I want some kind of aviation performance table.

[aviatoreb]

On 6/28/2023 at 3:23 PM, 0TreeLemur said:

Weekend before last I landed our J at SAF on rwy 20 with winds 230@18G30 , temperature 29C, and density altitude 9200'.  So busy dealing with gusty crosswind component that the 8000' runway seemed immense.

RJ's and 737s use that runway.  Runway length is a non-issue for a piston single.

Have a good trip.

Thanks!

Yeah I scoped out the activity on flight aware and yes indeed lots of jets.

So folks - I am utterly confident the runways there are plenty plenty big since I have a good feeling I can land anywhere a 737 can land.

But nonetheless - I would like to understand how this works.  Just for learning sake.

That Koch table - is that for engine performance or is that for performance of the air foils.  

-When landing say at 9000ft density altitude, I know our TAS is high as compared to sea level - as we still stall based on IAS or better yet, AO, but the moment the tires are on the ground, there is more speed for the brakes to dissipate.  So is the Koch table the one that tells me the equivalent lengths?  or is that for engine performance - of what - of NA?

-Even a Turbo has diminished runway performance at altitude - yes power may be 100% same, but again, it takes more TAS to get off the ground since we leave the ground at a certain IAS, or better said AO.  So again - is that AO?

I just want to know for sure how this all works....just because I like to know stuff.

E

[0TreeLemur]

27 minutes ago, aviatoreb said:

When landing say at 9000ft density altitude, I know our TAS is high as compared to sea level - as we still stall based on IAS or better yet, AO, but the moment the tires are on the ground, there is more speed for the brakes to dissipate.  So is the Koch table the one that tells me the equivalent lengths?  or is that for engine performance - of what - of NA?

When I landed I had about 20 knots of headwind component, so I wasn't going that fast groundspeed.   Still 70 KIAS over the fence.  I landed on rwy 20 leaving an enormous amount of runway to coast.  I couldn't even see the end.   I used no more brakes than usual, just to make a turn-off.

If no headwind, a little more wear on tires and bearings landing at higher TAS.  It felt normal.

The ground roll on takeoff on the other hand was noticeably longer.   Instead of the usual 10-11 seconds, it was probably more like 20-25 seconds.  With your four bladed fire breathing beast, you might not even notice much difference.

[aviatoreb]

12 hours ago, 0TreeLemur said:

When I landed I had about 20 knots of headwind component, so I wasn't going that fast groundspeed.   Still 70 KIAS over the fence.  I landed on rwy 20 leaving an enormous amount of runway to coast.  I couldn't even see the end.   I used no more brakes than usual, just to make a turn-off.

If no headwind, a little more wear on tires and bearings landing at higher TAS.  It felt normal.

The ground roll on takeoff on the other hand was noticeably longer.   Instead of the usual 10-11 seconds, it was probably more like 20-25 seconds.  With your four bladed fire breathing beast, you might not even notice much difference.

Thanks - what you describe is what I expect.

At this point I have no worries in the least for runway length at SAF but I am just continuing the discussion for learning sake to enumerate the changes in performance.

[Skates97]

17 hours ago, aviatoreb said:

-Even a Turbo has diminished runway performance at altitude - yes power may be 100% same, but again, it takes more TAS to get off the ground since we leave the ground at a certain IAS, or better said AO.  So again - is that AO?

 

17 hours ago, 0TreeLemur said:

The ground roll on takeoff on theother hand was noticeably longer.   Instead of the usual 10-11 seconds, it was probably more like 20-25 seconds.  With your four bladed fire breathing beast, you might not even notice much difference.

I don't have a turbo, so can't comment to any diminished performance, but you will have diminished performance from your prop. That combined with the diminished performance of the wing will contribute to a longer ground roll to get the required IAS to lift off. Something that sometimes catches people off guard if they have not landed at a high DA airport is the visual difference flying at the same IAS but a higher TAS and ground speed than they are used to seeing in the pattern and they can get slow. Easy enough to overcome by just paying attention to the airspeed indicator but something to keep in mind.

[PT20J]

If you want something simpler than the Koch chart, you can get a DENALT computer. https://www.ebay.com/itm/275872215202?chn=ps&mkevt=1&mkcid=28

These adjust SL takeoff distance and ROC for density altitude. They don't have landing distance because you can always land shorter than you can takeoff.

The wing doesn't really care about density; it only knows TAS. However, the engine and propeller performance decreases with altitude. The combination of reduced power and increased groundspeed due to increased TAS is what eats up runway and decreases climb angle and ROC.

Great video from the past: 

 

Skip

[0TreeLemur]

Fun video @PT20J.  I'm flying to New Mexico again tomorrow.   Planning to land at LAM, with SAF as plan B.   Also planning to control my energy on final better than Harry Bliss!

[PT20J]

1 minute ago, 0TreeLemur said:

Fun video @PT20J.  I'm flying to New Mexico again tomorrow.   Planning to land at LAM, with SAF as plan B.   Also planning to control my energy on final better than Harry Bliss!

Good for you. If you go to SAF, grab a crew car and get lunch at Maria's. I think the terminal is still under (re)construction, but Signature always has taken good care of me and they have self serve fuel.

[aviatoreb]

Sadly - I’m not flying myself to Saf tomorrow / and the weather is perfect for the trip!  I am having an oil pressure issue then we couldn’t resolve in time.  I bought an airline ticket yesterday.  :-(

[jlunseth]

Most of the airports in that general area are flatland airports, as someone already said about KSAF. Taos, SAF, Double Eagle are all like that. They are not airports tucked into a mountain valley with high peaks close by, such as Kalispell. The only one I can think of in that area where you really have to be on your toes is Angelfire, known for its treachery. There is a good video on YouTube from a local pilot with all the ins and outs of landing and leaving from Angelfire.

One trick I learned early, for a safe climb out to cross mountain peaks, is that most of the airports along the Rockies have a VOR that is offset from the airport and inside the valley. The standard climb out is not to go straight at the peaks, but fly to the VOR, which may be north or south of the field, and if necessary spiral up. This technique will come into play on days when the winds aloft are blowing rapidly toward the peaks.

I haven’t had any difficulty at all, either landing or taking off, from any airport in that general area, in my 231. Have not done Angelfire though.

Turbulence, as noted, is harsh. I attended a Mooney PPP there about three years ago and everyone was affected. It is mostly ground turbulence, so you can fly to, say, 5,000 AGL and be out of it or mostly out of it, but 5,000 AGL is about 10 MSL in that area, and flying to 5 AGL does not help when you need to land. 

Afternoon is worse than morning for turbulence, and most areas are prone to afternoon Tstorms. That is true at ABQ and all up and down the Rockies, or anywhere (such as KRAP) where there is orographic lifting potential.

Doesn’t your aircraft POH have tables for landing and takeoff? If tables did not come from Rocket, then it must be the case that the STC provides to use the 231 tables. I am sure that tables are a required part of certification.

[toto]

53 minutes ago, jlunseth said:

There is a good video on YouTube from a local pilot with all the ins and outs of landing and leaving from Angelfire.

Here’s the Angel Fire video. I have watched this a bunch of times, but still haven’t ever made the trip. Every time we go to Angel Fire we land at Raton and drive in.

Having spent a lot of time in the area, my big fear is getting in and then having to wait days to get out. The crosswinds can be insane.

 

 

[A64Pilot]

On 7/6/2023 at 7:57 PM, PT20J said:

 

The wing doesn't really care about density; it only knows TAS. However, the engine and propeller performance decreases with altitude. The combination of reduced power and increased groundspeed due to increased TAS is what eats up runway and decreases climb angle and ROC.

I beg to differ.

The wing only “knows” indicated, not true. For instance on an approach to a high altitude airport the aircraft will stall close to the bottom of the white arc on the indicated A/S even though true airspeed will be much higher. So fly indicated airspeeds in the pattern, ignore TAS on the fancy glass.

Roc suffers primarily from lower engine power, but climb angle suffers from the higher ground speed required to get to the indicated Vy airspeed.

Vy does come down with DA but at airport altitudes it’s not a whole lot

Edited July 9, 2023 by A64Pilot

[PT20J]

1 hour ago, A64Pilot said:

The wing only “knows” indicated, not true.

Lift is a function of dynamic pressure, q, where q = 1/2pV^2, p being air density and V being TAS. As altitude increases, p decreases, and at the same configuration, weight and angle of attack. TAS must increase to make up the difference.

The airspeed indicator actually measures q, but it is calibrated in knots. Since the TAS increases to make up for the loss of density, q stays the same and that's why the IAS performance numbers (Vs, Vx, Vy, etc.) don't change. But the wing is going through the air faster and you see this in increased groundspeed during landing and takeoff.

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[jlunseth]

2 hours ago, PT20J said:

Since the TAS increases to make up for the loss of density, q stays the same and that's why the IAS performance numbers (Vs, Vx, Vy, etc.) don't change. But the wing is going through the air faster and you see this in increased groundspeed during landing and takeoff.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I think I must be misunderstanding. Vx and Vy do change with altitude. The change is not large unless you are quite high, but if you are planning a Vx climb over a peak at 14k you need to adjust your Vx as you go up. I don’t use Vy at all, and Vx maybe once a year, so it does not matter much to me. I do, however, remember having to adjust Vx to climb out of Kalispell once several years ago, which is how I learned it is better to go to the off-airport VOR and spiral up than get in a hurry to climb straight out with a strong wind at your tail.

[PT20J]

39 minutes ago, jlunseth said:

I think I must be misunderstanding. Vx and Vy do change with altitude. The change is not large unless you are quite high, but if you are planning a Vx climb over a peak at 14k you need to adjust your Vx as you go up. I don’t use Vy at all, and Vx maybe once a year, so it does not matter much to me. I do, however, remember having to adjust Vx to climb out of Kalispell once several years ago, which is how I learned it is better to go to the off-airport VOR and spiral up than get in a hurry to climb straight out with a strong wind at your tail.

I shouldn't have included Vx and Vy because they are affected by more than aerodynamics as is the wing. They are also affected by power and thrust available. Vy decreases with altitude because it is the speed at which there is the maximum excess power available and that speed is the difference between the power available and the power required. Due to the shape of the curves, the speed for maximum excess power decreases with altitude. Vx is the speed where there is maximum excess thrust available and it increases somewhat with altitude. The two speeds, Vx and Vy meet at the absolute altitude and this is the only speed for which the airplane will maintain altitude.

When I'm flying a normally aspirated airplane at high altitudes, I just climb at a speed half way between S.L. Vx and Vy. It's east to remember and it is pretty close to the optimum speed.

Sorry for the confusion,

Skip

[A64Pilot]

Vx increases and Vy decrease with altitude, when they converge it’s the only airspeed you can fly without descending and of course the highest altitude you can climb to.

@PT20J and I are saying the same thing but differently. In my opinion as far as flying is concerned TAS in a sub 250 kt GA airplane is pretty much irrelevant, for instance our 196 kt VNE at 15,000 ft is over 250 true I think without checking, it’s interesting to know true, but all our V airspeeds are in IAS. Fast airplanes are different and I have no personal experience with Mach tuck, compressibility and barber poles etc

‘In my opinion you might want to reconsider how your climbing, Vx is angle, getting over the trees at the end of the runway, or maybe trying to climb out of a box canyon in an uh-oh moment.

Vy is rate of course, if your circling in a large area to get over the ridge line, you’ll get higher faster at Vy than any other airspeed, but just as important or maybe moreso the engine will run significantly cooler at the higher airspeed. Personally unless I have to I climb much faster than Vy just for engine cooling, but it’s been a long time since mountains were a concern for me and luckily I’ve never found myself in a box canyon

[Fly Boomer]

On 7/9/2023 at 10:45 AM, jlunseth said:

Doesn’t your aircraft POH have tables for landing and takeoff? If tables did not come from Rocket, then it must be the case that the STC provides to use the 231 tables. I am sure that tables are a required part of certification.

The only thing I can see in the Rocket documentation regarding performance is the following snippet:

CLIMB (BEST RATE):
- Power-38" MP and 2650 RPM
- Mixture-Rich
- Cowl Flaps-Pulled open
- Airspeed-105 KIAS at sea level, Decreasing 1 Knot for each 4000 FT of Altitude

CLIMB (BEST ANGLE):
- Power-38" MP and 2650 RPM
- Mixture-Rich
- Cowl Flaps-Pulled open
- Airspeed-71 KIAS at sea level, Increasing 1.5 KIAS for each 5000 FT of Altitude

Mostly, they just said "use your factory AFM/POH numbers, and we guarantee you can beat those numbers".

[aviatoreb]

17 minutes ago, Fly Boomer said:

The only thing I can see in the Rocket documentation regarding performance is the following snippet:

CLIMB (BEST RATE):
- Power-38" MP and 2650 RPM
- Mixture-Rich
- Cowl Flaps-Pulled open
- Airspeed-105 KIAS at sea level, Decreasing 1 Knot for each 4000 FT of Altitude

CLIMB (BEST ANGLE):
- Power-38" MP and 2650 RPM
- Mixture-Rich
- Cowl Flaps-Pulled open
- Airspeed-71 KIAS at sea level, Increasing 1.5 KIAS for each 5000 FT of Altitude

Mostly, they just said "use your factory AFM/POH numbers, and we guarantee you can beat those numbers".

That's what I see - we guarantee you can beat those numbers is all I got too.

And I didn't find in my POH much about landing distance requirements.  Just take off.

[aviatoreb]

...and as I write you from hours at the Denver airport - I wrote that my trip to Santa Fe by Bollt airlines was cancelled for an oil pressure issue from last week not yet fixed.

So Ill complain a bit and remember why I love Bollt airlines.  Instead on the standard airlines today - left the house at 430am to make my 8:25 flight out of Syracuse - its a 2:30 drive.  Got a message on the phone 1 hour out that my flight was delayed 2 hours.  Causing me to miss my connection from Denver to SAF.  So now next flight - from Denver - I am sitting waiting 5 hours.  So all in, assuming this goes on time, it will be 16 hours.  I can do it in just over 8.5 hours on Bollt airlines.  Tortiouse and the hare - just are so fast, but using them is so slow - unless I can afford 10 or 20 million for my own.  Then it gets very fast.

[Hank]

2 hours ago, aviatoreb said:

So all in, assuming this goes on time, it will be 16 hours.  I can do it in just over 8.5 hours on Bollt airlines.  Tortiouse and the hare - just are so fast, but using them is so slow - unless I can afford 10 or 20 million for my own.  Then it gets very fast.

Relax, doc! Airnav says that's ~1350 nm. In my C, that's twomfuel stops guaranteed. I once went 1320 nm west [KHTW --> KCOD via a couple places in Iowa, Rapid City and Yankton, SD], my groundspeed averaged 129 knots . . . .   Came home at 151. So the definition of "fast" depends on your point of view.

[aviatoreb]

1 hour ago, Hank said:

Relax, doc! Airnav says that's ~1350 nm. In my C, that's twomfuel stops guaranteed. I once went 1320 nm west [KHTW --> KCOD via a couple places in Iowa, Rapid City and Yankton, SD], my groundspeed averaged 129 knots . . . .   Came home at 151. So the definition of "fast" depends on your point of view.

It’s just over 1500nm home base kptd to Ksaf.

Well driving google says 29 hrs - not even double the airline travel time.

 

[Pinecone]

I did KBJC (Denber) to NE Maryland non-stop in 7 hours flying time.  Add maybe a hour for preflight, taxi, taxi to hangar, put plane away, say 8 hours.

Commercial non-stop flight o BWI would have been 3.5 hours.  But have to be at the airport 2 hours early.   Longer drive from my friends house to DEN, so add another 45 minutes.  At least an hour from gate to baggage to transport and drive home ( my hangar is 7 minutes from my house) adds up to over 7+15.  Assuming the flight is not delayed.

The friend I was visiting had her early morning flight out of DEN cancelled.  So she missed an appointment and got rescheduled for 5 weeks later.

[0TreeLemur]

When I arrived in the SAF area Sunday after surfing some mountain wave, wind at LAM were 9G18.   Diverted to SAF.

Enroute, with DA of 10,100 at LAM, calculate 70 KIAS over the fence would actually be 81 KTAS.   When I landed at SAF wind was 20 knots right down runway 20.