High DA Flap Settings?

[cocolos]

If you're at a high density altitude is it better to setup for something similar to a shortfield take (flap settings and all) or just a normal takeoff with no flaps. For references I fly PA28-180 and C152.

 

[MAKG1]

Is the high DA field short? Then use short field techniques.

"Short" means the takeoff roll table in the POH yields a concern. A short field at high DA is longer than a short field at sea level. Use the 50 ft height numbers plus 50% margin.

If you fly up to TVL and the performance table says you will be at 50 feet after a 4000 foot roll in actual conditions (that's for a fully loaded 172 at 90 deg F), do a normal takeoff. The runway is twice as long as that.

If you fly to Blue Canyon, the 3300 foot length may present a concern on a hot day.

Make sure you lean at run-up and leave it leaned. That's a common and potentially serious error.

 

[cocolos]

I see I was just wondering if the flap settings would help you create a bit more lift but I guess that would proportionally add drag. Thanks.

 

[poadeleted20]

I see I was just wondering if the flap settings would help you create a bit more lift but I guess that would proportionally add drag.

They do indeed increase lift, although the increase in drag may not be directly proportional to the increase in lift. That varies with both wing/flap design and speed. If the folks who designed the plane determined that you'd do better at high DA with more flaps than at low DA, they'd say so in the POH/AFM. If it's not there, stick with the "normal" flap setting unless you need to shorten the takeoff roll, in which case use the "short field" flap setting.

Either way, keep an eye on what it says about obstacle clearance after takeoff. Sometimes getting off in the shortest distance requires a configuration which affects initial climb so much that you do better over a close-in obstacle with a different configuration such that climb is improved more than takeoff roll is degraded. The book recommendations and the performance data in it should help you decide on that.

 

[Sac Arrow]

I see I was just wondering if the flap settings would help you create a bit more lift but I guess that would proportionally add drag. Thanks.

In general, yes you want an increment or two of flaps on takeoff at a high DA but consult your POH on specific recommendations.

Another thing to remember at a high DA airport is that when you are in the pattern for landing, don't richen the mixture.

 

[midlifeflyer]

How high a DA? In most cases, not much difference - the takeoff method appropriate to the runway length. But in exceptional cases (Leadville is one), some instructors teach a modified soft field takeoff, the idea being to get the airplane off the ground and into ground effect in order to eliminate runway friction and better accelerate to climb speed.

 

[bnt83]

Here's a thought.

How many of these older aircraft even considered and tested partial flap takeoffs?

In the manual flap 150B, I pulled 1/4 flap near rotate speed then retract when established at climb speeds, and it was a blast to fly that way.

The 1968 (150 horse) 177 needs the 1/3 flaps for hot days or it seems like I'm on the ground forever.

Go out and practice a few of your own. Just because partial flap takeoff isn't written doesn't mean it wont work better for you. Most are the first availabe setting or notch if it's written in the book at all. I think the 205 has it written 20 degrees max for takeoff.

 

[poadeleted20]

In general, yes you want an increment or two of flaps on takeoff at a high DA

Why? In most cases, the additional drag is going to hurt performance, not help it.

but consult your POH on specific recommendations.

Agreed, and I don't know any light plane POH which recommends extra flap at high DA's.

 

[bnt83]

Indeed. C205 shows max performance takeoff with 20 degrees (1/2) flaps.

Play with the airplane and see what works for U.

 

[MAKG1]

How high a DA? In most cases, not much difference - the takeoff method appropriate to the runway length. But in exceptional cases (Leadville is one), some instructors teach a modified soft field takeoff, the idea being to get the airplane off the ground and into ground effect in order to eliminate runway friction and better accelerate to climb speed.

Given where he lives, I suspect he's talking about Lake Tahoe or other Sierra airports, most of which are in the neighborhood of 6000 or 7000 feet, with summer density altitude up to 8000 or 9000. Blue Canyon is a problematic airport because it's only a little lower (5300 MSL), but the runway is quite a lot shorter (3300). And it's quite a bit closer to Sacramento than Lake Tahoe is.

 

[MAKG1]

Here's a thought.

How many of these older aircraft even considered and tested partial flap takeoffs?

All of them.

The POH takeoff distances are measured with short field technique. I have yet to find an aircraft that has flaps and doesn't use them for a short field takeoff.

 

[tonycondon]

All of them.

The POH takeoff distances are measured with short field technique. I have yet to find an aircraft that has flaps and doesn't use them for a short field takeoff.

either the C-172N or P says no flaps for short field. The other one says 10 degrees. pretty sure the 150M's (I think) that I taught in said that 10 degrees decreased the ground roll but increased the distance over a 50 ft obstacle.

 

[MAKG1]

either the C-172N or P says no flaps for short field. The other one says 10 degrees. pretty sure the 150M's (I think) that I taught in said that 10 degrees decreased the ground roll but increased the distance over a 50 ft obstacle.

172N uses 10 deg. I did my checkride in one.

 

[cocolos]

In general, yes you want an increment or two of flaps on takeoff at a high DA but consult your POH on specific recommendations.

Another thing to remember at a high DA airport is that when you are in the pattern for landing, don't richen the mixture.

Ok a bit of a sidetrack but for the mixture do you leave is as is if for example you're at 10k and airport is at 7k or do you just enrich it by a couple of turns?

 

[MAKG1]

Ok a bit of a sidetrack but for the mixture do you leave is as is if for example you're at 10k and airport is at 7k or do you just enrich it by a couple of turns?

At that altitude, lean for best RPM with fixed pitch. Best RPM at 7,000 will be different from best RPM at 10,000.

You don't need to get it exact, but there is no need to artificially enrich beyond best power. You're not going to detonate above 5000 feet, even in a full-throttle climb at Vx.

 

[tinerj]

The Cessna 150 POH says that 10 degrees flaps will get the plane off the air in shorter distance, but offers no advantage in clearing a 50 ft obstacle.

 

[poadeleted20]

either the C-172N or P says no flaps for short field.

All the Grummans, too. And the amount of flap for which they call varies, too. But what I've never seen is a lighht plane POH/AFM which calls for different amounts of flap at low versus high DA.

 

[poadeleted20]

172N uses 10 deg. I did my checkride in one.

Cessna's recommendation for the 172 changed after either the 1979 or 1980 model year (I forget which). I discussed this with Cessna's tech support about ten years back, and after consultation with flight test and design, they were unable to tell me why the aerodynamically identical planes had different short field flap recommendations.

 

[Clark1961]

All the Grummans, too. And the amount of flap for which they call varies, too. But what I've never seen is a lighht plane POH/AFM which calls for different amounts of flap at low versus high DA.

The POH/AFM may not call for it but the performance charts sure show the advantage of flaps for take-off on the Frankenkota. The advantage increases with increasing DA.

Not telling the pilot specifically what to do may be a liability thing. Or it could just be the Piper folks saying the pilot should be able to figure out what is best. YMWV.

 

[tonycondon]

Cessna's recommendation for the 172 changed after either the 1979 or 1980 model year (I forget which). I discussed this with Cessna's tech support about ten years back, and after consultation with flight test and design, they were unable to tell me why the aerodynamically identical planes had different short field flap recommendations.

My friends in flight test are very careful to avoid retesting as much as possible just in case they get a different answer than the first time around.

 

[poadeleted20]

The POH/AFM may not call for it but the performance charts sure show the advantage of flaps for take-off on the Frankenkota. The advantage increases with increasing DA.

But does the amount of flap called for in the short-field takeoff procedure change with higher DA? IIRC, the PA28's all call for 25 flap (2 notches) for short-field without regard for DA.

 

[PilotAlan]

All the Grummans, too.

Ron, correct me if I'm wrong. IIRC, the issue with Grummans is that the flaps are activated by an up-down switch, with no indicator, so there was no FAA-approved method of consistently setting flaps.
So for certification, there's no flaps settings for takeoff.

Again, IIRC, flaps do in fact make a big difference, and the real-world way of setting them is to deflect one aileron all the way down and set the flaps to match that deflection.

 

[rottydaddy]

But does the amount of flap called for in the short-field takeoff procedure change with higher DA? IIRC, the PA28's all call for 25 flap (2 notches) for short-field without regard for DA.

I can't see why it would; never heard of such a thing in a POH.
Here's how I see it: any feature of the airplane that enhances short-field takeoff performance (meaning distance to clear a 50-foot obstacle) is going to enhance it regardless of DA. Drag (either parasitic or induced) caused by flaps would not increase as a result of the air being thinner- that's nonsensical.
Short-field performance is all about climb angle after takeoff, when you get down to it. Rate of climb doesn't matter, and a short ground roll is good, but neither of those will get you out of a short field like a good angle of climb. Flaps, whether used for takeoff or landing, allow a steeper angle of climb or descent at a given airspeed. For takeoff, it also stands to reason that flaps will help the airplane get off the ground at a lower airspeed, which allows you to get Vx before you run out of room to use the resulting angle of climb. Some people swear by dropping flaps after they are well into the takeoff roll, but I don't see how that would help, no matter how rough the runway is.

I can see the temptation to start with the flaps up when leaving a mountain strip on a hot day... that should give you more "giddyup", right? Maybe. But more rapid acceleration on the roll doesn't necessarily mean a shorter ground roll, or a better angle of climb. Starting the roll with the airplane clean doesn't improve short-field performance at any altitude... if the POH says "X amount of flaps will get you over a 50-foot obstacle at X distance, while yielding X angle of climb at Vx", you can believe it.

Then there's the actual crux of the problem- power. The problem with high DA is that the less-dense air contains less oxygen, which leaves the engine at a disadvantage. The published service ceiling for an airplane refers to the altitude where it won't climb more than 100 fpm, and that has nothing to do with the wings, flaps, or any lifting surface- it's about horsepower. Get high enough (even if you're still on the runway at a high-elevation field on a hot day), and you could be looking at a DA that is higher than your service ceiling. In that situation, flaps or no flaps, you'll want to take off from a cliff, preferably a very high one. Under ordinary high-DA conditions, it isn't so dramatic, but you may find that even with full power, leaned, etc., the rpms will be lower, and the airplane just won't climb like you want it to, even at Vx. The whole "lift/weight/thrust/drag" thing from ground school becomes evident here, as well as the true relationship between airspeed and angle of attack. A given V-speed is attained with a different A of A at different altitudes, and at very high altitudes, that can be game-changing, because the wing needs more than a certain speed to do what you want it to do- it needs to fly at that speed within a specific A of A range. And if thin air is robbing you of thrust, the A of A/airspeed relationship changes, because the whole thrust/drag/lift/weight thing changes.

This is why most performance charts list different ground roll and obstacle-clearing distances for different DAs. Vx is always the same number, the best angle of climb speed, but that best angle will be shallower.

I guess that extremely high DA can affect the performance of lifting surfaces, including flaps, but the DA would have to be well above the service ceiling for that to happen. And it wouldn't matter anyway, because the engine would be struggling so hard you'd probably never leave the surface. But again, in such a scenario, a tall cliff might help.

 

[MAKG1]

Actually, Vx is a little higher in IAS at high density altitude. Vy is lower. They are equal at the absolute ceiling. So, there will be some variation in the effectiveness of flaps with density altitude. BUT it is not enough to warrant a different configuration.

One can derive these by drawing tangents and intercepts to the power curve. Density altitude moves the power curve down, but maintains its shape.

 

[Clark1961]

But does the amount of flap called for in the short-field takeoff procedure change with higher DA? IIRC, the PA28's all call for 25 flap (2 notches) for short-field without regard for DA.

My post already answered your question. "The POH/AFM may not call for it..."

The original post asked: "If you're at a high density altitude is it better to setup for something similar to a shortfield take (flap settings and all) or just a normal takeoff with no flaps. For references I fly PA28-180 and C152."

And I noted that the performance charts for a PA-28-201T showed better performance with flaps at higher DA.

The performance charts are only for no flaps and flaps 25 in the manual for the Frankenkota so I cannot address the question of how much flaps. In practice flaps 25 seems to do a little better job of getting off the ground quicker than flaps 10.

 

[tonycondon]

Again, IIRC, flaps do in fact make a big difference, and the real-world way of setting them is to deflect one aileron all the way down and set the flaps to match that deflection.

thats usually what i do in cessnas too

 

[Sac Arrow]

Why? In most cases, the additional drag is going to hurt performance, not help it.

Agreed, and I don't know any light plane POH which recommends extra flap at high DA's.

Depends on the constraint - yes as a general rule flaps tend to decrease climb angle, but they will get you off the runway sooner if that's the issue.

Ok a bit of a sidetrack but for the mixture do you leave is as is if for example you're at 10k and airport is at 7k or do you just enrich it by a couple of turns?

I wouldn't enrichen it at all (I don't even enrichen from cruise to landing at sea level airports.) On most engines, the mixture tends to automatically enrichen on a power reduction anyway. Engine outages caused by over rich settings in the pattern have taken more than one pilot out at high DA airports.

Taking off from your 7K airport, you want to be leaned for best power, which is normally accomplished in a full power runup.

 

[MAKG1]

That depends on how long your descent is. If you're descending from over the Sierra (say, 10,500) down to Sacramento, you'll need to enrich somewhat or your engine isn't going to be happy at 1000 MSL, especially if you need to increase power to extend a downwind or somesuch. If you're descending from 3500 to Sacramento, that's a lot less important. Same deal with descending into Lake Tahoe (though I'd want to approximate best-power mixture in case of a go-around -- that's much more fiddly at a high altitude airport than it is at sea level). Mountain airports sometimes (not always) have terrain as a factor in go-arounds.

 

[Lance F]

I am not an aerodynamicist, and yes I know jets can be different than light single engine airplanes in some ways. However, it may be of interest to this discussion that the Hawker 800 has tables for takeoff speeds (and other info) for both 0º and 15º flap settings. The interesting thing is that at high density altitudes they do not have charts for 15º. I can only assume from this that for high density altitudes takeoff performance is better with no flaps. Whether or not this applies to a PA28, I don't have the slightest idea.

 

[Clark1961]

I am not an aerodynamicist, and yes I know jets can be different than light single engine airplanes in some ways. However, it may be of interest to this discussion that the Hawker 800 has tables for takeoff speeds (and other info) for both 0º and 15º flap settings. The interesting thing is that at high density altitudes they do not have charts for 15º. I can only assume from this that for high density altitudes takeoff performance is better with no flaps. Whether or not this applies to a PA28, I don't have the slightest idea.

The performance charts for my PA-28-201T have ground roll and 50 foot Barrier (their word, not mine). The charts cover both flaps 0 and flaps 25. The range of OAT and pressure altitudes on the performance charts for both flap conditions is approximately the same (the 10,000 altitude curve for flaps 25 is truncated at 28 C compared to the flaps 0 10,000 altitude curve which continues to 40 C).

The charts show that flaps 25 produces shorter distances to clear the 50 foot barrier in all cases.

I have no data for the normally aspirated PA-28's to see if they have similar performance.

 

[rottydaddy]

I am not an aerodynamicist, and yes I know jets can be different than light single engine airplanes in some ways. However, it may be of interest to this discussion that the Hawker 800 has tables for takeoff speeds (and other info) for both 0º and 15º flap settings. The interesting thing is that at high density altitudes they do not have charts for 15º. I can only assume from this that for high density altitudes takeoff performance is better with no flaps. Whether or not this applies to a PA28, I don't have the slightest idea.

Interesting. I guess I need a blanket disclaimer for all my ramblings here, along the lines of "unless I specifically mention jets, do not assume this applies to jets".
Maybe, somehow, ground roll distance or dstance required to reach Vx is affected by the flaps with that airplane. You mention speeds as well; in my piston experience, indicated Vx is always best angle of climb, regardless of how it relates to TAS (affected by DA). It makes some sense to me- jets are pretty drag-critical overall. But I have no firsthand experience with jets, so what do I know?

 

[midlifeflyer]

That depends on how long your descent is. If you're descending from over the Sierra (say, 10,500) down to Sacramento, you'll need to enrich somewhat or your engine isn't going to be happy at 1000 MSL, especially if you need to increase power to extend a downwind or somesuch. If you're descending from 3500 to Sacramento, that's a lot less important. Same deal with descending into Lake Tahoe (though I'd want to approximate best-power mixture in case of a go-around -- that's much more fiddly at a high altitude airport than it is at sea level). Mountain airports sometimes (not always) have terrain as a factor in go-arounds.

Agree. I enrichen on the descent so that I have power available for a go-around. And approximating tends tends to work out fairly well; just be prepared for the need to tweak.

 

[Alexb2000]

Here is the Cessna logic I use in Taos (7100' MSL) that you might want to apply to the 152. Cessna's have single slotted fowler flaps (at least all those I can think of). So deploying the flaps to the first notch increases the wing area and lift at a minimum cost of drag. In practice every high DA takeoff seems better IMO with a single notch of flaps. It comes off much easier then just hold it in ground effect for additional speed. I don't retract them until about 500 AGL just because I don't want to change the wing configuration at low altitude.

On leaning for mountain flying, if you plan to do that kind of flying often then break the habit of full rich. Don't let yourself slam home the mixture as the checklist says even at sea level. Rather train yourself to quickly adjust mixture for a go around. Everyone knows that taking off full rich in a NA bird at high DA isn't good, but neither is landing that way. You will kill the engine. I have flown with several people who landed at a high DA airport without even realizing their engine was dead and the prop was just wind milling. If I would have said, "we're deadstick" we probably would have crashed so I didn't and just hoped nothing obstructed the runway.

 

[poadeleted20]

Ron, correct me if I'm wrong. IIRC, the issue with Grummans is that the flaps are activated by an up-down switch, with no indicator, so there was no FAA-approved method of consistently setting flaps.
So for certification, there's no flaps settings for takeoff.

That is not correct. The manufacturer determined that there was no significant advantage, and several potential disadvantages, to making takeoffs with flaps extended.

Again, IIRC, flaps do in fact make a big difference, and the real-world way of setting them is to deflect one aileron all the way down and set the flaps to match that deflection.

Also incorrect. Flight tests have shown no significant advantage in the use of flaps to shorten takeoff roll, and some disadvantage in initial climb rate. That's why the AYA (the Grumman owners group) Pilot Familiarization and Safety Programs recommend following the POH and making all takeoffs with flaps up.

 

[poadeleted20]

My post already answered your question. "The POH/AFM may not call for it..."

The original post asked: "If you're at a high density altitude is it better to setup for something similar to a shortfield take (flap settings and all) or just a normal takeoff with no flaps. For references I fly PA28-180 and C152."

And I noted that the performance charts for a PA-28-201T showed better performance with flaps at higher DA.

The performance charts are only for no flaps and flaps 25 in the manual for the Frankenkota so I cannot address the question of how much flaps. In practice flaps 25 seems to do a little better job of getting off the ground quicker than flaps 10.

Well, we knew that going it based on the POH. Point is, if you want short-field in a PA28, you use 25 flaps regardless of DA, and you do not change takeoff flap setting based on DA -- which is the question about which the OP asked.

 

[SbestCFII]

You may be able to get up and then accelerate faster while in gound effect for a better climbout. Before the takeoff roll, lean to the best power setting and don't use any more than 1 notch of flaps. In general 1 notch adds more lift than drag and thereafter the ratio is not as advantageous.

 

[Clark1961]

Well, we knew that going it based on the POH. Point is, if you want short-field in a PA28, you use 25 flaps regardless of DA, and you do not change takeoff flap setting based on DA -- which is the question about which the OP asked.

No, Ron, the OP asked whether to use flaps 0 or setting up for short field when at higher DA. That's all they asked.

 

[PilotAlan]

That is not correct. The manufacturer determined that there was no significant advantage, and several potential disadvantages, to making takeoffs with flaps extended.

Also incorrect. Flight tests have shown no significant advantage in the use of flaps to shorten takeoff roll, and some disadvantage in initial climb rate. That's why the AYA (the Grumman owners group) Pilot Familiarization and Safety Programs recommend following the POH and making all takeoffs with flaps up.

OK then, glad I asked. Is that an OWT, then? I know I've heard that story multiple time, including from Grumman pilots. But then there's Cessna pilots that think slipping with flaps makes the wings fall off.

 

[bnt83]

OK then, glad I asked. Is that an OWT, then? I know I've heard that story multiple time, including from Grumman pilots. But then there's Cessna pilots that think slipping with flaps makes the wings fall off.

I slip every Cessna i fly regardless of flap setting never hand any issues. I think it's an OWT. Some lawyer made cessna put the placard in to "avoid or prohibit" it IMO.

 

[Alexb2000]

I slip every Cessna i fly regardless of flap setting never hand any issues. I think it's an OWT. Some lawyer made cessna put the placard in to "avoid or prohibit" it IMO.

Should be considered mandatory training.