Gas mark 5
Member
- Messages
- 225
- Location
- Leeds / Harwell, UK
Hi all,
Long time since I've been able to get hands on with anything interesting, but now I'm doing some bits for a satellite ground station at work, might be of interest to some, more importantly I was hoping someone might be able to point me in the direction of some big engineering book of tables / formulas for calculating the strength of the boom .
It's basically a pair of yagi antennae mounted on a altitude / azimuth rotator (points antennae left, right, up and down). Here's a smaller one we have to get an idea:
The new installation is going to be in Cornwall near the coast and is a bit more mission critical so I want to make sure it can cope with the wind speeds. I've pinched an existing design for the boom (the part that connects the two antennae), but now with the bits in my hand they look a bit weedy. As the boom has to pass through the rotator it is limited to 1 5/8" diameter. So we have a 1 5/8" solid aluminium round bar going through there, and a pair of fibreglass tubes that slot on either side. The fibreglass is 50mm OD with 8mm wall thickness, so the aluminium centre section would need turning down to the ID of 34mm, but this looks very small to me to cope with the weight of an antenna blowing about in the wind. I've attached a quick sketch to try and illustrate it (not to scale):
The fibreglass itself weighs 3kg, the antenna around 4.5kg at the end of the 1.5m boom, and the wind loading for the antenna is quoted as 180N at 160km/h. 180N equates to 18.35kg of force, worst case scenario if that was blowing down you've got the weight of the antenna and boom adding to that (okay the boom isn't a point load it's distributed over the length but as a quick estimate) that's 25kg at the end of a 1.5mm boom all born by a 34mm section of aluminium round bar - 368Nm of turning force at that point if I have my sums right. And gusts may be even faster than that and I want a margin of safety too. Can anyone tell me if that immediately sounds insufficient or if I am worrying over nothing?
Or ideally, how would I go about calculating the force the aluminium bar could handle in this configuration? I'm sure it can't to too complicated, but most of the information I've found applies to deflection of a uniform beam instead of a joint like this.
Any advice appreciated!
Thanks,
George
Long time since I've been able to get hands on with anything interesting, but now I'm doing some bits for a satellite ground station at work, might be of interest to some, more importantly I was hoping someone might be able to point me in the direction of some big engineering book of tables / formulas for calculating the strength of the boom .
It's basically a pair of yagi antennae mounted on a altitude / azimuth rotator (points antennae left, right, up and down). Here's a smaller one we have to get an idea:
The new installation is going to be in Cornwall near the coast and is a bit more mission critical so I want to make sure it can cope with the wind speeds. I've pinched an existing design for the boom (the part that connects the two antennae), but now with the bits in my hand they look a bit weedy. As the boom has to pass through the rotator it is limited to 1 5/8" diameter. So we have a 1 5/8" solid aluminium round bar going through there, and a pair of fibreglass tubes that slot on either side. The fibreglass is 50mm OD with 8mm wall thickness, so the aluminium centre section would need turning down to the ID of 34mm, but this looks very small to me to cope with the weight of an antenna blowing about in the wind. I've attached a quick sketch to try and illustrate it (not to scale):
The fibreglass itself weighs 3kg, the antenna around 4.5kg at the end of the 1.5m boom, and the wind loading for the antenna is quoted as 180N at 160km/h. 180N equates to 18.35kg of force, worst case scenario if that was blowing down you've got the weight of the antenna and boom adding to that (okay the boom isn't a point load it's distributed over the length but as a quick estimate) that's 25kg at the end of a 1.5mm boom all born by a 34mm section of aluminium round bar - 368Nm of turning force at that point if I have my sums right. And gusts may be even faster than that and I want a margin of safety too. Can anyone tell me if that immediately sounds insufficient or if I am worrying over nothing?
Or ideally, how would I go about calculating the force the aluminium bar could handle in this configuration? I'm sure it can't to too complicated, but most of the information I've found applies to deflection of a uniform beam instead of a joint like this.
Any advice appreciated!
Thanks,
George