Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
March 28, 2020, 12:55:54 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: 1 2 [3] 4 5 6 7 8 9   Go Down
Print
Author Topic: VP Hubs - for the techies among us  (Read 20043 times)
0 Members and 1 Guest are viewing this topic.
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #50 on: October 11, 2012, 02:35:54 AM »

Oukey dokey, I'll have to try that.

There is one thing where the lenght of the wire inside the tube may matter: it will also be the hinge points against which the blade rotates (opening end of the tube and the very inwards tip of the wire. The shorter the distance between the two, the stronger the moments, and the more the hinges will "bind". Or, the less the friction, the smoother the action of the VP...
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #51 on: August 23, 2013, 01:09:03 AM »

Inspired by the carbon hubs of Kang, Jake and Tom, I also built a new one. I am still a bit worried about the friction between two putruded carbon parts, so I thought of a way to replace one of the bearing surfaces with plastic. My older hub ( http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=2318.msg86479#msg86479 ) used piano wires inserted into grooves slotted onto the carbon tube, but these were wuite tedious to work. Yet I stuck to that solution, making the center part of the hub wider and hinging the blades onto a wider center. Unlike Kangs design, the center tube is just a muffle to insert carbon rods onto, and the hinges are the short pieces of plastic tube wrapped onto the blade roots. In addition, this construction omits the tissue tubes to attach the blades onto; the hinge tubes are solid, but if base pitch of the blade needs to be adjusted, the piano wire controlling the angle can be re-glued. For F1D hub I might make that of carbon rod and install permanently; if prop angle needs to be adjusted it can be dissolved from the stub spar and reglued.

I have not yet added lock rings to keep the blades in place, but they can be added if needed. The cross-arm on the shaft has holes in the ends, not slots, so those should also keep the blades in place. We'll see.

This prop is for F1M, it weight altogether 680mg. 100mg reduction from my previous prop. The blades are a bit lighter, but so is also the hub. I do not have a comparison weight to old hub, as the stub spars are nowe a part of the hub itself.

Ahh, for the scale, the adjustment screws are M2. I save the smaller ones for F1D... :-)
Attached files Thumbnail(s):
Re: VP Hubs - for the techies among us
Re: VP Hubs - for the techies among us
Re: VP Hubs - for the techies among us
Re: VP Hubs - for the techies among us
Re: VP Hubs - for the techies among us
Logged
THB
Gold Member
*****

Kudos: 17
Offline Offline

Australia Australia

Posts: 629


WWW

Ignore
« Reply #52 on: August 23, 2013, 05:08:41 AM »

Tidy work Tapio - I'm going to have a go at these soon. Magnifiers help - or are your eyes still good enough?
cheers
Tim
Logged

Tim
"Life is what happens while you're busy making other planes."
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #53 on: August 23, 2013, 09:47:23 AM »

Thx.

They are good enough, I have build-in reading glasses: ~+3 diopters, so I can see sharply at close distances without my spectacles. But need those to see further away :-)

Logged
Maxout
Titanium Member
*******

Kudos: 97
Offline Offline

United States United States

Posts: 2,729


WWW

Ignore
« Reply #54 on: August 23, 2013, 01:25:32 PM »

Tapio,

 That looks nice and less difficult to build/maintain than your previous designs. Let us know how it works for you.
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #55 on: August 23, 2013, 03:08:15 PM »

Wilco. First session tomorrow! :-)
Logged
THB
Gold Member
*****

Kudos: 17
Offline Offline

Australia Australia

Posts: 629


WWW

Ignore
« Reply #56 on: August 27, 2013, 07:44:37 AM »

First session tomorrow! :-)

Good luck Tapio. Your eyesight is better than mine I think. I found these in a local Red Cross charity shop. No really!
If glasses make you look smart (see Marilyn Monroe quotes from How to Marry a Millionaire) then these would make me irresistable, I reckon. Just ask my ex-wife...   Cool
Attached files Thumbnail(s):
Re: VP Hubs - for the techies among us
Re: VP Hubs - for the techies among us
Logged

Tim
"Life is what happens while you're busy making other planes."
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #57 on: August 28, 2013, 01:32:14 AM »

No luck past Saturday; for the summer time the electric keys to the gym had been deactivated, and the guy responsible for them had forgotten to activate them... But now they should work, so another attempt next Saturday....
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #58 on: August 31, 2013, 03:54:51 PM »

Yes, it works. With a rather soft spring, and the IIFI contest on the way, I thought to try to set the prop up for low ceiling flying. My local gym is 7 meters (20 feet) high; I started with a quarter motor to get adjustments about right, then went to full motors. After a few trials and start-collisions to the wall (the gym is only 15 meters wide, so making the first turn within the gym is tought) managed to get one decent flight under my belt. Climbed to the ceiling, came half-way down, the climbed again to scrub the ceiling for two minutes. Overall time in the clock 13'44", but that lacks a few seconds, as I only started the clock after launch, and had to wiggle with the stopwatch on my mobile. Ah well, inofficial time anyway.

But yes, the adjustments were repeatable and predictable, and on the best flight the bump the ceiling (at top pitch) did not change flight pattern compared to the previous that did not bump. So it seems that the hinges are not binding.
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #59 on: September 01, 2013, 12:47:03 PM »

There was a question of my prop dimensions in FB. So I measured. Diameter 440mm. High pitch 1100 mm (at 145mm radius), low pitch 550mm. Changeover from 21g*cm to 17. Motor was 360mm long, took 1800 turns at 40 g*cm max torque, and model landed with 600 turns left.
Logged
Maxout
Titanium Member
*******

Kudos: 97
Offline Offline

United States United States

Posts: 2,729


WWW

Ignore
« Reply #60 on: September 01, 2013, 01:07:10 PM »

Tapio, that's a really good flight time. Landing with that many turns indicates you could decrease the low pitch some more (55 cm seems a little high to me anyway) provided that extra ceiling bumping doesn't carry the risk of a snag.
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #61 on: September 01, 2013, 02:54:06 PM »

Yup, maybe open the spring up just a tiiny bit to let the model come down lower before the second climb starts, to have more room for the climb. But then again, the practice gym is really small, and for the fine-tuning I should fly in a place where the initial turn does not go from one wall to another...
Logged
Maxout
Titanium Member
*******

Kudos: 97
Offline Offline

United States United States

Posts: 2,729


WWW

Ignore
« Reply #62 on: September 01, 2013, 04:01:53 PM »

Tapio,

 Soft springs really do put you in a position of having to resist the urge to do something unless you absolutely have to. With a little work, though, you can consistently get a model to descend within 5 ft of the floor before leveling out and climbing away. Either way, running low rpms on the second climb is hurting you if you're landing with so many turns...there's something to be said for just letting the model bounce away. If IIFI is in the usual place, ceiling bumping shouldn't be a problem, and using up those remaining turns would give you 14 minutes+. I only know of two people who have done that in Cat I.
Logged
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,565

Topic starter


Ignore
« Reply #63 on: September 01, 2013, 07:22:04 PM »

Tapio,

 Soft springs really do put you in a position of having to resist the urge to do something unless you absolutely have to. With a little work, though, you can consistently get a model to descend within 5 ft of the floor before leveling out and climbing away. Either way, running low rpms on the second climb is hurting you if you're landing with so many turns...there's something to be said for just letting the model bounce away. If IIFI is in the usual place, ceiling bumping shouldn't be a problem, and using up those remaining turns would give you 14 minutes+. I only know of two people who have done that in Cat I.

And one of them is way behind the other one!
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #64 on: September 02, 2013, 12:47:53 AM »

If IIFI is in the usual place, ceiling bumping shouldn't be a problem, and using up those remaining turns would give you 14 minutes+.

Or, bend me a little harder spring, so that the transition would start at the same torque, but end at lower, therefore making the second climb later/slower....
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #65 on: September 16, 2013, 05:55:53 AM »

Another session two days ago. This time only managed 12'12" and 13'24". I had fixed the prop after previous session (asymmetry in the yoke made the pitch change uneven and caused some shakes. Replaced the yoke & shaft), now had to start adjusting anew. Also weather inside the hall was worse now, with model doing some "waterfalls" (wing and tail stall resulting in vertical loss of altitude) and therefore losing some precious height. I took a videoclip of the 12 minutes flight so that I can calculate prop RPM later (too hard to do in real time, but much easier from vid), which shows the turbulence in the hall, as well as the tight space during the first round (had to steer to avoid collision to sidewall. The video also shows nicely the flight pattern: quick climb to ceiling in less than 3 minutes, then descent to half height until 7; another climb to ceiling and then final descent. If anyone is interested to see that, I uploaded it to youtube (but will probably replace the clip with a better one if I improve my time :-) ... http://www.youtube.com/watch?v=zsGacO8u7JI&feature=youtu.be

Looks like I should avoid standing on the models flight path, the initial flight shows a stall when the model flies into turbulence generated by my body heat... Also I wonder if I should try to reduce the model decalage and also reduce downthrust, now the model seems more stable when climbing out, and makes the more severe "waterfalls" during the descent part of the flight.
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #66 on: September 16, 2013, 08:57:54 AM »

Um, forgot to add: 370mm loop of Tan II, 2000 turns wound to 40g*cm, no backoff, 880 turns left. The motor would take up to 50 g*cm if risking breakage, but 40 was a safe torque to fly multiple flights from the same motor. The residual turns are still a bit high, so maybe reducing bottom pitch and opening the spring to let model sink further before second climb would result in a longer flight. But as you see on the video, this small gym is quite turbulent and my model "waterfalls" if it hits the eddies, so tweaking out more is risky, I might easily run out of altitude after such a "waterfall".

 
Logged
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,565

Topic starter


Ignore
« Reply #67 on: September 16, 2013, 11:05:48 AM »

I flew F1M at St. Lukes this past Saturday. I had numerous issues all day with various things breaking. One flight looked like a sure record breaker when it was at almost 14 minutes and cruising about 6' up. then it landed at 14:01 due to a loop of rubber wrapping around the prop shaft. At the end of the day I finally got the model to turn tight enough to stay in the high part of the site. It was about 30 feet up at around 11 minutes and looked like it would do 15 but then it landed at 14:09. I don't know what happened to that one.

The model I'm flying has all kinds of problems. It's mostly a bunch of old parts. The tip ribs have too much camber, the stab has been broken many times, the tail boom was adapted from my one and only F1D effort and was too weak for the F1M and the prop spars have been broken and fixed several times. Hopefully at some point this year I can get a whole new model built before I have to deal with Larry Coslick again! (Larry won F1M at USIC this year - my first loss since 2006)

I'm still using one climb. This may not be the best plan but it makes sense to me that as long as the model eventually gets to the high point of the site then it will use less energy than with two climbs. I certainly may be wrong about this.

My biggest frustration of the day was that I forgot to take my new camera that I bought especially for taking shots of flying models. Here's a camera phone shot of the F1M on its last flight. Also a short video clip near the end of the flight:

http://youtu.be/2yY_9GFoblc

Rubber data - 12.5" loop of 5/99, 1580 turns in, max torque .98 in-oz, 370 turns remaining, 86 average RPM, 14:09 flight time.
Attached files Thumbnail(s):
Re: VP Hubs - for the techies among us
Logged
Maxout
Titanium Member
*******

Kudos: 97
Offline Offline

United States United States

Posts: 2,729


WWW

Ignore
« Reply #68 on: September 16, 2013, 12:24:16 PM »

Tapio,

 Several items...

1. Very nice flying. Your prop is well-tuned.
2. The "waterfall" is a typical stall. Models in this speed range don't pitch down a lot in a stall. You need to move the CG forward and/or reduce stab incidence. You mentioned downthrust...downthrust is usually bad on these models because it requires you to use more incidence than needed on the first climb. This results in prop stall in the first descent, requiring the prop to come in sooner than necessary. The air didn't look terribly bad in that video, so I think you're just too close to the edge. It will only take a small amount of tweaking to get the model flying better in this regard, especially if you use a lower low pitch setting.
3. I'd reduce your high pitch slightly. Let it go all the way to the ceiling and bounce just a little for say 30 seconds.
4. If you are landing with 800 turns, you should be going a lot lower on low pitch. Your prop RPM at the end is much, much lower than Bill's, and I think he's using a bigger prop than you. Don't be afraid to let the model bounce around in the ceiling...Bill spends a very long time on the ceiling, more than even I am comfortable with, but he has to because of that stiff spring as he mentioned.

Do all that and you should have enough energy available to do 15 minutes or so in there.
Logged
ykleetx
Gold Member
*****

Kudos: 14
Offline Offline

United States United States

Posts: 652




Ignore
« Reply #69 on: September 16, 2013, 02:22:58 PM »

Tapio,

1. Use thicker rubber and increase low pitch instead of lowering low pitch.  Your P/D for low pitch is already too low, in my opinion. 
1b. You may also want to use a prop with slightly smaller diameter.  Aki uses 420 mm.

2. slightly less decalage.  Got to get rid of those vertical drops.

-Kang
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #70 on: September 16, 2013, 03:31:00 PM »

Thanks, guys, for the comments. I calculated my prop RPM, starts at 80 and tapers off to 60, then the pitch change starts and the prop accelerates to 90. I think I'll try a fatter motor first, as the bottom RPM seems quite high compared to the initial. Also the discussion of downthrust, what I intended to say that I wondered if the fact that the model only stalls during descending flight suggest that I have too much decalage and have compensated that with downthrust, and I interpret your comments that this is the way. There is no downthrust of the thrustline to the fuselage, but I'll reduce the effective downthrust by reducing the rigging angle of the wing, possibly so much to need to reduce the angle of the tailplane too. About the air in the site, it is mostly OK, but I suspect that AC in on in the dressing rooms (downstairs, but the staircase is open), as there are quite localized places where the model tends to stall. Ah well, this is a practice site anyway, too small for efficient flying. But we get to fly there every fortnight :-)

Ps. Maybe moderator could move this F1M trimming discussion to another (new or existing) thread, as this is really not related to VP's.... 
Attached files Thumbnail(s):
Re: VP Hubs - for the techies among us
Logged
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,565

Topic starter


Ignore
« Reply #71 on: September 16, 2013, 04:48:55 PM »

My RPM is about 89 in the video and the video was shot about a minute from landing.

I'd like to make a digital VP calibration tool but haven't figured out how to do it yet.
Logged
ykleetx
Gold Member
*****

Kudos: 14
Offline Offline

United States United States

Posts: 652




Ignore
« Reply #72 on: September 16, 2013, 06:03:48 PM »

Here is Aki's Cat I record F1M in the last 2 minutes of flight:

http://www.youtube.com/watch?v=2BTvudH2oVI&list=PL11C0EC125B4CE40C&index=44
Logged
Tapio Linkosalo
Platinum Member
******

Kudos: 29
Online Online

Finland Finland

Posts: 1,207



Ignore
« Reply #73 on: September 17, 2013, 12:18:05 AM »

I'd like to make a digital VP calibration tool but haven't figured out how to do it yet.

Bill, what do you mean with "digital VP calibration tool"?

Aki's prop seems to be turning around 90 rpm at the end (from 86 to almost 100 when the model pitched down).





 
Logged
Olbill
Titanium Member
*******

Kudos: 69
Offline Offline

United States United States

Posts: 2,565

Topic starter


Ignore
« Reply #74 on: September 17, 2013, 01:50:53 AM »

Several years ago I made a tool for measuring torque vs. spar rotation angle. It used most of a twisted wire type torque meter. I'd like to have something similar that uses a digital sensor like in my digital torque meters.
Logged
Pages: 1 2 [3] 4 5 6 7 8 9   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!