Brakes

[s35pilot]

Hi,

 

I've also posted this on the c-a list but since some may not be on that list I posting this here also.

 

I presently have the Cleveland 199-152 brakes. They are ok but I would like a little better braking action. I've done some looking and it looks like my options are as follows:

 

Cleveland makes an upgrade kit (199-196) that converts the existing 199-152 brakes from organic linings to metalic. The piston gets changed so that an insulator can be added between the baking plate and the piston to prevent heat transfer. No one I can find has these kits in stock and they cost about $175.

It should take the brake energy from 192,000 ft-lb to 289,000 ft lb. The Cleveland technical rep said it would be a noticable difference.

 

The other option is the 5 inch Grove Ultra High Performance which is a dual piston caliper with organic linings. The disc is listed as their thickest (for heat absorbtion). They list their energy capacity as 246,715 joules which I think is 181983 ft lb.

 

It appears that the Grove has less energy rating than the Cleveland with the upgrade installed.

 

Has anyone actually done this upgrade to the 199-152 using metalic linings? What was your experience? Is anyone using metalic linings? It is possible to just change to metalic linings but it would probably heat the piston and fluid.

 

Is anyone using the Ultra high performance Grove 57-1 brakes? My gut

feeling is that (despite the published numbers) more pistons mean better braking and heavier disks mean less fade. Experience or thoughts?

 

Has anyone converted to the Grove form the Clevelands? Do I have to make any modifications to the strut, etc? Or is it just a bolt on conversion?

 

 

Thanks in advance

[s35pilot]

Hi,

 

I've learned a lot about my brakes in a short period of time... Thanks to Rob Grove. I would recommend Grove and any of their products based on the know how and honesty they exhibited.

 

I'll try to put down what I've learned. Excuse me if it's not perfect but I'll do the best I can.

 

There are really a couple of primary issues around brake performance.

 

One parameter is the ability to absorb energy until brake fade occurs. Brake fad is caused by the binder melting and the friction between lining and disc decreasing significantly. Metal linings help with this and allow the brake system to continue to function at higher temperatures....Thus absorbing more energy. Heavier discs also hold more heat so increase energy capacity. Rob's opinion was that metallic linings are probably not a good idea on a plane with glass gear legs.

 

The other parameter is the maximum braking force available. In my case I've never had any issues around brake fade. I just wanted to have the ability to stop quicker...(greater brake force). Linings apparently don't have a big effect on the friction coefficient between brake and disc. I really need more force on the brake linings. The brake force is proportional to the normal force on the lining times the friction coefficient. Since I can't do much about the friction coefficient of the lining it looks like I might need to work on the normal force pressing the lining against the disc.

 

This normal force is the brake fluid pressure times the piston surface area. My brakes have the 2 inch piston so I've pretty much maxed out that parameter. I need to work on my brake pressure. When I built my plane I made the lever arm on the brake master easily adjustable and set it to something that seemed "about right". My brakes work good but not as good as I thought they should. The standard for the brake pressure is 400 to 500 psi at the caliper with 100 lb force on the pedal. That's my goal.

 

My brakes are a little spongy, but I think that it is due to the nylon brake lines swelling while under pressure. No easy way to fix that....

 

So that is what I've learned so far......

 

Kindest regards.....Tim

[dust]

I didn't pop in as i am no expert, but i will say that his advice is good, as the concern with heaverier braking power is the increased heat which could deform the strut, i know this is john slades favorite subject

 

enjoy the build or in this case the flying

[Jim Sower]

There was quite an extensive back-and-forth on the Velocity forum last fall about brake performance. It all started when a fellow tried to launch a moderately heavy velocity (maybe 2100 lb - what one would expect on take off) on a ~3000 ft runway. For whatever reason, he changed his mind and tried to abort with 1000' remaining. Sad story is that his brakes faded and he dribbled off the end of the runway at something on the order of 20 kts. As seems to be the rule, there was a drainage ditch in the overrun and he wiped out his landing gear and CS-prop.

 

Lots of chatter about 600 k ft-lb brake systems. Much of it shrill and some a bit hysterical. Not many did the math. If the guy had shut down his engine as step one of his abort procedure, he probably would have made it. 100 lb of residual thrust over 1000 ft = 100 k ft-lb of work. A 2200 lb airplane at 20 kts has just under 39 k ft-lb of energy. If he only had 50 lb residual thrust, he would still have saved work equivalent to 25% more energy than his plane had when it left the runway.

 

How about someone who's flying document this for us (Marc - are you out there?): Shut down the engine coming over the fence, land on the numbers and let it roll. If the first turnoff is as far down the runway as 2000', and your Cozy is anything at all like my Velocity, you'll have a tough time making it (go ahead, John, ask me how I know this .... )

 

For years, I have used "Mixture - OFF" as a primary procedure any time I have more energy than I want, whether it be inability to slow down in the groove or short field or expedited stop or aborted takeoff or whatever. Just shut it down, stop (or land or whatever...)with lots of room to spare, light it off again and taxi to the line. Easiest thing you ever did

 

If you want to stop quickly .... TURN OFF THE F--KING MOTOR !!!

 

A small fraction of the money spent on brake upgrades will pay for a LOT of remedial math training. Sadly, there aren't many reliable courses on "Thinking Outside the Box".

 

Just a theory .... Jim S.

[John Slade]

i know this is john slades favorite subject

 

Wrong, actually.

[Chris Byrne]

Wicks Cat quotes Joules.

Robbie Grove says they are ft/lbs.

 

From comparing pad sizes the Grove pads appear to be at least the same dimensions as the highest energy Clevelands. Not sure if they are made of the same material or if their discs are as thick( therefore as capable of energy absorbtion).

 

There have been numerous discussions on energy absorbtion and the need to have at least brakes capable of the high 200's.

From what I can determine and someone may correct me but C210's and the like have brakes capable of less than 200000ft/lb(this of course dosnt make them acceptable or correct)

 

Here's a different way of looking at the energy requirement.

 

Someone (an experienced Cozy owner)said that the 192000lb Clevelands are capable of locking the brakes on a Cozy. So I deduct that if I stand on the brakes hard enough to lock the brakes (and as yet the Cozy dosnt have anti skid)the tire absorbs all the energy and as long as the brakes are capable of locking you dont have to have brakes capable of absorbing 318000ft/lbs.

Of course the tire might not handle the energy requirements either.

 

Theres many issues in this stopping thing, locked brakes is but one.

 

For what its worth.

 

I purchased the Grove 57-1, havnt seen them yet.

 

Wicks have them listed for less than buying direct.

[John Slade]

So I deduct that if I stand on the brakes hard enough to lock the brakes (and as yet the Cozy dosnt have anti skid) the tire absorbs all the energy and as long as the brakes are capable of locking you dont have to have brakes capable of absorbing 318000ft/lbs.

I don't think this is a meaningful consideration, Chris.

The last thing you want to do in an emergency is lock the wheels, especially in a plane that's steered with its brakes. The brakes need to stand HARD braking without overheating and/or fading. If we're talking about the Cozy, then the Matco triple puck brakes (I got mine from infinity aerospace) seem like the best solution to me. Twice the braking power of the plans Clevlands for less $. Marc Z is using them happily with no heating issues I've heard of.

 

I see this one as a 3 step process...

 

1. Install the most powerful brakes you can buy

2. Like Jim says, have "stop the engine" on your checklist

3. Be ready to lower the nose gear.

 

If you get really good at the last two you could skip the runway all togther and simply touch down on the ramp, then slide the 50 ft into you're parking space.

 

This is after the obvious, don't land fast on a short strip etc. etc.

Those with plans Clevelands seem to use the logic that you should fly the plane in such a way that you avoid the need for good brakes, and that's worked for most of them... so far.

[mplafleur]

John,

 

So what is your favorite subject?

[John Slade]

[No4]

Turn off the motor?

If you turn off the motor the prop will stop spinning "dead sticking "is the phrase I believe, and you will be worse off than having it windmill and creating drag.

You will find it very difficult to go around.

There is very good reason they teach you to land with mixture rich and full rpm on a csu prop.

I'm sorry but I think that's very bad advice

[s35pilot]

Hat,

 

I agree that if the idle speed is set properly and the aircraft attitude is maintained with a high angle of attack that will help. Today I measures the nylaflow tubing swell from no pressure (0.166 in) to (0.204) under max pedal pressure. I am going to switch to a combo of nyloseal and stainless steel after oshkosh. Just didn't wantg to modify it just before a long trip. Just my 2 cents....

[Jim Sower]

<... If you turn off the motor the prop will stop spinning ...>

Exactly. That's the object of the exercise. No idle thrust means that work equal to the energy of the airplane at touchdown (or abort decision time) DOES NOT HAPPEN.

 

<... you will be worse off than having it windmill and creating drag ...>

A. It's not windmilling. It's running at idle (actually, considerably above idle) and creating thrust.

B. If you really REALLY need to stop, you'll be MUCH better off. Idle thrust down a 4000' runway does work (pushes the airplane) that equals or exceeds the kinetic energy of the airplane at touchdown. Do the math.

 

<... very good reason ...>

They teach you rote procedures for normal operations and other rote procedures for emergency operations. They do NOT teach you to think outside the box. Most often, that kind of thing is [vigorously] discouraged.

 

<... teach you to land with mixture rich and full rpm on a csu prop ...>

I'm not talking about every day operations. I thought I was clear regarding imperative stops. This whole thread is about overburdening brakes on an "expedited" stop. A bunch of thrust pushing you forward in an imperitive stop situation is the very LAST thing you want. I would invite your attention to the Velocity abort anecdote in my original post. That guy destroyed an airplane that took him several years and maybe $60,000 to build because of his mindset that "... there's a very good reason they teach you ..."

 

An exceptional situation calls for exceptional action .... Jim S.

[No4]

A dead stick landing is encouraged in the case of a loss of power, as you will have a better gliding distance than if the prop is turning. The standard procedure for an engine failure with a constant speed prop is to go to lowest rpm, which gives the best glide speed. A prop on a plane will work like changing down in a truck to descend down a hill. The air drives the prop which turns the crank and absorbs horsepower through the cylinders. If you had two cars at 100 mph, both went to idle power, one remained in 5th gear, one to neutral, which would travel further? The car in neutral. It's only when you get down to 10 mph that braking action would be better in the car in neutral.

 

Your velocity anecdote simply tells me that this plane was not airworthy, or that the pilot made a poor decision in aborting.

I fly every day into very short strips in the mountains, and would never consider cutting the engine as an aid for a high performance landing. If you are in an aircraft with no/insufficient brakes and no/insufficient steering, and approaching an obstacle, yes I agree it's a good idea to kill the motor; but surely a good pilot with an airworthy plane should never get in that situation.

 

Re. doing the maths, I very much doubt you are getting 100 lbs thrust with the throttle closed. Then you quote ft lbs which is a torque, but seem to be relating it to runway distance available and thrust, and then you say it is work, but that's horsepower, then you say it's energy, but that's calories.

 

 

Again I have to say that I think that is bad advice to give people, and dangerous.

 

 

 

[Jim Sower]

<... A dead stick landing is encouraged in the case of a loss of power ...>

I had always thought that a dead stick landing was INEVITABLE in the event of loss of power:confused:

 

<... standard procedure for an engine failure with a constant speed propstandard procedure for an engine failure with a constant speed prop ...>

You keep changing the subject on me. I have not been (nor do I intend to start) discussing constant speed props. This is the Cozy forum and CS props are not common on Cozys.

 

<... tells me that this plane was not airworthy, or that the pilot made a poor decision in aborting ...>

The plane was perfectly airworthy. The pilot was launching heavy in a high density altitude, short runway situation. He determined a go-no-go speed for the 2000' point on the runway. He got there, didn't have his "go" speed and aborted. He did the standard abort procedure: Throttle - IDLE; Brakes - Max Braking. If he'd substituded Mixture - OFF for the first step, he'd still be happily flying his airplane. Thats my WHOLE point!!!

 

<... very short strips in the mountains, and would never consider cutting the engine as an aid for a high performance landing...>

Why not? Aside from vague references to go-around you have given no reason for this mind-set. My own description of high performance landing involves having the field made (power off) and NO reason to go around. Under those circumstances, why not dramatically improve your ability to stop by shutting down the engine? Help me out here:confused:

 

<... no/insufficient brakes and no/insufficient steering, and approaching an obstacle, yes I agree it's a good idea to kill the motor...>

Now we're getting some place! What I have been describing is an EMERGENCY PROCEDURE !!! You do it in an EMERGENCY. May I suggest that if you wait until you have "no/insufficient" brakes before you shut down, it's already too late for that action to help. Idle thrust has already contributed to your brake failure. You shut down any time your brakes are going to be challenged so you can PREVENT "no/insufficient" brakes

 

<... a good pilot with an airworthy plane should never get in that situation ...>

I disagree. A PERFECT pilot in a PERFECT airplane will never get into that situation. That line of reasoning has all of the intellectual allure of stating that "a good pilot with an airworthy airplane will never have an emergency". OK for you perhaps, but neither I nor my airplane are perfect, and neither are the "emergency procedures" I learned as a student. The procedures are, however, a good point of departure and can and should be improved upon. That is what I am advocating. I am suggesting that a "one size fits all" approach will inevitably have holes in it through which people will fall and get hurt needlessly.

 

<... very much doubt you are getting 100 lbs thrust with the throttle closed ...>

That was an estimate. It might be 50 lbs. What do you think idle thrust is? My Velocity will taxi at about 10-20 kts at idle. When I push it, it feels like a lot of shove to get it moving and keep it moving. Has anyone measured this??

 

<... you quote ft lbs which is a torque ...>

Actually, torque is lb-ft. Ft-lb is the measure of both work and energy. They are intimately related in that they produce and consume each other. As you raise an object off the ground, you do W ft-lbs of work (in the amount of W=wd where W is work, w is weight and d is distance). When you drop it, it hits the ground with with E ft-lb of kinetic energy (in the amount of E=mv^2/2 where E is inergy, m is mass and v is velocity). W and E will be equal in this experiment.

 

<... you say it is work, but that's horsepower...>

Horsepower is POWER which is the RATE at which you do work and is measured in ft-lb/sec (work/time).

 

<... you say it's energy, but that's calories ...>

True. Also ergs. Further discussion will require at least a nodding acquaintence, on your part, with Mr. Newton.

 

I never stated or implied that engine shutdown should be a daily activity. I said that in instances where brake capacity might be challenged, it will very significantly reduce the amount of work the brakes have to do.

[No4]

Jim,

I apologise for calling ft-lb's torque, it's a unit I have not encountered before as work or energy. I have seen it used as a measure of torque.

I don't really have a problem with you suggesting cutting the motor on the ground, but I think the main benefit to your friend is that it would have done less damage to the prop/ motor.

As for encouraging people to make dead stick landings, I think you are wrong about the benefits.

If I am worried about landing I will make a low pass in bad weather configuration, slightly to the right of the strip, make one more circuit, then come in with full flap as close to the stall as possible, with as much power as I can use, then cut the power when i cross the fence.

At any point I can go around, If I get a gust of wind, a plane lines up on the runway, an animal, other traffic, or if I misjudge the approach . With a dead motor you are committed.

I really don't think it is good advice to encourage people to do this.

[Jim Sower]

I think we're repeating ourselves, but I will submit this one LAST post.

 

<... don't really have a problem with you suggesting cutting the motor on the ground ...>

I had always thought that was where aborted takeoffs took place:confused:

 

<... encouraging people to make dead stick landings ...>

I have never done that. I have suggested that shutdown JUST PRIOR TO TOUCHDOWN when UNAVOIDABLY high/fast (like when there is an obstacle - such as a tree line - near the runway threshold that makes deceleration in a VERY CLEAN airplane impossible). How you got from "expedited stop" and "aborted takeoff" to "dead stick landing" is beyond my comprehension. How shutting down a second or two before touchdown becomes a "dead stick landing" is a stretch I am unable to make. Perhaps we should both revisit my original post.

 

<... the main benefit to your friend is that it would have done less damage to the prop/motor ...>

Once again, PLEASE do the math:

100 lb thrust for 1000' = 100,000 ft-lb work

2100 lb airplane at 30 kts = 83,700 ft-lb energy

 

50 lb thrust for 1000' = 50,000 ft-lb work

2100 lb airplane at 20 kts = 37,200 ft-lb energy

 

If he ran off the runway at 20 kts and 50 lb residual thrust, or 30 kts and 100 lb residual thrust, shutting down the engine instead of merely "chopping power to idle" WOULD HAVE PREVENTED HIS BRAKE FAILURE (FADE) ALTOGETHER. He would have STOPPED with ROOM TO SPARE.

It would have worked for him. It HAS worked for me.

 

<... encouraging people to make dead stick landings ...>

I'm suggesting that it is a VIABLE, VALUABLE TOOL under appropriate conditions to shut down JUST PRIOR TO TOUCHDOWN. This is NOT a "dead stick landing". I am NOT recommending it for daily or regular or indiscriminate use. Please revisit my original post. I recommend shutdown before touchdown as ONLY an UNCONVENTIONAL or EXCEPTIONAL PROCEDURE for use ONLY in an APPROPRIATE situation. However, shutdown instead of merely chopping power to idle will ALWAYS be beneficial in ANY situation that requires an "expedited" or "high-performance stop".

 

<... low pass in bad weather configuration, slightly to the right of the strip, make one more circuit, then come in with full flap as close to the stall as possible ...>

I should have caught this MUCH sooner. You are talking about Cessnas or something that lands very slow and has big old flaps and stuff like that. This is the COZY forum. EVERYTHING I have said relates to a VERY clean airplane, with NO flaps that comes across the fence at about 80 kts, does NOT have a CS prop and NO DRAG of any consequence (certainly nothing like flaps and rivets and fat and CS props). Do you have any experience at all in such an airplane? I would not be advocating cutting engines on the Cessna list or the Piper list. Rutan derivatives (Long-EZ, Cozy, Velocity) are VASTLY different from Cessnas and Pipers. They operate in a different envelope and have much different parameters. Your comments are sort of like a C-130 pilot lecturing an F-104 pilot on aborted takeoffs or short field landings. Your stuff works great in your world, but is mostly irrelevant in mine.

 

<... At any point I can go around, If I get a gust of wind, a plane lines up on the runway, an animal, other traffic, or if I misjudge the approach ...>

If you are less than 100-150 meters from touchdown (coming over the fence in my parlance) when you finally become aware of one of the conditions you list, you are on instruments (in the sense that there is "no visual reference to the horizon when you have your head up your ass") .

 

Best regards,

Jim S.

[ekisbey]

Jim,

 

I'm not really qualified to interject here, but something is nagging at me that I hoped you could clarify. You speak of thrust generated by an idling engine. It would appear to me that there is a kind of threshold speed above which the drag generated by an idling prop is equal to or greater than drag generated by a stopped or windmilling prop, especially if it's been installed to stop in the dead zone behind the strakes. In other words, above that airspeed, the prop is not providing thrust, but is instead contributing to drag.

 

I don't know whether this is true or not, but if it is true, it points to my question. At what speed does this occur and is this speed significantly different from the normal landing speed of the MkIV?

[No4]

Yes Evan you are correct.

Idle thrust at all speeds would be found if we were using rocket motors or jet engines.

A prop connected to a turbine, for example a PT6 in a King Air is merely connected to a gearbox and a small turbine wheel, a separate turbine is connected to the compressors. This is why you will see turboprops attach strops to the props on the ground to prevent them windmilling.

A prop connected directly to a reciprocating engine however will try to turn the pistons, and experience resistance through compression. Watch someone try to hand start a prop. An aircraft such as a DC-3 has 1830 cu in of compression, and if the prop is left at full course, the prop is unlikely to start windmilling at anything less than a gale.

Thrust figures do not give the full picture of how fast an aircaft will travel. Excuse if I work in metric. To achieve 10 newtons of thrust you can accelerate 10 kg of air at 1 metre per second, or 1 kg of air at 10 metres per second. The first example will not be able to travel at greater speed than 1 m/s, the second not more than 10 m/s. Out of interest if you use the equation for kinetic energy 1/2 m v2, you can see that the first example uses 5 joules, and the second 50 (sorry I'm on a public computer and may have used the wrong units). To equate this to aircaft read helicopter, prop, high bypass turbo fan, low bypass turbofan , and ultimately pure jet, all have limiting speeds due to the amount of thrust they produce, and the rate at which the air is forced away from the aircraft.

At Idle the engine ticks over at 800 rpm, and I doubt if it makes more than 20 hp. A fixed pitch prop will be 70% efficient at it's ideal design speed, so at idle a 150mph cruise prop will propably be somewhere around 40% efficient, 8 Thrust horsepower, or less.

The prop will provide thrust at idle up to a walking pace which is usual in my experience, then go through a period of neutral thrust, and then if the plane is travelling any faster it will absorb energy through the prop into the compression of the cylinders.

I can push a cherokee with one arm, and at a maximum equate it to lifting a 20 lb weight above my head. I think 20 lbs of residual thrust below 30 knots is all the residual thrust you will experience.

Cutting the mix will remove a small amount of power, but if the prop stops spinning above 30 knots I believe you will be worse off. I have made those numbers up, to calculate it properly you would have to consider density, engine condition, prop pitch etc, etc,

I draw again to the analogy of the automobile.

3 lanes of traffic approach a red light. In lane one you have a Kenworth shifting down through 14 gears, using the engine brake constantly keeping the revs high, and using the wheel brakes, similar to the constant speed prop, lane two the driver leaves his car in 3 rd gear and uses the brakes, similar to the fixed pitch prop, finaly the 3 rd car slips into neutral and coasts in on the brakes, a stationary prop.

The point at which drivers 1 and 2 finaly depress the clutch and slip into neutral to stop crawling forward is equivalent to the point at which you may receive some benefit of cutting the mixture. But again if you need to do that you may be approaching a collision in which case I would also cut the masters, mags, turn off the fuel cock, fasten my safety belt, open the door to avoid it jamming, and concentrate on finding a soft spot to hit.

Jim, I like your analogy of the C-130 to the Starfighter, and yes I fly dirty old 172's and Cherokee's. You are correct that I have never flown a greasy canard, yet hopefuly one day I will, I'm still working my way through Dust's book of good excuses. However I understand that canard's don't stall, just develop sink, so surely to achieve a similar descent you may use power off and a say a neutral canard position, or a slight amount of power with the stick slightly further back and a slightly higher angle of attack? If that is possible, wouldn't it be advantageous to approach like that and cut the power, as opposed to gliding in?

[Jim Sower]

<... there is a kind of threshold speed above which the drag generated by an idling prop is equal to or greater than drag generated by a stopped or windmilling prop ...>

With the clear understanding that I can't quantify this, I'll give the physics a qualitative shot.

 

When the airplane is at rest or at low speeds, engine at idle, the engine is driving the prop and the prop is producing thrust. At flying speeds engine at idle, the prop is driving the engine and the prop is producing drag. Obviously, at some speed in between, you will reach a point (determined by speed/rpm/pitch) where the prop and engine neutralize - there is no thrust or drag from the prop. at faster speeds, the prop produces drag, at slower speeds it produces thrust. The forward speed at which this neutral point occurs is a function of prop rpm, prop pitch and velocity (TAS). You have probably noticed that an engine that idles at 600 rpm in the chocks can't be slowed below 1000-1200 rpm at 80 kts in the landing pattern. This is caused by the prop driving the engine to a higher rpm than the power setting would otherwise permit.

 

I have heard folks claim that a stopped prop has less drag on the airframe than a windmilling prop. Their explanation of the physics involved was pretty fuzzy, so I take no position. I intuit that the difference is not at all substantial. As for a windmilling prop having less drag than a prop with the engine running, I don't believe that notion would pass muster in a high school physics class. It's patently bullshit. A windmilling prop has to turn the engine. Overcoming compression requires work and absorbs power. The power required will be the drag on the prop times the speed of the airplane. If the engine is running, however slowly, it is producing power. Period. No exceptions. At a given speed, the power produced by the engine running is subtracted from the power required to windmill in the previous example, reducing the amount of power the prop has to apply to the engine (since the engine is helping out). At the same airspeed, the drag on the prop must therefore be smaller.

 

One thing about windmilling v. stopped engine: If you have any ambitions about restarting the engine, KEEP IT WINDMILLING. My best information is that an O-235 will almost certainly windmill above about 85 kts, and will definitely be stopped below about 75 kts. Once stopped, the airspeed has to be increased to upwards of 120 kts to get it started windmilling again. You might want to keep that in mind as you select a glide speed.

 

I've only had one really, truly, no sh*t, no drill dead stick landing. I ran out of gas (funky transfer problem) at 6500 ft about 6 miles NE of the airport I was trying to get to. I shot the approach at 80 kts and the engine windmilled throughout (although I didn't notice at what rpm - my attention was focused elsewhere). The airport (PHN) had a 5000' runway that I thought I could make a downwind entry to. I found it very valuable and comforting to be looking at substantially the same picture flamed out as I do every day. I played the belly board to arrive high at the 180 and deepend my 90 a little when I saw I was still high. I was still a little high in the groove so I did a [bit too much of a] high dip, retracted the belly board, just cleared the overrun and ended up planting it pretty much right on the numbers (terrible idea to do shoot for that - you squander all of your slack just to look good, and stopping is never a problem when you're flamed out).

 

Anyway, since brakes is the name of this thread I'll point out that I couldn't hardly make the damned thing roll to the midfield taxiway. I barely was able to clear the active and had to push it the rest of the way to the ramp. If I'd braked hard, I would have stopped in under 1000' (it typically takes me 2500'-3000' of moderate to heavy braking to stop - depending on what I weigh how much I want to abuse my brakes). Soooooo .... shut down the engine ANY time you find yourself in a situation where your brakes even MIGHT be challenged. After you're safely stopped, you can restart and taxi to the ramp as if nothing happened.

 

Just a theory .... Jim S.

[mplafleur]

I have a friend who has the followinf problem with his Matco brakes:

 

There is no mushiness. When we bleed the brakes everything is very firm. Then after several weeks of inactivity I get about 3 inches of air in the line directly below the master cylinder. The brake pedal goes all the way to full travel... no amount of pumping makes it better. I have transparent brake lines, so I can see the air in the line. This , to me, says that all of the fluid in the master cylinder and its reservoir has gone some where and is displaced with air. Maybe I am miss interpreting???

 

He cannot find any leak or fluid outside of the system. Any ideas?

[Jim Sower]

No4 (is that a given name or a surname?)

<... use power off and a say a neutral canard position, or a slight amount of power with the stick slightly further back and a slightly higher angle of attack? If that is possible, wouldn't it be advantageous ...>

What you are describing sounds wierd to me and seems to presuppose a very draggy airplane of conventional configuration.

 

<... I understand that canard's don't stall, just develop sink ...>

Canards DO stall. The MAIN wing on a canard airplane doesn't stall. The canard does, you lose pitch authority, the nose drops, you pick up a little speed, the canard starts flying again, the nose comes up, canard stalls again, the nose drops again and on and on. That's what we call "pitch bob". The airplane just continues to porpoise.

 

You seem to be sneaking up on the notion of flying an approach at or near canard stall and try and land that way. You can do that. It is an accepted emergency procedure for loss of airspeed indication. Pull the stick full back, use the power for altitude control and pitch-bob all the way home. The problem is that with the canard at or near stall, you have NO pitch authority. Like, it's impossible to flare for landing. The nose will NOT go up. That's dicey on a good day, and I find it unacceptable except in dire circumstances.

 

We seem to find ourselves back in the 172-EZ C-130 F-104 disconnect again. How about, just for perspective, I tell you how I came to be so enthusiastic about shutting down and its dramatic effect on energy reduction.

 

From the day I bought my Long-EZ, landings were frustrating. I weigh about 250 lbs and my wife is another 150-160. That being the case, 70 kts is where I start to really run out of pitch authority, so I can't go as slow as I would like, or as some folks do. Additionally, I like to fly a fairly tight pattern. From the downwind entry all the way to touchdown, I like to ALWAYS be situated where if the engine quits, I can retract the speed brake and land [relatively] safely.

 

My pattern was 80 - 90 kts at the 180, idle, belly board out; 80 kts at the start (top of the groove, rolling out of turn to final); 75 over the fence, touch down at 70. I would be set up nicely at 80 kts at the start. Throttle wrapped around the idle stop, belly board out, both rudders deployed and find myself STILL at 80 kts coming across the fence. I would hold off to touch down at 70 kts and find myself floating well over 1000' down the runway bleeding off those last 10 kts. Sometimes, if I was even a little bit high at the start, I would actually ACCELERATE in the groove from 80 to 85 or so. Despite no power at all and every drag device available fully deployed.

 

One day, in total frustration at 85 kts as I crossed the fence (at the end of the overrun - maybe 150 meters or so from the runway) I decided SCREW THIS and shut the engine down. Voila' - squeaked on nice as you please, right on the numbers, right on speed. I restarted on rollout and went on about my business. I was doing this maybe every third pass, when I was real fast and it always worked perfect. If I waited until I was stopped before I cranked it up again, I found it childs play to make the first turnoff - something I'd NEVER been able to do heretofor.

 

This is a VERY effective decelerator, but NOT right for day to day operations. That's when I discovered that I could slow down with a high-dip in the groove - from a 3-deg glide slope, dive down to a 2-deg slope and kind of drag it in flat. This was not as radical as shutting down in the overrun, and it worked pretty reliably but I was always a little uncomfortable with real flat approaches. If there was any kind of obstacle (like a tree line) off the end of the runway, I could always fly a normal glide slope and shut down on late final. That's how things stayed until I finally discovered and addressed the root cause of the problem.

 

Anyway, that's how I got the way I am. I never had enough drag to slow down without assertive measures.

[Jim Sower]

mplafleur, was said:

<... Then after several weeks of inactivity I get about 3 inches of air in the line ...>

 

Do the brake lines "rise" all the way from the calipers to the reservoir? That is, is it "uphill" ALL the way to the master cylinder and reservoir - no "high" places - so a bubble could even theoretically travel all by itself from the caliper to the reservoir? If not, can the plane be oriented (like block the nose up) so as to achieve that situation?

 

I had a situation once where the outlet of the master cylinder (to the brakes) was just a tiny bit higher than the inlet (from the reservoir) and I had a bubble in the master cylinder that was impossible to bleed out. I had to remove and tilt the master cylinder.

 

One step in the trouble shooting sequence .... Jim S.