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« Reply #25 on: January 07, 2017, 10:02:22 PM »
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City: Vasco da Gama
State: Goa
RC Skills: Not into RC
Posts: 324
Join Date: Jul, 2016

Next on my to do list is to make a twin prop rubber powered outdoor. Have been advised by the Hippocketaeronautics experts that a good model to start would be the Double Top.

Here is a post from Hippocketaeronautics on use of a Torque Meter for Twins to get the right thrust on both engines

A tad long -- but wort reading and going to the linked references for more info

I have been using a torque meter for the last year or so in flying my models and have been absolutely delighted with the results. This has all been with single engined models and I started after flying with Don DeLoach for a number of years and watching his overall success with flying scale models in general. At a Geneseo Nats a couple of years ago I was his mechanic as he won 5, yes 5, mass launches in a row. I was astounded and after being hit over the head with this 2X4 I figured I could learn something from his methods. Like all the guys in the FAC he was more than willing to share his knowledge and techniques and among them is the use of a torque meter which he learned from flying competition free flight. He subsequently published 2 articles in the Flying Aces Newsletters entitled "One Flyer's Approach to Better Performace", Part I and Part II and found in the Sept-Oct 2012 and the Nov-Dec 2012 issues. These articles, if you want to really up your performance and enjoyment, should be absolutely memorized by a modeler. I have read them again and again to get the concepts in my head. In the articles he makes the case why torque measurement is so much more USEFUL than counting turns. I have since taken my expensive turn counter off my winder as it really does me no good after using a torque meter.

In a nutshell, a torque meter tells you what power is going to come out of the nose accurately and reliably every time. It does not matter what kind of power you have in your model whether it is neatly braided 1/8" strip, an inner tube, a broken motor, or squirrel running in a cage. The winding is done to pack all the available winds that could possibly be put in the motor and what that number is, is meaningless as you can't get any more in anyway. Guys will say "I am flying on 1200 winds" which is smoke in the air as it is 1200 winds of what? 2 loops of 1/8"? 10 loops of 1/4" And how long? 8", 15" 36"? all have differing effects on the released power. The number of prior flights has an effect as with each winding to 1200, the released power goes down as the motor get tired. I will let you read Don's articles. I subsequently had an article published in the FAC newsletter too on how to trim a model using a cook-book approach and a torque meter titled "Torque, Trimming, Voo Doo and Beethoven". I can't remember the issue but if any one wants it, email me and I'll send it.

So, on to twins. I at first was leery of it as reading a torque meter is a moving needle and at first glance, the discrimination on the face of the meter doesn't look fine enough for get a consistent reading. In practice it is not an issue. As the torque goes up the needle does not wiggle but is locked hard at whatever torque is under strain at the moment. You only need to read the units to halves anyway, i.e. 4.0 inch-oz, 4.5 inch-oz, 5.0 inch-oz and so on. Both motors of a twin can be wound to practically identical torques reliably as a result. Even if you have mixed motors or a fresh one in one nacelle and an old one in the other, you can launch knowing that the pull power in both are matched even after many flights. You just cannot get that by counting winds as continual flights will weaken motors unevenly and you will have turn problems that defy solving......or at least I did.

Incidentally I use my self made torque meter during my indoor flights and have a log that has a record of Torque to height of climb to ensure that my model remains just below the rafters.


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