Departing a hot and high airport

[RobertE]

Next week I've got to pick up my wife and her friend from Wells, Nevada. I'll be sure to have little enough fuel so as to stay 100 or 200 lbs below max gross in my M20J, but the airport IS at 6K and may be fairly hot. This got me thinking of takeoff performance. The POH say ground roll will be 2500 feet and it will be 5000 feet to clear 50 feet. This at max gross, but we'll 200 lbs below. The runway is 5000 feet.

Would all of you feel comfortable with those margins?

Thanks.

[MB65E]

What temp did you use? I wouldn't feel up to it! It will probably be really surprising for you unless you caculated the departure at 100f. If you caculated using the 100f already and it's anything less than 100f and a headwind component, only then I'd consider it.

I think 100f vs 59f (standard day) would be more noticeable than a couple hundred lbs...

But to make it work,

You could leave at dawn or later in the evening, Hopefully it's blowing 25kts, and maybe get gas down the road at a lower elevation/temp.

Have fun!!

-Matt

[larryb]

I fly out of Truckee in a J. That is 5900 feet. The plane will take off fine but climb poorly. This is an issue at Truckee surrounded by mountains. But the satellite map for wells looks pretty flat. I think you should be ok. I would do it early morning. You should take off and then let it accelerate to 90 knots before starting to climb. I lean for 14.5gph on takeoff at that altitude.

Sent from my iPad using Tapatalk

[Lood]

Don't know the elevation of the airport you're using, but FWIW, I've taken off from a 5300' grass runway in my F, MAUW, no wind, temperature probably not more than 70 deg F. I used about 2100' of 2850' available to get airborne and the climb-out was around 250ft/min, IIRC.

If there's no immediate high ground or obstacles to clear, you should be fine, especially if you are 200 lbs below and using a paved runway. First thing you'll notice is the rather poor acceleration, more so as you get closer to rotation speed. I let it run about 5mph faster than normal before I rotated and after rotation, I immediately leveled out and tucked the gear away to gain speed asap. Initial climb out was done at VX and not the normal VY plus  a few knots.

Make sure that you set the mixture correctly for that altitude and I would be a little wary if temperatures increased towards 80 deg F.

[N9405V]

Do it early in the morning. Looks like lows will be around 45 degrees. Plus your passengers will appreciate flying when it's cooler.

[N201MKTurbo]

I've taken off from telluride at gross weight in my M20F a few times. That airport is over 9000 feet elevation. It will be just fine, just be sure to watch your airspeed as usual and accept the fact that it is not going to climb as fast as you are used to.

[stevesm20b]

I have taken off at gross weight in my B model from Flagstaff AZ in the summer with no problems. Flagstaff is 7,000ft. I also fly out of Big Bear (6,750) in the summer all the time. I think the 3 blade prop helps.

[piperpainter]

In wells you have no obstacle to climb at all and a long runway. You'll be fine even at gross weight midday. The only thing with midday is that you'll have bumps on the way home! So early or late is better for a smooth flight! I'd take my C in there with no prob! I've taken the C off from KPNA (7000ft MSL with DA around 9K) with no problems. Endemic climb but I didn't have much for obstacles! Have fun, be safe!

[chrisk]

I've gotten to pieces of advice which are some what contradictory:

• You should have at least 71% of rotation speed at the 50% mark on the runway, if not abort. (Mountain Flying Bible)
• You should be wheels up at the 50% mark on the runway, if not abort.

Since I don't have much experience in high altitude take offs, I opt for the more conservative of the two. 

 

I took off at Angle Fire last year, which has a long runway.  I didn't come close to using half, but it was a long take off run.

 

And read up on leaning for high altitude take offs.   Too rich will rob you of power.

[DaV8or]

I fly with only a very few additional graphs and charts, but one of the MANDATORY charts is the Koch Chart.  This is a MUST for ANYONE flying high density and high altitude airports. The chart is everywhere on the Internet.  Here is one such example...

 

http://www.learntoflywithkris.com/koch_chart.html

 

Download and print this one...WELL worth it.

 

Pmccand

 

Thanks for the heads up! I had never heard of the Koch Chart before. I searched and found this one that I like a little better than the one you posted because it just gives you simple multiplication factors to plug in for the results. I have been wondering what to put on the back side of my power setting chart and now I know! 

 

Thanks again!

 

[DaV8or]

And read up on leaning for high altitude take offs.   Too rich will rob you of power.

 

This is the lesson that us flat, sea level pilots never really get. I have been told to lean at the run up to basically find a little ROP peak I think by leaning until the RPM increases, then enrichen a few turns back in. I have done this a few times and I keep a careful eye on the engine monitor. This method seems to make the EGT and CHT skyrocket, so as I'm climbing out I will keep going rich until it settles down.

 

I don't know if I'm satisfied with this method, or that I'm doing it right. What do you real mountain men do?

[FoxMike]

I have been operating at high density altitude airports for 40 years or so.  After you do your check list at the end of the runway, increase RPM to about 2000 and find peak.  Start down the runway making sure you have peak mixture.  If you are below peak (LOP) you will have a lot less power and if a little rich you will have a little less power than being at peak.  Make sure you start on the centerline and stay on it.  The extra workload of keeping the mixture on the sweet spot has caused more than a few pilots a trip into the weeds.  Use the same IAS as usual for rotation.  If you are not getting  enough power when you climb out of ground effect you will come back to earth so don't get into a rush to retract the gear.  Getting the most performance from the engine is an art form that comes from repeated tries.  You won't get it exactly right the first time.  Also remember the wing does work as well in high density altitude so make sure you maintain at least best rate airspeed until you get the airplane cleaned up.  High DA takeoffs are not hard but require attention to detail.  Over the years I have seen lots of them screwed up and the result is sometimes fatal.  I have never been to Wells but it might make sense to circle over the airport until you are sure you can clear the terrain enroute.   

[RobertE]

This is very helpful, gentlemen. How lucky we are to have experts just a few key strokes away. Just one follow-up.

If I look at the performance charts in my POH the rate of climb at max gross at the 8k density altitude that I'm guessing will prevail I see a climb rate of about 500 FPM. But if I interpolate from the takeoff charts ( i.e. the number of feet after TO roll to reach 50 feet AGL) the implied climb rate is half that. Now the performance charts assume no flaps or gear, but flaps at low altitude ought to help, not hurt, and the gear could be cleaned up moments after lift off. So what gives?

Actually, two follow ups. I never climb at VX. That wing just doesn't feel like it was designed for that. How many others stick with VY?

[carusoam]

Be confident with your ability to calculate or obtain density altitude.

Be confident with your ability to calculate T/O distance.

Be confident with your weight and balance.

When hot and high, trees appear large in the windscreen.

If not confident in these skills, seek professional assistance...

Let me know if this statement is too strong.

Best regards,

-a-

[DaV8or]

This is very helpful, gentlemen. How lucky we are to have experts just a few key strokes away. Just one follow-up.

If I look at the performance charts in my POH the rate of climb at max gross at the 8k density altitude that I'm guessing will prevail I see a climb rate of about 500 FPM. But if I interpolate from the takeoff charts ( i.e. the number of feet after TO roll to reach 50 feet AGL) the implied climb rate is half that. Now the performance charts assume no flaps or gear, but flaps at low altitude ought to help, not hurt, and the gear could be cleaned up moments after lift off. So what gives?

Actually, two follow ups. I never climb at VX. That wing just doesn't feel like it was designed for that. How many others stick with VY?

 

I never use Vx because I really don't have a need for it. However, there are those that use Vx to get as high as possible while still in the vicinity of the airport in case of engine failure. I tend to climb Vy for the first few hundred feet and then nose over a bit to about 110 mph, but there aren't a lot of obstructions the places I fly. I would guess that in the high DA environment going Vy is the way to go unless there were some trees, or a mountain, or something.

[Hank]

At my 3000' home field, I rotate, establish climb, raise gear and hold Vx until over the trees (just a few seconds), then finish my climb at Vy. But then again, it's pretty low. Don't recall my loaded departure from Cody, WY, but also don't remember any issues. It was also pretty long )the runway and my takeoff roll).

[Lood]

I only use VX when there are obstacles or high ground in the immediate vicinity and then very temporarily. Otherwise, I always climb out at 110mph - 120mph IAS - on my F.

With regards to the mixture setting, peak will certainly give you optimum power, but then you have to keep a sharp watch on your CHT's. Might be different on other airplanes, but if I take off on a hot day, I find that the CHT's on my F goes up very quickly if I am not at sea level EGT or burning somewhere around 16 gal/hr at take off.

This will also differ slightly with different altitudes.

[dfgreene61]

My home airport is at 5,700. We get close to 8,500 da in the summer. I fly early or late to avoid bumps. I also use my egt on #2 cylinder to set climb. As long as #2 is around 1,280 in climb, I'm good to go. Before takeoff I set mixture using prior experience, then during the roll I adjust if I'm too hot. Works great. You can do the same based on your egt during full rich climb at sea level. Use your full rich, sea level egt as your high da target during climb. I also clean up quickly and climb out at 95 knots. '82 m20j

[wishboneash]

I try to pay attention to the ground roll since it you will be up to a fairly high ground speed before you take off. Losing control on the runway is something I worry about. I usually don't have a problem once airborne since I am quite light. Truckee has been the highest DA I have experienced (around 9000 ft).

[Super Dave]

This is very helpful, gentlemen. How lucky we are to have experts just a few key strokes away. Just one follow-up.

If I look at the performance charts in my POH the rate of climb at max gross at the 8k density altitude that I'm guessing will prevail I see a climb rate of about 500 FPM. But if I interpolate from the takeoff charts ( i.e. the number of feet after TO roll to reach 50 feet AGL) the implied climb rate is half that. Now the performance charts assume no flaps or gear, but flaps at low altitude ought to help, not hurt, and the gear could be cleaned up moments after lift off. So what gives?

Actually, two follow ups. I never climb at VX. That wing just doesn't feel like it was designed for that. How many others stick with VY?

It's a popular misconception that flaps improve climb. In reality, flaps degrade climb rate and climb angle at any altitude. They do however help you get airborne sooner on the takeoff roll, so setting takeoff flaps may help you clear a close-in obstacle. Also, you may already know this, but Vy decreases with altitude. There is probably a table or graph in the performance section of your POH that shows a decrease of about 1 knot per thousand feet.

Others have suggested setting peak EGT for best power, but best power mixture is 80-100 ROP.

[PTK]

I have been operating at high density altitude airports for 40 years or so. After you do your check list at the end of the runway, increase RPM to about 2000 and find peak. Start down the runway making sure you have peak mixture. If you are below peak (LOP) you will have a lot less power and if a little rich you will have a little less power than being at peak. Make sure you start on the centerline and stay on it. The extra workload of keeping the mixture on the sweet spot has caused more than a few pilots a trip into the weeds. Use the same IAS as usual for rotation. If you are not getting enough power when you climb out of ground effect you will come back to earth so don't get into a rush to retract the gear. Getting the most performance from the engine is an art form that comes from repeated tries. You won't get it exactly right the first time. Also remember the wing does work as well in high density altitude so make sure you maintain at least best rate airspeed until you get the airplane cleaned up. High DA takeoffs are not hard but require attention to detail. Over the years I have seen lots of them screwed up and the result is sometimes fatal. I have never been to Wells but it might make sense to circle over the airport until you are sure you can clear the terrain enroute.

Excellent FoxMike! A lot to learn!

One question related to this as it pertains to maximizing power. The APS guys talk about the concept of leaning to target EGT out of any da airport. That being a value noted at takeoff out of a sl airport on a standard day.

Is your purpose of having peak mixture and that of leaning to target EGT one and the same? IOW do we end up at peak mixture simply by applying target EGT method?

Thanks.

[Hank]

Sea level takeoff should be safely ~200 ROP. So leaning to that same number for high DA departure should still be safely ~200 ROP, the same setting that is used for climb. Personally speaking, Peter, I would not want to climb at peak . . . .

[PTK]

Thank you Hank. 

 

I don't feel comfortable climbing at peak either.

 

So if I'm understanding correctly:

 

1. Climbing at peak is the best we can do as far as maximizing power, but

2. Target EGT does not put the engine at peak, and therefore does not give us best power, necessarily, but it's easier and safer for the engine (sufficiently rich).

 

Is this correct?

 

Does target EGT ever approach yielding maximum power under some conditions?

 

Can the original poster then apply target egt method assuming he has a precise value? 

[Rhumbline]

Sea level takeoff should be safely ~200 ROP. So leaning to that same number for high DA departure should still be safely ~200 ROP, the same setting that is used for climb. Personally speaking, Peter, I would not want to climb at peak . . . .

 

I agree.  I would not take off or climb at peak EGT.  Back in the "good ol' days" when I was instructing, the procedure would be to lean during the run-up  until the RPM dropped or the onset of engine roughness (usually simultaneous and the latter is the best indication with a constant speed prop), enrich back to peak RPM or engine smoothness and then further enrich by 1 1/2 turns on a vernier mixture control or 1/4" (I find that 1/2" or a bit more is best on my plane) of travel on other mixture controls.  A crude and inaccurate way to go but better than a setting too rich or lean.  A more accurate method is to do a full power run-up and find peak EGT and then enrich to whatever value ROP you intend to use.  I personally do not do this as I am concerned about prop FOD among other things so I use the crude method and make certain I'm a little richer rather than leaner and tweak it a bit if the EGT looks high or low on the take-off roll and then carefully monitor CHT after takeoff and during climb.

 

In an effort to keep my CHT reasonably low, I had been using 200 ROP during the climb and accepting the consequent power loss.  After conferring with a relatively well known engine and maintenance guru after watching one of his webinars, however, he strongly advised using a setting around 125 ROP at the altitudes I'm operating at (field elevations above 6 & 7 thousand and DA's often much higher) as there is a great likelihood the richer setting will lead to fouling problems.  I've found that I can lean to 125 ROP (as opposed to 200 ROP) without violating most of the other rules of thumb. 

 

Disclaimer: I'm imparting what I know on the matter and that ain't much so do your homework. Please bear in mind that, in my case, I am referring to a normally aspirated and carbureted motor.  Shouldn't matter much for the injected folks but this is obviously not for the folks with turbos too.     

[Bartman]

I would not use 200 ROP at 5000ft in my J model. Density altitude will likely be over 7500 and less than 75% power.

I would find peak as close as possible on the ground, and then shoot for about 25-50 ROP in ground roll/climb which would be about 1400 EGT on my monitor. After I had the aircraft cleaned up and cleared obstacles I would add fuel as needed to achieve close to 1250-1300 EGT until about 8500 DA (which is close to target EGT and 200ROP).

As I climb above about 8500 DA my SOP is to gradually lean more aggressively such that I am 0-25 ROP by the time I am 10,000ft DA. For cruise above 10,000 I do not necessarily use EGT, just fuel flow and best power by feel.

That's my opinion. TIFWIW.