Electronics Bays for mounting electronics instead of nose cones

I'm reasonably new to HPR, and I have a question. Why are electronics almost always mounted in a separate electronics bay on rockets? Why not nestle them in the nose cone?

I am no expert...

However, the following three considerations come to mind:

• Altimeter accuracy when placed too close to the nose cone. I believe that the altimeter likes "clean" air-flow as opposed to the turbulent air by the nose cone.
  
• In the case of a dual-deploy setup where the altimeter controls the firing of your ejection charges you will have to get tricky in order to connect your altimeter to the drogue section ejection charge. (This is not an issue if you are using the motor ejection charge for the drogue section)
  
• The nose cone is a good spot to put your tracker/GPS hardware when working with smaller diameter dual deploy rockets because the tracker transmitter can interfere with the altimeter functions.

I hope that helps.

Cor

MJT said:

I'm reasonably new to HPR, and I have a question. Why are electronics almost always mounted in a separate electronics bay on rockets? Why not nestle them in the nose cone?

Click to expand...

Hi MJT! Welcome to TRF! That's really a good question and I'm just walking point in the minefield but I'll start off with a few generic answers.
1) The most common reason for 'av bays', 'e-bays', 'sleds' or 'payload compartments' is to keep the electronics isolated from the corrosive effects of black powder most commonly used in deployment
2) In 'dual deployment' where there is a drogue and a main chute, there needs to be space above and below for the 'laundry'-chutes, streamers, etc. These two individual compartments can be pressurized independently of each other in sequence.
3) certainly there are instances where the altimeters, trackers or other sensors are housed in the nose cone, the atmospheric 'ports' needed to equalize the atmospheric ambient inside the rocket need to be located away from turbulent flow from the nosecone/body tube shoulder. This allows the barometric (most common type of altimeter) to sense the lowered pressure at higher altitude and 'do it's thing' based on those readings. You also want to to prevent the shock wave of the deployment charge from damaging your fragile circuitry.
These are just rudimentary answers to a complex question but may serve to start you on your road to discovery. My fellow TRF's will prolly join in with other aspects and opinions, but we all play well together so welcome to the team! Good flights, sir!

I had an old rocket that got zippered and I decided instead of adding an av-bay in the normal configuration, I just shortend the airframe and put my altimeter in the nose cone. This is a 3" nose cone in the picture and you can see my vent hole in the shoulder. This type of deployment set up also require a tether or cable cutter type system to deploy your main chute. Im also doing this same set up in a 5" NC for my Gizmo.

All the reasons in the posts so far are good ones. Having said that, it is entirely possible to have the altimeter in the nose cone. One reason for doing this is if you're trying to minimize the length of the rocket to the absolute minimum, but still have dual deploy. Such was the case for the rocket pictured (that's the motor tube serving as the coupler).

The typical way I do this (which is the case for the rocket in the pic) is to have a bulkhead located in the position where the bay would be. Then, I have two sets of wires that go through the "main" bay to charges just above and just below this bulkhead. The charge below the bulkhead is connected via breakwires so that when the main charge goes off, the wires break so that the main can come out.

I have a few rockets that I've flow dozens of times this way, and I use trackers and gps units in the cone along with the altimeter. My belief is that some altimeters are affected by RF interference and some are not (I use the latter).

Two problems with this configuration are that the switch for the altimeter (in my configurations anyway) is on the bulkhead on the bottom of the cone. Thus, I have to turn on the altimeter and then install the nose cone and shear pins with the altimeter on. Again, some altimeters are better for this than others. Another limitation is that this configuration is only practical with a single altimeter. Therefore, in my opinion, it should be limited to use in smaller rockets (i.e., not rockets you might normally expect to have redundant altimeters for safety reasons).

Jim

Heres is another good example.https://www.rocketryforum.com/showthread.php?50744-Wildman-5-quot-Jart-DD-Upgrade

Thanks for the replies! This was actually really helpful. Especially the pictures.

You can also bind the main with a Tender Descender or similar unit and have both the main and the drogue come out with the nose cone. You do want to vent the body tube at least 2C down from the nose cone shoulder so the airflow can settle down for the altimeter's baro sensor, but if you have an HPR bird you're going to be venting the tube anyway to prevent a pressure separation. This is a relatively easy way to add DD to a rocket that was originally built for SD, too.

cerving said:

You can also bind the main with a Tender Descender or similar unit and have both the main and the drogue come out with the nose cone. You do want to vent the body tube at least 2C down from the nose cone shoulder so the airflow can settle down for the altimeter's baro sensor, but if you have an HPR bird you're going to be venting the tube anyway to prevent a pressure separation. This is a relatively easy way to add DD to a rocket that was originally built for SD, too.

Click to expand...

There's no need with modern altimeters to put the vent far down the body tube. Disappearing Act broke Mach on its I59 flight and the altimeters had no issue with the vent being about 4 inches from the tip of the (rounded) nosecone.

Just handing out conventional wisdom for the newbie.

I would still vent below the NC shoulder at least 1C, even with shear pins. My concern would be a crossflow close to the baro sensor that might induce noise or otherwise cause spurious readings. I would go a little further and keep the vents at least 1C from the sensor.