Density Altitude – Flight Lesson 07-02-14

John HurlbutFlyingLeave a Comment

After a week in California helping my dad recover from his Pacemaker surgery (read: laying in the 105° sun), I have been itching to get back in the air and continue my flight training.  I called the FAA on Monday to make sure they had received all my medical records and letters from doctors, etc.  I was told that everything was received and scanned in, a letter had been written and it was just waiting for a doctor’s signature.  It sounds like FINALLY, the wait for my 3rd class medical certificate might be over!  According to the person from our local office of aerospace medicine, I will be given a “special issuance” 3rd class medical.  Which means simply that in addition to my regular flight physical every couple of years, I’ll need to provide them with additional information.  Specifically about my sleep apnea and usage of my Cpap machine.  No problem.  I’m pretty used to my machine now and rarely do I use it for less than 4 hours per night, the minimum amount needed to remain compliant.  I often use it more than 5 hours per night and I’ve even had a couple nights in the 6-9 hour range!

So with any luck, by early next week, I will finally officially be a student pilot!  Super stoked! 

Yesterday was a gorgeous day for flying!  The sun was out, Mount Rainier shining in all her glory, it was really warm, not a lot of wind, awesome!  The only “problem” is when it gets warmer, the air behaves differently.  As the temperature and dew point get further apart, you get what’s called “density altitude”.  Meaning that even though Thun Field hasn’t changed its elevation of 538′ above sea level (ASL) the plane thinks and performs as if it’s at a higher altitude.  Yesterday at the time of our flight lesson, the plane thought we were at 1,621′ a full 1,100 feet above field elevation.  So I had to take extra care when figuring out how the airplane would perform on takeoff especially.  Your ground roll distance increases (Ground roll is the minimum distance the airplane needs to become airborne) as does your distance to clear a 50 foot obstacle.  Even though Thun Field has a nice longish runway of 3,650 feet and we rarely use even half of that to clear our mythical 50 foot obstacle, you really need to be cognizant of density altitude when taking off from shorter runways.  If you want to get an idea of what taking off with density altitude is like, have a look at this video.  Now this guy presumably flies out of this airstrip all the time, and flies this plane all the time.  According to his Pilot’s Operating Handbook (POH) he should have been able to take off from this strip just fine.  But even though the POH says it’s technically possible, better to err on the side of caution when doing those calculations and add another 10-20% for safety.  A runway can never be too long, but it certainly can be too short.  Thanks to FlightChops for making me aware of this video!

That looks like fun right?!  NOT!

So after getting my weather, doing weight & balance, and pre-flighting the airplane (Found 3 Meg Frogs today!) we were off.  My takeoff wasn’t spectacular. Not quite on the centerline, MORE RIGHT RUDDER JOHN, and a little wobble right after we lifted off.  I think N1151M is just a little more touchy than is N84823. I don’t know for sure, having only flown 3 hours in 823 and probably 15 in 51M, but my takeoffs and landings sure were better in 823 than they have been in 51M!

We headed out to the northeast over towards Enumclaw to the practice area.  We did the “High Show” today.  Climbed up to 4,000′ and practiced my turns at 20°, 30° and 45° while maintaining altitude.  It’s pretty clear that I really prefer turning at 30 and 45° than at 20°!  I seem pretty hesitant at 20° and I’m usually at 15 or 30° instead of 20!  But tell me to do a 30 or 45° turn and no problem!  I love the steep turns.

We also practiced some slow flight and some power off stalls.  I really enjoy both of those things.  When non-pilots hear the word “stall” they think we’re shutting down the engine, that’s not the case at all.  A stall is simply the wing losing the ability to produce lift.  (Yes, when a wing doesn’t produce lift, that’s a bad thing, but not catestrophic….usually). Knowing how to recover from a stall quickly is paramount to learning how to fly.  When the wing stalls, you’ll hear the stall warning horn going off to let you know it’s about to happen.  Generally you just lower the nose a bit and crisis averted.  A lot of flight training focuses on how to recover from unusual attitudes and potentially emergent situations.

I also got some “under the hood” time.  Under The Hood refers to when your instructor puts a “view limiting device” on your head so you can’t see outside and you have to fly by feel and instruments alone.  For your private license you have to have a minimum of 3 hours under the hood.  I have 0.6 hours so far including the 0.2 yesterday.  As I was putting the hood on, Meg was pitching and rolling and yawing the airplane all over the place.  With no reference to outside, I will say I had my stomach in my throat for the rest of the flight.  Note to self, put the hood on faster next time!!  On an intro flight many years ago, I got sick.  Doing steep turns over Commencement Bay, ironically the thing I love doing now.  So my biggest fear getting into flight training was that I was going to be prone to motion sickness.  This was the first, and I hope the last.  We did some turns and maneuvers under the hood, then it was time to head back.

My landing wasn’t bad, Meg helped on the rudder just a bit.  But I AM feeling like I’m doing more and more of the takeoffs and landings on my own.  Overall it was a great flight and I had a lot of fun! I feel good about my progress, but I cannot wait until we do a day of NOTHING BUT takeoffs and landings.  We’re officially on Lesson 7 and 8 in my syllabus.  Both of those are review lessons.  Lesson 9 is my first solo.  If my medical certificate shows up in the next week (gotta have it before lesson 9) very soon, I could be flying an airplane all by myself!! Both frightening and super exciting all at the same time!  I told Meg that after my medical arrives, I WILL be recording all of our flights because I absolutely want my first solo on video.  After I solo, my Garmin VIRB elite will be a constant companion on all my solo flights and I’ll be posting more videos of my flight training.

Flying again Sunday!

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