How does the CH-47 Chinook balance itself?

[roineust]

How does the Chinook balance itself with only 2 main rotors and no tail rotor? Is it the difference of height and angle between the front and back rotor, equivalent to the stabilization function of a tail rotor?

 

[MulderFBI]

From what I know rotors on Chinook are counter rotating rotors and that makes up for tail rotor. The same principle works on Kamov-type helicopters with coaxial rotors. They are also counter rotating. That construction allows to transfer whole engine power into lift.

 

[roineust]

How come most of the drones i see flown by hobbyist have 4 rotors and a smaller amount have 3 rotors and hardly any have 2 rotors, especially not in a non-coaxial construction, such as the CH-47 have? Is is a matter of weight difference, in comparison to hobbyist drones, that makes the CH-47 more stable?

 

[MulderFBI]

There are RC helicopters in classic setup:

You can also find RC helicopters in coaxial setup. Especially in a cheapest, toy like models:

Here you can see tandem type RC helicopter:

I think it's just a matter of how complicated and expensive model is. Most RC models are cheap and mass produced and therefore Kamov-type coaxial rotors are simpliest to manufacture. They use small and weak engines which need to be in that setup to give a proper lift.

 

[roineust]

It seems though, that the CH-47 construction be it hobby size or full size, can not balance well with small diameter and fast rotating rotors, such as there are in quadcopters?

 

[CWatters]

I think the issue is control rather than balance. Helicopters use cyclic/tilt and collective pitch for control. Drones generally have much simpler fixed pitch blades and rely on speed and asymmetric speed control.

It's easier to control the speed of an electric motor than control the pitch of the blades as they rotate like a cyclic/collective helicopter does.

 

[David Lewis]

It seems though, that the CH-47 construction be it hobby size or full size, can not balance well with small diameter and fast rotating rotors, such as there are in quadcopters?

Tandem helicopters are unstable in pitch when they move forward. The rear rotor disk has a more negative angle of incidence than the front rotor to eliminate this problem.

 

[Joseph Patrick Kane]

In the real Chinook Helicopter, the word "stability" means different things, depending on what flight mode you are in or what RPM you are transiting through (I. E. Start up or hover flight mode.). The rotor blades on the Chinook helicopter are mounted on a rotor hub that allow them to "Lead", "Lag", "Flap" and "Hinge". The blades also vary in pitch during each rotation by the use of a "Thrust" control, which is called a "Collective Pitch Control" in most other types of helicopters. The real difference is that the collective pitch adjustments are different in each rotor system, and thus are more accurately described as "Thrust". The whole "rotor disc", (Sometimes referred to as the rotor dish) is actually a cone that varies in shape continuously during each rotation depending on RPM, air speed over the individual (wing) blade, and the "swashplate" settings caused by the "Cyclic" control input, and the weight imposed on the rotor disc in flight mode. The "Cyclic" variation during each rotation uses the principle of gyroscopic precession to vary the pitch of each blade continuously during each rotation. (Desired action occurs 90 degrees after input.) The effective shape of the rotor dish cone varies depending on the weight loads and the forward speed through the air stream. Centrifugal force of the rotor blades at individual RPM also contribute to rotor disc cone shape. There are other inherent stability issues that are controlled by the on-board "SAS" or stability augmentation system.

I doubt that any RC Model in existence today has the type of rotor complexity or real flight envelope of the real helicopter. RC models usually vary their lift/thrust, and thereby their speed, by rotor RPM. The real helicopter uses a relatively constant RPM during flight, and uses different thrust angles to achieve directional movement. (The old Piaseki H-21 was also a twin rotor helicopter that had a slightly different rotor system, and it could actually fly faster sideways in some tests, than it could fly forward!)

 

[Joseph Patrick Kane]

There are RC helicopters in classic setup:
View attachment 218978

You can also find RC helicopters in coaxial setup. Especially in a cheapest, toy like models:
View attachment 218979

Here you can see tandem type RC helicopter:
View attachment 218980

I think it's just a matter of how complicated and expensive model is. Most RC models are cheap and mass produced and therefore Kamov-type coaxial rotors are simpliest to manufacture. They use small and weak engines which need to be in that setup to give a proper lift.

What model RC Chinook is shown in the picture? It looks like it has a fairly complicated rotor-head?

 

[Janosh89]

The K-max ,now under the Lockeed Martin corporate umbrella I think, is another interesting variation on the counter-rotating
blade "disc" principle -the blades inter-mesh and the discs are (angled) side-by-side ( in the yaw axis)
The helicopter has migrated from 1960s two+ seater , to one-seater(pilot only), to 0 seater -a drone in the US Marine aviation core,
used today.

 

[Joseph Patrick Kane]

I have never flown the K-Max, but I have flown the Kamann Husky. It was a real dog lift wise, and speed wise, but it was a real stabile "hoverer". It was also very sensitive to cyclic control input. As a logging helicopter, the huskie was a dog. The K-Max is supposed to have good "low density altitude" lift capability, and that would seem to be ideal for some logging operations if it was as stabile, and had better "High Density Altitude" performance than the "Huskie". I have also flown the Aerospatialle SA-315 "Llama", which has the most reliable helicopter engine, and still holds the worlds altitude record for a helicopter, 40820 feet (June 1972, by Pilot Jean Boulet.). I have also flown the SA-316 Alouette III, with the same engine and transmission as the Llama, (Artouste IIIB engine) at 20000 feet. The Alouette III is not as stabile as the Llama. The Llama and the Alouette III have approximately a 2200 pound hook limit based on the airframe structural limit, and is virtually not restricted by density altitude performance decay in most Stateside applications.

 

[Janosh89]

Great experiences to have! The trend nowadays is to compound-driven helos, hopefully to take maximum speed, eventually, above
200kts. On this side of the "pond" we had the first-generation Westland Lynx which held the official speed (circuit) record for
some time. These machines, from late-1960s, have been withdrawn as UK military utility (Army) and ASW (Navy) use completely in
the last 13 months or so.
The replacement for these roles is the Lynx Wildcat - but in much reduced numbers!

 

[Joseph Patrick Kane]

I have seen the Lynx, but never even touched one. I was impressed with their acrobatic capability to do a roll or loop. That being said, Helicopter manouvers in civilian life and military life never involve rolls or loops. One or the pilots told me that he had an engine failure at a high gross weight OGE hover, and the remaining engine took up the load without the loss of any flight envelope. That impresses me! I look up the typical information on Wikipedia , and I am disappointed with the ceiling and load capabilities. Little of my real life flight experience involved Standard Day / Standard Temperature flying, and I infer that most of the flight parameters shown in Wikipedia paint a relatively low performance from the helicopters that came about after I stopped flying. I talk to younger pilots and learn about electronic and power capabilities the newer versions of some of the helicopters that I have flown, and I feel like a WW-1 Bi-Wing pilot in the jet age!

 

[Joseph Patrick Kane]

In reply to Roineust's first question about how the Chinook first balances itself; I do not understand the question. The flight envelope balance? The dynamic rotor Forces balance? Fore and aft CG Balance? Waterline (vertical CG) balance?

 

[Joseph Patrick Kane]

How does the Chinook balance itself with only 2 main rotors and no tail rotor? Is it the difference of height and angle between the front and back rotor, equivalent to the stabilization function of a tail rotor?

If you google CH 47 Chinook destroyed by "Ground Resonance", you will see a very interesting phenomena that happens with the CH 47. A CWO-4 Prouty was able to forestall this destruction at Fort Sill OK when he re-hovered as soon as it started, and then landed after they stacked a huge pile of bed mattresses from building 5030 for him to land on without the wheels touching the ground.

 

[berkeman]

If you google CH 47 Chinook destroyed by "Ground Resonance", you will see a very interesting phenomena that happens with the CH 47. A CWO-4 Prouty was able to forestall this destruction at Fort Sill OK when he re-hovered as soon as it started, and then landed after they stacked a huge pile of bed mattresses from building 5030 for him to land on without the wheels touching the ground.

Holy smokes! This is a different video, but pretty amazing. I didn't know about this...