at this time.


Bob also gives us a "heads up" for accessing FAQ's on the AMA site.

I'll probably use your questions in a future FAQ.  By the way, please tell your club members that they should also use the FAQ portion of the AMA website. Access is not direct, you must go to Publication, then Model Aviation, then Exclusive On-line Features and finally to FAQ. I write 3000 words a month, but only half appears in MA, the total 3000 words appears a month or so later on the website. The website is sorted by category, then by Q/A number.
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