Pitot Tubes... On the fence

RV7Factory · Post by **RV7Factory** » Mon Sep 18, 2006 1:51 pm

Hey guys.

I am at the point where I need to drill the skins for pitot tube and I am conflicted.

A few months back I ordered the SafeAir1 mast because I wanted long-term flexibility, but now I am thinking... Flexibility for what? A heated pitot? I am not instrument rated, and even if I were, I can't see myself flying into those types of conditions especially in an RV-7, so why would I possibly need a heated pitot and the small amount of weight/complexity it brings?

I was looking over a georgeous RV-6 (grand champion) this weekend and all he had was Van's SS pitot... simple, light, effective, it looked fine to me, and it is cheap! After seeing this and watching Chad's progress unfold, I am now starting to think that the stock mount is the way to go.

Anyone care to push me off the fence, in either direction?

Thanks,

svanarts · Post by **svanarts** » Mon Sep 18, 2006 1:57 pm

If you are not planning a heated pitot tube, and you aren't considering Dynon's AOA solution then I would go with Van's tube. Do shell out the money and buy the SS model. The alum tubing is just too flimsy IMO.

RV7Factory · Post by **RV7Factory** » Mon Sep 18, 2006 2:00 pm

Thanks for the nudge Scott.

I am favoring (heavily) the AFS EFIS/AOA combo... I really like Rob's stuff.

JohnR · Post by **JohnR** » Mon Sep 18, 2006 3:18 pm

Brad, I had the same debate and already had the Safeair mast in hand. I found a Dynon pitot with the AOA from someone who was upgrading and selling it for about 1/2 price and bought it. Since then I have prepared the lower skin for the mast. I figured even if I went with something other than a Dynon the pitot should be fine. I don't see myself flying anything other than VFR in the RV but I guess you never know. My tech advisor got his instrument rating in his 6A.

Womack2005 · Post by **Womack2005** » Mon Sep 18, 2006 3:27 pm

I have to agree that the Dynon AOA is a slick deal. If I decide against it though, I would just go Vans AL tubing.

RV7Factory · Post by **RV7Factory** » Mon Sep 18, 2006 3:32 pm

JohnR wrote:My tech advisor got his instrument rating in his 6A.

Did he install a heated pitot?

captain_john · Post by **captain_john** » Mon Sep 18, 2006 4:37 pm

Yah... I (of course) have to be conflicting on this one!

The heated pitot is one sticking point I have even for a VFR ship. Look at all the Skyhogs and Worriers you have flown... they all gottem!

I gotta have one! Even in VMC! I have the Safeair mast and a Falcon heated pitot and MIGHT just be IFR but yannow...

Anywhoooo... it was just something I considered mandatory.

Dunno... this is just the first plane...

YMMV,

CJ

JohnR · Post by **JohnR** » Mon Sep 18, 2006 6:32 pm

RV7Factory wrote:
JohnR wrote:My tech advisor got his instrument rating in his 6A.
Did he install a heated pitot?

I believe he did. If I remember correctly he put in a Cessna/Piper/? unit that he bought before all of us homebuilders caused them to be so expensive.

I'll double check next time I talk to him.

N200PF · Post by **N200PF** » Mon Sep 18, 2006 9:13 pm

Remember - Nobody EVER thinks they're going to get caught in IMC or even MVFR. Ever fly VFR over a scattered layer and have it close up in front of you only to turn around and see it closed behind you?

I'm instrument rated so I'm going heated but agree with CJ that it's something you really shouldn't ever be without...especially over 10,000!

- Peter

cjensen · Post by **cjensen** » Mon Sep 18, 2006 10:02 pm

This is really a personal preference choice. I know there is always a possibility of inadvertent IMC while VFR, but with this airplane, I plan to not even leave the ground if it's possible IFR conditions may exist. If I HAVE to get somewhere, I'll take something that is capable (rent or borrow), take the airlines, or drive...I'm not planning any gyro's other than a TC.

The Van's SS tube is more than enough for what I need.

Womack2005 · Post by **Womack2005** » Tue Sep 19, 2006 11:35 am

The way we are building these aircraft, IMHO they are not suitable for IFR. The primer issue alone does it for me. The aircraft would not survive a substantial lightning strike.

RV7Factory · Post by **RV7Factory** » Tue Sep 19, 2006 12:03 pm

Womack2005 wrote:The primer issue alone does it for me. The aircraft would not survive a substantial lightning strike.

Lucy, pleeze splain dis to me!

Womack2005 · Post by **Womack2005** » Tue Sep 19, 2006 12:48 pm

Ricky!!

If you prime all the mating surfaces, the structure will basically explode when subjected to a lightning strike. The problem is that the primer is not a good enough conductor. Especially the epoxy kind.

That is why all mating surfaces on certificated aircraft are bonded (bare aluminum).

I am priming all of my internal structures with VariPrime or NAPA. My skins are only alodined (with a pen) around the rivet holes. Thus on all my mating surfaces I have a layer of poorly conductive primer.

Also, in areas where ProSeal is used it is even worse (fuel tanks).

At least this is the theory I was taught in A&P school and then again later in engineering as well.

The practice of bonded surfaces is strictly adhered to on all aircraft modified or repaired here. That is also the way they are built at the Gulfstream factory in Savanna.

Food for thought.

tshort · Post by **tshort** » Tue Sep 19, 2006 1:37 pm

Interesting ... I didn't know that.
My skyhawk (1997) is epoxy primed throughout ... I can't see bare metal anywhere at all. I guess they could have primed after the thing was assembled, but it is my recollection that the rivet heads are not primered ... I'll have to look next time I go flying.

I don't ever plan on being anywhere near enough to anything that generates lightning for that to be an issue! These days, with all the in cockpit weather resources (even if they are a little delayed), I don't think there's much excuse for straying into a thunderstorm even when IFR.

T.

captain_john · Post by **captain_john** » Tue Sep 19, 2006 2:46 pm

WHAT!?!

Will, this just isn't possible. Electricity is conducted via skin effect. It travels on the outside of a conductor.

When a bolt of lightning travels from cloud to ground (or vica versa) and passes through an airplane, it utilizes the outside of the structure. Very little energy is conducted through the interior structure.

Also, this electricity has just traveled miles from it's origin. A little bit of primer isn't going to be an obstacle.

I would agree that some carbon between the skins and at the rivet heads would be a possibility, but EXPLODE!?! Nawwwww...

They (Gulfstream and the other big planes) bond (electrically and mechanically join) the structure for radio noise. This makes the static wicks effective and keeps the radios working.

You WILL live through the lightning strike, but your radios may not. That is true even of the skins are bonded or not.

CJ

Womack2005 · Post by **Womack2005** » Tue Sep 19, 2006 3:04 pm

Thomas,

If you look at the internal structure of your 172 it probably looks like there is primer everywhere. But if you were to actuall seperate the pieces you would probably see a bare surface.

Its just a sore subject for me because I have been hit twice now.

Womack2005 · Post by **Womack2005** » Tue Sep 19, 2006 3:16 pm

CJ, not gonna argue about it with you here (thats what VAF is for

) I'm only an electrical/avionics engineer so I asked the mechanical guys and they confirmed the primary reason for bonding is for lightning protection. Secondary is radio noise.

I had a lightning strike in a Piper Seminole. You could clearly see the entry burn in the top of the wing skin near the tip and the exit burn on the bottom of the mid wing. When the skins were removed we had to replace two ribs that were burnt where they attached to the skin. The current went right through the wing (and through the wing structure).

RV7Factory · Post by **RV7Factory** » Tue Sep 19, 2006 3:32 pm

Womack2005 wrote:Its just a sore subject for me because I have been hit twice now.

Well that explains SOME things.

Womack2005 · Post by **Womack2005** » Tue Sep 19, 2006 3:34 pm

Bradford, left myself wide open on that one I guess

captain_john · Post by **captain_john** » Tue Sep 19, 2006 3:47 pm

Well, we better get George (GMCjetpilot) here to settle it!

He could go on with a 10,000 word diatribe and disagree with us BOTH!

CJ