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#11
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Drag of Transponder Antennae compared
Thinking totally outside the box here and open to ridicule :).....
Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable. Just a thought for someone to expound upon. Bob 7U |
#12
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Drag of Transponder Antennae compared
On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote:
Thinking totally outside the box here and open to ridicule :)..... Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable. Just a thought for someone to expound upon. Bob 7U I still say on many performance threads on RAS...the nut behind the stick is worth more than the money spent on the ship....unless normally at the top of the sheet.... |
#13
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Drag of Transponder Antennae compared
On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote:
Thinking totally outside the box here and open to ridicule :)..... Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable. Just a thought for someone to expound upon. Bob 7U I think you could do that, but there are a couple challenges 1. RF cable is heavy and significantly affects the signal. On sailboats, it's suspected that a stern-rail mounted VHF radio antenna actually performs better than a masthead mounted antenna. So sending it 5-10m to the wingtip instead of keeping it close to the TX unit could noticeably decrease range. 2. Even when in perfect shape, RF connectors are a big source of energy loss, which further reduces range. 3. The connector would have to be properly connected/disconnected every time the plane is pulled out of its trailer. A powerful RF transmitter which is disconnected from an antenna can actually destroy itself, so the consequences of a forgotten connection are not necessarily limited to only being invisible that day. |
#14
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Drag of Transponder Antennae compared
On Thursday, 11 February 2021 at 05:10:10 UTC, Kenn Sebesta wrote:
On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote: Thinking totally outside the box here and open to ridicule :)..... Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable. Just a thought for someone to expound upon. Bob 7U I think you could do that, but there are a couple challenges 1. RF cable is heavy and significantly affects the signal. On sailboats, it's suspected that a stern-rail mounted VHF radio antenna actually performs better than a masthead mounted antenna. So sending it 5-10m to the wingtip instead of keeping it close to the TX unit could noticeably decrease range. 2. Even when in perfect shape, RF connectors are a big source of energy loss, which further reduces range. 3. The connector would have to be properly connected/disconnected every time the plane is pulled out of its trailer. A powerful RF transmitter which is disconnected from an antenna can actually destroy itself, so the consequences of a forgotten connection are not necessarily limited to only being invisible that day. Cable losses per metre are greater with higher frequency. This is why systems such as satellite TV and even some terrestrial TV installations convert to a lower frequency before the downlead. Transponders are working at UHF, and hence a short antenna cable distance is desirable, and the unit may be remote mounted in the centre section rather than in or behind the instrument panel. Winglets are probably made of carbon fibre, so the antenna would be screened and not work inside. I'll consider putting the transponder antenna inside a glass fuselage, and wonder how far from spaceframe and control rods/cables is desirable or feasible. Might need some contortionism to fit it. Might end up outside anyway. |
#15
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Drag of Transponder Antennae compared
Kenn Sebesta wrote on 2/10/2021 9:10 PM:
On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote: Thinking totally outside the box here and open to ridicule :)..... Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable. Just a thought for someone to expound upon. Bob 7U I think you could do that, but there are a couple challenges 1. RF cable is heavy and significantly affects the signal. On sailboats, it's suspected that a stern-rail mounted VHF radio antenna actually performs better than a masthead mounted antenna. So sending it 5-10m to the wingtip instead of keeping it close to the TX unit could noticeably decrease range. 2. Even when in perfect shape, RF connectors are a big source of energy loss, which further reduces range. 3. The connector would have to be properly connected/disconnected every time the plane is pulled out of its trailer. A powerful RF transmitter which is disconnected from an antenna can actually destroy itself, so the consequences of a forgotten connection are not necessarily limited to only being invisible that day. A better location would be in the fin, and I think some manufacturers offer that location. The cable would shorter than going to a winglet (about 22' vs 30'); it could be even shorter (15') if the transponder box (eg, a Trig unit) was mounted behind the gear instead in the instrument panel. The fin could not be made of carbon, of course. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 |
#16
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Drag of Transponder Antennae compared
Eric Greenwell wrote on 2/11/2021 5:19 AM:
Kenn Sebesta wrote on 2/10/2021 9:10 PM: On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote: Thinking totally outside the box here and open to ridicule :)..... Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable. Just a thought for someone to expound upon. Bob 7U I think you could do that, but there are a couple challenges 1. RF cable is heavy and significantly affects the signal. On sailboats, it's suspected that a stern-rail mounted VHF radio antenna actually performs better than a masthead mounted antenna. So sending it 5-10m to the wingtip instead of keeping it close to the TX unit could noticeably decrease range. 2. Even when in perfect shape, RF connectors are a big source of energy loss, which further reduces range. 3. The connector would have to be properly connected/disconnected every time the plane is pulled out of its trailer. A powerful RF transmitter which is disconnected from an antenna can actually destroy itself, so the consequences of a forgotten connection are not necessarily limited to only being invisible that day. A better location would be in the fin, and I think some manufacturers offer that location. The cable would shorter than going to a winglet (about 22' vs 30'); it could be even shorter (15') if the transponder box (eg, a Trig unit) was mounted behind the gear instead in the instrument panel. The fin could not be made of carbon, of course. Note: my length values are for a 15M glider. The winglet location would be even worse for 18M and larger gliders. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 |
#17
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Drag of Transponder Antennae compared
Still thinking inside the box. There is no reason why the TX unit needs to be in the cockpit. It could easily be mounted in the fin with a remote head in the cockpit.
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#18
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Drag of Transponder Antennae compared
wrote on 2/11/2021 6:49 AM:
Still thinking inside the box. There is no reason why the TX unit needs to be in the cockpit. It could easily be mounted in the fin with a remote head in the cockpit. You'd avoid a long RF cable, but would have run 12VDC power and the communication cable to it, plus provide the access to remove it for repairs. I think mounting the box behind the gear well, and running 15' of coax to it is easier and work just as well. 15' is not far with good quality coax. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 |
#19
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Drag of Transponder Antennae compared
On Thursday, February 11, 2021 at 11:43:16 AM UTC-5, Eric Greenwell wrote:
wrote on 2/11/2021 6:49 AM: Still thinking inside the box. There is no reason why the TX unit needs to be in the cockpit. It could easily be mounted in the fin with a remote head in the cockpit. You'd avoid a long RF cable, but would have run 12VDC power and the communication cable to it, plus provide the access to remove it for repairs. I think mounting the box behind the gear well, and running 15' of coax to it is easier and work just as well. 15' is not far with good quality coax. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 These comments appear to be by people that have never had to work in the the rear of a fuselage or in the fin. Mounting a thin antenna, without the little ball as far back as can be reached from the front area is a practical trade off. Slightly behind the gear and up the side a bit helps access and lets the gear doors protect the antenna. A simple wrapped fairing would be a clever small improvement. This far back the boundary layer is pretty thick so drag is likely minimal. As far as drag reduction, sealing the canopy well would yield a far greater return on time invested. BTDT UH |
#20
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Drag of Transponder Antennae compared
Hank Nixon wrote on 2/11/2021 10:52 AM:
These comments appear to be by people that have never had to work in the the rear of a fuselage or in the fin. My original comment was I would not personally mount the antenna in the fin, but I would select that as an option when buying a new glider :^) It was hard enough getting the coax from the panel to just behind the gear... -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 |
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