SpudFiles

Apple sent. Sorry I missed it. Thanks for the measurements. I found instructions for installing Google Earth in Ubuntu. I'll tackle it on the weekend.

Is the launch point shown correctly? It looks further into the field than the GPS point. We launched from under the tree due to the drizzle before the rain set in.

I got 396 yards to the apple on my program.

EDIT, I noticed that Google Earth and Google Maps are using different date photos. Photo offsets may explain the differences.

Technician1002 wrote:Is the launch point shown correctly?

Bear in mind, there may be small inconsistencies between the co-ordinates and the actual images. (Not to mention that GPS is usually only accurate to a few feet)

For example, if you try using GPS at my house, Google Earth will often show the co-ordinates as being in the middle of the house across the street. It's also been used for tracking journeys by car, and quite frequently shows the car on the other side of the road, in a field nearby, etc...

That's not exactly shabby - still accurate to about 10 metres or so, even through the accumulated inaccuracies of both the GPS and the Google Earth satellite imagery.
In short, if the two correlate to within about 10 metres or so, it's probably "right".

Ultimately, you should use one or the other, to avoid accumulating conversion errors - as you're dependent on the GPS for the landing coordinates, then you should use the GPS for the launch coordinates as well, not the imagery.

Updated all of my previous pictures.
All points are GPS coordinates.
The mid tree point to the launch coordinates is about 19.8 yds differential.

As requested by Tech, a picture of the launch and landing site...

Wow, Gun Freak. If that image is to scale that looks to be close to 450m.


Playing around in ggdt, I can't get anything close to 450m from the external ballistics calculator. Is there something I'm missing?

Matt_NZ wrote:Wow, Gun Freak. If that image is to scale that looks to be close to 450m.


Playing around in ggdt, I can't get anything close to 450m from the external ballistics calculator. Is there something I'm missing?

Try a Cd value of between 2-2.5 for a golfball. Personally I use 2.2 as I hear that is close to the real value.

I was trying to use the "Windy day at the lake" as part of the reason for the distance. I re-watched the video to see the direction of the ripples and.. this is shooting into the wind..

MrCrowley wrote:

Matt_NZ wrote:Wow, Gun Freak. If that image is to scale that looks to be close to 450m.


Playing around in ggdt, I can't get anything close to 450m from the external ballistics calculator. Is there something I'm missing?

Try a Cd value of between 2-2.5 for a golfball. Personally I use 2.2 as I hear that is close to the real value.

I assume I enter the value as 0.22. I decided to see if I could find more information on the CD of the golfball. This link has some detailed information on the golf ball.
There are numerous claims for the CD but most are .22-2.5.

Yeah sorry I missed a few decimal places...dunno why I always do that.

Two things to say:

Different golfballs vary a lot. Some designs have a good Cd, some less so. Without testing, or having a specific Cd I knew for certain related to the golf ball in question, I wouldn't assume that any had a Cd less than about 0.3. This goes particularly if you're using cheaper brands - which, I would assume you probably are.

Secondly, wind has a big effect, and the GGDT calculator doesn't offer this as an option.

~~~~~

Now, I missed this one earlier:

Gun Freak wrote:Yeah, you're not gonna get a half mile with a golf ball, but you might get like 700-800 yards.

Without the aid of the wind (and don't assume that just because it's not a tailwind, it's not helping - crosswinds can help provide lift), you'd need considerably supersonic muzzle velocities with a golfball to make it past 600 yards. I wouldn't even hold Larda's hybrid monster as capable of putting its golf balls out to 700-800 yard ranges.

With something as relatively unaerodynamic as a golfball (with a mass/drag area ratio of only ~120 kg/m²), and with such poor transonic performance as the sphere shape has, range scales very poorly with muzzle velocity.

This is why, despite having muzzle velocities well in excess of twice that of a golf drive, it's still something of a challenge to get more than twice the range (a good golf drive is in the 250+ yard range). To put that inefficiency into perspective, bear in mind that without drag, range would scale as the square of velocity.

@Rag, Thanks for clearing that up, my claim was just an estimate. I figured a cannon of his level of performance would be very capable of exceding my range of 450 yards but I guess it was exaggerated.

@Matt, the external ballistsics calculator is very crude, as stated on the GGDT website, and isn't very reliable in these applications... I once used it for this gun and I think it predicted around 750 feet, which is what, like 250 yards which is way under the range of this gun on the pressure I calculated with.

@Tech, I don't think I was shooting directly into the wind. I shot NNE, and there was pretty much a west wind. The ripples might be decieving.

Gun Freak wrote:I figured a cannon of his level of performance would be very capable of exceding my range of 450 yards but I guess it was exaggerated.

I wouldn't be surprised by a quarter mile range claim from most of the decent golf ball cannons from this site.

Sure, you'd need the weather on your side a bit, a decent velocity, and ideally a good ball, but I can't say ~470 yards is impossible.
After all, the record for a golf drive in competition is 515 yards, and that didn't have this kind of velocity behind it.
(There are longer claims, but they're usually outside of competition under conditions designed to maximise range - and quite often very dubious anyway.)

In short, I'm not disputing your claim (it's certainly possible) - what I'm doubting is your optimistic estimates the ranges Tech might manage. Sure, golf balls could theoretically go 700-800 yards, but it would be more about favourable weather than velocity.

No problem, I'll take your word for it over most people here, so yeah Tech might not be able to shoot one 700 yards but I was just saying he could most like shoot one further than my cannon could. You shouldn't even THINK about disputing my claim... I have evidence. The ball I used was a Callaway range ball, so it was of pretty good qulity despite being driven numerous times before me. I can assure though that my drive was the furthest that ball had ever seen and ever will see

New piston, threaded rod with washers and two o-rings. Works like a charm but it is even heavier than the old piston and you can feel it when you fire the gun...

Compared to the original piston:

New chamber designed with low volume for mobile firing using my bike pump. I tried not to make any primer stains It looks pretty good and the tee in the back makes a good shoulder rest.

Gun Freak wrote: tee in the back makes a good shoulder rest.

Nice, job there 8).
Does this new chamber mean it can be shoulder fired yet, or is the the barrel too long?