The Groundspeed is .....What?

[MIflyer]

My high school physics teacher was a USN aviator in the 1930's and 1940's.

One day he took off from North Island NAS, San Diego, and headed East, to a USN airfield near El Centro. Not long after takeoff he found himself flying over an undercast that obscured the ground. Radio reports from El Centro informed him that the sky over the base was clear, so he knew he would have no problem landing there. But as he continued on he grew increasingly puzzled. El Centro reported clear but the undercast stretched ahead of him as far as he could see. And after over an hour of flight the situation was still the same.

The weather he could see below him was not at all what El Centro was reporting, but should have been there already. Other airfields to the north and south of El Centro also reported clear conditions, so even if he was off course he should have left the clouds behind.

Finally he decided he had no choice but to descend through the clouds and see if he could figure out where he was. He was stunned to emerge from the clouds over the ocean, continued to fly East and landed at NAS North Island two hours after he had departed there.

Above the clouds there had been a strong wind from the East which gave him a small net negative groundspeed. He was going backwards over the Pacific coastal marine layer that so many of us who have flown in California have learned to be wary of.

 

[Kaibutsu]

That's crazy! - He was being pushed out to sea by strong winds.
I've never heard of that.

 

[mikewint]

Your post question was: What is groundspeed and you seem to have answered it yourself. As you observed, it is the speed of the aircraft relative to the earth below it. You don't say the year this occurred in nor the aircraft he was flying. In 1929 the USN had an F4B/P-12 biplane. It had a top speed of 189MPH so he would have had to have experienced a +190mph headwind. Non-pressurized open cockpit biplanes seldom flew over about 12,000 ft. A +190mph wind at that altitude would be a VERY rare occurrence.
Now while his speed over the ground was negative (being pushed backwards) his AIRSPEED would still be +189mph.
A better visualization might be a powered boat in a moving river. The boat's motor is capable of pushing it through water at 10mph...period. It doesn't know or care where it is nor what the water is doing. The river water likewise is moving at 5mph due South. If the boat travels South the motor will still push it at 10mph through the water BUT the river water is moving South at 5mph SO from the bank of the river a stationary observer would see the boat traveling at 15mph due South relative to the bank. Likewise if the boat turns around and heads due North the observer on the bank would see the boat moving at 5mph relative to the bank. The boat however would still be traveling ant 10mph through the water.

 

[MIflyer]

This occurred in the mid to late 1930's. He graduated from the USNS in 1932, I think.

I would guess that the airplane may have been a Curtiss Seagull; he flew floatplanes and flying boats a lot but not exclusively. He had to have a radio so it probably was not a Stearman trainer. Actually the Seagull might have been a bit late for him; it did not come out until 1934. The Vought O2U Corsair would probably be more likely, which had a 160 mph top speed at sea level

You do not cruise at full power. Ever. The 60% power cruise speed of an F4B-4 was 160 mph. The long range cruise speed of a PBY is 75 mph. The SOC Seagull had a top speed of around 150 mph and a cruise speed more like 100 mph or less with a stall speed of 55 mph; the O2U probably was even slower.

I would guess he had a net groundspeed of about -5mph, since he ended up out over the Pacific and was able to get back to NAS North Island pretty quickly once he came down below the clouds.

 

[mikewint]

Even given the lower 160mph speed I find it difficult to give credence to his story. While the Polar Jet Stream can reach 250mph it averages 110mph BUT it's located at +20,000 feet, well above any non-pressurized aircraft. The Jet streams also flow from west to east and make north to south turns and south to north turns, but I have problems accepting an east to west flow. Especially during the daylight hours when coastal winds are from the cooler Ocean towards the warmer land.
Now there are strong upper atmosphere winds but again a 160mph wind is a category 5 hurricane wind
So I suspect a story concocted to illustrate the differences between airspeed and groundspeed

 

[AMCKen]

"located at +20,000 feet, well above any non-pressurized aircraft." Many have flown to 50,000 without pressurization. One needs additional oxygen above 10-12,000, but not pressurization.

 

[gumbyk]

"located at +20,000 feet, well above any non-pressurized aircraft." Many have flown to 50,000 without pressurization. One needs additional oxygen above 10-12,000, but not pressurization.

Not 50k. Above about 40,000 ft, pure oxygen is insufficient, and it has to be supplied at positive pressure, which requires special breathing techniques (pressure breathing). So, although the cabin may not be pressurised, the breathing system is. And these systems aren't readily available for use, and may not even have existed at this time.

 

[Builder 2010]

I worked for a fellow who flew Piper Cubs. Their takeoff speed was so low that he had a situation where the headwind upon takeoff was so strong that he ended up actually flying backwards to the starting end of the runway. Walking up a down escalator is a good example of ground vs. airspeed.

 

[gumbyk]

I worked for a fellow who flew Piper Cubs. Their takeoff speed was so low that he had a situation where the headwind upon takeoff was so strong that he ended up actually flying backwards to the starting end of the runway. Walking up a down escalator is a good example of ground vs. airspeed.

I've hovered in the Tiger Moth. Also had my aircraft type questioned by a controller due to my lack of groundspeed: 50kts in a Piper Warrior (105 kts airspeed)

 

[AMCKen]

"Not 50k. Above about 40,000 ft, pure oxygen is insufficient, and it has to be supplied at positive pressure, which requires special breathing techniques (pressure breathing). So, although the cabin may not be pressurised, the breathing system is. And these systems aren't readily available for use, and may not even have existed at this time. "

I didn't say they stayed at 50,000.
Only a very few could do the flight, and they didn't stay there very long.

 

[N4521U]

A bit on subject.
Doing flight instruction before prac exam.
Cessna 150 D model over the Altamont in CA.
Ralf asks me "how slow can this fly, in ground speed".
So I give him landing approach speed, he says "slower"
Power back, flaps down, I580 below is Overtaking us!!!!!!!
The winds over the Altamont drive big@ss windfarms.
Flying can be fun...............

 

[fliger747]

One night flying Shanghai to Anchorage in a trusty 747-400 we hit 709 knots groundspeed over the Japanese Inland Sea, at that speed life even looks fast at 35,000'. Years earlier, flying an early model 737 (no GS readout) from Seattle to we asked Vancouver Center what our Ground speed was, the reply "You don't want to know... 250 knots".

The location and gradient of the Winter Jetstream was always an item of interest in Trans Pacific flight planning. Calculating (forming a WAG) whether the change in altitude against the Jet would be favorable enough to offset a non optimal step climb.

Flying my cub in the mountains, I remember coming around the East Buttress of Denali at about !%^*$ feet' and getting down to under 30 knots.

 

[MIflyer]

On one of my launches at VAFB the balloon data showed that over the last 4 hours the winds aloft had gone from 30 kts to over 100 kts. I asked our meteorologists if that could happen and they said, "No." Then they started calling aircraft and getting pireps, and they came back with, "Yes, the balloon data is accurate."

We did not launch that night!

 

[Gnomey]

Interesting stuff!

 

[Dimlee]

Reminded me about An-2 "helicopter". As here: