Has anyone tried a Chinook? (Full Version)

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crazyplane1 -> Has anyone tried a Chinook? (8/15/2006 5:22:12 AM)

Has anyone ever tried to build a scale CH-47 Chinook. I've ridden in one a couple of times and they are fun. I got some pics from a ride.



BarracudaHockey -> RE: Has anyone tried a Chinook? (8/15/2006 3:52:41 PM)

Hirobo makes one, I think its about 3 grand or so for the kit.

http://www.modelrectifier.com/search/product-view.asp?ID=3441



cobramech -> RE: Has anyone tried a Chinook? (8/28/2006 1:28:21 AM)

I just recently purchased a ch-46 sea knight from ms composit. It is electric and I bought it for $800.00, including all electronics....Mixer, 6 servos, 2 gyros and speed control. The kit came with an outrunner motor and scale 3-blade rotor heads. It is super cool. I am making mine a marine corps version, as I was a plane captain in the marines on cobras(Ah-1J's). I flew on Ch-46's many times and always loved how the front of the heli always becomes airborne before the rear. It sorta dragged its butt until the pilot pushed forward on the cyclic. I miss flying in the military. [&o]



Mustang Fever -> RE: Has anyone tried a Chinook? (8/28/2006 3:27:51 AM)

I was a powertrain mechanic with the 34th GSG, and the "Hook" was always my favorite. I'll never forget the one that made an emergency landing in the James River while I was in training at Ft. Eustis. The hull plugs had been left out and it sank until only the rotors and engines were showing.

I remember reading somewhere that without a flight computer of some kind, the A/C wants to go end over end due to unbalanced lift from the separate rotor assemblies. Hirobo and others have evidently solved that problem. Their unpainted Hook is $2500 on the modelrec.com website.

Anyone flown one of these, that or the 46 version? I'd really like to know. I fly fixed wing, but this could get me into rotary someday.



cobramech -> RE: Has anyone tried a Chinook? (8/30/2006 1:33:15 AM)

Yes, they seem to have solved that problem....In the instructions for my ms composit sea knight, it states that when setting it up you need to check that when the elevator stick is pushed forward, that the forward swash plate increases pitch slightly, while the aft swashplate decreases pitch slightly. This helps prevent the end over end problem you talked about. The mixer also adds the necessary left /right roll to the swashplate to compensate for the forward twisting forces generated in forward flight. I know it sounds confusing....but just keep in mind that the mixer does most of the work for you. You only need to adjust your transmitter according to how the model flies. No model will have the same characteristics. You first get it hovering the way you want it, and than you set it up for forward flight. It doesn't sound easy, but the results are ALWAYS worth the effort! Be sure to check all the sites like runryder and scalercheli.com for the latest updates and changes....



47steve -> RE: Has anyone tried a Chinook? (9/9/2006 5:18:37 PM)

That's interesting how they have the fore and aft rotors responding. I know in our helicopters, they react the opposite. You mention end over end....in our aircraft, the actual tendency is for both of the rotor disks to fly parallel, not go end over end. It makes sense as they both want to fly. When the computers are turned off, much more pedal input is required to keep the aft end from coming around.

I want to build a 47 model and have a good idea of how I am going to go about it, just reading about what others are experiencing.




Hookpilot -> RE: Has anyone tried a Chinook? (9/20/2006 7:31:28 AM)

I would suppose that the aerodynamics of a large model of a Chinook would be very similar to the full-sized machine. If that's true, the stability problem is not end-over end, but yaw control. I have 3500 hours in A,B,C and D model Chinooks (full sized that is) the A models had a SAS system that could be switched off. When off you had your hands, or should I say feet full. The tendency was for the helicopter to swap ends at 100 knots. We practiced SAS-off flight and it was doable, but you had to be READY for it to come off. Also, Chinooks do not tilt the swashplates forward under pilot stick inputs to go faster. When you push forward on the cyclic, the aft swashplate increases pitch in the blades, the aircraft tips forward and the thrust vectors for the two rotor systems moves forward. the swashplates do tilt forward as airspeed increases, but that is done with a system called LCT (longitudinal cyclic trim) It automatically programs the swashplates forward as airspeed increases and starts to do this at 60 knots. They are fully programmed at 160 knots. This system's function is to relieve stress in the aft vertical shaft and relieve stress in the aft rotor blades and maintain a level flight deck which reduces aerodynamic drag. The LCTs retract as you slow down and are fully retracted as you pass back through 60 knots. Dual AFCS systems (advanced flight control system) are incorporated in the latest versions of the Chinook. You cannot turn the systems off. The Chinook and its baby brother the Sea Knight both are highly unstable without a bunch of black boxes to make it feel like a conventional helicopter. Pilot workload would be overwhelming without them. One system overcomes an odd characteristic of tandem rotor system, that of zero stick gradient. Without this system, as you push the cyclic forward and increase speed, normally you would have to hold the stick forward to maintain that speed, as in a Huey, say. But the Chinook cyclic does some funny stuff without this black box we call the licorice stick. Lets say you push the cyclic forward and hit 140 knots. Without that system, you would find yourself pulling the stick back to zero or center, and you are still whistling along at 140 knots. So to have positive stick gradient, this box electrically extends the length of a control tube in the pitch axis and drives the cyclic stick forward proportional to the airspeed. This is just a pilot-convenience feature. It doesn't move the flight controls in either rotor head. I'm wondering if your models have the same aerodynamics and no compensation for it? The Chinook has no inherent stability in any axis and there is no cross-coupling which means that it can be rolling left, yawing right and pitching aft, all at the same time, and this is with no pilot inputs, (SAS off) There are several documented accidents where A model Chinooks swapped ends at cruise airspeed tearing work platforms off and putting a few non-military wrinkles in the skin because of a dual SAS failure.

The forward twisting motion mentioned above does not happen in the full sized machine. I don't know what you mean by "forward twisting motion." You mean roll induced by forward speed? I worked with an RC helicopter company building computers for tandem rotor models and they had a problem with the aft end of the helicopter dropping as the machine started to transition into forward flight. If this is characteristic of all model tandem rotor designs, your suggestion to program a little pitch in the forward swashplate is puzzling as this would aggravate the tail droop problem. It doesn't happen in the full sized Chinook. Interesting stuff.

Hope this sheds a little light on tandem rotor design and flight characteristics. I'd love to see someone take on the challenge of building a large scale twin turbine Chinook model. That would be impressive! See pictures of the full sized helicopter working out on my website at: http://homepage.mac.com/hookpilot/PersonalPage.html

Mike in Honolulu



heli_Rod -> RE: Has anyone tried a Chinook? (9/20/2006 1:53:35 PM)

Hi Mike,

That was an interesting post on the "Hook". You answered a lot of questions I had about how they flew. I am a civilian pilot and learned to fly helis in an old brantley B2B with time in an Enstrom F-28 and Bell Jet Rangers.

The "HOOKS" are a most impressive heli inflight. I'd love to get to try on out. What an awesome ride![:D]

heli_rod



47steve -> RE: Has anyone tried a Chinook? (9/20/2006 8:33:12 PM)

Mike,
Funny you should post as I have seen yuor site before. Very impressive and interesting stuff. A B C and D!!! You're likely an icon in our community, which I am new to myself! Did some single progressed to dual AFCS off in the clouds today.....sim at least :) I was also a bit confused about the "twisting motion" and how the mixing apparently works the fore and aft discs seemed backwards. I'm guessing you called the dash the licorice stick or the CCDA?? I am starting to draw out plans for a model with systems classes in mind. There is a guy that sells a computer board that he uses to mix the flight controls and he even refers to the -10. Looks to be a very stable platform. The only thing is that all models are 2 bladed....do any have crossing of the tip path planes? Existing 3 blade rotor heads are very expensive so I'll have to figure out something for that.



Hookpilot -> RE: Has anyone tried a Chinook? (9/21/2006 7:13:15 AM)

Steve:
I worked with a group building a small tandem electric helicopter. They also sell the mixing controls. I think they called their heli the Drangonfly. We had many excellent technical discussions about overcoming some odd characteristics of scale tandem machines. Their videos are very impressive and it seems they've overcome the instabilities.

I think the Dragonfly is set up much like the full size Chinook with overlapping rotor systems. They don't use 3-bladed heads as you indicated you'll be using. I sent him some -10 links off the Internet and that's what you probably saw. I was very impressed with their helicopter design and reasonable price.

Based on your location, I guess you might be going through CH-47 Q-course. If so, enjoy flying the greatest helicopter ever made. It floats, it goes fast, (the Apache pilots can't keep up with us) it makes great sounds when working hard, and it provides a nice big dry place to sleep when everybody else is in tents. We call it the Boeing Hilton... It's been a few years since I flew the Hook, I though you couldn't turn off both AFCS systems. Refresh my memory. I'm sure in the sim you can fail both systems. The last Hook I flew SAS off was the C model and that was a lot easier than the old A model. The A didn't have the strakes along the fuel pods and the aft pylon was teardrop-shaped (no flat cut-off tail) this dramatically increased yaw stability during SAS off flight. I imagine the C and D fly the same with stabilization off.

Since you are starting your career, you'll have the fun of flying the F model. We got excited when we picked up our Ds, That was the first Army helicopter many of us had flown with an autopilot. I did fly the CH-34 many moons ago and it had an autopilot -of sorts. It was very strange to take your hands off the controls and sit back and actually relax. The glass cockpit will bring the Chinook into the modern digitally integrated battlefield. But, it's still a HOOK, two turnin', two burnin', bends in the middle and goes C H U G!

Keep in touch

CW4 Mike Jones
hookpilot@msn.com




Hookpilot -> RE: Has anyone tried a Chinook? (9/21/2006 7:57:10 AM)

Rod:
Yes, the Hook is a great machine to fly. There is something intoxicating about grabbing the thrust lever and pulling in power as you lift a 20,000 pound load. The blades cone, the engines begin a strange high pitch whine as the compressor section spools up, and the helicopter starts to shuffle, shiver and shake. I imagine it was a lot like the engineers who ran big steam locomotives. You know when you are working a Chinook hard. She talks back. I flew in an Army Chinook flight demonstration team for many years and we amazed even ourselves with what we could do in them. One maneuver was a max performance vertical climb with full rudder input. We could peg the IVSI indicator at 3000 FPM - straight up. We knew we had a good spin going when the oil in the aft transmission got slammed to one side of the transmission case causing a LOW OIL PRESS caution light to come on for a few seconds. After the first practice fights, our flight engineers learned to strap in for the demo. We'd go zero Gee and do other whacky stuff they probably wouldn't allow these days. Like they say "Mastering the prohibited maneuvers in the operator's manual is the best insurance you can have."

We also played around with seeing what the Chinook could do 0 to 60. Mind you that we are talking about a machine with 2, 3750 hp engines and an operating weight of just over 30,000 pounds, empty. So, with our flight engineer seated in the jump seat, stopwatch in hand, we found out! the chief said "go" and 7 seconds later we were passing 100 Kts! That's quick for a big machine like the Hook. It was pretty exciting to do - pull in thrust to the torque limit, jam the cyclic forward and hold on. Essentially what we were doing was convert 20,000 pounds of useful load carrying into 10 tons of thrust to propel us forward, almost instantly.

What other twin engine helicopter can take on a 3 ton load, crank one engine, pick up to a stable hover and fly off with it... We use to pull engines on our pilots during checkrides just after takeoff from a pinacle with an 8000 pound concrete block on the cargo hook. The Chinook was able to not only gain altitude, it would accelerate too. This was done in a mountainous environment, 4000 feet up. Engine failures are a yawner in the Hook, unless you were really heavy, say 42,000 pounds or more, or there was an associated engine fire. then you had to put down the Playboy and tend to business.

Keep your rotor in the green and the shiney side up.

Mike




47steve -> RE: Has anyone tried a Chinook? (9/21/2006 10:15:19 PM)

Mike,

The model I was referring to is the twin-rexx. http://www.tech-mp.com/twinn_rexx.htm Elsewhere on his page, he sells the electronic mixing boards so a DIY is that much easier at a reasonable price. Very interesting stuff to read about his progression and related building issues.

-Steve



straitnate14 -> RE: Has anyone tried a Chinook? (11/25/2006 5:37:48 AM)

if your in IL thoes are probly from the unit i just joined?



Pro-E -> RE: Has anyone tried a Chinook? (1/4/2007 11:11:48 PM)

Here is a video of a good size one.
You need Real Player for it.

http://www.mcgirt.net/real/boingch-47d_chinook_fertig.ram



Mustang Fever -> RE: Has anyone tried a Chinook? (1/5/2007 1:36:07 AM)

I like that. Wish they had shown the landing. Looks very realistic.



47steve -> RE: Has anyone tried a Chinook? (1/5/2007 1:59:37 PM)

That is a nice looking bird. I could the different pitch of the rotor systems when it when it was in a turn...just like the real one. A lot of mixing going on inside that thing!



Bxcar32 -> RE: Has anyone tried a Chinook? (1/17/2007 10:44:59 PM)

It has been refreshing to read of people interested in scale Chinooks. I appreciate Hookpilot’s system class for the interested masses. I to, found MS Composit’s explanation of Differential Collective Pitch (DCP) rather confusing. I have been working on plans for a scale Chinook in about the 1/18 scale using, non other then, the real thing as my template. So far this is what I’ve come up with. I am going to run electric since it would be easier to mount Brushless motors (2ea) in scale locations, the power output is impressive and this should open up cabin space for future expansion. Since it is electric, I think I can get away with using only one sprag clutch on the tunnel drive shaft. With a V-tail mixer, I can coordinate the roll/yaw aspect of control. I am also looking at the idea of running only 4 servos for control (1 pitch, 1 thrust, 1 each head for roll/yaw). I have yet to figure out how to build a functioning LCT unit. I think for now. I’ll just make them both links fixed link and attached to the lower pivot mount to keep the swash plate from rotating and allow adequate thrust movement. I also plan on building a complete 6 bladed rotor system. I think for now I’ll just use symmetrical blades. For power, I am thinking of running a few (4ea) Li-Po’s in parallel (2 per motor/esc). I have yet to settle on the actual motors (suggestions).

There are issues regarding this build. Those being, that if I want to build larger then 1/24 is the difficulty in finding a 3 bladed head and swashplate. Plus I haven’t figured out about the drive arm as of yet. I am just starting this and have not yet progressed to actual assembly of the airframe. If anyone has suggestions on how to mold the airframe from plastic, resin, fiberglass, or lexan, I’d like to hear from you.

My intention for this project is as a launch platform for a larger (1/6) scale project for the future. I am looking at expanding the idea to include scale features that make the Chinook distinct. I have plans for power steering, ramp control, working cargo hook, Fire bucket operations, Water operations, LAPES and Paradrops.

Now its time to pick this project apart. If anyone sees something interesting that I have forgotten to mention, doesn’t work, is a stupid idea, or you just want to share some insight, please drop me a note.


Remember, a good landing is any landing you can walk away from. A great landing is one you can use the airplane afterwards.



Bxcar32 -> RE: Has anyone tried a Chinook? (1/17/2007 11:23:02 PM)

Does anyone know the best way to manufacture asymmetrical rotor blades?



tiredofchex -> RE: Has anyone tried a Chinook? (3/14/2007 12:50:20 PM)

HookPilot: I heard chinooks have to be carefully hovered above the ground to prevent this type of incident http://www.liveleak.com/view?i=95b554d514

Your thoughts?



heli_Rod -> RE: Has anyone tried a Chinook? (3/14/2007 2:22:21 PM)

That is a ground resonance problem that all helicopters are Susceptible to. Those were test done to show the results of the ground resonance if left unchecked. This only happens when on the ground.

Watch your model as the rotor RPM spools up. It will do the same thing at some point. You just have to get through the the zone quickly and operate outside it. If your model it allowed to stay in the zone of resonance, it too will suffer damage.

Rod



47steve -> RE: Has anyone tried a Chinook? (3/14/2007 11:59:43 PM)


quote:

ORIGINAL: heli_Rod

That is a ground resonance problem that all helicopters are Susceptible to. Those were test done to show the results of the ground resonance if left unchecked. This only happens when on the ground.

Watch your model as the rotor RPM spools up. It will do the same thing at some point. You just have to get through the the zone quickly and operate outside it. If your model it allowed to stay in the zone of resonance, it too will suffer damage.

Rod



Well, you are partially correct, but the intent is correct. The ground resonance in the video occurs because the aircraft is chained down too tightly. This prevented the struts from functioning properly, thus exacerbating the ground resonance. The test originated as a ballistics test that went wrong as evidenced by the final product.

Most typically, ground resonance occurs in aircraft that have fully articulated three bladed rotor systems. What happens is that a sort of shockwave travels through the aircraft from an inbalance of the rotor system that would normally be absorbed by the shock system on the wheels. Think of the three bladed rotor head with each blade spaced 120 degrees apart, and with one rotor leading and the other lagging, thus creating the "imbalance" in the system. The scary part is that ground resonance is self-energizing and will progress on its own, without and pilot input.

When we start up and shut down the helicopter, there is really no zone of resonance. When I was flying the Bell 206, we had a rotor rpm range that we would "accelerate through" because of, if I remember correctly, rotor drooping. Different subject. We have no sort of range in the chinook.

Hope this clarifies things a bit.....or should I say, "Clear as mud?"

tiredofchex:

We don't have to hover carefully because of this. When we touch down, it should be smooth because you can easily trigger the resonance if you hit one side harder than the other. I have never personally experienced this as a symptom, but Mike would likely have some good stories.

Oh yeah, if you read this Mike, can you send me that pic of the FOD under the tunnel cover? Did I tell you we found a wrench and some bolts under there recently!!!!

hooker50:
Do you really need LCT's? That would be really nice, but in a model, it may be a bit too complex. The DCP is really to understand, if broken down properly. First, understand how a single rotor system works and then integration of another system is easy and actually makes sense.




Bxcar32 -> RE: Has anyone tried a Chinook? (3/15/2007 7:13:12 AM)

A few years ago, a Chinook was on a ferry flight when the flight control hydraulic system jammed up. This caused the helicopter to enter into an inverted (rolled greater then 90°) and nose low flight condition. Luckily, the jammed flight control condition subsided and the crew was able to regain control (I believe the article in Flight Fax stated 300’) and land the aircraft. I was told that this aircraft is the one you see in the video. The Boeing engineers took the gear off (to the objections of the Flight Engineers) and strapped it down to the pad. I hadn’t heard of the other description, so it appears I might be mistaken.

Just some miscellaneous information about the video, each blade weighs 350# (give or take a lb or 2) with the diameter of the rotor disk at 60’. Since the NR is 225 RPM, this makes approximately 8 miles a minute that the rotor tip is traveling. As the helicopter starts to buck and dance, one of the aft blade damper horns separates from the blade. And thus, the demise of a great (I’m a little partial) helicopter is inevitable. On an additional note, I have the slow motion angles if anyone is interested.

Ground Resonance, as stated above, happens in articulated rotor systems due to its intended design. As the blade travels along its rotation, the CG will change with the rise and fall of the blade allowing for the blade to increase/decrease (lead/lag) its own rotational speed relative to the rotational speed of the rotor disk. The blade dampers installed at each blade assist in controlling the amount of lead and lag and dampening this effect.

There are multiple actions that cause ground resonance. On the ground, oleo struts absorb the movement of the helicopter as the blades spool up. Where pilots get into trouble is primarily upon landing. If you smack the gear on the ground hard enough, the blade advancing to that side of the aircraft increases its lead and off sets the balance of the rotor system. Each successive blade will do the same until, it subsides (not possible with power applied), you come to a hover, or the aircraft destroys itself. Which you can see is pretty impressive.

I’m sure that the Army has specified that this is not the preferred method of removing the aft pylon from the aircraft. There are photos on the web of the British removing their aft pylon in a similar fashion. Though theirs had help from the dirt.



47steve -> RE: Has anyone tried a Chinook? (3/15/2007 5:45:37 PM)

I read that flight fax article. Those are some lucky guys as they recovered so low to the ground. The pilots reports are amazing from that flight. If I remember correctly, they had picked the aircraft up from the Depot in Corpus Christie. This is the one where they found some metallic particles in the hydraulic fluid? I have also heard that this aircraft is the same one in the video. I was told about the ballistics testing by some IPs and academic instructors here at Rucker. One IP says you can see a round hit the aft pylon if you watch closely. If you watch the video, that big cable off the nose of the aircraft is how they were operating the aircraft. Anyway, it still turned out to be a great demonstration of ground resonance in which your example far surpassed mine. I guess I need to get back in the books!

About building a model, I am going to attempt the same and had the same idea as you to mount the engines in their proper locations. I think it is entirely possible to make one work. As I mentioned earlier, there is a company that sells computer boards that does the mixing for the DCP, etc... I have been so busy here, I have had no time to work on it.

-Steve



Bxcar32 -> RE: Has anyone tried a Chinook? (3/15/2007 5:49:48 PM)

I've been pretty busy as well and have had to shelve the project for a bit. I did pick up an Autocad program to assist with the design and have seen other autocad chinook designs as well. I'll get you the website when I can find it again.

Good luck on your model and keep me appriased of your progress.



Bxcar32 -> RE: Has anyone tried a Chinook? (3/15/2007 11:57:47 PM)

I found it. Check this link out. Dutch RC Chinook



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