Short Field Takeoff - Arrow II

TMetzinger

TMetzinger

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Tim
So, I'm practicing for the CFI checkride (Wednesday, weather permitting), and I'm reviewing the short field takeoff procedure.

Here's what the POH says for a short field takeoff over an obstacle:
Flaps 25
Rotate at 60-65 MPH
Accelerate to 85 MPH (Vx with gear down)
Retract Gear
Retract Flaps
Pitch for normal climb past obstacle.


Here's my problem: On this particular arrow, when I rotate at 65 MPH - the airplane climbs like a homesick angel. I'm over 100 AGL before the airspeed hits 70 MPH ( and I'm not holding the nose up).

My trainer and I tried to see how much distance it would take if we rotated at 65 and then tried to hold the nose down to minimize climb and maximize accleration - the amount of force was extreme AND it took a fair amount of distance to hit 85. I'd never want to try and clear an obstacle that way.

So... what should I do on the checkride? Follow the "standard" practice of rotating, pitching for a steeper than normal climb, gear up at positive rate (this isn't an airplane where raising the gear INCREASES drag), and then pitching for "normal" climb after clearing the obstacle and then cleaning up the flaps as we accelerate?

Or should I try to do it "by the book", even though I'd probably scare the inspector by not letting the airplane climb right away?

What my trainer recommends is to do the standard technique, and talk it through "OK here we go - rotate, positive rate, gear up, pitch for and accelerate to Vx, we're clear of obstacle, pitch for and accelerate to Vy, clean up the flaps..

I'm interested in your opinions.
 
yea that's a tricky one... you could explain what youve found before takeoff. then when you OUTPERFORM the book, they cant really ding you for doing it wrong since you clearly just proved the book # incorrect.
 
It's a max performance takeoff -- let it perform.

I'm guessing the book procedure is MGW at some CG besides just two up and some fuel...?

My first Short Field t/o on the C205 was on a cold day -- holy cow did the earth drop away fast! I couldn't see a thing straight ahead.

Only caveat would be to drop the nose to see ahead once you reach 200' AGL -- you should be over obstacles by then.
 
Ask EdFred. IIRC, he got failed on his CFI ride for doing something "better than book" rather than "by the book."

Sigh. :frown2:
 
Show the inspector the procedure. It's a good bet he's familiar with it. Tell him you and he will both be uncomfortable with the deck angle. But 50 feet is accomplished very very rapidly- when you pitch over you will already have 50 feet, almost no matter how quick you are with the trim and with the gear.
 
I also took my CFI ride in the Arrow. Best to discuss these things ahead of time......(!)
 
Just out of curiousity, is the trim rigged correctly on that particular a/c? What you are describing sounds like taking off with too much nose up trim. I am working on my CFI in an Arrow II and haven't experienced the same climb profile. Then again, if it is just a matter of rapid climb and the nose isn't getting/staying too high, it could be just the temp diff - I see your in VA and it's been in the mid-70s here in SoCal.
 
I flew an Arrow II for the Commercial and an Arrow IV for the CFI checkride.
This may sound silly, but is it possible that you're seeing the book MPH and the AI is in KTS? That might make a difference and I've seen students have issues with that particular problem.
The other possibilities I'm thinking of might be some sort of position error or other problem with the pitot's calibration... or maybe some prop pitch issue.
A long time ago when I was a student pilot, I wanted to use an aircraft for a checkride... it was a Tomahawk, and I'd flown it a LOT. Interestingly enough, it always cruised faster than the book said. Apparently some mechanic had done some mod (said it was legal) and put some different cylinders on the engine (or something like that) and I KNEW from experience that it cruised at X KTS. So that's what I planned for the X/C portion. Well that did NOT go over well with the examiner and we ended up not only re-doing the X/C, but using a different aircraft. It's too bad that bird was lost in a fuel starvation accident (not the plane's fault). It was a great bird.

Ryan
 
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bbchien said:
I also took my CFI ride in the Arrow. Best to discuss these things ahead of time......(!)
Click to expand...

Oh yeah, I had a number of things to brief hours before we even stepped foot in the aircraft. Taking a CFI ride with no brakes on the copilot's side was interesting but not all that challenging, it just required positive coordination with the inspector.

Discuss ahead of time so you and the inspector are on the same page. Maybe you'll just end up talking about the "short field landing" as your "maneuver to teach." I normally find the procedure is as described above in your first post, Tim. Rotate, accelerate to Vx, obstacle cleared, positive rate gear up, pitch for and maintain Vy, then flaps up.
 
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we all know the definition of Vx, so if you can do better than the book, then clearly the book is incorrect. the likely reason is you're not at gross weight, and Vx decreases with weight. and of course the ability of the airplane to climb is due to excess amount of thrust vs that which is required to maintain level. more power = more excess thrust, and lower pressure altitudes = more power. if it's really cold, your airplane could think you are below sea level. yesterday i was on the ground at 1100msl and the Dynon showed my DA at -660msl
 
TMetzinger said:
So, I'm practicing for the CFI checkride (Wednesday, weather permitting), and I'm reviewing the short field takeoff procedure.

Here's what the POH says for a short field takeoff over an obstacle:
Flaps 25
Rotate at 60-65 MPH
Accelerate to 85 MPH (Vx with gear down)
Retract Gear
Retract Flaps
Pitch for normal climb past obstacle.


Here's my problem: On this particular arrow, when I rotate at 65 MPH - the airplane climbs like a homesick angel. I'm over 100 AGL before the airspeed hits 70 MPH ( and I'm not holding the nose up).

My trainer and I tried to see how much distance it would take if we rotated at 65 and then tried to hold the nose down to minimize climb and maximize accleration - the amount of force was extreme AND it took a fair amount of distance to hit 85. I'd never want to try and clear an obstacle that way.

So... what should I do on the checkride? Follow the "standard" practice of rotating, pitching for a steeper than normal climb, gear up at positive rate (this isn't an airplane where raising the gear INCREASES drag), and then pitching for "normal" climb after clearing the obstacle and then cleaning up the flaps as we accelerate?

Or should I try to do it "by the book", even though I'd probably scare the inspector by not letting the airplane climb right away?

What my trainer recommends is to do the standard technique, and talk it through "OK here we go - rotate, positive rate, gear up, pitch for and accelerate to Vx, we're clear of obstacle, pitch for and accelerate to Vy, clean up the flaps..

I'm interested in your opinions.
Click to expand...


I think you're reading something that isn't there. I see no instruction to hold the nose down and be level as you accelerate. As long as you are still accelerating as you climb, you are fulfilling the POH method. The angle you hold the nose will vary with your weight. As long as your airspeed increases toward Vx after you take off and doesn't stagnate or decrease, you have done the task as spelled out in the manual.
 
bbchien said:
Show the inspector the procedure. It's a good bet he's familiar with it. Tell him you and he will both be uncomfortable with the deck angle. But 50 feet is accomplished very very rapidly- when you pitch over you will already have 50 feet, almost no matter how quick you are with the trim and with the gear.
Click to expand...

That's the truth - we hit 50 feet in less than two seconds.

I'll have the discussion with him before we go fly - the airplane has an STC'ed three blade Hartzell Top Prop on it, and a factory-reman engine with less than 100 hours. So it's probably got better performance than the book predicts for the original two-blade prop. I'll brief that we'll rotate at 60-65, climb while accelerating, and hold the gear until we're above the obstacle and through 85.
 
TMetzinger said:
That's the truth - we hit 50 feet in less than two seconds.

I'll have the discussion with him before we go fly - the airplane has an STC'ed three blade Hartzell Top Prop on it, and a factory-reman engine with less than 100 hours. So it's probably got better performance than the book predicts for the original two-blade prop. I'll brief that we'll rotate at 60-65, climb while accelerating, and hold the gear until we're above the obstacle and through 85.
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That's also the way we teach it at Purdue.

  • Flaps 25
  • Full power
  • Rotate at lift off speed as referenced in the POH (51 - 59 KIAS depending on weight)
  • Accelerate to barrier speed (POH chart) 54 - 62 KIAS
  • Gear up when obstacle is cleared with a positive rate of climb
  • Accelerate to Vx (78 KIAS) and retract flaps at 200 AGL
  • Accelerate to Vy (90 KIAS) and resume normal climb
With so much power and at lower than gross weight, accelerating in the climb is pretty common.
 
I'm guessing that the plane is climbing so well because you're well below max gross and it's pretty cold this time of year. Remember that Vx varies with weight and DA, and you're operating with both pretty low. Point that out to the inspector while teaching the maneuver before demonstrating the maneuver. Then talk about the proper pitch attitudes to hit in order to make the speeds you want so you aren't chasing the airspeed indicator all over the sky. Finally, do the maneuver by the book using the proper attitudes to hit the right speeds for actual weight and DA. That should work just fine.
 
TMetzinger said:
I'll have the discussion with him before we go fly - the airplane has an STC'ed three blade Hartzell Top Prop on it, and a factory-reman engine with less than 100 hours. So it's probably got better performance than the book predicts for the original two-blade prop.
Click to expand...

Doesn't the Top Prop come with documentation including revised performance charts, and maybe even procedures? Seems to me you should be using data for the particular airplane you're in, not a generic one.

If not, well... That's certainly yet another thing that bears explaining to the examiner!

BTW, I wouldn't expect a factory reman engine, even a new one, to have better than book performance - After all, book performance was figured with a NEW engine. OTOH, I might expect that an old worn-out engine might result in worse than book.
 
Generally, stc will only revise performance charts if the performance is worse than original. Otherwise they validate that they meet original specs only to minimize costs. The prop does alter limitations section and those changes are documented.

sent from my android
 
One of the things about being a good flight instructor is 'splainin' to students the difference in book knowledge and real world experience.

CFI examiners like it when you actually teach them something. They look for that in a CFI applicant. This is your opportunity.

Big airplanes, really high performance airplanes, and such, have performance charts for a wide variety of weights, temps, etc., but light GA (training) airplanes only show charts and speeds for max gross on a standard day.

As a light airplane pilot and instructor, we want to teach how to fly a specific airplane at light weights and max performance by feel, but also when instructing in preparation for certification checkrides, how to do it 'by the book'.

The examiner usually wants to see a book example because that is the most standard way of evaluating your teaching technique. He is not interested in seeing max T.O. performance; he is interested in seeing and hearing you talk him thru the book maneuver.

He knows you will teach a more maximum T.O. performance because you will tell him beforehand during the initial briefing of your lesson plan, when you 'splain' how you will get a much higher angle of climb with the 'real' Vx because of your weight and temp, and then let him tell you he would rather use the book numbers.

The main point is that you both come to a mutual understanding and conclusion about what the maneuver is supposed to teach before you take-off.
 
Explain the maneuver "by the book" but also that you have seen it do better...Just fly it nice and comfortably the way you prefer talking the whole time and you will be fine.
good luck Tim.

FYI Ron it right on about hitting some pre-determined attitude marks to help guide you. After all an airspeed represents an AOA anyway. I would be sure to "teach" that to the examiner...really does make it easier for a student in the beginning.
 
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TMetzinger said:
Generally, stc will only revise performance charts if the performance is worse than original. Otherwise they validate that they meet original specs only to minimize costs. The prop does alter limitations section and those changes are documented.
Click to expand...

I'm glad they didn't want to meet original specs or reduce costs on the STC for our STOL kit, then! :eek:

Definitely a POH "Addendum" for the Robby... Including the insanely cool but slightly crazy "Robertson-method" STOL takeoff, selecting Flaps 30 in the 182 after starting to roll from a brakes-held full-stop at full power. Did a few of them one day by myself. Eerie.

Obstacle performance is worse by far than a normal takeoff, due to all the flippin' drag, and having to level off to accelerate, but you're off the ground in rediculously short distances.

The addendum POH book says...

2800 lbs, Sea Level DA, 59F -- 390' ground roll, 735' to clear 50' obst.
Indicated Airspeed at 50' should be 49 MPH. Begin liftoff at 45 MPH.
With a 10 knot headwind, 275' and 560' respectively.
With a 20 knot headwind, 175' and 410' respectively.

The "best" numbers in the book are...
2000 lbs, Sea Level DA, 59F
20 knot headwind
Target IAS at 50' 43 MPH
65' ground roll, 185' to clear 50' obstacle

Since we're over 2000 lbs with me on board and no fuel, I guess I will never see if it can do less than 100' of ground roll. :)

It's just downright freaky. Oh one of the other "gotchas" is that the modified checklists included in the R/STOL addendum is "Rudder Trim, Full Right". It needs it, too! Problem is, as you (hopefully rapidly) accelerate, you have to push left rudder until your attention can be diverted to mess with the trim again, which feels very awkward at first. ;) :cornut:

It's kinda sad that the hey-day when STC creators were actually trying to compete and wanted to confirm it with a modified POH were over long ago, due to product liability concerns. It'd be better if they had to modify, good or bad, to receive the STC so you'd know exactly what the change did to the aircraft. (And could compare competing STCs "apples to apples" by just cracking open the two POH Addendums.)
 
I still don't understand why you can't climb and accelerate at the same time....
 
denverpilot said:
I'm glad they didn't want to meet original specs or reduce costs on the STC for our STOL kit, then! :eek:
Click to expand...

I posted my original comment on my phone so kept it short. A more lengthy version would be that UNLESS they have a good economic reason to do flight testing to revise things like performance charts, or they have a REGULATORY reason, they won't bother.
 
Henning said:
I still don't understand why you can't climb and accelerate at the same time....
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Of course you can. And you will while you're transitioning from liftoff to Vx. But once at what you think is Vx, if you're still accelerating, then you're not achieving best angle of climb, because if there's still some excess power being used to accelerate, you could instead pitch up to use it to climb faster at the lower speed.
 
Henning said:
I still don't understand why you can't climb and accelerate at the same time....
Click to expand...

I agree. Re-reading Tim's original post, it sounds like the airplane is rotating at 65 and wanting to stay at 65 with considerable stick force required to keep the nose down.

If the airplane rotates at 65 and wants to stay at 65, that tells me the airplane is trimmed for 65.
 
Ron Levy said:
Of course you can. And you will while you're transitioning from liftoff to Vx. But once at what you think is Vx, if you're still accelerating, then you're not achieving best angle of climb, because if there's still some excess power being used to accelerate, you could instead pitch up to use it to climb faster at the lower speed.
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Right, which is why a take off is arc shaped.
 
Firstly, good luck on your checkride...
Secondly, He can't ding you if you do what the manual tells you to do.
 
Fearless Tower said:
I agree. Re-reading Tim's original post, it sounds like the airplane is rotating at 65 and wanting to stay at 65 with considerable stick force required to keep the nose down.

If the airplane rotates at 65 and wants to stay at 65, that tells me the airplane is trimmed for 65.
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Sort of... the airplane will in fact stabilize at about 85 after rotation if left alone. It's just that you're at 700+ AGL by the time that happens.
 
TMetzinger said:
Sort of... the airplane will in fact stabilize at about 85 after rotation if left alone.
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That depends on how you trim it.

It's just that you're at 700+ AGL by the time that happens.
Click to expand...
If speed doesn't stabilize at Vx until you're above 700 AGL, you left a lot of performance in the locker room. You should have the speed stable at Vx for the conditions by 50 AGL. If not, you're not doing it as required for maximum short-field/obstacle takeoff performance.
 
Ron Levy said:
That depends on how you trim it.

If speed doesn't stabilize at Vx until you're above 700 AGL, you left a lot of performance in the locker room. You should have the speed stable at Vx for the conditions by 50 AGL. If not, you're not doing it as required for maximum short-field/obstacle takeoff performance.
Click to expand...

So... what magic formula determines Vx for the conditions? How do I determine that speed before start when all I've got in the "book" is a Vx for max gross on a standard day with a different prop?
 
TMetzinger said:
So... what magic formula determines Vx for the conditions? How do I determine that speed before start when all I've got in the "book" is a Vx for max gross on a standard day with a different prop?
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The purpose of Vx is to provide the best angle so you can get over an obstacle.

Where are the runway end obstacles greater than 200'?

(If they are, I'd turn)
 
TMetzinger said:
So... what magic formula determines Vx for the conditions? How do I determine that speed before start when all I've got in the "book" is a Vx for max gross on a standard day with a different prop?
Click to expand...
Some POH's give Vx and Vy at various weights and altitudes. For the rest, you'll have to do some guessing unless you have a lot more data and computational power than is typically available in the cockpit or even the flight planning room.

As you know, Vx goes up with altitude and Vy goes down, and they meet at absolute ceiling. Peruse a few POH's with the data, and you'll see that typically that meeting point is somewhere around 1/3 of the way from Vx to Vy (e.g., Vx at SL is 70, Vy at SL is 85, and they meet at absolute ceiling at about 75). So, if your absolute ceiling is 15,000, and Vx/Vy are as stated, then at 10,000 Vy will be about 78 and Vx about 73. It's not exact, but it's reasonably close.

The effect of weight on Vx/Vy is rather more difficult to quantify, but for typical 2000-3000 lb light planes with stall speeds in the 50-60 knot range, a reduction of 1 knot for every 100 lb below max gross will probably not be too far off.

Of course, if your POH gives you the numbers, use those, but if it doesn't, this is as good a guess as any.
 
TMetzinger said:
So... what magic formula determines Vx for the conditions? How do I determine that speed before start when all I've got in the "book" is a Vx for max gross on a standard day with a different prop?
Click to expand...
Specific experience with that aircraft and those conditions is the only formula for aircraft with nothing but gross weight/standard day charts. You should be training your students and the examiner that the book performance profile is as it would be with a full load. It would not climb like an angel if it was fully loaded on a warmer day at the lower ias that you will see in this actual performance t.o. In that case, the lower ias for Vx would not produce the max angle of climb. It might even be dangerously close to stall.

Ideally, you should load the airplane to max gross with sandbags or something, and teach how the airplane handles with a full load.
At least, this should be a minimul part of the knowledge part of short-field training; that there is a big difference in 'school' lightly loaded performance and real world heavily loaded performance.

So, anyway, the demonstration 'by the book' isn't concerned with actual aircraft or pilot performance, but with how you describe the show as you perform it. It's just a show.
 
Vx and Vy are normally defined for a specific configuration and if you change the configuration, the performance numbers change as well. On my Bonanza, the only airspeed's provided in the POH are in the clean configuration and although not stated, they are the numbers for 5000 feet and at maximum gross weight. Some POH's will provide more information, and in fact, prior to there being a POH for the Bonanza, there was an "Owner's Manual". It has a lot more information which has since been suppressed by the lawyers in the POH.

Here are the numbers provided for Vy in the clean configuration at 5000 feet at MGW from the Owner's Manual. Clean is 96 Kts (agrees with POH), gear down is 80 Kts, and gear and flaps down is 68 Kts. In fact, the airplane will not climb or at best is very anemic if you attempt to climb at clean Vy while the gear and flaps are down. So, in this instance, if you use the POH 96 Kts for Vy, don't expect any climb on the go around.

The point I am making is know what Vy configuration you are talking about and if your POH is silent on configuration, you are very likely to find out that the value in the POH doesn't apply.

There was a video recently of a G36 that would not climb out of a sea level airport, he had heard a few beep-beeps of the stall warning and lowered the nose and climbed at too high of an airspeed. The climb was so anemic that he flew between the trees and was fortunate he didn't crash. The airplane will climb quite nicely, but you need to use the proper speed.

In the Bonanza, we use the approach flap position for a short field takeoff or if the airplane has the continuous position flaps, we recommend setting 20 degrees of flaps. I teach to accelerate to the recommended liftoff speed, and start bringing the nose up 3 or 4 knots before reaching the lift off speed so that the main wheels will leave the runway at the desired speed and to set the pitch to a predetermined attitude (10 to 12 degrees pitch up) to hold during the initial climb. The airplane continues to accelerate during the maneuver and arrives at the 50 foot obstacle height at the desired speed.

It has been a while since I owned an Arrow, but I recall the gear generating significant drag, which would suggest that at least until the gear was up, climb performance would fall off rapidly as airspeed was increased due to parasitic drag. To a lessor extent, the same is true for the flaps. Faster is not always better. My old Arrow manual suggests liftoff around 56 Kts, positive rate - gear up, accelerate to 70 Kts to obstacle, flaps up while accelerating to 83 Kts.
 
nosehair said:
Specific experience with that aircraft and those conditions is the only formula for aircraft with nothing but gross weight/standard day charts. You should be training your students and the examiner that the book performance profile is as it would be with a full load. It would not climb like an angel if it was fully loaded on a warmer day at the lower ias that you will see in this actual performance t.o. In that case, the lower ias for Vx would not produce the max angle of climb. It might even be dangerously close to stall.

Ideally, you should load the airplane to max gross with sandbags or something, and teach how the airplane handles with a full load.
At least, this should be a minimul part of the knowledge part of short-field training; that there is a big difference in 'school' lightly loaded performance and real world heavily loaded performance.

So, anyway, the demonstration 'by the book' isn't concerned with actual aircraft or pilot performance, but with how you describe the show as you perform it. It's just a show.
Click to expand...

In my own airplane, I have a set of performance numbers based on configuration at three different weights, light weight, medium weight, and full gross weight. I don't memorize the numbers but look them up based on weight.

If on a short field takeoff, the airplane airspeed is accelerating in a particular configuration and pitch angle as it climbs, it is getting further and further away from a stall.
 
John Collins said:
[snip] It has a lot more information which has since been suppressed by the lawyers in the POH.
[snip]
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Damn lawyers are everywhere now. Do we have to install seatbelts in the POH now?
 
John Collins said:
In the Bonanza, we use the approach flap position for a short field takeoff or if the airplane has the continuous position flaps, we recommend setting 20 degrees of flaps. I teach to accelerate to the recommended liftoff speed, and start bringing the nose up 3 or 4 knots before reaching the lift off speed so that the main wheels will leave the runway at the desired speed and to set the pitch to a predetermined attitude (10 to 12 degrees pitch up) to hold during the initial climb. The airplane continues to accelerate during the maneuver and arrives at the 50 foot obstacle height at the desired speed.
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John, IIRC the A36 POH does not include short field guidance.
 
Ron Levy said:
Some POH's give Vx and Vy at various weights and altitudes. For the rest, you'll have to do some guessing unless you have a lot more data and computational power than is typically available in the cockpit or even the flight planning room.
Click to expand...

nosehair said:
Specific experience with that aircraft and those conditions is the only formula for aircraft with nothing but gross weight/standard day charts.
Click to expand...

Hmmm.

Couldn't changes in Vx and Vy be calculated based on some combination of L/dmax, Vs, and excess horsepower?

I'm only asking this as a theoretical question, I haven't thought through what the formulas would be yet, but it seems like a change in Vy could be calculated in a simple enough manner that it could be done without too much hassle.
 
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