Hot day, max load, should I use flaps on takeoff

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RonP

Pre-takeoff checklist
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1969 Cherokee 140B, 34 gallons fuel, max weight at 2,150 pounds and balance just in. A&P put on a climb prop when the stock prop was red tagged a few years ago at annual. Airport elevation 49 feet MSL. Temperature was 95 and density altitude 2,200. As expected with 150Hp the climb out at 85MPH was anemic at a tad over 500 FPM. Would taking off with 1 or 2 notches of flap be prudent and improve the climb out even though the POH does not suggest it as a hot day procedure?
 
Indeed it will
 
No.

On a Cherokee, I like the first notch of flaps for takeoff.......but then retract them slowly airborne for a Vy climb.

ALL normal general aviation aircraft climb better with NO FLAPS.

Some weird STOL airplanes like the DeHavilland DHC-2 Beaver climb with climb flaps. But no Cessnas or Pipers.
 
I've never heard of a "hot day procedure" with regard to takeoff/climbout. Does the density altitude/runway length/aircraft performance on this particular day require that you should follow "short field" procedures? If so, then do. It probably calls for a notch of flaps for getting airborne, but then retracting them once you're clear of obstacles. So do that. Climb out however you would climb if you were already at 2200 feet, because the wings can't tell the difference between that and a hot day at sea level.
 
I was always taught for most GA aircraft (Cherokees included) flaps on takeoff will get you off the runway quicker, but won't help you clear the trees. Good for soft/rough field takeoffs with no obstacles. Not so much otherwise.
 
I don't notice a huge difference in climb between 10º flaps and a clean takeoff in my particular plane but having some power on the nose helps that. You mentioned a 500' FPM climb rate as anemic and I agree. Then I remembered some of the VW powered Sonex guys talking about climbing out at 300' FPM or less and being thankful that they were in Kansas where it's real flat with no obstacles and lots of landing options. :rolleyes:
 
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Although I would not necessarily consider a DA of 2,200 to be "high", I guess it is all relative. Donno about the Cherokee, but the Warrior II's POH allows for "minimal" leaning prior to takeoff at higher altitudes. I typically use 5,000' MSL as my decision point for pre-takeoff leaning.
 
RonP said:
1969 Cherokee 140B, 34 gallons fuel, max weight at 2,150 pounds and balance just in. A&P put on a climb prop when the stock prop was red tagged a few years ago at annual. Airport elevation 49 feet MSL. Temperature was 95 and density altitude 2,200. As expected with 150Hp the climb out at 85MPH was anemic at a tad over 500 FPM. Would taking off with 1 or 2 notches of flap be prudent and improve the climb out even though the POH does not suggest it as a hot day procedure?
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Are you trying to improve the angle or rate?

Flaps will not improve the rate, but they may or may not improve the angle. What's the POH say for short-field takeoff?
 
Hot here with 2000’ DAs at sea level. Leaning for takeoff improved RPMs by almost 250, which means a lot more power. That’s more important than a notch of flaps.

1 notch will get you into ground effect, but for climbing, it’s just drag.
 
Depend how long is the runway, runway surface and obstacles after TO.
Read the POH.
even if the cherokee 140 is an old airplane the POH should describe the correct procedure.
 
In most light singles, partial flaps will typically decrease ground roll but degrade climb rate. The net effect for clearing obstacles is usually negative. The POH will normally provide the optimal configuration for operations for clearing obstacles. Do that. Flaps can't compensate for performance losses due to higher density altitude.

In an AA-1 or AA-5 partial flaps is not a recommended procedure, but can be useful on high friction turf strips where reducing ground roll can get you in ground effect faster. But climb rate does suffer.
 
RonP said:
1969 Cherokee 140B, 34 gallons fuel, max weight at 2,150 pounds and balance just in. A&P put on a climb prop when the stock prop was red tagged a few years ago at annual. Airport elevation 49 feet MSL. Temperature was 95 and density altitude 2,200. As expected with 150Hp the climb out at 85MPH was anemic at a tad over 500 FPM. Would taking off with 1 or 2 notches of flap be prudent and improve the climb out even though the POH does not suggest it as a hot day procedure?
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“...balance just in...” ???
 
I'm not an expert, nor did I stay in a Holiday Inn Express last night...

The Archer short field procedure is 20 deg flaps, Vx climb until clear of obstacles, then accelerate to Vy and retract flaps. It feels like you're in an elevator.

In our club's tapered wing Cherokee's, at slow speeds 10 flaps provides mostly lift, 20 flaps some lift and some drag, and 40 mostly drag. Don't know if this is the same on the Hershey bar wings, which I assume is what you have. You can experiment by seeing how the various flap settings effect the stall speed and the power required to maintain slow flight.

In the scenario you describe in MY plane, i would use flaps 20 if I was concerned about RW length. Some people use a technique of allowing the plane to accelerate to Vr, and then pull in the flaps, to eliminate the drag in the ground roll. I haven't played with this, but it makes sense in theory.

Remember that you can't change physics. You're lifting a certain weight with a certain amount of power. Adding flaps will increase your climb ANGLE, but not your climb RATE, at least not very much.
 
Flaps on GA airplanes will NEVER better Vx or Vy.

They will decrease the distance needed to climb over "close-in" obstacles. But once the close in obstacles are cleared, a clean wing will give Vx and Vy.
 
All great advice. With regards to W&B being “just in”, with baggage, fuel and live load I was at 2,150 pounds and an arm of 89.9. The W&B chart shows the max arm at 2,150 is 90. 89.9 would be just inside the graph. The runway was 3,500 feet long with a farm field at the end. Had no obstacles to clear and at 500FPM was climbing although slow. When the stock 1969 prop was sent out at annual for inspection it was red tagged. The A&P had a used prop with log and recent inspection documents. He said it has slightly less pitch than the stock prop hence he said it will improve low speed pulling such as in a climb. I do not notice a difference at cruise with less pitch. With regards to climb performance this was the first time the Cherokee was at max weight on a hot day. Yes it does have the Hershey bar wing. Having been flying rental 172s, Warriors and Archers took me awhile to get used to the stubby wing during landing. It is definitely a floater like the tapered wing airplanes. Thanks again for the input.
 
kgruber said:
No.

On a Cherokee, I like the first notch of flaps for takeoff.......but then retract them slowly airborne for a Vy climb.

ALL normal general aviation aircraft climb better with NO FLAPS.

Some weird STOL airplanes like the DeHavilland DHC-2 Beaver climb with climb flaps. But no Cessnas or Pipers.
Click to expand...

Throw the Cessna182 with the Peterson STOL mod (front mounted elevator canards) into the “weird” category. Flaps 20 for a radical take off (short, soft, high DA).
 
It probably still climbs better once it obtains Vx or Vy if you retract the flaps. They're causing you a lot of drag at that point.
The 172 switched the procedure for short field takeoffs over the years, but not because the aerodynamics changed. While 10 degrees will greatly decrease ground roll, it won't get you any shorter distance to the 50 foot obstacle. Of course, if you have an old manual flap one, you can start your run with the flaps up, drop them to 10 to rotate, and then retract them to climb.

The Navion will have an incredibly short ground roll if you put in full flaps (not recommended, but I screwed up and did it once). It won't climb worth crap though.
 
First notch for takeoff in a Cherokee.
 
More flaps will decrease your ground-roll and initial (prior to flap retraction) climb performance.

Less flaps will increase your ground-roll and initial climb performance.

If climb performance will be marginal, less flaps is desired--providing there is enough runway for the longer ground-roll.

As runway length decreases, more flaps will give you a shorter ground-roll providing initial climb requirements allow.
 
kgruber said:
Flaps on GA airplanes will NEVER better Vx or Vy.

They will decrease the distance needed to climb over "close-in" obstacles. But once the close in obstacles are cleared, a clean wing will give Vx and Vy.
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I question this. Have you conducted tests. I feel reasonably confident that 10 degrees of flaps will increase my C-210D angle of climb but not RoC.
 
Our club has the Archers std take-off setting with one notch of flaps(10deg). I often wondered why(but too lazy to ask, since I follow the established manual not the club "Expert") since the manual does not state to do that but I have a feeling its because you get off the runway quicker and that puts less stress on the plane? The thing I dont like about starting out with one notch on a routine basis is that there is a small chance you forget to loose the flaps and long term that has more serious implications than doing a 50 foot longer takeoff roll.
 
Couldn't find a C210D flight manual, but a T210N......Vx is clean wing.

SECTION 4 NORMAL PROCEDURES CESSNA MODEL T210N If it is necessary to climb rapidly to clear mountains or reach favorable winds or better weather at high altitudes, the best rate-of-climb speed should be used with maximum continuous power. This speed is 100 KIAS from sea level to 17,000 feet, decreasing to 97 KIAS at 24,000 feet. If an obstruction dictates the use of a steep climb angle, climb with flaps retracted and maximum continuous power at 82 KIAS.

But for "close-in" obstructions, when there isn't enough distance to accelerate to 82 KIAS...........like right after takeoff...... then you would use your 10° flaps. But don't confuse that speed/technique with Vx.

"""SHORT FIELD TAKEOFF If an obstruction dictates the use of a steep climb angle, after liftoff accelerate to and climb out at an obstacle clearance speed of 78 KIAS with 10° flaps and gear extended."""
 
Snowmass said:
I question this. Have you conducted tests. I feel reasonably confident that 10 degrees of flaps will increase my C-210D angle of climb but not RoC.
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I think what's meant is that flaps will not change the 'speed' at which you get max rate or max angle. The actual rate or angle at that speed may change with flaps
 
RonP said:
Would taking off with 1 or 2 notches of flap be prudent and improve the climb out even though the POH does not suggest it as a hot day procedure?
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You answered your own question.

If it were the thing to do, the POH would say so. And it wouldn't be considered a suggestion.
 
KGRUBER
Thank you for your explanation. The 210 has the old Cessna airfoil, non laminar flow, which might have an effect or this might be universal. So now should I be able to find VERY stable, crack of dawn air, I will measure climb angle with 10 degrees of flaps and 0 degrees. As we used to say at the Hughes lab, "One test is worth a thousand opinions". By noting RoC vs. airspeed I should be able to calculate the angles but if small it may take a lot of testing to offset air instability.
 
Daleandee said:
...You mentioned a 500' FPM climb rate as anemic and I agree...
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As an absolute metric I would agree. But the OP said it was a 1969 Cherokee 140, with full fuel, loaded to gross weight and 2200 ft DA.

How much faster do you think it should climb in that situation?
Any time I loaded my Cherokee 160 within the last 100 lbs of gross it was truly noticable how performance degraded and the handling, especially in roll, got sloppy.
 
luvflyin said:
I think what's meant is that flaps will not change the 'speed' at which you get max rate or max angle. The actual rate or angle at that speed may change with flaps
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Because even 10 degrees of flags creates drag, it will change the numbers, at least slightly. If you enjoy being a test pilot, I'd encourage you to take someone along to record data and find out what that penalty is.
 
While I understand I answered my own question that the POH does not address my post that is not why I posted my question. It may be my misunderstanding regarding an internet source such as this that there are probably many more Experienced pilots with many more hours In a Cherokee 140 than at the time the POH was written 51 years ago. I am tapping into that experience and knowledge base regarding the topic. The side benefit is also getting great responses that also increase my personal knowledge base and a practical understanding of items that were not as clear before. No doubt the POH is the “go to” for performance specs but experience and hours in type also give practical information and experience 51 years after the POH was written. Thanks again to those who posted great answers and explanations.
 
If I may tag on your question: To the fellow experts here:
What are the pros and cons of using 10 deg flaps for std takeoff in an Archer, as my club mandates for all takeoffs?
And pros and cons for 1 or 2 notches - for RonP's fully loaded Cherokee 140?
 
RonP said:
No doubt the POH is the “go to” for performance specs but experience and hours in type also give practical information and experience 51 years after the POH was written.
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Not to put too fine a point on it, but if something goes awry and your defense is "The POH is 51 years old and SGOTI has a lot of success with xyz" you're going to be completely hosed.

RonP said:
The side benefit is also getting great responses that also increase my personal knowledge base and a practical understanding of items that were not as clear before.
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Phone your CFI. Don't type out for SGOTI.

I'm sure it seems dickish to you, but the book is the book, and your CFI is where to learn.
 
flyingron said:
The 172 switched the procedure for short field takeoffs over the years, but not because the aerodynamics changed. While 10 degrees will greatly decrease ground roll, it won't get you any shorter distance to the 50 foot obstacle.
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Yet they went from not recommending flaps for clearing an obstacle to recommending them which is the opposite that seems to be implied above.

172L,M: "The use of 10° will shorten the ground run approximately 10% , but this advantage is lost in the climb to a 50-foot obstacle."
172N: "Use of 10° flaps is not recommended for takeoff over an obstacle at high altitude in hot weather."
172P,R,S: "Using 10° wing flaps reduces the ground roll and total distance over an obstacle by approximately 10 percent."
 
Flying Doc said:
If I may tag on your question: To the fellow experts here:
What are the pros and cons of using 10 deg flaps for std takeoff in an Archer, as my club mandates for all takeoffs?
And pros and cons for 1 or 2 notches - for RonP's fully loaded Cherokee 140?
Click to expand...

Don't mind the gallery, POA tends to be snarky for sport. In non-swept, subsonic wing planforms of moderate to high aspect ratios (essentially these light piston clam traps), flaps change the effective camber of the wing, which shift the Pr and Tr curves up via extra drag (combined). This has the effect of hurting the angle of climb capability of the airplane, lowers the service ceiling as well. But it also changes the VX and VY numbers as provided by the OEM (to the left), because the calculation of Vx and Vy is made with the wings in the clean configuration, and labeled for max gross weight.

Conversely, decreased weight for the same powerplant and wing configuration increases the power loading, which increases the angle of climb capability (excess thrust and power points in the curves respectively). That's why naturally, the airplane performs better in the climb when it's lighter.

But that's climb. Now let's talk about your question, takeoff. There is a competing relationship between 1) acceleration to liftoff speed, and 2) liftoff speed calculation as a function of flap angle. Piper essentially is telling you that two notches of flaps, eg 25* ,is the optimum combination for minimizing ground run. Why is that? Because the effective camber of the wing with flaps at 25* yields the quickest convergence point to the attainment of liftoff speed, which minimizes ground run (all weights) when compared to flaps 40*, flaps 10* or flaps 0* takeoff attempts.

You have to remember from the prior discussion, that flap angle changes camber, which changes Cl per alpha, and that changes liftoff speed. Yes, flaps 0* will have less drag during acceleration than flaps 25*, but the aircraft has longer to attain the higher no-flap liftoff speed. Conversely, 40* has the slowest of all liftoff speeds, but the drag penalty in acceleration still yields a ground run longer to reach this lower liftoff speed. Piper did the homework for you and showed you that two notches, not one, not three, not zero; 25* gets you the minimum ground roll to wheels off the pavement.

Flaps 10* use in your clubs case? Sorry, it's just placebo. You'll have a marginally shorter ground run than flaps zero, but your climb gradient will be poorer than the clean wing takeoff counter. If you want to minimize ground run, 25* is the optimum choice. If you're worried about settling in high temp/DA days and prefer to have that "positive feel" when climbing away, flaps zero and a longer ground run to liftoff speed closer to Vx and Vy is the ticket. Flaps 10 is generally an instrument approach sight picture enhancing setting prior to breaking out the clouds and committing to flaps 25 or 40 on the visual landing. Perfectly fine to use it on takeoff, but you're not gaining anything deemed important when taking off. Flaps 0 or 25 are the answer for the PA-(2,3)X-xxx series.

As to the POH. What @Ravioli was hinting in his matter-o-fact way is that the POH is a legal instrument for the FAA to hang you with. Citing deviations from the POH, even if immaterial to the accident, is in his opinion is opening yourself for scrutiny and fault-assigning. Bear in mind, POHs have been laden with safety-detracting directives and information. First two that come to mind are the recommendation to lean to 50ROP above 65% of pre-restart Pipers and Cessnas, the other one being non-altitude compensated power tables for a blown conti 360 in the turbo arrow. That one can get real scary real quick, especially with an intercooler mod and a neophyte at the helm.

It's a bit of hyperbole that the FAA is gonna yank your ticket because you chose to fly flaps 10 and porked a takeoff, but the principle behind using the POH as the catch all to cover yourself from the hall monitor types at the FSDO is probably sincere advice.
 
GRG55 said:
How much faster do you think it should climb in that situation?
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I wasn't speaking specifically to his aircraft or situation. The ability of an airplane to climb, IMNSHO, is more important than the ability to go fast. As Tim Taylor would say, "arrgghh ... more power!"

I'm reminded of the car commercial that showed the little fuel sipper economy car sitting at the stop sign waiting to get on a fast traveling four lane expressway as the car went ripping by. The voice over came on and asked, "what good is 50 MPH on the highway if you can't get on the highway?"
 
Hindsight2020, thanks for the GREAT explanation without finger waving. So far no harm, no foul as I followed the POH. Great info presented here.
 
but....stall speed is reduced with 10 degrees of flaps. So, aren't we making more lift?o_O
 
Checkout_my_Six said:
but....stall speed is reduced with 10 degrees of flaps. So, aren't we making more lift?o_O
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Climb angle is a function of excess thrust = thrust available — thrust required. Flaps increase drag so increase thrust required, but since propeller driven aircraft create more thrust at low speed, more thrust is available as well. The answer is, it's complicated, follow your POH (heck, even Aerodynamics for Naval Aviator says that).
 
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