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Author Topic: Ministick and microstick - trying to get back into indoor!  (Read 16268 times)
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Flyguy
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« Reply #125 on: February 08, 2018, 02:49:52 PM »

Thanks, I think the no area behind the spar stuff has been done for quite some time (like in easy b), but I like to check things empirically, so I started with prop blades that had area behind the spar, flew some flights with that, then took a razor blade and sliced off the area behind the spar, then put up a few more flights, so that gives you a pretty good comparison - I thought the sliced props were better, so there you go. Didn't try it yet with the minis, I'm also curious as to how the mini prop works with the tiny bass spar, hopefully I'll find out next week. I'm also experimenting with the shape of the blade, left on a little extra so I can try trim it at the field like before to see what happens.
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Flyguy
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« Reply #126 on: February 10, 2018, 07:31:36 PM »

The idea behind the lollipop prop was that since there was no twist allowed in the blades, a conventional 6" prop would have part of the blade flying efficiently while the rest of the blade would be fighting it. It seemed like concentrating the blade area in a small part of the prop disc would minimize that effect.

I'm also wondering about these kinds of things. On a related note, I'm curious as to whether the widest part of the blade should be towards the tip, the middle, or the center. I've seen all three variations on various plans, my current blades are widest in the center of the blade. Of course I can make props to test this, I've made some progress testing various props but it still takes time! Any thoughts appreciated.
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OZPAF
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« Reply #127 on: February 11, 2018, 03:55:29 AM »

Conventional propeller theory states that the thrust is at a peak at the 75% radius point. The variation of thrust along the radius of the blade is a 3d problem in some ways similar to the span loading of a wing. Just as the plan form does not dictate the lift loading(it does however dictate how efficiently the wing handles this lift distribution) - it is basically elliptical regardless , as it needs to drop to zero at some point close to the tip.

Thus to me it would seem that the area distribution and pitch distribution will not alter the thrust radius loading but can make a noticeable difference to efficiency. I would then believe that the area should be most efficiently distributed around the 75% or very close to it.

For these models where helical pitch or any twist is not allowed - it might make more sense to have an exaggerated Larrabee plan form ( but as a "lollipop" all area in front of the spar) with a narrow root swelling out to a max at 75% and then reducing quickly for the tip?

Actually rereading OLbill's comment - he seems to be saying something similar but my suggestion is to make this even more extreme.

It would need a long prop spar to maintain the strength of the prop and the widest part of the blade would stick out a long way, and may be too fragile?

Anyway food for thought and good luck.

John
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Flyguy
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« Reply #128 on: February 11, 2018, 12:42:19 PM »

Thanks for the feedback John, extremely interesting. Right now the max width on my mini blade is at about 50%, for the A6 it's at about 75%, I just eyeballed the prop shapes, modifying some of my earlier props (using drawing software), so that they looked 'right'. Looks like I'll have a chance to test the ones shown in reply#123 on wednesday, can't wait!

I also found this old Aeromodeller article at Volare about Larrabee props, http://www.volareproducts.com/PFFT/LarrabeePropDesign.pdf  From his figure, it looks like, for the P/D ratios used in indoor, the max width will be in about the 50-75% range, which is encouraging. I might try another mini prop where the width is shifted a little from 50% where  it is now to about 75%; also I can see what the A6 prop does since that's already around 75%. On the other hand, I noticed that Stan Chilton's mini prop has the max width lower, like at maybe 30%, that's what got me wondering, since he clearly gets fantastic performance.
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OZPAF
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« Reply #129 on: February 11, 2018, 06:03:50 PM »

Perhaps Stan is using a lower P/D? Propellers are an amazing bit of complexity all wrapped up in the simplest looking physical devices.

it's interesting to speculate with a semi theory approach but it's the fellows like Olbill and Chilton and the others who achieve the times that are the true masters

I liked the comment in Reg Boorman's article in that props of the 30' - 40's were closer to a more efficient design than the shovel shaped props of the 40's and later.

I have an early (1920) edition of an early English text book on prop design and it describes the thought behind the design of some of the early WW1 props - eg the BE2 and the SE5A. The detail is fascinating.


Good luck with your mini's and A6.

John

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« Reply #130 on: February 11, 2018, 06:38:26 PM »

I was very interested in a prop design from way back.  The design was used on one of the NC-4 flying boats and when they changed to a more standard design the performance went down but they stayed with the normal design.  The big difference was a huge hub area and a fairly quick taper to a smal chord tip.  I even chased down the designers son out east somewhere and got some info from him.  I wanted to use the design on F2D planes but never got past carving one in balsa.  It would have been very hard to mount on to the motor and I just quit at that time. I still think the design had some merit.
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Flyguy
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« Reply #131 on: February 17, 2018, 11:29:57 PM »

Well I almost posted that I had 2 flying sessions without losing any planes, feeling confident, just skimming the lights, but this past week I lost both a mini and an A6! Had the altitude under control for two weeks of sessions, lots of flights, and I also have Olbill's torque meter thanks to Mike Kirda, really nice, but I tested a new prop at the end of the day, even wound to a lower torque to be safe, but it still climbed a few feet too high (over 30 ft.) and the girders ate it, it's an unforgiving site - that's 6 planes lost in two months of flying! Another modeler also brought his first A6 and lost it as well, we couldn't even see anything sticking out.

Nice thing about A6 is that you can easily build one over the weekend. Already built the original design three times, and it flies nice as the video shows, but I wanted to try something else so this one is a higher-aspect ratio version - of course I knew when I built the first one that high AR was popular but I like to work my way from the ground up! 16" projected span, 1 7/8" average chord, bass spar prop, came out to 1.18 grams. Looking forward to flying it next week and seeing how it compares to the other one. I think it at least looks nicer!
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cessnadriver
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« Reply #132 on: February 18, 2018, 09:01:23 AM »

Great looking plane Flyguy! I notice that the tail boom seems to be in line with the motor stick. Is there an advantage over the drooping tail boom? Any chance you have a design sketch (fancy drawing not necessary), or some dimension you could post?

Thanks for all the inspiration!

Al
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OZPAF
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« Reply #133 on: February 18, 2018, 09:05:25 AM »

I think you will need to plant balsa trees if you keep losing models at that rate Larry. Smiley

I'm a fan of high AR's when there is no span limitation and I agree it does look interesting. how did the different props work - I guess the model eating rafters didn't give you much of a chance to compare them.

John
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Olbill
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« Reply #134 on: February 18, 2018, 11:48:59 AM »

The A6's look very nice!

I decided on a "medium" AR b/c of the large spars required by the rules. There were people trying 20" span A6's a few years back. I had a hard time understanding any advantage to such a narrow wing with 1/16" sq. spars on each end of the airfoil.

I'd actually like to try a low AR wing with tip plates. Whether I'll ever get around to it is a big question.
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Flyguy
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« Reply #135 on: February 18, 2018, 12:39:58 PM »

Great looking plane Flyguy! I notice that the tail boom seems to be in line with the motor stick. Is there an advantage over the drooping tail boom? Any chance you have a design sketch (fancy drawing not necessary), or some dimension you could post?

Thanks for all the inspiration!

Al
Thank you. I haven't tried the droopy tail boom, so I can't comment on it, I think the idea is to get the stab out of the wing's 'wake'. The wing has an average chord of 1 7/8" and a projected span of 16" (giving 30 sq in of area). I have full size plans I still have to finish up. Hope it get's you flying, I've noticed that a few other club members have shown up with A6's now that they've seen mine flying! It's a fun category.

I think you will need to plant balsa trees if you keep losing models at that rate Larry. Smiley

I'm a fan of high AR's when there is no span limitation and I agree it does look interesting. how did the different props work - I guess the model eating rafters didn't give you much of a chance to compare them.

John
You guessed it John - didn't get a lot of prop testing in! The bass spar props clearly give an advantage but can be tricky. I had one that was wobbling a little, but the wobble wore out as the flight went on so it seemed the spars weren't flexing equally. Checked at home - blades were at exactly the same angle but pushing on the blades with a thin balsa strip I could see that one side was more flexible. Sanded the spar on that side a little, we'll see what that does next time. I tested a second bass spar prop, flexed nice and flew as smooth as glass, really nice! Of course that's the one I lost in the rafters. Have a few new ones for this week.

The A6's look very nice!

I decided on a "medium" AR b/c of the large spars required by the rules. There were people trying 20" span A6's a few years back. I had a hard time understanding any advantage to such a narrow wing with 1/16" sq. spars on each end of the airfoil.

I'd actually like to try a low AR wing with tip plates. Whether I'll ever get around to it is a big question.
Thanks for that information Bill, that's extremely useful! So you didn't notice any apparent flying advantages for the 20" span? I was wondering about that, a 1 1/2" chord or less just seems too small, in my eye. My current one is 18" flat, 16" projected, 1 7/8" av chord, that seemed as high as I could go and still have it 'look right'. The original was 14" flat, 12" projected, 2.5" av chord, that might be closer to what you call low AR? I don't use tip plates, but the tips have very high dihedral. It will be very interesting to compare the two AR versions flying wise, the only real difference is the wing/stab aspect ratios. Speaking of low ARs, I have flying video for my micro with a AR of 2, should probably post it.


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Olbill
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« Reply #136 on: February 18, 2018, 05:08:47 PM »

I never tried a skinnier wing than what my current model uses. My first try at A6 was a low AR model that didn't perform very well but there are lots of possible reasons for that: bad prop, not enough rubber, knots piling up, etc.

If I ever try a low AR wing it would probably have an AR of around 3 and would be a flat wing with tip plates like my F1M and LPP. Those models work well b/c both are span limited. An A6 is not span limited so it may not be worthwhile.
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Flyguy
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« Reply #137 on: February 18, 2018, 10:02:19 PM »

Agreed, the span isn't limited in A6 so you want the optimal AR, the problem is figuring out what that is. If the span is limited like with pennyplane, and like with my micro, then it might pay to use the widest chord possible, we've seen that in pennyplane, and that's why I built the wide-chord mini. I'm glad I got it flying with an AR of 2, and it looks good so far. We'll hopefully get some info this week on how the higher AR wing does, plus the margin of stability calculations gave me some other ideas.
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« Reply #138 on: February 19, 2018, 01:05:59 AM »

I would imagine the optimum span is related to the fixed? prop diameter. Thus too low a span may give problems with roll control under high torque?

John
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Flyguy
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« Reply #139 on: February 19, 2018, 11:50:47 AM »

That's an interesting point John, that one has to consider the prop size as well.

So we know that the lift/drag ratio goes up with aspect ratio, but probably at some point various drawbacks kick in. Gliders and human-powered vehicles (probably the closest thing to rubber power, without the burst, just a cruise phase) use incredibly high ARs, so is it worth it to go any higher for A6? That's why this comment by Olbill intrigues me:

There were people trying 20" span A6's a few years back. I had a hard time understanding any advantage to such a narrow wing with 1/16" sq. spars on each end of the airfoil.

Does anyone have any info on what happened with these 20" A6's? How did they fly? Any apparent gains? Structural problems? It's got me wondering.

Can't wait to fly the higher AR A6 on weds., and I still have my medium AR A6, it's too bad I have to go to work after lunch, I'd love to spend the day flying!

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Flyguy
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« Reply #140 on: February 21, 2018, 01:34:41 PM »

OK, well it's my first 'higher AR design' and today was my very first time flying it, did 6:48:50, which seems good for the first time out, really wish I could have gotten some more flights in but I have to go to work. Bottom line - I think the higher AR flies better, looks like I can crack 7 min. with it. Really curious about those even higher AR designs Bill mentioned, hoping maybe someone is out there who can answer my question about the 20 inchers in my last post, otherwise I guess I'll have to build one to find out, but it would be nice to know if it's worth it! Looking forward to some more flying time with the new A6 next week.
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Olbill
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« Reply #141 on: February 21, 2018, 01:56:23 PM »

I don't know if anyone actually built an A6 with 20" span. One more reason not to do it is that the long wing spars would make the 1.2g minimum weight harder to achieve. My personal weight issue is my large stab but the way the model flies makes it worthwhile.

https://www.youtube.com/watch?v=mAg3wC-CyQM

https://www.facebook.com/bill.gowen/videos/10214005488038512/
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« Reply #142 on: February 21, 2018, 03:55:56 PM »

That is an amazing climb! What size motor did you use? (I.e., cross section, length, strand count).

Thanks for videos, and any further details!

Al
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Flyguy
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« Reply #143 on: February 21, 2018, 04:55:12 PM »

I don't know if anyone actually built an A6 with 20" span. One more reason not to do it is that the long wing spars would make the 1.2g minimum weight harder to achieve. My personal weight issue is my large stab but the way the model flies makes it worthwhile.

My two last A6's both came in under 1.2 grams and I wasn't trying to build light (sturdy instead), so I'm pretty sure that I can make a higher AR wing and still keep it around 1.2 g, in fact, my high AR version weighs less than my medium AR version, and they are both underweight. However, right now I'll stick with the current wing, 8.5 AR, since it looks like it can do over 7 min and I've barely flown it, first time out and it's already close, and it stayed under 35-40 feet the whole flight, that's all the altitude that's available, plus it just looks 'right'.

However if anyone out there knows anything about higher AR A6's (category has been around forever, seems like someone must have tried it) let me know, otherwise sooner or later I think I can build a light A6 with like a 13 AR, if I do I'll report back, nothing like actual flying to figure out these things, plus this is what makes it fun - actual data. new balsa from greenman should also be here any day now...
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« Reply #144 on: February 21, 2018, 07:05:37 PM »

That is an amazing climb! What size motor did you use? (I.e., cross section, length, strand count).

Thanks for videos, and any further details!

Al

For the Tustin flight the motor was a  20.5" x 1.15g loop of 5/99. It was wound to 3920 turns, launched at .4 in-oz and landed with 230 turns remaining - very low turns remaining for my way of flying. Later that day I got 10:20 with a thinner motor.

For the USIC 2012 flight the Cat 4 record was bumped up to 11:02. Motor was a 21.25" x .95g loop of 3/02 wound to 4600 turns and .33 in-oz.
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Flyguy
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« Reply #145 on: February 24, 2018, 07:27:31 PM »

Never say it can't be done! Looks like there's no answer to my question in posts #139 and 143 about a 20" A6, so I decided to check it out myself. Examined a few possibilities, but I thought the 20" projected span, 1.5" chord looked doable. The flat wing is 22" long, first photo. I used 3.8 lb. balsa instead of 4 lb, added two more ribs. The high AR wing actually came out slightly lighter than my other ones, around 262 mg! Total weight of the plane with prop shown in the picture is 1.2 grams (I have some lighter props in which case it's a little under). I think the next flying session is going to be very interesting, can't wait to see this thing in the air.
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cessnadriver
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« Reply #146 on: February 24, 2018, 09:25:19 PM »

Beautiful work Flyguy! I will be anxiously waiting to see how it goes! Please make sure the first flight stays well below the girders as you won’t be the only one to be disappointed if it doesn’t!
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« Reply #147 on: February 24, 2018, 10:17:57 PM »

Flyguy,
I don't have any 20", high AR models but I think you would find the following interesting. Google 'NORWIND' Indoor flyers and you should be able to open the 'Norwind' web site put up by Tom Tomlinson.  On the top line the is a heading 'plans' and scrolling down you will find a plan for an 'Easy A6 foam duration Model' designed by John Taylor.  To my eyes it is a beautifully proportioned aeroplane with 15" span an an AR of  8. The plan says it flies on a 10" loop of 0.04 rubber. Obviously with the foam surfaces it won't be down to 1.2g but people tell me they will do three or four minutes.  John Taylor is an interesting chap. An aeromodeller as a boy so naturally applied for an apprenticeship at nearby AVRO. He was bright so they sent him to Imperial College ,London to get his 'bits of paper'. He was put in charge of the wind tunnel, then was involved in many things, including the Vulcan' and finished up as Technical Director. When he retired he took up aeromodelling again and that is when I met him. One of his aerodynamicists was Reg Boor who made Larrabee's work accesible to a lot of modellers. It is interesting that Reg helped Bernard Hunt with his spreadsheet and John was co author of Bernard's paper on testing balsa wood.
John
 
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Flyguy
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« Reply #148 on: February 25, 2018, 10:29:10 PM »

Thanks for the comments, waiting to see what happens with the 20" AR6. On another note, almost 4 years ago back in post #27 in this thread, I mentioned that I was experimenting with a wide chord micro - the original had 5" wingspan and 2" chord, 2.5 AR, but given that the wing was limited to 5", I wanted to see what happened with a very low AR of 2, that is a 5" span with 2.5" chord. Had some problems getting it to climb, even with the usual fuselage twist, and so it sat in storage for years. I recently put a larger rudder on it, and it looked good in the living room, so I gave it a try at the Armory, https://www.youtube.com/watch?v=F_mMikCY8fk   Not bad! Might play with it some more, though right now I only have enough time to focus on either the mini or the A6.
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« Reply #149 on: February 25, 2018, 11:38:30 PM »

Love the wide wing Micro “footage”! Am building my first Micro from your plan posted above, earlier. I figure that if I can achieve basic building skills on this “little guy” that will make a future A6 build that much easier. I’m just getting my feet wet on this indoor stuff.

What changes would yo make on the Wide Wing Micro to tighten the turn and reduce the bank?
I’m guessing more left Rudder, more RH Stab Tilt (fuselage twist), and more Left Wing Washin?.......or are the last two redundant?

What are the motor dimensions on the Wide Wing Micro?

Thanks for any help!

Al

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