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Odd aerial formation

by Bill Osler / April 2, 2007 10:58 AM PDT

I saw this at Yahoo - a formation of 4 VERY different aircraft flying together:
Ventura Air Show

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Hmm. That's gotta be
by Steven Haninger / April 2, 2007 11:07 AM PDT
In reply to: Odd aerial formation

some super high shutter speed camera to stop the prop.

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I wondered about that ...
by Bill Osler / April 2, 2007 11:45 AM PDT
In reply to: Hmm. That's gotta be

I also noted that there is no evidence of exhaust from the engines and that the undersides of the planes are much better exposed than what I usually achieve when I'm shooting a bird against a bright sunlit sky. Of course, I would expect a professional photographer to get better results than I do, but that does not answer the question you raised or the lack of exhaust.

I HOPE it wasn't photoshopped ... but we'll probably never know.

Of course, I don't know what the RPM would be for a P51 engine. Maybe a fast shutter could do the job?

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Prop speed
by Steven Haninger / April 2, 2007 7:31 PM PDT

should be no greater than 3000 RPM but is generally lower as props lose efficiency and at higher RPMs as well as can suffer failures. But I'd think even at a shutter speed of 1/2000 there'd still be some blurring. And the exhaust is also missing as you stated. I have to wonder if it's manipulated or perhaps a shot from a bed towards the ceiling in a kids room with some well constructed models. Happy

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Re: Prop Speed
by Bill Osler / April 2, 2007 10:13 PM PDT
In reply to: Prop speed

I'm not 100% sure I got the math right, but if the prop is rotating at 3000 RPM then a 1/2000 exposure should capture about 9 degrees of rotation.

At the resolution allowed by the small image on the page I'm not sure a 9 degree rotation would be clearly visible.

I just don't have enough experience to be certain here.

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No expert here either
by Steven Haninger / April 3, 2007 6:49 AM PDT
In reply to: Re: Prop Speed

but these are basically reciprocating type engines which have mechanical limitations similar to automobile engines. I remember reading that old VW air cooled engines were a popular choice for amateur builder/pilots. These motors had a realistic red line in the 5000 RPM range. But, I think one issue with props is that you need to keep the velocity of its tip below the speed of sound..no breaking of the sound barrier. So the prop radius would be a factor in determining the maximum safe RPM...if you care to do more math. But, 9 degrees of rotation, I would think, should be detectable. It should be at least one width of the prop...maybe more. One of my jobs in the service for a while was to process and print military photos including some recon shots. If this was a military camera and film, it could be of a type you can't get at your local photo shop. It would do the job seen here. Personally, I think the shot would have been better with some blur of the prop. Panning with the formation could have minimized the blurring of the planes but the prop needs to show motion to look real.

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addendum some specs here
by Steven Haninger / April 3, 2007 7:22 AM PDT
In reply to: No expert here either

looks like the prop was 11' 2" and non feathering. My rough calculation is that max prop speed would be about 1900 RPM to keep the tips below 1100 fps (roughly the speed of sound). So, 3000 RPM would be well above the destruction point. This makes the prop freeze more realistic.

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Interesting ...
by Bill Osler / April 3, 2007 7:59 AM PDT
In reply to: Forgot link

I'm not sure how to explain the discrepancy between the information from Boeing and the information I found. I was still preparing my post when you put yours up. 'Ships passing in the night'.

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I found this ...
by Bill Osler / April 3, 2007 7:51 AM PDT
In reply to: No expert here either
Prop Pitch - Airwarfare:
The P-51 uses a Constant Speed Prop. It automatically adjusts itself (its propeller blade angle) to maintain a given RPM (it was the most common WWII 'system', just as it is the most common 'high performance' system of today).

So, in a P-51, you (the pilot) Can Not directly influence Propeller Pitch (the blue text on the screen is a mis-leading generic term, they had to use Something). What you Are directly influencing, is the RPM of the engine; again, the prop will adjust itself automatically to maintain your RPM settings (for any given speed), to its best ability (its best ability in FB/PF is notably better than real-life(tm), but thats a whole different story).

So, for the P-51, you achieve the most horsepower (maximum 'thrust', for a given manifold pressure) at '100%', which happens to be about 3000RPM or so. If you are only flying at 2500RPM, you are flying at a decreased power setting (not best speed), though you are saving engine (overheat).

P-51 power settings go something like this:

Climb/Combat: 3000RPM/67Hg MAP (manifold pressure) Fast Cruise/Normal Climb: 2500RPM/47Hg MAP Economy Cruise: 2300RPM/41Hg MAP.


I don't know how a propeller adjusts its pitch automagically but maybe it's just one of those wonders of modern engineering.

Anyway, that link suggests the RPM was probably in the 2000-3000 RPM range when the picture was taken. What I have not found is any information about the width of the P-51 propeller. My impression is that the tip-to-tip measurement was about 86 inches (but there was apparently some variation in propeller used at various times), so 9 degrees of rotation works out to about 7 inches. I'm not sure a 6" blur at the tip would be visible on the photograph at the resolution available on the web page but that's just a guess.

The other thing that puzzles me is that if the propeller length is 86" that gives a radius of 43". At rotation of 3000 RPM (50 Hz) the speed of the tip would be 2*43"/12*Pi*50Hz or ~1125 ft/sec (~767 mph). If the speed of sound in air is about 767 mph at room temperature then 3000 RPM risks exceeding one of the design specifications. Or did I mess up the math?

All of this pushes my engineering training a bit beyond my competence.
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Well, there's nothing more reliable but the facts
by Steven Haninger / April 3, 2007 8:01 AM PDT
In reply to: I found this ...

but nothing more fun than amateur speculation. Happy

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I just talked about this in my physics class
by jmhal / April 3, 2007 9:05 AM PDT
In reply to: I found this ...

and apparently it is quite common for the tips of the blades of a prop, on a plane or helicopter, to meet or exceed the speed of sound.

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Some of my info is obviously incorrect
by Steven Haninger / April 3, 2007 9:40 AM PDT

It's from past memory and not new research. There is a point at which a props, depending on several factors, are at risk of self destructing. The point where the speed of sound is just exceeded is a high stress moment. Perhaps some old props failed at that threshold. There is a point at which efficiency drops. I would guess it's because no further volume of air can be captured and pushed behind (thrust) and the plane just produces more noise. Here's an interesting site if you want to plug in some numbers.

http://www.pponk.com/HTML%20PAGES/propcalc.html

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OK, Doc, it's
by drpruner / April 3, 2007 9:27 AM PDT
In reply to: I found this ...

3 AM; time to put down Jane's and get some sleep. Happy

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That's a pretty standard formation at air shows these days.
by Kiddpeat / April 2, 2007 9:12 PM PDT

I've used 640 to stop a prop. Perhaps a shutter speed as low as 500 will also do the job.

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Thanks ...
by Bill Osler / April 2, 2007 10:08 PM PDT

I haven't ever taken a picture of a prop plane while the prop was spinning so I have no experience to fall back on here.

I do wonder, though, about the apparent lack of exhaust/turbulence in the picture. I know that visible effects of turbulence could get lost in a uniform blue background but I would have thought some evidence of exhaust would appear. Or not? I'm guessing here. Most of the time when I view planes there is some sort of background that makes the exhaust/turbulence obvious by distorting the background. I don't often have a chance to view planes up close against a uniform background.

There is another view of 3 of the planes elsewhere in that same slide show. In this view there is a little bit of blurring of the P51 prop but still no exhaust evident:

Side View

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Here are two I took in Chicago last summer.
by Kiddpeat / April 3, 2007 3:12 AM PDT
In reply to: Thanks ...
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BTW, the shutter on the old birds is 1/640. It's probably
by Kiddpeat / April 3, 2007 3:18 AM PDT

the same on both since I was shooting with shutter priority that day.

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Thanks ....
by Bill Osler / April 3, 2007 4:45 AM PDT

Well, it looks like I was trying to be 'too clever by half' in deconstructing the original photo I linked to.

I'm curious about technique you used. I do not reliably get good results when I try to photograph objects that have bright backlight like a clear blue sky. You said you were shooting shutter priority, so you were apparently using the camera's native metering. How do you make sure you get the foreground objects of interest properly exposed?

When I'm indoors the obvious answer is 'fill flash' but that doesn't work too well for outdoor photographs like this picture of a howler monkey before and after I adjusted gamma. The gamma adjustment helps some ... but it isn't the same as getting a good picture to begin with.

So, do you set exposure compensation when you are in this sort of situation? Or is there some sort of 'trade secret' I'll have to go to school to learn?

Thanks

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I usually have the exposure compensation set down at least
by Kiddpeat / April 3, 2007 10:16 AM PDT
In reply to: Thanks ....

one stop, sometimes a bit more. In something like an airshow, you can check your results in the LCD or via the histogram and adjust accordingly. I also shoot in raw format which provides a great deal of latitude once the image gets to the computer. Even after raw processing, Photoshop CS2 has a shadows/highlights filter that can produce excellent results with some shots.

For the air show, I was using a 70-200mm f2.8L IS lense with a 2X extender on a Canon 20D. This gave me an effective focus length of 640mm with the camera capable of 5 frames per second for the largest jpegs. You do your best to get the focus, but sometimes it's a bit like aiming a shotgun.

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I wish I'd planned some of my shots better ...
by Bill Osler / April 3, 2007 11:35 AM PDT

The problem with being relatively unschooled is that I've picked up bad habits ... like not checking (or not comprehending) the histogram ... and not planning things as well as I'd like.

I've also discovered that I'm not as fast on my feet (or in my thinking) as I'd like to be. A few minutes before I shot the underexposed howler monkey picture I saw these monkeys. I had to tweak the exposure a bit in Photoshop, but the camera did a much better job on this one even though it still had some problems with backlight. I'm still learning to process what I see and figure out how the camera will interpret the varying brightness. It seemed like I was seeing things so quickly that I was not thinking past the excitement (I'd never seen monkeys in the wild before) and I didn't remember to check camera settings or histograms as often as I should have. Maybe that comes with practice and planning. I'm hoping the proportion of good pictures increases with time and practice.

I'm really gonna have to spend some money on an IS lens. I was using a 28-300 zoom that lacks IS. Shooting handheld at 300mm without IS doesn't work in any of the real world situations I've ever wanted to photograph. Shooting with a monopod in a small boat, even when it's not moving much, is hard. The monopod helped, but it was very awkward, especially when I was trying to get birds from the moving boat. It's not like you can set up all your images in advance when you don't know when or where the birds will appear.

There's nothing wrong with the camera, BTW. When I haven't messed up the settings it does OK: Kids loved seeing their pictures on digicams

Oh well. It was fun watching the animals even if the pictures didn't come out as well as I'd like.

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The pros all say that you should shoot a lot of pictures.
by Kiddpeat / April 3, 2007 1:15 PM PDT

The reason is that most of them won't make it, but there will usually be a few keepers. Nice shots by the way.

The stabilization in the 70-200 f2.8L is phenomenal. You can feel and see it kick in when you press the shutter button halfway. You can see the image stabilize in the viewfinder. Like you, I frequently carry a tripod or monopod, but I also frequently take the camera back off and hand hold it. If it's an action situation, you usually can't keep up unless you handhold the camera.

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This explains the fighter:
by drpruner / April 3, 2007 9:29 AM PDT

"425 mph indicated (490 mph in P-51H)" No problem flying any modern jet that "slowly".

Don't know about the Warthog.

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Wow! You and this guy must have been
by John Robie / April 3, 2007 3:36 PM PDT
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prop speed
by jonah jones / April 3, 2007 12:26 AM PDT

if it's 3000rmp, a 1/4 second exposure, on a clear sunny day should suffice...

3000/240=12.5

,.

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Huh? A 1/4 second exposure is far too long to freeze a prop.
by Kiddpeat / April 3, 2007 2:49 AM PDT
In reply to: prop speed

Your own calculation shows the prop would rotate 360 degrees 12.5 times while the shutter is open. The camera might see a blur, but it would not see the prop.

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I've seen a similar photo, not Shopped.
by drpruner / April 3, 2007 9:23 AM PDT

The trick is to put pedal to the metal on the prop planes while staying above stall speed on the jets. (BTW a Mustang still moves very well when called upon. Check its stats and equipment.)

That said, IMO the sky is "too blue" and the aircraft outlines are too sharp.

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The P51 was one of
by John Robie / April 3, 2007 4:30 PM PDT

our best fighters of WWII and when the Korean war started (June 1950)our local Air National Guard flight of P51's were called up, led by the city District Attorney, called back as Commander.

It was said the the P51 just did not get into it with a MIG15 jet as it was no match. It was used during the first part of the war for bombing and strafing. Throughout most of the conflict there were no reports circulated of a P51 doing combat with the MIG. However a 1st Lt. Lingling, a USAF pilot, did shoot down a MIG15 in May 1952. At around 5000 feet after a bomb run he found himself flying straight on with a dot in the distance that turned out to be a MIG15. His gun cameras recorded that he stayed on the head-on course, opening fire with the six .50Cal machine guns and brought down the MIG.

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Apparently it is....
by John Robie / April 2, 2007 12:51 PM PDT
In reply to: Hmm. That's gotta be
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Could've been an April Fools trick
by Dragon / April 3, 2007 11:54 AM PDT
In reply to: Odd aerial formation

I had seen one by Google, earlier.

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Nah, check the P51 in the
by John Robie / April 3, 2007 3:41 PM PDT

links of my two post and DM's photo of the P51.

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