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Low Head Speed Helicopters Low Head Speed Helicopter Setups and Flying info


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Old 11-27-2016, 10:59 AM   #1
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Default Ultra Low Oxy 3

Testing the Oxy 3 stretch on 285 as part of a low HS speed discussion, I got it down right around 2000. This was only to see what was possible for those wanting very scale flight. Take-offs and flight were slow, but not unstable. Below 2000 it got unstable pretty quickly, and 2100 was rather more comfortable than 2000. I would guess that on an unstretched Oxy (255) you would want to add 200 RPM to these numbers, as that is the typical delta between the two for comparable performance. (Also had one report from someone flying a 255 that he was not able to get it off the ground at 2000, but have not confirmed since I only have a stretch.)

To try this with the Lynx 4100kV that most folks fly, you just need 3s and the 11t pinion that comes with the kit. The optional 10t pinion would make it even easier.

Note that my heli was ~670g AUW for this test including a Glacier 3s 1300mah and a 15g connector/adapter. If you were going for an ultra light weight build for scale flight, you could easiliy take 70g off this with a lighter ESC (I fly the HW50A) and 12g servos. I would stick with the same size battery for light weight, but you could ditch the connector.

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Old 11-27-2016, 11:10 AM   #2
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This would be interesting to try with my 255. I do have an external HW RPM sensor that is being used by the mini VBar so that would make adjustments easier than just using an ESC governor. As you know I've recently gotten interested in playing around with lower HS.
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Old 11-27-2016, 11:19 AM   #3
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I just played with the Tx throttle curve here. Did not try to govern.
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Old 11-27-2016, 01:29 PM   #4
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What are you using to measure your head speed? I'm curious to see how low my 255 oxy3 would go, but I have no way of measuring the head speed. I would also use throttle curves and with AFW running on the YEP I'd have no problems there.
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Old 11-27-2016, 07:06 PM   #5
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There are a couple of tachs that are cell phone apps. (Audio rather than visual.) You just start them and put the phone on the ground, then fly your heli. They track over time and folks have found them quite accurate. Only cost a buck or two. Love to see how low a 255 would go. Post if you get some results!
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Old 11-28-2016, 09:47 AM   #6
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I still recommend optical tach - more accurate and actually consistent reading. Phone apps work but my experience is mixed.
If you have no-one with you - take main and tail blades off and spool it up - you can measure head speed that way. However since its not under load you measure about 100 rpm more than it might be with blades.

For myself -> I use telemetry and occasionally verify the info with optical tach using someone at the field.

I think 2100 for the Oxy3 is pretty cool - no video???
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Old 11-29-2016, 02:33 AM   #7
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Quote:
Originally Posted by im4711 View Post
I still recommend optical tach - more accurate and actually consistent reading. Phone apps work but my experience is mixed.
I've found the phone works pretty well. The one I use is more accurate if you put in an expected HS that is fairly close. If the expected is within a few hundred of the actual, the reading will be quite accurate. If not sure at all, it might take a couple of 20 second flights to dial it in.

I imagine the opticals will always be slightly more accurate, but +/- a few dozen RPM is good enough for me and you can't beat the convenience.
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Old 11-29-2016, 12:48 PM   #8
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I downloaded one of the apps, but am not sure how quickly I can do the test. It's supposed to be windy the next few days and there's not much light available to fly after work now. I'll at least run a test after work and see what my current 3 modes tach out to. I really don't like to fly LHS when the wind is up.
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Old 11-29-2016, 06:55 PM   #9
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No rush. I would not be comfortable flying the Oxy at these headspeeds with much of any wind! It was no more than 2-3 mph when I was playing around.
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Old 11-29-2016, 10:47 PM   #10
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I ran outside and tach'd my 255 oxy 3 real quick. The 3 head speeds tach'd out to
  1. 3169
  2. 3886
  3. 4037

Running the numbers on MrMel's calculator I should have gotten
  1. 3785
  2. 3890
  3. 3995

That was 80%, 85% and 90% on the YEP with governor store running. The specs on Mr Mel's was:
  • 4s
  • 140t main gear
  • 10t pinion
  • 4100kv motor
  • 90% efficiency
  • YGE governor on governor store
  • packs at 4.0/cell for gov learning

I'm going to rerun the test on FM0 again tomorrow. I may not have let the motor run long enough on that first try for it to correctly read the RPM. The pack was not fully charged so I was a little concerned I'd run it too low and get into LVC and damage the pack. It was sagging a bit at the end, but didn't get any puffing.
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Last edited by gstoneberg; 11-29-2016 at 10:54 PM.. Reason: Botched the math
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Old 11-30-2016, 07:30 AM   #11
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I reran the 80% test this morning and got a more realistic RPM. I also ran as many tests as a pack would allow and got these results:
  1. 80% - 3684
  2. 75% - 3431
  3. 70% - 3179
  4. 65% - 2927

I flew it a little at 2927 and it lifted and hovered fine. Punch-outs were sluggish, but it had enough collective left to make me comfortable enough to flip it, though I didn't do it right next to the pool. I'm skeptical that I will get anywhere near 2000 and still be able to hover it safely.

I would continue testing, but I have an appointment with the dentist to put a crown on and I'd hate to miss that.
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Old 11-30-2016, 11:03 AM   #12
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Took the time to do 3 more test flights and make a video. Before all that I will say that my enjoyment of flying the heli went away at 2180, the lowest RPM I tried. Not sure I'll try to go lower unless somebody really wants to see it. Here's the data on the last 3 flights:
  1. 60% - 2671
  2. 55% - 2422
  3. 50% - 2180

The video is pretty boring, just brief hovers in my back yard. The tail got progressively looser as the RPMs diminished, I would certainly have to raise tail gain to fly at the lower head speeds. At the lowest head speed the FBL seemed to lose the ability to hold the heli level and it wanted to tip back towards me. It was super quiet though.

Here's the video.
Oxy3-LHS (3 min 5 sec)
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Last edited by gstoneberg; 12-09-2016 at 02:10 PM..
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Old 11-30-2016, 05:13 PM   #13
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Thanks! The video is great and your experience is consistent with mine. I wouldn't fly 285 below 2000, so not surprised that you would not recommend 255 at 2150. At least it shows how low someone can safely go if looking for a super low HS experience on the Oxy.
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Old 12-08-2016, 10:53 PM   #14
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Quote:
Originally Posted by Wargamer View Post
Testing the Oxy 3 stretch on 285 as part of a low HS speed discussion, I got it down right around 2000. This was only to see what was possible for those wanting very scale flight. Take-offs and flight were slow, but not unstable. Below 2000 it got unstable pretty quickly, and 2100 was rather more comfortable than 2000. I would guess that on an unstretched Oxy (255) you would want to add 200 RPM to these numbers, as that is the typical delta between the two for comparable performance. (Also had one report from someone flying a 255 that he was not able to get it off the ground at 2000, but have not confirmed since I only have a stretch.)

To try this with the Lynx 4100kV that most folks fly, you just need 3s and the 11t pinion that comes with the kit. The optional 10t pinion would make it even easier.

Note that my heli was ~670g AUW for this test including a Glacier 3s 1300mah and a 15g connector/adapter. If you were going for an ultra light weight build for scale flight, you could easiliy take 70g off this with a lighter ESC (I fly the HW50A) and 12g servos. I would stick with the same size battery for light weight, but you could ditch the connector.

good work.

i also got my oxy3 qube 285 down to 1800 for hover with relatively heavy equipment (3s2600mah, hobbywing 60a esc, the bigger lynx 2222 motor, thick wire, mks 93/95i) a few months ago. i remember the hovering is with roughly 7-9degree pitch. the challenge fo is tail control at such low rpm. the stock 47/50mm tail blades were not up to the task anymore. I used 3 of 62mm plastic tail blades from 450size with a few washers to increase control.

after i am done with my new JR e12 low rpm stretch project, i will come back to oxy3 for further weight reduction, such as align 35a esc, 3s1800mah, thinner wires and smaller plugs, maybe the lighter 2214 motor... i expect to lower the rpm by another 200-300 for stable circling and cruising. i even got a few 18650 ion battery for their higher energy/weight ratio.
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Old 12-12-2016, 07:59 PM   #15
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I went out today, determined to flip the oxy inverted at as low a head speed as possible. I flew around a little while at 2400 and was sure I didn't have enough collective so I flipped it up to 2600. It seemed to have a lot more collective there so I gave it a try. Now I need to repair it as I broke the shaft on the motor when it hit. Also stripped the main gear. Haven't checked the shafts. I tried it too low and was too slow getting on the negative pitch. I got the sad ending on video but haven't put it on YouTube yet.
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Old 12-13-2016, 01:58 AM   #16
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Ouch. Sorry to hear it ended badly. They are quick and easy to fix. I'm waiting for an entire frame and extras for mine bought here. It's deal time right now so keep an eye on the used section for spare stuff cheap.
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Old 12-13-2016, 02:35 PM   #17
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Finally had a chance to put the video up. It flew around fine at 2400 rpm, but I needed a little more altitude to complete a flip at 2600. I have a new motor shaft ordered, hope to have it back in the air this weekend if the weather cooperates.

ox3 low head speed with crash (2 min 32 sec)
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Old 12-13-2016, 08:20 PM   #18
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Oops... but I think you had enough altitude - it was the video that caused the crash!

On a more serious note, I was playing similarly with my stretch at around 2400, but at about 50' (and no camera watching, so of course no issues...) The more times I fly it down there, the more I think I prefer HS above 3000. But I still haven't flown back to back for a real comparison.
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Old 12-13-2016, 10:38 PM   #19
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I definitely prefer 3700-4000 for my oxy, but it flies well all the way down to 3000. After yesterday's flight I'm sure it'd be fine at 2400 for sport flying, though the tail wasn't as solid as it is at higher rpms.
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Old 12-14-2016, 09:50 AM   #20
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Thanks for sharing the video. Based on the look of it its not that you did not change collective quick enough - you went a bit aggressive.
Looking at the flight at 2400 rpm I can see that you should be easy to do a slow motion flip. At 2600 rpm even easier. Give it positive collective to give it upward motion first. When it is in the climb you slowly push elevator forward and slow (with speed of the turn) pull collective to the negative. The crash simply shows it was done a bit in a rush. I fly a lot in extreme low rpm where I hardly have any lift and as long as you have lift with a bit climb rate you can always flip it. Go to at least 3-4 times the altitude for the first trials at low rpm and you will develop a feel for it. Its definitely cool
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