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Scale Model RC Helicopters > Century Blackhawk converted to a Seahawk...Trex600e
 
 
Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Bad News...and an opportunity.

Today I learned what full scale rotary pilots refer to as LTE or loss of tail rotor effectiveness.

Everything was working well with the Seahawk in hovering. I pushed out into FF and flew slow circuits. She looked great in the air. When I slowed down to come into a hover to land, reducing the collective, the tail released. The Seahawk piroutted hard counterclockwise and I was not able to get it to counteract to the right.

Before I could hit the throttle hold it impacted the ground and the base of a large oak tree...the tree and ground won.

I think its a total loss...a few days will determine that (I had to put it away because I couldn't stand to look at it.

The pirouttes were due to torque but there was no failure of the flex drive or gyro (Futaba 611). The rotor blades due to the set up were turning down into the wash.

I understand that when we are flying 3d and hover inverted that there is no issue with the tail rotor direction. I also understand the we are running a higher head speed at the time.

So, I am convinced that I should have done what Rodan suggested and reverse the one way bearing and direction of main rotation. That would have given me the tail rotor rotation coming up into the wash.

I will rebuild this one or another...but maybe someone can learn from my opportunity to learn without the pain.
Rckfish
07-19-2009 05:48 PM
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Copter Doctor
Elite Veteran
Location: daleville/ft.rucker, al- home of army aviation

My Posts This: Topic  Forum		dude, i hate to hear that, after all you have come so far and done so much. i have to say though, that your tailrotor direction with the blade going down with the rotorwash shouldnt be the problem. my md500 has the blade doing exactly that and have no issues. on models its not so critical that you have to make sure you dont do it. the fullsize md500 has it the same way with no issues. i believe the failure must have come from somewhere else. now if your rotor rpm is low and there is more torque there than can be counteracted, you will lose t/r effectiveness til your main rotor rpm comes back up, this is so no matter what your t/r setup is like. maybe a post crash inspection may reveal another issue, but til then keep it outta sight, it takes me at least a week to recover from that kind of trauma.

drive a rotary, fly a rotorcraft
07-19-2009 06:05 PM
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FrittsLogic
Senior Heliman
Location: Honolulu, Hawaii

My Posts This: Topic  Forum		Did you have a lower headspeed than when it was just a pod and boom? In my Apache, the tail servo is placed in the back (you can see in my gallery). Kerry from Indy Helis told me that they originally used a golden rod tube to drive the tail with the servo up front, but found it not as effective as they would like. Also, in addition to having four blades on the tail, the size of the blades was upped to give more authority.

We don't need no stinking flybars!
07-19-2009 06:07 PM
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Rodan
Senior Heliman
Location: Prescott Valley, AZ

My Posts This: Topic  Forum		Oh, man, that sucks!!

I know how you feel... I put my 88" Extra in two weeks ago, and I still haven't had the heart to really dig into it...

I don't mean to contradict what you said, but if you were slowing from forward flight into a hover, you would normally be increasing collective to counteract the loss of translational lift. This would be increasing the torque, and the demands on the tail.

I asked earlier if you were still using the 2 blade tail? If so, and you lowered the headspeed, you might not have had enough tail for the increased weight with the fuse.

Really sorry to hear this, but better now than after all the paint and detailing... I know, small favors...
07-19-2009 06:18 PM
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Hoverup
Elite Veteran
Location: Gulf Coast

My Posts This: Topic  Forum		Rckfish - I have to agree with the previous posts telling you that the direction of the T/R "up and into main rotor disc" or 'down and away from the main rotor disc" is one of the many things that are just not scaleable in these models and I mean up to and including my IndyHelis Apache. As was pointed out, many full size helis ignore this so-called rule about T/R direction of rotation. It could not have been the cause of your crash. Hope you are able to salvage the imporatant bits and have another go. I feel your pain.

Cheers - Boyd
AMA 80393
IRCHA 3355
Major USAF
Retired
07-19-2009 07:44 PM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Thanks Guys,
What is important is figuring it out. Rodan, you are correct. I was increasing collective. I was running a 2 blade tail. I am going to have to think on it when my brain clears.

I had not changed the power or pitch curves, ie, headspeed. Eventually I will figure it out. Just don't want to go down the same path and make the same error.
07-19-2009 09:55 PM
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FrittsLogic
Senior Heliman
Location: Honolulu, Hawaii

My Posts This: Topic  Forum		I'm getting ready to do a BO-105 which has 4 main blades but only two tail blades. I'm a little nervous about this after your unfortunate incident. I think I will do the standard thing of testing the mechanics first, but adding weight to it to simulate carrying a fuse, to get a max torque test of the tail. Someone also posted somewhere here recently about the idea of using a separate motor to drive the tail. I'm thinking of trying this as well. The tail motor could be fairly small, and placed in the tail fin with a short torque tube. Also will put the tail servo back there as well, with a direct linkage. Then adjust the main battery position forward as necessary to keep c/g correct. A separate tail motor would allow higher tail speeds than the stock gearing allows, and could be put on a governor mode to ensure head bogging doesn't take away tail speed just when you need it most. The trick will be to configure the radio so that the tail spools up at the same time as the mains, or else it won't look scale.

We have to figure out how to get your Seahawk in the air. This was my next big project as well! (I'm an ex Navy submariner with lots of memories playing cat and mouse with Seahawks).

We don't need no stinking flybars!
07-19-2009 10:51 PM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Hey Fritts,
Oh I am not giving up...even if it takes a new fuse...I did not check head speed from pod & boom over to mechs in the fuse. The weight...which by the way was withing ounces of a Century Jet Ranger with Trex600 mechs, could have been the issue with an older motor...

Older and wiser. We will figure it out. By the way coming down the field and nose in was quite striking.
07-19-2009 11:08 PM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Resolution- Builder Error.

Everyone knows what pilot error is...but I have fallen victim to myself as builder.

When I set up the Approach Belt to Shaft lowering unit I used a shorter belt (to fit my length requirement) like the one that came with the unit for a Raptor conversion. It is 1/4" w. and fits the Raptor tail belt pulley the you mount on it. Well on a Trex600 you run a 3/16" w. belt. The front pully is a Trex the rear one a Raptor. I should have used a belt to fit the smaller pulley width.

Under high load (such as raising collective too quickly)the belt was slipping and the result was loss of tail rotor.
So we will begin again.
Thanks for everyone's imput.

If anyone knows of a Century Blackhawk Fuse for sale, let me know.
07-20-2009 02:50 AM
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Richard Morgan
Senior Heliman
Location: Virginia Beach, Virginia USA

My Posts This: Topic  Forum		Oh man Rckfish, I am really bumed about this. I swear if had another one here at the house it would be in the mail headed your way. Not knowing the extent of the damage, maybe a couple body parts from Heliworld might get you cranking again? They carry all of the spare body parts for the Blackhawk. Don't give up the project just yet.

Richard

Richard

Is it just me, I thought all Helicopters flew in 3D......Hmmmm?
07-20-2009 11:49 AM
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Copter Doctor
Elite Veteran
Location: daleville/ft.rucker, al- home of army aviation

My Posts This: Topic  Forum		FRITTS,
no worries with that setup, a two bladed tail will certainly handle a 4 bladed main, you just have to change the rules a little. rotor rpm is very important and you can increase t/r blade length/width or a combo of both to get things working correctly. the rules sometimes change when it comes to scale stuff

drive a rotary, fly a rotorcraft
07-20-2009 04:10 PM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Never say die

Richard,
Thanks...nope not giving up. I will have a Seahawk. First thing is to get the mechanics back working.

Copter Doctor...thanks for the call, I am on the road but will catch up with you later in the week.

Now that I know what caused it I am confident in moving forward. I don't think the fuse is rebuildable, but even if not I will buy another. I just look at this one as my prototype process!!! lol.
07-20-2009 04:26 PM
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FrittsLogic
Senior Heliman
Location: Honolulu, Hawaii

My Posts This: Topic  Forum		Thanks Copter Doctor!

We don't need no stinking flybars!
07-20-2009 06:58 PM
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Totto
Senior Heliman
Location: Norway

My Posts This: Topic  Forum		Bad News...and an opportunity.

Hello Rckfish,
That is sad to hear......


Best regards
Totto

http://www.tottoshobby.net
07-22-2009 11:44 PM
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jackheli
Elite Veteran
Location: Vancouver - Canada

My Posts This: Topic  Forum		If this is any consolation I also had mishaps on maiden flights with two different birds:

1- The receiver battery on my Ecureuil went dead... I managed to land but the engine went to full throttle at 0 pitch. It wobbled on the ground for about three full minutes while I watched in desperation, until a gulf of air caught it from beneath the blades and tipped it over.

2- The braces that held the frames of a T-Rex 600 to an Airwolf fuse gave in during spool up trepidation and the swash tore though the upper fuselage deck with no shame...



Anyone who has never made a mistake has never tried anything new
Albert Einstein
07-22-2009 11:55 PM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Totto and Jackheli,
Thanks guys,

We all know when you commit and put them up into the sky we are taking a risk.

I am order an new fuse kit and will take all that I have learned and the great support and advice of all of you...

I will have a Seahawk!

Thanks for your support and help.
07-23-2009 02:10 AM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		back on track

Time to resurrect the thread.

The new fuse arrived and is speeding along. I had pulled all the dimensions and made sketches of the crashed one. The new fuse is coming together quickly with the landing gear mounted, the mechanics frame built and mounted and some cut out work done. Next we move to the tail drive and flex.

Having built one previously I am making all the changes I wished I had done in the first one...a real bonus.

I will post new photos one I get to the hover test stage. I will also share some changes I am making during assembly...
08-24-2009 02:29 AM
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Bear808
Heliman
Location: Kailua, Hawai'i

My Posts This: Topic  Forum		Nice! Welcome back. Hope all goes well.

Keep thy head speed up, less the earth come up from below and smite thee.
08-24-2009 02:33 AM
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jackheli
Elite Veteran
Location: Vancouver - Canada

My Posts This: Topic  Forum		The new t600esp has a nice cnc A-arm to go instead of the anti-rotation bracket. You should look into that...



Anyone who has never made a mistake has never tried anything new
Albert Einstein
08-24-2009 08:35 PM
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Rckfish
Senior Heliman
Location: Little Rock,AR

My Posts This: Topic  Forum		Thanks Bear

Will do Jack.
08-26-2009 11:44 PM
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ReadyHeli . Power Helis . CANOMOD

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Scale Model RC Helicopters > Century Blackhawk converted to a Seahawk...Trex600e
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