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Old 26th Jan 2012, 09:20   #21 (permalink)
 
Join Date: May 2011
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This is where the rotating at TOSS nonsense comes from. Day VFR syllabus, page 2-32 Unit A2 Take off aeroplane.
Element A2.2
Accelerates aircraft along the centreline to the take-off safety speed,
allowing for wind
Rotates aircraft to the target climb attitude at approximately 3 per
second

Also, I forgot to finish a sentence in a earlier post. Dinner was ready.

There are some instructors at Moorabbbin that teach their students to hold Seminoles on ground until blue line before rotating! Why? They believe its safer in case of EFATO. I reckon at 88kts, the only thing still on the runway will be the nose wheel. I wonder if this was a contributor to a number of nose gear collapse incidents and resulting AD that followed.
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Old 26th Jan 2012, 09:38   #22 (permalink)
 
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Quote:
There are some instructors at Moorabbbin that teach their students to hold Seminoles on ground until blue line before rotating!
Where do people get this sh!t from?

They should go fly a twin in PNG!
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Old 26th Jan 2012, 09:53   #23 (permalink)
 
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Quote:
go fly a twin in PNG
....or find themselves a paddock somewhere without too many stumps and do some limited MAP/RPM take offs.
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Old 26th Jan 2012, 09:55   #24 (permalink)
 
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ROFL!!!

Blue line? seriously?
in a smellymole?



The only number to worry about in a smellymole is Vmca....oops you accelerate through that before the bugger will fly anyway

And what ever happened to accelerating in ground effect

Cripes, even a trouble-air will happily accellerate to Vx without its feet being on the deck.
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Old 28th Jan 2012, 07:57   #25 (permalink)
 
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Nomad, can't see any logic in flying at any speed other than Vx for obstacle clearance, especially if that speed is less than Vx.

TOSS is normally set as 1.2 Vs in the takeoff config. Bear in mind Vs changes with weight, so short of having a card with varying speeds for weights on it (assuming your a/c has a wide enought range of weight to worry about it), why not refer to the POH?
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Old 28th Jan 2012, 09:38   #26 (permalink)
 
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I agree with post #24. Get the wheels a couple feet off the runway and accelerate in ground effect.
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Old 28th Jan 2012, 12:46   #27 (permalink)
 
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MakeItHappenCaptain, I agree that Vx is normally the climb that you are looking to establish for obstacle clearance.

However, in the takeoff scenario, if you reference the POH as you say, a number of POH's will actually advise you to maintain TOSS until obstacles are cleared on take off for a performance/short field takeoff scenario. Makes sense really.

Take a bigger single like the 750XL for example. Zero flap Vx is 85 kts. All take offs require a 20 degree flap config. For a performance take off with 20 degree flap it is recommended to initially climb at 74 kts (this is the max weight TOSS and it refers you to the Performance section for TOSSs to use at lower weights - it can be as low as 59 KIAS at 4500lb) until clear of obstacles. You don't want to be retracting flap and accelerating to Vx 85 kts and plowing into trees until you have climbed above the obstacles in the initial climb phase.

A quick look at something smaller like a Warrior II POH expresses similar concepts for obstacle clearance on all take offs. Take the 25 degree (two notches) flap take off for example. Piper says: "40-52kts (depending on weight) back pressure to rotate to climb attitude. Accelerate to and maintain 44 to 57 kts (TOSS, Piper calls it '50 ft barrier' speed, depending on weight) until obstacle clearance is achieved and climb out at 79 kts (Vy). Retract flap slowly."

The reality is, most of the time we are not faced with a scenario where we are wanting to squeeze the last drop of performance out of our machine so we take off, clean up and cliimb at Vx if we feel like it for a best angle climb. But according to what your manufacturer recommends, if you want the best take off performance you will fly it by the book speeds and instructions. At the very least, certainly common sense should tell you that to change the take off configuration (eg raising flap) before safely clearing obstacles will only lead to tears (or some tense pucker moments if you are really lucky)!
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Old 29th Jan 2012, 02:46   #28 (permalink)
 
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Seems to be some confusion between clean and flap-down Vx. If taking off with flap, use the appropriate Vx (or Vy), which is will certainly be less than the clean Vx (or Vy).

As Capt Nomad said, the manufacturer provides the best numbers to use. In light Cessna and Piper aircraft, the manufacturer's quoted TOSS's are actually pretty close to Vx anyway for that configuration. (Not quite identical though.)

In light aircraft I generally found that the attitude for Vx (or Vy) climbs was very similar across all take-off flap settings, once clear of ground effect. Very helpful if you want to avoid chasing the airspeed indicator in a steady climb.

Now in those immortal words from Capt to FO: "take off flap please".
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Old 29th Jan 2012, 05:52   #29 (permalink)
 
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Hot, High or Heavy............more TOD required. Pretty basic stuff.There are some instructors at Moorabbbin that teach their students to hold Seminoles on ground until blue line before rotating! Christ they're aircraft not fu**ing race cars. Who is teaching this sh*t???
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Old 29th Jan 2012, 06:52   #30 (permalink)
 
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Looking at the POH for C172P model - can see a fair parallel between TOSS and Vx.

Cessna quote 60KIAS in section 4.3 - but in section 4.8 they use 56KIAS. Probably easier to eyeball the 60 mark on an analog ASI though.

There are some discrepancies in TOSS in the POH though:

* in the general notes, (4.8), Cessna quote 56KIAS as TOSS
* by calculation, using 49 as the 10 degree Vs - you get 49 x 1.2 = 59KIAS

Probably not even noticeable in practice though?

One interesting note is that they state you gain 10% by using 10 deg flap for t/o - which is why I've only used that stall speed for calcs.

Of interest to this thread is that the 'lift nosewheel' recommendation is actually in the C172 POH. ie, there is a Vr implied.....or are we being too strict in our read of the POH?

In section 4.8, it's stated to lift nosewheel at 55KIAS. But, elsewhere they use 56KIAS as their general TOSS number. Using the 10 deg flap stall speed of 49K - you can calculate a Vr of 54K, (x 1.1).

Using zero flap, you can calculate a Vr of 57, and will quickly reach a calc TOSS of 62 before reaching the 50ft barrier, and from there you may as well accelerate thru to Vy (76).

Conclusion - provided your runway is smooth, then Vr might be acceptable - but in real life strips, forget the Vr calculation and get your nosewheel lifted early. Doesn't prevent you complying with other speeds such as TOSS, Vx, and Vy though.

happy days,
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Old 29th Jan 2012, 07:03   #31 (permalink)
 
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Take care when calculating factors for Cessna aircraft. Pressure error is very large - in the order of 10kts at Vs from memory.

If pilots want to factor by 10% or 20%, use CAS not IAS. You can use the pressure error chart in the flight manual to convert back to IAS. Yes, it does make a difference in Cessna aircraft.

Example, using random numbers.
Vs is 48 KIAS. Pressure error at this speed 8kts. 56 KCAS x1.2 = Vx 67 KCAS. Pressure error is 6kts. Vx is 61 KIAS.
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Old 29th Jan 2012, 15:56   #32 (permalink)
 
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Nomad and Oktas, well picked. Was actualy hoping another user was going to spot this one first. (Most here know I'm a fan of POHs.)
Your response about retracting flap and losing performance is bang on. Slight thread drift, but sure PACs and 208s behave similarly during EFATO turnbacks. Even going from 10 deg flap to 0 causes a MASSIVE performance loss.
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Old 29th Jan 2012, 20:40   #33 (permalink)
 
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Cool Ahh the old ones are the best ;)

Back in 2001, we were talking (in a more erudite fashion, I might ad ) about this:
Blue line speed on an Aztec

.. and again in 2003:
http://www.pprune.org/dg-p-general-a...n-trouble.html



Multi-engine aircraft are divided by FAR 23 into two weight classes - above and below 6000lbs, and those below 6000lbs are divided into two classes depending on Vso (stall speed in the landing configuration) above and below 61 knots CAS.

Only those twins that weigh more than 6000lbs or have a Vso higher than 61 knots need to demonstrate any single-engine climb performance at all for certificaion, and the requirements are pretty meager. Basically the regulation says that these aircraft must demonstrate a single engine capability at 5000' (ISA) with the inop engine feathered and in a clean configaration.

The only requirement for an aircraft less than 6000lbs, and with a Vso less than 61kts (like the Aztec) is that its climb performance (positive or negative) be determined.

There is nothing in the FAR which says an aircraft must fly while in the take-off configuration with one engine inop.

Talking about rotation, manufacturers tend to have a philosophy about this that shows up in in the aircraft design, wing incidence and gear positioning.

Piper recommends that most twins be rotated at Vmc, Cessna on the other hand suggests a lift off at a speed much higher than Vmc and very close to best single-engine angle of climb speed. In the case of a C-310, Vmc is 75 knots, recommended rotation speed is 91 knots and best single engine angle of climb speed is 94.

Try and hold a Seneca or Aztec on the ground much beyond Vmc plus 5 knots (zero flap) and the aircraft will begin to wheelbarrow! Cessna twins (and most cabin class twins) will happily stay on the ground for much longer than that.

A Navajo for instance (stretching the old memory) will happily go by road, if you don't positively rotate it - you hardly have to "force the aircraft on the runway well past VR and until a few knots past Blue Line"!

I would rotate a light (FAR 23) twin not below Vmc+5 (or the recommended rotate), and I pull the gear up just after getting airbourne, then climb at the best all engine climb rate (which is faster then blue line) until clear of obstacles in the area.
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Old 29th Jan 2012, 21:11   #34 (permalink)
 
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CAA performance

CB - Do the Brits still have the performance 'Class" system for aircraft and the examaination for it??.

The Perf A was a bugger, but as I remember Class C was the PA 31/ P166 etc. and so on.

Sorry about the slight drift, but curious.
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Old 29th Jan 2012, 22:30   #35 (permalink)
 
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EU-Ops.

From memory:
Class A - defined performance for continued flight after EF at V1. A is for Airliner.
Class B - no specific performance required at any stage of flight following an engine failure. B is for Bugsmasher.
Class C - large or heavy or turbojet aircraft that really should be in Class A, but lack the OEI performance. C is for Classic aeroplane, think DC3.

I don't recall the precise weight / seat numbers / powerplant requirements that distinguish the categories.
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Old 31st Jan 2012, 10:29   #36 (permalink)
 
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Certification V speeds vs real world

I know, same guy again - but clearly someone that thinks for themselves and has flown all the good stuff, C-46, B-29, DC-3, P-51 etc etc.

So while we're on the subject:

Pelican's Perch #22:<br>Short- and Soft-Field Takeoffs FAA vs. Reality
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Old 1st Feb 2012, 03:36   #37 (permalink)
 
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Good article. I remember many a conversation with Russ Evans about 'certification' flying vs 'real world flying.' Anyone else who has done an instructor renewal with him will probably also remember as it is one of his pet subjects - especially with regard to multis also.

This quote is what I was getting at earlier:
Quote:
If you will allow me to separate the takeoff maneuver itself from the climb well after the takeoff maneuver is complete, then Vx and Vy have nothing to do with the takeoff. Vx and Vy are steady-state airspeeds that are useful for steady-state conditions. The takeoff is not such a steady-state condition, and these speeds are not useful below 50' (except for test pilots during certification).
Having flown in this environment with soft fields, short fields, and fields with crazy slopes and obstacles, one way strips with tailwinds etc. this advice is very much worth paying attention to. Even seasoned bush pilots can get undone on this one and a P-Chart determined TOW could kill you:
Quote:
Soft Fields - These are among the most challenging of all conditions faced by bush pilots. The "softness" of the runway is very seldom constant along the runway, there will be "soft spots" and "hard spots," and speed gained on the "hard spots" may be lost again in the "soft spots." There is simply no book data that will help, and no reliable rules. Soft fields simply cannot be simulated properly, and few pilots will ever have the opportunity, or the desire to play with them. Few wish to expose expensive machinery to deep mud or snow for fear of damage, and even deep wet grass can make an awful mess.
One bit that he mentions regarding 'cleaning up' I would like to add a caution note to:
Quote:
With more experience, and in some conditions, it may be better to be able to retract the gear without looking for the switch (with practice), and retract it early to get over some distant obstacle, or even to get out of ground effect.
One of the things that really ticks me off these days is seeing people take off on a long runway in a single-engine retractable gear machine and wouldn't you know? The wheels have barely left the runway and already they are being retracted! On most runways this just simply isn't necessary. I know of a fellow in the States who belly landed and damaged a perfectly good Bonanza back on a huge runway after having the proverbial 50' engine failure. If he had just left the wheels down there would have been NO damage at all. Leave this bit of performance advice to when you really need it - don't do it as standard practice all the time on long runways with low-level density altitudes. There is absolutely no advantage in doing so.
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Old 1st Feb 2012, 11:20   #38 (permalink)
 
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Quote:
via #23; ....or find themselves a paddock somewhere without too many stumps and do some limited MAP/RPM take offs.
Oooooh, ah dunno about that..

Unless yer in a chopper i woulda thought its better to practice the more 'involved' stuff on a nice big bitumen runway. Though i'm not an instructor, so...




.
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Old 1st Feb 2012, 11:33   #39 (permalink)
 
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Quote:
via Captain Nomad; ...Leave this bit of performance advice to when you really need it - don't do it as standard practice all the time on long runways with low-level density altitudes.
If yer operating to some demanding airstrips at times wouldn't it be better to make it a 'standard practice' so its just what yer do every flight ? - Less distractions then.




.
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Old 1st Feb 2012, 11:53   #40 (permalink)
 
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So you are in a 210 at YSSY taking off from 34L Even if you have been given a departure from 07/25 you still have shed loads of room. You raise the gear at 30ft because that's how you do it out bush. 50 feet you have an engine failure. You now have to get the plane on the ground under control and get the gear out?

Hell I've taken 182s with retractables out of places like Albury or Canberra and been a couple hundred feet and still with runway and clearway underneath me. I'd sure rather have the gear down so all I have to do is push the nose forward when the donk dies!

Yes the above examples are simplified and exaggerated but the principal works.
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