How do I stop from taxiing too fast?

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rookie1255

Pre-takeoff checklist
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rookie1255
I'm not supposed to have the throttle below 1000 RPM because it could foul the spark plugs. However, 1000 RPM lets the Cessna 172N taxi MUCH faster than walking speed. I'm also not supposed to ride the brakes to keep us taxiing slowly.

I think part of the problem may be due to the fact that this 172 had the STC for a 180 HP engine to replace the old 160 HP one.

Best solution to the taxi speed issue?
 
With proper leaning during taxi, the plugs should not foul, so pull the power back below 1,000 RPM to control the speed. If you're taxiing at walking speed outside a ramp area (i.e. on the taxiway), it'll take you forever to go get down to the end of some of the longer runways. My normal taxi speed is in the 10-15 kt range (I use the GTN650 as my "speedometer").

I also pull the yoke to the full aft position which allows the elevator to act as a giant speed brake. Got that trick from a Beech PPP instructor during my transition training.

Cheers,
Brian
 
Are you aggressively leaning the mix for taxi? If so, you shouldn't have any issues with fouling the plugs. Assuming this is a rental 172, It's either A: you taxi with a higher power setting and burn up their brakes or B: you lean the mix accordingly for taxi and use a lower power setting that doesn't require constant braking. I've always done the latter and have not had any issues with fouled plugs, in both carb'd or fuel injected engines.
 
Riding the brakes causes the energy in the brakes to build up without giving it a chance to dissipate. A method that is often used is to allow the aircraft to speed up to 15-20 knots (based on your comfort and abilities) and then check the speed all the way back down to almost stopped. This keeps the energy (heat) from building up in the brakes and causing a serious problem.

I'm also not a fan of taxiing around at 1000 RPM, but somebody else already addressed that.
 
Normal taxi speed is around 8 to 10mph, which is faster than walking speed. That walking speed is from before GPS's. Now with GPS we know how fast we actually taxi. But you still hear that walking speed quoted as the correct speed. I've never heard of any FAR/AIM taxi speed limits. Some airlines have them as rules and some planes have limits on some taxi operations. Mostly just a "safe" speed.
 
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rookie1255 said:
I'm not supposed to have the throttle below 1000 RPM because it could foul the spark plugs. However, 1000 RPM lets the Cessna 172N taxi MUCH faster than walking speed. I'm also not supposed to ride the brakes to keep us taxiing slowly.

I think part of the problem may be due to the fact that this 172 had the STC for a 180 HP engine to replace the old 160 HP one.

Best solution to the taxi speed issue?
Click to expand...

Who told you that malarkey about not letting the engine go below 1,000RPM and plug fowling? I'd be highly suspect of their experience.

As to your question, less power more leaning, at low RPMs you can't hurt the engine leaning the snot out of it, it should be leaned to the point that trying to give it full power would starve the engine of enough fuel to be able to continue to run.

When I'm on the ground, shy of some oddball hill or weirdness, I'm ether below 1,000RPM or at takeoff power, on the water coming up to a dock in the float plane I have the power as far back as I can get it, and I don't fowl plugs, this is also in a 6 cylinder 300HP engine.


So less power, more lean.
 
Occasionally, you need to keep 1000 RPM, but the issue isn't plug fouling. If you're about to launch into a low ceiling, you'll want enough RPM to keep the vacuum in spec so the AI and DG are ready to go right away. Not an issue for VFR or student pilots, or even pilots of airplanes with decent or backup vacuum systems.

Sometimes there is just enough slope on the taxiway that you still need brakes at idle. Just don't RIDE them, ever.
 
Alao note that if you lean as far as you should, most engines will stumble if you advance the throttle at all from idle. A last ditch, shouldn't count on it but it'll happen, reminder that you missed pushing the red knob forward, when you apply power to either start moving again or take the runway. Don't take off leaned...! I'm

At high DA you'll sometimes find the engine RPM will *increase* slightly when you lean on the ground, too. And you'll have to lean past that point to get it to come back down a bit.

Other things that can affect taxi speed:
- Wind direction and speed (hold those controls appropriately for any wind!)
- Taxiway slope (I roll downhill quicker to 17 than going uphill to 35 at KAPA because the airport has a mild slope to it... And have to plan to tap the brakes at the far end...)
- Aircraft weight (to a lesser extent)
 
Hold brakes for a few seconds, slow down to a normal taxi speed, then release the brakes.
 
I've never heard of this 1000 RPM minimum because of fouled plugs. I'd honestly be more concerned with wear/tear on the brakes.
 
Lower engine speed ,lean during taxi,if your worried about fowling the plugs.
 
Normal walking speed = 3mph

My runway length = 1 mi (and I often use 10000' runways)
ergo, ~20mins from one end to the other.

I must need patience training!
 
rookie1255 said:
I'm not supposed to have the throttle below 1000 RPM because it could foul the spark plugs. However, 1000 RPM lets the Cessna 172N taxi MUCH faster than walking speed. I'm also not supposed to ride the brakes to keep us taxiing slowly.

I think part of the problem may be due to the fact that this 172 had the STC for a 180 HP engine to replace the old 160 HP one.

Best solution to the taxi speed issue?
Click to expand...

The old adage that one must never taxi faster than a person can walk is a load of crap. It's sound where people are actually walking, between hangars and on ramp areas, but on dedicated taxiways it just wastes time and money.
 
The 1000 RPM thing is an OWT. The engine manufacturers specify an idle speed of around 650 RPM, and the engine is happy there. I have never noted plug fouling to be any better or worse at either 650 or 1000 RPM.

Riding the brakes to control speed is no worse than letting the speed build and then braking. The energy dissipation is the same either way, and the brakes wear out just as fast either way.
 
Dan Thomas said:
Riding the brakes to control speed is no worse than letting the speed build and then braking. The energy dissipation is the same either way, and the brakes wear out just as fast either way.
Click to expand...
The difference is that giving the brakes a break allows them to cool between applications, so the end temperature will be lower than if you ride them all the way.

Not a huge deal for light planes, but if someone has plans to fly professionally, it's easier to start right than to change.
 
MauleSkinner said:
The difference is that giving the brakes a break allows them to cool between applications, so the end temperature will be lower than if you ride them all the way.

Not a huge deal for light planes, but if someone has plans to fly professionally, it's easier to start right than to change.
Click to expand...

Braking to reduce speed involves more energy dissipation per second than riding the brakes, and the discs get hotter doing it. The result is more and wider thermal cycles and increased risk of the metallic lining trying to weld to the disc and tearing it up. There are plenty of ways to misuse those brakes. They're tiny compared to the brakes in your car, and were never intended for the same sort of use you might see on the street.
 
dillardrg said:
Here is where your 1000 RPM comes from;

http://www.lycoming.com/sites/default/files/SL185B Fuel, Higher Octane Aviation, Use of 100LL for Engines Rated 80_87 Octane (1).pdf

Note that it is suggested only when you are stopped. When taxing use the throttle as needed.
Click to expand...

When I maintained six to eight flight school airplanes, we taught idle taxiing. 1000 RPM ate up brakes and discs and also hurt the prop, since dragging the brakes pulls the nose down and the prop gets closer to the surface, and that 1000 RPM sucks up any loose debris and dings up the prop. The tires also suffer increased wear, from that bit of drag. Airline guys will tell you that it isn't the landings that eat their tires; it's the braking.

Believe me, if you own an airplane you start paying attention to keeping costs down, and if you have to pay for new brake linings and discs and tires and prop repairs, you change your habits once someone points out what's causing the wear. I find a lot of discs worn below the manufacturer's minimum thickness, sometimes from bad habits, sometimes because the previous mechanics didn't check them or didn't know there were minima. Thin discs heat up faster and brake effectivness fades real quick.

I did not find plug fouling from idle taxiing. That came from too much circuit work, with the engine windmilling much of the time. Beat the fouling by switching to REM37BY plugs, which are very foul-resistant.
 
The average taxiing speed at my busy Class D airport is about 30 knots... I can see that by looking at my GPS ground speed while taxiing on the main taxiway and just going with the flow. Obviously I go more slowly leaving the hangar and moving towards the main taxiway. Once on the taxiway though... Nobody goes at walking speed.
 
Dan Thomas said:
Braking to reduce speed involves more energy dissipation per second than riding the brakes, and the discs get hotter doing it. The result is more and wider thermal cycles and increased risk of the metallic lining trying to weld to the disc and tearing it up. There are plenty of ways to misuse those brakes. They're tiny compared to the brakes in your car, and were never intended for the same sort of use you might see on the street.
Click to expand...
If by "tiny" you mean capable of stopping a vehicle weighing somewhere from 15,000 pounds to upwards of 500,000 pounds from speeds in excess of 150 knots, I think most people would disagree...and at least one manufacturer of those airplanes seems to disagree with your assertion that allowing the brakes to cool during taxi is bad.
http://www.boeing.com/commercial/aeromagazine/aero_17/brakes.pdf
 
flight2000 said:
I also pull the yoke to the full aft position which allows the elevator to act as a giant speed brake. Got that trick from a Beech PPP instructor during my transition training.
Click to expand...

A "giant speed brake" probably has no measurable effect at speeds we're talking about here... Sounds like another useless "trick".
 
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MauleSkinner said:
If by "tiny" you mean capable of stopping a vehicle weighing somewhere from 15,000 pounds to upwards of 500,000 pounds from speeds in excess of 150 knots, I think most people would disagree...and at least one manufacturer of those airplanes seems to disagree with your assertion that allowing the brakes to cool during taxi is bad.
http://www.boeing.com/commercial/aeromagazine/aero_17/brakes.pdf
Click to expand...

A Boeing uses far different brake materials than your lightplane, and they're in packs that are harder to cool. Other than that, hot brakes are less effective than cool brakes, since brakes turn kinetic energy into heat, and hot brakes can't absorb much more heat. That article is more about uneven heating and accumulated heat between short flights.

At any rate, I replaced too many brakes worn out by poor taxi technique.
 
Dan Thomas said:
At any rate, I replaced too many brakes worn out by poor taxi technique.
Click to expand...
Yeah, I've had a couple of jobs where I've been told "we hired you, and all of a sudden our brakes last longer."

Come to think of it, I went through almost TBO on my Maule without ever replacing brakes.
 
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mtuomi said:
A "giant speed brake" probably has no measurable effect at speeds we're talking about here... Sounds like another useless "trick".
Click to expand...
I can sometimes pick the tail up off the ground while taxiing so that suggests that there is some effect.
But you have to be faster than walking speed to do that.
 
coloradobluesky said:
Normal taxi speed is around 8 to 10mph, which is faster than walking speed. That walking speed is from before GPS's.
Click to expand...
"Walking speed", specifically "No faster than a brisk walk", is from before brakes.

WWI, and before, the airplanes did not have brakes. The military used wing-walkers who walked/ran alongside the taxiing airplane to aid in stopping and turning. If you taxied "faster than a brisk walk" they couldn't keep up. People have been repeating it, without understanding it, for nearly one-hundred years.
 
I think CFIs say "walking speed" to keep students from taxiing at 25 mph and risk having an inadvertent lift-off or loss of control. 10-12 mph (a pretty reasonable taxi speed) "seems" almost like walking speed from the elevated perch of the left seat.

With a lightweight composite prop, my engine doesn't idle well at all at 700 rpm, so I'm usually at 850 to 900. Yes, I do have to drag the brakes lightly when taxiing, but brake pads are pretty cheap in the overall scheme of things.
 
I taxi at whatever speed I get at 1000 RPM and the mixture so lean that trying to pull from grass parking onto asphalt will kill the engine unless I push the red lever forward some. Often around 10-12 knots per the Garmin.

En again, on my first Cessna flight in several years, I pulled the mixture back in rollout like I always do in my mooney, and the engine died. :rolleyes: I was able to coast off the runway and crank her back up.
 
Dan Thomas said:
The 1000 RPM thing is an OWT. The engine manufacturers specify an idle speed of around 650 RPM, and the engine is happy there. I have never noted plug fouling to be any better or worse at either 650 or 1000 RPM.

Riding the brakes to control speed is no worse than letting the speed build and then braking. The energy dissipation is the same either way, and the brakes wear out just as fast either way.
Click to expand...

Caution: Not true on all engines. Dig for the manufacturer's data.

hindsight2020 said:
I taxi with the red lever. True story. :D
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I can do that. Another true story. But it slows the engine below the manufacturer's recommended idle speed on mine. The vernier mixture helps... Just a leeeeeetle twist... It'll stumble but not die.
 
roncachamp said:
The old adage that one must never taxi faster than a person can walk is a load of crap. It's sound where people are actually walking, between hangars and on ramp areas, but on dedicated taxiways it just wastes time and money.
Click to expand...

Agreed. Big airports make this really obvious. According to google, it's 2.51 miles from my hangar to departure end 36L at HSV. A brisk walk is (again according to googled sources) 3mph. That's a 50 minute taxi, following the "no faster than you can walk" rule.
 
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