Modern Pitot on '48 Ragwing

[gobrien]

Hi all,

Has anyone put a "modern" pitot like the one below on a fabric wing? I'm assuming I will need to remove a section of the fabric and attach an aluminium panel spanning the ribs onto which this will mount. I'm a bit nervous about messing with the fabric system. I'm not sure how far back from the leading edge to open the fabric and then how to attach it in to the leading edge of the Al panel. However, the original pitot tube is broken off at the point where it exits the fabric so one way or the other it has to be replaced. The EFIS I have installed (MGL) will show AOA using the Dynon dual port pitot so I figure while I'm at it, go the whole hog with the heated Dynon unit.

If anyone has any input, I'd be happy to have it.

Thanks,

Gareth.

[3958v]

if yours is like mine it would be easy to replace the original as there is an inspection plate and a connector just inside the wing. if your going to cut the fabric hopefully you have dope on your fabric and not some of the other finishes.

[Bruce Fenstermacher]

Some thoughts. The first thing you need to do is determine where the pitot should be located. As the 170A and 170B have the same wing and airfoil as the 172 it is rather easier to locate a later heated pitot the same place as method as Cessna did. But the 48 being a different airfoil and construction, where would one place a heated pitot so that it would work. One might assume if the end of the new pitot was at the same place as the old pitot tube and at the same angle, it would work. If one did to this, would the mount of the pitot be behind the leading edge sheet aluminum? If it was behind the sheet aluminum or that is just where you decide it should be mounted, you need to determine what covering system was used to cover your wings. Once that is known you can look at the STC for it and find out what holes or patches can be made in order for you to install aluminum plate between the ribs. When your done, you would use the STC instructions to close up the opened covering. As for how to install a plate spanning the ribs one would have to look at other examples of the same type of thing that Cessna did or look in AC 43.13 for proper methods.

[sfarringer]

I would take the easy way out and duplicate the original pitot tube. I have not needed (or wanted) a heated tube yet in my '48.
As stated earlier, there is an access opening already there in the leading edge skin to get to the internal connection. It may not have been cut out since the last recover job, but a knife and an inspection cover would fix that.
But, if you really want AOA, then that could over-ride simplicity!

[n2582d]

Gareth,
Not sure if you’ve already bought the L-shaped pitot or not or if you’re set on having a heated pitot. If no is the answer to both of those questions one idea would be to buy Dynon’s unheated boom mounted pitot, p/n 100532-000.

Item 605 in the TCDS for the C-170 shows that a heated pitot on a boom was an available option for the ragwing. You can find the drawing number 0511051 for this option here. If you’re not redoing the fabric installing the bracket that attaches the boom to the front spar will be a real challenge.

[GAHorn]

There is NO approval for a 170 of any model for flight in icing conditions. I do not recommend a heated pitot and suggest you manufacture an exact replacement for the original (drawings available in the 100 Series Service Manual) and avoid all the complicated issues associated with a heated pitot.

[gobrien]

Thanks all for the helpful feedback.

The inspection port is open and I have removed the stub of the original pitot by disconnecting and dismounting. I have the 100-series manual drawing and I'm ordering up some tube and fitting to fabricate a replacement.

The AOA functionality in the EFIS can be used with differential ports, in effect a pair of additional "static" ports on the upper and lower surface of the wing "slightly aft" of the leading edge.

So, for now I'm going to replace the original pitot and add the differential ports (I'll sump the upper facing one at least), meaning I have AOA and airspeed. Once she is back flying, which I hope will be in March, I can start looking at ways to add the heated pitot (if there turns out to be any point). In any case the wiring is already done, the extra tubes I'll run now, so the work to later retro-fit the heated system will be all localised in the wing.

Cheers,

Gareth.

[gobrien]

There is NO approval for a 170 of any model for flight in icing conditions. I do not recommend a heated pitot and suggest you manufacture an exact replacement for the original (drawings available in the 100 Series Service Manual) and avoid all the complicated issues associated with a heated pitot.

Hey George,

My intention is to help ILAS (Irish Light Aviation Society) convince the IAA to certify a permit aircraft as 1. Night VFR and 2. IFR capable; currently all permit (similar to FAA Experimental) aircraft are Day VFR only. This will be a long bureaucratic haul and under EASA she'll require a heated pitot for any IFR. The plan now is to hold off on installing this and replace the original as per my other post. If/when we get agreement that "all she needs is a heated pitot" I can come back to putting one in.

However, can you clarify here please?

I'm not under any circumstances looking for a FIKI C170! I just want to be able to train and fly IFR flight plans and be able to punch through a layer when necessary; this will increase the number of flying days around here big time! I understand there have been (and I imagine continue to be) IFR-certified C170s in the US, right? When you say there is no approval for a 170 flying in icing are you referring to Flight Into Known Icing or IFR in IMC?

Thanks,

Gareth.

[DaveF]

Hi Gareth,

A heated pitot tube is not required for IFR in the US. My vacuum instruments run on venturis, so I stay well away from freezing temperatures when I'm IFR. Pitot tube ice would not be my biggest problem.

I once had an inspector refuse to sign off a 2-year static altimeter and system inspection, believing heated pitot was required for IFR. He finally reluctantly did, but with the logbook notation, "NO HEATED PITOT INSTALLED".

Dave

[GAHorn]

Gareth, DaveF has given the same answer I would... There is no requirement in the U.S. for a heated pitot in IFR conditions. The U.S.will not certify an airplane for flight in known ice without extensive testing and certification of anti-ice/de-ice capability. The 170 was never considered for that, likely due to the expected “mission” profile of a light, single-engined, personal airplane of the period.

There are some examples of airframes which previously had no approval for icing conditions but subsequently modified and certified for ice... I’m thinking of the Mooney and some Cessna 210 aircraft, etc. with “weeping” wings (TKS systems). Those aircraft of course also required additional equipment such as propeller, windscreen, pitot/static anti-ice systems.

There are also some aircraft which, although similar to known-ice-approved sister-ships... were equipped with anti or de-ice equipment which were certified on those sister-ships... but in-fact were never certified for icing conditions. I’m thinking of the time I attended recurrent training in King Air 200 aircraft in Arizona (Sim-Com) who learned that I personally owned a Baron... and as a “sweetener” gratuitously offered me their copy of the Baron series Training Manuals which contained an entire section on how the Baron was to be operated in icing conditions.
Although my Baron had pneumatic boots, and alcohol props and windscreen.... NO Baron was ever approved for flight in icing conditions, regardless of all that anti-de-icing equipment. (Never say Never, of course, ... perhaps some day some Baron might gain that approval, but I was certainly surprised that a well-respected training facility was publishing and training Baron operators how to operate illegally.)

So, while it might be comforting to have a heated pitot on an airplane if one plans to fly in clouds near freezing.... the pitot system is NOT what keeps one flying.... It is, of course, the wings, tail, flight-controls, propulsion systems, and the Weight & Balance considerations of ice accumulations that matters. If YOU want a heated pitot...then certainly there’s no reason it cannot be accomplished... and of course, your Certification Authority is quite different than ours here in the U.S.... but since most IATA Members rely upon the Country-of-Origin certification for basic airworthiness considerations, I would wish you the Best in your pursuit that change of status, but would not personally invest much money into the project without First consulting with the decision-makers at your CAA who will be responsible for that. (I would think that a heated AOA system might be more useful and that insisting upon compliance with a retrograde pitot system as required equipment simply because “we’ve always done so” seems non-progressive.)

Hope this helps.

[gobrien]

I think the EASA theory is that if you're in IMC you should have a heated pitot. Like any large bureaucracy they're not huge on logical discussion and "safety" is generally the reason for any CYA ruling they come up with ... Who can argue with safety, right? Don't get me started on how difficult, expensive and time-consuming they have made it to get an Instrument Rating, while IR statistically improves safety.

I've decided to get her flying with an original pitot and install the AOA using differential pressure measurements, which will save several hundred dollars. I have installed the circuit for pitot heat with a disconnect at the wing root so if it later becomes worthwhile installing I can retrofit it with less hassle.

Thanks for all the input,

Gareth.

[gobrien]

Gents,

Today's aviation work included making the replacement pitot. All based on the info in this thread. I have changed to 6mm (1/4") PTFE pitot static lines so the original line that came down the A post from the wing was on a shelf complete with AN4 fitting. Some cutting, bending to match the template from the service manual and a new pitot is ready to go.

Thanks,

Gareth

[hilltop170]

One thing I did years ago was to carefully bend the pitot down slightly so when tied down outside, when it rains, it will drain instead of collect water. It's probably not by the book but it hasn't affected the indicated airspeeds and eliminates water in the system.

[GAHorn]

One thing I did years ago was to carefully bend the pitot down slightly so when tied down outside, when it rains, it will drain instead of collect water. It's probably not by the book but it hasn't affected the indicated airspeeds and eliminates water in the system.

Richard, that’s an interesting comment. I never would have believed that water could enter the pitot tube because of the upward-curve of the tube. I believed that the water simply could not travel up-hill.

I believed that until Jamie and I took a trip to Vicksburg for a few days and it rained one night. It rained one night
.
Our next stop was Ft. Smith, AR (Mount Magazine Park) and on take-off my airspeed went wild with fluctuations.... and I believe the relative wind played with the water inside that tube... I don’t believe it travelled all the way to the instrument... but as the air pressure “bubbled” past the water trapped in the pitot tube it caused lots of fluctuating of the needle for about a half-hour... until it dried out in-flight. Never had another problem with it.

Anyway, I don’t believe it’s a real hazard to the instrument but it certainly might cause a goofy needle for a while.

BTW, later Cessna’s had a “sump” jar in the static line to prevent water from causing fluctuations and to provide “volume” to the system. Our ‘62 Skyhawk has one.

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[hilltop170]

George
That is exactly why I bent the pitot to where it would drain. My 170 sat outside under a shade hangar the first 5 years I had it and would regularly have the airspeed go nuts after a rain storm. I have no idea how far the water got into the system but I knew it wasn’t good for it.