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Author Topic: Flight times for 2017 SO Wright Stuff  (Read 6375 times)
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wlsguy
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« Reply #125 on: May 25, 2017, 09:42:33 AM »

The FinnyPlane lives!
Yes it does !!
I scaled an old "Leading Edge" plan which stole many of the design clues from your Finny design to give to the teams I was mentoring.
Several people have asked me why use tip plates instead of a traditional dihedral and rudder configuration. I can honestly say, I have no idea, it just seems to work. If you would be willing to offer any insight to the design of the airplane and it's history, I'm sure future fliers will appreciate it. I'm particularly interested in the dropped tail which is a key difference in the designs.
Thanks
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Olbill
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« Reply #126 on: May 25, 2017, 04:40:41 PM »

I lost a post that I had worked an hour on. I'll try again when I'm done being aggravated.
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frash
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« Reply #127 on: May 25, 2017, 10:03:25 PM »

Bill,

I have done that several times. Maybe we should save a temp scratch file to Word or somewhere whenever we have 10-20 lines done. Once or twice I have done that, but don't do it every time and sometimes I regret not saving periodically.

Fred Rash
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Olbill
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« Reply #128 on: May 26, 2017, 07:57:25 AM »

Agreed Fred. I sometimes do that but was too lazy this time.
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wlsguy
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« Reply #129 on: May 26, 2017, 09:14:09 AM »

I lost a post that I had worked an hour on. I'll try again when I'm done being aggravated.

That happens to me all the time. I write something wonderful and then the computer eats it. My dog used to do that with my homework when I was a kid but now I have a computer instead:)
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Crtomir
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« Reply #130 on: June 05, 2017, 03:13:01 PM »

Hello, I'm new on this forum, although I've tried to read through earlier posts.  I coached our middle school Wright Stuff team this past year.  We had built decent planes early on, but never seemed to get over 1:30-1:45 while other teams were eventually getting 2:30-2:45 in high school gyms with ceiling heights of 24-26 ft.  We are trying to figure out what was limiting us.  I'm pretty sure we could have went with thinner rubber.  We only had 1/16" Tan SS.  For a 42cm loop of that, we could get 1800-2000 winds.   From reading the above posts, it seems we should have used closer to 0.055 in rubber and tried for 2500-3000 winds.  We didn't have a rubber stripper, but someone gave us one loop of thinner rubber and we were flying okay for a few flights, but eventually the rubber broke and we had to go back to 1/16" rubber. 

So, besides thinner rubber, I was wondering what was the optimal aspect ratio for the wings for this past Science Olympiad season?  We tried to make the wing as big as possible according to the rules (near max. span and near max. chord length) which ended up being an aspect ratio of about 4.  Does anyone have any thoughts on how aspect ratio plays a role in flight duration?  Would aspect ratios of 5 or 6 have been better?  Does a higher aspect ratio reduce drag?  What is the rationale behind choosing a specific aspect ratio?

 
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Olbill
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« Reply #131 on: June 05, 2017, 03:38:20 PM »

Aspect ratio has almost zero effect on indoor rubber powered duration models. My F1M model's wing is 8.25" x 18". 4 national records and one world record.
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Crtomir
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« Reply #132 on: June 05, 2017, 03:49:43 PM »

Maybe we had too much drag then?   I'm not sure.  How do you limit drag on Wright Stuff planes?  Maybe our wings had too much camber?  The planes our kids built were usually just under the legal 7.5g, so they would add a bit of tape as ballast to bring them just over 7.5g.  So our weight was okay.  I'm just trying to figure out why we were so limited in performance.  Three kids building nearly the same plane with the same props and rubber and ended up with nearly the same performance.

Here are the plans for the planes our kids built this year:  https://drive.google.com/open?id=0B-oLtzfbPGOnTjZUdjRhZ1o5Nms
(Too big a file to attach here)
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Olbill
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« Reply #133 on: June 05, 2017, 04:04:08 PM »

The only thing I noticed (other than how complete your plans were) is that the rib camber looked excessive. I don't know if your drawing was meant to be to scale. I normally use 3% or 4% camber on a wing and 2% on a stab.

I hate using a tube socket for a tailboom. If I had to use one I would glue the tailboom into the socket once trim adjustments were finished. Other wise the model will get knocked out of trim every time it hits something or even in handling.
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Crtomir
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« Reply #134 on: June 05, 2017, 04:30:45 PM »

The diagram for showing how to cut the ribs was only meant to be a cartoon.  The actual ribs were not nearly as dramatic.  The camber was much less, but still maybe too much.  The three kids each designed their own ribs so I would have to go back and measure the cambers.

Having the tail boom attach with a tube made it adjustable.  That way they could adjust the flight circle diameter for different gym conditions.  But, you're probably right.  Having too much ability to adjust things probably only made the results less predictable. 

Our kids are working this summer to see if they can improve their current designs according to last years rules, but I'm kind of at a loss as to how to help them get any better.  We don't know next year's rules yet, so we are just continuing on with this past year's rules. 

 
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Crtomir
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« Reply #135 on: June 05, 2017, 04:32:49 PM »

One of the major design factors for us was storage and transportability.  That's why we had so many removable/separable parts.  The whole plane can be taken apart and stored in a tiny space.   
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ceandra
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« Reply #136 on: June 05, 2017, 04:34:47 PM »

If your rubber is fixed size, then play with prop pitch. How many winds were left after flying?

You can get custom rubber cut by Dave at Freedom Flight.

Chuck
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Crtomir
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« Reply #137 on: June 05, 2017, 04:49:41 PM »

Generally, there were very few winds left after flying.  Probably 10-50 winds.  Sometimes, depending on how the planes were trimmed, there were no winds at the end.  Also, we did play around with adjusting the Ikara prop pitch a little, but did not get better performance.  That may be due to poor testing on the part of our kids.  They were not always systematic and careful. 

Another problem we had was not being able to get enough altitude.  We usually had no trouble getting to the top of a 24-28 ft gym.  However, at the state tournament in Ohio, the facility was the French Field House, which had a 45-60 ft ceiling.  We could not get over 25-30 ft no matter how we trimmed the planes.

We had a significant dihedral on the wing.  A lot of the better teams didn't use a dihedral, but used tiny vertical wingtips instead.  We tried that on one plane in practice before state, but still couldn't get over 1:30-1:45.     
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ceandra
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« Reply #138 on: June 05, 2017, 04:52:22 PM »

I suspect the greatest issues were in prop/rubber matching. How much were you backing off? What was the initial climb like (first few laps, climb per lap)? If using up rubber, need thinner rubber, generally. Any record on what pitch you ended up with on the props?

Chuck
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Olbill
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« Reply #139 on: June 05, 2017, 05:01:39 PM »

Generally, there were very few winds left after flying.  Probably 10-50 winds.  Sometimes, depending on how the planes were trimmed, there were no winds at the end.     

This is an indication of a too thick motor.
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mkirda
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« Reply #140 on: June 05, 2017, 05:14:10 PM »

Generally, there were very few winds left after flying.  Probably 10-50 winds.  Sometimes, depending on how the planes were trimmed, there were no winds at the end.  Also, we did play around with adjusting the Ikara prop pitch a little, but did not get better performance.  That may be due to poor testing on the part of our kids.  They were not always systematic and careful. 

Another problem we had was not being able to get enough altitude.  We usually had no trouble getting to the top of a 24-28 ft gym.  However, at the state tournament in Ohio, the facility was the French Field House, which had a 45-60 ft ceiling.  We could not get over 25-30 ft no matter how we trimmed the planes.

We had a significant dihedral on the wing.  A lot of the better teams didn't use a dihedral, but used tiny vertical wingtips instead.  We tried that on one plane in practice before state, but still couldn't get over 1:30-1:45.     

Do you have any idea of the torque the model was wound to?

Most do not wind hard enough. I've given the example previously, but most 'wind hard' to about 1/4 or 1/3rd of max torque.
Just enough to climb slightly, then on to the cruise portion of the motor run.

Where are you located in the US?

Regards.
Mike Kirda
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calgoddard
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« Reply #141 on: June 05, 2017, 06:14:27 PM »

Crtomir -

Kudos to you and your team for wanting to take the next step.

You came to the right place.  There are many experts on HPA willing to help.

Are your students flying with a torque meter? That is essential to consistently get max flight times indoors.

Are they keeping detailed flight logs?  This is also crucial to analyzing and improving performance.

I think you are being too hard on yourself and your team.  It is very challenging to consistently fly more than 120 seconds under the 2017 WS rules in a high school gym.  My personal best was 147 seconds.  The highest time I have heard of is 157 seconds and that was done by a world class indoor flier. See the top six times for the 2017 National WS competition posted in Reply #122 of this thread.

See pictures of my two 2017 WS models posted in Reply #6 and Reply #31 of this thread.  Both needed about 2 grams of ballast to get up to the 7.5 gram minimum weight.

In WS, the design of the model makes very little difference in IMO.  All you need to do is max the area of the flying surfaces and make sure the model is within a couple of hundredths of a gram of the minimum legal weight.   All free flight models need some form of dihedral.  Tip plates are extreme form of dihedral.  I don't think they provide any flight duration advantage, they just make the wing easier to build.

The longest flight times are achieved by optimum trim, matching prop to rubber, and good winding.  Most batches of TSS rubber are pretty good.  I doubt any of the top WS fliers were flying with May 99 TAN II - well known to be the best rubber for indoor fliers and very, very difficult to obtain.

Stripping rubber is much easier than re-pitching an Ikara prop.  Buy a rubber stripper from Ray Harlan.  Learn to measure rubber motors by length and weight, and not by width.  The latter is not an accurate measurement of the size of the rubber motor.

If your students were not winding to max torque, and backing off to a suitable launch torque for a no-touch flight, that was probably costing them a minimum of fifteen seconds of flight time, and perhaps more.  

        

  
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dslusarc
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« Reply #142 on: June 05, 2017, 08:54:23 PM »

The school I was helping was eventually able to get into the 2:45 and broke 3 minutes in a gym by using the stock 6" Ikara prop with tips just trimmed to fit the diameter. No pitch changes, and a long loop about 19-20" of June 2016 Tan Super Sport with 3200+ turns and very little or no backoff. They would still land with a fair amount of turns. The key was really getting the trim right to fly like this. I was surprised that this method worked so well. I had been flying pitched up props and wide blade props but the small low pitch prop flew the longest.     
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Crtomir
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« Reply #143 on: June 06, 2017, 09:58:55 AM »

Wow!  You all are very helpful.  I really appreciate it.

I'll try to answer all the questions the best I can.

1.  [ceandra]  We did play with the prop pitch some, but found that the 6" Ikara prop had the best flights with a pitch of around 22 degrees (I think).  This seems to be what [dslusarc] found with his team also. 

2.  [ceandra]  At one point, we realized that if we wound to near maximum winds then backed off a few winds till the torque was such that we would not hit the ceiling, we would have more winds with the same torque than if we had just wound straight up to the desired torque.  Our torque meter was home-built and not calibrated, but we used only that one torque meter all year till it broke in the practice flights right before the final flights at state.  So I can't give any meaningful figures for torque, but on our meter, it was showing 0.3-0.4 oz-in. for 1/16" Tan SS rubber with 41-42 cm length loop.  I think we tried to wind up to 0.5 oz-in. and then back to 0.3-0.4 oz-in., but we found this didn't improve the flight duration at all.  We still got about 90 sec. both ways:  winding straight up to desired torque or over-winding and then backing off a few winds to desired torque.  I was always puzzled by why we didn't get longer flights with the over-wind/back-off method.  The climbs were typically about 2-4 ft per lap (circle) with a circle diameter of about 18-20 ft. 

3.  [Olbill]  Yes, I think the motor was a bit too thick.  We are going to try thinner motors this summer and see if we can't improve our flights.

4.  [mkirda]  The torque was close to 0.3-0.4 for 1/16" Tan SS rubber with 41-42 cm length loop to get up to a ceiling height of about 22 ft.  Again, though, our torque meter was not calibrated, but the values are probably close.  This year, I have an idea for building a torque meter using a gram-scale and lever arm (no twisting wire) to measure torque directly.  I'm still working on the concept.   We are located in Centerville, Ohio (suburb of Dayton, Ohio).

5.  [calgoddard]  We did use a torque meter, but as in the above comments, it wasn't calibrated.  We took good flight logs (sometimes).  Our kids definitely took enough flight logs to make sure they never ran into gym rafters and such, but probably not enough to really figure out how to get much better.  I'm still working on convincing them to record most of their flights.  There were a few teams in Ohio this year that could get 150 sec. or better in standard high school gyms.  Nationals was in a tighter gym, so flight times were somewhat lower.  Still, I think 150 sec. is pretty close to the optimal time as you say.   Thanks for pointing out a better way to measure rubber (using density, weight, and length rather than thickness).  We will start doing that.  Actually, this summer, I really want to get the kids into some serious rubber testing.

6.  If I can get access to a good camera, I can start taking videos of some of our flights.  Maybe that will help.

Again, I really appreciate all the good advice.  I'm going to try and encourage our students to get an account on this HPA forum so they can ask questions directly.  I think it would be very beneficial to them.   



 
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mkirda
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« Reply #144 on: June 06, 2017, 10:04:45 AM »

4.  [mkirda]  The torque was close to 0.3-0.4 for 1/16" Tan SS rubber with 41-42 cm length loop to get up to a ceiling height of about 22 ft.  Again, though, our torque meter was not calibrated, but the values are probably close.  This year, I have an idea for building a torque meter using a gram-scale and lever arm (no twisting wire) to measure torque directly.  I'm still working on the concept.   We are located in Centerville, Ohio (suburb of Dayton, Ohio).


So that is about half of breaking torque, depending on a lot of factors of course, but 0.6 in-oz should be relatively easily achievable.

If you need a calibrated torque meter, I can get you one made up in a couple of days.

I know it isn't close, but you should consider heading to Rantoul for either the June contest or the indoor NATS.
Seek me out, I'd be happy to help.

Regards.
Mike Kirda
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Crtomir
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« Reply #145 on: June 14, 2017, 03:10:55 PM »

Special thanks to wlsguy for coming down to help us out at our Wright Stuff practice last Thursday night.  From what we learned, it seems our biggest performance limiter during the season was not using a thin enough rubber motor.  We had been using a 1/16" (0.065") motor about 41-41cm long weighing pretty close to 1.5g and getting only 1:30-1:45 in the gym where we practice (24ft ceiling).  After wlsguy helped us strip some thinner motors, we increased our flight time to 2:20.  We're going to do a little bit of re-design of our wing, but going with thinner motors was the way to go.  By the way, we are using the Ikara 15cm props trimmed to just under 14cm without changing the pitch (which I think is about 22 degrees.)

This week, I'm planning on having the kids start a motor log and do some rubber testing.  It seems to me, at least for this past year's Wright Stuff event, the key is keeping accurate records of both the rubber motors and the winds/torque values.  Getting the kids (especially the boys) to keeping everything organized and recorded in a log book is the biggest challenge.  They can build a decent plane, but without good reliable data and organized (labeled) rubber motors, they probably will not get too far.

Again, thanks to everyone here for their suggestions.  I'm sure I'll have more questions.  And a special BIG THANKS to wlsguy for taking time to drive all the way down to help us out last Thursday. 
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JasperKota
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« Reply #146 on: June 14, 2017, 05:20:37 PM »

It seems to me, at least for this past year's Wright Stuff event, the key is keeping accurate records of both the rubber motors and the winds/torque values.  Getting the kids (especially the boys) to keeping everything organized and recorded in a log book is the biggest challenge.  They can build a decent plane, but without good reliable data and organized (labeled) rubber motors, they probably will not get too far.
Congrats on improving the flight times! Trial and error, recording results, looking back and adjusting accordingly is a huge part. I think the intention of the event is not to focus on design and construction (plus, kits are fair game), but more of the testing and solving problems part of the engineering. I had numerous labeled plastic baggies for rubber, each labeled with motor weight and width. There is a nice editable flight log template bernard on scioly.org posted in one of the past Wright Stuff threads if your students keep forgetting to jot down certain things. In the future, (seeing as there's a long summer ahead) testing with a trimmed down ikara flaring blade prop might also be good and something that your students might be interested in (personally I loved flying and testing new things). I found that I ran out of winds less quickly, and climbed more slowly with it, so may be an alternative to using thinner rubber.
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  If I can get access to a good camera, I can start taking videos of some of our flights.  Maybe that will help.
Definitely a good idea. I posted videos of my flights, along with the data (torque, number of winds, motor length, etc.), and the great people here were able to help me improve my times before states.
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