Braking efficiency

[flint4xx]

Does anyone (preferably an engineer) have a rule of thumb for what to do when your POH fails to provide accelerate-go and accelerate-stop distances for anything other than paved dry runways?

I need to know about grass and gravel for a multi-engine turbine certified before present regs.

Thanks.

[djschaut]

flint,

Sorry, I have no turbine time and don't know the answer. Did someone type-rate you in the turbine? He should be able to help. Or, if you have a turbine dealer close by, or know the e-mail address of one, they should be able to help you. There are turbine dealers at www.aso.com/

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DJSchaut

[flint4xx]

FAA didn't require these charts until recently, therefore the manufacturer has none.

Thanks anyhow.

[wxwatcher]

Flint,

DJ emailed me a heads-up question on this a few minutes ago and I was able to catch my local FSDO contact. If the manufacturer doesn't have those charts available, they suggest you contact your local FSDO office and explain the problem. They may be able to help out.

Personal opinion.. You may be able to talk them into an exemption for up to 180 days while you bug the ******* out of the manufacturer to get the charts done or the FAA certification office comes up with something.

If you don't know the location or number of your FSDO office, check the following url:
http://www.faa.gov/fsdo/

That's the national locator page for the FAA's FSDO offices.

Jerry



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Comments and opinions are my own and do not reflect those of my employer.

[wxwatcher]

Flint,

I have one other possibility to check, but I need to know what type acft you have. The FAA has certification offices assigned to the various types of aircraft depending on the type/manufacturer. With that info, I can find out which region has certification authority for the aircraft and may be able to find out how they are going to handle the new requirement for "older" equipment certified before the requirement came out.

Email a note with the info to 9-awp-oak-web@faa.gov. That's the email address for the Oakland AIFSS web page. I'll get it and see what I can track down.

Jerry

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Comments and opinions are my own and do not reflect those of my employer.

[djschaut]

Is that service, or what?

[flint4xx]

Hey guys,
Pretty impressive response!

I work for a government agency operating Beech 1900C's outside the US. I know that one of my co-workers is bugging the manufacturer for more info.

Would you have any idea on where to find the braking coefficients of different surfaces for any aircraft?

Thanks.

[pawpaw]

from looking at flint's handle (flint4xx)
I bet he flies a Conquest.

flint, is my guess right?

[sideslip]

While you are chasing down Goverment/Manufactures information, a starting point for a guesstimate would be landing and takeoff charts for other airplanes. Looking at the charts for a 152 and a 172 (very different aircraft than yours) the takeoff roll is increased by 15% and the landing roll by 45% on dry grass as compared to dry pavement. These figures represent mainly the influence of the coefficient of friction of the landing surface. Thus, as an engineer (not aeronautical engineer) my first guess would be that your plane would behave similiarly. However, I want to repeat that this is just a starting guess and you should pursue people that would be more knowledgeable than me on the subject.

I would also think, from experience, that wet grass will greatly increase the rollout distance over dry grass. Also, from experience, wet grass doesn't affect takeoff distance over dry grass nearly as much as the height and density of the grass. That applies to dry grass verses pavement too.

Gravel, I think, could vary greatly depending upon the makeup and consolidation of the gravel, but would always be greater than dry pavement (another guesstimate as I do not have much experience on gravel). How it compares to grass again would depend on the makeup of the gravel.

The above statements were the Engineer talking. Below is the pilot talking.

My experience on grass is that each strip is different and that you can basically read the POH values and then throw away the book. Grass strips vary so much in surface roughness that the POH values are meaningless. My local airport has a very well kept grass strip. In a 152 or a 172 I can make landings on the grass that are much shorter than those predicted by the POH. However, if I go to a friends private strip the landing roll is considerably longer because the surface is rough and thus, hard to keep the wheels on the ground. Getting out is another story.

One suggestion. If you don't have alot of experience in unimproved field landings, I would find someone that does and learn from them. The big problem in many unimproved fields is the approach and departure path. The standard lefthand pattern is usually a rare exception. In the final analysis, landing and takeoff distance is all about pilot technique. With some good help and lots of practice you will be able to judge strips by flying over and looking at them and will know whether you and your plane are capable of getting in and out of a strip.

Good Luck.

[sideslip]

While you are chasing down Goverment/Manufactures information, a starting point for a guesstimate would be landing and takeoff charts for other airplanes. Looking at the charts for a 152 and a 172 (very different aircraft than yours) the takeoff roll is increased by 15% and the landing roll by 45% on dry grass as compared to dry pavement. These figures represent mainly the influence of the coefficient of friction of the landing surface. Thus, as an engineer (not aeronautical engineer) my first guess would be that your plane would behave similiarly. However, I want to repeat that this is just a starting guess and you should pursue people that would be more knowledgeable than me on the subject.

I would also think, from experience, that wet grass will greatly increase the rollout distance over dry grass. Also, from experience, wet grass doesn't affect takeoff distance over dry grass nearly as much as the height and density of the grass. That applies to dry grass verses pavement too.

Gravel, I think, could vary greatly depending upon the makeup and consolidation of the gravel, but would always be greater than dry pavement (another guesstimate as I do not have much experience on gravel). How it compares to grass again would depend on the makeup of the gravel.

The above statements were the Engineer talking. Below is the pilot talking.

My experience on grass is that each strip is different and that you can basically read the POH values and then throw away the book. Grass strips vary so much in surface roughness that the POH values are meaningless. My local airport has a very well kept grass strip. In a 152 or a 172 I can make landings on the grass that are much shorter than those predicted by the POH. However, if I go to a friends private strip the landing roll is considerably longer because the surface is rough and thus, hard to keep the wheels on the ground. Getting out is another story.

One suggestion. If you don't have alot of experience in unimproved field landings, I would find someone that does and learn from them. The big problem in many unimproved fields is the approach and departure path. The standard lefthand pattern is usually a rare exception. In the final analysis, landing and takeoff distance is all about pilot technique. With some good help and lots of practice you will be able to judge strips by flying over and looking at them and will know whether you and your plane are capable of getting in and out of a strip.

Good Luck.

[flint4xx]

No Conquest currently but some in the past.

[flint4xx]

Sideslip, I agree that transposing similar rules to this situation is why I am here in the first place. I was hoping to find a generally accepted rule of thumb for these runways.

Thanks.

[wxwatcher]

flint,

Checked with local FSDO Part135 inspector. He's not aware of this requirement and would like to know where you found it so he can do some checking. It's possible what you saw was a proposal and not an actual requirement yet. If you could email me that info, I may be able to get a more deffinnative answer to your questions and some idea where to go for the info.

I'll be in the office until about noon local CA time Friday, email: 9-awp-oak-web@faa.gov]
If you don't catch me then, it will be sometime Monday before I can get the answers.

FSDO also wanted to know if you're a Part135 operator, but if you're flying for the fed, guess that question is answered.

Jerry

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Comments and opinions are my own and do not reflect those of my employer.

[djschaut]

flint,
I confess I've never operated a turbine, but don't they publish in emergency procedures a maximum ground roll when there are no brakes? That is, using full prop-reverse thrust? I mean, you can stop the thing without brakes, right? So, I guess a rough guestimate about braking efficiency on very loose gravel or grass wouldn't be any worse than using full thrust-reversers on ice, right?

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DJSchaut

[sideslip]

Flint:

I don't think there would be a really good general rule other than transposing like I did. The variability of the landing surface as compared to pavement is so great that a general rule just would not work like it does for paved runways. My experience has been mainly in Super Cubs and I would say that about 80% of the time, I can land and takeoff in less distance than what would be predicted by transposing the Cessna rule and applying it to Super Cub values. The other 20% of the time I will exceed those distances because of very uneven surfaces and/or approach/departure paths (ok, so I blew a few too). Now I am no where near an expert on off field/unimproved field work, so someone with more experience and skill than me could probably do much better.