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Author Topic: Another Gowen LPP  (Read 4803 times)
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calgoddard
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« Reply #25 on: December 24, 2015, 11:38:12 AM »

Got it Bill.  Sorry for the oversight. I assume that the same trim would be advantageous for a Wright Stuff model.  

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Olbill
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« Reply #26 on: December 24, 2015, 11:59:03 AM »

I can't guarantee that my methods are advantageous for anything. But they are what I use.
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Hepcat
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« Reply #27 on: December 24, 2015, 06:44:08 PM »

response to #17 and #19.

My turns calculator which usually gives reliable figures for Super Sport gives 2750 turns for the 22.8" 3.03g motor. That is Max, no little bits assumed for safety!

John
 
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piecost
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« Reply #28 on: December 26, 2015, 11:15:26 AM »

Thanks for the replies Bill & others & thanks to Bill for going to the effort of posting pictures.

In reponse to the questions; the Venue is a CAT III site. The first flight (in my last post) reached about 70' (about 5' above the level of the crane beams) and the second only 40'. I am perhaps guilty of swapping between different motors too readily rather than getting the most from each of them. I also wonder if I am tending to use motors on the heavy side i.e. over 2.6g.

I have been using Jan 2014 Tan Super-Sport and have tested the torque versus turns and maximum turns. I have not tested 5/99 so cannot really compare but I think that my rubber is getting a similar torque unwinding curve but compressed into 17% less turns. I also have max turns of 9% less than Hepcat posted. I am using the best S-S that I could buy in 2013/2014. I test at room temperature whislt flying at around 12.5 deg C; which may be reducing the turns to reach a target torque level further. I really must test at different temperatures so see the effect. I have some data on Tan II with temperature but wonder if S-S has the same sensitivity.

My aim has been to get the model to reach the beams with a launch torque/turns at the knee of the unwinding curve and not employ the rapid kick-up of torque at high turns. Perhaps this strategy is not suitable for a Cat III site? I will certainly wind my motors harder in the January session.

I did think the decalage rather high and suggestive of a forward CG. I don't think that I have excessive downthrust; the models glide OK. I don't think that the wing is over-cambered i.e. requiring more decalage, since the ribs are sandwhich construction and are very stiff. I will move the wings aft if nessesary.

I mentioned that I have made propellers with the same chord distribution but with the spars set at 75% chord rather than at 100% on the blade trailing edge. I understand that flairing props are using such high chords (over 2 inches max) to achieve the flair. So, is there any disadvantage is keeping the spar at the trailing edge and trimming some chord of the leading edge to reduce the flair? These flairing props must be working at a very low local blade lift coefficient which can't be good for efficiency. Is a 5% camber suitable? If the local lift coefficient is low then would less camber be warrented? Am I missing something about the workings of these flairing props?

Is the helical distribution optimal for flairing props or would some washout at the tips likely help?






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ykleetx
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« Reply #29 on: December 26, 2015, 09:49:00 PM »

Piecost,

Your flight RPM is very low at 136, and your launch torque is very low for a 70' climb.

You indicated that your flights were made at about 12 C. Were these flights made recently on December 14 at Brabazon? I'm asking just to understand the conditions at the hangar.

I think you can get many more turns out of your motor without winding it too hard. And be sure the motor is well broken in so that you can get more turns.

-Kang

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piecost
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« Reply #30 on: December 27, 2015, 06:13:07 AM »

Kang, the flying
session was on december 9.

The repeated advice is to push the motors harder, so i will give that a go.
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Hepcat
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« Reply #31 on: December 27, 2015, 08:11:08 AM »

Response to # 29, quote<And be sure the motor is well broken in so that you can get more turns.>.

Kang,  Can you clarify that quote a little?  If a motor is 'used', 'pre-stretched', 'broken in' it will be longer than when it is new and will take more turns, I have no argument with that.  However I have the feeling that a new motor possibly has more energy and I would assert (with no proof) that after 80 years of winding rubber motors that if I keep winding the same motor time after time there will be a loss of power.

I think I have answered myself whilst I have been writing this.  In Indoor flying the turns are more useful than the torque as proved by 'backing off' turns.

John.
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Olbill
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« Reply #32 on: December 27, 2015, 12:34:04 PM »

I don't have any data for a 70' climb. At West Baden my launch torque varied from just under to just over .4 in-oz with my last record attempt at .48. This is for a 90' site. At Kent where my usable height is under 50' the launch torques were around .3 in-oz. Kent is a place where repeatedly bumping the ceiling is almost sure disaster.

The other thing to consider is that in my experience the torque for TSS rubber drops off more quickly than for high grade 5/99 Tan2. This would indicate the need for using a higher launch torque than you would use with 5/99.

Whatever rubber you use, if the model isn't climbing high enough, and if you don't see any signs of misbehaving, then it needs more grunt. The limit for most models is the point where the outside wing washes out and the model either races around in circles without climbing or it actually spins in. That limit for my LPP's is usually around .9 in-oz but it varies depending on the stiffness of the particular model.

You mentioned something about downthrust. I have something similar to what people refer to as downthrust because of the incidence setup I use. Normally there is a few degrees of incidence in the wing and the stab is close to flat (all relative to the motorstick). If I have a problem with the right wing washing out at launch then I might try changing the incidence of both surfaces to give a little more nose up attitude. Sometimes pointing the nose up a little will help get thru the high power at the beginning of the flight. Actually the only place I've ever done this is at Lakehurst (app. 180' usable).

I never use down thrust (or side thrust) in the bearing. Side thrust is accomplished by aiming the motorstick to the left.

Are you using sleeves? Is the model coming down with knots gathering around the rear hook? A clump of knots at the rear hook will destroy the cruise and letdown. A clump of knots at the front can end the flight. If you're using my front hook up system then you shouldn't get clumps of knots at the front. If you're using sleeves and you're still getting clumps of knots then you need to shorten the motors a little. The limit for me seems to be around 22". Your 17.5" motor was certainly too short. The longer one should work if it had sleeves.
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piecost
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« Reply #33 on: December 27, 2015, 01:09:37 PM »

Thanks Bill. This advice is invaluable. I will do some studying of your torque levels. I will also investigate the models cg to reduce the decalage and and incorporate more downthrust. I use a reverse s-hook on the propeller but don't use sleeves. I have had problems with bunching on longer motors and put this down to lack of finess in winding. Can you elaborate on the use of sleeves please?
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mkirda
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« Reply #34 on: December 27, 2015, 03:19:11 PM »

Thanks Bill. This advice is invaluable. I will do some studying of your torque levels. I will also investigate the models cg to reduce the decalage and and incorporate more downthrust. I use a reverse s-hook on the propeller but don't use sleeves. I have had problems with bunching on longer motors and put this down to lack of finess in winding. Can you elaborate on the use of sleeves please?

Experiment with soda straws. You'll find a size that fits onto the front hook and lets the motor mostly unwind. When you find a good source, grab a few extra.

Regards.
Mike Kirda
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piecost
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« Reply #35 on: December 27, 2015, 04:13:29 PM »

Thanks for the tip mike, won't the sharp edges of the straws xut the rubber? I was wondering if heatshrink is suitable.
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Olbill
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« Reply #36 on: December 27, 2015, 05:00:43 PM »

After an hour looking for the pictures that I was SURE I had posted somewhere I finally gave up and took new ones. Here are the specs for the o-rings, hook and sleeves:

Hook - .018" wire. Outside width of the hook is .160". The turned up end is necessary to keep the sleeve from sliding forward.

Sleeve - app. 1/8" inside dimension black heat shrink tubing. I think I got this from US Plastics.

O-ring - sliced from .155" outside dimension black semi-rigid nylon pressure tubing, also from US Plastics. I use the same size for F1M.

The o-rings, hook and sleeves can be different from this as long as you can slide the sleeve over the o-ring and hook.

For the rear the sleeve is just pushed back against the rear hook. It's held there by the motor knot.

For A6 everything is the same except smaller. For A6 I found plastic straws that were perfect for sleeves. The A6 o-rings are cut from the next size smaller nylon tubing.

For both A6 and LPP the limit on motor length is knotting at the rear hook. I almost never have problems at the prop hook.

For F1M I don't use sleeves. The front hook for F1M is a reverse S.

Now anyone can do it!
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Re: Another Gowen LPP
Re: Another Gowen LPP
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piecost
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« Reply #37 on: December 27, 2015, 05:16:41 PM »

Thanks for your continuing efforts bill, it is really appreciated. But, can you tell me if the prop hook is a reverse s or a plain hook?
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Olbill
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« Reply #38 on: December 27, 2015, 05:54:00 PM »

It's a plain oval hook. You can't do this kind of hookup with an S hook.
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mkirda
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« Reply #39 on: December 27, 2015, 07:57:01 PM »

Thanks for the tip mike, won't the sharp edges of the straws xut the rubber? I was wondering if heatshrink is suitable.

No more so than heat shrink tubing, which would also be suitable.
Bill uses straws on A6 - He gave me a couple for use.

Regards.
Mike Kirda
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piecost
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« Reply #40 on: October 05, 2016, 07:07:43 PM »

I thought it a good time to make another post since I am delighted to report that I won the 2016 UK indoor duration LPP class using the Gowen LPP deisgn. Thanks to Bill and others for providing the plan and much advice.

The best two of my four competition flights were 10m08s and 9m47s combined to give a combined score of 19m54s, 7% ahead of the next 3 competators (they were all within 6 seconds of each other). My strategy was to start making competition flights once I had exceeded 9m30s. I was a little disapointed that I didn't manage to push the time up to 11m,  since I had achieved that in a couple of previous sessions. My plans didn't work out when I hung a model up on my second competition flight. Though frustrating, This was not a big problem as I had allready been using two models, to experiement with different motor lengths prior to the competition flights. So I used the remaining model. Once I had a lead I then concentrated on other classes instead of trying to reach my target duration.

Data for the two best competition flights

Prop: 22" pitch x 1.5" chord minimum induced loss planform & twist
Temperature 18.5ºC
Rubber: Tan II May 97, 2.71g/m x 19.25" Loop 2.66g
Wind to 1820 turns & 0.92 oz.in
Back of 130 turns to 0.37 oz.in
Touched light at 2m58s and recovered. Dived in from 20' when out of turns
Landing turns 0
10m07s

Prop: 22" pitch x 1.5" chord minimum induced loss planform & twist
Temperature 18.5ºC
Rubber: Tan II May 97, 2.71g/m x 19.25" Loop 2.66g
Wind to 2050 turns & 0.92 oz.in
Back of 160 turns to 0.33 oz.in
max height 45', no touch
Landing turns 160, torque 0.14 oz.in
9m47s

I used Bill's published wind/launch torque levels as a guide for my own motors (allowing for different mass per length of my motors). I have also been experimenting with my own propeller designs, modifying them to utalise a similar launch torque that Bill uses. I previously found that I could not use the same prop as shown on Bill's plan (Lakehurst planform, with helical twist and 22" to 24" pitch). The propeller required too much launch torque. Even moving the spar to 75% or chord at 75% radius still required a higher launch torque than Bill employed; well into the non-linear torque region. Since, I reasoned, that the  large chord was intended to maximise the flair; moving the spar forward negated this effect and thus the need for such a large chord. So, I next designed a 1.5" chord propeller aiming to keep the distance between the assumed centre of pressure of the propeller and the spar the same. The new propeller had the spar moved to near the trailing edge again and employed a minimum induced loss planform and twist distribution with 22" of pitch (at 75% radius). I achieved similar times with the new propeller as with the 22" Lakehurst prop with a 75% spar position. So, I switched to using the my new propeller, if only for the satisfaction of using an own design. This new propeller required a launch torque much lower than before and approximatly the same as that which Bill employed.
 
I had built 3 new models for the competition and was very pleased that they performed reliably with the minimum of trimming. I was fed-up with the diffculty of attaching wing and tail posts accuratly so employed a jig to assemble the stick, prop hanger, boom and posts. A wing and tail setting jig ensured that the models required the a minimum of trimming.

To achieve the competition win; I have spent 2 years worth of monthly practice (in the competition venue), have built 7 models, 13 propellers and lodged 3 of them in the ceiling. It was worth it!
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ykleetx
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« Reply #41 on: October 05, 2016, 11:46:53 PM »

Well done, piecost.
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OZPAF
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« Reply #42 on: October 06, 2016, 03:25:54 AM »

Congratulations again Piecost. Winning in 2 classes at your nationals. You were a very busy man! Thanks for your detailed report - your results show the benefit of a methodical careful approach and lots of practice.
I think you should publish a paper on your approach and findings for your FF symposium digest.

John
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Pete Fardell
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« Reply #43 on: October 06, 2016, 07:27:14 AM »

Brilliant! Well done! I really enjoyed reading this report, and also the one on your no-cal win.
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Olbill
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« Reply #44 on: October 06, 2016, 08:52:26 AM »

Now that you're in the winner's circle I think it's time you started giving me lessons on how to do it. Some of the people I've mentored have started beating up on me every time I fly!
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frash
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« Reply #45 on: October 10, 2016, 10:04:11 PM »

piecost, OlBill, and All,

Obviously this design and these flyers win and set records. Congratulations. Attention to construction details, improved methods, and flying strategy is impressive from you folks.

I noticed that piecost used a minimum induced loss platform and twist for the prop blades. This is sometimes called a Larrabee prop since he developed the minimum induced loss methods for human powered flight several years ago. I attempted to code his method into "Larrabee Lazarus Propeller Design" in the HPA Plans Section>Airfoils and Propellers. The source code in Lazarus Pascal is also posted for anyone to edit, modify, improve, repost, or whatever. Lazarus Pascal is a free download from Source Forge, but is unneeded just to try the prop design program.

If someone will enter their inputs from one of these known good designs, the Cl, Cd, and Alpha of the prop blades maybe can be corrected and improved. Form 3 already has provision to move the spar forward or backward on the blade.

Thanks to any and all for suggestions for improvements.

Fred Rash
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cvasecuk
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« Reply #46 on: October 11, 2016, 08:49:15 AM »

Fred, form 3 will not accept a change of "flare". I can put in a number greater than zero but I can not input a decimal!!!
Ron
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frash
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« Reply #47 on: October 11, 2016, 02:28:45 PM »

Thanks, Ron. You are correct that there is a problem. My local copy also has this problem if I ever delete the decimal. I must try a fresh download since there is no guarantee that the local copy that I tried and the posted one are identical.

My local copy that I tried, if I kept and never deleted the decimal, showed for flare = 1.0, all the blade forward of the spar as expected like you and Bill Gowen probably are using. Entering 0.5 gave the blade symmetrical on the spar, and 0.0 gave all the prop blade behind the spar. This value is  working but never desirable in practice. My default value was 0.72 for flare in earlier versions.

I'll download fresh and try to clean this up. You are very helpful. Finding errors can be hard. Thank you.

Fred Rash
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frash
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« Reply #48 on: October 11, 2016, 09:31:46 PM »

Ron,

The "fresh download" from HPA also showed and confirmed the problem that you found. If you can keep your decimal point in the Flare Box in the third screen and not delete it, I think that you can continue. I think that I have fixed the problem, but 1-2 days may be required to post the newer version to the HPA Plans section.

Thanks for finding this. There may be more...

Fred Rash
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cvasecuk
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« Reply #49 on: October 12, 2016, 04:58:02 AM »

Thanks, Fred. I have tried it, not deleting the decimal and it works OK.
Ron
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