Holding the Brakes

[Dan Thomas]

I'm in a 152 set to idle below 1000.

From a 152 POH:

What does the "or less" mean? Does it say 1000 RPM minimum? It does not. The CFI is not reading too carefully.

A few pages later in that same POH, Cessna writes this:

To keep the speed and the use of brakes to a minimum, you must use minimum power when taxing. There is no magic there.

The 152 has the Lycoming O-235. Those engines are famous for plug fouling, but as I noted before, the extended-nose plugs fix that permanently. REM37BY or, better yet, UREM37BY. They pay for themselves quickly by extending the plug-cleaning intervals.

 

[Jim_R]

I don't know why you abuse your airplanes, but idling at 1200 RPM and dragging your brakes is stupid. It would help if you had some dual from a knowledgeable instructor.

I don't know why you think I idle at 1200 when I explicitly said that I do not.

I don't know why you think idling and taxiing are the same thing. Not all planes are float planes.

I don't know why you keep talking about taxiing when the OP's situation involved holding the brakes prior to takeoff.

 

[Albany Tom]

I'll be a jerk again. Not to the student, but to the CFI and school - if you want to idle really fast, because you don't lean the engine on the ground, then you should also make sure the brakes work. Someone's going to take one of your planes to a busy place and have an accident at your expense. Especially not having a working parking brake, that's just stupid.

To the OP, if the school is doing things that are stupid and obvious, what things are they doing that are equally stupid but less obvious? Be careful.

The place I learned had PA-28's, like probably half of the schools in the US, and they had some problems with fouling from CFI's that didn't lean on the ground. The simple fix is to lean. And fouling is one of many reasons to do the mag check on the ground. That checks that the plugs are working just as much as the mags, and it is possible to have a plug fouled enough to not work.

 

[Lindberg]

I don't think I've ever used the parking brake on an airplane. On some tail draggers, they're downright dangerous.

 

[Dan Thomas]

I don't think I've ever used the parking brake on an airplane. On some tail draggers, they're downright dangerous.

In some POH's Cessna tells the pilot to set the parking brake for the runup. I've never done that; I don't trust those brakes enough. But they are handy once in a while to hold the airplane on a slope while you get out and chock the wheels.

Never use them to hold the airplane long-term; those Buna O-rings in the master and caliper cylinders will take a set from the pressure and will start leaking, particularly the caliper O ring, once the pressure is off.

 

[Albany Tom]

I don't think I've ever used the parking brake on an airplane. On some tail draggers, they're downright dangerous.

I agree about tailwheel, for that matter I try to avoid using brakes at all when landing a tailwheel. But I always use the hand brake for tricycle on run-up. If the plane also has toe brakes, I'll apply those as well, but I think I had my PPL before I flew more than a couple of times with an airplane fancy enough to have toe brakes. No matter what, first check of the run-up is to make sure the brakes hold.

Maybe because of my background, or maybe because I'm weird, between the two I'd rather have a functional hand brake than toe brakes in a PA-28. Maybe because it's easier for me to brake on a slippery runway with handbrake.

 

[Capt. Geoffrey Thorpe]

For currency with a tailwheel, the FAA requires full stop landings. So I typically stand on the brakes while doing stop and go's to give me the maximum length of run way in front of me for the "go".

 

[Dan Thomas]

For currency with a tailwheel, the FAA requires full stop landings. So I typically stand on the brakes while doing stop and go's to give me the maximum length of run way in front of me for the "go".

A technique taught by JAARS International, a mission aviation agency that used a lot of Helio Couriers in overseas work, involved touching down tail-low, at minimum speed, and then raising the tail to level or even a bit nose-down, and applying fairly heavy braking while modulating the brakes and using full elevator to keep the airplane from nosing over. This took the lift out of the wings by taking the AoA to nearly nothing and gave max traction for braking. I've used it in the Citabria but never taught it to anybody. Too much risk. It's amazing how short one can land this way.

 

[dbahn]

A technique taught by JAARS International, a mission aviation agency that used a lot of Helio Couriers in overseas work, involved touching down tail-low, at minimum speed, and then raising the tail to level or even a bit nose-down, and applying fairly heavy braking while modulating the brakes and using full elevator to keep the airplane from nosing over. This took the lift out of the wings by taking the AoA to nearly nothing and gave max traction for braking. I've used it in the Citabria but never taught it to anybody. Too much risk. It's amazing how short one can land this way.

I'm told by the Maule company that they don't teach wheel landings (they log the endorsement to exclude them) because the CG is high enough above the wheels to make a nose over more risky.

 

[GeorgeC]

A technique taught by JAARS International, a mission aviation agency that used a lot of Helio Couriers in overseas work, involved touching down tail-low, at minimum speed, and then raising the tail to level or even a bit nose-down, and applying fairly heavy braking while modulating the brakes and using full elevator to keep the airplane from nosing over. This took the lift out of the wings by taking the AoA to nearly nothing and gave max traction for braking. I've used it in the Citabria but never taught it to anybody. Too much risk. It's amazing how short one can land this way.

There are other ways to land? That's how my t/w instructor taught all of his students. Lasers, eight o'clock, day one!

 

[Dan Thomas]

I'm told by the Maule company that they don't teach wheel landings (they log the endorsement to exclude them) because the CG is high enough above the wheels to make a nose over more risky.

A true wheel landing does not require the tail that high. The tailwheel might only be a few inches off. It all depends on the airspeed, after all. Remember that airspeed and angle of attack are linked inseparably, and a few knots faster will give a competent pilot a nice wheel landing in a crosswind, while an incomperent pilot will get a nasty bounce out of it.

Taildraggers are typically designed to have the main wheel axles 15 degrees ahead of the airplane's CG, located both longitudinally and vertically, in level flight attitude. It would take some aggressive action to actually tip the thing over. "Safe" trikes do it frequently by landing on soft ground where the nosewheel digs in. A taildragger is actually a lot safer there because the momentum, centered at the CG, isn't trying to drive the wheels down into the surface.

 

[Chrisgoesflying]

Good thing my Comanche only has a parking brake and no toe brakes. I was the master of riding brakes in the Cessnas I got my license in lol. Just a really dumb habit I couldn't lose until I started flying Pipers with no toe brakes. Being hunched over to pull the brake all the time gets old real fast so learning how to taxi without needing the brakes all the time was the only way to keep looking cool in an airplane haha.

 

[Zeldman]

I don't think I've ever used the parking brake on an airplane.

For small GA type planes, I haven't seen one with parking brakes that work properly. Embarrasing to have to call maintenance to come to the runway and unlock the park brakes, hence a reason to NOT use the park brake.

 

[Joepilotmsp]

Back in the dark ages when I was earning my ppl and flying clapped out 152‘s, I thought it was normal the parking brake didn’t work. When I moved beyond to aircraft that were maintained by owners and technicians that actually cared, I realized how handy they could be. I like others here would suggest a back pad to scoot the butt and legs forward. I use one but due to a trashed back. It does make for easier brake applications for us vertically challenged!

 

[Pinecone]

Just had a interesting one.

Landed, taxied to parking, shut down, next thing I know, I am rolling backwards at a pretty good clip.

Hmm, maybe should have set the parking brake. Remember, not all ramps are level.

 

[Half Fast]

Remember, not all ramps are level.

Including fuel farms, which can make things interesting terrifying.

 

[MRC01]

From lycoming service letter l192b:

Avoid prolonged closed throttle idle engine speed operation (when possible). At engine speeds from 1000
to 1200 RPM, the spark plug core temperatures
are hot enough to activate the lead scavenging
agents contained in the fuel which retards the for-
mation of the lead salt deposits on the spark plugs and exhaust valve stems.

Service Letter No. 192 B

Supersedes Service Letter No. L192A January 19, 1988 Models Affected To all Owners and Operators of Lycoming Aircraft Engines. In many cases spark plug fouling resulting from the tetraethyl lead (TEL) in aviation fuels can be reduced or eliminated by proper operating techniques.

www.lycoming.com

If you lean aggressively for ground operations, you will never foul a spark plug. And you'll save gas, reduce pollution, keep the spark plugs & valves cleaner, and reduce the likelihood of carb icing.

Using full rich during ground ops, then idling at 1000+ RPM to prevent plug fouling, is ... well I can't think of a polite word so I'll say it's simply idiotic counterproductive.

 

[Jim K]

If you lean aggressively for ground operations, you will never foul a spark plug. And you'll save gas, reduce pollution, keep the spark plugs & valves cleaner, and reduce the likelihood of carb icing.

Using full rich during ground ops, then idling at 1000+ RPM to prevent plug fouling, is ... well I can't think of a polite word so I'll say it's simply idiotic counterproductive.

Who said anything about idling full rich?

It's worth noting here that with the throttle plate closed, the idle jet controls the mixture, and it has it's own adjusting screw. It draws its fuel from the power circuit, which is why you can shut the engine off with the mixture control, but the amount of fuel we're talking about is so minuscule that it's difficult to choke the power jet down enough with the mixture knob to actually effect the idle mixture without killing the engine (speaking about the common Marvel-Schebler carburetor). It's easier to get the engine into a lean condition with a little throttle (say....1000rpm) as the power circuit starts to come into play. In addition, it gets the combustion chamber temperatures up to the point that the Ethylene dibromide can react with the lead and carry it out the exhaust instead of forming lead oxides that condense on the plugs, pistons, and combustion chambers.

You can believe Lycoming, or not, I couldn't care less. The question was asked why idle at 1000 RPM, and I answered it; because the engine manufacturer says it's a good idea.

Here's a second opinion from Shell:

The Tetra Ethyl Lead used for octane boost in the fuel naturally degrades to form Lead Oxide when it is burned. In reality it is this oxide which gives the octane boost. The problem is that Lead Oxide is a solid up to about 900 deg C which is well within the wall temperatures inside a piston engine.

In order to prevent these deposits from forming, a Lead scavenging compound is added to Avgas 100LL - this compound is Ethylene Dibromide. This scavenger is designed to react with the Lead oxide to form Lead Bromide which is more volatile - becoming a gas at around 200 - 250 oC. This is a low enough temperature to ensure that the Lead is removed from the engine as a gas end it subsequently goes back to the solid phase as the exhaust gas cools in the atmosphere.

As a point of interest the pale brown / ash coloured staining that is often seen leading from the exhausts of high powered engines, such as those found on the warbirds, is in fact Lead Bromide.

To enable this reaction between the Lead Oxide and the scavenger to work, there needs to be a relatively high combustion temperature.

What a lot of people do is conduct the warm up with the engine power lever on the idle stop, and this is inappropriate. The technique for the common Teledyne Continental Motors and Textron Lycoming General Aviation engines is as follows.

After start up, the engine should be operated at 1000 - 1200 rpm for the initial warm up period and not at the 600 -650 rpm idle speed. This serves a number of purposes.

The higher cylinder pressure encourages the rings to seal properly, not only limiting oil egress into the combustion chamber, but also reducing the amount of corrosive combustion by-products going the other way into the sump oil. This technique thus also helps reduce the risk of corrosion problems in the long term by reducing the amount of acids and Lead being pumped into the oil.

Meanwhile in the combustion chamber, Lead Oxides tend to form deposits because of the low combustion temperatures. The temperature for Lead deposits to form tend to be favourable around the spark plugs (as the whole mixture is quite cool before the flame starts to propagate) and on the exhaust valve stem (as the mixture cools after combustion).

Lead Fouling | Preventing Lead Fouling in Aircraft | Shell Global

This article discusses lead fouling, what causes it and the most efficient way to prevent it in aviation engines. Read the full details here.

www.shell.com

 

[MRC01]

Who said anything about idling full rich?

Plenty of pilots and even CFIs say "full rich below X thousand feet", period, no matter where the throttle, RPM & power are. But I did not intend to imply that it was you.

It's worth noting here that with the throttle plate closed, the idle jet controls the mixture, and it has it's own adjusting screw. It draws its fuel from the power circuit, which is why you can shut the engine off with the mixture control, but the amount of fuel we're talking about is so minuscule that it's difficult to choke the power jet down enough with the mixture knob to actually effect the idle mixture without killing the engine (speaking about the common Marvel-Schebler carburetor). It's easier to get the engine into a lean condition with a little throttle (say....1000rpm) as the power circuit starts to come into play. In addition, it gets the combustion chamber temperatures up to the point that the Ethylene dibromide can react with the lead and carry it out the exhaust instead of forming lead oxides that condense on the plugs, pistons, and combustion chambers.

This is true, which is why leaning aggressively is the key word. The mixture knob will be close to cut-off. This is where it is far enough back to lean the mixture at idle. When the engine is idling, in most planes the mixture knob doesn't do much until the last few half-turns

You can believe Lycoming, or not, I couldn't care less. The question was asked why idle at 1000 RPM, and I answered it; because the engine manufacturer says it's a good idea.

Oh, I believe them for sure - what Lycoming and Shell say is true, so far as it goes. Yet their advice is incomplete and misleading because it ignores how effective aggressive leaning is, when eliminating fouled plugs. Not to mention several other additional benefits of leaning aggressively for ground ops, which is why I like to mention it especially for student pilots like the OP, who might not know about it.

 

[Dan Thomas]

Idling at 1000 isn't a bad idea if you run leaded fuel.

Lead Fouling | Preventing Lead Fouling in Aircraft | Shell Global

This article discusses lead fouling, what causes it and the most efficient way to prevent it in aviation engines. Read the full details here.

www.shell.com

If holding a 152 at 1000 rpm is fatiguing, something is wrong. I can't imagine that it should take more than a few ounces of force.

That article actually says this:

What a lot of people do is conduct the warm up with the engine power lever on the idle stop, and this is inappropriate. The technique for the common Teledyne Continental Motors and Textron Lycoming General Aviation engines is as follows.

After start up, the engine should be operated at 1000 - 1200 rpm for the initial warm up period and not at the 600 -650 rpm idle speed. This serves a number of purposes.

The higher cylinder pressure encourages the rings to seal properly, not only limiting oil egress into the combustion chamber, but also reducing the amount of corrosive combustion by-products going the other way into the sump oil. This technique thus also helps reduce the risk of corrosion problems in the long term by reducing the amount of acids and Lead being pumped into the oil.....

....Engines that have been involved with long, low power descents, or have taxied for some distance, can have quite low cylinder temperatures and this - as we now know - can lead to lead fouling. Again the advice from Textron Lycoming and Teledyne Continental Motors to remedy this is: once on the aircraft is on the stand, the engine speed should be kept between 1000 and 1200 rpm until the engine temperatures have stabilised.

Once the temperatures are stable, the engine speed should be increased to 1800 rpm for a period of 15 to 20 seconds, which should generate enough temperature to burn off any deposits. Once this period is past, the engine speed should be reduced to 1000 - 1200 rpm once again and then immediately shut down using the mixture control.

Shell certainly isn't telling anyone to taxi at 1000 RPM. They're telling us to run the RPM up once it's parked.

And Lycoming isn't asking anyone to taxi at 1000 RPM either.

You can believe Lycoming, or not, I couldn't care less. The question was asked why idle at 1000 RPM, and I answered it; because the engine manufacturer says it's a good idea.

From the Lyc Service Letter:

They say to use 1000 RPM after startup and during initial warmup. In the last sentence there, they say to use only the power settings required to taxi. How does one read that to say we should use 1000 RPM to taxi?

And:

As with what Shell says, once you're parked, run the RPM up to clear the plugs. This also helps with the common oil fouling in the smaller Continentals where the lower plugs are so low and close to the cylinder wall that any oil, sucked past the rings at idle, flows into them and fouls them.

 

[GeorgeC]

They say to use 1000 RPM after startup and during initial warmup. In the last sentence there, they say to use only the power settings required to taxi. How does one read that to say we should use 1000 RPM to taxi?

They don't. I know that "A implies B" is not the same as "not-A implies not-B", but I inferred from the above statement that "below 1000 rpm, temperatures are NOT hot enough...". I'm willing to be wrong

Maybe I'm projecting my own habits. A typical pattern: after start, warm up for ~5-10 mins, then it's a short ~1000' taxi to the runup area, do my runup, and then go- long taxi or wait times are not usually a concern for me. If I'm stuck behind a conga line after runup, I'll pull the throttle back.

Thanks for pointing out the cooling aspect or the increased risk of prop damage, those hadn't occurred to me. Maybe not so much a concern for me personally, but certainly true in general- a friend with canard aircraft had to be very careful with temperature management on the ground.

 

[Hang 4]

You can aggressively lean AND idle at 1000 rpm. Both help with lead deposits.

 

[Jim K]

And I will agree that 1000rpm is too much for TAXI most of the time. Get the plane moving and reduce the throttle to control speed rather then dragging the brakes; most of the time that's more like 800rpm. Might be low idle and still dragging the brakes on a windy day.

The OP's question however was regarding holding the plane stationary awaiting takeoff. I maintain 1000 rpm is good practice whenever the plane is stationary to prevent fouling. The planes I fly don't get hot at that rpm, even in the peak of summer. If you fly a radial, a pusher, or something tightly cowled, ymmv. Use low idle if you're flying a B-36