Advice on Creating Side Electronics Bay

I have a short fat rocket that I want to create a side access AV Bay. I am extending the motor mount so I can add a third centering ring. I want to install the av bay between the second and third centering ring, with access from the side of the rocket.

My main worry is cutting the body tube cleanly and creating a decent way of reattaching the body tube as an access hatch and making it look clean. Also, the body tube is 7.5" and wondering what size holes to drill for sampling air and whether the holes should be evenly spaced around the rocket.

I am in the same situation on a crayon rocket, but I only have 3 inch diameter body tubes instead of 7... Will be watching.


Modern HPR2 covers this, IIRC.

I have a 75mm 3D sled for my RRC2+ and will use some all-thread mounted through the centering ring to secure it. It's the access panel and a way to attach it that I'm interested in how others have done it.

I would say to cut the hatch opening without regard to keeping the removed piece. Get the opening trimmed up as square and straight as you can. Then cut pieces of, or a single piece of coupler to fit inside the opening, such that the coupler creates a 1/2" lip or so all around. This coupler surface can be drilled in the corners for PEM nuts or similar. The lid would then be another piece of airframe cut to be slightly large for the opening and then block sanded down till it just fits and then drilled and countersunk for, say, 4-40 machine screws. This method uses a lot of material and time, but gets you the tightest fitting hatch. Reusing the removed section requires keeping the kerf and errors to an absolute minimum, especially the kerf of the cut.

Mount a board vertically between the centering rings, nearly back against the motor tube, with threaded inserts. Mount altimeter to another board with holes to match the insert layout, then use long machine screws with nylon standoffs to get clearance off the back of the board if you need it. Altimeter is then removable and mechanically secured into the rocket.

Treat the venting hole size problem like any other rocket, compute the volume of the space the altimeter is in, determine vent holes accordingly. I like to do more than one, and slightly larger than "necessary". Have experienced no troubles with that approach on different size airframes.

N

No room in the nose cone? That's where you should put it if you can.

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This is a short squat rocket and some of the motors I plan on using (Kosdon 54/2550 case, AT 54/2560 case) will extend into the nosecone. I have a 7-1/2" coupler 54mm centering ring in the nosecone to allow the motor room and still have a u-bolt shock cord anchor attachment.

If it's short and squat, what about a tube on the side (get an upper ring with a offset hole, and the center hole) and do it all from the top, except the switching on- done through a hole in the side (use a pushon pushoff switch? No need for a hatch. Unless of course..... it's already built.

N

Wingarcher said:

If it's short and squat, what about a tube on the side (get an upper ring with a offset hole, and the center hole) and do it all from the top, except the switching on- done through a hole in the side (use a pushon pushoff switch? No need for a hatch. Unless of course..... it's already built.

N

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Nothing built at this point.

It would also need to be vented to the outside with only part of its tube in contact with the outer tube to allow for sampling . . . this will not do. It's an outside access panel to the electronics or none at all. Your earlier suggestion is obviously more to my taste, though expensive unless I post [Wanted] 6" piece of 7-1/2" body tube in order to avoid having to purchase a 48" section from PML at considerable cost. Though, I might just find the material to fashion the parts for the inner part of the hatch and be very careful with the cutting of the body tube and use some rubber gasket material to make the gap snug.

As Wingarcher suggests, put a window frame of coupler in so you can put in blind nuts. Consider glassing the inside of the rocket around the frame to assist with transferring stresses. If you're really good, you could make the whole frame out of glass, I've never tried it inside a rocket before but if you google for splitting an r/c aircraft cowl there are multiple guides on rcuniverse, rcgroups, flyinggiants and probably more on how to create a composite lip you can put nuts in, just like you want.

Alternatively, you could also just cut plywood squares and mount them in the corners of your frame, then drill through them and the cover to make your mounting points.

I'd put a lot of effort into covering the gap inbetween the AV Bay cover and the airframe, tape the edges of the cover up with clear packing tape or stickytape and then fill the gap with epoxy or putty once hte hatch is installed. The tape will stop it from getting glued in.

Here's some CFD I prepared earlier of a side hatch AV bay to give you an idea of just how much the flow will trip from a 0.2mm gap.

Wow, that is trippy and quite an eye opener for someone like me who rarely ever thinks about drag but should. Thanks for the visualisation . . . Like they say, a picture is worth paying attention to

Issus said:

Here's some CFD I prepared earlier of a side hatch AV bay to give you an idea of just how much the flow will trip from a 0.2mm gap.

View attachment 167009
View attachment 167010

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What Mach number is that?

hball55 said:

Nothing built at this point.

It would also need to be vented to the outside with only part of its tube in contact with the outer tube to allow for sampling . . . this will not do. It's an outside access panel to the electronics or none at all. Your earlier suggestion is obviously more to my taste, though expensive unless I post [Wanted] 6" piece of 7-1/2" body tube in order to avoid having to purchase a 48" section from PML at considerable cost. Though, I might just find the material to fashion the parts for the inner part of the hatch and be very careful with the cutting of the body tube and use some rubber gasket material to make the gap snug.

Click to expand...

I know of folks that have contacted PML about short/scrap pieces of airframe/coupler tubes and purchased them at reasonable prices.

I have a 7.5" Estes Fat Boy upscale with a 98mm motor mount that has the electronics between the fins. I cut my hatches in the tube then I glued a section of coupler tube behind the hole then I cut the access hole in that. This made a nice way to mount the hatch cover.
I attached the altimiter to a piece of G10 mounted between the centering rings. The switch was mounted through the body tube below the hatch. Because the altimiter was mounted between the fins I couldn't have the vent holes there. I installed a third ring above the fins and drilled my vent holes between the second and third rings. I had drilled some large holes in the second ring above the altimiter bay to allow for the free movment of air. It works well.
My motor tube is extended up into nose cone where it coupled with a tube attached to the nose. There is a bulkplate just below the coupler and this is where I mount my ejection charges. This puts the charges above the chutes so no protectors are needed.

I do plan on mounting my electronics between the second and third centering rings and drilling the vent holes on that level around the body tube. My motor tube will also extend up into the nosecone coupler area and the chute will be below and sort of snugged around the motor tube to keep it free from ejection gases. My rocket, too is a Fatboy upscale, the Chubsy that Smokin Rockets once offered; the nosecone and body tube all being PML parts. I have a coupler centering ring for the nosecone, to attach a u-bolt and I figure that's as good a place to have the ejection charge, just inside the motor tube so that it acts just like motor ejection, blowing upwards, and keeping the parachute free of the gases.

It was the compartment hatch that I was most interested in hearing about and the piece of coupler made into the opening and way to secure the cover was definitely the idea I was seeking. Looking forward to building it.

I will contact PML about those scraps, thanks for suggesting that.

CarVac said:

What Mach number is that?

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1.2 or so

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new2hpr said:

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Nice work, are those 6-32 threaded inserts? With the extra room I have in a 7-1/2" airframe, I'll have the switch access hole in the av bay cover. Actually the sled design demands it, but that's a plus and not a negative. The sled will be one of Landru's 3D sleds; waiting for the mailman to deliver this very moment and it should only be minutes away.

No threaded inserts, although that may have been easier. I used plastic rivets.
-Ken

new2hpr said:

No threaded inserts, although that may have been easier. I used plastic rivets.
-Ken

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Oh! In the pic I thought I saw the glint of brass. I always have trouble with threaded inserts, getting them in straight; now I have the tools for installing them, thanks Doghouse Rocketry! I hope they make the job easier:lol: I have a nack for making simple things difficult.

I would secure the battery to the battery holder.....

Bob

hball55 said:

I do plan on mounting my electronics between the second and third centering rings and drilling the vent holes on that level around the body tube. My motor tube will also extend up into the nosecone coupler area and the chute will be below and sort of snugged around the motor tube to keep it free from ejection gases. My rocket, too is a Fatboy upscale, the Chubsy that Smokin Rockets once offered; the nosecone and body tube all being PML parts. I have a coupler centering ring for the nosecone, to attach a u-bolt and I figure that's as good a place to have the ejection charge, just inside the motor tube so that it acts just like motor ejection, blowing upwards, and keeping the parachute free of the gases.

It was the compartment hatch that I was most interested in hearing about and the piece of coupler made into the opening and way to secure the cover was definitely the idea I was seeking. Looking forward to building it.

I will contact PML about those scraps, thanks for suggesting that.

Click to expand...

Boy am I glad that post showed up. My computer was acting up and I didn't find out until this afternoon that the post made it.
I will try to take a couple pictures of my avbay area and ejection charge area.
I need to repair a fin on my Fat Boy. It stuck a fin in soft ground on landing and the chute pulled the rocket over snapping my 1/4" plywood fin.

bobkrech said:

I would secure the battery to the battery holder.....Bob

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The battery holder holds it top, bottom, and side to side. Once the hatch is cinched down, it's snug on the battery. Nowhere for it to go. I tried to run a tie wrap around the battery (and central 38 motor tube). Not only very difficult to snake it around, but once I got it cranked down, the hatch would not settle down into its recess.

Hasn't failed yet (knock on balsa).
-Ken

I said I woul post something showing how I did this on my 7.5" Fatboy.
The electronics boards were mounted with quarter turn fasteners.

Altimiter Bay.


Timer Bay.


Ejection Charge Holders at the top of the motor mount tube. The wires for the ejection charges come up from the avbay to the ejection charges through a tube.


Nose Cone attachment points and Tracker bay. The tracker bay is in the upper right in the nose cone.



Side view of the ejection charge holder at the top of the motor tube. The the ejection charge holder is actually a coupler tube and it slips into the tube in the nose cone.




Air Start terminal points.




Sorry for the dirt on things but I haven't cleaned it up because after the fin broke I am still trying to decide if I want to fix it or build a new rocket.

Don't fret about the dirt, she's battle-worn and bluff and there's no reason to be ashamed. Sorry for the weird language, I'm currently in the middle of an audio book (Treason's Harbour) that is part of the Aubrey/Maturin series by Patrick O'Brian. Love those 18th/19th Century sailing novels. I figure someone with the name Sailor Bill would appreciate that. I too served in the Navy, '74-'78 aboard the Turner Joy DD 951 and the Hepburn FF-1055.