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Author Topic: Another Gowen LPP  (Read 8929 times)
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piecost
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« Reply #50 on: October 12, 2016, 06:34:02 PM »

Hi Fred,

Thanks for your compliment. I consider the major contribution to my performance was that the venue for the competition was my home site and thus I could practice every month, concentrating on LPP to the exclusion of other classes. This gave me ample time to match the rubber to my propeller, relative to those who could only attend the competition or made ocasional visits.

I enjoyed designing a new propeller but have to admit that the assumptions for the inputs were not well defined and much care was needed to give an output that looked similar to well proven designs. I used Hepcat's Prop Picker with a selected pitch and chord to give the power and rpm and a MIL spreadsheet to derrive the chord and pitch distribution.

Whilst I have a method for determining the MIL propeller shape; I must admit to not seeing the underlying the maths. Can you provide a copy of Dr Larabee's original paper? I would be interested in playing with your propeller design code and seeing what it made of my propeller. Can you prove a more explicit instructions on how to download the Lazarus Pascal? I am rather a dummy at this sort of thing.

I found your May 1999 Rubber Turns, Torque Calculator very interesting and adopted it for my own motors. So, thanks for taking the time to publish such tools.

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Hepcat
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« Reply #51 on: October 13, 2016, 08:14:50 PM »

Piecost,
Belated congratulation on your double Nationals win.  That took some dedication.  Also, as so many others have said, thank you for the detailed information you pass onto the rest of us.

Do you have all the Larrabee information that you want?  I have the 1979 NFFS Sympo (16 pages covering the subject in English and French!) which has several descriptive pages and an appendix with 21 numbered calculation steps.
I also have the 1977 Sympo in which Larrabee had an 8 page paper talking about minimum loss propellers in a more general way and, finally: 'Propeller Design for Motor-soarers' which he gave as a NASA Conference report in 1979.  This is an 18 page report covering the subject in a more technical manner.  As a matter of interest I do have a copy of Sydney Goldsteins famous 1929 paper which proved Betz and Prandle were correct but I don't recommend it, I was lost by the end of the first page.

I was very interested when you said that you had a method for designing an MIL propeller but did not see a clear connexion with the underlying maths because that is exactly how I am.  I know my mathematical abilities are slipping away with age.  Not that they were ever more than was needed for basic design engineering but I can look at an expression nowadays and it just appears as a jumble of symbols. It can be very upsetting at times.

Strangely I cannot pass much comment on Larrabee's two Symposium papers because I have never used his approach.  Once, when I changed jobs, I had a long break from modelling, and during that time the Sympos started.  When I eventually saw one I wanted all the others but it took some years to get them second hand.  By the time I saw the Larrabee ones I had other methods I did not want to change.
John

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John Barker UK - Will be missed by all that knew him.
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« Reply #52 on: October 14, 2016, 08:20:53 AM »

Thanks Hepcat and piecost,

I already had the Larrabee paper scanned from the 1979 NFFS International Symposium so I emailed it to piecost yesterday. I have a paper copy of the 1977 Sympo paper somewhere but have not yet found a scanned copy here. Perhaps for John to send the 1977 paper to piecost would help the most. However, this is really not my call.

Interest in Larrabee and most other methods from you two and others is very welcome.

Thanks to you both and to many others for making HPA so strong, particularly to the guys that run HPA. Ratz again properly sorted out my attempts to post corrections and delete old versions.

Fred Rash
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piecost
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« Reply #53 on: October 14, 2016, 10:08:06 AM »

Hello John,

Thanks for your congratulations.  By, the way; I also came third with your Bar Fly design in Legal Eagle, see link:

http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=16906.0

Fred kindly sent me the 1979 NFFS Symposium Report, but I will appreciate it if you can send me any others.  I still read your propeller articles from time to time and appreciate their clarity. It is very likely that I will get bogged down with Larrabee's maths as it is a bit too much like work and I'd rather spend my modelling time using my hands rather than my brain. I'd like to have a play with Fred's programme if I can get over the slight hurdle of installing the code and getting it running.

I understand that the Larrabee propellers revolutionised human powered flight, enabling the Gossamer Albatross and the MIT Daedalus to make long distance flights. But, I don't have a feel for its impact on rubber powered duration models. Was it a flash in the pan, fashonable for a while and then only considered by aero/programming enthusiasts? Or has it continued to influenced propeller shapes, even if poeple don't remembering it doing so. A successful concept may be adopted long after the oringal rational is forgotton?

Or do other constraints render it impractical for indoor duration? Such as:
  Only working fully at a design point, not over the motor run; is it still good off-design?
  Useful for variable pitch propellers?
  even such things as a propeller tip radius being too tight to bend the propeller outline around (not a problem for sheet LPP props)
  contraints on pitch distribution such as tip washout to prevent seperation at lauch

I suppose that human powered flight is the ideal application of MIL propellers since the flying speed and power requirements are constant and efficiency is all important.
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piecost
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« Reply #54 on: September 19, 2018, 04:22:04 PM »

I am pleased to report that I won gold in LPP in the 2018 UK nationals. After a break of 2 years both models were still in trim! In the single practice session before the competition I employed the same long, heavy motor that I had used in the Brabazon hanger under 56" beams in the Eton sports hall with ─░ts 28' beams:

Jun 16, 2.54g/m x 22" & 2.88g

This was combined with a similar propeller as employed before, but with a 2 Rod Gowen hub and the pitch reduced from 22' to 17.5. The practice session yeilded a near 8 minute flight so I was confident. This was the first time I had steered a model using a roach pole. This was a skill I
not developed in the 300' by 300' floor of the Brabazon hanger.

I spent the first day of the competition becoming very frustrated. I found that the motor bunching badly yielding fluctuating torque levels. More importantly, my digital torque meter was drifting by 0.10g. Since it measures 10 oz.in per gram; the torque levels were varying by a massive 1 oz.in. This was causing my model to have alternate flights refusing to climb or bashing into the roof. Indeed; I lost my best model on top of a roof beam. My trimming flights put up good times but the first two competition flights yielded under 5 minute tines. My third of 6m0s minutes was half way down the field of 11 entries with the best two models reaching around 7 minutes. On the second day I resorted to sharing a torsion wire torque meter and things became more.orderly. It was frustrating having to adjust the length of the winder to meter to match my model prior to each flight and not being able to stretch wind the motor hard tor fear of breaking the shared meter. But I found the 1g.cm scale more conducive to fine adjustments and crucially the reading did not drift.

I changed to a thinner and shorter motor to eliminate the bunching problems:

Super Sport, 2.34g'm x 16 1.97g

This worked well so made up 18', then 20 motors without problems. My third flight gave an improved but uncompetitive 6m0s, whilst the 4th suffered a beam hit,
ollowed by scraping down the net that divided the hall, landing in under 4 minutes.

With 2 lights remaining everything came right. The details are:

Super Sport of unknown vintage 2.12gmx 20 loop & 2.20g
Wind to 2050 turns, 41g.cm
Back off 410 turns, 13.9 g.cm
23 max height no touch
Average pm 161
8m315

I tound a broken slrand on landing. Whilst I had not been winding hard I had nol been resting the motor.

The sum of my best two flights was 14:41 which put me into the lead with 14:01 in second place. I was prepared to use my last competition flight if nessesary, but this was not.needed.

Reviewing the best flight I concluded that even though I had employed a.lighter and shorter motor than usual; I still had not wound it hard. The launch torque was half that I had used with the heavier motor in practice.

I had made a 20" pitch propeller but had not had time to tey it. It will certainly lower the rpm and require a.high launch torque so may yeild higher times.
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« Reply #55 on: September 19, 2018, 07:18:20 PM »

Congratulations and thanks for the report.

John
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« Reply #56 on: September 19, 2018, 11:24:33 PM »

Wow! Good job!
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piecost
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« Reply #57 on: March 19, 2019, 04:01:06 PM »

I really enjoyed competing in the BMFA North Wast Gala at the Manchester Velodrome on 16 March 2019. 1t was great to be flying under a high ceiling after losing access to the Brabazan hanger. The duration competitions were run to unlirnited number of flights but i was limited by alternating between flying and timing for my mate . we managed a flight every quarter of an hour.

Care was needed to prevent the mcdels climbing above the nettng (to prevent the models escaping and landing on the cyclists) . the top of the net was 40'8", exceeding this which resulted in a disqualified fighl. The white steel roof structure provided the marker for the maximum
height.  Lucky people had models hit the lights or speakers mounted below them losing enough height to remain legal.

It was a close competition with the best time ol 5m08s, 2nd place at 4m58 and 3 place with 3m57s. I must admit being disapointed in achleving 3rd place. I am not being totally conceiled because in Ihe 2018 nats my best flight achiaved 8m30s compared to about 7m for the other competitors. However, my result at the nats was tempored by the fact that I cnly achieved one standout flight with the others being similar to my competitors. This good tlight was late in the day I would not have such tima avalable at the Velodrome.

Problems at the nats with my digital torque meter causng a model lost in the girders result in my being very caurious in progressively increasing launch torque in each flight. It usually takes me into the alternoon of a day's flying to reach the ceiling. I did not have the time lo do this in the velodrome since the flying was limited to three slots of about an hour's length.

The competition limited rubber to 0.75g with 0.75g ballast. I employed a 50% spacer.

I changed trom the 22" pitch with 4 rod Hub Minimum Induced Loss planform and twist propeller that I had employed previously lo 20" piich and 3 carbon rod Hub, I thought that increased fairing and lower pitch might be helpful.

I managed a practice session Under 25' ceiling with a motor and spacer scaled to 62% of the completion setup and found that I needed 1.98gm rubber af 4.75" loop achieve a no touch time of 3m02s. This scaled to 4m53s in the Velodrome ceiing. Not a bad mach to the competition time. In fact. I was not sure of the maximum allowable height in the Velodrome before the event.

I made up a variety of motors for the completion and ended up selecting 1.83g/m, since a thinner motcr worked well on my Legal Eagle model. I had reduced the mass/length by 8% from my practice setup which proved to be too much.

l used 3 identical motors and progressively increased the launch torque in each flight. However, I was not getting over half of the available height with most flights. I kept thinking that in the next flight the model will "light up and reach the caling. I found that I was winding up the peak of the torque curve and any backing off was reducing the torque beyond my target

I found that over 35g.cm the motar stick bends down causing the model to complete a circuit or so fast and flat before climbing as the torque drops. Over 40g.cm the stick twists so much as to cause noticeable warp and an outside banking turn , again before the wing straightens out and the model climbs.i did not notice lhis behaviour when practicing with a short motor under a low ceiling. Iguess that the stick still deforms but the torque draps off quicker and daes not kill the intial climb so much as under full height conditions.

The impact of the increasing the launch torque was being negated by the stick bending, killing the initial climb. Especialy when launch in the non-linear part of the rubber curve where the torque level drops off quickly.

Details ol my best flight:

Propeller Minimum Induced Loss Planform & Twist, 20" pitch, 3 Rod hub
0.75g  x 8" loop of June 2016 Super Sport
Wind to 950 turns, 48g.cm
Back off 50 turns to 37g.cm
Max Height 20' time 4m57s

In hindsight; l should have been more aggressive in increasing the launch torque. Thus discovering that the
motor was too thin earlier and switching lo a more appropriate mctar.

It may also have bean a mistake to use the more flairing lower pitch propeller.  Stick bending may be the limiting
Factor

I think useful to perform a back to back test using tho old propeller and the new one using the same motor.

I look forward to flying in the veledrome again
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piecost
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« Reply #58 on: March 19, 2019, 04:09:58 PM »

The velodrome
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« Reply #59 on: March 19, 2019, 08:21:55 PM »

Thanks for another of your very detailed reports - It really highlights the skill required to be competitive in this area.

John
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« Reply #60 on: March 19, 2019, 10:05:11 PM »

Hi piecost.  Thanks for explaining all of those details of how those things work - very interesting and all new to me - and thanks for the pic of your flying field "Velodrome".

LASTWOODSMAN
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« Reply #61 on: April 01, 2019, 10:07:20 PM »

My Science Olympiad kids have been really inspired this year, so we decided to plan to visit Round Valley in April (Cannot make the Nats, because SO nats same weekend in Ithaca NY).

Since we were already using Bill's construction techniques, it made sense to build Bill's Carbon LPP. We built 5, one by me and one by each WS kid. We had a very short shared test session a few weeks ago, and got basic trim on all the planes. We struggled with a few things, so had to have another build session to improve our prop hooks and a few rogue joints.

I am pleased to report that ALL of the kids built between 3.1 and 3.2g! Mine was the heaviest at 3.2g.

We have 3 test sessions planned before Round Valley. The kids are really looking forward to this!. They can also fly in F1M with these planes.

Two of my glider kids built Lit-L-Sweeps, as their SO gliders won't go to 100'.

Should be a fun time. Maybe I'll meet some of you there!

Chuck
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« Reply #62 on: April 02, 2019, 08:17:01 PM »

Chuck -

It's great to hear that you and your students will be flying at the Round Valley Dome. It will be an incredible experience for these young people.  I am going to the AMA/NFFS Nats being held from May 29 - June 2, 2019 at the same venue. Sorry I will miss you.

I am taking three LPPs, four A-6 models, two P-18s and one P-24.  My No-Cal and indoor Embryo models just would not be competitive in that venue so I won't be taking them, well maybe one Embryo.

Good for you that you mentored several of your Wright Stuff students in building LPPs.  It is a wonderful indoor class. It's very impressive that they built at or near the minimum weight of 3.1 grams. Your students are probably amazed by the slow turning prop of an LPP model.

I recently built my fourth LPP, based on my own design. I have been flying the same LPP for the past five years and it has performed very well, but my local competition is creeping up on me and therefore I wanted to implement some improvements.  

Josh and Hope Finn of J & H Aerospace have a new LPP kit out. It looks like a very competitive design. I wish I had seen this kit before my latest effort building a new LPP. It would have saved me a lot of time. I used a helical prop form from Mike Kirda to build several LPP props, including two flaring props and one that does not flare.  I think I will probably use the latter at the Round Valley Dome to hopefully get my new LPP near the 104 foot peak.  

I built one of the J & H Aerospace Intruder A-6 models and plan to fly it this Sunday in a local A-6 contest if I can get it trimmed. The J & H Aerospace kit included really nice contest grade balsa wood.  The pre-formed prop hook and rear hook were very nice, as was the polyimide tubing for the wing post sockets.

Let us know how you and your students do at the Round Valley Dome.  Good luck to you and your team at the SO Nationals in the Wright Stuff event.

PS - I coached a Division C team in ELG a few years back.  They flew Stan Buddenbohm's LIT'L SWEEP glider and won the gold medal.  The ceiling height was low (24 feet) but they still beat all the FFM flappers.  Nobody knows more about HLG and CLG than Stan.  Few can beat him, indoors or outdoors.  If you have not seen it, check out Stan's record setting indoor flight (F1N) at Tustin on YouTube. The flight time was one minute and fifty-two seconds. Here is the link:

https://www.youtube.com/watch?v=DWpwLfVqBso
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« Reply #63 on: April 02, 2019, 09:44:45 PM »

Cal:

I'll certainly post an update here after Round Valley.

Our team has done well. Last year at Nationals my mid schoolers missed gold by 0.07 seconds, at 2:29.50. Third place was less than 2 minutes. High school took gold in heli at Nationals. This year WS is going very well, good enough that we took the break to do AMA. Gliders is still a challenge. I think they are harder to trim than WS! We are hoping to use the Round Valley experience to test some higher launches, as Nationals will be a 40' ceiling.

This forum (the SO page) has been incredibly helpful in getting us from nothing to contenders.

We have stolen much of Bill's LPP design for our SO planes over the last 3 years, so transition to LPP was not hard. We have early Regionals and States, so we are not able to wait for kits. Much better to have our own design anyway!

I have been watching the videos Josh put out on his new kit. He gives Bill credit, as you can see a lot of influence in the design. A very complete kit! We had already bought all the carbon anticipating, so we built from plans. Just ordered more carbon today. Josh put me on to the poly tubing, and i found some on Ebay which I snagged for about half price.

Chuck
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« Reply #64 on: April 15, 2019, 12:16:40 PM »

My Science Olympiad kids went with me to Round Valley Dome this weekend for our first ever indoor contest. Four high school kids (plus me) built Bill Gowen's Carbon Penny and competed in LPP and F1M. Two mid schoolers built Stan's Lit-L-Sweep and competed in Std Catapult Glider.

All of the kids got to around 10 minutes in both LPP and F1M, not bad for our first attempt at a contest like this. They learned to get to the rafters at nearly 100'. We even picked up some thermals, as the dome has skylights.

Josiah Rose came out on top in F1M, taking a new National Record for Youth Sr at 10:15.3. It was very closely competed. He had put his plane away for the day when another team member put up a flight within 2 seconds, and she had one more flight left. So Josiah had to re-assemble the plane and defend his time at the end of the day. All four high schoolers had planes in the air at last call, trying to knock Josiah off the top. They all put in times right at 10 minutes in both LPP and F1M. Josiah had a 10:45 in LPP on Saturday, and I got an 11:45.

I am really proud of my kids, and I had a great time even without flying very much at all!

These kids want to do more testing and flying this week! I think they are hooked!

Chuck
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« Reply #65 on: April 15, 2019, 02:27:01 PM »

Well done Chuck to you and your team,

Can you post any pictures of the site and the models? I am particularly interested in the propeller as i struggled to get Bills original design working consistently. Any details of motors and torque levels alao gratefully received.


Cheers

Tim
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« Reply #66 on: April 15, 2019, 04:37:27 PM »

Tim:

We pretty much built per Bill's plan, except the prop. All 5 planes flew great on Friday, and all very similar, so the plan appears solid. We got a lot of compliments on how well they flew, and especially how resilient they were when pounding the rafters. Unfortunately, two planes were badly damaged when we got in a hurry cleaning up that night. After disassembly and placement in the box, a notebook was dropped into the box. We repaired in the hotel room, but those planes struggled the rest of the weekend (they did gradually get better. One simply could not get to the rafters anymore no matter what we tried. The other as soon as it touched, dove to the ground. It acted like the stability was gone, but we moved CG as much as a cm ahead of plan, and it did not improve. I think we lost stiffness in the stab, but we will try to fix it later. It flew great until a touch. All others flew perfectly with CG on plan.

The props were formed on Don Slusarczyk's 20" prop block from Thingyverse. The blade shape was copied from the Ikara flaring prop (9.5" diameter) blades, but scaled to 12" diameter. Each kid had two props, one with nothing behind the spar, the other with the extended blade behind the spar. @ used the trimmed prop, 3 used the full prop. The spar was a 1/16" square basswood, turned 45 degrees. Each side was sanded to 1/32" thick from about 3mm outside the shaft to the tip. The spar was 6" diameter. Several props were stiffened by adding 1/32" sheet to the sanded portion for the exposed portion, as they were over flaring. The basswood definitely differed plane to plane. The blades were generally set to 40 degrees at 4" radius, or about 21" pitch. However, some were closer to 35 degrees, and two (mine and Josiah's) were increased to 50 degrees. We adjusted pitch by heating the exposed part of the spar with a Monokote heat gun and twisting.

In LPP, we seemed to converge on about 2.3g of rubber, whereas we started testing with 2.5g. Some kids (and I) had issues with bunching at either end around 7 minutes in, even with sleeves. We spent some time improving our winding technique (keep it turning more at the end when coming in fast) and the bunching went away. It was fun to see the kids adapt techniques quickly as we learned. The rubber was 0.054g/in for the heavy props, and 0.049g/in for the lighter props.

For F1M, with 1.5g of rubber (lubed we were around 1.49g), the heavy props were happy at 0.052 to 0.051 g/in. The lightest prop dialed all the way down to 0.039 g/in! She did a lot to adjust here winding style, whereas I thought changing the pitch may have been better. It was late Sunday, so it was quicker to adjust the rubber. She actually got within 2 seconds of the heavy prop kid, sparking a last minute flurry of competition.

The main thing as times increase was to dial in the rubber density for each kid, so that they had only a few turns when they landed, and were not pounding the girders quite so much. Every kid increased time throughout the day. I spent the day processing rubber request slips and cutting rubber for them! You know they are studying the data when they have on 0.052 and want something "maybe just a little larger than 0.051 g/in".

I suspect these numbers may change at lower altitude. I also think we need to try a higher pitch prop block, but it was convenient to use Don's. He has camber built in. We had made a few prop blocks for SO, but they were 14" and 18" and required a camber form to be carved as well. We'll make something around 24 or 26" before we make more props.

Overall, except after the damage, the planes flew very similar, very stable, very consistent. This allowed the kids to focus on the prop/rubber optimization. I gotta hand it to Bill, the plane is easy to build (even 5 at a time in a group), and it is very tough!

Oh, in general the high pitch guys (including me) were launching at 0.52 oz-in or even a bit higher, and the low pitch at perhaps 0.4 to 0.45 oz-in. We were winding generally to 1.2 oz-in (I think the rubber could take more, but we were trying to extend life a bit so I did not have to cut for every flight). At high torque, the planes would climb at maybe a 60-degree angle for a lap or so. Someone commented they thought it looked like F1D. I think this was more pronounced in F1M, in which case some would actually power stall, but then recover and continue climbing. In LPP, with more mass, they just tractored on up. In general they were to the rafters in a minute or so, at least the aggressive winds were.

We did get stuck twice, once on conduit at the top, and once on speaker hanging cables. Both times we got help with a pair of party balloons and recovered the planes without damage.

When the sun hit the floor through the skylights there were some nice thermals to ride. ON Sunday the wind was howling outside, and it made little difference inside. I have heard of issues with wind, but they did not seem to have an issue this weekend. The planes on Sunday would circulate right in the middle, cruising at 95' for 5-7 minutes without moving out of the peak of the dome.

Chuck
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« Reply #67 on: April 15, 2019, 07:21:40 PM »

Well that was a great report Chuck and congratulations! Wish we had something similar here in Oz. Good on you Bill - your design has well and truly proven itself.

John
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« Reply #68 on: April 15, 2019, 07:39:02 PM »

Thanks John!

While Science Olympiad got kids to me that were interested, it is limited in that only two kids compete in the flying task, out of 15 on the team. With the success and fun of flying, the flying tasks have become extremely popular, and only a few get to fly. But, with AMA competition, any and all can join in. I am not going to spoon feed, but if the kids are willing and able to do the work, I will bend over backward to help them along. We built the planes less than a month ago, and that was a busy time!

I am finding kids, once exposed, love aviation. While SO may not be down under, perhaps you can start an after-school club at a local high school. If you can interest 2-3 kids, word will get out. This would also give you access to a gymnasium for testing and practice!

If we don't inspire the kids, nobody is going to replace us.

Chuck
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« Reply #69 on: April 15, 2019, 07:42:01 PM »

Chuck -

Thank you for the two reports on your success at the Round Valley Dome.  Congratulations to you and your students.  They will never forget the experience. Kudos to you for mentoring them.

I am going to the AMA Indoor Nats from May 29 - June 2 at the Round Valley Dome.  I will use some of your info to trim my LPPs and make up additional rubber motors as needed. I have very little experience flying LPPs in anything other than a CAT 1 site.

I generally fly my LPPs in a CAT 1 site with a 2.2 gram rubber motor. I was thinking of going to 2.6 gram rubber motors at the Round Valley Dome.  I believe that Bill Gowen and Kang Lee have had success with 2.6 gram motors for their LPPs. I am not in their class.  You saved me a lot of time.  I think I will go with my already made 2.2 gram rubber motors and strip more at the Round Valley Dome as needed.  My two best LPPs are very near the 3.1 gram minimum and I may have to ballast up a tiny bit if they lose weight in the very dry conditions in Eagar, Arizona.

I built three new props for Eager using a 23-inch prop block from Mike Kirda.  Two have all the prop blade area in front of the spars. One of those uses Bill Gowen's design and has four carbon fiber spars so that the blades will flare at high torque. I don't think I will be using it much at Eager as I need to get max climb.  The prop with some blade area behind the spars is supposed to be non-flaring so I can at least get one of my LPPs up to the rafters.

Let us know if your student gets his official AMA record.
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piecost
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« Reply #70 on: April 15, 2019, 08:10:02 PM »

Chuck,

Thanks for the comprehensive report! I will be taking a detailed look at your data in due course. I am most impressed with yor teams performance. It is interesting that you found the model easy to build, since I found it rather fiddly and had lots of problems with carvon to carbon tip joints and wing and tail tube stiffness. Rhe latter solved with Bills patient advice. I agree that it is a great model and am convinced it is more efficient than other LPPs Ive seen in the UK.

It is interesting that we are using similar motors with different propellers. Perhaps it is not too sensitive. I am supprised that you mention a steep climb and reaching the ceiling in about a minute. I wonder if your propellers are really flairing much at all. My experience suggests that switching to flairing props delayed the top of climb from approximarely  25% to more like 33% of total duration. I was allways flying under 60' ceiling or less. What do you think?

I would love to watch your high torque launches. I found that launching at higher torque causes the model to perform a fast flat circuit rather than climb, due to the stick bending. My experiment with a bass spar and a flairing blade with the spar at the trailing edge didn't seem to flair at all.

Cheers

Tim

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Olbill
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« Reply #71 on: April 15, 2019, 09:20:46 PM »

A few comments:

I've hung on the ceiling at Lakehurst (190') with a flaring prop.

The flat high speed circles at the beginning of a high torque launch will waste a lot of energy and affect the total climb available. On my models the cause of this is usually the right wing washing out. That's one of the main reasons I use washin on the right side.

Both props that I'm flying now have the area behind the spar removed.

I seem to fly the same general weight motors in all different ceiling heights. Motor weights are in the range of 2.4 to 2.8g or so. Test results on motors carry more weight in my decision making than exact weights or lengths.

Due to occasional problems with bunches of knots at the rear hook I've been flying 20" motors more than longer ones. The worst problem with knots at the rear hook is a CG shift messing up the cruise and let down. My sleeve arrangement now is about 3/8" of heat shrink tubing at the front and 3/4" to 1" of a larger diameter plastic straw at the rear. The picture attached shows older rear sleeve from HS tubing. The straw weighs about half as much as the HS tubing.

Since I never have trouble with knots at the prop hook I usually try to move all the knots forward as much as possible before launching.
Attached files Thumbnail(s):
Re: Another Gowen LPP
Re: Another Gowen LPP
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ceandra
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« Reply #72 on: April 15, 2019, 09:40:32 PM »

The bass spar, sanded to half thickness, flared pretty well. The blades were 1/32" C grain, about 6.5#, sanded to 0.025. We cut blades from two sides of the wood (3" wood), but match pairs from the same side. In retrospect, one side was more C grain than the other, and so there was a distinct difference in flaring stiffness.

We measure flare stiffness by placing the blade against a scale and rotating the prop shaft until the blade flexes to flat. In these cases it was anywhere from 6.5 to about 9 g, the basswood and the blades varied. But each pair was pretty consistent. The props that we stiffened flexed at 10-12 grams. I am thinking this is not a good measure, because some spars may "wind up", especially the Gowen style carbon spars. I need to make a fixture that will measure the flex stiffness for 10 degrees of flare, not 45.

I was more in favor of a slow graceful climb, but the kids loved the rocket climb. They pointed the plane straight ahead, but if immediately rotated to a steep climb, and seemed happy. I am hoping a parent has a video of a launch, then I can post it somewhere and post a link here. I was too busy for photos and videos! I think at 60', we would not have been above 0.5 torque and the climbs may have been more slow.

It was interesting to me that we did not see a huge difference in performance between the full prop and the ones without the trailing edge. Some of us switched because the full prop was not getting us up, and the thinner prop did, but this is probably more a reflection in the various stiffnesses.

We went in planning on 2.5g as a baseline. I had some shorter rubber in the box, and the kids tried it out and it worked better in terms of time. Remember the air is thin, so the weight penalty may be greater than sea level. Another interesting point is that by the end of Sunday (We did F1M exclusively Sunday) they had progressed from 7.5 minutes to over 10 minutes, and had got very close to their LPP scores. I have to wonder if a few more days they could have improved greatly on LPP base don what they learned Sunday. Another flyer (I forget name) slipped in a 13:45 flight, his only flight. So while we were very pleased with our first ever, there is room for more!

On the rubber width, note that the lower pitch props went all the way down to 0.039g/in. But, most were grouped around 0.051g/in (for 1.5g in F1M).

Bill responded while I was typing. We definitely saw better performance with right wing wash in, as suggested by Bill. A few mm is all. On SO planes, the wing has less chord, so the twist form motor stick has less impact (and we launch often with less torque), so we generally run those flat.

I think the main reason we went down to 2.3g is the bunching. However, as the weekend progressed, teh kids got better at controlling the bunching be careful end game on winding. Bunching was eliminated. Since we were running fairly thin rubber, the lengths were getting pretty long, and we tried to cap it at 56cm (22"). But Bill is right, keeping under 20" seemed better. I think if you could pitch up a bit more than we did, go with rubber approaching 0.060 g/in or more, you may be able to carry more mass without bunching.

My 11:45 was with my prop with no TE surface area.

Chuck
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ceandra
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« Reply #73 on: April 15, 2019, 09:44:54 PM »

Tim:

We have used Bill's construction techniques for a few years in SO, so it was not hard. When gluing tip plates on, we wrap with a half thread of polyester embroidery thread. That makes it bullet proof. we wrap 2 turns, put a dot of thin CA, all before cutting the bottoms off.

Chuck
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« Reply #74 on: April 15, 2019, 10:12:00 PM »

I actually changed the tip plate connection a few years ago. I think Tim was building the earlier version. Now on the LPP and the SO models I just extend the spars a little past the end rib and set the tip plate between the spars.
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