Every day at around 5PM, a C-17 flies over my house at what looks like a speed of about 17 MPH. I have no idea why, it’s like MASH’s ‘Five O’Clock Charlie’ on steroids and Viagra. I’m glad they’re on our side, otherwise I’d crap my pants every time I saw one.
Anyway, how slow could this beast be going? Sometimes it nearly looks like it’s hovering.
Was the wind blowing? Given enough headwind, an aircraft can even fly backwards.
I have little way of knowing what the air currents were doing at 1500 feet, but I never notice any remarkable wind when this happens. And it’s not just the one time, but roughly every day at 5-ish. It is damned disconcerting to see something that huge and heavy wheeling above like a vulture from hell.
I am an aviation buff and I had never heard of this but it appears your powers of observation are acute. There is something weird going on with C-17 technology. The exact numbers are classified as far as I can find but it does seem to be an interesting technology that escaped mostly under the radar so to speak. Other points are that some of it is an illusion because a C-17 is a fat profile plane and we are used to seeing smaller airliners zipping into airports in a more agile fashion.
“The positions of the engines allows the use of propulsive lift technology, first tested on the YC-15, in which the engine exhaust is trapped under the wing and forced to flow over both sides of the single split flap on the wing trailing edge. The exhaust then leaves the flap trailing edge at an angle related to the flap deflection. A full span leading edge slat helps the wing maintain optimum lift and stall characteristics. The combination of the features allows a steep, low speed final approach with a low landing speed.”
According to this page it has an approach speed of 115 knots (213 kph, or 130 mph.) It’s slow for an aircraft of it’s size but nearly as slow as it looks.
After some searching I have seen a couple of hearsay-type sites that suggest the published minimum approach speed is not the actual minimum. It’s really difficult to estimate speed of a craft at that altitude, especially with the normal cues of size and speed at odds, but I have a strong perception that I’m seeing them closer to 100 knots. It takes like 4 minutes to cross the sky from treeline to treeline. Freaky. Would not want to be on the receiving end of a C-17 gunship.
Both an AC-130 and a hypothetical AC-17 are going to simply establish an orbit above you and pummel you–no difference in the punishment between the two, assuming both platforms have the same guns.
As for the OP, no doubt 90% of what you’re seeing is the optical illusion of seeing something that big in the air. I’ve seen plenty of them take off and land, and it never fails to amaze me at how slow they seem to go (I get the same thing with C-5’s). I definitely have trouble wrapping my brain around a 115 kt approach speed–that seems low to me for an aircraft that size, but I suppose you never know. 1920’s cite looks legit, so I guess using the exhaust in that manner can shave 15-20 kts off the approach speed. If I ever get a space-A hop on one, I’ll have to try not to think about how slow I’m going. I have to assume they’re only a few kts away from stall speed.
I dont know why it would be either secret or classified, but it does make sense as the original proposal was for the aircraft to land on dirt strips or unprepared runways.
It seem that the need for the capability was dropped but the aircraft still retains it in reality.
Declan
Enjoy these clips on YouTube showing a variety of C-17 short field landings. Gawk at the frankly ridiculous approach speeds. I would absolutely believe this is moving around 100 knots at landing in some of these clips. The official Air Force page claims that it can land on a runway less than 3,500 feet, but other pages include this quotation (original source unclear):
I would guess the approach speed at around 110-115 knots with a stall speed around 90. I hope they do FOD checks before the short field landing demo’s. In the first clip you can clearly see the plane sucking up the water off the runway when it backs up.
For comparison, a Dash 8 300 which is a straight wing turbo-prop designed for short field operations, has a landing speed of around 100 - 110 knots depending on weight and an approach speed of 110 - 130 knots. For a swept wing heavy jet to have similar approach speeds is remarkable.
Information from here also states that the C-17 stall speed is classified, but notes that the stall speed of the C-130 is 100-115 knots, and the C-5 is 115 knots. Both of those lack the technology employed on the C-17.
This NASA document confirms a 100 knot landing speed at full flaps.
Here’s a nice video of a C-17 flying around and landing. The good part is at 6:30.
I suspect the true stall speed is below, perhaps well below, 100 knots. If you know when the airplane will fly by, go rent a radar gun and measure the speed. That should cause some excitement in the cockpit: lighting them up with track radar. 
I’ve been watching a C17 doing laps of my house doing night vision goggle training. Sometimes doing landings and go arounds. I’ve seen speeds below 90 knots on approach.
It’s quite common for military vehicles to have actual capabilities that are beyond the officially-published capabilities, but they’re probably not going to exceed the officially-published capabilities on a routine operation (which this certainly sounds like). For one thing, if the true capabilities are secret, they probably want to keep it that way, and for another, exceeding the official capabilities might be risky (possibly less risky than not exceeding them, in a combat situation, but again, not for a routine operation).
Also if the craft is not loaded, it probably can fly much slower since it’s designed with a cargo capability almost the same as its empty weight.
I wonder if the pilots have numbers - “your gross weight is X therefore your stall speed is Y and a safe approach speed is Z” which varies with load? It does appear to have some hefty flaps plus…
The thrust reversers can also be used in flight at idle-reverse for added drag in maximum-rate descents.
I guess the other question is how fast you want to descend. f your airspeed has a significant downward component, it will have less of a forward component I assume.
I live on top of (well, 1/2 mile away) the continental divide. I am apparently on some sort of National guard training route. I get a couple of C-130 buzzing my house about once a week. These suckers are really low. I guess they have to adhere to 500 ft AGL, but sometimes I think they bend the rules.
I certainly hear them, but have to be outside to see them. They are gone in a flash.
It’s kinda cool. Dogs don’t like it much though.
Bit of a hi-jack, but the pass I live on also seems to be a favorite for testing new car models. I guess elevation stress test or something. I see a lot of those camouflaged cars