max time to warm up engine before engaging clutch?
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No One
Member Since : 2018
Posts(232)
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max time to warm up engine before engaging clutch?

02-05-2012 07:14:34

In colder climates it is difficult to fire up and engage the clutch without the engine bogging down and then quite.  It could happen two or three times before it is ready to go.  I would like to let it warm up before applying the rotor load; any thoughts or experiences with letting the engine run for a few minutes before throwing the clutch?

Replies

simon
Member Since : 2007
Posts(321)
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02-04-2012 08:38:39
I have the same issue. When the cold engine stumbles and quits on startup, I think it is hard on the machine so I try to avoid it.
My latest try is to increase the RPM and therefore the HP , up to about 70% for the time the clutch starts moving the main rotor. As the engine lungs down I increase the throttle, there is a noticeable noise/feeling when the clutch has fully engaged the main rotor, then I decrease the throttle to idle and let it warm up untill everything is in the green.
That is how I overcome the cold engine stumble and quit.
I hope some of our more technical and AMO's have time to comment on the problem and critique my solution

Dean in Canada
It gets cold here
Rubaga
Member Since : 2011
Posts(49)
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02-05-2012 07:03:00
We use one of the following technics.

1. Either increase rpm but it requires skill in order not to get rpm too high or not to stall the engine.

2. Switch on clutch in 3 steps. You switch clutch on and wait for pressure to go to 14-15 and engine about to stop. At this point switch off clutch. Repeat up to two more times. On new helis you may need 3 times to do switch on/off. On more used helis one or two times needed.

Hope I am clear enough on how to get it done
michaelcahn
Member Since : 2008
Posts(5)
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02-06-2012 05:07:20
Well, you are clear but I suggest that you take a look at the POH.
When you switch the clutch to the "off" position the clutch motor runs in the opposite direction and you are disengaging the clutch, not what you want. To make it easier to get the rotor up to speed when the engine  is cold, AFTER turning the clutch switch "on" you can get the rotor up to speed by using the "Schweizer 300 rotor spin up proceedure" by "teasing" it, using the clutch circuit breaker. This will allow you to tighten the drive belts more gradually, and bring the rotor up to speed. If you are not familar with the Schweizer proceedure talk to someone that is. 
jabr800
Member Since : 2008
Posts(134)
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02-06-2012 06:49:20
In the world of Airliners, we are told to never use a circuit breaker, as a "Switch", as part of a normal or everyday procedure.
Bad for the circuit breaker over time usually, and I know in the Big Jets, the FAA frowns at this practice.

Using the Clutch Circuit Breaker to stop a Run Away Clutch in a Robbie, is an approved Robinson abnormal procedure and part of the POH checklist.

Using the Clutch Circuit Breaker to modulate the belts during start up, would probably get more than a scolding from the FAA, Robinson, and your Insurance people, if you created an electrical issue or other, that ultimately took the aircraft out of the sky, at a later time!
Just saying.

My several years of flying my Beta II at 5,893msl elevations in very cold weather, taught me to really finesse the throttle on the early stages of the engine start sequence, and it worked well for me.
This incorporated a usually top notch battery, low time engine, and belts of average age and time in service!

Never really an issue, just a little extra skill that a person in a cold weather environment, needs to develop.
Of course each machine seems to be different than the next one too!

Disclaimer:
I'm not a technical guy (No A&P or IA license), but I have been flying for 40+ years !
Hopefully as someone said, maybe a tech. guy will show up here soon, and give some better guidance than mine?

Take care.


Jeff Abrams
Beta II, N222JA
Ocala, FL (Formerly Denver, CO)
michaelcahn
Member Since : 2008
Posts(5)
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02-06-2012 09:30:51
You are correct modulating the clutch CB is not approved and neither is flipping the clutch switch, which can be much harder on the clutch and  the belts. As you note the only approved manual operation of the clutch CB is in the event of a run away clutch. However utilizing the clutch CB is preferable to flipping the switch and having the clutch running "in and out" continuously. A very light touch on the throttle can work sometimes but if the belts "grab" as they have a tendency to do, (more so in the 44 than the 22) you end up stalling the engine. Then you have to wait until the clutch "unwinds" and start the whole procedure all over again which can over heat the clutch motor and kills the battery pretty quickly. The CBs are manufactured by Klixon a division of Texas Inst and are rated at between 2500 and 5000 cycles under load and 10,000 cycles under no load so, a couple of operations on a cold day a couple of times a year is not going to damage it. Now if you really want to avoid the whole issue (do like I do) keep the chopper in a heated environment, get yourself a good (approved) crankcase heater to keep the oil nice and warm, prime it, and start the sucker as soon as you get it out the door! Also I believe that I read somewhere that Robinson says you can run the engine for about 30 seconds before you flip the clutch switch but that is not in the POH and as such would not be approved. Not sure how much good 30 seconds would do anyway.
deckav
Member Since : 2012
Posts(3)
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02-08-2012 02:17:05
Hi All, new to the forum,
Would it be a problem to run the engine for 2-3 minutes before engaging the clutch?
No One
Member Since : 2018
Posts(232)
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02-08-2012 06:20:50
The following is my personal experience with a tanis heater equipped R44 II I fly:  My cold starts are more in line with "simon".  The first start of the day requires me to finesse the throttle to just above 60%.  Any less and the engine quits, and I don't need any more to keep it running.  I ensure the rpm's are stabilized and engage the clutch, usually around 30 sec. have elapsed.  If I am correct about the mechanics, the aux. fuel pump is now engaged which seems to help stabilize the engine.  As the clutch engages I work the throttle to maintain 60% until you get that brief engine "bog"  when the belts tighten to the point the main rotor is now working with the engine and not against it.  I then lower the rpm's to 55% until the clutch light extinguishes and proceed with the checklist.  Again, personal experience that seems to work for me.  I am a lower time rotor pilot but high time fixed so if there are any red flags in my sequence, please let me know. 
Blue Thunder
Member Since : 2007
Posts(156)
main
02-10-2012 08:45:24
Hi All, new to the forum,
Would it be a problem to run the engine for 2-3 minutes before engaging the clutch?

I think this might be a bit long.  Just thinking of a spinning part rotating that long on a stationary part, but I can't say for certain.  Are we talking Raven I or II in these instances?  I have a II, and although it mostly lives in a heated hanger, I do a few colder starts at the office.  It runs a bit rough, but I too get the RPM to about 60% and hit the clutch switch.  This in turn connects the electric fuel pump (and also confirms that the engine driven pump is operating sufficiently prior to engaging the clutch/electric pump). 

Jeff, I agree that operating the circuit breaker isn't the best idea, but they are good for many cycles.  The Jet ranger boost pumps are operated exclusively with two separate circuit breakers, I haven't flown one in ages, but back in the day, I can't say I ever had one fail on me.  I think the newer ships (407 for example) used a toggle circuit breaker.  Maybe folks have changed up the circuit breakers in the 206's by now as well.  Another solution may to back the slack belt tension off a bit, give some time for the engine to start before the first 'grab', but then again, we're only talking seconds. Here.  My 2 cents.
Chopperpilotgod
Member Since : 2015
Posts(3)
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02-17-2012 09:50:22
Ok....from a high time robinson guy and A&P I was always instructed to do the following
Cold starts for the R-22 and R-44

1. Normal start and engage clutch switch.
2. after the rotor starts to move count three slow seconds and pull breaker.
3. Now, let the ship idle as normal and do not increase any throttle. Just watch as the rotor "slowly" builds rpm (creating minimal drag on engine) and comes nearly to speed. U will hear belt squeel but thats not a problem.
4. After the rotor is swinging with some good speed, Usually say 20-30 seconds, re engage the circuit breaker and allow belts to come to tension. U can judge when the rotor is moving fast enough...just get it moving and this helps lessen the drag on the motor tremendously...I never have one shut down on me ever.

At this point the heavy burden on the motor is gone and the rotors have some rpm.... You may hear a slight decrease in motor noise as the motor finishes speeding up the rotor but its minimal and not going to shut the motor down.
According to the A&P's, its no more work on the ship and it is less work for the cold expensive engine......Look at it this way,  its a switch. Which would you rather replace  when it breaks? The clutch motor, a dead battery from over cranking the cold engine or the circuit breaker??? The circuit breaker is made well and a failure is unusual as well as being cheap.
I start my ship (R-44) like this all the time in cold temps regardless of being in the hangar or cold on the ramp. It starts the same everytime and I have never broken anything.
Just my two cents...