1/24 Chinook - CH47D

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1/24 Chinook - CH47D

Postby TwoHeads » Mon Mar 21, 2016 9:14 am

I have been flying model helicopters for many years, longer than I care to remember, but twin rotor machines have always held some magical appeal... you could almost call it a quiet obsession!

The larger Vario / Hirobo tandem machines always looked appealing but well outside my budget or physical space for storage, hence my desire to create a smaller tandem machine. This is my story of discovery and development to my current MK3 Chinook...

My first attempt some 10 years ago (2006), was based on two Ikarus Piccolo heads (some of you may remember those). Even a Piccolo in its standard form was not exactly a precise flying machine, but the Mk1 was a real learning exercise, especially as no 3 axis gyro system existed then. It had a brushed 400 class electric motor, and two rate gyros to help tame the yaw and elevator axis. If I recall correctly I tried two drive systems between the front and rear of the aircraft. The first was a toothed belt system, the second being a more traditional bevelled gear. Unfortunately these were just not up to the job and really could not handle the transfer of power between the heads. The control mixing was done in the transmitter.

Image

It was about that time that the first Align Trex 450 came on the scene, a much more precise aircraft and that to me seemed a much better candidate for a tandem rotor machine... and as you can see from the video, the MK2 did at least hover in a bit more controlled fashion. Although this was never going to fit in a scale fuselage, as I hadn’t discovered any scale plans at that time. The MK2 utilised Trex 450X fly-barred rotor heads and collective pitch mechanics and even a brushless motor. The bevelled gear drive system utilised came straight off a model car, and at least could handle some of the transmission power, although it still had no 3 axis stabilisation system... well in 2007 they still weren’t available. The mixer electronics were created by a friend. This efficiently mixed the signals from a standard Futaba receiver and rate gyros to drive the front and rear servos. This was a voyage of discovery and project in its own right.

The MK2 :

Image

Image

Image


Video of the MK2 and the development of MK3 to follow in the next installment!
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Re: 1/24 Chinook - CH47D

Postby BrokenRotor » Mon Mar 21, 2016 9:47 am

Very nice. Keep the info coming. Building one of these is on my list to do.

Thanks for sharing.
Steve

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Re: 1/24 Chinook - CH47D

Postby Mercuriell » Mon Mar 21, 2016 12:09 pm

Fascinating story, looking forward to next instalment!
John
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Re: 1/24 Chinook - CH47D

Postby copterdoctor » Mon Mar 21, 2016 12:12 pm

wow! very impressed! :coolpics: :coolpics: :coolpics:
life is all about flying a rotorcraft<br>and driving a rotory
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Tue Mar 22, 2016 3:01 am

Here is a video I found of my MK2 in 2007... it was as much as this could do to hover...

phpBB [video]
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Re: 1/24 Chinook - CH47D

Postby BrokenRotor » Tue Mar 22, 2016 8:07 am

Doesn't look too bad hovering. Was it hard to control?
Steve

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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Tue Mar 22, 2016 8:50 am

Hi Steve,

I think that is one reason why this project has stuck with me so long... the controlability of these machines is more challenging (read that as dam difficult at times) than single head machines.Well it certainly was with the gyro technology that I originally used.

The majority of the time I tend to fly these indoors, and this video was one very rare occasion that it felt sorted enough to give it a go outdoors, if only to see how it reacted to a light breeze. At least it survived to fly another day - always a bonus!

Setting up a twin rotor machine always seemed really difficult, not least because there is no setup manual and also very few people to ask what to do to get it setup right. Hence the project always progressed really slowly and never to a stage where I would be happy to fly a circuit. The elevator control input always being the most difficult aspect to sort out - mainly because Differential Collective Pitch is used and they never seemed particularly controllable in any kind of forward flight. At times just getting them stable in the hover was difficult enough.

Phil
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Re: 1/24 Chinook - CH47D

Postby BrokenRotor » Tue Mar 22, 2016 9:12 am

Hi Phil,

Thanks for sharing your info. There are a few guys on here that have mastered these monsters. They would be a great source for information. Maybe you have already read their build threads and contacted them. If not Joel and Chris are the two names I know off the top of my head. They have even make their own mechanics, and fuselage I think.
Steve

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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Tue Mar 22, 2016 9:44 am

Now for the second installment of my ongoing development... and for the more astitute, you will have noticed that the MK1 and MK2 really don't look anything like a Chinook or 1/24 scale anything!

The project got shelved for a while – until about October 2014 to be precise. Then something just rekindled my interest in the project, thinking back I reckon it was that I just discovered Flybarless Controllers and had converted my regular Trex 450 Pro to a DFC head initially with the Align 3GX controller and then laterly with a Tarot ZYX S2.

So the MK3A was born which was based on Trex 450 Pro mechanics, this required totally redesigned side frames based on Trex 450 PRO bearing blocks, heads and drive gear. The drive gears were deliberately sourced to be able able to handle the transmission power and drive shaft/main shaft diameter of 5mm as used by the Trex 450. This brought with it new mixer requirements as 3 servo 120 degree CCPM swashplates were used. The first flybarless controller used was a Tarot ZYX S2 which was fed into our custom mixer electronics mainly to support 3 servos per head, phase angle adjustment and custom mixing differential collective pitch.
The first motor used was a standard Align 450 3550KV brushless motor and main gear fed by two 3S 2200mAh LiPo packs in parallel. The motor was laterly upgraded to the a 450 Dominator 1880KV version running from the same power source together with a 35A Castle Creations ESC which made for a very cool running setup and about 10 minute flight time.

So this video shows the MK3A, this was in March 2015...

phpBB [video]


... again still not very scale like frames, especially the rear...

Then I found the scale plans of the Chinook 47D online, what a revelation, why hadn’t I discovered these before!

The side frames were reworked again and the MK3B was born... to be continued...
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Re: 1/24 Chinook - CH47D

Postby BrokenRotor » Tue Mar 22, 2016 10:25 pm

Very impressive Phil. Any plans for your design to be reproduced and available for sale?
Steve

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Re: 1/24 Chinook - CH47D

Postby goodhunting » Wed Mar 23, 2016 6:47 am

Impressive...

Gh


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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Wed Mar 23, 2016 8:06 am

Hi Steve

Not really considered making a kit for sale as I didn't really consider it to be good enough...

The vast majority of parts are standard off the shelf, the notable exception being the side frames which I could provide the drawing/template for. The only other custom parts are the drive shafts and main masts which are made from 5mm steel, so a pillar drill is required to put the necessary holes in. I would also have to comile a complete parts list...

I suppose it depends if there's enough interest to warrant doing this... would anyone else be interested in this information?

Phil
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Re: 1/24 Chinook - CH47D

Postby goodhunting » Wed Mar 23, 2016 8:46 am

It can't hurt. I would love a chinook like this...

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Re: 1/24 Chinook - CH47D

Postby v22chap » Wed Mar 23, 2016 1:08 pm

FYI ,,,,,Sorry ,,, the chinook market is a niche market ... and one model company and one lone individual have both done 450 size ones ,,, and then closed down . MS composite did a hornet type one and a man in I believe Arizona did a trex 450 size one named the twin rex ... I have had both and both hovered really good ,,but FF was a nightmare as they wanted to dive nose down when you slowed to come in for a landing from FF .. or maybe it was drop the tail ... been so long ago I don't remember for sure . Any how ,,, just a heads up.
I do love the work you have done on this bird .. it has a lot of resemblance of the twin rex that was made ... and maybe ,,, just maybe with a modern day flight controller gyro system it could be made to behave like a lady :fro:
Larry C ,,,Bergen R/C Helicopters and anything VTOL
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Thu Mar 24, 2016 10:38 am

Hi Larry,

I was aware of some of the other twin variants you mention. I have noticed some of the oddities in flight performance that you mention in my own machines...

I am in the process of trying some of the newer flight controllers (Skookum and Demon) and intend to report on my progress with them shortly.

Phil
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Re: 1/24 Chinook - CH47D

Postby v22chap » Thu Mar 24, 2016 11:35 am

It will be interesting to see if any of the newer technology can tame these beast :fro: :starwars:
Larry C ,,,Bergen R/C Helicopters and anything VTOL
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Wed Apr 06, 2016 10:35 pm

... to continue this saga the MK3B was developed which has side frames that would actually fit in a scale fuselage. This meant reworking the rear frame to reposition the motor and main gear. This was originally flown using the Tarot FBL system and home grown mixer.

In late 2015 a Skookum 720 Black Edition controller was used as it reportedly supported tandem rotor helicopters. This was chosen primarily because it supported three servos per head in a 120 degree CCPM configuration.

This was used with some success, however there are currently issues with the firmware which meant reverting back to two blade heads because it doesn’t correctly support phase angle offset. Another characteristic of the SK720 is that although differential collective pitch can be introduced there is no ability to alter the proportion that is applied between the front and rear rotors. This means that the forward flight characteristics cannot be optimised, although hovering and slow forward flight is pretty good...

The following video was taken in February this year...

phpBB [video]


I have been in dialogue with Skookum to try any resolve the phase angle issues and also suggested adding the extra features to the software to improve the forward flight characteristics... I am still waiting to get a resolution to this.

... as a result I finally bit the next bullet and purchased a Demon 3SX... this is still a work in progress and in the next post I'll get some photos of the modification that I made to the swashplate control to adapt to two servos per head...
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Re: 1/24 Chinook - CH47D

Postby HerefordHeli » Wed Apr 06, 2016 10:51 pm

Hi Phil,

This is a great tale of persistence and is leading to a very appealing model! Version 3B seems to fly in a very scale manner, well done sir!

I recognise those buildings although I've never flown there (my machines are all rather too big!) However you are only about half an hour away from me so its nice to see someone relatively local to me on the forum!

Cheers,

Paul
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'Helicopters do not really fly, they merely reject the earth for a while...'

Current project:
Westland Wessex Mk 5 (1:8) http://scalerchelis.com/phpBB2/viewtopic.php?f=17&t=17170
Sikorsky HH-52A Seaguard (1:6) http://scalerchelis.com/phpBB2/viewtopic.php?f=9&t=17865

Most recent previous projects:
Sikorsky HH-3F Pelican (1:10) http://scalerchelis.com/phpBB2/viewtopic.php?f=17&t=16545
Sikorsky H-19/Westland Whirlwind (1:8.5) http://scalerchelis.com/phpBB2/viewtopic.php?f=9&t=16334
Vario Schweizer 300 (1:4.5) http://www.scalerchelis.com/phpBB2/viewtopic.php?f=17&t=15749
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Thu Apr 07, 2016 4:26 am

Hi Paul,

Many thanks for the comments.

The indoor flying halls we use are at the 3 Counties Show Ground in Malvern, so not too far from you. You are most welcome to come over and join / meet us, please PM me so we can arrange.
A number of us in the club also fly outdoors - obviously larger models including some scale... the most recent addition to my fleet being a restored vintage Hirobo Jet Ranger DDF SST... something else for me to post on here when I get a chance, here's a preview...

Image

Cheers,

Phil
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Re: 1/24 Chinook - CH47D

Postby Darren » Thu Apr 07, 2016 10:30 am

I love what you are doing with this aircraft development
Can't wait to see it when it has a fuse, I've never seen a scale RC version in flight

keep us updated :cool:
Hirobo 30 scale UH-1B FBL electric conversion (under construction)
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Mon Apr 11, 2016 6:57 am

Darren,

Actually a fuselage is in the planning... I have had a 3D CAD design done... just waiting for the airframe to warrant it.

Phil
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Mon Apr 11, 2016 7:11 am

A Bavarian Demon 3SX is now being trialled (March 2016)... this now brings the development right upto date.

The issue with the 3SX is that is only supports two servos per head via a ‘V’ link arrangement. The following modifications were required to adapt the 3 servo CCPM Trex Pro heads to that required for the 3SX. The 3SX only uses differential collective for elevator control inputs.

Image

Image

The first flights showed that the machine will hover ok, but at the moment not as stable in the hover as the SK720.

At the moment it has a tendency to bounce/oscillate the rear of the aircraft whilst hovering, I guess because the gain/sensitivity is too high in the longitudinal / elevator axis. I’d really appreciate any tuning advice from any Demon 3SX experts on this forum as to what parameters might need to be optimised for a small tandem aircraft as the 3SX instructions indicate it’s default optimisation is for the a medium size machine!

.. I’ll get a video posted shortly to show this problem...
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Re: 1/24 Chinook - CH47D

Postby Mercuriell » Mon Apr 11, 2016 8:10 am

That's neat linkage engineering! Would changing the head dampers help the rear 'bounce' ?
John
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Re: 1/24 Chinook - CH47D

Postby TwoHeads » Tue Apr 12, 2016 8:02 am

John,

That is a good thought... I'll look into it.

Here is a video showing the issue...

phpBB [video]
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Re: 1/24 Chinook - CH47D

Postby Mercuriell » Sun May 01, 2016 8:30 pm

I like the mechanical linkage but it would be neat to keep the existing Tri servo arrangement on the swash, Imwonder if a multi rotor controller could help, for and aft pitch and collective achieved the same was as on a tandem. Just thinking .... Great project. Have you looked into the controller of the ill fated Twister Chinook?
John
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