Friday, July 23, 2010

Electric Elevator Trim on Ultralight Aircraft

First a friendly reminder:  This blog has many, many posts on many different topics.  Please explore the various posts -- I've written on all kinds things -- some serious, some contemplative, some informative.  Have a look around!  Now, on today's topic:  Electric Elevator Trim Tabs on Ultralight Aircraft.

Another item on our price list which is kind of unique is our electric elevator trim.  I thought I'd show a few pictures as to how we do it.

One of the joys of flying in an ultralight aircraft (such as our FAR Part 103 Belite Aircraft) is taking photographs.  In order to do this, I like to fly 'hands free', without the plane diving or climbing.  And I like to do it at various throttle settings, which means that I need a flight variable trim system.  There's a variety of ways to do this, but here is a system which meets all of the flight trim objectives AND provides an additional redundancy of elevator control, in the event of an elevator control system failure.  Just like a real airplane...  Jumping to what it looks like when it's all done, here's the electric elevator trim and manual rudder trim, as installed on our Belite Black Dragon Superlite (YES, the paint job is spectacular...):

The rudder trim is permanently set, and when properly set eliminates any left or right rudder tendencies.  (The big engine requires a lot of right foot, without rudder trimming, so I LIKE the rudder trim.)  The elevator trim uses an electric servo (designed by Belite) and a custom designed controller circuit board (which we'll get to in a few moments.) 

Now let's back up and look at these two trim tabs in the paint shop:

Well, that's kind of a boring picture.  But it does show the general clutter around the workshop fabrication bench, as well as our big battery charger.  So let's move on to some closeups.  Here's a pic of the rudder trim, prior to placement on the rudder:

And here's a shot of the elevator trim tab, complete with hinge, servo, linkage and control horn.  (Some of which is covered by painted masking tape):

This trim tab weighs about 9 ounces, as pictured.  With cable up to the cockpit, and controller board, the entire weight is about a pound.  The big holes which are drilled on the attachment tabs are used to tie wrap this to our elevator.  Let's mount this trim tab on the elevator:

You can clearly see the black tie wraps, along with the electric cable which has been snaked around the back of the elevator.  The wires have not yet been hooked up, but the linkage is clearly visible from the servo to the control horn.

Now let's move up to the cockpit, and look at the panel:

The big red push button switch is for the electric starter relay, the two red toggle switches are magneto kill switches (left and right) for our big Hirth F23 50HP engine, the white switch is the master avionics switch, and the black toggle switch is our electric trim switch.  It is shown in the central (neutral) position.  Moving it up causes the elevator trim servo to move one direction, while moving it down causes the trim to move in the other direction.  VOILA!  Easy elevator trim.

Now let's take a sneak look behind the panel, and see what's attached to that black toggle switch:

You can see a module which is 'shrink wrapped' and attached to the toggle switch.  It contains a small circuit board which regulates power and controls power polarity from the toggle switch to the trim servo.  This entire design is a product of Belite and is available on our assembled aircraft for $200.  This includes the servo, the electric trim tab, the controller board, the wiring, all installed.

You can see the Black Dragon Superlite, complete with electric trim and several other surprises, at 2010 Oshkosh.  Please come by our booth in the North display, and we also have a booth in the south Ultralight area.

Wednesday, July 21, 2010

Vortex Generators and Ultralight Aircraft

Vortex Generators.


Vortex generators are mounted on the top side of wings, and are designed to create small vortices as air passes over the wing.

As a result of these small vortices, vortex generators (Let's call them VGs, OK?)  are responsible for doing some pretty amazing things.  Concerning VGs, Wikipedia says the following:

"Vortex generators are likely to be found on the external surfaces of vehicles where flow separation is a potential problem because vortex generators delay flow separation. [3] On aircraft they are installed on the front third of a wing in order to maintain steady airflow over the control surfaces at the rear of the wing.[2]boundary layer, and run in spanwise lines near the thickest part of the wing.[1] They can be seen on the wings and vertical tails of many airliners. Vortex generators are positioned in such a way that they have an angle of attack with respect to the local airflow.[1] They are typically rectangular or triangular, about 80% as tall as the boundary layer, and run in spanwise lines near the thickest part of the wing.[1] They can be seen on the wings and vertical tails of many airliners. Vortex generators are positioned in such a way that they have an angle of attack with respect to the local airflow.[1]

A vortex generator creates a tip vortex which draws energetic, rapidly-moving air from outside the slow-moving boundary layer into contact with the aircraft skin. The boundary layer normally thickens as it moves along the aircraft surface, reducing the effectiveness of trailing-edge control surfaces; vortex generators can be used to remedy this problem, among others, by "re-energizing the boundary layer".[1][2]

The use of VGs on FAR Part 103 ultralight aircraft has been debated at least a little; I've decided to get into the debate by actually giving them a try on our Dragon Superlite.  A couple of days ago, I temporarily attached a set of VGs to the Superlite and then flew the plane.  Here's what they look like:

How did they work out?  I don't really know.  The wind was gusty aloft, so it was difficult to check out stall speed, landing characteristics, and I've reached no conclusions so far.  But I've decided to leave them on the Superlite as it heads to Oshkosh.  Come on by our North display area and take a look.

Tuesday, July 20, 2010

Amy Arrow and Never Again

Oshkosh preparations have been running us 7/24.  We've been preparing 3 ships for Oshkosh Airventure; on top of that we just completed a customer delivery and we have another which we won't get done before Osh.  (But we wanted to.)  And on top of all that is our 'secret ops' which are preparing some major whammy to talk about at Osh.

But never mind that.  Time to write a blog post...

Please back up about 15 years in my life....  to a memory from my past.

I was heading to Denver, Colorado to attend a "Promise Keeper" event.  I had arranged to rent a retractable Piper Arrow, which boasted a 180HP engine, good range, and a useful load of about 850 pounds.  The owner of the airplane affectionately called her 'Amy Arrow'.

It was hot in the summertime; we landed at Centennial airport without issues.  The Promise Keepers event was soon over, and we headed back to Centennial for the flight home. I had myself and 2 friends on board, (or, as I liked to say when I filed a flight plan, 3 souls on board).  

I had filled the tanks for the flight home.  I had also carefully reviewed the flight manual:  the flight manual called for 25 degrees of flaps in order to produce a short ground roll.  I dialed in 25 degrees, per the manual.  (Very stupid... as you shall soon see.)  Our plane was exactly at gross weight.  Density altitude was somewhere around 8500+ feet.  That shouldn't be a problem with an airplane that had a service ceiling well over 13,000 feet...   right?!

We were cleared for takeoff at Centennial.

I advanced the throttle, and Amy Arrow started to move down the runway.  Slowly.

Somewhere around 3 or 4 thousand feet down the runway, I started to pull back on the elevator.  Amy dutifully rose about 8 feet above the ground.

And stayed there.  5000 feet of runway remaining.

And stayed there.  4000 feet of runway remaining.

And stayed there.  3000 feet of runway remaining.

And stayed there.  2000 feet of runway remaining.

And stayed there.  Still 8 feet off the ground, 1000 feet of runway remaining.

I refused to set it back down and abort the takeoff.  Why?  More youthful piloting stupidity.

I saw a ridgeline off in the distance, straight ahead.  That was a problem.  I would hit it.

I saw a descending valley off to the left.  If I turned that way, I would have terrain descend, thus improving my relative altitude to the ground.

I slightly turned to the left.

I realized I was hovering over the ground... the plane would not climb.  I had two opportunities to reduce drag:  Get the gear up.  Reduce flaps.  I also realized that if I rapidly retracted flaps, the plane would immediately settle to the ground.  First things first... I retracted the landing gear.

Then, I grabbed the manual flap handle, and   s l o w l y  went from 25 degrees, to 20, then to 15, then to 10 degrees of flaps, then to five, then to zero.   The plane seemed to stop mushing over the ground.

We flew over a golf course.  Since the terrain was descending, and we were now probably climbing at 50 feet per minute, we had perhaps 150 feet of altitude over the course.  Some golfers looked up at this strange sight of an airplane, so close to the ground, passing over to them.

And then I realized that the plane had perhaps 250 feet of the ground, and that positive climb was definitely occurring.  We would be okay.

And then I realized something else was occuring:  the tower at Centennial was talking to me.  I hadn't heard them, because the crisis had shut down that part of the brain that listens to outside voices.

"are you OK....   are you OK...   are you OK..."  I could also hear our N number, recited over and over.

"Yes, I'm OK".

They couldn't see me:  my plane had turned left and disappeared below their horizon.

I soon cancelled flight following and headed home for Wichita.  I kept wondering what my passengers were thinking:  had I just nearly killed them?

Here is my list of stupidities:

  A)  Dialing in 25 degrees of flaps is great for reducing ground roll, but does not improve Vy.  In fact, it has the opposite effect.  You can't climb with 25 degrees of flaps in a 180HP Piper Arrow.

  B)  Density altitude is a killer.  A non-turboed Arrow is a horrible climber in high DAs.

  C)  Flying at gross weight in high DAs is also a killer.

  D)  Lean the engine!  

  E)  And most importantly:  aborting the takeoff.  I had multiple opportunities to abort and I did not do so.

As Flying magazine says, Never Again.