What is the L/D penalty of outside mounted GoPros?

I am thinking about trying to do some soaring videos. Inside the cockpit footage only is boring and I want to be more like Balleka with amazing outside camera shots. The reason why I haven't done much is concern over the performance penalty of outside cams while trying to do longer XC flights.

Anyone smarter than me (I know most of you are, other than TT) able to figure out the drag penalty of a GoPro either mounted on the wing or on the tail of a 27? It would be attached with the adhesive mount and not the larger suction cup mount in hope of reducing the drag. The GoPro in its larger case to accommodate an extra battery is 41mm H x 59mm W x 40mm D.

What I am hoping to figure out is if it is a 1-2 point L/D penalty or something more like a 4-5 point drop. Those of you who have flown with me know I need every L/D point I can get.

Here's to hopefully a lot of fun 2015 soaring videos shared from a bunch of us!

Bruno - B4
Oh yeah - and Nephi is amazing!

On Saturday, January 3, 2015 12:55:47 PM UTC-8, wrote:
I am thinking about trying to do some soaring videos. Inside the cockpit footage only is boring and I want to be more like Balleka with amazing outside camera shots. The reason why I haven't done much is concern over the performance penalty of outside cams while trying to do longer XC flights.

Anyone smarter than me (I know most of you are, other than TT) able to figure out the drag penalty of a GoPro either mounted on the wing or on the tail of a 27? It would be attached with the adhesive mount and not the larger suction cup mount in hope of reducing the drag. The GoPro in its larger case to accommodate an extra battery is 41mm H x 59mm W x 40mm D.

What I am hoping to figure out is if it is a 1-2 point L/D penalty or something more like a 4-5 point drop. Those of you who have flown with me know I need every L/D point I can get.

Here's to hopefully a lot of fun 2015 soaring videos shared from a bunch of us!

Bruno - B4
Oh yeah - and Nephi is amazing!

Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs. At 60 knots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq ft, adding 1.2 lbs drag, increasing your total to 22 and reducing L/D to 45.5. That is probably pretty worst case (drag coefficient probably less than 1, not in free stream, etc.). A tiny bit of streamlining on it could improve that a great deal I would think.

I knew I could catch a smart fish with that bait. Thanks! I try not to fly around too much at 60 knots but cruise more in the summer months around 85+ knots...I said try.

Please check my math and reasoning on this: I went to an online calculator and it said 85 knots at 15k alt is ~24.4 lbs/sq ft. Therefore, about 2.5 lbs of drag. Looking at the polar of a 27 at 85 knots, you are about 39/1 at that weight and speed...I think. So you would then be 36.5/1 with one camera or a drop in performance of around 6.5%.

I was seriously considering a camera on the tail and one on the wing. If both together add up to at 13% penalty, that is pretty harsh to impose upon yourself when attempting longer 750km - 1000km flights. If these calcs are correct, looks like the external cameras will be for the soft weather local flying days only.

Thanks!
Bruno - B4



Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs. At 60 knots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq ft, adding 1.2 lbs drag, increasing your total to 22 and reducing L/D to 45.5. That is probably pretty worst case (drag coefficient probably less than 1, not in free stream, etc.). A tiny bit of streamlining on it could improve that a great deal I would think.

Bruno, your XC videos are exceptionally fine as they are. For pretty
pictures for non-glider-pilots outside cameras are fun but for for me
what is really interesting in XC flight videos is watching from the
pilot's point of view and seeing ahead to the land, sky and
instruments.

John Galloway

At 22:15 03 January 2015, wrote:
I knew I could catch a smart fish with that bait. Thanks! I try not
to
fl=
y around too much at 60 knots but cruise more in the summer
months around
8=
5+ knots...I said try. =20

Please check my math and reasoning on this: I went to an online
calculator
=
and it said 85 knots at 15k alt is ~24.4 lbs/sq ft. Therefore, about
2.5
l=
bs of drag. Looking at the polar of a 27 at 85 knots, you are about
39/1
at=
that weight and speed...I think. So you would then be 36.5/1
with one
cam=
era or a drop in performance of around 6.5%.

I was seriously considering a camera on the tail and one on the
wing. If
b=
oth together add up to at 13% penalty, that is pretty harsh to
impose upon
=
yourself when attempting longer 750km - 1000km flights. If these
calcs
are=
correct, looks like the external cameras will be for the soft
weather
loca=
l flying days only.

Thanks!
Bruno - B4


=20
Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs.
At 60
k=
nots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq
ft,
addin=
g 1.2 lbs drag, increasing your total to 22 and reducing L/D to
45.5. That
=
is probably pretty worst case (drag coefficient probably less than
1, not
i=
n free stream, etc.). A tiny bit of streamlining on it could improve
that
a=
great deal I would think.

On Saturday, January 3, 2015 2:15:41 PM UTC-8, wrote:
I knew I could catch a smart fish with that bait. Thanks! I try not to fly around too much at 60 knots but cruise more in the summer months around 85+ knots...I said try.

Please check my math and reasoning on this: I went to an online calculator and it said 85 knots at 15k alt is ~24.4 lbs/sq ft. Therefore, about 2.5 lbs of drag. Looking at the polar of a 27 at 85 knots, you are about 39/1 at that weight and speed...I think. So you would then be 36.5/1 with one camera or a drop in performance of around 6.5%.

I was seriously considering a camera on the tail and one on the wing. If both together add up to at 13% penalty, that is pretty harsh to impose upon yourself when attempting longer 750km - 1000km flights. If these calcs are correct, looks like the external cameras will be for the soft weather local flying days only.

Thanks!
Bruno - B4



Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs. At 60 knots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq ft, adding 1.2 lbs drag, increasing your total to 22 and reducing L/D to 45.5. That is probably pretty worst case (drag coefficient probably less than 1, not in free stream, etc.). A tiny bit of streamlining on it could improve that a great deal I would think.

When you are doing these calcs do not correct the air density for altitude (unless you also correct your airspeed to true). The airspeed indicator shows dynamic pressure directly. So the dynamic pressure at 85 knots IAS @ 15K is the same as the dynamic pressure at 85 knots IAS @ sea level. Or if you are using true density at 15K then you must use true airspeed - you will find the result to be the same. Dynamic pressure is about 0.5 * .002378 * (airspeed in ft/sec) at sea level standard conditions. Your drag at 85 knots at 15K will be more than you estimated.

On Sat, 03 Jan 2015 14:15:39 -0800, brunovassel wrote:

I knew I could catch a smart fish with that bait. Thanks! I try not to
fly around too much at 60 knots but cruise more in the summer months
around 85+ knots...I said try.

Please check my math and reasoning on this: I went to an online
calculator and it said 85 knots at 15k alt is ~24.4 lbs/sq ft.
Therefore, about 2.5 lbs of drag. Looking at the polar of a 27 at 85
knots, you are about 39/1 at that weight and speed...I think. So you
would then be 36.5/1 with one camera or a drop in performance of around
6.5%.

I was seriously considering a camera on the tail and one on the wing.
If both together add up to at 13% penalty, that is pretty harsh to
impose upon yourself when attempting longer 750km - 1000km flights. If
these calcs are correct, looks like the external cameras will be for the
soft weather local flying days only.

Thanks!
Bruno - B4



Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs. At 60
knots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq ft,
adding 1.2 lbs drag, increasing your total to 22 and reducing L/D to
45.5. That is probably pretty worst case (drag coefficient probably
less than 1, not in free stream, etc.). A tiny bit of streamlining on
it could improve that a great deal I would think.

Did your calculation include drag from turbulence set up by the flat back
of the camera?

What would be the result of adding a streamlining cone with an A/R of 5
to 10 to the back of the camera, and maybe extending it down onto the
wing or tailplane surface to get rid of interference drag under it?

You could make one pretty easily (cheaply too) by carving and sanding
white or blue insulation foam to shape, and then filling the surface with
spackle to make it smooth before finish sanding, painting and polishing
it.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Saturday, January 3, 2015 4:03:06 PM UTC-8, Martin Gregorie wrote:
On Sat, 03 Jan 2015 14:15:39 -0800, brunovassel wrote:

I knew I could catch a smart fish with that bait. Thanks! I try not to
fly around too much at 60 knots but cruise more in the summer months
around 85+ knots...I said try.

Please check my math and reasoning on this: I went to an online
calculator and it said 85 knots at 15k alt is ~24.4 lbs/sq ft.
Therefore, about 2.5 lbs of drag. Looking at the polar of a 27 at 85
knots, you are about 39/1 at that weight and speed...I think. So you
would then be 36.5/1 with one camera or a drop in performance of around
6.5%.

I was seriously considering a camera on the tail and one on the wing.
If both together add up to at 13% penalty, that is pretty harsh to
impose upon yourself when attempting longer 750km - 1000km flights. If
these calcs are correct, looks like the external cameras will be for the
soft weather local flying days only.

Thanks!
Bruno - B4



Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs. At 60
knots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq ft,
adding 1.2 lbs drag, increasing your total to 22 and reducing L/D to
45.5. That is probably pretty worst case (drag coefficient probably
less than 1, not in free stream, etc.). A tiny bit of streamlining on
it could improve that a great deal I would think.

Did your calculation include drag from turbulence set up by the flat back
of the camera?

What would be the result of adding a streamlining cone with an A/R of 5
to 10 to the back of the camera, and maybe extending it down onto the
wing or tailplane surface to get rid of interference drag under it?

You could make one pretty easily (cheaply too) by carving and sanding
white or blue insulation foam to shape, and then filling the surface with
spackle to make it smooth before finish sanding, painting and polishing
it.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

I think you get L/D bonus points after you land

Sean Franke

On Saturday, January 3, 2015 4:03:06 PM UTC-8, Martin Gregorie wrote:
On Sat, 03 Jan 2015 14:15:39 -0800, brunovassel wrote:

I knew I could catch a smart fish with that bait. Thanks! I try not to
fly around too much at 60 knots but cruise more in the summer months
around 85+ knots...I said try.

Please check my math and reasoning on this: I went to an online
calculator and it said 85 knots at 15k alt is ~24.4 lbs/sq ft.
Therefore, about 2.5 lbs of drag. Looking at the polar of a 27 at 85
knots, you are about 39/1 at that weight and speed...I think. So you
would then be 36.5/1 with one camera or a drop in performance of around
6.5%.

I was seriously considering a camera on the tail and one on the wing.
If both together add up to at 13% penalty, that is pretty harsh to
impose upon yourself when attempting longer 750km - 1000km flights. If
these calcs are correct, looks like the external cameras will be for the
soft weather local flying days only.

Thanks!
Bruno - B4



Very roughly: at 48:1 flying at 1000 lbs, total drag is 20.8 lbs. At 60
knots, dynamic pressure is 12.2 lbs/sq ft. Camera is roughly .1 sq ft,
adding 1.2 lbs drag, increasing your total to 22 and reducing L/D to
45.5. That is probably pretty worst case (drag coefficient probably
less than 1, not in free stream, etc.). A tiny bit of streamlining on
it could improve that a great deal I would think.

Did your calculation include drag from turbulence set up by the flat back
of the camera?

What would be the result of adding a streamlining cone with an A/R of 5
to 10 to the back of the camera, and maybe extending it down onto the
wing or tailplane surface to get rid of interference drag under it?

You could make one pretty easily (cheaply too) by carving and sanding
white or blue insulation foam to shape, and then filling the surface with
spackle to make it smooth before finish sanding, painting and polishing
it.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

A roughly cubical shape is going to have a drag coefficient of around 1. A "boat tail" might cut it in half or so, if the front had to be left open. For one at the wing tip pointed in, you could have both a leading edge and trailing edge since you are looking out the side. Even a thickness ratio of 3:1 will gain a very large reduction in drag.

On Saturday, January 3, 2015 3:55:47 PM UTC-5, wrote:
I am thinking about trying to do some soaring videos. Inside the cockpit footage only is boring and I want to be more like Balleka with amazing outside camera shots. The reason why I haven't done much is concern over the performance penalty of outside cams while trying to do longer XC flights.

Anyone smarter than me (I know most of you are, other than TT) able to figure out the drag penalty of a GoPro either mounted on the wing or on the tail of a 27? It would be attached with the adhesive mount and not the larger suction cup mount in hope of reducing the drag. The GoPro in its larger case to accommodate an extra battery is 41mm H x 59mm W x 40mm D.

What I am hoping to figure out is if it is a 1-2 point L/D penalty or something more like a 4-5 point drop. Those of you who have flown with me know I need every L/D point I can get.

Here's to hopefully a lot of fun 2015 soaring videos shared from a bunch of us!

Bruno - B4
Oh yeah - and Nephi is amazing!

It's noticeable when flying with others. On the order of 5 ft/minute in cruise, but I didn't attempt to quantify in any serious way.

Evan Ludeman / T8

Bruno,

I used a Drift HD170 on the tail and wings. It is a very slim camera with VERY little frontal area( I mean almost nothing). When I had it on the wing, it was not noticeable at all.
Email Paul C and get in touch with me that way, and I can send you pics and videos.
Drift has improved the camera tremendously as well. The remotes have RED/GREEN lights so you know camera is on. You can use one remote for two cameras so if you ever wanted a split screen, the image time lapse would be perfectly synchronized. Front lens rotates 180deg, so you can place the camera virtually anywhere and adjust the lens to be level with horizon. Each camera has a nice LCD screen to set up the shot, then you can turn of the screen to save battery.
Check out DRIFT website.
I am not affiliated nor an investor in the company 8-)
Hope to see you in Nephi, with a glider this time....
Justin