At Spruce Creek right now....

[Hank]

2 minutes ago, Pinecone said:

Anything you have is good.

The 50/70 is just another tool in the toolbox.  

If you fly off of IFR marked runways, you have a 1000 foot marker.   In the USAF we had a 1000 foot check speed.  If you were not at or above a certain speed at 1000 feet of takeoff roll, you aborted the take off.

I'm generally in the air at the 1000' mark (when there is one).

[Jerry 5TJ]

20 hours ago, cbarry said:

I realize the Malibu is pressurized (the Matrix version is not…), but other pressurized aircraft seem not to have an empennage separation issue such as this…

Perhaps it’s that the pressure hull is much stronger than the unpressurized areas so under severe stress the aircraft tends to break at that juncture. 

[Pinecone]

1 hour ago, Hank said:

I'm generally in the air at the 1000' mark (when there is one).

Then, you know things are going OK.

For the T-38, the 1000 foot check speed was typically a bit over 100 knots, but but most times you were WELL above the minimum.

[Jim F]

On 2/5/2023 at 11:16 AM, Jerry 5TJ said:

When I operated out of a 2000’ strip (CA35) I had a go/no go point pre-established:  If not at >50 knots when abeam of the compass rose, abort the takeoff.  That pre-set test prevents (some of) the decision delay. 

I totally agree.

A couple years back there was a discussion on a 231 that was not making power and hit a levee. 

After following the discussion on MS I started the following.  I to fly off a short strip (1800ft 4CA2) so I marked the mid point of the runway with mid point marks and now I must be above 63MPH(My margin number) by mid point.  On the roll I get takeoff power, verify airspeed is alive, look for all six cylinders working, 100% power, >63MPH by the mid point.

Jim

[larrynimmo]

FYI….at KESN, 72’ MSL…with baro at 30.72, 10k head wind 25 gallons of fuel, two light adults actually took off in less than 500’ with a J…

[PT20J]

I did the math on the 50/70 rule years ago. If you assume uniform acceleration, and ignore drag, you will lift off exactly at the end of the runway. Unless it is obstacle free, you’ll hit something. Actually, it’s worse than that because thrust decreases as speed increases while drag increases, so the acceleration isn’t constant.

 

[Fly Boomer]

5 minutes ago, PT20J said:

I did the math on the 50/70 rule years ago. If you assume uniform acceleration, and ignore drag, you will lift off exactly at the end of the runway. Unless it is obstacle free, you’ll hit something. Actually, it’s worse than that because thrust decreases as speed increases while drag increases, so the acceleration isn’t constant.

 

As I posted above, I haven't been able to see how that rule is useful to determine stopping distance.  That rule seems more appropriate to use as a "if I DON'T abort, will I be off by the end of the runway" rule than it does as a "if I DO abort, can I get stopped" rule.  Your math has very likely discovered the intent of whoever  published that originally.

 

[Pinecone]

The way it works for stopping is simple.  The airplane stops better than it accelerates.  If you abort, still on the ground, at the half way point, you will stop before the end.  No math needed.

252/Encore, at max gross at sea level, zero wind, 15C OAT, it is a 1750 foot ground roll.   Same conditions, the landing distance is 1200 feet.

So if the runway is 3500 feet long, and I abort at halfway, I will be just at liftoff speed.  But can stop 550 short of the end of the runway.

 

[Mooneymite]

20 minutes ago, Pinecone said:

The way it works for stopping is simple.  The airplane stops better than it accelerates.  If you abort, still on the ground, at the half way point, you will stop before the end.  No math needed.

252/Encore, at max gross at sea level, zero wind, 15C OAT, it is a 1750 foot ground roll.   Same conditions, the landing distance is 1200 feet.

So if the runway is 3500 feet long, and I abort at halfway, I will be just at liftoff speed.  But can stop 550 short of the end of the runway.

 

While I agree with you "on an average day", I can tell you for sure this is not true on wet grass!

[Fly Boomer]

1 hour ago, Pinecone said:

The way it works for stopping is simple.  The airplane stops better than it accelerates.  If you abort, still on the ground, at the half way point, you will stop before the end.  No math needed.

252/Encore, at max gross at sea level, zero wind, 15C OAT, it is a 1750 foot ground roll.   Same conditions, the landing distance is 1200 feet.

So if the runway is 3500 feet long, and I abort at halfway, I will be just at liftoff speed.  But can stop 550 short of the end of the runway.

 

Now that's beginning to make sense to me.  Thanks!

[Hank]

1 hour ago, Mooneymite said:

While I agree with you "on an average day", I can tell you for sure this is not true on wet grass!

It's still better to run off the end and into whatever while braking, well below 40mph where ASI starts, than to do the same at 65 or so while trying desperatelyto fly . . . .

[Pinecone]

41 minutes ago, Hank said:

It's still better to run off the end and into whatever while braking, well below 40mph where ASI starts, than to do the same at 65 or so while trying desperatelyto fly . . . .

This too.

[Mooneymite]

12 hours ago, Hank said:

It's still better to run off the end and into whatever while braking, well below 40mph where ASI starts, than to do the same at 65 or so while trying desperatelyto fly . . . .

Hank, I guess you missed the point of my post.  The abort point is not cut and dried.  There are many factors that affect the decision...and the outcome.  Wet grass is just one example.

[Pinecone]

No, there is never one right answer for all conditions.

But the rule of thumb works for most people most of the time.  You just need to realize when it does not.

But do you know your stopping distance from say 50 knots on wet grass????  If you don't have that data, you have no way to figure out what to use to consider an abort.

[Mooneymite]

3 hours ago, Pinecone said:

  If you don't have that data, you have no way to figure out what to use to consider an abort.

Absolutely correct!

[0TreeLemur]

The question remains, if one has a good engine monitor, in what order should we check things?   My personal experience the perceived time from when I begin to advance the throttle to the time I'm airborne is just ridiculously short.  What is the optimal way to budget that limited time to detect a problem and act on it before too much speed is accrued.

As an aside, on heavy airliners doing trans-oceanic travel, I like to time the takeoff roll.  45 seconds is not uncommon.  An eternity compared to our 10 second takeoff rolls.

What is the best way to spend that 10 seconds, aside from keeping the airplane on the runway with our eyes and feet?

Here's my thinking, with numbered items having eyes inside cockpit, <steer> indicating eyes outside cockpit:

1.  Advance throttle

<steer>

2.  Read power indications (rpm, MP) or %pwr from engine monitor if avail.

<steer>

3. Verify airspeed alive

<steer>

4. Oil pressure green

<steer>

5. 70/50 point?

<takeoff>

Any thoughts?

[Hector]

Twice in over 30 years of flying I’ve had to abort a takeoff because I was not making expected RPM/MP. I could also tell acceleration was sluggish. Both times were a result of taking off on a very lean mixture. Both times I did not use a checklist. The last time was on a short runway with power lines at the end (FD51 Summerland Key Florida) and if I had continued the takeoff I would have never made it over the power lines. Lots of lessons learned. Passenger distracted me so I never completed run up checklist, didn’t check RPM/MP until I noticed sluggish acceleration. Both mistakes scared the crap out of me and reinforced how this passion of ours is unforgiving of carelessness.


Sent from my iPad using Tapatalk

[Jim Peace]

So is % power on an engine monitor good enough?  Can you display 100% without having the proper power settings?

note: I know on the JPI 900 I have that the number is adjustable in the settings. So you should cross check the RPM and MP before you rely on it. 
 

Going forward if you tweak it right would the % power be enough to look at?

[ArtVandelay]

So is % power on an engine monitor good enough?  Can you display 100% without having the proper power settings?
note: I know on the JPI 900 I have that the number is adjustable in the settings. So you should cross check the RPM and MO before you rely on it. 
 
Going forward if you tweak it right would the % power be enough to look at?

Since JPI uses RPM, MAP, FF, OAT to calculate HP I see no reason to be checking those as well.

[T. Peterson]

3 hours ago, 0TreeLemur said:

The question remains, if one has a good engine monitor, in what order should we check things?   My personal experience the perceived time from when I begin to advance the throttle to the time I'm airborne is just ridiculously short.  What is the optimal way to budget that limited time to detect a problem and act on it before too much speed is accrued.

As an aside, on heavy airliners doing trans-oceanic travel, I like to time the takeoff roll.  45 seconds is not uncommon.  An eternity compared to our 10 second takeoff rolls.

What is the best way to spend that 10 seconds, aside from keeping the airplane on the runway with our eyes and feet?

Here's my thinking, with numbered items having eyes inside cockpit, <steer> indicating eyes outside cockpit:

1.  Advance throttle

<steer>

2.  Read power indications (rpm, MP) or %pwr from engine monitor if avail.

<steer>

3. Verify airspeed alive

<steer>

4. Oil pressure green

<steer>

5. 70/50 point?

<takeoff>

Any thoughts?

The fact that you are short on time is evidence the engine is working well!! Fly and enjoy. If you take everything posted on this forum to heart you will soon be hiding under your bed beating your head against the floor!!

[0TreeLemur]

7 hours ago, T. Peterson said:

The fact that you are short on time is evidence the engine is working well!! Fly and enjoy. If you take everything posted on this forum to heart you will soon be hiding under your bed beating your head against the floor!!

I don't suffer from that problem.  Been flying since 1981.   Just interested to hear what other folks do.  There are some really smart people on MS that I learn from.

[Sue Bon]

I only have a NA engine and an engine monitor is being installed as we speak, but without the engine monitor I have always held the brakes and increased throttle until 25" MP and then released the brakes. I call out 25" minimum power, speed alive, takeoff (max) power between 27" and 29" depending on DA. After releasing the brakes, the distance covered between minimum power (brakes released) and takeoff power (max) is less than 100 meters.

[T. Peterson]

6 hours ago, 0TreeLemur said:

I don't suffer from that problem.  Been flying since 1981.   Just interested to hear what other folks do.  There are some really smart people on MS that I learn from.

Of course! I was just making a funny, but it is true that if your airplane is jumping into the air it is most likely making full power.

[Mooney in Oz]

On 2/12/2023 at 6:30 AM, 0TreeLemur said:

The question remains, if one has a good engine monitor, in what order should we check things?   My personal experience the perceived time from when I begin to advance the throttle to the time I'm airborne is just ridiculously short.  What is the optimal way to budget that limited time to detect a problem and act on it before too much speed is accrued.

As an aside, on heavy airliners doing trans-oceanic travel, I like to time the takeoff roll.  45 seconds is not uncommon.  An eternity compared to our 10 second takeoff rolls.

What is the best way to spend that 10 seconds, aside from keeping the airplane on the runway with our eyes and feet?

Here's my thinking, with numbered items having eyes inside cockpit, <steer> indicating eyes outside cockpit:

1.  Advance throttle

<steer>

2.  Read power indications (rpm, MP) or %pwr from engine monitor if avail.

<steer>

3. Verify airspeed alive

<steer>

4. Oil pressure green

<steer>

5. 70/50 point?

<takeoff>

Any thoughts?

Your list is mostly the same as I do.

The only minor difference that I do is in relation to No. 4. Instead of particularly observing the oil pressure, I check by glance that all indications are in the green.

[Pinecone]

This why I like my JPI 830, if things are not in the green, they are flagged in flashing red.  So a quick glance tells me things are OK.

One gripe though, is you set the max RPM to 2600 (for my plane) it flashes red AT 2600. IMO, it should be when it EXCEEDS the set value.  So I had to set max RPM on the JPI to 2610