NX1279 Improvements

[M Lightsey]

So I've enjoyed some nice cross country trips in NX1279, but they weren't exactly fast trips. 85mph was about all I was getting which seemed a little slow for a O-290 powered ship. After last summer's flying adventures, I decided to see what I could do to clean the airplane up to squeeze a little more speed out of it. The first thing I did was replace the Aeromatic prop with a Culver fixed pitch wood prop. I didn't notice any big speed increases, maybe 5mph but I was getting that same speed at about 200 rpm less and the climb performance didn't seem to suffer at all. I think Aeromatics are great props, but not well suited to slow draggy airplanes like the Hatz.
Next I installed wing gap fairings for the lower wings. While these aren't shown on the plans, I think most builders install them. They were one of those things I always meant to get to, but you know how it is. Once you get the airplane flying, it's too much fun and you mentally switch from the building mode to the flying mode. Anyway, I couldn't believe what a difference those gap seals made. An honest 10 mph increase. I was shocked. It also made the stall even slower and more gentle.
I added some gap seals on the elevator. No noticeable speed increase, but made the elevator feel a little lighter.
Next on the list was windshields. The rear cockpit has always been really windy. I was just about to start making a new larger rear windshield and frame, but had the idea to removed the front windshield first to see what kind of difference that made. It was night and day. Much calmer in the rear, although noticeable more windy on my feet now. I decided I could live with the rear windshield now, especially because I know how much time it takes to make that frame.
I now needed something to keep the wind off my feet. I'd made a canvas rain cover for the cockpits, so I snapped the front cover on and fired it up to see how it reacted. I was most worried about the cover trying to lift, but as soon as I ran the engine up, is was clear that the force on the cover was straight down. Really high pressure in that area, which is what I was feeling on my feet. I actually tried one flight with the canvas cover, but it was a little unnerving to see how much it was deflected down, so I decided to make a hard cover.
I had some .050 6061 laying around, so I made a pattern and formed it to conform to the cockpit coaming. It's held in the front and on the sides with some Z brackets that hold the cover in place. In the rear I just picked up one of the 8-32 holes that hold the cockpit sheet metal in place.
Took the new cover for a ride this evening and it was solid as a rock.
At this point I'm indicating 105 mph at 2400 rpm, which is a big improvement considering I only hold 18 gallons. I figured that most cross country trips are solo so there's no loss in covering the front pit. When I take the plane to the midwest this summer, I'll do the cross country with the cover in place and the windshield removed. Once I get there, the process is easily reversed for giving rides.
Got some wheel pants I'm making out of aluminum, but they're kind of on the back burner due to some of the other projects in the shop right now.
Anyway, that's what I've been up to. It would be interesting to find out what kind of performance others are getting with the various engine/prop combos.
Mark

[dougm]

Next I installed wing gap fairings for the lower wings. While these aren't shown on the plans, I think most builders install them. They were one of those things I always meant to get to, but you know how it is. Once you get the airplane flying, it's too much fun and you mentally switch from the building mode to the flying mode. Anyway, I couldn't believe what a difference those gap seals made. An honest 10 mph increase. I was shocked. It also made the stall even slower and more gentle.
Mark

Great write-up, Mark! I've read a few articles on drag and recall the sections regarding wing root fairings being something really worth considering. Great to hear of someone doing it on a Hatz and providing some real comparison numbers. +10mph just for the fairings and +20mph overall?! That's substantial especially for a Hatz! How about some pictures of the wing root fairings?

[mtaylor]

Great report, Mark! Glad you posted it! I've been flying too much and adding fairings too little since I first flew last Aug. I cruise at about 100 mph behind an 0-320 (150 HP) at around 2250 rpm. I'm turning a slightly over pitched prop of 74/56.

My thought has always been towards the flying/landing wire attach brackets. The front set on top and bottom wings add up to a pretty large frontal plate area and is directly inline with the oncoming air (as is the landing gear center attach point for the bungees or springs). I mocked up a fairing that would easily attach to the flying /landing wire brackets using the existing wire lug attach bolts- no extra hardware- and it's made of .016" aluminum (actually off of a roll of flashing material). Anytime I've mentioned this on the forum, I get the guffaws about how the Hatz is a DRAGGY BIPLANE with a CLARK "Y" AIRFOIL. But, if I can get an extra 5 or 10 MPH, hey I'm payin' for the gas, so I'm planning on doing it.

I'm looking at how best to attach the wing to fuselage fairings. What did you do there? Also, I covered my gear legs and need fairings at the top of my gear legs, but don't have blind nuts under the top gear leg channel. I suppose just #8 sheet metal screws?

Good post!

Thanks!

[M Lightsey]

Here are some pictures of the lower wing fairings I made. I think I used some .050 3003 H-14 I had lying around. I wanted something soft enough to work with for the front section which has a surprising amount of shaping in it. I screwed the fairing to the wing since there's plenty of meat in that area. It just resting against the fuselage fabric with a little bit of pressure. I put a piece of rubber channel on the fuselage side so it doesn't cut into the fabric. The bottom side required a little bit of a bend in it to keep it tight against the fuselage.
Mark

[M Lightsey]

Here are some detail shots of Walt Bowe's Laird Speedwing I took last summer. Take a look at these fairings and let your imagination run wild......

[M Lightsey]

A couple more.

Laird fairing 6.jpg (68.58 KiB) Viewed 11840 times

Laird fairing 7.jpg (100.86 KiB) Viewed 11840 times

[dougm]

Great stuff, Mark! Thanks for posting!

[mtaylor]

In a word...beautiful!

Thnx for posting, Mark

[stearmoth]

Dear Mark,

Thank you very much for posting your improvement experiences! Very interesting are your achievents based on closing of the wing/fuselage joints! Do you agree that it is more closing the gap than the stremline fairing!?
We made our bottom wing sheeting to closely follow the fuselage fabric surface and will add some very soft foam between the base rib and the fuselage fabric to really close the seal.
A question: what is that nice walkway ? is it press formed aluminum? Where can it be obtained?

Kind regrads
Hans & Sam, H.C. no. 78, Switzerland

[M Lightsey]

I'm sure the improvement is from closing the gap, but it sure looks better with some curve to it.
The wing walk material came from Restoration Supply Company http://www.restorationstuff.com/
It's very light weight, but slippery when it's wet.
Mark