Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Mounting bent whip Com antennas
- Thread starter apatti
- Start date
robertahegy
Moderator/Tech Counselor
I made a doubler about 6" in diameter. I think I used some 0.040 AL. I do not want any cracks developing in the belly skin.
Roberta
Roberta
tomcostanza
Well Known Member
2 words for you...
Aloe Vera
Martin Sutter
Well Known Member
I mounted mine in a manner that allows the two aft mounting holes to be located on the forward flange of the center section (RV7A) and one of the rear mounting holes on the outboard floor stiffener. This way three of the mounting points are on a very rigid structure and no doubler is required. The connector ends up under the gear truss, out of danger of being stepped on.
Martin Sutter
building and flying RV's since 1988
Martin Sutter
building and flying RV's since 1988
Captain_John
Well Known Member
Oooooh, the TENDER underbelly of the beast MUST be protected!
Say, I have been noodling (WAY too long) over this and consulted the AC43-13b (yah, call me nuts!) and some friends who are A&P's and have deceided to scrap my "flat stock" design for another with flanges as described in AC43-13b.
Here is my old design:
...and this is my new design:
It now sports some fine features as described in the circular such as a flange that ties into the adjacent rib structure and thicker (0.040") material than the stuff it is doubling.
Honestly, I think the first one is overkill... so this one is over the top!
Heck, look at RV6guy... his is fine and he did nothing but slap it on the belly (perhaps with a little lotion?)!
Mmmmmmm, personal lubricants!
CJ
Say, I have been noodling (WAY too long) over this and consulted the AC43-13b (yah, call me nuts!) and some friends who are A&P's and have deceided to scrap my "flat stock" design for another with flanges as described in AC43-13b.
Here is my old design:
...and this is my new design:
It now sports some fine features as described in the circular such as a flange that ties into the adjacent rib structure and thicker (0.040") material than the stuff it is doubling.
Honestly, I think the first one is overkill... so this one is over the top!
Heck, look at RV6guy... his is fine and he did nothing but slap it on the belly (perhaps with a little lotion?)!
Mmmmmmm, personal lubricants!
CJ
robertahegy
Moderator/Tech Counselor
You Guys!! No wonder it takes you all so long to build. You're too easily distracted.
Roberta
No wonder it takes you all so long to build. You're too easily distracted.Roberta
gmcjetpilot
Well Known Member
Shear Tie Structural Doubler = Goodness
You made a structural doubler. With out the flanges and tie into adjacent structure, you're really just making a spacer.
The new design is stiffer. Tying into the adjacent rib with a shear "load path" is classic. If Boeing did it, they would also tie into the other "longeron". Flat sheet in bending is not efficient.
Our fwd belly skin is thick compared to the other parts of the RV. Also support structure is closely spaced, so a doubler is less critical than say on the back of the plane, with wide space supports and thinner skin.
Bottom line version 2.0 is stiff, stronger and adds nil weight. With out it the antenna might vibrate a little more. Flying in icing is a no-no in a RV, but ice build up on an antenna causes much higher loads, and it can cause the antenna to flutter.
"When in doubt, make it stout"
For just normal air loads, it does not matter and is overkill. But what about abuse loads?
I'm reaching here, but stay with me. Say if you snag the antenna during ground ops, its more likely to shear the screws and make a clean break, before it bends & creases the supporting structure, ie belly skin, if you make a structural doubler. Structural doubler is one "shear tied" into structure. If something catches the antenna you probably have other issues. The more likely scenario is a little kid crawling under the plane during an airshow and pulling and kicking the engine.
Never mind Roberta is right, we are easily distracted.
Overkill? No, sufficient kill.It now sports some fine features as described in the circular such as a flange that ties into the adjacent rib structure and thicker (0.040") material than the stuff it is doubling.
Honestly, I think the first one is overkill... so this one is over the top!
You made a structural doubler. With out the flanges and tie into adjacent structure, you're really just making a spacer.
The new design is stiffer. Tying into the adjacent rib with a shear "load path" is classic. If Boeing did it, they would also tie into the other "longeron". Flat sheet in bending is not efficient.
Our fwd belly skin is thick compared to the other parts of the RV. Also support structure is closely spaced, so a doubler is less critical than say on the back of the plane, with wide space supports and thinner skin.
Bottom line version 2.0 is stiff, stronger and adds nil weight. With out it the antenna might vibrate a little more. Flying in icing is a no-no in a RV, but ice build up on an antenna causes much higher loads, and it can cause the antenna to flutter.
"When in doubt, make it stout"
For just normal air loads, it does not matter and is overkill. But what about abuse loads?
I'm reaching here, but stay with me. Say if you snag the antenna during ground ops, its more likely to shear the screws and make a clean break, before it bends & creases the supporting structure, ie belly skin, if you make a structural doubler. Structural doubler is one "shear tied" into structure. If something catches the antenna you probably have other issues. The more likely scenario is a little kid crawling under the plane during an airshow and pulling and kicking the engine.
Never mind Roberta is right, we are easily distracted.
Last edited:
Captain_John
Well Known Member
George,
Thanks for the confidence. I like V2 better too. I think that in an extreme abuse situation, the antenna base would possibly crack instead of tearing the skin, which is certainly preferable.
For anyone who is reading this and is thinking of doing the same, I am going to remove the paint and alodine the parts before riveting this into place.
The base serves as the ground plane for the antenna and needs to have a low resistance between the plates. Direct contact is best and the many rivets will only help in "short circuiting" the connection between the plates.
I am alodining because alodine is a conversion application (like bluing on a gun) and actually "converts" the top layer of the material while remaining electrically conductive. All the while, the metal is protected and corrosion will be mitigated because there is a barrier between the substrate and the environment (the converted layer being the barrier).
I hope this helps anyone who is doing the same!
CJ
Thanks for the confidence. I like V2 better too. I think that in an extreme abuse situation, the antenna base would possibly crack instead of tearing the skin, which is certainly preferable.
For anyone who is reading this and is thinking of doing the same, I am going to remove the paint and alodine the parts before riveting this into place.
The base serves as the ground plane for the antenna and needs to have a low resistance between the plates. Direct contact is best and the many rivets will only help in "short circuiting" the connection between the plates.
I am alodining because alodine is a conversion application (like bluing on a gun) and actually "converts" the top layer of the material while remaining electrically conductive. All the while, the metal is protected and corrosion will be mitigated because there is a barrier between the substrate and the environment (the converted layer being the barrier).
I hope this helps anyone who is doing the same!
CJI just mounted mine close to the existing stiffeners and spar flange. Mine have been forced landing tested (I'm sure the others posting here have not performed this actual testing)
Bent the heck out of the whip but nary a wrinkle in the skin. Sometimes flexible is good.
)Bent the heck out of the whip but nary a wrinkle in the skin. Sometimes flexible is good.
bent whip position
I'm undecided as to where best to place my bent whip antenna.
option one is just forward of the 705 (just between the seat belt anchors). This gives me more than the 3ft required from the transponder antenna (which I plan to put near to the firewall bulkhead) but it's quite near to my strobe unit which I have put under the baggage floor (10 inch away) and the strobe wire, albeit shielded passes just behind the 705 so I'm concerned with interference.
Second option is aft of the main spar which does not give me cause for concern over the strobe unit/wires but does limit the min distance for the transponder. Any comments would be appreciated.
Martin
I'm undecided as to where best to place my bent whip antenna.
option one is just forward of the 705 (just between the seat belt anchors). This gives me more than the 3ft required from the transponder antenna (which I plan to put near to the firewall bulkhead) but it's quite near to my strobe unit which I have put under the baggage floor (10 inch away) and the strobe wire, albeit shielded passes just behind the 705 so I'm concerned with interference.
Second option is aft of the main spar which does not give me cause for concern over the strobe unit/wires but does limit the min distance for the transponder. Any comments would be appreciated.
Martin
Captain_John
Well Known Member
Ross, Way to really test the install!
I am glad it proved to be a good one!
That is really going the extra mile... or isn't it!?!
CJ
I am glad it proved to be a good one!
That is really going the extra mile... or isn't it!?!
CJRoss, Way to really test the install!
I am glad it proved to be a good one!
That is really going the extra mile... or isn't it!?!
Actually the extra mile would have seen me make the runway instead of the plowed field!
Captain_John
Well Known Member
Yah, I was afraid those were the circumstances.
CJ
CJ
Captain_John
Well Known Member
Hey All,
I have an update!
I installed my dubblahs!
They look great! Hopefully they will perform equally as well!
I used a bonding brush to clean the bolt terminations and the corner rivets in order to eliminate and capacitive effects and short circuit the potential difference in the ground plane. I think it will last a lifetime!
Thanks to Kevin and Mitch!
Whatcha think?
CJ
I have an update!
I installed my dubblahs!
They look great! Hopefully they will perform equally as well!
I used a bonding brush to clean the bolt terminations and the corner rivets in order to eliminate and capacitive effects and short circuit the potential difference in the ground plane. I think it will last a lifetime!
Thanks to Kevin and Mitch!
Whatcha think?
CJ
