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Author Topic: Right Thrust Questions  (Read 727 times)
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calgoddard
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« on: May 31, 2018, 12:57:03 PM »

All of my outdoor free flight models have right thrust - including Embryos, Jimmie Allen, OTR, P-30 and F1G.  The right thrust counteracts the substantial torque at launch.  Most outdoor rubber powered free flight models with free wheeling props are set up to fly a right-right pattern, i.e. they circle right in the power phase and glide in a right circle.  The free-wheeling action of the prop tends to induce a right turn. This is the standard approach.  Without the right thrust the model can roll hard left into the ground.  F1G models have right thrust, but many fly a right-left pattern since they have folding props.  

However, all of my indoor free flight models have left thrust - including A-6, Limited Penny Plane (LPP), No-Cal, and Embryo. They circle left in climb, cruise and descent. With indoor stick duration models like A-6 and LPP it is conventional to use about 1-3 degrees of left turn in the thrust bearing. Rudder and stab tilt are used to control the circle size. Again this is the standard approach. The circle size stays constant with my indoor duration stick and No-Cal models.

Here is a link to a YouTube video of a trim flight of one of my A-6 models.  I have it set up to circle left in a very small diameter circle.  This is because I fly it in contests at a site where I can fly up to about 26 feet instead of only 22 feet if the model stays between large, closely spaced steel I-beams. In the video my A-6 is being flown in a different site that does not have the large I-beams I referenced.

https://www.youtube.com/watch?v=g6sdcA-fYlM&t=38s

I have had problems with my indoor Embryo and P-18 models circling nicely to the left for most of the flight, and then straightening out and flying into a wall during the descent. Rudder adjustments will not cure this problem. Ditto for stab tilt adjustments (which are unsightly on an Embryo).  

I noticed that some indoor models use right thrust and circle right. Is this done to avoid the problem I am encountering with my Embryo and P-18 models? How do you decide when an indoor model should have right thrust? I have always understood that an indoor duration stick model should circle left so that it is not "fighting" the torque of the rubber motor and therefore wasting energy.

Thanks in advance for your input.
« Last Edit: May 31, 2018, 01:12:09 PM by calgoddard » Logged
hurleyi
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« Reply #1 on: June 25, 2018, 10:29:11 PM »

I have not had a problem setting up my "P18 cruisers" to fly left in small (~15 foot) circles to touch down, when built as per plan.
 How much left rudder and stab tilt have you tried with p18s? Increases in these have both worked to cure this problem in Science Olympiad models flown at Teaneck Armory. Embryo and scale rubber flyers here do fly right-right, typically with higher flight speeds and shorter durations than P18s and A6s.

The A6 in your video seems to fly much faster than walking speed. Is this correct, or is it an video artefact?
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Hepcat
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« Reply #2 on: June 26, 2018, 06:48:02 AM »

Cal, I suspect I may have said the following before but with my brain nowadays I can’t be sure.
From the earliest days of flying with propellers, both full size and model, I think it has been generally found that it is safer turning against the torque than with it.  So, why do lots of indoor flyers turn their models to the left?  I wonder if it started in the 1920s when, I think about that time, some US flyers had permission to fly models in large buildings. Presumably to avoid bad weather, particularly high winds.  If you had a chance of flying indoors I guess you would build a light, slow flying, model without too much power because you don’t want it to bang up into the ceiling.  The first time in the hall I think the flyer would go into the middle, away from the walls, and not too many turns in case it hits the ceiling, but lo and behold a nice safe flight with the model in a turn to the left with the torque.
However modellers being modellers they want to win so they start increasing the number of turns until the torque starts dipping the left wing and tightening the turn.  What the model needs is a bit more lift on the left wing, Lets make the left wing bigger by moving the wing over by one panel.  That works well for a long time but the models get lighter and lighter and a bit floppy but we can get over that with some tungsten wire bracing and the beauty of that is that if the left turn gets too tight we can warp the wing a bit with the bracing.
We are nearly up to date now.  The bracing is getting to be a nuisance when transporting models to competitions and it adds weight and drag, let’s get rid of it and reduce the size of the model a bit.
Up to date now with a minimum of bracing and a simple structure that distorts intentionally with the torque of the motor to warp the surfaces to give the flight path required.
Now having gone through why I think that left turn started and continued I will suggest why it continues still.  Indoor models are fragile and a collision often causes considerable damage so if most of the aeroplanes are circling left it is probably safer to go with the flow. It is interesting really that you Americans drive on the right (wrong?) side of the road you follow the English ‘Keep Left’ rule in the air.
 So far my concentration has been on free flight models but before closing I should mention that Indoor Scale models, in England at least, usually turn left. I am not a scale modeller and I certainly don’t know the US scale rules but I will say a couple of things in the hope that some scale modellers will give a more knowledgeable point of view than mine.
In the UK Indoor sites are usually very small and themodel is expected to take off and fly for about twenty seconds, which, almost inevitably involves flying in tight circles. Most scale models have a higher wing loading and more drag than a duration model and will need more power to take off. If this amount of power is used in an efficient, right hand circling, climb I think the model might be in the rafters. Instead it appears to me that the expert scale men fly left and do some very careful trimming to burn off any extra thrust by highly banked circles at quite high speed and judge the run down point of the motor to give a landing before the circles open out and the wall is hit.
John.
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