Throttle cable snapped

[lpaaruule]

I have the Rotec Mk1, and haven't done my first flight yet, so I don't have any harrowing story to tell. However, I've read some of the threads on the VAN's site after hearing through private email about John's engine out experience. It appears to me that the Mk2 TBIs have a fuel flow valve sticking problem. I don't know if the Mk1 regulators have the same issue, but my guess would be yes.

I sent 2 emails to Rotec a couple weeks ago, asking them about this, and posted a very polite question on their forum about a week ago. I also tried to call them on their toll free number, but only got a busy signal. The other number didn't go through, but I might not have international calling enabled on my home phone. On the forum I included a picture I found of the "new" flow value next to the "old" flow valve. The new flow valve is longer, and has the o-ring attached instead of floating.

So far I haven't heard anything from them!

I'm about 90% convinced I need to uninstall the Rotec TBI, and either buy an Aeroinjector, or try using the bing. If I decide to, this will probably set my first flight back a month.

I have a friend that is using the Mk1 in his zodiac 601, and it's been running well lately, but he told me that Rotec rarely will answer questions via email, and calling them is about the only way to get an answer.

To make it worse, if I decide to uninstall the Rotec TBI, I won't feel right selling it to anyone, so it'll be a total loss.

Unfortunately the fuel system seems to be the week link in the system, there is no redundancy.

[radfordc]

The air straightener is from a computer supplier, Tony Spicer idea.
http://www.saxonpc.com/120mm-airflow-ho ... us120.html

I once spend a lot of time building a device to make the air flow as turbulent as possible. The idea was to get better fuel atomization in the intake pipes. You're going the other way....smooth air flow. What improvement is expected?

[WaiexN143NM]

Hi charlie, all,
We purchased a flow grid straightner from ac spruce, was for the ellison tbi, and used it on our rotec tbi from the start. Had read that it was good to use to keep cht/egt's similar, which it does. John prob has more to tell about this. I think he has experience with and without.
Your device you made to make it more turbulent, did it work? What kind of carb were u using? And type engine?
WaiexN143N
Michael

[fastj22]

The air straightener is from a computer supplier, Tony Spicer idea.
http://www.saxonpc.com/120mm-airflow-ho ... us120.html

I once spend a lot of time building a device to make the air flow as turbulent as possible. The idea was to get better fuel atomization in the intake pipes. You're going the other way....smooth air flow. What improvement is expected?

On the Jabiru, the induction is path is very short for the back two cylinders(5 and 6) and they typically see higher EGT (less atomization?) The aerocarb even needs to be oriented vertically on the Jabiru so each side sees the same size throat at partial throttle settings. I don't think there's any need on the Aerovee due to the long induction plumbing.

The best turbulator would be the pull through turbo. Completely atomize the fuel prior to induction. And a fairly long path to the heads. Also, the benefit of turbulence is after the carb, not before. The Jabiru has a airfoil shaped bar just inside the intake manifold to do this.

Prior to the carb the challenge is getting an even flow across the throat. A swirling flow would be asymmetrical and consistent atomization would be difficult. Even flow at least would provide consistency. Cars with throttle body fuel injection use these straighteners prior the the mass air flow sensor to get consistent readings.

The Rotec installation manual warns against a swirling flow as their spray bar needs a clean airflow over it to work properly. I figured why not try that with the Aerocarb too?
But the Aerocarb really isn't spray bar but a hole that's plugged with a graduated needle. But it does suck fuel out as the needle is extracted and thus, would probably benefit from a smooth airflow.

With the Rotec and air straighter I was able to even out my EGTs within 50 degrees of each other. The unstraightened Aerocarb I always saw the back two cylinders 100-150 degrees hotter. I'm still in the process of retrofitting the Aerocarb and have only done run ups with the air straightener on it, but so far so good.

[markschaible]

Hello SonexBuilders.net,

We want to comment on the AeroConversions Throttle Quadrant cable changes we’ve made through the years:

• A solid boden wire cable was originally included as this provided positive opening and closing of the throttle slide. However, this proved to have two potential weak areas. If the wire’s 90-degree bend for engagement with the throttle slide was too tight, or marred by the tool a particular builder used to make the bend, the wire could fatigue and break. Similarly, the wire at the throttle quadrant could break if the wire swivel was not swiveling freely in the throttle arm.
  
• To eliminate those potential failure modes we changed the supplied cable to a 1x19 strand, 1/16" diameter cable, which proved capable of opening and closing the throttle, particularly when the engine was running and the engine’s suction naturally tries to suck the throttle closed. This cable could also handle tighter installation radii. Some customers, however, experienced bending of the unsupported cable between the throttle lever and the cable adjuster, particularly when closing the throttle when the engine was not running.
  
• The current cable is thicker ( 5/64" diameter 1x19 strand), and handles the throttle closing forces better when the engine is not running. This cable has been standard equipment since approximately June 2013.

The current cable compensates for all of the issues discussed here. Builders/pilots must still ensure that the wire retainer swivel is free to swivel, and it's a good idea to avoid abrupt, forceful closing of the throttle lever when the engine is not running (note that we're not especially careful with the factory prototypes in this regard and we have yet to kink one of the new cables).

Also discussed in this thread is the possibility of cutting the cable with the washers in the wire retainer swivel assembly over-time. This is something we have not seen, and feel would be less likely with the current 5/64" diameter cable. The washers are meant to act as crush plates, and it's probably not a bad idea to deburr any sharp edges on the washers, or make sure that the smooth sides of each washer are the sides contacting the cable (you'll notice that AN washers typically have a small, smooth radius on one side, while the other side has a sharp edge).

For anyone wishing to upgrade to our current 5/64" diameter cable with teflon housing, it is sold in a 120" cable length with a cast barrel end to fit the AeroInjector slide (no ball-end adapter needed) for $22.50 at: http://www.sonexaircraft.com/eshop/cart ... ory_id=398

The AeroConversions Throttle Quadrant installation instructions can be download from the AeroConversions web site at: http://www.aeroconversions.com/support/manuals.html

As always, please feel free to contact us directly with your technical questions on this, or any other issue!

Regards,
-Mark
--
Mark Schaible
General Manager
Sonex Aircraft, LLC
phone: 920-231-8297
fax: 920-426-8333
http://www.SonexAircraft.com
http://www.AeroConversions.com

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[radfordc]

Your device you made to make it more turbulent, did it work? What kind of carb were u using? And type engine?
WaiexN143N
Michael

My device was attached to the throat of my Aerocarb on my Aerovee. It was nothing more than a set of twisted vanes to disturb the air as it flowed into the intake pipe. It didn't seem to make much difference.

You can find lots of devices if you google "carb turbulator".

[peter anson]

The Jabiru has a airfoil shaped bar just inside the intake manifold to do this.

My early type engine has this but I think it might have been replaced with two cylindrical spacers on recent engines.

This is exactly the reason the Bing carbs on Rotax engines have a spring to go full throttle. Which saved my ass once as I took off from Peterborough, ON with my wife in our Rotax-powered CH701. As I throttled back from WOT, the Vernier knob came off in my hand. Turned out well as the engine went back to full throttle and I was able to to a 180 and re-join downwind, using the mag switch to kill the engine on final

The Bing carbs on Jabiru engines are sprung to go to full throttle.

Can't say I've ever heard a convincing argument for getting rid of the Bing. All the fuel consumption and performance figures I have heard with Aerocarbs seem very similar to my own. Don't think I've heard of too many people with Rotax engines getting rid if their Bing carbs.

Peter
Sonex 894
Jab 3300 293 hours

[Bryan Cotton]

Here's my modified Aerocarb using a reversing arm and push/pull cable. Much smoother than the wire/boden cable setup. The aluminum thing on the intake is my air straightener.

John,
With this setup the travel of the throttle cable at the pilot's controls is very small. Is that how yours is? Any issues?

[Bruce593SX]

It's not the first time this has happened. Perhaps Mr. Mika will share his OSH story :D

It's probably best to install something using quality components for the throttle...

http://www.aircraftspruce.com/pages/ap/ ... -12631.php

http://www.aircraftspruce.com/catalog/a ... kkey=16852