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Old 06-30-2017, 10:07 AM   #341 (permalink)
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Thanks for the extra background info on the thought process that goes on behind the design of these blades. Listened to your insight on the 'Rotor Heads' episodes as well. Very interesting and sounds like your got a real passion for what you do.

TBH, i've wanted to to try the blades for a while but circumstances haven;t allowed me to as yet. Going in 'both feet; is what I do so i'm looking forward to comparing them to what I have over a wide range of heli sizes against the VTX's. Personally never been a fan for Edge blades but didn't have many options for 475mm size apart from Rotortech's. I'm hoping by using the VTX557 on the Logo550SX i've just started flying, it will give me a little more out of the stock power system, or atleast not stress it as much. I managed to shutdown the stock YGE90LV ESC on it's second flight and pushed it's replacement, a Scorpion 120 Tribunus to a 180A peak current at 2100 headspeed on flight 4. Can't wait to see what the ESC data logs tell me.

Also, if your work ever brings you our shores down here in Oz, be more than happy to meet in person over a beer or 2.

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Originally Posted by VTX Designs View Post

The VTX477's "design" head speed is 2090 rpm, and what that language means is that 2090 is the center of the rpm envelope. 2090 is said to be our "recommended" operating speed, but rather its really best understood as the center of the design operating envelope. So what speed you run is really dependent on your flying style.

Many advanced pilots who want harder 3D will find they like to turn faster, which is perfectly fine. I'm seeing the more advanced 3D pilots flying the 477's at around 2400 rpm. They also will fly considerably slower like down to the low 1000's range if that's what you like to do. The absolute max speed for the VTX477 is 2700 rpm - operating above that risks a crash due to mach/compressibility effects driving aerodynamics on the blade tip well beyond what it can handle safely.
Dennis, will be interesting to see if we both come to the same findings using the VTX's on a F3C routine. It's always a trade off between stability in a hover vs flying like your on rails in precision aero's.
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Old 07-02-2017, 03:36 PM   #342 (permalink)
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Happy with the 697's. Flew 6 flights on them today with very light winds and it was HOT (about 90f) I ran 1700-1900-2050. I only switched into 2050 for a moment as it was WAY too fast for me. I noticed a increase in overall collective feel. I still need to tweak a few FBL settings. Looking for slightly faster cyclic rates.

Keep in mind I moved up from 660mm blades at 175grams each. Now 697's and 201grams each. Of course they will be slightly slower off center without adjusting any settings. Will be easy to tune for.


Looking forward to more flights!
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Old 07-02-2017, 09:56 PM   #343 (permalink)
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Bugcatcher - I've been down your way back in '97 when my wife and I honeymooned in NZ and AUS for two weeks. Man, did we have a great time! Tempt me with a beer - I'm down for that!

Relysis - yes there will be some tweaks needed to get these blades working at their optimum. I think it might be a good idea if we started a "VTX Tuning" thread just for this purpose. I'm certainly not the guy to talk to about tuning, but I do see our pilots and customers making changes in their VBAR control to accommodate our blades and their flying style. Looks to me like there's more than one way to go about that...

I'll see if we can get that ball rolling... thanks for your input!

Bill.

EDIT: VTX tuning thread is here now! Once again MUCH thanks to Jonas W (Johnny31297) for getting the ball rolling I think this will be a good thread for y'all to read up on, and please DO contribute your ideas also.

Last edited by VTX Designs; 07-03-2017 at 10:39 PM..
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Old 07-03-2017, 05:19 AM   #344 (permalink)
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VTX tuning thread sounds like a great idea Bill.
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Old 07-03-2017, 07:25 AM   #345 (permalink)
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I think for now I'm going to try about 20 degress/second more for ail/elev. Actually elev. seems great, it's a bit slower on ail. Again, i'm coming from 660mm paddles which were also lighter by 25g each. So I expected a bit of tuning to be made. Will update later
Overall very satisfied.



-Markus
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Old 07-06-2017, 11:40 AM   #346 (permalink)
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Default VTX557 Operational Data

Once again we have the extreme pleasure of introducing a brand new blade release for the VTX lineup: the VTX557 is here now and shipping out!

The item of greatest interest on a new blade design is "how fast can I run these blades?" I'll get right to that question but also lets talk about the design envelope for the VTX557, while addressing the "max speed" question as well:

One caveat before reading on: I was not privy to any of the flight test of this blade, and so what you're reading here in this post is derived from aero data directly from my design work, plus feedback I heard from RotorLive. I suspect there will be some areas where you - our customers - find quantitative and/or qualitative differences between how you perceive the blades to work and how I *think* they should fly coming right off the computer here.

We did notice on our prototypes, the extreme outboard blade tips were manufactured very much under design trailing edge thickness. As a result, the prototype blades had tips that were very fragile and almost all of them broke in use or transit. The design thickness on the trailing edge, as well as the blade tip is .76mm (about .030") which is thick enough to hold up under normal use. I believe production blades are shipping with foam protectors on the blade tips and should conform to spec.

Weight & balance
Production 557 blades should weigh 120g and balance at 48.5% span, as measured between the blade bolt center and extreme blade tip. Keep in mind, due to manufacturing techniques there will be some variation in blade weight and cg. There is no hard tolerance for how far off they can be to be called "out of spec".

Aerodynamics
This blade once again features an entirely new airfoil on the outer 48% blade span, transitioning again in the extreme blade tip to control compressible flow issues. It shares the same structural section inboard of 48% with the VTX477.
The airfoil used in the main paddle section, internally designated the VTX6235, is a 13.5% thick section. This section features a slightly more "sharpened" nose for tighter collective & cyclic response near center stick as well as a modified aft portion (called the "pressure recovery" side of the airfoil) to run with slightly better efficiency in the upper end of the speed range.
And yes, of course, this section is the result of all the experience gained so far PLUS several hundred more CFD runs spanning a wide range of reynolds number and mach.
Blade area: The 557 represents a light blade loading - somewhere in between the VTX477 and 697. Its design area is tailored to absorb the installed power while offering a light enough loading to keep AOA under control in hard maneuvers. Design flying weight was 3.15kg (6.94lb). One other benefit of this design ideology is improved autorotation characteristics. Let us know on that please...

Design RPM Envelope
All VTX blades are designed for what I will call a "target" rpm which we also consider to be the center of the design speed envelope. For the 557, the center design speed is 2100 rpm.

Running above 2100 is perfectly fine, up to a point. I see positive tradeoffs in performance up to about 2350 - at the cost of reduced flight time. 2350 will put the blade tips at about 0.45 mach; at that speed keep in mind we're pressing a 13.5% thick section at near half the speed of sound and things get worse quickly above that when trying to extract high AOA performance from the airfoil. Ops above 2350 will still fly OK, but the tradeoff will mostly just be more noise, less flight time and no real gain in performance.

Do not exceed 2650 rpm. Doing so will drag up the blade tips so badly that experience shows the FBL and/or heli mechanics can't cope with the phase problems, control rigidity, etc. Prior analysis has proven to be spot-on correct as to the dangers of high rpm operation.

Low rpm ops should be extremely good. Our other blades can fly mild 3D with as little as 1000 rpm head speed, and the 557 should be capable of that as well. Give this blade 1800-2100 rpm and she'll be happy all day long.

Final thoughts
I really do think the 557 is my best work so far. The airfoil used here on the outer blade section is absolutely phenomenal. Blade planform is once again the result of a "clean sheet" design effort and is totally unique among the other VTX designs. The blade tip has also been very slightly re-contoured and we think it looks great and flies great.
The testing at RotorLive earlier this year was a bit of a surprise also. Mikado team pilots flying prototype 557's commented some of the blades were too fast (can you believe that?) and selected the "F" blade set which was one of the heavier sets to choose from. Of course, you can dial back the gains, and make the machine feel just about as soft as you like, but from what I've heard this is the quickest maneuvering blade we've done so far.
Finally - I mentioned this already - but much of what I just posted is straight out of my aero analysis and not really based on my own witness as to how these blades fly. VTX has heard enough from qualified pilots to release the 557 for production.
Now its in your hands, folks. Please do contribute here with flight test reports as you see fit. We encourage feedback, as this really is all about making the sport better for everybody.

Cheers,
Bill.
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Old 07-06-2017, 07:17 PM   #347 (permalink)
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Well, I got one flight on the 557s and they definitely make more thrust than the rail 556s. Cyclic speed didn't feel noticeably different for me.

I did notice that they seem to whistle some at maybe 4 degrees collective which was really annoying at ~1350rpm as it was right around hovering pitch.

Anyway, I'm hoping to get some more flights on them tomorrow.
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Old 07-06-2017, 07:55 PM   #348 (permalink)
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Bill, thanks for detailed post on the new 557's. Looking forward to trying them. Just noticed AMain show they are coming in on the 17th so still got a couple weeks to wait.

As you mentioned that the 557's are your best work and like everything, you improve on past efforts. Will there come to a point where you may put some of these improvements back into the 697/717 sizes to improve them even more? How much design improvement are the 557's over the 717's for example? Re-tooling would be the big cost I would expect to change what is already in production but something that just came to mind.

Something completely on a different tangent. I'm curious as how do these designs would hold up against full-size helis' running headspeeds around 350rpm. Obviously the big company's have really smart designers at their disposal but your designs seem radically different to what the big company's use. And I understand full-size heli's have completely different design requirements depending on their intended use, military vs civilian.
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Old 07-06-2017, 08:25 PM   #349 (permalink)
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Quote:
Originally Posted by prototype3a View Post
I did notice that they seem to whistle some at maybe 4 degrees collective which was really annoying at ~1350rpm as it was right around hovering pitch.
.
possibly the speed control motor combo singing to you? I notice more of that at the lower head speeds.
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Old 07-06-2017, 08:28 PM   #350 (permalink)
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Nope.
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Old 07-06-2017, 10:13 PM   #351 (permalink)
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P3A - yeah I've heard a few other VTX flyers mention the "whistle" also. Some describe the sound as a "whisper" ... the first one to bring it to my attention was Jason Bell a couple years ago at IRCHA. Honestly, I couldn't really hear it myself, but then again my hearing is pretty well shot due to years around jet engines. My first guess is its related to the tip vortex, but who knows... interesting.

Bugcatcher - well, thanks for that vote of confidence. But I really don't think my RC blade design methodology would work well, and probably not at all on a full scale heli. The thing would probably spool up, get airborne and then snap the main mast off.

Yes, I do see room for improvement on the 697/717 blades now in retrospect. I also have some new ideas that might warrant at least prototyping to see how they work. So VTX might release a "v2" version of all these blades some day. You know its really a matter of financial thrust. But we do need to keep pushing our applied aerodynamics forward. I think there could be more to gain in better rotor head mechanics as well. Again, these are only ideas at this time and would need to be discussed with VTX as well as the airframers out there.

How much improvement on the 557 over the 717 you ask? Hmm tough question to exactly quantify but I can tell you the primary airfoil on the 557 will produce nearly as much lift coefficient as that on the 717 even though the 557 runs at a much lower reynolds number. The 557 airfoil also has a slightly re-profiled nose for better near center response. I think it will be a noticeable difference. And somebody should put up a picture of the 557 right next to a 697 or 717. You will instantly see how the planform was modified. All this adds up to better performance.

Thanks...

oh yeah - best wishes with your new VTX557's. Give us some feedback when able. Cheers!

Last edited by VTX Designs; 07-06-2017 at 10:27 PM..
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Old 07-07-2017, 02:17 AM   #352 (permalink)
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i already posted very first impressions of first flights in some frantic minutes... had the luck to do some other flights in the evening... so let me add:

pitch: visibly faster in high-speed flying and *extremely* increasing rpm in overspeed manoevers… *wow* holy shit… never before i heard such a great sound… first i thought the bird would destroy itself in the air, but then had to do it again (and again)… *oooh shivers*

in the end this is consistent with the auto-performance (clearly above Edge 553s and even 603s) and the great pitch-performance… maybe i will reduce 0.5 pitch… not sure now. motor was (only slightly) bogging 2 or 3 times in hard manoevers @2200rpm with lipo voltage ~19.6V (telemetry log – so maybe even lower) … did not happen with the [email protected]/[email protected] (hw100v3/vgov, 4025-1100, 153/15). could well be due to dull fingers in the evening… will observe it.

cyclic: i had one or the other CRs in the vbar logs before... with the 557s (clear) better cyclic agility this will not happen again ... i will not have to bend the cyclic stick anymore.

headspeed (in-flight-comparision): 2200 vs. 2100 is not huge but noticeable better for me… clearly bigger difference for 1700 vs 1800. not sluggish @1700, @1800 just feels more reactive & "light". Maybe because my bird is a little heavy (CF frame, just under 3.4kg TOW with 6S/5000 40C) and/or the blades entering the sweet-spot @1800. did not try lower rpms yet nor higher.

flying time +/- the same, even a little bit improved… 5’ flying resulting in avg cell-v ~3.78 instead of ~3.73 before. will add 15-20” flying time… *thx vtx* => if confirmed in further flights this would imply slightly increased efficiency (but with higher peaks / load on drivetrain!).

no tuning till now… just tail gain had to be reduced @2200 (3-4 clicks)… so still just “first impressions” and not a “hard review”. but cozy’s over with this bird – now it’s really inviting to be pushed!

Ciao
Michael

nb: weather on weekend will be fine => will try them on t-rex 550 too... i clearly preferred Edge 523 over 553 there. maybe i'll *have* to order a 2nd set 557s after this test
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Old 07-07-2017, 02:38 AM   #353 (permalink)
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Thanks Bill. It's really great to see this level of sharing the development process. Hope this continues in future as you get more adoption. I found your hypothesis humourous as to what would happen if your design were applied to full size. I think our usage in terms of scenarios are quite different in that we can really benefit from more specific analysis which is great to see you doing. Looking forward to seeing your work on speed
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Old 07-07-2017, 08:37 AM   #354 (permalink)
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Yeah, a "whistle" is the only way I know to describe it and it is much louder on the 557s than on the 697s I have.

I remember that Cyclones made this noise over a much wider pitch/rpm range where the VTX557s seem to do it only at one very specific pitch angle.
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Old 07-07-2017, 08:46 AM   #355 (permalink)
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The only noises I care about when flying are the ones that indicate I have a mechanical problem....then it is time to LAND!!
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Old 07-07-2017, 09:26 AM   #356 (permalink)
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Bill, I really enjoyed the posts on rbs and specifics on how the blade is designed. We can appreciate the time invested to understand the ideas. When you talked about speed limitations and why a pitch up or down after reaching transonic airflow on the proceeding blade tips, this was at one time a hobby of mine to estimate how the tips could break the sound barrier. I spent time analyzing ww2 props in a dive with all reports of blades breaking off when they reached near the speed of sound due to the drag flow mentioned.

You also mentioned a change in phase is probably needed in order to assist the fbl more and I'm heavily convinced to that fact. My helis all now have reduced phase for a few small reasons, gyro procession being one of them.

One thing you try to be clear on is the fact that total pitch on the advancing side of the rotor may equal zero if not even - when a heli is tilted. Odd, you can have one or the other but not both, that is either the fan is an air screw or it is a lifting apparatus. When helis pitch the rotor beyond 6 degrees or maybe 8 they have reached the point of going into negative pitch on the advancing side, result is advancing side down. The retreating side may follow if the rotor has completely lost effectiveness on the air around it, total stall that is.

What I find interesting is that you miss some key components in airflow over the entire disc at speed in order to better help anyone wanting to try them. If I understand correctly the blades have an inboard airfoil resembling stol ones, bulgy? KBDD quarter crescent tips are very quiet too and thin out gradually in airfoil like yours.

I am interested in trying them, 717s only. Sorry to say the smaller ones are looking less attractive visually and btw, the whistle is a vortice on those 557s. If all the VTX blades looked identical except for length and root thickness for grips I would be more interested in a variety of them for my helis.

One thing I've learned in life is if something isn't broken don't fix it, I think the planform of the 697 and 717' are fine for all sizes. Would be accurate if it was said you've taken a plank propeller paddle and made it symmetrical airfoil for use as a heli blade? can I go canoe-ing with them? When you make the 997's we'll make a video doing that up the Grand Canyon, sound fun?
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Old 07-07-2017, 03:34 PM   #357 (permalink)
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Quote:
Originally Posted by prototype3a View Post
Yeah, a "whistle" is the only way I know to describe it and it is much louder on the 557s than on the 697s I have.

I remember that Cyclones made this noise over a much wider pitch/rpm range where the VTX557s seem to do it only at one very specific pitch angle.
I only notice that on my 700 when flying low rpm. And even then I "blame" it on the tip vortices, being grateful that they pin the airflow down onto the airfoil so I don't just stall and drop like a rock
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Old 07-07-2017, 04:50 PM   #358 (permalink)
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My set came in. Cg is very close to one another. Weight is 128.5 and 129.2. Does this seem ok? Going to have to add several layers of tape at cg to get weight the same.

Last edited by Lowknifedge; 07-07-2017 at 04:55 PM.. Reason: Edit
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Old 07-07-2017, 06:58 PM   #359 (permalink)
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Got three more flights on the 557s today and I think they're just a tiny bit quicker than the Rails but definitely more thrust on collective.

A few friends were there as well and I also got to fly a Logo 700 with 717s. One friend is actually an acoustical engineer who specializes in quieting down propellers and he commented that the whistle was strange. I noticed that the 570mm Zeal blades on his Logo550 seemed to whistle all over the place almost similar to cyclones.
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Old 07-07-2017, 08:13 PM   #360 (permalink)
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Default Heavy 697's

I just received my vtx 697 blades and am super excited but my blades come in weighing 207 grams a piece. I see the specs say 196 per blade. I realize there's variance and all but seems a little on the heavy side. On a side note, balanced to within 0.1 grams!
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