Pitot decision help

I'm nearing the point of attaching the bottom skins to the wings. I figure it's time to think about making a pitot decision.

I'm half thinking of just going with the standard bent-tube pitot; it's simple and cheap. On the other hand, I'll very likely end up with a Dynon panel, and would like to be able to have AOA indication. Or, I could decide on Garmin. I'm not making any decisions on avionics yet, because no one knows what the landscape will look like two years form now when I actually need the stuff. I do plan on building the plane for instrument flying (and getting an instrument rating), but don't know how important a heated pitot would be.

It looks like retrofitting a bigger pitot mast later on would be a pain in the rump. Should I go with a Gretz or Falcon mast, or is it not really that big of a job to add one after the skins are installed? Or should I just leave the bottom skin off the left wing until later on? What would y'all do?

Or you could go with the AFS AOA system and have a glare-shield-mounted indicator.

Then you could use a simple pitot tube like this one.



Of course it's not heated.

http://www.vansairforce.com/community/showthread.php?t=99034

Dave

I would suggest that you put in the pitot mast parts. Just don't cut out the oval shaped hole in the skin. You can do that later. If you want to use the pitot mentioned in the plans you will be able to that by just drilling the hole for the AN fitting. It should be too difficult later to add the required mast etc.

If you are planning ifr then plan on a heated pitot.

Gretz heated pitot

I built my wings with a Gretz pitot. I would find installing a Gretz after the fact VERY challenging, though I'm sure others have done it. Much of the install would have to be done thru the bell crank access door in the bottom of the wing, and then laterally thru the lightening holes into the next bay. Doing that upside down under the wing would be tough going. You also have to install a printed circuit board and string a small wire bundle, along with power, back to the panel.
Now is definitely the time to make your decision.

Pitot heat

Pitot heat is not required for IFR flight. The only reason I can think of to install a heated mast is if you want to include an AOA sensor like Dynon. Otherwise, the simple bent stainless steel tube offered by Van is the best solution.

Heated pitot is required for flight into known icing. RV's should NEVER be flown into any icing conditions much less known icing conditions. If airframe icing is encountered, the pilot must exit icing immediately. IMHO this ranks right up there with a VFR pilot continuing flight into IMC. Losing your airspeed due to an iced over pitot will be the least of your problems. Even if you were able to regain your IAS after turning on your heated pitot, you still would not know what your stall speed would be from minute to minute, therefore, your IAS would be of little use to you.

Planning for heated pitot can effect other requirements such as alternator size. If you need a mast to operate AOA and it includes heated pitot, so be it, but otherwise use the KISS principle!

Above poster is correct - pitot heat is not required, legally. Yet practically every single engine Cessna or Piper out there, none of which is certified for known ice, has a heated pitot. Why? Because the pitot tube tends to be particularly suceptible to ice. Even a trace of ice, picked up during a 30 second climb and which has no discernable effect on the wing, can disable the pitot. Modern heated pitots are thermostatically controlled, they should be on anytime you're in the clouds near or below freezing.

Rupester said:

Much of the install would have to be done thru the bell crank access door in the bottom of the wing, and then laterally thru the lightening holes into the next bay.

Click to expand...

Yeah, and I have gigantic hands. My idea of an access panel is the wing skin.

After further reflection, I think I'll pick a pitot mast and install it now. As I get closer to the end of the build I can pick a pitot tube. There are some inexpensive ones if I decide to hold off on the IFR for a while, or I could build something to fit the mast. If I come across a good deal on a heated Dynon pitot/AOA at some point, the pitot section of that should work with anything.

Now it's just a question of Gretz, Falcon, Safeair1, or whatever else I find. Each seems to have advantages.

As for the heated vs unheated debate... I completely agree that flying an RV into any kind of icing would be a Very Bad Idea(tm). Right now I'd put the heated pitot in the same class as a lot of other "just in case something goes wrong when we don't plan for it" things like dual mags, life rafts, etc. I figure by the time I'm forced into deciding I'll have some instrument training and have a better handle on whether I think I need it or not.

I am with Danny. Even IFR and you loose your pitot you still have ground speed on your GPS.
I am full IFR and plan on only tube pitot.

In Canada a heated pitot is required for night flying and also IFR.

I agree 100% with Bob Turner. Your pitot can and will ice over without any signs of ice on the flight surfaces. I have had this happen, although not in an RV. A small horn of rime was visible on the OAT, and my pitot was indeed iced over.

Shame on me for not having pitot heat turned on already, but when I did get it turned on the reaction of the ASI made it obvious that the pitot had been iced over.

Some on this board will say that is not possible to have ice only on your pitot. However, that is exactly what trace icing did to me.

an interesting, somewhat related tidbit

A number of years ago, a friend (he might still be monitoring this forum) built a -6A & in addition to normal steam gauges, he had a GRT engine monitor with the air data option. He plumbed a 'pitot' line through the back engine baffle above the cylinders to the airspeed input on the GRT. He said that the 'stock' steam gauge ASI & the GRT ASI agreed within a couple of knots all the time. He had what he considered a good reason to suspect that it would be reasonably accurate (he's an aero engineer).

Something to think about, if you don't trust GPS speed for backup...

Charlie

Mile High Relic said:

...Some on this board will say that is not possible to have ice only on your pitot. However, that is exactly what trace icing did to me.

Click to expand...

Ice tends to accumulate on small-radius surfaces first. I was once driving in fog in below freezing, and ice accumulated on the radio antenna, but wasn't accumulating on the front of the (unheated) side mirrors. So, I would expect ice to accumulate on a pitot before a wing.

Perhaps you can put the pitot in the last bay in the wing near the removable top. That way you can install and maintain it with the wing tip removed even when built. Has anyone done this?

I would suggest the you install it where the plans call for. Any other location might lead to a bunch of unnessary headaches.

I am installing a Gretz in an RV 6. To avoid tie down rope, I am thinking of putting it in the last bay near the wing tip. It has excellent access. Has anyone done this. If so, are there any issues?

If you plan on flying IMC, a heated pitot should be a no brainer. Required equipment in the army for IFR, probably for good reason. The last thing I want when flying in the soup is to lose my airspeed and try to get out of ice at the same time. The 8 I bought has the bent tube and I plan to retrofit a garmin heated tube. A trusted forum member had an issue with the dynon heated pitot putting out heat but the water had not drained properly or something and froze above the heating element, rendering his airspeed inop. You can do a search for that thread (i dont know all the details, not trying to knock dynon, coud have been an anomaly or bad unit) but it was enough to make me look at garmin and gretz. $300 for the new garmin manually controlled pitot tube is cheap insurance and not a whole lot of complexity IMO. Probably desirable at resale, also, if it is an IFR ship.