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HelicopterScale Model RC Helicopters › ULSRS (Ultra Low-Speed Rotor System) Project
09-10-2007 12:00 PM  10 years agoPost 1
heli_headcase

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Hovering around​Atlanta

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Hey Scale fans,

I could post this message in any number of forums but think the scale heli pilots would possible benefit best from what I'm learning with this project. I can see this as a next step in improving the 'presentation' aspect of a model heli trying to replicate a full-size. Read on to learn why.

I've been thinking about what would control the lower limit of main rotor RPM and how a heli would fly, IF it could fly. How low is needed to help with the visuals of a scale-like rotor appearance?

Over the last several months I've been building a custom rotor head with this very idea in mind and last Friday was able to do the first simple test hops. Main rotor RPM: 600 even. Heli weight, soaking wet: 6000g.

The airframe is a modified Miniature Aircraft Ion-X with a rather high motor-to-main rotor gear ratio of 34-1. Main blades are Vario #415, 950mm with 22mm thick roots.

The tail boom and torque tube needed to be stretched over the Ion's stock parts and the final boom length is 1180mm vs 860mm.

CSM Heading Lock gyros will be handling the rotor system stability a little later but for now I'm handling rotor control manually. It's very easy to fly but the gyros will be 'icing' if you know what I mean.

The initial hops were with a couple different length tail blades knowing I'd run out of tail thrust with the low tail speed and "short" blades. Vario 120mm blades were tried first just to see what would happen. Also thought it best to give myself as much tail blade clearance from the ground as possible just in case the tail dips on first lift. Two speeds were programmed and the lower speed, approx 560RPM, allowed the Ion to lift up but the tail could only hold for a couple of seconds before stalling and letting the nose start to yaw. Flipping the switch to 600RPM allowed just enough tail thrust to hold a steady hover but I had no confidence in the tail's ability to provide surplus holding power. Later installed some salvaged MX400 carbon main blades cut down to 183mm and these were more than adequate but tip to ground clearance was very marginal.

Today I'll be testing this platform again with numerous tweaks such as softer damping in the head, longer carbon boom supports, 150mm tail blades and finely balanced main blades. If there's time I'll connect the gyros to the swash and try to tune them for a feel I'll like.

*Forgot to mention something important! The main blades produce a sound so close to that of a full-size heli, you'd think there was one flying near-by instead of believing the "whop-whop-whop" was emanating from a model heli! It's a sound I'd consider as the "Holy Grail" of scale flight I've done it with this model and if anyone reading this is going to Darrel's Dalton Scale fun-fly, you'll be able to see and HEAR it there.

Check out the upper section of my gallery for more information and many pictures of the rotor head I built for this test. I'll add more to it later today if I can get some decent flight pictures. Wish me luck flying and shuttering at the same time!


HHC

So many heli's - too little time...

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09-10-2007 01:10 PM  10 years agoPost 2
HFr

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Lagrange ,in USA

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Way to go HHC ,, keep us posted and a vid from Dalton please.

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09-10-2007 04:26 PM  10 years agoPost 3
Copter Doctor

rrProfessor

Enterprise/ft.rucker​,al- home of army​aviation

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WOW!!!
that is a seriously looooong boom
i bet that sounds awsome!!
keep us posted on the progress.

drive a rotary, fly a rotorcraft

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09-10-2007 05:59 PM  10 years agoPost 4
chopper jockey

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uk

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If you are doing this project for "visual" reasons, there is another trick you may wish to know.
That is to paint one blade white and the other blade black. The black blade becomes invisible and the end result is the head speed appears to be half.

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09-10-2007 06:26 PM  10 years agoPost 5
heli_headcase

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Hovering around​Atlanta

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More than one reason...

I know of the method of tricking the eye with contrasting blades, yes.

Ah, but now use both processes together at the same time! I'll have the opportunity to try this out at Dalton. There's an identical set of 950mm blades owned by Darrel Sprayberry available for lend and I'm very interested in trying them. One is black, the other white.

Regardless, painting the blades won't give "that" sound I was describing. Only slowing the rotors can generate it. Also, most of you don't know I was doing the extreme opposite with head speeds 10 years ago, looking for maximum speed in an attempt to challenge a world speed record. This is far more rewarding and fun in comparison


HHC

So many heli's - too little time...

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09-10-2007 07:48 PM  10 years agoPost 6
Airwolf crazy

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Lancaster, PA

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Greetings,

I am looking forward to seeing this this weekend.

I once acheived the "whop-whop-whop" sound from a set of wooden blades but not because I was trying to get it. The tracking/ balancing tape was coming off. The trailing edge was whip cracking in the air or some how slapping the surface of the blade. It was a really cool sound but not what I wanted to have happening with the blades.

I will have a camera there so I hope to get some good video footage of this.

Christopher

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09-10-2007 08:54 PM  10 years agoPost 7
heli_headcase

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Hovering around​Atlanta

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New News...

I ran a second-ever 'tank' of electrons through the Ion a short time ago to see how my tuning was going. Very well I must say!

Instead of the 12S LiPo battery flown last Sat (not Fri as remembered erroneously), I tried the lightest weight 10S setup charged. The tail was heavy but not too bad and certainly flyable.

First lift off was clearly a lower head speed than last tests. The 150mm tail blades were barely able to hold the nose on course and I could hear them complaining via much sound turbulence. But just how slower was the head turning? Would you believe it was turning only 500RPM? The rotor blades were so slow their characteristic 'whop-whop' was gone Control of the cyclic was perfectly OK though and I was able to fly one-handed to check the blade speed with my tach. This speed was with the throttle curve set to 75% across the board, a setting that gave 600RPM on the 12S battery setup.

Throttle curve upped to 90%, tested again and I think I remember reading 550 or 560. Flew very nice and plenty of tail power. Went the full 'Monty' next and set the entire curve to 100%. Bingo! 600RPM and a very strong tail.

I did "oops" it once - used Idle-Up1 with the old 50% throttle setting and know the head was way below 500RPM. The tail was useless and went 'round on me. I tried to set the heli down careful but tapped a tail blade to the ground. Good thing it was slow speed and just grass otherwise I'd be replacing gears now instead of typing.

Here's a pic shot today with a Bergen Intrepid canopy installed. It's a little heavier than the original Fury Ion unit and allows me to slide the battery packs back to maintain balance. Also the rearward packs fit inside this canopy without stressing anything.

Next: Start setting up the cyclic gyros and get the "heavy flybar" feeling this heli deserves.


HHC

So many heli's - too little time...

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09-11-2007 01:48 AM  10 years agoPost 8
heli_headcase

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Hovering around​Atlanta

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I Lied...

I said my next posting would be some results of using gyros on the cyclic. I'm working on the gyro programming right now but I wanted to get one more gyroless flight in with a correctly ballasted heli before leaving the 'wonderful world' of totally flybarless flight

Installed an old set of Tanic 10S3P, 7500mah batteries and got the CG just right. As the current drain is somewhat under 15A I guessed that the 10C drain rating of the battery would have no issues with pulling only 2C.

Set the TX count-down timer for 10min, started the video camera and clicked into Idle-Up 2. Forgot to mention - the CC110HV ESC governor gain was set at 50% for the previous tests and the droop in rotor RPM when loaded was obvious. At 80% the speed was much more constant and no sign of overshooting in flight.

That was a very enjoyable 10 minutes of slow hovering around, pirouettes CW and CCW, coming up close to the camera for a good recording of the blade noise and just a good overall study of the lack of vibration. This machine is big, very easy to fly and has a very, very high 'cool' factor. If I can tune the gyros the way I like them this heli could turn into a "daily flyer". I know it will last a lot longer if I can keep from tapping the tail in the dirt!

Other than youtube, where's a good place to host video clips? I want ya'll to see this thing. (Oh my, the south is coming from my lips...)

Later


HHC

So many heli's - too little time...

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09-11-2007 02:56 AM  10 years agoPost 9
marc28

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new york

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great work steve,I will see you at dalton

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09-13-2007 05:58 AM  10 years agoPost 10
heli_headcase

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Hovering around​Atlanta

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Busy Readying for Dalton

There's not as much to report as I was hoping to be able. Tuesday brought forth a power outage and then rain, severely stunting my ability to get anything finalized.

As the sun light was just about gone and more rain threatening to come down, I flew a partial tank of orbiting electrons to see how the cyclic gyros were tuned. Felt pretty good but then this heli handles good without electronic assistance in dead-calm conditions. There was zero wind and this didn't tell me much.

Dalton bound tomorrow and lots of time to play. If you're there, come on over and say Hi. I'll also have my Du-Bro Whirlybird 505 in plain sight so you can't miss my pit spot.


HHC

So many heli's - too little time...

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09-18-2007 05:26 AM  10 years agoPost 11
heli_headcase

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Hovering around​Atlanta

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New info added to my gallery

I'll not repeat here what I've written in my gallery but I will say that Dalton was excellent save for the torrential downpour we suffered on Friday. The weather on Sat and Sun more than made up for the rains.

I flew the ULSRS machine whenever batteries were hot and I wasn't busy with taking video or still pictures or helping others. Except for a gyro drifting problem on elevator, tapping the tail blades on the ground (oops!), there were no scary moments and handling was superb.

A lowest RPM of 480 was tached during one flight but there was no reserve lift with the top pitch programmed into the curve. Cyclic authority was always strong and not sensitive to RPM at all. More testing is needed to explore the limits but first a smaller and faster tail rotor is needed.

I'll post some videos if someone can suggest sites for simply the uploading of files, not the playing of videos such as youtube.com. That's too low quality for me. Maybe ask Augusto what's needed for his site.


HHC

So many heli's - too little time...

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09-18-2007 09:16 AM  10 years agoPost 12
ben1101

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Australia

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HI,

You could try machining up a 4 blade tail rotor hub? Fit some low aspect ratio tail blades for the extra bite and cut some holes out of your tail fin to feed the tail?

Great project!

Ben

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09-18-2007 09:39 AM  10 years agoPost 13
heli_headcase

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Hovering around​Atlanta

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One Step Ahead of you...

Hi Ben,

I already own a four-blade tail hub and grips but have hesitated to use it due to weight. The tail gear box is sooooooooo far aft that even a small amount of extra weight back there means a much greater mass has to be added forward of the main shaft to compensate. Higher RPM tail is the trick as ultimately "everybody wins".

Supposedly there's a set of gears from Vario that will give a speed-up and fit inside the X-Cell gear case. Someone is looking into this for me, right Christopher J?

By the way, thanks to Airwolf crazy, Copter Doctor and Helitronix for shooting video of the slow heli and my cool but very noisy Du-Bro Whirlybird. The pictures came out great. Helitronix in particular must be given extra credit for having to suffer through the "Wah-wah-wah" of the Du-Bro. I will never fly it close again without some form of hearing protection. I'll offer the same to whomever is holding my camera and shooting pictures for me. It's only fair.


HHC

So many heli's - too little time...

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09-18-2007 05:04 PM  10 years agoPost 14
bcopters500

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Texas

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My Robbe runs at 900 rpm and I use Graphite 120mm from century,,low mass blades is a trick plus using 950 mm tailboom. The tail must be light . Even real helicopters have very thin skinned tailrotorblades.
I use 800mm Vario on the head at 75mm cord. Very good popping sounds.

You did really good good luck!

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09-19-2007 04:16 AM  10 years agoPost 15
Christopher J

rrElite Veteran

Kansas City, MO​Californian lost in​land of Oz

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Supposedly there's a set of gears from Vario that will give a speed-up and fit inside the X-Cell gear case. Someone is looking into this for me, right Christopher J?

Huh, what..who...me?

News: This is my first evening off work so I hunted the gears down. Tooth count is 17T and 22T. These gears were not made by Vario, they are Miniature Aircraft gears made for the X-cell back with it used the plastic gear box. The box was so similar to Vario's that I could use the gears in my Vario ship.

Better news: sent you a PM.

Christopher J
same as I ever was
"Still all set & Flying the original"

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09-19-2007 04:35 AM  10 years agoPost 16
heli_headcase

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Hovering around​Atlanta

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Great News!

I just looked at the tooth numbers and this set of gears bumps my tail RPM up to 3600 from 2800. That's significant. I can trim my tail blades by quite a bit, once I do some rough calculations, and gain some more ground clearance.

Let's see - With the 150mm blades still (barely) effective at a head speed of 480RPM, and a stock tail drive ratio of 1-4.667, that gives me 2240RMP on the tail.

The 'proper' head speed of 600RPM times 4.667 is 2800 revs on the tail rotor and a very effective tail thrust with the 150mm blades.

The 21/17T gears speed up the tail box output by 1.235 or a final RPM of 3458, a decent speed for trying the 120mm blades again. Good ground clearance, here we come

Thank you Christopher J!


HHC

So many heli's - too little time...

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09-19-2007 07:58 PM  10 years agoPost 17
mbrewer

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Corpus Christi, TX

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Just wondering if this will be able to generate enough lift to get off the ground when a scale fuse and fixtures are installed..

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09-19-2007 08:42 PM  10 years agoPost 18
heli_headcase

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Hovering around​Atlanta

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Not sure...

Much would depend on the weight of the fuse. So far it's clear the fuse would have to be ultra light weight but still have to finish optimizing the gear ratios for the lighter battery packs and their lowish voltage. See my latest update in my gallery for more info there.

Wanted to start doing payload tests but they won't be valid until the motor can see a better load. The 34.2-1 motor-to-main rotor gear ratio was a little high for holding a 600RPM head speed with a 10S LiPo battery. Going to 30-1 will be much better. Will be very interesting to see what happens at collective pitch above 15 degrees Will it fly or fall? That is the question...


HHC

So many heli's - too little time...

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11-30-2007 03:20 AM  9 years agoPost 19
heli_headcase

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Hovering around​Atlanta

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Small Update...

In an effort to test other types of main rotor systems on this testbed of an airframe, I'll be removing the somewhat rigid rotorhead currently installed and will substitute a free teetering head constructed of old Hirobo Eagle and GMP Competitor parts.

The configuration will closely simulate what the head of a Bell Jet Ranger or AH1 Cobra would have, flybarless too. I'll first test fly it without any cyclic stability system and depending how purely 'evil' it handles, will then add gyros to calm it down.

Now it's back to the shop to work on the new head.

Later!


HHC

So many heli's - too little time...

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12-05-2007 08:23 PM  9 years agoPost 20
heli_headcase

rrKey Veteran

Hovering around​Atlanta

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Some Progress...

It's almost ready but pitch arms need to be finished. That's today's job.

Here's the basic configuration of the much modified Hirobo SSR II head:

The bent pieces of aluminum are trial tests before forming the actual pitch arms. My gallery has other pix of the head construction and next week the completed head will be seen.


HHC

So many heli's - too little time...

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