General Twinn Rex Chinook Lift Issues

[Pro_Stock]

Greetings all,

I bought a Twinn Rex Chinook quite some time ago, and have basically been working on the thing ever since.

The problem is the thing is the pitch is so touchy as far as wind goes.
Up and down, up and down, on and on.

Doesn't matter what headspeed I run or how much pitch I run, it's the same thing.
There is basically always around a 10-15mph wind here in my part of Ohio.

I'm guessing there is just too much rotor area for the weight of the heli.
After all, the real Chinooks were designed to be heavy-lift helicopters.

So it seems there are 2 potential fixes:

1 - Shorter main blades (currently running 325mm on 3 blade heads. I have invested a lot of time and money in these heads).
2 - Increase the weight as needed.

Any thoughts would be greatly appreciated.
Thanks!

 

[James M. Lewis]

Hi Pro Stock, thanks for the information you sent about the 1.5mm rods. Fran11784 has been working with me on the Sikorsky Sky Crane "Hulk Jr." We got that problem fixed. While on active duty in West Germany worked on CH47 Chinook and yes they can be tricky, especially with tandem rotor heads. First of all stay with the 325mm blades, they can do the job, are they carbon fiber? Second is to check on your pitch settings. What I learn is a good rule to follow is: 0%, 25%, 50%, 75%, & 100% to start with. You can adjust accordingly and anything above 50% should see your heli getting light on the ground. That goes to say your throttle setup are also an important factor working in concert with the pitch. Fran set up Hulk Jr.'s throttle at 0%, 37%, 64%, 75% % 80%. With 6 blades this should work being one head is CCW and the other CW. Hulk Jr. is just under 7 lbs for a 450 size bird with a 5 blade main head and 4 blade tail rotor. And the most important thing to remember is FBL setup, again Fran is a pro setting these so I'm an avid student learning. Been flying fly bar birds for a while so FBL setup is new to me

 

[Pro_Stock]

James,

You're welcome for the Drills and Cutters information.
I stumbled across them when I was fabricating custom turnbuckles and needed some left-hand dies.
That Sky Crane sounds pretty cool.

I'm running the same Align 325mm CF blades I run on my B400 and Trex 450's.
I run -1 degree to +9 degrees of pitch on all 3 heli's.
I have no need for any more negative pitch since I don't fly upside down.

This pitch sensitivity is confined to the Chinook.
I can fly either the B400 or the Trex 450 on the same day and neither have this floating tendency.

Head speed makes no difference.
The wind will drive the heli up or down 2' to 3' when the gusts hit it.

My wife says I should start flying kites...

 

[Pro_Stock]

I forgot to mention that I don't have a lot of room to fly at my house.
I just putt around over the driveway and front yard, about 4' to 5' above the ground.

There is a very nice flying field north of where I live, but I don't have the money to join the AMA and the field.
Also, it's plankers that hang-out there, so I really don't want to try to fly around them.
(AMA is required)

 

[James M. Lewis]

I forgot to mention that I don't have a lot of room to fly at my house.
I just putt around over the driveway and front yard, about 4' to 5' above the ground.

There is a very nice flying field north of where I live, but I don't have the money to join the AMA and the field.
Also, it's plankers that hang-out there, so I really don't want to try to fly around them.
(AMA is required)

 

[James M. Lewis]

I can really appreciate your situation when it comes to having the personal space to fly. We're lucky here in Virginia Beach to have plenty of room. I have both a large fence in backyard and my son's 3 open acres. Plus we have several schools with large fields and a church parking lot with land (about 20+ acres). Also there is a private RC flying club with it's own runway. Have to be an AMA member and pay dues to the club. Which can be a nice penny. If you haven't already can view Hulk Jr. on this forum, latest one Hulk Jr. ready for ground and flight testing

 

[James M. Lewis]

James,

You're welcome for the Drills and Cutters information.
I stumbled across them when I was fabricating custom turnbuckles and needed some left-hand dies.
That Sky Crane sounds pretty cool.

I'm running the same Align 325mm CF blades I run on my B400 and Trex 450's.
I run -1 degree to +9 degrees of pitch on all 3 heli's.
I have no need for any more negative pitch since I don't fly upside down.

This pitch sensitivity is confined to the Chinook.
I can fly either the B400 or the Trex 450 on the same day and neither have this floating tendency.

Head speed makes no difference.
The wind will drive the heli up or down 2' to 3' when the gusts hit it.

My wife says I should start flying kites...

Just a thought, take your Chinook to -3 to +9 degrees. Main rotor head with 3 or more blades usually don't require a lot of positive. Plus the fuselage mass of your bird should be enough to keep it stable in flight.

 

[Admiral]

Hi Pro Stock, have you thought about running a constant head speed either with a governor or pitch settings 80%, 80%, 80%, 80%, & 80% on IU #1 that way when you as you increase collective your not increasing head speed as well. Worth a try you may have to play with those setting to suit your helicopter. Start you helicopter on normal pitch setting and the select IU #1 when ready to lift off.

 

[Pro_Stock]

Greetings Admiral,

I do run 3 constant head speeds and use the same pitch curve on Normal, IU1 and IU2.

I have heard guys who fly 700's about how different heli's are "floaty", and that's exactly how this thing reacts to wind gusts.
If the wind os calm, it flies just fine with no surprises.

 

[Pro_Stock]

Jim,

The only time I am in a negative pitch mode is when I land and turn the motor off.

EDIT: I'm still figuring out how to use the forum software.

 

[Pro_Stock]

Hey guys, I'm not a rookie.
I've been flying since about 2015 or so.

Several people who have these Chinooks have mentioned the difficulty flying them, but most of this is related to front rotor wash effects on the rear rotor.

I was basically wondering if the theory of too much rotor disc area/weight sounded right or not.

 

[RandyDSok]

Hey guys, I'm not a rookie.
I've been flying since about 2015 or so.

I don't think anyone that has responded has actually thought you were a rookie ... but none of us have our "resume" posted anywhere either, so it's always good when someone takes some time to explain things of why they do something or are suggesting something... even if it is a reply to someone with experience.

Which brings the probably more important reason when it comes to any forum including this one. Tech oriented forums do like to keep each thread independent of other threads even if they are similar since minor differences can mean a lot. In addition, they also serve as a research for others that may be researching a subject. So explaining something to even an expert who may not need that explanation can be a huge help to people that come by later and read the thread.

You are certainly the one being helped here ( known as the OP or original poster )... but isn't just about you, me or the next person... it is a community that all try to help each other no matter what our experience level is. Being a little pedantic and over explaining is better than not giving enough information and having to come back to explain what was meant earlier.

 

[Pro_Stock]

Well, I figured none of that would come out right.

Thanks for the help guys.
I'll get this figured out.

 

[James M. Lewis]

I don't think anyone that has responded has actually thought you were a rookie ... but none of us have our "resume" posted anywhere either, so it's always good when someone takes some time to explain things of why they do something or are suggesting something... even if it is a reply to someone with experience.

Which brings the probably more important reason when it comes to any forum including this one. Tech oriented forums do like to keep each thread independent of other threads even if they are similar since minor differences can mean a lot. In addition, they also serve as a research for others that may be researching a subject. So explaining something to even an expert who may not need that explanation can be a huge help to people that come by later and read the thread.

You are certainly the one being helped here ( known as the OP or original poster )... but isn't just about you, me or the next person... it is a community that all try to help each other no matter what our experience level is. Being a little pedantic and over explaining is better than not giving enough information and having to come back to explain what was meant earlier.

Bravo and well said .