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Author Topic: LPP motor questions  (Read 1395 times)
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cglynn
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« Reply #25 on: November 15, 2013, 08:34:27 AM »

Got to fly the LPP this morning.  I was able to get two flights in before classes started for the day.  I am still under winding a bit and really need to take the time to break a motor to see exactly how much my motor can take.  Barring the exact breaking torque of my motor, I wound to a high, but safe torque, backed off about 60 turns, and let her go.  I got a nice climb to the ceiling, and managed a no touch 4:10.  The model was showing a bit of a stall so I raised the rear wingpost.  Wound up to the same torque and launched near the floor.  The climb was noticeably faster, and the model got to the ceiling in about 30 seconds.  It did touch a few times, but no major dives or anything like that.  The cruise was much more stable and steady, as the model was not stalling anymore, and I managed a 4:23.  Both flights were launched with launched with 2300 turns in, and landed with around 900 turns left.

So now I am questioning where to proceed from here.  This gym is most likely the only site I will have access to, and I am starting to get the motor figured out.  I still have a few options to test though.  I could explore using a longer motor to try and get more from the cruise torque.  I could also try a slightly larger cross section, and keep the length, but I figure at the same launch torque, I will be in the ceiling for a long time, and this ceiling is dirty.  Girders, lights, speakers, and a big flag really warrant no touch flying, so I don't think that is the best idea.  So where should I go from here? 

Thanks
CG
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Olbill
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« Reply #26 on: November 15, 2013, 10:28:51 AM »

Not enough motor data to recommend anything. Length? Weight? Ceiling height? (maybe I missed that)

In the example that Kang gave I backed off 580 turns. Since you only backed off 60 turns my guess is that your motor is too thin. Also you need an accurate torque meter to measure max torque and launch torque and you need to record those numbers faithfully. All of my data is kept in a netbook computer that fits in my tool box.

At Kent it will be crucial for you to have this info. Before the lights were changed at Kent you could get away with some ceiling banging (if you were lucky). The new lights make no-touch flying the way to go. Last year I hung my last 2 official flights trying to better the 11:22 that I did on my 2nd flight.

In 2007 I had my best LPP flight there at 12:20. I think it tapped the bottom of the girders a couple of times. The Cat 2 record of 12:53 was set by Jim Richmond at the same contest. He put his model in a clear spot at the very top of the roof and bounced off the ceiling for several minutes. It would take a LOT of luck to get away with that with the new lights.
« Last Edit: November 15, 2013, 10:45:58 AM by Olbill » Logged
cglynn
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« Reply #27 on: November 15, 2013, 12:18:56 PM »

Bill, motor is 22" of 3/32 Tan SS.  Haven't weighed it yet.  Will do so next time I fly and report back.  I may still be under winding.  I put 2400 turns into this 22" motor, and it still had some give to it.  When I got to what I felt was near max torque, I had reached the hook to hook distance of my model, and the torque was climbing really fast.  I took four turns off the winder (15:1) and my torque reached a suitable value for launch in this site.

I was thinking about using a slightly thicker motor, same length, and since you suggested it, it seems I am on the right path.  Am I correct in assuming the thicker motor would hold fewer turns than my 3/32" motors, require more back off to get to proper launch torque, but that the motor would sustain torque for longer?  Or would it provide more power per turn, thus better utilizing the cruise torque?  In the end, it doesn't matter what really happens, as long as it works, but I do like to know why things happen and theory/reality behind thing, which is why I ask.  I figure if I know how things work and why they work, I will eventually be able to correctly diagnose and solve my aero modeling conundrums.

I really appreciate the advice you, and everyone else has been providing.  One thing I am really understanding and only starting to seriously apply is the level of precision required to really fly indoor.  Its one thing to wind up a motor, slap it on a plane, and watch it circle for a minute or two, but to get consistent high times, that is a new world for me.  Someone, somewhere, mentioned letting beginners drown in their lack of dedication, when referring to classes are are supposed to be "beginner" classes, and that really good (expert) fliers step in and start winning.  I am seeing how much dedication is needed to really get good at this.  Everything from the construction of the model, the overall model itself, and the data taken and applied to flying, has to be so precise.  And those who are deemed experts, are so because they have put in the time and effort it takes to really understand and be good at indoor flying.

Thanks guys
CG
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ykleetx
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« Reply #28 on: November 15, 2013, 01:31:20 PM »

CG,

Be sure to take your turns remaining accurately.  You mention that there were "around" 900 turns remaining.  If this is so, this means that during your flight, you used 2300-60-900 = 1340 turns during a 4:23 flight, or an average RPM of 304.   This is way too high.  This often means that your model is under elevated (not enough incidence between wing and stab).  It is probably flying much faster than it should if it is well trimmed.  I know that your model is slightly overweight, which also contributes to faster flying speed, but I don't believe that's the main reason.

It's also clear that your model is under powered if you back off only 60 turns to reach 25', as Bill mentioned.  For sure, a thicker motor is required, possibly shorter, too.  Try .100" width.
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cglynn
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« Reply #29 on: November 15, 2013, 03:25:34 PM »

Kang, thanks for running those numbers.  I will look into getting some thicker rubber, say some .095 and .100 before I fly.  I was suspecting the model was under powered due to its weight. 

I will look into the incidence also.  Though if I add any more incidence to the wing, I fear I am going to get some stalling.  Then again, I took 1/32 of incidence out of the wing (raised the rear post 1/32) and had no stalling at all.  I might put back 1/64" and see what that does.  I know these models fly the best times when flown just on the verge of a stall.

Next time I fly, I will make it a point to get some accurate data to share.  When I started asking about getting some good times, I had no idea how involved this stuff was, and was ignorant as to the amount and precision of data required. 

I'll get a flight report out there next time I fly, probably late next week/weekend.  This stuff is so addictive, I wish I could fly all day, everyday, but alas, students need taught, the kids need raised, and the house needs work.

Until the next time
CG
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Olbill
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« Reply #30 on: November 15, 2013, 05:43:33 PM »

I normally fly on 3/32 5/99 and a 22" loop should weigh around 2.6g and should go to around 3000 turns and something over 1 in-oz. max torque. I normally don't wind that hard when I'm flying in a low ceiling. Your 2400 turns sound a little low though.  I think you should wind to around 1 in-oz and then back off to a launch torque of around .25 in-oz. If that much torque won't get your model to 25' then there's probably something not working right. And you should have to unwind a ton of turns to get down to that torque.
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piecost
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« Reply #31 on: November 16, 2013, 07:16:06 AM »

I have read this thread with interest. I do not fly LPP but am trying to understand rubber motors better. Therefore I would like to ask why poeple wind up to near breaking before backing off?

From a small amount of testing I performed on Super-Sport rubber I found that no matter what number of turns I wound to; the unwinding torque versus turns curve was the same. If this is true then there is no benefit in winding so high. The hysteresis took about 50 turns, so I only had to wind 50 turns more than required before backing off to the desired torque.

Thanks
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mkirda
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« Reply #32 on: November 16, 2013, 08:16:48 AM »

I have read this thread with interest. I do not fly LPP but am trying to understand rubber motors better. Therefore I would like to ask why poeple wind up to near breaking before backing off?

When I first started, this didn't make sense to me either. I learned via trial and error that winding a motor to 3 on my torque meter would get me to the ceiling.
I only wound up to 3. Correspondence with a few fliers suggested I should wind higher then back down. So I wound to 10, then backed down to 3.

Now, instead of just barely making it to the ceiling with maybe a bump or two, the model took one turn to make it to the rafters and proceed to bump and grind with great abandon until the wing came off.

Winding up, then down to launch torque the rubber has a LOT more energy stored in it than just winding up to launch torque. In my case I now wind up to torque to get a sense of what will get me to the ceiling. I slowly increase on each flight. Once I have the ballpark figure, I will wind up then down to a LOWER number than this ballpark figure to test. i.e. in the above example, I'd wind up to 10 and back off to 2.2 and launch. Then maybe 2.3-2.5 depending upon what it did.

One thing that REALLY helped me was writing it all down and getting a better torque meter. If you can get one of Gowen's meters, they are pretty nice to use.

Regards.
Mike Kirda
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mkirda
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« Reply #33 on: November 16, 2013, 08:19:44 AM »

CG,

Be sure to take your turns remaining accurately. 

http://indoornewsandviews.com/2013/03/13/the-un-winder/

This is what I used after listening to Kang.

Regards.
Mike Kirda
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ykleetx
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« Reply #34 on: November 16, 2013, 02:40:46 PM »


From a small amount of testing I performed on Super-Sport rubber I found that no matter what number of turns I wound to; the unwinding torque versus turns curve was the same. If this is true then there is no benefit in winding so high. The hysteresis took about 50 turns, so I only had to wind 50 turns more than required before backing off to the desired torque.


Piecost,

I think you have cracked the code.  I have also concluded the same, but with a caveat.  In my tests, the unwinding curves are equal only after the motor is broken in.  In your example, I found if I wind the motor to only 600 turns before the motor is broken in, its unwinding curve falls below that of the 800 turns wind.  But once the motor is broken in, the unwinding curve soon become the same after some unwinding.

I believe for many people, winding to 800 then backing off helps because the motor has not been broken in, and the act of winding hard breaks the motor in.  On subsequent winds, it's not necessary to wind to max turns/torque.

However, a caveat.   my conclusion and yours are arrived at by "looking" at curves and likely from limited experiments.    I'm not sure I can say for sure that the unwinding curves are identical, say, to 5% of each other.   That is, limited testing probably cannot reveal any advantages under 5%.  And in practice, a 5% advantage is huge.  I am not ready yet to completely dismiss the observations made by many people over the years.   If you have the time, I would encourage more extensive testing.

Thanks,

-Kang
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cglynn
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« Reply #35 on: November 22, 2013, 09:28:35 AM »

I got to fly my LPP this morning.  I've been taking in all the great advice I've received from everyone and started to take better records.  I was only able to get one flight in today, but I was happy enough with it.  Here is the flight data:

2.8g loop of 3/32 SS (22" from inside the knot to the end)
2300 turns in
400 back off
12 x 22 prop
.3 in-oz torque
4.30 flight
900 turns remaining

I know from past flights that the above launch torque gets the model higher than the ceiling, so I launched right at the floor, and that did the trick.  The model climbed to the ceiling, but it may have been a bit fast.  I forgot to record time to the ceiling but I think it was around 45 seconds to get to 22ft.   It touched once on a girder and lost a bit of altitude, but recovered and maintained altitude.  Flew up in the ceiling for until 3.30 then started to descend.  With the heavy rubber, the model fell really quickly.  Took a minute to get to the ground and the watch read 4:30. 

Here are my thoughts on the flight.  I went with the long, heavy motor to try and get the most out of the cruise torque.  That may not have worked out so well.  The weight was such that the model flew fairly fast, especially once the torque dropped off.  It didn't quite fall from the sky, but it lost altitude really fast.  The motor was new, and that was the first flight on the motor, so it was not totally broken in, but I don't think that's all of the issue.  My guess is that I need a shorter (lighter) loop of thicker rubber that will offer more torque during the cruise and descent phase of the flight, even if it takes slightly fewer turns.  Also, I am sure a lighter model would help too.  I plan on getting another LPP together in the next few weeks, and will build this one to weight.

Any comments or critiques of my flight or thinking are greatly appreciated. 

Thanks
Chris
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Olbill
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« Reply #36 on: November 22, 2013, 11:55:45 AM »

At this point just try what you think will work and see what happens. Make sure that your model's wing and stab are straight without any unwanted twists or warps. I fly with a tiny bit of washin in the the right wing panel at rest. I use a little bit of left rudder, a little bit of stab tilt and about 3 degrees of left thrust to make the model turn. If all this looks good then you may need better rubber or a better prop. Some pictures of your model might help.
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cglynn
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« Reply #37 on: November 22, 2013, 12:15:00 PM »

Thanks Bill.  I kind of figured that since the model is behaving and turning out consistent times, at this point, its most likely not an issue of "I don't know what I am doing with this model," but more of refining technique, and optimizing the prop and trim.  Better rubber wouldn't hurt either.  This is some SS that I bought from a2z a few years ago, and based on numbers that you and others have published, I am thinking I should be getting better times. 

I've got some new rubber from a generous HPA member on its way, and I am planning on another model.  This one will most likely get donated to my after school program, as while it doesn't turn in great times, it was a great model to learn with.

The past two weeks of flying and asking questions have been invaluable to my progress in flying.  I feel like I have a much better idea of how to set up a motor for flying and get a program together for a given model that will work.  Before this thread and all the advice I was given, I would just sort of crank some turns into a motor and let it rip.  Now I have an idea of how to get the most out of a motor, torque values to wind to, and how to approach the various problems one may encounter.

Thanks
CG
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ykleetx
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« Reply #38 on: November 22, 2013, 02:30:28 PM »

CG,

You mentioned that this is the first wind.  Did you break in the motor?   If not, fly it again, and you should get 100 to 200 more turns, and there will be more torque as the motor unwinds.

If it was already broken in, I would try to shorten the motor by 2" then try.   you had 900 turns remaining on a wind of 2300 - or 39% turns remaining.  This indicates that your model is underpowered.  You can either use a thicker motor of the same weight (not length) or the same motor thickness of a lesser weight.  I bet you can get 5:00 if you shorten the motor.

-Kang
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cglynn
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« Reply #39 on: November 22, 2013, 02:52:42 PM »

Thanks Kang.  I will give that a go next time I get to fly.  I have a 20" motor made up for this model.  Weighs 2.5g and has been flown several times, so I know its broken in.  I think I have figured out the torque this model likes for Cat1 no touch, so I will use that as a starting point.

Btw, are you planning on attending Kent this April? 

CG
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ykleetx
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« Reply #40 on: November 22, 2013, 03:38:09 PM »

Yes, I plan to be there.

If you have the time, I would definitely try motors of 2.5g, 2.0g, and even 1.5g.  Many have flown top times with each of these weights.   Perhaps one will work better for you -- perhaps not.  Won't know until you try.   Have fun.
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