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Lindbergh's panel-- Ryan NYP-- what is this instrument and how was it used?

See this link-- it should allow you to zoom in by mousing around

https://www.amazon.com/Instrument-Successfully-Atlantic-Charles-Lindbergh/dp/B077RBRZTT

Consider the "T" shaped instrument at the lower center--

The top (horizontal) part is a bubble level -- it acts exactly like a slip-skid ball except the bubble deflects in the opposite direction as a ball would--

The lower (vertical) part is some sort of pitch level. It is calibrated to show pitch attitude. The glass tube may possibly have a part that we can't see, that disappears into the panel.

So why how was the vertical glass tube intended to be used? Was it intended to provide useful information in cloud? If so, would it actually have provided any useful information, or not? Or was it just intended to display a precise measure of the aircraft's pitch attitude and thus angle-of-attack, during unaccelerated straight-and-level cruising flight in visual conditions, for the purpose of optimizing the airspeed and angle-of-attack for long-range cruising flight?

The calibration suggests that the instrument was intended more to detect large deviations than for fine-tuning the angle-of-attack in cruising flight in visual conditions, but it is hard to see how this would be of much practical use during actual cloud flying. It's pretty much analogous to a simple pendulum, but with more damping.

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  • $\begingroup$ Sorry, bum link needs replacement. Need a good photo clearly showing the instrument (see photo in answer) actually mounted in place in panel. Ideally we need to find a photo that may be included in the question. $\endgroup$
    – quiet flyer
    May 3, 2020 at 19:51

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Its an Inclinometer which provided pitch and roll information

In the early 1920's, the US Government contracted Rieker Instruments Company to produce bubble style pitch and roll indicators for the fast emerging aircraft market.

One of the most famous inclinometer fluid filled vial type installations - if not the most famous - was the use of a pair of Rieker glass tube instruments on the panel of the Ryan NYP "The Spirit of St. Louis". In 1927 Charles Lindbergh chose the lightweight Rieker P-1057 Degree Inclinometer to give him climb and descent angle information.

enter image description here

(source)

This was useful to the Spirit of Saint Louis as it had effectively no forward visibility with the exception of the periscope. He may have also chosen this in the interest of weight as it would be much lighter than an early gyroscopic instrument.

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  • $\begingroup$ Right. Its just that, based on my experiences, I can see how the slip/skid information would be somewhat useful-- the ball tends to ride to the low side of a bank/ turn, and the bubble to the high side -- but seems to me the physics are such that the pitch indication would be completely useless at any time that you can't actually see out the window. Now, granted, the Sp of St Louis had a lousy forward view, so maybe that had something to do with it-- even in visual conditions where there are no crazy accelerations going on, a guide to climb/ dive angle might be useful? $\endgroup$
    – quiet flyer
    Nov 1, 2018 at 17:50
  • $\begingroup$ PS I have used something exactly like that upper part on a lightsport plane AND a hang glider, many times. Just to satisfy my curiousity-- doesn't serve much purpose in a rudderless aircraft-- $\endgroup$
    – quiet flyer
    Nov 1, 2018 at 17:52
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    $\begingroup$ PPS it goes without saying that NEITHER pitch nor roll information is actually provided, unless the aircraft is known to be in an unaccelerated 1-G condition. $\endgroup$
    – quiet flyer
    Nov 1, 2018 at 17:54
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    $\begingroup$ Good historical answer though. Thank you. $\endgroup$
    – quiet flyer
    Nov 1, 2018 at 17:56
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    $\begingroup$ I read Lindberg's book on the trip but I don't recall if he mentioned what the inclinometers were for. I would assume the longitudinal one was for knowing pitch attitude in unaccelerated flight for the purpose of correcting fuel quantity indications with the very large tank in front of the cockpit. Lindberg's main problem was constantly drifting off to sleep and wandering off course toward the end of the first night, and hallucinations from fatigue. When he got to Paris he had enough fuel and considered continuing to Rome, but the thought of a night flight over the Alps changed his mind. $\endgroup$
    – John K
    Nov 2, 2018 at 1:34

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