Conductivity nightmare

[Trenman]

Ok perhaps I am too worried but I have a CF rocket (Conducting 45ohms/12"), in an aluminum sled (also conductive) with my avionics hooked up. Wont this ground out my electronics? How can I attach these avionics to the rocket without inherently grounding out everything?

 

[Trenman]

ahh i need "standoffs". Answer solved.

 

[WillMarchant]

Yes, you usually want standoffs to avoid pressing the electronics board directly to your support board. Sometimes there are delicate things on the back of the avionics. Some avionics, MAWD for example, have the pressure sensor on the back so you need to maintain a minimum clearance.

You need to decide if you want insulating standoffs or ones that will tie the groundplane of your avionics to the sled. I'd probably try to isolate mine. Your mileage may vary.

This is also a chat to have with your local HPR flyers and your mentor(s).

 

[FredA]

You WILL want standoff's.
The backside of the board has via's and thru-hole component leads coming through as well as any backside components.

You also need to look at the mounting holes. Make sure they are all no-connects or ground-connects. You could be shorting things inadvertanly.

When in doubt, use standoffs and Nylon screws....

 

[bobkrech]

Ok perhaps I am too worried but I have a CF rocket (Conducting 45ohms/12"), in an aluminum sled (also conductive) with my avionics hooked up. Wont this ground out my electronics? How can I attach these avionics to the rocket without inherently grounding out everything?

Liam

Your GPS receiver and ARTS transmitter will not function properly inside this rocket because the CF will act as an RF shield because it is conductive. The GPS signal will not get into and the the transmitter signal will not get out of the avionics bay without external antennas.

I also have to ask why you want to use an aluminum sled. It's conductive, heavy, and overkill. A good aircraft grade Baltic birch plywood sled is plenty strong, and if for some reason you want to go with a composite, use G10 FG.

I've been reading your posts on this rocket since they started. You need to be certified by either NAR or TRA to launch this rocket with L1 or L2 high power motors so you will need to find a local club and mentor to help you get high power certified before you can really use this rocket so I would suggest that you do it now rather than later. You need to obtain a FAA Waiver if the motor contains more than 125 grams of propellant and/or the rocket weights more than 1500 grams loaded. Doing this on your own will require 60 day and some paperwork. Once you are certified, you can fly with the club under their waiver and you don't have to deal with the FAA.

You can find a local NAR club here https://www.nar.org/NARseclist.php

and a TRA club here https://www.tripoli.org/prefecture/us.shtml

Bob

 

[DAllen]

What is the advantage of using aluminum? I use birch ply or G10 and don't worry a bit about that stuff.

-Dave

 

[Trenman]

Liam

Your GPS receiver and ARTS transmitter will not function properly inside this rocket because the CF will act as an RF shield because it is conductive. The GPS signal will not get into and the the transmitter signal will not get out of the avionics bay without external antennas.

I also have to ask why you want to use an aluminum sled. It's conductive, heavy, and overkill. A good aircraft grade Baltic birch plywood sled is plenty strong, and if for some reason you want to go with a composite, use G10 FG.

I've been reading your posts on this rocket since they started. You need to be certified by either NAR or TRA to launch this rocket with L1 or L2 high power motors so you will need to find a local club and mentor to help you get high power certified before you can really use this rocket so I would suggest that you do it now rather than later. You need to obtain a FAA Waiver if the motor contains more than 125 grams of propellant and/or the rocket weights more than 1500 grams loaded. Doing this on your own will require 60 day and some paperwork. Once you are certified, you can fly with the club under their waiver and you don't have to deal with the FAA.

You can find a local NAR club here https://www.nar.org/NARseclist.php

and a TRA club here https://www.tripoli.org/prefecture/us.shtml

Bob

I certainly appreciate your input. The reason I am pushing high end/ "overkill" size components is because I want to build this this strong and with good components. I expect to take the better part of a year to get the thing built if not longer due to the precision. I have created a 3d autocad file that I have been following and modifying. I am not out so set a record. I dont care how heavy the rocket is. I just want a well built, high quality, precise and novel rocket.

Regarding attenuation: I have several build sources that have claimed little to no attenuation in the nosecone. My findings indicate that attenuation of all signals are this way. From what I have found the "graphite" nose cone is actually fiberglass with graphite coating. Time will tell.

I understood before I built this sled that there would be problems associated with grounding via the AL sled. I addressed these in the design of the sled. There will be no short circuiting.

I really do appreciate all the wisdom shared on this forum. It is a welcoming, warm place. Cheers all! Liam

Tripoli
NAR L1
PARA# 520

 

[Trenman]

What about scrapping the nose cone and avoiding to potential for an issue all together? Like creating a very shallow canopy (2-3mm thick plastic/ resin) and recessing the antenna into the side of the rocket with the canopy acting like the window. Keep in mind, the actual antenna is on a very long wire and is about 1.5"x1.5".

How much would 2-3mm of plastic on one side affect the stability?

 

[bobkrech]

Regarding attenuation: I have several build sources that have claimed little to no attenuation in the nosecone. My findings indicate that attenuation of all signals are this way. From what I have found the "graphite" nose cone is actually fiberglass with graphite coating. Time will tell.

Liam

You are asking for advice and I have been trying to help you out. My professional job for the past 33 years has involved studying all kinds of aerospace problems including RF/MW transmission/reception through a variety of materials so I'm giving you correct information based on facts and real measurements, and not just hearsay.

Most plastic and fiberglass NC and radomes transmit RF/MW. They are transparent at GPS frequencies and 0.9 and 2.3 GHz modem frequencies. There's lots of commercial MW antennas that use plastic and FG covers.

Metal, CF composite, or "graphite" coated FG composite NC are conductive so the RF/MW will not get through. GPS and modem frequencies will not get through a conductive NC. There are no commercial MW antennas that use CF, metal or graphite coated FG or plastic covers. Metal and graphite coating of plastic and FG enclosures is actually a time tested shielding method used by the electronics industry to prevent computers and digital electronics from emitting RF noise and interfering with other electronics.

Bob

 

[H_Rocket]

Trenman

You have questions on this project on both TRF and Rocketry Planet. In private conversations, a few skilled fliers are beginning to wonder if you have bitten off way more than can be chewed. There is no engineering reason whatsoever for an aluminum sled in anything you are not planning to fly at BALLS (and then it would be questionable). I've been at this for six years and never seen one. If you want something special and the idea of wood does not met your likes, consider G10 or FRS composite.

Several very experienced fliers have offered you advice on how to proceed. Some are skilled engineers who have provided guidance on making some rather interesting design criteria come together.

I want to ask you again to set this on the table, step back, and think about what you are doing. You are describing quite a complex beast and, from the questions you are asking, do not have the experience to do it entirely right. I want to take this point and encourage you to consider breaking this into phases. Test different subsystems on different airframes. I think in the end once you develop those individual skills, you will be much better suited to aggregate them into the project you are working on.

Otherwise, I have the uneasy feeling you are going to be disappointed.

This is not personal. Many high power fliers, myself included, have had the "dreams bigger than skills" syndrome, and if you ask around, quite a few have learned the hard way.

Of course it is your money, and if you pull it off, bravo.

Just one opinion and YMMV.

 

[blackjack2564]

The nosecones on the Mogoose series WILL transmit. I have personally used trackers in them with great success as well as many other fliers I know.

That being said i really don't know what they are made of but it works.

I personally placed my tracker inside and drove 1 mile away and could not tell any difference between the reception using a Mongoose NC and a standard glass cone from a 4in Wildman kit. Hope this helps.

If you want to know for sure yourself, just place your components in flight configuration, set them on top a 6ft ladder and drive a mile or more away and see how well you get a signal. Keep uping the distance till you no longer get the signal. Then you will know for sure. Ground testing is what it's all about on extreme project. Check my signature.LOL


By the way when I first started i did use a couple of aluminum sleds custom bent for me at a fabrication shop [HVAC shops can usually make up anything sheet stock for you]. Hopefully to save a little weight and space. Monell [spelling?old timers will know what these are]] rivets were used to secure the sled components together I used electrical tape and silicone to insulate the components from the sled. Tape on the sled under the altimeter and silicone on the components. Not all components will allow for this. [silicone]

I found after several uses I was getting a lot of loose nuts and batteries after flights. My take on it was harmonics and vibration issues. There is a lot of vibration during boost and wood seems to dampen that the best followed by g-10.

Aircraft ply and G-10 are alot easier to work with [cost was not an issue for me, the custom work was free on the aluminum].

But hey, go with your gut feeling you may figure out something new, just test it first on a scaled down version so it doesn't end up costing you a bundle in the long run. Good luck.

 

[Trenman]

Thank you for your reply. Your personal experience has helped me a great deal. Others feel as though I have bitten off more than I can chew. I disagree. I have designed on CAD 2010, several varying designs for bulkheads for the nosecone and have solved the problems involving the AL sled. Those were the only 2 issues I was asking for help with on the forums. I understand how others may feel that I have bitten off more than I can chew. They see several posts and comments, perhaps some newb(ish) questions and recommend starting smaller. To them I reply: Thank you for your concern. The mongoose 98 is a background project that I am thinking will take about a year to complete, taking my time. To learn the art of electronic deployment I have bought a Wildman Jr. kit to learn. I dont know why people make such a fuss about materials and how they are more than one might need. Who really cares? Im my own modeler making my own model the way I want.... I dont see how the products make a diff at all. I have a feeling when I post completed pics people are going to answer differently.

Thanks to all those who have helped me. This isnt supposed to communicate attitude. I simply become more motivated when others tell me i cant.

 

[Trenman]

Liam

You are asking for advice and I have been trying to help you out. My professional job for the past 33 years has involved studying all kinds of aerospace problems including RF/MW transmission/reception through a variety of materials so I'm giving you correct information based on facts and real measurements, and not just hearsay.

Most plastic and fiberglass NC and radomes transmit RF/MW. They are transparent at GPS frequencies and 0.9 and 2.3 GHz modem frequencies. There's lots of commercial MW antennas that use plastic and FG covers.

Metal, CF composite, or "graphite" coated FG composite NC are conductive so the RF/MW will not get through. GPS and modem frequencies will not get through a conductive NC. There are no commercial MW antennas that use CF, metal or graphite coated FG or plastic covers. Metal and graphite coating of plastic and FG enclosures is actually a time tested shielding method used by the electronics industry to prevent computers and digital electronics from emitting RF noise and interfering with other electronics.

Bob

I certainly appreciate your insight. I hope you are not becoming tiresome of my questions. I understand that CF attenuates signals. I also however see that 3/3 builds of the 98mm mongoose have used GPS successfully in the nose cone without attenuation problems, including the individual 2 posts up. The reason for my persistent questioning and asking for clarification is for this very reason: Everyone that uses the graphite NC says there are no attenuation issues.

Regardless, CF attenuates scientifically. Apparently there is a step in the manufactureing process on the performance rocketry graphite NC which allows the signal to pass. All I was asking for is for the one or two people who have done this to speak up to give me insight.

I seem to have people becoming disgruntled with my questions. I apologize. I just was asking for those with first hand knowledge to share their experiences.

I thank the engineers, scientists and regular Joes like myself for all of the insight provided in the last few weeks.

 

[H_Rocket]

I dont know why people make such a fuss about materials and how they are more than one might need. Who really cares? Im my own modeler making my own model the way I want.... I dont see how the products make a diff at all.

Many of us are engineers and feel very strongly about using the appropriate materials/technology for the job. Nothing more/nothing less. If in the process of building your project, you want to choose the advice that meets your goals, go for it like Jim says. We will cheer you on when you walk to the pad, hold our collective breath when the button is pushed, and clap you on the back or weep for your loss when it is over.

My thoughts were meant to be constructive if you took them otherwise, my regrets. I've flown some pretty impressive airborne yard sales as a result of not listening to people who knew a lot more than me.

Like you said It's your project, and it's a hobby, so have fun -> you might even prove us conservative types wrong!

Regardless, CF attenuates scientifically. Apparently there is a step in the manufactureing process on the performance rocketry graphite NC which allows the signal to pass.

I don't believe there is any particular process Curtis does to make the NC RF transparent. I believe it's simply that the NC is actually fiberglass with lampblack added as a colorant. The nifty metal tip simply prevents chipping like often happens with gel coated pointy nose cones.

 

[Trenman]

I certainly appreciate your feedback. Thank you.

Many of us are engineers and feel very strongly about using the appropriate materials/technology for the job. Nothing more/nothing less. If in the process of building your project, you want to choose the advice that meets your goals, go for it like Jim says. We will cheer you on when you walk to the pad, hold our collective breath when the button is pushed, and clap you on the back or weep for your loss when it is over.

My thoughts were meant to be constructive if you took them otherwise, my regrets. I've flown some pretty impressive airborne yard sales as a result of not listening to people who knew a lot more than me.

Like you said It's your project, and it's a hobby, so have fun -> you might even prove us conservative types wrong!




I don't believe there is any particular process Curtis does to make the NC RF transparent. I believe it's simply that the NC is actually fiberglass with lampblack added as a colorant. The nifty metal tip simply prevents chipping like often happens with gel coated pointy nose cones.

 

[kramer714]

At the 'day job' typically carbon fiber parts use a thin veil of fiberglass on the surface. This can be a thin layer of cloth (I use 120 style fiberglass primarily) or random mat type of veil. These do a few things for you, they provide electrical insulation to the surface of the part, give you a sanding layer for finishing or bonding, plus prevent corrosion of aluminum in contact with the graphite.

oh, and I know what monel is.... I'm more of a Hastalloy guy myself (that is when I'm not playing with T-300 or epon 828)

 

[bobkrech]

I understand that CF attenuates signals. I also however see that 3/3 builds of the 98mm mongoose have used GPS successfully in the nose cone without attenuation problems, including the individual 2 posts up. The reason for my persistent questioning and asking for clarification is for this very reason: Everyone that uses the graphite NC says there are no attenuation issues.

Regardless, CF attenuates scientifically. Apparently there is a step in the manufactureing process on the performance rocketry graphite NC which allows the signal to pass. All I was asking for is for the one or two people who have done this to speak up to give me insight.

Since I'm currently under contract with DOD to investigate the radar transparency of high velocity missile nose cones. DOD is certain and I'm certain that CF NC's don't transmit RF and MW so the only reason why you can transmit RF/MW through the Mongoose NC is that it is neither CF composite nor graphite. I do not know exactly what it is, but it is neither of the above as evidenced from the craftily worded text in https://www.wildmanrocketry.com/pdf/Kits/Perf_Rocketry/mongoose54.pdf

"The nosecone offered in the Mongoose kits is a Pro Line Nosecone, these cones offer the finest qualty available on the market. The exterior has a high temp 500F graphite finish with a screw on aluminum tip."

This is quite a different description than that of the fin layup of the airframe filament winding description found in the above reference.

"Fin material is manufactured using uni-directional carbon fiber prepreg in a quasi-isotropic layup and capped on either side with a cosmetic plain weave prepreg layer. The manufacturing process uses a 300 ton down acting heated press, the only way high quality high precision plate is manufactured."​

"Filament wound Carbon Fiber tubing is manufactured in house using propriority band patterns and wound using multiple wind angles. Using different wind angles in stacked layers offers a substancial increase in overall strength specifically for the use of rocketry. Tubes are manufactured with a high temp toughened epoxy resin and cured and post cured in our oven for a max operating temp of 500F. We use a High Modulus Carbon Fiber Tow (T1000G) the higest tensile strength carbon fiber available. T1000G was designed specifically for aerospace aplications. To offer a precise smooth finish we use a centerless grinder."​

While the NC may look like CF or graphite (which are not the same), it is simply finished to look like graphite.

Bob

 

[GregGleason]

Very informative post, Bob. Thanks.

Greg

 

[quickburst]

My suggestion?

Loose the aluminum sled, you're asking for trouble.

 

[kramer714]

As a side note, there are lots of materials that work well for this kind of thing that are cheaper than G-10 (besides wood).

Grade XX is a paper phenolic laminate, actually lighter than G-10 while not as strong. It can be cut with a saw or router, you can tap it or put in tapped inserts. It is flame resistant and a great insulator.

Bonding doublers onto plate can make a very stiff part, add bosses for attachments as opposed to standoffs. It can also be made into sandwich of XX and foam or balsa makes a great bulkhead or can be used to stiffen up a sled.

Use epoxy when you bond plus break the shiny surface and it works well.

A sheet from McMaster 3" X 48" by 1/8" is 5 bucks or so.

 

[Trenman]

Bob- all I can say is EUREKA. Finally some feedback I can really sink my teeth into. So it seems that my "graphite" nc must not actually be graphite. This explains what the educated members of this forum were trying to get across as well as my persistance with not being satiated with a question that wasn't really being answered. Finally the common ground!

So what do you suspect it is made of?

 

[cjl]

I'll agree with the comments to lose the aluminum sled - it's completely unnecessary, and there's no reason to use it instead of G10 or some similar material.

 

[Trenman]

I'll agree with the comments to lose the aluminum sled - it's completely unnecessary, and there's no reason to use it instead of G10 or some similar material.

One might argue that building a rocket that flys past Mach is unnessecary. I like AL because of the cool blue anodizing. I like it for aesthetic reasons. Who really cares? It kills me how many people comment on the materials. As if there was a wrong choice. I'm building it to go up and come down. The issues associated with my choice of metals has been resolved. And half the board has kindly informed me of my overengineering. It'll be
ok. Promise

 

[dixontj93060]

To each his own.

 

[Trenman]

To each his own.

Cheers to that my friend

 

[GregGleason]

I like AL because of the cool blue anodizing.

Once the fabrication of the AL sled is complete, please post a pic.

Greg

 

[cjl]

One might argue that building a rocket that flys past Mach is unnessecary. I like AL because of the cool blue anodizing. I like it for aesthetic reasons. Who really cares? It kills me how many people comment on the materials. As if there was a wrong choice. I'm building it to go up and come down. The issues associated with my choice of metals has been resolved. And half the board has kindly informed me of my overengineering. It'll be
ok. Promise

IMHO, the comparison you make with flying past mach isn't really relevant. The Al sled is an internal component for mounting electronics, and is neither visible nor does it affect the performance of the rocket. Going past mach is a performance goal, which is separate. If you want to use aluminum, go ahead, but I always try not to overdo things on my rockets whenever possible (structurally). I'm not concerned that your sled will fail, but I've seen so many people actually lose performance due to the eternal presence of overbuilding in the rocketry community. So many people think that overbuilding their rockets is necessary, and in most cases, all they are doing is decreasing their performance and increasing the per-flight cost.

As long as you're doing it for a purely aesthetic reason (or for some other reason that basically amounts to "because I want to"), go right ahead. I just want to make sure that you know it isn't necessary, since I've seen so many questions from inexperienced new rocketeers that basically amount to "Holy cow, my rocket sims to mach 1.2 and I'll use 12 layers of carbon - will it be enough?".

Of course, I definitely would rather see an aluminum sled than a styrofoam one

 

[Trenman]

Once the fabrication of the AL sled is complete, please post a pic.

Greg

I sure will! And frankly my craftsmanship will be of high quality however this WILL only be my second sled and I may have small things I could improve upon. Any and all suggestions will certainly be appreciated ) Its not so much that people LIKE what I create so much as ACCEPT it as how I want to build MY rocket and it being my CHOICE.

Either way I would be posting the finished AvBay. I will also be posting pics of the mongoose build because I am not a veteran of this, I DONT know it all and i NEED others to constructively criticize so I can make a rocket that works the first time.

 

[Trenman]

"The Al sled is an internal component for mounting electronics, and is neither visible nor does it affect the performance of the rocket."

"I always try not to overdo things on my rockets whenever possible (structurally)."

If it doesnt affect the performance, electrical issues aside (since they have been resolved), how/ why is it "overdone".

This is in no way an argument, I am simply asking so I can become more educated.

"I've seen so many people actually lose performance due to the eternal presence of overbuilding in the rocketry community. I just want to make sure that you know it isn't necessary..."

As you mentioned above this is an internal part. Just curious, the weight will be similar to that of birch or FG, how do the materials make this an overdone avbay. Im certainly aware that other cheaper materials could have been used. That has been made redundantly clear. Costs aside though, this is where I struggle.

 

[dixontj93060]

Trenman,

It is tough to make any comments without seeing the design in its entirety (i.e., the whole rocket), but I think what you are running into here is, dare I say it, a prejudice against the use of metal components as they are typically associated with increased weight, and degraded performance (along with the electrical shorting risks when used near your electronics). Clearly different metals and alloys have different properties and to say they shouldn't be used without seeing the whole design is a uninformed opinion at best. If you have equivalent or better weight characteristics and have protected the electrical circuitry then you should be "golden"--still even that is an uninformed opinion without seeing the whole design/build.

-Tim


.

If it doesnt affect the performance, electrical issues aside (since they have been resolved), how/ why is it "overdone".

This is in no way an argument, I am simply asking so I can become more educated.


As you mentioned above this is an internal part. Just curious, the weight will be similar to that of birch or FG, how do the materials make this an overdone avbay. Im certainly aware that other cheaper materials could have been used. That has been made redundantly clear. Costs aside though, this is where I struggle.