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Author Topic: SO Wright Stuff 2020  (Read 1217 times)
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ceandra
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« Reply #50 on: September 09, 2019, 01:43:36 PM »

Autocad has a free student version; I don't know how good it is, and you're at the mercy of AutoDesk.

LibreCad is free open source software, but can be user unfriendly.  But -- open source.

FreeCAD is free open source 3D modeling software, can be really user unfriendly, and isn't really intended for 2D (but you can make 3D models with it!).

There's always butcher paper, straightedge and pencils -- and a camera if you want to share.

These are pretty simple planes. We use Microsoft publisher to draw up surface outlines and then print tiled on regular paper, tape together, and build on it. Or draft it by hand. Nothing too complicated here.

Chuck
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TimWescott
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« Reply #51 on: September 09, 2019, 01:48:47 PM »

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wait so you mean literally stacking two ikara props together making a longer wire shaft and making them turn in the same direction??

Yes - only slightly longer though. The rear prop would most likely need more pitch if they were turning in the same direction.

John.

Were you thinking butting the props together, i.e. a cheezy 4-blade?  Or spacing them out by a prop chord or so, i.e. a cheezy "biplane" prop?  I suggested the "biplane" prop earlier, and it ought to work on the same principle as a real biplane.  In the case of a biplane prop, I'm not sure that adjusting the rearward prop's pitch is necessary, as long as the plane is moving fast enough w.r.t the forward motion so that the pair is in undisturbed air.

The advantages would be more area for a pre-manufactured prop, and getting less induced drag than the same thrust from a single-plane prop.  Probably not much beyond that.
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Olbill
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« Reply #52 on: September 09, 2019, 04:19:13 PM »

I've used AutoCAD for over 30 years. It isn't an easy program to learn.
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OZPAF
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« Reply #53 on: September 12, 2019, 07:24:49 AM »

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Were you thinking butting the props together, i.e. a cheezy 4-blade?  Or spacing them out by a prop chord or so

Spacing them out but probably not quite that far Tim. It was a desperate idea Smiley

The reason for suggesting an increase in pitch was due to the slight increase in axial velocity that the rear prop would be working in at the same rpm as the front prop. However the increase would be so slight compared to the rpm.

It would make the front end a bit more fragile - however extra weight may be needed anyway.

John
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Olbill
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« Reply #54 on: September 12, 2019, 11:24:57 AM »

Using double props would probably make it necessary to use a thicker prop shaft to keep everything from wobbling. This might not be a deal breaker but it would require some consideration about the bearing to be used in order for the prop to be removable.

Speaking of which do any of the people new to indoor flying need to know how to use a pigtail bearing so their prop will be easily removable?

When I first started I had to ask so it doesn't necessarily mean you're stupid if you don't know.
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cglynn
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« Reply #55 on: September 12, 2019, 11:57:26 AM »

This might be out there, but has anybody thought about using a geared prop?  Large gear on the motor, small gear on the prop.   Increase prop RPM for the same rubber RPM, but also increase the torque required. 

Or is the torque requirement for climb already so high that increasing it through the gear drive would be asking too much of a rubber motor?

It seems to me that through using such a system, fliers could get the necessary RPM/thrust, with a slower turning motor, thus increasing flight time. 

This concept is similar to what is done in competitive mousetrap powered cars, where a large pulley is attached to a skinny drive axle.  One rotation of the pulley results in proportionally more rotations of the wheels.  The car travels at a slower speed due to the increase in torque requirement (to acheive the same speed as a 1:1 ratio) but by using the energy stored in the mousetrap over a longer period of time, increases distance.

It would take some doing to build the gearbox, and find the perfect gear ratio, but is there any reason this wouldn't work, at least in theory?
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TimWescott
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« Reply #56 on: September 12, 2019, 12:27:18 PM »

... but has anybody thought about using a geared prop?  ...
... but is there any reason this wouldn't work, at least in theory?

So, the theory that I know is that as long as the prop isn't stalling, the efficiency mostly comes from the diameter.  And building small, low-friction gears would be an absolute bear.

So if you did want to reduce prop speed, going to paddle blades would be the way -- in theory.

Or, use lots of thin rubber to turn a "normal" prop fast, because the real problem (that I see) is that the efficiency is going to be down because the prop diameter is small.

Note that I'm very carefully avoiding even thinking about the (to me) absurdly small Reynolds numbers involved.  I have no clue how that impacts things.
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ceandra
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« Reply #57 on: September 12, 2019, 01:01:19 PM »

This might be out there, but has anybody thought about using a geared prop?  Large gear on the motor, small gear on the prop.   Increase prop RPM for the same rubber RPM, but also increase the torque required. 

Or is the torque requirement for climb already so high that increasing it through the gear drive would be asking too much of a rubber motor?

It seems to me that through using such a system, fliers could get the necessary RPM/thrust, with a slower turning motor, thus increasing flight time. 

This concept is similar to what is done in competitive mousetrap powered cars, where a large pulley is attached to a skinny drive axle.  One rotation of the pulley results in proportionally more rotations of the wheels.  The car travels at a slower speed due to the increase in torque requirement (to achieve the same speed as a 1:1 ratio) but by using the energy stored in the mousetrap over a longer period of time, increases distance.

It would take some doing to build the gearbox, and find the perfect gear ratio, but is there any reason this wouldn't work, at least in theory?

It appears you have it backwards on torque. If you gear for higher RPM (at the prop), then you will have lower torque. In reality, the prop governs the RPM, so for a given prop (and given POWER input), the prop RPM remains the same, as does the prop torque, The RPM of the rubber hook goes down by the gear ratio, while the torque at the rubber hook goes up (ignoring frictional losses in the gear train). POWER is torque times RPM, so as you increase one, the other decreases (for a given power). You can increase POWER to the prop with wider rubber (it will result in higher RPM and higher torque), but then could climb too high or run out too early.

Given a fixed prop diameter, the only advantage to gearing UP (prop faster than rubber) is to reduce the number of turns on the rubber (wider rubber), which would shorten wind time. However, this is at the expense of gear losses, which will not be insignificant. You would also have a wider, and thus shorter, piece of rubber if you hold the energy storage the same (rubber mass held constant), and this would allow a shorter MS.

Usually prop gearing is utilized when the source (engine, motor, etc) is efficient at a higher RPM than the prop, typically because a large prop (for efficiency) needs to turn very slow, whereas peak efficiency of the engine (IC or turbo) is at a higher RPM. The increased efficiency of a very large prop offsets the gearing losses. IMHO, you will not see efficiency changes to offset the gearing losses with the reverse gearing.

But, this is SCIENCE Olympiad, so try it and see what the stopwatch tells you!

Chuck
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cglynn
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« Reply #58 on: September 12, 2019, 01:27:21 PM »

This might be out there, but has anybody thought about using a geared prop?  Large gear on the motor, small gear on the prop.   Increase prop RPM for the same rubber RPM, but also increase the torque required.  

Or is the torque requirement for climb already so high that increasing it through the gear drive would be asking too much of a rubber motor?

It seems to me that through using such a system, fliers could get the necessary RPM/thrust, with a slower turning motor, thus increasing flight time.  

This concept is similar to what is done in competitive mousetrap powered cars, where a large pulley is attached to a skinny drive axle.  One rotation of the pulley results in proportionally more rotations of the wheels.  The car travels at a slower speed due to the increase in torque requirement (to achieve the same speed as a 1:1 ratio) but by using the energy stored in the mousetrap over a longer period of time, increases distance.

It would take some doing to build the gearbox, and find the perfect gear ratio, but is there any reason this wouldn't work, at least in theory?

It appears you have it backwards on torque. If you gear for higher RPM (at the prop), then you will have lower torque. In reality, the prop governs the RPM, so for a given prop (and given POWER input), the prop RPM remains the same, as does the prop torque, The RPM of the rubber hook goes down by the gear ratio, while the torque at the rubber hook goes up (ignoring frictional losses in the gear train). POWER is torque times RPM, so as you increase one, the other decreases (for a given power). You can increase POWER to the prop with wider rubber (it will result in higher RPM and higher torque), but then could climb too high or run out too early.

Given a fixed prop diameter, the only advantage to gearing UP (prop faster than rubber) is to reduce the number of turns on the rubber (wider rubber), which would shorten wind time. However, this is at the expense of gear losses, which will not be insignificant. You would also have a wider, and thus shorter, piece of rubber if you hold the energy storage the same (rubber mass held constant), and this would allow a shorter MS.

Usually prop gearing is utilized when the source (engine, motor, etc) is efficient at a higher RPM than the prop, typically because a large prop (for efficiency) needs to turn very slow, whereas peak efficiency of the engine (IC or turbo) is at a higher RPM. The increased efficiency of a very large prop offsets the gearing losses. IMHO, you will not see efficiency changes to offset the gearing losses with the reverse gearing.

But, this is SCIENCE Olympiad, so try it and see what the stopwatch tells you!

Chuck

I see what you are saying Chuck.  I was thinking that gearing up the prop might be a worthwhile pursuit in that it would allow the use of a motor capable of storing more energy (heavier) than one used for direct drive, and releasing it over a greater period of time.  No doubt the system would be inefficient, but if the effective motor run time can be increased without putting the model through the ceiling, it could be worthwhile.

Or am I getting dangerously close to trying to get something for nothing?
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Olbill
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« Reply #59 on: September 12, 2019, 01:45:18 PM »

A new person writing the rules would be a good move for the future.
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Tmat
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« Reply #60 on: September 12, 2019, 02:10:27 PM »

Gearing would be a way to get a short motor stick and shorter overall fuselage. You could use a thicker, shorter motor. Some P30 (outdoor) fliers have done the same thing. They use a short, thicker motor and gear it down to get a longer motor run.

Tmat
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TimWescott
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« Reply #61 on: September 12, 2019, 02:57:51 PM »

Gearing would be a way to get a short motor stick and shorter overall fuselage. You could use a thicker, shorter motor. Some P30 (outdoor) fliers have done the same thing. They use a short, thicker motor and gear it down to get a longer motor run.

Tmat

I thought that the usual way to accomplish that was by braiding a long thin motor -- or does braiding only work up to a point, after which you need gearing?

And I thought P-30 was supposed to be entry level.
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ram
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« Reply #62 on: September 12, 2019, 03:05:59 PM »

Braiding doesn't effect the cross-section of the motor it only effects the relaxed length.

Rey
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dslusarc
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« Reply #63 on: September 13, 2019, 10:41:27 PM »

Jack McGillivray use to use 2:1 gear up boxes in a lot of his scale models until the FAC banned the use of gearboxes (other than 1:1 ratio). It allowed him to use a shorter loop of rubber in the model so it would not be subject to motor bunching. The most memorable one of his I recall was his peanut scale Issac's Fury. Would do 2 minutes easy with that gearbox and the model was about 11 grams ( a little high for that size indoor peanut). I messed with the gear boxes on my WWI peanut combat models around that time and felt that my flight times were about the same with our without the gear box. Main issue I had on a peanut was the fuselage instead of having to hold the torque of a loop of 1/16" rubber it now had to withstand a loop of 1/8" rubber. But for this SO application it may be beneficial as long as the gearbox is smooth. 

Don
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Little-Acorn
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« Reply #64 on: September 15, 2019, 01:14:20 AM »

may i ask why nails? like why not clay or something else
also i saw your models from last year and this year, why is the bearing of the prop always like far out from the motor stick
Nails, from force of habit. I'm sure clay would work fine too.

I use a piece of 2mm aluminum tube so I can easily bend in downthrust or side thrust. It's proven very useful in the past.
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Maxout
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« Reply #65 on: September 15, 2019, 05:57:11 PM »

A new person writing the rules would be a good move for the future.

For real. There's a difference between rules which regulate performance and rules which make the airplanes a pain in the neck to operate. Cutting the props to 5-6" diameter and doubling the max stab span would have gone a long way to making these models much more fun, and at the cost of only a little higher flight times, say 2-2 1/2 minutes. If they REALLY had to keep the flight times below 2 minutes, then raise the minimum weight to 10 grams with the above specs. I mean seriously, these planes are just plain ugly, and they fly like crap because that tiny stab provides so little pitch damping, plus the prop is darned finnicky about being in the perfect flight regime.
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calgoddard
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« Reply #66 on: September 16, 2019, 10:53:28 AM »

I have been involved with WS since 2004 as a coach, event supervisor, and workshop presenter. 

The WS 2020 rules largely dictate a rubber powered model airplane which is inherently unstable and difficult to trim, and will lead to much student frustration and disappointment.  Many students will therefore probably give up on free flight after competing in WS.  Did anyone on the particular SO rules committee actually build and fly a WS airplane that meets the WS 2020 rules before they were formally adopted? If the goal of the WS 2020 rules was to limit flight times, there were much better ways to do this. Let me give you one example.
 
Several years ago, I proposed an event for SO called Rubber Powered Airplane (RPA). The goals of RPA were to increase experimentation and the variety of designs at competition, and to simplify judging at check-in.  The RPA rules can be found at the following link (see Reply #19):

https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=21883.0

Basically, under the RPA rules any design of rubber powered airplane that fits inside a FedEx large box (with or without the propeller installed) while in flight configuration and that weighs a minimum of 5 grams is permissible.  There is no limit on the size of the rubber motor or the diameter of the prop. The sizes of the wing, stab, fin and motor stick are only limited by your ability to fit the fully assembled air frame into the FedEx large box.

Maxout’s simple RPA design is displayed at Reply #11 at the link above.

Stable and easily trimmable models are readily achievable under the rules of the RPA event. It was successfully run as a trial event at the 2017 SoCal SO State Finals.  The winning flight time at that competition was only 69 seconds partly due to late publication of the RPA rules and the minimum effort students were able to devote to competing in a trial event.  RPA flight times of 2+ minutes are possible in a standard size HS gym.  RPA flight times could easily be further limited by simply increasing the minimum weight of the airplane to 6, 7, or even 8 grams, without compromising the ease of achieving stabile designs.

The RPA event was praised by WS coaches and expert indoor fliers. It could have been adopted by the Nationals SO organization and renamed WS to continue the tradition of that event.  Instead RPA died as a potential SO event in 2017 without any real reasons for its non-acceptance being made public. I only heard comments from the powers that be that I needed to promote the RPA event some more.

Draw your own conclusions.
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dslusarc
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« Reply #67 on: Today at 07:22:14 AM »

I suggest reviewing this past post.

https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=19661.msg188623#msg188623

This is the section of that post that always comes to mind to me when I see people ask why the rules are written as they are for aircraft or criticize the design as being hard to fly. You just need to stop acting like you are "entitled" :-)
  

"... I have noticed a sense of entitlement amongst the free flight community. Science Olympiad was not founded with the intention of specifically increasing the number of high level indoor fliers. Science Olympiad events are not AMA events. As one of the rules writers and event supervisors, I'm frankly not that concerned with the elite competitors who might go on AMA and FAI events. Those students will find their way and hopefully be connected with some mentors who will guide them to great success. Instead, I am concerned with increasing overall participation, getting the vast majority of students who have never seen a free flight plane before and will not make it out of their regional competition to be able to build their first model. Suggesting we eliminate an event because the top level competitors are not getting the same experience they would at an AMA event completely disregards this massive audience and is frankly insulting to the novices who simply don't know what they are doing through no fault of their own. If you'd rather have no flying events than make small compromises on their quality, you are truly misguided and clearly concerned with setting records and individual performance over outreach and getting more people exposed to free flight."



My reaction to this comment is similar in a way. If we are perceived as "entitled" then I do not expect the SO organization in any way or form to ask for "our" help in promoting their events, running their events, or helping those who participate. For them to expect that would be them acting "entitled" to our collective knowledge and talent. It goes both ways.  

Don
 
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Olbill
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« Reply #68 on: Today at 08:27:06 AM »

Truly.
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Olbill
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« Reply #69 on: Today at 08:31:08 AM »

I suggest reviewing this past post.

https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=19661.msg188623#msg188623

This is the section of that post that always comes to mind to me when I see people ask why the rules are written as they are for aircraft or criticize the design as being hard to fly. You just need to stop acting like you are "entitled" :-)
  

"... I have noticed a sense of entitlement amongst the free flight community. Science Olympiad was not founded with the intention of specifically increasing the number of high level indoor fliers. Science Olympiad events are not AMA events. As one of the rules writers and event supervisors, I'm frankly not that concerned with the elite competitors who might go on AMA and FAI events. Those students will find their way and hopefully be connected with some mentors who will guide them to great success. Instead, I am concerned with increasing overall participation, getting the vast majority of students who have never seen a free flight plane before and will not make it out of their regional competition to be able to build their first model. Suggesting we eliminate an event because the top level competitors are not getting the same experience they would at an AMA event completely disregards this massive audience and is frankly insulting to the novices who simply don't know what they are doing through no fault of their own. If you'd rather have no flying events than make small compromises on their quality, you are truly misguided and clearly concerned with setting records and individual performance over outreach and getting more people exposed to free flight."



My reaction to this comment is similar in a way. If we are perceived as "entitled" then I do not expect the SO organization in any way or form to ask for "our" help in promoting their events, running their events, or helping those who participate. For them to expect that would be them acting "entitled" to our collective knowledge and talent. It goes both ways.  

Don
 


Hmmmm.....
Seems it was my post that set off Mr. Chalker. I'm really sorry about that.
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cglynn
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« Reply #70 on: Today at 12:01:55 PM »

I have coached SO in the past, and can say that without a doubt that WS and ELG are the most time consuming of all SO events.  The time it takes to build a model, optimize it, then build version 2, optimize it, and so on, is orders of magnitude greater than any other event.  Maybe I will sound entitled here, but if students and their coaches are willing to put in all that time and effort, I personally think they deserve a set of rules that results in a model that at least has a chance of flying well, and that they deserve a competition site that allows for fair competition....ie find a place that doesn't have all sorts of junk hanging down from the ceiling while the HVAC system is blasting full bore.  Give the kids a chance at least. 

A fair competition may or may not result in more AMA indoor fliers.  While I am always happy to see indoor grow in terms of participation, I don't really mind if SO does not fulfill that goal.  But as a former coach, indoor flier, and now parent, it seems almost disrespectful to the competitors to specify a model that has little chance of flying even remotely well unless one is an absolute expert.  I get that its SO, and it supposed to be challenging.  But ANY indoor flying is challenging enough in its own right.  The rules and available flying sites should not make it prohibitively difficult to competitive.

My .02 

Of course, if it were up to me SO would be LPP rules with a 1.5 g max motor, specifically so the SO competitors WOULD have an AMA (and FAI) legal model that could continue to work with after SO season ends.
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calgoddard
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« Reply #71 on: Today at 12:56:09 PM »

Don -

Here is a quote from Matt Chalker's post that you reproduced.  The bracketed part is my insert as it was obviously Matt's intention.

"Instead, I am concerned with increasing overall participation, getting the vast majority of students who have never seen a free flight plane before and will not make it out of their regional competition to be able to build [and fly] their first model."

My RPA event serves this goal much better than the WS 2020 event because the latter makes it much more difficult for novices to achieve stable free flight.

I don't feel that by suggesting improvements in the SO rules I am acting like I am entitled.  Some of my suggestions have actually been formally adopted by the SO National organization, such as elimination of the maximum rubber weight rule, and banning mechanisms that actively change the angle of the blades or diameter of the prop.
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