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Author Topic: VP Hubs - for the techies among us  (Read 19689 times)
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ljr8378
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« Reply #25 on: October 04, 2012, 08:13:55 PM »

Anyone know haw they get the kevlar wrapped so nicely?
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mkirda
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« Reply #26 on: October 04, 2012, 11:28:00 PM »

Anyone know haw they get the kevlar wrapped so nicely?

A needle helps. I pull kevlar from tow, add a bit of thinned ambroid to it to make a thread, then glue, hold, knot. Mostly it is practice and just fiddling with it until you get it good enough. There must be a better way, I just haven't figured it out yet...

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Mike Kirda
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green-man
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One of my F1D VP propeller hubs - weight 104 mg.



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« Reply #27 on: October 05, 2012, 02:53:56 AM »

It really helps to have a weight on the free end of the kevlar - several grams of modelling clay or similar will do the trick. That way, the thread is always under tension and that helps to make nice tight hinges. I suspect that Ivan may have some sort of mechanical contraption to aid the process - he makes and sells a lot of hubs now.

Nick.
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Tapio Linkosalo
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« Reply #28 on: October 05, 2012, 03:02:07 AM »

Indeed. I have not actually ever managed to make any good kevlar hinges, but my efforts have improved when I have:

- made a jig that holds the hub body and the tissue tubes firmly in place, and frees my both hands to work the kevlar, and
- have pulled the kevlar quite tight. Much tighter than I initially thought. If the jig that holds the tissue tube is steel (same mandrel that it was turned on), it will support the tube, and if the hub body is balsa, the kevlar needs to crush it a bit (or at least almost) to be tight enough.

But you can take that with a grain of salt, I have never been happy with my kevlar hinges... :-(
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jakepF1D
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« Reply #29 on: October 05, 2012, 07:09:46 PM »

he makes and sells a lot of hubs now.

Are purchased VP hubs legal in FAI competitions?  They really aren't hard to make so I'm not sure I understand why someone would buy one anyways.
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Tapio Linkosalo
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« Reply #30 on: October 06, 2012, 01:00:16 AM »

They are. I have always wondered why buying the single most important part of the model does not violate the BOM rule...
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green-man
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One of my F1D VP propeller hubs - weight 104 mg.



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« Reply #31 on: October 06, 2012, 03:16:38 AM »

Not all flyers find VP hubs easy to make and some Juniors would find it impossible. I think it's relatively straightforward for most flyers to complete a hub that works but much more difficult to get it down to the necessary weight. A hub that weighs anything more than about 220 mg is probably too heavy and useless if you're trying to get down to a 1.2 g total. Ivan's hubs weigh around 80 mg so that's a considerable advantage. In addition, some flyers probably buy them thinking that Ivan's success may rub off on them Roll Eyes

Nick.
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ykleetx
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« Reply #32 on: October 06, 2012, 11:23:02 AM »

I've built many VP hubs recently.  Although I can build the parts, I find that assembling them is not easy.  I believe that building the VP hub is the number 1 barrier to entry for F1D.

At the same time, it doesn't seem to me that having a Treger VP hub is a ticket to high performance.  I'm pretty sure that the top 5 finishers use their own VP hubs.  Do any of you know which top 10 finishers this year used a bought VP hub?

These being the case -- 1.VP hub is a barrier to entry, 2. bought VP hub is not necessary for top performance -- means that the BOM rule for VP hub is detrimental for this event and should be relaxed.
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leop
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« Reply #33 on: October 06, 2012, 01:45:03 PM »

Nick, did you mean 120mg for the maximum weight of a useful F1D vp hub rather than 220mg?

Jake had a reasonable question about the legality of purchased F1D vp hubs.  Some at the 2012 Indoor F1D WC used purchased hubs.  But, has the use of purchased hubs ever been protested in an F1D competition, national or international?  Is there some ruling by the FAI that such purchased hubs do not violate the BOM rule?

Leo
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green-man
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One of my F1D VP propeller hubs - weight 104 mg.



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« Reply #34 on: October 06, 2012, 02:39:20 PM »

AAAAAAAAAAAAAAAAAAAAAAAAAAARGH! Yes, I meant 120 mg (too much balsa dust affects the little grey cells).

Yes I agree, Jake's query is entirely reasonable and although bought hubs have been used for years, I'm not aware of any protests at major F1D comps regarding their use. If they are the same as the BMFA rules, the exact FAI rules state
Quote
The entrant must be the constructor of the model. The constructor may employ generally available building aids or small components in the production of their model but the airframe must be the competitor’s own work.
- Hmmmmmm that seems to imply that bought hubs should not be allowed. Anybody else see it differently?

Nick.

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leop
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« Reply #35 on: October 06, 2012, 03:24:38 PM »

The FAI's BOM rules reads as follows:

B.3.1 Competitor
         a)  Unless otherwised stated, the competitor named on the entry form must be the builder of the model aircraft entered.

There is no more detail given, unlike the quoted BMFA rule.  The AMA rule for US fliers in a somewhat more detailed:

6. Builder of Model: The CD shall make every reasonable effort to assure himself that each flier has completely “constructed‟ the model(s) he uses in competition, including the covering where used, with “constructed” to be interpreted as the action required to complete a model starting with no more prefabrication than the amount used in the average kit. Models which are completely prefabricated and require only a few minutes of unskilled effort for their completion shall be excluded from competition. In the case of rubber-powered models (excluding Indoor duration models), commercially available balsa, plastic, and hardwood propellers may be used. Materials and design may be obtained from any source, including kits. The builder-of-the-model rule applies to every AMA event unless specifically noted otherwise in the rules governing that event.


I am of the opinion that complete vp hubs are contrary to the BOM rules for both the AMA and the FAI.  However, the FAI rules apply for the F1D class in the US and any FAI rulings and interpretations apply.  Certainly if complete vp hubs may be purchased, why not preglued balsa tubes with boron applied  and spars with boron applied, etc.?

Leo
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mkirda
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« Reply #36 on: October 07, 2012, 10:48:54 AM »

I wonder if you are heading down the rabbit hole here...
Want to grow your own balsa and lay your own mylar?
How about that forge for making the steel in the music wire?
Or making your own tissue and glue? How far do you want to go?

If VP is the biggest barrier to entry and they are available commercially, why disallow them?
If the builder does 95% of the model, but purchases the hub, seems to me that they built it.
The hub is just one part of the whole.

Others that feel differently - Lobby to change the rule to disallow purchased hubs. There must be a process to allow for rules changes in FAI. I'm pretty ambivalent myself.

Regards.
Mike Kirda
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jakepF1D
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« Reply #37 on: October 07, 2012, 08:24:02 PM »

All I know is if I was flying at the WC's and someone beat me with a purchased hub, I would be upset about it. 

Regarding construction, I don't think perception is reality.  They seem hard to build, but I can build several in a weekend with a few extremely simple jigs and fixtures.
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mkirda
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« Reply #38 on: October 07, 2012, 09:14:38 PM »

All I know is if I was flying at the WC's and someone beat me with a purchased hub, I would be upset about it. 

Regarding construction, I don't think perception is reality.  They seem hard to build, but I can build several in a weekend with a few extremely simple jigs and fixtures.

Please share pics of the jigs and fixtures... I'd love to see what others are doing...

Regards.
Mike Kirda
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jakepF1D
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« Reply #39 on: October 07, 2012, 10:09:30 PM »

Most of what I use has been published by others at one time or another.  The only thing possibly unique about mine is how I drill the carbon yoke.  When I have a chance I'll take pictures of everything I use to make mine, but it's all pretty simple.  All you need is a drill press.
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jakepF1D
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« Reply #40 on: October 08, 2012, 04:11:42 PM »

I need to build some props this winter so I've decided to do a comprehensive VP build thread.  I'll take pictures of all the jigs and fixtures I use and outline the process step by step.  I'm certainly not the authority on VP props, but my mechanisms look nice, they're very consistent, and they're easy to build.  I'm essentially using the mechanism Steve Brown wrote about in the mid 90's with a few upgrades like a carbon fiber yoke and a top hat bend in the shaft.  I'm also using hypodermic tubing instead of aluminum bearings.

I don't use tube sockets so I don't know the weight of just the mechanism, but my last 19" prop weighed ~265mg finished.  I've identified places to save weight and I anticipate the next set of props will be about 250mg.  I'm also going to add low pitch adjustment on these new props.
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ljr8378
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« Reply #41 on: October 09, 2012, 01:37:49 PM »

I look forward to your posts on the build of F1D VP props.  With Stan Chilton as my mentor, I built a couple of F1D models several (~8) years ago.  I have built both fixed pitch and VP props also using guidance from Stan and Steve Brown's articles. I will try and post a picture of my prop block/jig this evening.

I build the prop hub by cutting a length (~6 in) of 6 lb balsa that is the proper width (0.10 in) and thickness (0.068 in).  The using the excess material as a handle/hold I drill a prop shaft hole (~ 0.013 in).  I use a Dremel mounted in a drill press type holder to drill the prop shaft hole. I am not sure how accurate the hole is drilled in relation to the length and width of the hub (i.e. how perpendicular it is).  Do you have a jig or some other method for drilling the propshaft hole?

Thanks,

Lauren Rezac
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ram
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« Reply #42 on: October 09, 2012, 03:03:40 PM »

Jake,

Looking forward to following your VP Hub build.

Rey

PS:  is this you?
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Re: VP Hubs - for the techies among us
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jakepF1D
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« Reply #43 on: October 09, 2012, 06:21:30 PM »

Where did you find that?  That is me, and I think that mini-stick was the first model I ever built.
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ram
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« Reply #44 on: October 09, 2012, 07:22:56 PM »

It's from Gitlow's indoor book.  Near the beginning.  I'm not home right now so I don't know exact page.

Rey
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jakepF1D
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« Reply #45 on: October 10, 2012, 01:13:44 AM »

I was working for Lew when he published that book, but I didn't hang on to a copy of it.
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Tapio Linkosalo
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« Reply #46 on: October 10, 2012, 02:12:32 AM »

About hub construction; mine (pic in message #23) weights about 130mg, which is a bit too much. I could get rid of lots of pultruded carbon if I shortened the main cross bar. That part being a tube I could easily adapt similar prop hangers as those used by the Romanians and Ukrainians, a T-shaped piece of piano wire where the vertical part actuates pitch change, one cross bar (single wire) goes into the tube as hinge and the other (folded double) holds the spar or tissue tube.

What makes me wonder though is that the prop blade can then pivot back and forward if the piano wire bends. Will a 0.3mm wire be stiff enough to keep the blades from bending in an uncontrolled manner? A longer main bar would mean a stiffer hub.
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ykleetx
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« Reply #47 on: October 10, 2012, 02:01:22 PM »

.3 mm wire is thick.  It's stiffer than the prop spar, so it should be more than strong is enough.
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Tapio Linkosalo
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« Reply #48 on: October 10, 2012, 02:06:42 PM »

How about thinner wire? 0.25 for instance? Would save weight, but is that too flexible then? What size of wire is usually used for such hubs?
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ykleetx
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« Reply #49 on: October 11, 2012, 02:02:14 AM »

You don't need a lot of the wire inside the tube nor extended for the prop spar. 

I experimented with .25 mm wire, and I think it's strong enough.
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