carbon fibre and antenna
 

Just finishing mold for V22 osprey project, Since the fuselage will be carbon fiber I am worried about the antenna. I was thinking of embedding it in the jell coat at the bottom of the plane.Not worried about upside down cause if it is, its over. Will this work or any better Ideas.

RE: carbon fibre and antenna
 

Man, you'll get a lot of different opinions on that question...

Search the "Jets" forum to find all kinds of radio experts discussing this issue, ad infinitum. General consensus is... Well there isn't one. You'll hear that carbon blocks RF and that it doesn't, so take your pick. The only proof is to do an installation and range check it under all possible conditions. One thing, though... It seems like a "forever" solution to embed the antenna in the gelcoat. You could just as easily run it through a lightweight tube somewhere in the plane, and then you'd have access to move it when you wanted to.


Hey, show us some photos! This is one of the most ambitious and interesting projects around here.

RE: carbon fibre and antenna
 

Thanks for the reply. Actually I would embed the tube inbetween jellcoat and carbon. Still I hear that also will cause a problem. Im going to take my radio reciever and antenna wrap them in a few layers of carbon and do a range test. When in doubt test. Okay heres a few pictures
of plug,mold,and engine. Still so much to do. I know the quality is not the best but this is my first scratch built anything! I made the nose section with foam and the rest ply bulkheads sheeted. Final shape took about 1/2 gallon bondo,most of which was sanded off. Ive never done any composite work,other than a pair of airducts for my car which I now know are really bad. Mike, I got most of my instruction from your website and your many posts here. Thanks so much for all the help

RE: carbon fibre and antenna
 

That's some very good-looking work... Nothing to be ashamed of in any way.

As we all know here on RCU, photos don't show the tiny pinholes, voids, paint chips, etc., that are the curse of composite builders. We all have some of these problems. (That's not to impune your work in any way, since I don't see those things in your photos... Just being honest about my own work.) The more we all share information, the better we all will become, and everyone benefits. Thanks for sharing your work with us, and I hope you'll share more.

The V-22, like a Harrier or F-35, is a very ambitious undertaking, and I wish you the best. Please keep us informed on your progress here... I'd love to see the details, as you progress.

Have you gotten into all the wing tilting and other mechanical stuff yet?

RE: carbon fibre and antenna
 

Actually Yes. Have built one prptotype head and mechanics. I cut up a hirobo shuttle that someone was scrapping for parts. Also got a 3 blade head for it.I made a mold for a blade with a proplike trailing edge,not flat like a heliblade. I did one right rotation blade. It ended up weighing
about 150grams,so not to bad. I also figured out all the servo mixes since it is really a nightmare when it rotaes to plane mode. I used right and left collective mixed to ailerons for roll, these will be gyro stabilized. Pitch is also gyro stabilized useing the normal cyclic,and of course elev. All of the heli cyclic and pitch controlls shut off at 60 degree pod rotation. It should be flying like a plane at that point. I will use flaperons that will tie into the pod rotation channel. That is unless I can scrape up the bucks for a 14 channel Futaba. Im really short on channels.Needs 9 full channels my radio only has 8 plus on off. I will first uce conventional rotor head with 2 blades and flybar before messing with 3 blade setup.

RE: carbon fibre and antenna
 

Fantastic...

Sounds like you're really going for it. I look forward to seeing more, as you get to it. Good luck!

RE: carbon fibre and antenna
 

Hi Rd,
I do composite work in the racing industry and can assure you that carbon will interfere with your antenna. If a race car uses a transponder system for scoring it will not penetrate the carbon. A kevlar "window is typically the way its "fixed". Remember though that in this instance the transponder only "looks' straight down at the track. When you say you want to imbed it in the gelcoat, its seems to me that will lead to an awfully thick section of gelcoat which could cause problems later.
On a different note,,,, this is a way cool model and from the pics I agree with Mike James, you should be proud of your acomplishment so far. I have seen professional work that is not nearly as nice as yours.

RE: carbon fibre and antenna
 

personnally, for my f22 raptor, I want to make full carbon body except from canopy to noze which will be either kevelar or fiberglass...
then I will put receiver under canopy and lead antena strait to noze and it will come out of body from small noze antena.
what do you think of this solution?

RE: carbon fibre and antenna
 

Rd, I would also be very interestd in hearing your planned lay-up schedule for the fuselage. Its posible that carbon would not be the only solution.

RE: carbon fibre and antenna
 

I don t fully understand your statement (I have a bad english...lol)...

carbon is not the only solution, but it gives a very rigid and light body and it is easy to shape and laminate.

RE: carbon fibre and antenna
 

That sounds like a good solution.
-David

RE: carbon fibre and antenna
 

I suspect race components may be a heavier thickness of CF? Anyway, Im glad you mentioned the constant orientation comment. Ive never understood how an external antenna on a carbon RC model 'fixed' the problem. Sooner or later the model will be in some flight orientation that requires the Tx signal to penetrate 2 layers of carbon corresponding to both fuse halves. One could then argue that an internal antenna will always be confined to only 1 CF layer at any given time. I also wonder if there is a antenna/CF contact issue, most guys dont elaborate on that with their success/failure results. Some people tape the antenna wire to the CF, some manage to suspend it inside the CF fuse. Since carbon its an RF conducter, you would think that would make a difference, no? FWIW Ive successfully used an Azarr type antenna within a CF boom, so no external wire hanging out.

RE: carbon fibre and antenna
 

I just did a test using my pcm receiver and antenna which was coiled up. I then wrapped that in 5 to 6 layers of 2 inch wide carbon tape. To my surprise I found no difference in range,about 60 ft, with or without the carbon. Transmitter antena collapsed and reciever antenna coiled. I figured this was a worst case senario. I was hoping to use 1 layer of 6ov carbon followed by 1 layer Aeromat then 1 layer 4 oz S glass. On the antenna the Idea was to lay a tube run the antenna thru on top of the gell coat then add a bit of micoballon thickend epoxy on each side then
cover with 6 oz carbon fiber cloth then aeromat finishing with glass. Perhaps I should move this layup arrangement to a new thread.My composite expierience is nill so I couls use some advise.

RE: carbon fibre and antenna
 

I did basically the same test a few years ago, with the same result. I was using unidirectional carbon with the antenna extended, and the fibers were oriented lengthwise with the antenna. No discernable difference in range was detected.

Not all carbon is the same, as electrical conductivity and rf conductivity/absorption are concerned. I used standard modulus carbon in my test and did not re-test with any sort of high or ultra-high modulus carbon. I've never, in fact, seen any radio problems in model planes which could be definitively linked to carbon.

In my limited UAV-type experience, I mounted the antenna externally, strung between the wing TE and the tip of the vertical stabilizer just for peace of mind. In a scale model it would obviously be desireable to have an internal antenna, if possible. In F5D pylon and F5B electric gliders, both with carbon tailbooms, the antenna is almost always run down the inside of the boom.

Ultimately, my advice (and practice) is to fully range test any new installation prior to attemping to fly.

-David

RE: carbon fibre and antenna
 

I agree about the range test. Im at a point where I could change from carbon to glass if necessary but weight is a major concern( ie stall speed.)I did try to measure the resistance with a meter it shows about 10 ohms on 5.6 oz carbon cloth and 20 on the tape, so obviously there
is a difference. Ill try the same test with the 5.6 cloth wrapped over a 2 inch cardboard tube 2 yards worth and drop the reciever and extended antenna inside and see what I get. Most interesting. To anyone reading this post I am not saying that carbob fibre has no effect on radio reception, I just ran a test and post the outcome because it wasn'nt what I expected. We plow on, I just love this stuff!!!

RE: carbon fibre and antenna
 

Ran another test. Took a roll of 5.6oz carbon 2 yards worth on a 2inch cardboard tube. I dropped both the reciever and the antenna,antenna was straight, into the tube. Range test with transmitter antenna collapsed gave over 150 feet. Im not sure that the carbon is realy bloxing the signal. But I would GUESS that since it is conductive any stray rf from metal to metal or electric motors etc could easily be transferd to the antenna if it is near the carbon. Im not knowledgeable in electronics but this appears to be more complicated than just carbon blocking the signal. if anyone out there has more info please enlighten me.

RE: carbon fibre and antenna
 

This is an all carbon fiber airframe which also includes an aluminum wing spar, flaps and gear doors.
The antenna is a Deans connected to a Futaba PCM receiver. Range is some where past my sight capability. Plane was built in 1994 and is still going.

RE: carbon fibre and antenna
 

Thanks for the insight. Nice plane.Im going forward with the carbon, seems like it can be done.

RE: carbon fibre and antenna
 

I've have several planes with the antenna run inside a carbon boom. During range checks and flying I have yet (key word) to experience a problem. Considering these are gliders I tend to fly them at a range somewhat further than is typical in a powered plane.

RE: carbon fibre and antenna
 

I have seen two events that could only be subscribed to a carbon mixture in the fusalage. I have a 3.3M YAK that has a carbon matrix throughout the inside of the fusalage. I looks like a fish net inside the wall. I could not get a signal through it. I placed the antenna on the outside of the plane and crossed the matrix at a 90deg angle and it gave me a good signal. If I draped the antenna wire on the outside of the fusalage it gave me about half of the distance. The final position is through the outside wall and attached to the top of the rudder. I have not had any issues. I tried to attach a Deans short antenna to the system and could not get a signal to work untill I totally insulated the antenna mount from the carbon matrix.

The second event lost a plane that had about thirty flights on it. Again a carbon reinforced interior wall with an inside antenna running in a tube in the middle of the fusalage about 6 inches away from the inside wall. The plane was lost when it went into failsafe low to the ground after having finsihed a pull out from a hover. It was flying directly away from the pilot and slowley rolled catching the wing tip. It was in fail safe for atleast 3 to 4 seconds. Three people watched as there was no control. In this case it was an event that could not have been predicted because it range checked ok. All of the surfaces functioned durning the post mortum and range checked ok.

A word of caution, you probably can not predict all of the attitudes and distances that the plane will get into and could have an event that can only be attributed to a "blocking" of the control signal. I would not place the antenna near any large surface area or volume of carbon fiber.

Chris

RE: carbon fibre and antenna
 

I do have concerns. But what to do, the entire fuselage is carbon. Mounting a deans would be blocked by fuselage attitude. Same for a antenna mounted outside near the fuselage. Still tests enclosing antenna in 7 to 8 layers including reciever show no drop in performance. Note this is without epoxy. Logically since the carbon fibre is conductive it must have some effect. Lots of tests to do. I will take 2 walkie talkies go to max range and move the plane into different attitudes and see what effect there is. The carbon fibre I am using is 5.7oz.

RE: carbon fibre and antenna
 

What about one of those sticky antenna's that I keep seeing advertised. Just peal and stick to the out side of the fuse.

RE: carbon fibre and antenna
 

The problem is even mounting the antenna on the outside,say the bottom of the fuselage, in a hard bank the signal now must penetrate 2 layers of skin. The side and then the bottom to get to the antenna. There are just as many opinions saying no problem as there are accounts of lost planes. I tried to post in the radio section but recieved few replies. I think I am going to call futaba and see what their opinion is. Anyone who has some hard scientific data PLEASE respond. This seems a subject with no concrete conclusions. I would expect some loss of signal,simialar to using a deans style but more study is required.

RE: carbon fibre and antenna
 

I used kevlar in my DF-22 just in case. Kevlar is different to work with because you cannot sand it or cut it that well. That just takes extra planning. The kevlar never comes to the edge of the mold, the edge of the mold are fiberglass so you don't have to worry about cutting kevlar. It might also help prevent a short because there will be 2 kilowatts of power going through the motors.

RE: carbon fibre and antenna
 

Just curious: have you tested for the type of modulation, basically the selectivity of the receiver? My racing partner and I noticed some tiny glitches when coming toward us and also sometimes on takeoff, going directly away. There's a lot of carbon in the front end of this particular design (a QM-40 Pole Cat), and the antenna is run internally down the tailcone. Switching from an FM (PPM) receiver or a single-conversion PCM receiver to a dual-conversion PCM receiver cured it. I don't remember now if the ground range was significantly reduced with the earlier receivers, but the one that's in there now -- again, a dual-conversion PCM -- doesn't seem to care.

I know this is very anecdotal, but it might provide a clue as to why some folks claim to have trouble with CF and others don't.

Duane Gall
RCPRO