Twinn Rexx - 3 blade rotor, any info?

[brett s]

Looking at getting a Twinn Rexx, would prefer 3 bladed heads for better scale appearance - anybody have any results to share going that route?

Ideally I'd prefer to have less clearance between the fudelage & rotors, getting rid of the flybar should make that easier. I know the 2 bladed one will be easier to set up & fly, just wanting to check out all my options - as a former CH-47 crewmember I've been waiting a long time for an affordable Chinook!

[v22chap]

brett
Joe is working on a set of 3 bladed heads for his bird and if you are just getting started in R/C multi bladed heads ,,it probably would be best to wait for his units ,,that way if you have problems he can help you with it .
There are several units from overseas that guys have been putting on with good results ,,but most of these guys have been flying multi heads for some time before they made the mod.
good luck with your tandem :thumbup:

[brett s]

I'm not new to r/c helicopters, been messing around with them for over 20 years now. My first was a Kalt Baron 28, in the mid 1980's :)

I'm definitely going to let others figure out what works best first though, not particularly interested in being a trailblazer here!

[v22chap]

Brett
Sounds like you been havin fun .. and sounds like you have the backing it takes to fly a bird like this and probably on multi heads ...but multi bladed heads are different as is the flying of a tandem .. I would suggest get the kit , build it and set it up with the two bladed heads and get use to it and then go on to the multi blades that probably Joe will have out by then
which ever I am sure you will like the rex tandem a lot :thumbup:

[chinookmark]

I've been experimenting with three blade heads, and it is a totally different animal. With two blade heads, the Twin Rexx is really stable, and just kind of lazily floats around. During my limited test flights with three blade heads, I found the helicopter to be a lot more work to fly. It kind of reminded me of a CPPro, except without the twitchy tail. Admitedly, I have very little experience with this mod, and have a less than ideal setup. But I agree with V22, definately start with two blade heads. I'm almost at the point I want one with three blades to look at and another with two blades to fly.

[ch53e]

Brett,

Sit back and listen to the trailblazers. I'm still finishing up my bird and can't wait to fly it. These guys have been working on their machines and flying them for some time now. They have been the test pilots for Joe. Every problem I have had, they have jumped in to help me. I've been flying currently for 13 years, but I too had a heli (Cricket) over 20 years ago. I for one am going to listen to all of them, swallow my pride and start with the 2 blade heads.

Good luck with your machine.

John

[brett s]

Thanks for the replies :)

[ShooShoo]

Anybody play with the 3 bladed heads from HeliDirect?

Shawn

[v22chap]

I have on a single rotor heli ,,, and I don' t think much of them ... I would not put two on my chinook ... they are weak and don't track good ,, I think the blade mounting holes are off .
I have read other post that guys have pulled threads out of the head and the blade and grip have went flying .....
I am waiting for Joe to get good ones built for the bird and in the mean time learning the flight charater of the bird with two bladed heads .:thumbup:

[avconslt]

Hi Guys:lol:,

Has Joe given out any projected timetable for the availability of the 3-Bladed Head? Also, will his TH-2 controller do tandem as well as multi blade swash mixing? Thanks.

Richard

[cbflys]

Joe has not give out (to me anyway) any projected release date. He did however tell me that the TH-2 will work with the new head.

[chinookmark]

Anybody play with the 3 bladed heads from HeliDirect?

Shawn

Yeah, those are the ones I got. I got tired of everyone at work asking me why I'm not putting three blade heads on, so I bought them to show exactly why they're not going to work. (How's that for justifying and impulse buy?)

They look cool, but that's about it. First off, they are a rigid design. We really need some sort of articulation or damping for the heli to fly right. Second, there's a lot of play in the grip bearings. The link balls suck. They are rough and out of round. I had to replace all the balls with Align parts. Also, the link rods are cheap. They're not really threaded rod, more like a rod with a spiral groove scratched into each end. They really need to be replaced, but that's not too bad, because they are also an odd length. If you just swap heads on a good setup, they don't give any positive pitch. I could get -12 to 0 degrees. I tried a band aid solution by moving all the servo arms up two spines. It works, but I really need to do a complete fresh setup.

Before I do that, I have other plans. The Twinn looks pretty cool with 3 blade heads, but the heads are high, and it just doesn't look right. I want to make new shorter hubs, and use the rest of the hardware from the Lightning heads. The design is pretty simple, so it shouldn't be too hard. Once I have that done, I'll cut the mainshafts down 5-10 mm, depending on how much room I have below the swashplates. That should bring the blade down to a nice scale location, relative to the fuselage.

Unfortunately, I'm leaving next week for an extended busness trip, so I brought the Twinn Rexx to hang up in my LHS for the next year. I know some other guys are flying theirs overseas, but I want to travel light, and not have to worry about my baby.

[v22chap]

(How's that for justifying and impulse buy?)


I have had worse for my excuse ;):noteworthy

Well at least now we have the facts first hand ..thanks for sharing Chinookmark

Sounds like a lot of work to get it flying right ...good luck ,,,and good luck on your extended business trip :thumbup:
I am sure your baby and us will miss you .:hug:

[ShooShoo]

I haven't heard a date yet but I asked about the th2. Since it doesn't do phase adjustments electronically you'll have to do it manually but it will work with 3 bladed heads. Perhaps he'll release an unpdated version of the software to allow this?

Shawn

[chinookmark]

The phasing is pretty easy to adjust manually. The only drawback is that the pitch links aren't 100% vertical. I don't think it's that big of a deal on a lightweight heli like this one. I'd be more concerned if it were, say .50/600 size. One thing I do like about the Lightning heads is the long pitch arms on the grips. Because of these, the pitch links end up pretty straight.

[cobrajet]

Just curious about what blades are being used on the 3-blade setups. Are you using the same blades from the 2-bladed/Flybar setups?

I love flying multi-bladed heads but have found throughout the years the best setups have the narrow-chord, CG corrected (forward) blades, and matched to the rotor system. Maybe it's the narrow chord, but I also find they are more flexible (flap) to accomodate some of the damping from the usual rigid head. That being said, we are probably limited to what's available in the 325mm range and I'm not aware of any purpose built blades on the market right now. Any out there?

[GunnarO]

Has anyone tried the 3 bladed head (http://www.deeteeenterprises.com/NS.DeeTee.Multi.Rotor.Heads.450.3-BladeHead.php) from TeeDeeEnterprises ? Looks like a good one, but quite expensive :(

[cobrajet]

Has anyone tried the 3 bladed head (http://www.deeteeenterprises.com/NS.DeeTee.Multi.Rotor.Heads.450.3-BladeHead.php) from TeeDeeEnterprises ? Looks like a good one, but quite expensive :(

Quite expensive, yes.....and no matched blades to go with it. :(

[v22chap]

They also are producted by an individual and Deetee sells them ... what is going to happen down the road a few yrs ... for parts and support ,, I wonder .
It is bad enough with big companies ...let alone with just a sole person having them made . I would have some by now ,,,except these thoughts scare me and they have stopped me from hitting the buy button for quite a few months.:confused:
I am going to wait however long it take for Joe to get them and get them right .

[cobrajet]

IMO, I think it's buyer beware at this point. From what I'm seeing there are folks out there capitalizing on 450 heli pilots with a strong urge to throw money at multi-rotor heads just to have 'the look'. I don't think the level of development is there yet, like you see with the larger scale jobs, such as Vario, Graupner, and others that offer a matched system.

Parts such as swashplates, servos, even that teensy stock jesus bolt should be looked at closer for the higher stress levels you'll see with more blades turning. Not to mention the aero loads feeding directly from the blade to the swashplate (no mixer/flybar) and on to those delicate little servos when you're flying around and the swash is tilted for FF. If one blade happens to lag just a little more than the rest, more feedback stress.

Although I have not flown a small multi-head, I question swash timing in relation to rpm. This should be an issue with electric-power as the battery unloads and motor rpm starts to slowly decay, so a governor would help. I know my favorite Vario head had a narrow operating rpm it liked to see, which was about 1400-1550, and easily maintained for the duration when nitro powered. Keep it in that rpm and it was a *****cat.

Consideration should be given in designing a complete package which also means offering purpose built and matched blades. So I think I'll wait and just put up with the proven two bladed system. I'm not the type that's gonna just hover around cuz my multi-blade system is not sorted out and is a handful in FF or does 'weird' things. Been there, done that....

My money's on Joe's setup and I hope someday he comes through with what we're all looking for.

[rha]

I've been experimenting with 450 size multi-blade heads and control systems for a while now and have not come up with a design that works 100% well. I think it was V22chap that once told me that when you scale something down it doesn't automatically work the same, he was correct. Multi-blade heads only require very small pitch changes to make big differences in flying control.

The problem with small scale multi-blade heads is that the radius distance from the feathering spindle to the blade holder ball link is small, therefore the amount of angular movement required for 1 degree of pitch change is very small. If you take an Align metal blade holder this radius distance is 11.5mm, for 1 degree of pitch change you need only 0.2mm (about 8 thou) of pitch rod movement. A standard 450 size swashplate bearing has a great deal more slop than this to start with and then couple that with the backlash in the swashplate driver and servo all of a sudden you have nearly 3 degrees of uncontrollable pitch change. On a larger scale setup these small amounts of backlash are the same but form a much smaller percentage of the required movement therfore have less effect.

One solution is to move the blade holder ball link further out increasing the radius distance like the Lightning Heli version to about 18mm, this means that you now require 0.3mm (about 12 thou) of pitch rod movement for 1 degree, still a very small movement!

The next problem is servos, there is very little multiplying or ratio's going on in a multi-blade setup, unlike a standard flybar arrangement so the servo rotation is again very small for even large changes in pitch angle. Moving the ball link into the first hole position on the arm is best but still it's important to use a good high resolution servo.

I've come to the conclusion that a successful small scale multi-blade design has to be manufactured very accurately and some form of multiplying must happen between the servo and blade holder.

My 3 blade head design I'm using on the small scale Chinook is a semi-rigid type and works well, the head itself is good but as Cobrajet says we need to look more closely at other components in the setup like swashplates and servos.

These heads are for my own experimentation and are not for sale so please don't ask, more work needs to be done on small scale multi-blade heads and I wish Joe the best of luck and will help in any way.

Rich

[cobrajet]

Rich,
Nice looking heads! Good point on the subject of pitch range. The last multi blade system I flew, the Vario 5 blade, hovered around 3 degs, and max pitch was around 6 deg. Total pitch range about 8 deg with the TT strap head. BTW, the force required to move the 5 blades was enormous with those TT straps. However, the constant torsional drag with that design would remove most any play in the system, so there were some advantages to it but you needed very strong digital servos to move that baby. Sure flew nice...

Speaking of swashplates, the one in my SE V2 feels like it's ready to separate after close to 200 documented flights. Amazingly, it still flies great, tracks straight in FFF, and just sits there in a hover, but it now has mechanical 'expo' and the deadband on center is definitely noticeable. Not the kind of play you want in a multi as you described so well.

I believe it's the Reynolds number that is responsible for changes as you downsize or upsize something and how its behavior changes. Which helps explain why a 450 heli requires around 2500 rotor rpm compared to a similar scale model of a .90 sized heli that would fly just fine at 1100 rotor rpm.

[rha]

Tom,
Thanks, the heads do look good but without the rest of the control elements being correct then the flying characterics are not so good.

I started off using Align swashplates and the photo below shows one that came apart in flight so beware! It might have been just a one off and not properly assembled in the first place but the effect of this happening in flight is catastophic with no hope of recovery.

Whilst pulling constant positive or negative pitch all the play in the control will be at one end, the problem comes when you change or take the load off and all the play now ends up at the other end giving an unexpected additional pitch change. Multi-blade helicopters are inherently "pitchy" especially in any wind and tandem rotor helicopters are even worse and work on DCP (Differential Collective Pitch), in a forward pitch up situation the gyro reduces the pitch on the front rotor (therfore taking the load off it and in extreme cases all the play and extra un-controllable pitch change takes place) to bring the front back level. This makes the gyro work very hard and it is difficult to achieve accurate scale flight.

I'm sure there is a way around this and I haven't given up yet.

Rich