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Fact or Fiction?


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I've come across a couple of rumors lately and since I won't be attending the Robinson Safety Course for a while, I thought I'd seek opinions here.

 

#1 I was flying with a guy in an R44, and during the sprag-clutch check he mentioned that (in addition to the needle split) we are checking the engine idle? He said that if its too low (I believe he said below 55%) then we shouldn't fly until a mechanic fixes it?

 

#2 During takeoff in an R22 I noticed the CAT was in the yellow. I went to pull in some heat when the cfi I was with said I didn't have to, because on takeoff carb ice is not an issue since we are at a high power setting?

 

#3 During the mag-check while in an R44, I was told that if I inadvertantly turn the key all the way to off, that I should not immediately turn it back on (it could cause the fuel to ignite in the wrong place)? I should instead pull the mixture to cut the engine, then start over again?

 

Number one sounds like it could be true, but number two sounds like total BS, and number three I just don't know? So,...what do you all think?

Edited by eagle5
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My take on your questions:

 

#1: As long as it's in the ballpark, probably not a big deal. It's just an idle adjustment.

 

#2: He/she's partly right, carb ice can occur in two different places in the intake tract and one of them is only really at risk at lower power settings. It also happens to be the spot away from the carb temp probe, so you pretty much ignore the temp probe for that one spot. HOWEVER: The carb temp probe is in the other spot that icing can occcur, so probably best to use carb heat to avoid the yellow.

 

#3: It's true, ask your mechanic. Same reason why they say if you pull the mixture and the engine doesn't stop you should stop the engine by turning the fuel cutoff switch and waiting for the engine to stop instead of turning the key off.

 

 

Having said all this, it's been a while since I've been heavily involved with Robinson products so anyone else can feel free to chime in here.

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Only one I'm going to comment on is #2. Partially right is correct. Even though it's not an issue at high power settings, you still want it out of the yellow during take-off.

 

My current pre-takeoff checklist (while in carb heat conditions):

1) Lights Out

2) Gauges in the green

3) Carb heat out of the yellow

4) Trim off

5) Fuel's good (in regards to amount)

 

Also, according to Safety Notice 25 in the R22 POH:

"During Takeoff: Unlike airplanes, which takeoff at wide open throttle, helicopters take off using only power as required, making them vulnerable to carb ice, especially when engine and induction system are still cold. Use full carb heat during engine warm-up to preheat induction system and then apply carb heat as required during hover and takeoff to keep CAT gage out of yellow arc"

 

That should pretty much answer that question. haha

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I've come across a couple of rumors lately and since I won't be attending the Robinson Safety Course for a while, I thought I'd seek opinions here.

 

#1 I was flying with a guy in an R44, and during the sprag-clutch check he mentioned that (in addition to the needle split) we are checking the engine idle? He said that if its too low (I believe he said below 55%) then we shouldn't fly until a mechanic fixes it?

 

Yes, because if you are practicing an auto and roll the throttle down, and if the idle is set too low, out goes the engine.

 

#2 During takeoff in an R22 I noticed the CAT was in the yellow. I went to pull in some heat when the cfi I was with said I didn't have to, because on takeoff carb ice is not an issue since we are at a high power setting? Most have already commented on this but I use full carb heat during warm up. I dont know many R22's with two people on board that are not using full power during take off, so yes, the carb ice probability is limited. But still be careful based on outside temp and humidity.

 

#3 During the mag-check while in an R44, I was told that if I inadvertantly turn the key all the way to off, that I should not immediately turn it back on (it could cause the fuel to ignite in the wrong place)? I should instead pull the mixture to cut the engine, then start over again?

Yes, big backfire is possible so I would suggest you start over.

Number one sounds like it could be true, but number two sounds like total BS, and number three I just don't know? So,...what do you all think?

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I say this assuming it's a fuel injected R44, if not, it still applies minus the fuel injectors.

 

Actually, now that I put some thought into #3, you should start over. This is building off of what Goldy said. In the event there is still fuel in the intake tract, a backfire could ensue. It's highly unlikely that this would happen, but if the fuel were to ignite, there is a possibility of damage occuring to the intake, the motor and the fuel injector. If the fuel injector gets damaged you also now have the possibility of the fuel in the lines catching on fire and creating even more damage.

 

Ever seen a car backfire through the carburetor? I have.

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I'm concerned about the reasoning on #1 regarding making sure it doesn't idle too low. If the throttle is all the way off it should idle at or below 55%. I always thought it was checking the idle to make sure that while practicing autos and rolling the throttle off, the engine won't die at 50-55%.

 

As for #3 I've personally seen this happen from the outside. Checking the mags, accidentally switches it off and back off. The R22 backfired. Great at scaring away the stray cats on the airport though.

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I once accidently turn the mags off when doing a mag check. I quickly, without even thinking turned them back on. The engine quit, but restarted immediately with no issue. I'm not saying that there couldn't have been an issue with this, but in my personal experience no harm was done.

 

I should probably keep it in mind that I should pull the mixture and restart the helicopter from scratch if this happens again.

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1. Yes you are checking to make sure that the engine, now that it has warmed up, idles between 50-60% and at the same time your making sure the engine doesnt sputter with the rapid closing of the throttle so you have a good idea if its going to die on you during a practice auto entry. That being said most people dont just snap it shut to enter the auto anyway, but better to know that if the student just snaps it hard off the engine hopefully wont quit.

 

2. It goes without saying always try to keep the needle out of the yellow, however there is a judgement call to make if you are taking off out of a confined area. You are going to want as much power available to you as possible and having the carb heat on can cut your hover ceiling down by 2000 feet. So what you can do it put the carb heat on full in the hover and get everything warm, melting whatever might be there and warming the intake. Then before your actually take off, push it away and off you go, as soon as you rotate through 40 knots and your on your way up and clear the obstacle or even on normal takeoff reach down and adjust again. You are not going to pick up a large amount of ice in 20 seconds. If you know power isnt an issue on takeoff from a wide open runway then nothing wrong with keeping it on for the takeoff, again its a judgement call. Now this is not bringing up the whole readjust your MAP limits for having carb heat on debeat.

 

3. Correct, sometimes you get lucky and the student quickly put the key back to both and the timing works out well enough that you dont get a buck or a backfire. However you do risk damage to magneto itself, the small gears inside are plastic and the shock of engine dropping and coming back online can damage them, seen it happen.

Edited by Brentd2183
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#2 is partially correct but kinda misleading as per the POH. Carb icing is not required at high power settings, which the POH specifies as 18" Hg or greater on the manifold pressure gauge, but SN25 says to keep it out of the yellow arc on takeoff. So which do you go by? I've only flown the R44 R II so have not really dealt with carb ice, other than what we discussed in ground school.

Edited by superstallion6113
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#2 is partially correct but kinda misleading as per the POH. Carb icing is not required at high power settings, which the POH specifies as 18" Hg or greater on the manifold pressure gauge, but SN25 says to keep it out of the yellow arc on takeoff. So which do you go by? I've only flown the R44 R II so have not really dealt with carb ice, other than what we discussed in ground school.

 

It's not contradictory.

Carb Icing can occur at any power setting, but is more likely to happen at low power (below 18").

Robinson specifies that in the R22, carb heat has to be used:

1) Whenever the CAT needle is in the yellow arc and/or

2) Whenever power is below 18"

 

Exception: If ambient conditions are such that carb icing is unlikely (e.g. extremely dry air - "conditions not conducive to carb ice")

 

 

In the R44 Raven I, the carb temperature probe has been moved to just behind the throttle valve, which is the coldest spot in the carburettor. Because of this, you can rely more on the CAT gauge and don't automatically have to apply carb heat below 18".

Edited by lelebebbel
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Wait, what? Fuel injected engines don't have carburetors... the fuel line gets split and goes straight to the injectors on the cylinder.

 

I can see how my post would be confusing. I was simply saying that under the wrong circumstances fuel could be ignited in the wrong spot causing damage. Guess I should have left the bit out about injectors...

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