Origin of the 80kt crosscheck and the Jay Beasley legacy

[HackerF15E]

I was doing a check flight on a 727 after a C Check (overhaul). We figured out on rotation that our pitot system was f'ed up (both matched at 80 kts then went miles apart). Flew pwer and attitude with no problem. Not a big deal.

I have friends at Hawaiian in A330 training right now. Click-click, click-click. AP & At are off and there are charts for power/attitude flying. Just like a Boeing. These Frogs got the utlimate pink sheet for airmanship.

Just as an aside...for a fighter punk who knows zero about flying an airliner....why is 80 knots the airspeed indicator check speed?

I recently heard that this is also procedure in the USAF's new King Air variant (the MC-12W), and the explanation was that 80 knots was the check speed used in the C-135 series of jets, and that pilots from those airplanes brought that procedure over to the MC-12.

Based on the other posts talking about 80 knots being used for the same reason in the P-3....there's definitely something behind it. I just am not smart enough to know what it is.

 

[ryan1234]

Just as an aside...for a fighter punk who knows zero about flying an airliner....why is 80 knots the airspeed indicator check speed?

I recently heard that this is also procedure in the USAF's new King Air variant (the MC-12W), and the explanation was that 80 knots was the check speed used in the C-135 series of jets, and that pilots from those airplanes brought that procedure over to the MC-12.

Based on the other posts talking about 80 knots being used for the same reason in the P-3....there's definitely something behind it. I just am not smart enough to know what it is.

The way I understand it is that 1) it's an airspeed below V1 (generally) and 2) it is a sufficient time (enough airspeed) to stabilize lag error between the pilot and copilot's plumbing.

 

[OnTopTime]

Just as an aside...for a fighter punk who knows zero about flying an airliner....why is 80 knots the airspeed indicator check speed?

At least in the P-3, I once heard a story that I'm trying to dig up from the depths of my memory, so the details are fuzzy, but here goes:

Jay Beasley was a longtime Lockheed test pilot who was known as "Mister P-3." He had over 31,000 landings in the P-3 and did much of the original test work for Lockheed, and this is what he recounted. In the early days of P-3 testing, the pilot not at the controls would call out the airspeed on the takeoff roll at a designated point on the runway, say the 6 board (or whatever), to make sure that the pitot system was functioning. More often than not, the indicated speed at that point was around 80 knots. Over time, the procedure evolved from calling out the speed at a certain runway location to just calling out "80 knots" when the airspeed indicator reached that speed.

Anyway, that's what I heard, as best as I can remember. I have no idea how or why this procedure would have transferred to other aircraft.

 

[scoolbubba]

Jay Beasley said so, therefore it is.

 

[HackerF15E]

As the C-135 series pre-dated the Orion (and the story has the "80 knots" coming from the Orion, and not the Electra), I have to say....either strange coincidence, or B.S. story.

In addition, HAL's post indicates that they used in the 727, too. It would be pretty unlikely that a procedure developed over time in the VP community would have transferred over to a civil Boeing.

So...doesn't seem to answer it IMHO.

 

[HAL Pilot]

I don't know why 80kts. It's been 80 kts in every jet I've flown. I do know that it's a good speed because at 80kts an abort is very mild. It gets worst from there and can be down right dangerous just below V1.

 

[CommodoreMid]

IIRC from primary we rotated at 85 knots in the T-6. I'm not a pilot nor do I know anything about aerodynamics and aircraft performance beyond what I learned in API, but it kind of surprises me that a single engine prop would have a similar rotate speed to a P-3 or a 727. Now I'm intrigued where these numbers come from in the first place.

 

[HAL Pilot]

No one has said a 727 or P-3 rotates at 80kts. We do an airspeed indicator cross check at 80 kts. Or in the case of the 767, it cross checks the airspeed indicators plus the autothrottles should go to a "throttle hold" annuciation (basically means they are at takeoff power plus a few other things) at 80kts. - Hey Hacker....this is a reason for the 767 at least.

 

[scoolbubba]

IIRC from primary we rotated at 85 knots in the T-6. I'm not a pilot nor do I know anything about aerodynamics and aircraft performance beyond what I learned in API, but it kind of surprises me that a single engine prop would have a similar rotate speed to a P-3 or a 727. Now I'm intrigued where these numbers come from in the first place.

We rotate bagged out full of gas closer to 135ish; depending on whatever numbers the FE's ouija board/chicken bones/rabbits foot has spit out.

 

[NavAir42]

After consulting the Prophet Beasley, this is what he saith unto thee:

80 Knots
"Historically , piston engines at idle rpm while taxiing or holding for takeoff would foul the spark plugs causing uneven firing and roughness when takeoff power is applied. Usually they would start operating normally after a short period at high power. If they didn’t you aborted the takeoff. At Lockheed we concluded that we could stop a P-2 abeam the Fire House but any distance beyond was critical for aborts. At this time the airspeed was usually about 80 knots. This became a useful number which is now industry wide. Since it did become a number it was elected to adapt it to the P-3, although a jet engine is not at all like a piston engine. What makes it important is that someone observes the power output and determines whether to continue or stop. “Call 80 knots for a power check” is sometimes mis-understood that you don’t heck the power until 80 knots. Check the power output with the initial application. If it’s bad at 60 knots, stop the aircraft. It won’t get any better at 80 knots like the P-2 engine might. A P-3 will stop on any Navy runway from an 80 knot speed. "

 

[HackerF15E]

Very cool -- I love those "from the horse's mouth" recollections. Thanks for that.

Interesting, as his post is talking about (what we call in AF-speak) "acceleration check speed" -- a distance at which we should have achieved a certain speed if the engines are producing the minimum acceptable thrust. If they're not, you abort (as that speed is always below the abort/refusal speed on every runway that you're going to be operating from).

Not sure it totally answers the question, also, as to why this number is used to check the airspeed indicators, and why they also do it in the Boeing series.

 

[NavAir42]

The way I had it explained to me while upgrading was that you wouldn't take a plane flying with a significant difference between ASIs. It provides a convenient place to make sure they match up. So when the copilot calls 80kts for the power check, the pilot can glance down to make sure his ASI matches. If there's a significant difference, you abort the takeoff.

 

[Pugs]

I don't know why 80kts. It's been 80 kts in every jet I've flown.

At 80 knots in the Prowler you got off the nosewheel steering and 100 kts was dividing line between high speed and low speed abort criteria. Rotation at most weights was about 142 kts IIRC.

 

[HackerF15E]

The way I had it explained to me while upgrading was that you wouldn't take a plane flying with a significant difference between ASIs. It provides a convenient place to make sure they match up. So when the copilot calls 80kts for the power check, the pilot can glance down to make sure his ASI matches. If there's a significant difference, you abort the takeoff.

Yes, I understand the concept -- I have since the initial post on the last page of this thread. Note in my initial post I'm asking HAL, 'where does the number come from'?

Why is it 80...and not 65...or 100. And, why does 80 seem to be used in more than one aircraft from more than one manufacturer and in both civil and military use. There's clearly more than coincidence here.

If we were talking only one aircraft type, I'd understand the rationale (certainly the explanation on the previous page regarding both the Neptune and Orion makes perfect sense), but we're talking several aircraft types that have differing takeoff performance.

 

[Alpha_Echo_606]

It's been a couple years since I've done a pitot static leak check and the last was on a P-3. I don't remember the exact points but we check splits at several places for both air speed and altitude. I guess next week I'll have to get into the MIMs and refresh the memory, I know I'll be doing a leak check in the near future. When I find it I’ll come back and post the check points and tolerances.