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Author
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Topic: Apollo 11: Glide slope angle and trajectory
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Lou Chinal Member Posts: 1332 From: Staten Island, NY Registered: Jun 2007
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posted 06-24-2015 01:47 PM
In studying the Apollo 11 landing profile, it seems to be about 15 degrees of a glide slope angle. Steep, but not too steep. I know a lot of things were involved but it was also very familiar. Traditional would be another word for the approach. Any trajectory types out there? |
David C Member Posts: 1039 From: Lausanne Registered: Apr 2012
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posted 06-25-2015 10:10 AM
I'm no expert Lou but in selecting any flying machine's approach angle there are a number of factors involved. Some of these are: terrain clearance, energy management, crew visibility, escape options, structure clearance and structural loads. I'm guessing that you derived 15 degrees as the average from High Gate to touchdown, which seems reasonable.To start with, I don't think that the term "glide slope" has any real meaning in this context since it really implies some kind of equilibrium state between aerodynamic forces, thrust and gravity — and there are no aerodynamic forces in this case. Secondly, whilst helicopters, and V/STOL airplanes may descend at a 90 degree angle (or even more depending on how you measure the angle), they don't normally start this from over a mile above the landing site and 300 knots. Finally, whilst the X-15, lifting bodies, shuttle etc flew very steep "Drinkwater" approaches, the vast majority of conventional airplanes fly an approach angle of between 2.5 to 4.5 degrees (with 3 degrees being by far the most common). So yeah, 15 degrees is within the range of terrestrial experience (anything from just over zero to just under 180 degrees is - which covers everything). But I don't see how you get from there to calling the LM's final descent either "very familiar" or "traditional". Also remember that Armstrong had to extend significantly down range, so the plan was originally for an even steeper average approach angle. Put another way, only one type of manned vehicle has ever flown an approach to touchdown in a vacuum and 1/6g - and it only did it 6 times. Nothing about that could be familiar or traditional. | |
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