WA to AK, Stall Warning Horn, Airspeed Indicator

[jaime72]

Wow, do you think I could fit more into one topic?!?!

So we are back from Renton Washington with our new bird. Here is a brief preview of the trip report. More details, times, distances, and pictures to follow.

Left KRNT just outside Seattle about 0900 local with clear skies and good weather. First stop was Blaine Washington to recheck weather and decide whether we would fly the interior route or attempt to coast to Ketchikan. Well, Blaine is no longer there! Closed on December 31st. Still in the AF&D and Sectional. Still present, just a few big "X's" along the otherwise nice looking runway. Wowa. Off to Lynden, WA.

Weather looked a little iffy up the coast. Filed a plan to Prince George and off we were. In Prince George refueled and weather briefed with 3 different briefer's, shopping for favorable reports! Our plan was to MacKenzie for the night and then the Trench to Watson Lake the next morning. All 3 briefer's discouraged anything East as weather was supposedly moving West to East, and MacKenzie as well as the Alcan route could be IFR in the morning. All 3 suggested West to Smithers BC. Quickly out the door and off to Smithers, the 1 route we didn't plan! Landed at Smithers in a perfect sunset. Ride to the hotel and started planning the next day.

Awoke to mostly good weather, valley fog and a few clouds but favorable to the north. Departed Smithers BC for a 487nm trip to Whitehorse. Made great time with a low power setting and tailwind. About 110kts with fuel burn of 6.9gpm with the O-360. Not too bad. Into Whitehorse with great weather, quick briefing, flight plan and customs to Northway AK, almost back to AK! Cleared customs in Northway and off to Gulkana. Low ceilings in some of the passes but made it to Gulkana no problems. With about 1.75hrs of light and 1.5 hours to Palmer AK we thought we could try and make it to Palmer that night. That would have made it 45 hours from leaving the house in Anchorage to back in Anchorage! Unfortunately we were met by a wall of snow and low ceilings at Sheep Mountain and turned around to Gulkana. Spent the night in Glen Allan, up the next morning and 1.5 hours into Anchorage with some snow, clouds, and beautiful sun!

I will post all the stats including fuel burn when I crunch the numbers. The Javelin Aux tank was a great addition, and 86C flew like a dream.

So today I had a couple of issue's with both the stall warning horn and Airspeed indicator. During preflight my stall warn device would not make it's audible sound when manually actuated with the master on. A departure from normal.

Then during flight ASI was all over. Not indicating until the end or after takeoff roll, low on climb out, steadied a bit in the pattern, sometimes very close to gps speed, then it would read higher and higher as I decreased my power setting and pitched my nose up. Reading over 100-120mph when the gps on a calm day read 60kts, confirmed to outside reference more or less. Then as I slowed and descended the ASI pretty much stopped indicating all together.

Thoughts on this?

Thanks, and look forward to a better report in the near future!

Jaime

[Roesbery]

Ice in your pitot line, will return to normal when it warms up. Had the same problem awhile back.

[Bruce Fenstermacher]

I was going to say ice in the pitot line as well. Anyway thea ti the first thing I'd clear and the static line as well.

[HA]

if there's water in the pitot line somewhere it might not drain on it's own. don't forget to disconnect the line from the airspeed indicator before you blow the line out with air (or you'll be shopping for a new indicator)

[cessna170bdriver]

At first I thought "Wow! Smithers to Whitehorse nonstop!" Then I read about you having the Javelin tank. I took that route to the 170 convention in Anchorage in 2000, but had to stop at Dease Lake for fuel. That stretch from Dease Lake to Whitehorse sure is a lonely one. I wouldn't want to try it single ship; we had three airplanes in our group.

Great Trip!

Miles

[GAHorn]

Blockage in the pitot line will make the airspeed indicator behave like an altimeter..... HIgher altitude looks like more airspeed.

[jaime72]

Miles,

Smithers to Whitehorse was a long and lonely leg, just us, the GPS and the Satphone. We had the Javelin, but get this. In Whitehorse we topped off the tanks with 26 gallons of fuel. Nice tailwind cruising at 2150rpm and 110-115kts. Not much of a safety factor for fuel, but with the Javelin felt comfortable to say the least.

I was guessing moisture had frozen, but we have had no new moisture since it was working. Yesterday was a balmy 20-25F and the black wing covers draw quite a bit of warmth to those wings. We will see today.

Also, I have always wondered, why can't you blow out a pitot tube without d/c'ing the ASI? Isn't blowing a pitot tube out essentially the same as ram air? Are we talking about blowing out with a compressor that will deliver far greater than ram air speeds? I can't imagine you would exceed ram air speeds by blowing with your mouth. Blowing by mouth acceptable? One of those long standing questions I have never understood.

Jaime

[blueldr]

I had a helluva problem with water getting in the pitot line when the airplane was tied down outside before I got a hangar. As a result I finally installed an under wing pitot head as on a C-172. Voila! problem solved. I did not activate the pitot head heater.

[Bruce Fenstermacher]

Jaime,

What ever you use to blow out the line you need to disconnect it from the ASI. Otherwise you may/ will damage the ASI and besides you wouldn't want what ever is in the line in the ASI.

[Jr.CubBuilder]

I look forward to hearing more about your trip and pictures to if you find the time. I've been wanting to fly to Alaska for years.

[jrenwick]

Also, I have always wondered, why can't you blow out a pitot tube without d/c'ing the ASI? Isn't blowing a pitot tube out essentially the same as ram air? Are we talking about blowing out with a compressor that will deliver far greater than ram air speeds? I can't imagine you would exceed ram air speeds by blowing with your mouth. Blowing by mouth acceptable? One of those long standing questions I have never understood.

Here's a reference I found that will explain things (but I can't vouch for its accuracy): http://www.rst-engr.com/rst/articles/KP89JUL.pdf

Basically, the pressure in your pitot tube is the dynamic pressure of the slipstream, and it's only a few PSI (5" of water at 100 MPH, according to this article). It would be pretty easy to peg your ASI by blowing into the tube, even with just your lungs. You don't want to do that!

[cessna170bdriver]

Also, I have always wondered, why can't you blow out a pitot tube without d/c'ing the ASI? Isn't blowing a pitot tube out essentially the same as ram air? Are we talking about blowing out with a compressor that will deliver far greater than ram air speeds? I can't imagine you would exceed ram air speeds by blowing with your mouth. Blowing by mouth acceptable? One of those long standing questions I have never understood.

Jaime

120mph comes to about 0.25 psi. You can generate upwards of 1.0 psi static pressure with with your mouth, or 240mph! Of course you can only do that if you seal your mouth over the tube, and don't have to generate any actual flow.

Miles

[AR Dave]

Try swabbing the Pitot Tube with a Pipe Cleaner. I had to land and heat our Pitot, with my pre-heater (single burner stove) twice, during our winter flight from AK to the Lower 48. The 2nd time I used the Pipe Cleaner, so the water didn't just re-freeze. The previous owner left a pipe cleaner, in the Pitot, when tied down.

[GAHorn]

...120mph comes to about 0.25 psi. You can generate upwards of 1.0 psi static pressure with with your mouth, or 240mph! Of course you can only do that if you seal your mouth over the tube, and don't have to generate any actual flow.

Miles

bluElder, what about that girlfriend you once had? How would she have compared to Mile's engineering data?

Jaime,.... pitot pressure is just a fraction of what your compressor will deliver. If you use your compressor to blow out the pitot lines without disconnecting the airspeed indicator .... don't let anyone sit in the cockpit or you'll blow the face of the instrument clear thru their chest and lodge it in the rear bulkhead.
(Blowing into a pitot tube with your mouth is always a bad idea. Your breath has moisture. Disconnect the line at the back of the instrument and blow it out with compressed air BACKWARDS ... (so that the air exits the inlet beneath the wing.)
BEWARE: Most airspeed indicators have TWO inlets at the back of the instrument. One for the pitot tube and one for static air. Be certain not to introduce any air pressure to either instrument inlet.