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Author Topic: Torque burner  (Read 1274 times)
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cglynn
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« on: October 07, 2014, 09:09:17 PM »

While browsing the Science Olympiad forum, I came across a discussion of torque burners for SO planes.  The concept is intriguing, and I was wondering if a TB would legal for AMA LPP competition?  I am assuming not, since nobody has used it in LPP competition, but I figured I would ask anyway.

If not legal for LPP competition, what about using the TB system on something like an F1M in conjunction with a VP prop?  Could it be a way to make those precious turns last a really long time?  Or is the TB difficult to use to the point where the risk isn't worth the reward?

Chris
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Maxout
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« Reply #1 on: October 08, 2014, 07:39:38 AM »

LPP specifically bans energy metering devices.

For classes were VP is allowed, the best results seem to be with pure VP action. I could see a way in which it might be possible to benefit from a torque burner, but the complexity would likely be its downfall. VP really is extremely efficient, especially if your pitch trim keeps the airspeed high enough to avoid blade stall at high pitch.

A much more beneficial gadget than a torque burner would be an electronic VIT.
« Last Edit: October 08, 2014, 09:04:39 AM by Maxout » Logged
lincoln
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« Reply #2 on: October 08, 2014, 11:41:25 PM »

Pardon my ignorance. Torque burner? VIT?

I've seen a VP prop in action, though it's been many years. It was in a pennyplane (NOT an LPP). Went up to 25 or 30 feet (or maybe a bit more?) came back down and spent some time at 2 feet, then went back up, I don't remember how high. This was Ray Harlan setting some kind of record.

I suppose that a VP or some other gadget might be useful when attempting the difficult task of building up to weight!
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Maxout
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« Reply #3 on: October 09, 2014, 08:14:04 AM »

Lincoln,

 VIT is Variable Incidence Tail. It's used mainly on fast gas models, FAI towline, and F1B Wakefield.

 A torque burner is a mechanism which effectively divides a rubber motor into segments so that each section unwinds in series with the others, causing multiple climbs and descents, so kinda like what you saw with Harlan's VP prop, only doing so (potentially) more than once.

 For the record, the double climb system with VP props is the norm, although my F1D record made it all look like one continuous climb. My hub was designed so that the hub itself would flex, not just the torsion spring, so it is effectively two springs, allowing me to flatten out that dip in the thrust curve.

 VP props can be made extremely light, so they don't really impact the weight budget as much as one would think. It's easy to build a pennyplane or F1M down to weight, so it's not an issue there anyway. F1D is another story! Shocked
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Tapio Linkosalo
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« Reply #4 on: October 09, 2014, 09:53:26 AM »

Double climb may be the norm, but mostly because adjusting a continuous climb is so difficult (the spring geometry, not just the pre-tension) needs to be just right, and the blade hinges must move very freely. Therefore at least my models do the double climb; I'm trying to work towards sustained level flight which I assume is more efficient, but have not been able to adjust the prop yet good enough... :-) 
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Olbill
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« Reply #5 on: October 09, 2014, 10:45:12 AM »


 For the record, the double climb system with VP props is the norm......


Okay - so I'm not normal. Most people suspected that anyway.
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Maxout
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« Reply #6 on: October 09, 2014, 11:49:17 AM »

Okay - so I'm not normal. Most people suspected that anyway.

Given that you're using the same hinge concept as me...does your hub twist at all at high torque? If it does, that gives the double spring effect I mentioned, which would greatly flatten out the torque dip.

For high ceilings there is a gain to be had from the continuous climb. In low ceilings, I've found that the more I stay off the ceiling, while still being at the ceiling as late in the flight as possible, the higher my times. I've never been able to achieve that without the double climb.
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Olbill
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« Reply #7 on: October 09, 2014, 02:13:08 PM »

My spring is sized for the pitch change to be zero at cruise torque - at least that's the idea I've always used. I'm sure the double climb works since so many people use it but it never made sense to me. My scheme has always been to keep the RPM's as low as possible for the whole flight. It may be a simplistic approach but old and sometimes feeble brains sometimes work better with simplistic approaches.

Of course the results haven't been too bad.

Which reminds me that maybe I should resurrect the DoublePenny idea with a few years more experience under my belt.
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Re: Torque burner
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leop
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« Reply #8 on: October 09, 2014, 03:09:50 PM »

Bill,

My brain does not understand "My spring is sized for the pitch change to be zero at cruise torque."  Does this mean that all the pitch change occurs before the cruise torque is obtained or is all of the pitch change after the cruise torque ends?  I suspect the former but both assumptions could be incorrect.

LeoP
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ykleetx
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« Reply #9 on: October 09, 2014, 03:31:28 PM »

A younger (but still simple) mind asks, "What is cruise torque?"
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Maxout
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« Reply #10 on: October 09, 2014, 03:47:57 PM »

Of course the results haven't been too bad.

That's the understatement of the year.
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jakepF1D
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« Reply #11 on: October 09, 2014, 06:20:38 PM »

A younger (but still simple) mind asks, "What is cruise torque?"

I would posit that this is the torque at which a given model with a given prop maintains altitude.  Of course that isn't necessarily a static number when a VP or VD prop is involved.
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Olbill
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« Reply #12 on: October 09, 2014, 07:45:28 PM »

Theoretically I like for all the pitch change to be done when the torque is at about .2 in-oz. The only adjustment that I usually make is to the high pitch screw to get the model to climb to the top of the site and then stop climbing. Sometimes a change in preload might seem like a good idea and this would of course change the torque where the pitch change is finished.

Maybe when I get older and more experienced I'll try some other way of doing things.
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