I was wondering if anyone has any practical guidelines they follow/know of for what the maximum altitude for a given size of rocket might be to allow a reasonable chance for recovery by purely visual means.

Obviously, the larger the rocket, or possibly more important the parachute, the higher you can see it. Conditions will play a factor too.

Eventually I'll get a radio or GPS locator together, but for now, eyes and binoculars are all I've got.

Any one have any thoughts?

How fast you want it back? 😉

Usally some one will find it. 🙂

Golly gee, once they're out of sight, what fun is it? LOL Rule of thumb for visual recovery is first fly a wind rabbit, then get all the extra eyes you can to watch. The color of the rocket and the chute, or the sparkly glint of mylar streamers helps and then use a rough guesstimation of drift to altitude and walk out there and it will be in the last place you look. But seriously, depending on the size (length and diameter) sonic beacons or transmitters aren't that heavy to screw up optimum mass calculations and help immensely in the recovery process. If you're really going that high and want it back, I'd lend my transmitter. Send me a PM.

The more eyes looking, the more launches before you go (trend setters) and a bunch of other factors play into this. Pandora is around here somewhere. 😆

How big of a bird, how high does it sim to, how fast do you want it to come back down?

For A-E birds, I use mylar chutes. Most of them have a hole cut in the center for faster descent. The mylar can be seen for a loooooong ways. I don't know if Tim from LGR has them, but I know Bryan from Rocket Garden does. That's where I get mine from.

Bigger birds, better set down, there are a lot of chutes to chose from. I have a 16"x24" plastic tub of them.....

If you're looking for a range where you don't have to worry much about it, I'd say probably around 1000' for a small A rocket, 2000' for a 38mm min diameter rocket. Above that, others could provide some estimates. Of course, it depends a lot on the cloud cover, with spotty clouds being pretty much the worst, in my experience.

The most extreme visual track I've seen is when Chad Moore somehow kept a binocular lock on my 24mm G37 record rocket when it went to about 8500 feet, which greatly helped the subsequent radio tracker recovery. But I would never count on such a feat being repeated.

The resolution of the human eye is one line pair per 0.6 arc minutes (1/100th of a degree for a pair, 1/200th for a single dark line). However, that is for discerning a black and white line pattern. You can see far greater detail for a linear feature when superimposed on a solid background. For example, you would think that a satellite image with 30 meter pixels should not be able to show a road thinner than 30 meters wide, but in fact all kinds of dirt tracks in the desert show up on those images. The human brain is hardwired to detect such linear features very well. So taking a wild a** guess based on the two classes I have in remote sensing, the theoretical limit for a linear feature is maybe 3x better, or 1/600th of a degree. For a 1" wide rocket of infinite length (not counting fins), that is about 3000' high. As your rocket is decreased in length, it will behave more like point, which the eye has less acuity for. So a very short stubby rocket would have a minimum visual acuity of about .4 arc min, or 1/150th of a degree for a point. For a 1" wide stubby rocket with no fins, that is only about 750'.

Now tracking smoke obviously helps, as does a specular reflection off the rocket, as does movement. If the rocket stops its relative motion, it will likely disappear, thanks to the brain's auto-filtering process. That "feature" prevents you from being driven insane by floaters in your eye or dust on your sunglasses. You can counteract this by keeping your eye moving just a little. Move too much (or the rocket is too fast) and it will be outside of the densest cluster of receptors in your retina, and you will also lose sight of it.

So that is theoretical. What will diminish that is 1) a low contrast object, like a gray rocket against a white cloud, 2) a very constricted pupil or very wide one, 3) an overly bright background sky that causes disability glare, or 4) low light... oh yeah, and this is all for a 20/20 eye with a clear vitreous humor.

Binoculars clearly help, but not as much as the power would indicate. The resolution limit is still bound by the pupil size, and at least half of the light (and thus the resolution) captured by binoculars is too wide of a light cone to fin into your pupil. Another factor is atmospheric turbulence which is too small scale to affect naked eye vision, but starts to become a factor with increased magnification. A Wild A** Rule of Thumb (WART) for good binos is to divide the power in half to get the resolution gain. So under ideal conditions and 8x top notch binos, Adrian's 24mm G record would be visible up to 12,000' away (somewhat less in altitude unless the boost was perfectly straight, and a even less since the rocket was not of infinite length).

So let me go out on a limb here and make a table for a rocket of 15:1 length to width ratio, small fins, good contrasting color, and no tracking smoke. I rounded to make easy numbers and accounted for atmospheric scattering a bit.

Naked Eye Visibility
Tube Size : Ideal Conditions /Typical Conditions / Poor Conditions
18mm: 1500' / 700' / 400'
24mm: 2000' / 1000' / 600'
29mm: 2200' / 1100' / 700'
38mm: 3000' / 1500' / 1000'
54mm: 4000' / 2000' / 1500'
75mm: 5200' / 2500' / 1800'
98mm: 7000' / 3500' / 2500'
150mm: 10000' / 5000' / 3000'

Ideal= blue sky, no clouds, no sun glare
Typical= hazy sky, or thin cirrus
Poor= mottled clouds, or thick haze, or sun glare

Chad Moore

Awesome explanation and scientific reasoning - thanks Chad. One of the best aspects of our club membership is the different smarts everyone brings to the range. Seems pretty straight forward to me and demonstrates why I've been able to eventually find most of my errant flights. Heck, even a blind squirrel finds a nut once in while.

Awesome explanation and scientific reasoning - thanks Chad. One of the best aspects of our club membership is the different smarts everyone brings to the range.

Wow, that is an excellent explanation. I spent a while looking for how to calculate visibility vs. size vs. distance, but sounds like I wasn't using the right terms. Will have to look up more info on remote sensing calculations.

Using mylar and sonic beacons are excellent ideas as well. I forgot to mention it, but I do have a sonic beacon I'll be using. I happen to have a couple 4" mylar streamers, which I hadn't thought of using, but will now 😀

I've acutally got a 54 mm dia. rocket that I've put up right about 2k ft. That seemed about the end of my comfort level, and matches up nicely with Chad's chart. The project I was posting about is a 4" (98mm) x 5' bird, which matches the 15:1 ratio perfectly 😀

Looks like I won't get going high enough right now to need a transmitter. Might take you up on the offer once I get the L2 project ready.

Thank you all for your ideas!

I really like Chad's chart too. It matches up well my experience with doing troglodite style tracking at NAR contests, as well as HPR.

Another practical example, i have a black rocket that is 2m * 98mm, which has good contrast with our usual high clouds, and optimal ratio by Chad's data. Its first launch the ebay wasnt ready, so was doing motor ejection and a little worried about loosing sight of it, so i recruited some visual trackers specifically. I am blessed with very good eyes, all four times i have launched it have been to right around 5000 feet, and on all four occasions i was the only one able to see it at apogee before the chute came out. So the optimal 7000 / 3500 / 2500 numbers match up very well on a rocket that i know i have paid particular attention to visual tracking by my own eyes and others.

Most of what I posted is from a guy named Blackwell. He did a LOT of human visibility work during WWII, and had these elaborate experiments and rooms full of women as test subjects (the men were off at war). He is like the godfather of vision, and is often quoted by astronomy, visibility studies, my own work with light pollution, and several other fields- now including rocketry! Great experimental science.

Chad

Most of what I posted is from a guy named Blackwell. He did a LOT of human visibility work during WWII, and had these elaborate experiments and rooms full of women as test subjects (the men were off at war). He is like the godfather of vision, and is often quoted by astronomy, visibility studies, my own work with light pollution, and several other fields- now including rocketry! Great experimental science.

Chad

I thought women, in general, had better vision than men.
Or a least my wife said she read, they have more sensitive vision to bright lights at night.
She always coplains, how bright brake lights at night are.

Scott e

Men have twice the number of rod cells in their retina than women providing better low light vision. Women on the other hand have more than double the number of cone cells than men providing far better color vision. I read that men can see and differentiate around 10,000 shades of color whereas women can differentiate more than 32,000.

W

I read that men can see and differentiate around 10,000 shades of color whereas women can differentiate more than 32,000.

Women do not see more colors, they just have a lot more names for them. 😆