General questions cessna 172R

[Mikezulu]

Hi was just wondering if anyone could help me out with some of these questions im having trouble with, part of my ground course study for my ppl.

max speed for moderate and severe turbulence? (flight manual gives me the recommended air penetration speeds but it doesnt say for severe or moderate turbulence) so not to sure..

what is the limiting factor for crosswind?

How did cessna arrive at their cross wind figure for the c172R?

factors that influence a particular figure to be nominated as Vne for an aircraft???

what is a trigger notam?

where would you find the table detailing when a SPECI should be issued?

what is the max carb/heat drop in rpm? (havnt flown in a carb heated aircraft yet).

Any help would be appreciated thanks.

[flyinkiwi]

Whats wrong with asking your instructor(s) for the answers? :confused:

[Mikezulu]

good question, i will but theres lots of questions to go around :)

[Steve888]

max speed for moderate and severe turbulence? (flight manual gives me the recommended air penetration speeds but it doesnt say for severe or moderate turbulence) so not to sure..


If there isn't a different number, I'd imagine it would be the same. That being said, severe and even moderate turbulence is not something you want to be flying in in a 172. If there is severe or moderate turbulence this will be outlined in the ARFOR or SPECI and I would seriously reconsider going if there fell on my route.


what is the limiting factor for crosswind?


For a high wing aircraft it's usually when you run out of rudder and/or aileron to keep the aircraft straight. For a low wing it's often the height of the wing above the ground. For some twins, it can be the height of the propellor.


How did cessna arrive at their cross wind figure for the c172R?


Often the crosswind figure in the POH will be defined as 'Maximum Demonstrated Crosswind Component'. This is the maximum crosswind that was used in flight testing.


factors that influence a particular figure to be nominated as Vne for an aircraft???


Since Vne is the point at which structural failure can occur, the structure of the aircraft, how it's built etc will contribute to this. There is also a safety factor added, but you should never go above red line.


what is the max carb/heat drop in rpm? (havnt flown in a carb heated aircraft yet).


This should be in the POH or checklist for the aircraft. The RPM will drop when you put carb heat on because the air coming in will be warmer and therefore denser so the fuel/air mixture enriches, lowering the RPM.

[VH-XXX]

Since Vne is the point at which structural failure can occur


I hope not!!!!

Don't worry MikeZulu, the wings won't simply fall off when you hit VNE.

[niksmathew24]

Hey mate,
Don't know all the answers, but a few I know.

First of all the speeds are just reference limitations issued by the aircraft manufacturer. They come at these numbers after a lot of flight test and performance tests.

According to one of my senior instructors the cross wind limitation speed is defined after they successfully land that plane with a X wind that strong. Its only a speed at which a very competent pilot has landed that aircraft safely above which it would be extremely difficult to accomplish a safe landing but its not impossible.

With the other speeds, they are also given by the manufacturer as a guideline and checked during aircraft type-certification testing. Using them is considered a best practice to maximize aviation safety, aircraft performance or both.

Beyond Vne, the aircraft will go through structural damage and stress beyond its temperament.

Trigger NOTAM
3.7.2 When an AIP amendment or SUP is published, a trigger NOTAM will
be issued on the AIRAC effective date to:
(a) serve as a reminder, through pre-flight information bulletins, of the
coming into effect of operationally significant permanent or
temporary changes to the AIP; and
(b) ensure that users are aware of changes that may affect their flights.

3.7.3 Trigger NOTAM, which remain in force for a period of 14 days,
contain:
(a) a brief description of the contents of the amendment or
supplement;
(b) the effective date; and
(c) the reference number of the amendment or supplement.

Hope this helps.

[ForkTailedDrKiller]

what is the limiting factor for crosswind?

Generally, its the pilot! :E

Dr :8

[Tarq57]

The below answers are my opinions based on experience, and not taken from any official source. I strongly recommend asking your instructor for the authoritative source for the answers, which in many cases will be the POH.
max speed for moderate and severe turbulence? (flight manual gives me the recommended air penetration speeds but it doesnt say for severe or moderate turbulence) so not to sure.. Use the flight manual speed for rough air. If it's very bumpy (severe turbulence) use Va. Or even a bit less, to allow a safety factor. I personally would avoid known severe turbulence where possible, but if flown correctly there is no reason why the 172 shouldn't handle it. History has shown them to be rather strong.

what is the limiting factor for crosswind? The ability of the pilot. Or were you after the value? 17kt, IIRC.

How did cessna arrive at their cross wind figure for the c172R? Probably the same as any other light a/c manufacturer. Planted it uncorrected on the pavement, ascertained that the landing gear was more than capable of handling the side load, deducted a knot or two for the legal department, and wrote that value into the handbook.

factors that influence a particular figure to be nominated as Vne for an aircraft??? Includes the strength of the structure, flutter resistance of all the control surfaces, and the point at which redline RPM will occur in a fixed pitch a/c, with the throttle closed. Vne is the redline. As part of the certification, there is a safety margin in this, the actual speed the aircraft was flown to is, I believe, referred to as demonstrated dive speed (Vdf) which is about 15% higher than placarded Vne.

what is a trigger notam?

where would you find the table detailing when a SPECI should be issued? Pass.

what is the max carb/heat drop in rpm? (havnt flown in a carb heated aircraft yet). If the 172 is a carburetted a/c, this limitation will be in the POH. It's usually in the order of about a hundred revs. And a correction to the above poster: The heated air is less dense, not more, and it is the reduced density more than the incorrect mixture strength that is responsible for most of the rpm drop.

If it drops more than the permitted drop, it's possible that there is ice present. Leaving the carb heat on should very quickly restore the rpm to within limits. Or, the mixture is over-rich, or there is an obstruction somewhere.

[ConfigFull]

max speed for moderate and severe turbulence? (flight manual gives me the recommended air penetration speeds but it doesnt say for severe or moderate turbulence) so not to sure..

I would also avoid any area of severe turblence - forecasts seem to overestimate the severity of turbulence but this is for a reason - have a look at AIP GEN 3.4 - 110 (http://airservicesaustralia.com/publications/pending/aip/gen/3_4_app110.pdf - the last page in this link)

You can't enter the yellow arc on the ASI in anything other than smooth air (so no light turbulence), then use the POH figures for moderate turbulence and plan to not be in severe turbulence!

where would you find the table detailing when a SPECI should be issued?

This is GEN 3.5 (your go-to part of the AIPs for anything meteorological). More specifically GEN 3.5 4.3 (page 8 of 24 in this link: http://airservicesaustralia.com/publications/pending/aip/gen/3_5_1-24.pdf)

Everything else has been answered however, make sure you're aware of the crosswind limit in the aircraft's POH - it will say 15kt. This doesn't mean that the test pilot(s) who took the first one out couldn't handle 16kt, just that this is the limit for the average pilot, on an average day, in average weather with an average runway - it's for the insurance companies really. Bust the aircraft at anything over POH limits and you're very much liable; best to stick to the book figures.

[bentleg]

what is the max carb/heat drop in rpm? (havnt flown in a carb heated aircraft yet).

Might be a trick question. The 172R that I fly is fuel injected - the question is not relevant. Maybe there are Carby 172R's - check yours, if fuel injected there will be NO carby heat knob next to the throttle and mixture.

[Steve888]

Maybe there are Carby 172R
Every 172 I've flown has a carburetor.

[bentleg]

Every 172 I've flown has a carburetor.

Try flying a later model! Have you ever flown a 172R?

The N and the P models are carbureter and the R and S are fuel injected, including the current model.

[mcgrath50]

This seems like an engineering exam style question, which at every institution I have flown at is a standard paper used across all types.

So you may be asked for your 152 to describe the CSU and Landing Gear Systems.

[poteroo]

Read the POH Mikezulu - then ask the difficult questions.

Both R and S models arefuel injected - just as bentleg says. What you really need to know is how to start them when hot....... again, read the POH - but your instructor might have a more foolproof method.

Take a good look at the Va speed range as it is determined from gross weight. You'll have a rethink about blasting thru any turbulence at normal cruise after that.

happy days,

[MakeItHappenCaptain]

You'll have a rethink about blasting thru any turbulence at normal cruise after that.

Moderate or above, actually.



Common misconception is that you are purely looking for a drop in rpm when you check an aircraft that has carby heat.
You will observe an initial drop due to the reduced density of the ingested air (less oxygen molecules per stroke = less bang/burn), but you should then wait for at least 5 seconds to see if the rpm begin to increase.

Cause?

Low rpm, high humidity,
Perfect conditions to develop carb icing.

Ice present has the same effect as closing the throttle.
You will not achieve the stated performance.

If the rpms rise, positive indication, but you will have cleared the ice, no drama. If you have a fair way to taxi and you had a positive indication, re-check prior to brakes release. A return of rpm to above the initial setting when you return the carb heat to OFF could also be a positive indication.

Secondary confirmation of full power availability is by checking static rpm as full throttle is achieved on take-off.
RPM too low= not enough power from the engine. Not good.
RPM too high = either prop worn beyond limits (not good) or headwind. Unless you have 60 kts headwind, you shouldn't see 2500rpm at the start of your take-off roll.

:ok:

[flyinkiwi]

Both R and S models arefuel injected - just as bentleg says. What you really need to know is how to start them when hot....... again, read the POH - but your instructor might have a more foolproof method.

Ahh the arcane art of hot starts. Now there's a thread in the making. :ok:

[Iflyjad]

Hi all I am new to the thread and am wondering what are the issues with hot starts. I regularly fly both the 172R and S models and need to do a hot start 50% of the time with no real issue. Are there problems with other aircraft etc?

Thanks.

[Weekend_Warrior]

I recall that Vne is 90% of Vd - (not joking) - which is maximum demonstrated dive speed during test flying.

I don't know how Vd is calculated - I guess the design engineers figure out how fast the plane will hold together and the rest is up to the test pilot.

From engineering perspective, maximum turbulence penetration is a few knots less than Va due to centre of pressure differences - Va is to cope with hi-G whereas turbulence penetration is to cope with sudden vertical gust onset - can't recall the rest but is all in a book somewhere on my shelf.
However Va is close enough for all light aircraft.

[tlf]

Only ever flew one 172, had no desire at all to try any others.