I picked up 10 MPH!

[Bdflies]

Well, sort of. My Patrol is a delightful plane to fly. Good short field performance, nice speed, excellent control authority and very predictable behavior. I never saw the speed I'd heard of, but just attributed that to her being a bit heavy and maybe not as clean as some. Until today.
Some background: 9BK sports a Bob built O-360 swinging a MT constant speed prop. On the panel is a Garmin G3X. From the beginning, 2550/25" was good for 140 MPH. Very respectable for a STOL aircraft, but not the 150 I'd heard of. Something that nagged at me, was the G3X wind indication. It's a great feature in that you always know what the winds are, where you're flying. Really nice feature for choosing cruise altitude. Problem was that I saw an awful lot of tailwinds, when I didn't expect them. With a limp windsock, I'd fly final with 6 or 7 MPH tailwind.. I figured that I had a static system problem, thinking that the side mounted ports were seeing higher than desired pressure. I stuck some tape blocks ahead of the ports and this helped a tiny bit. Still, I was perpetually blessed with tailwinds... Yeah right..... Mentioning this phenomenon, during lunch with a few other builder/pilot/smarter-than-me types, one fellow mentioned that I could have a pitot leak. Well, a light went off! I knew there was an issue and had absolutely convinced myself it was a static system flaw. Thinking about it, a pitot leak made sense!
Long ago, I read an article about using surgical tubing to test pitot static instruments. Slip some surgical tubing over the pitot and start rolling up the other end. It slowly builds slight pressure, allowing you to pressurize the pitot system without damaging the instruments. Mine was leaking so badly, I couldn't roll the tubing fast enough!
I used "Speedfit" tube fittings throughout my pitot/static system. https://www.usplastic.com/catalog/de...arentcatid=606. Great pieces that are easy to use and work well. I found one tube that hadn't been inserted quite far enough and one with some adhesive (presumaby from the tape that held the nylaflow tubing in a coil) in the fitting. After correcting these issues, I could roll up about a foot of the tubing, producing 70 MPH on the display and it held as long as I held the tube roll.
Couldn't fly yesterday, after the fix and thunder bumpers are building today, but I was able to take a quick lap of the area. That same 2550/25" now yields 150 MPH TAS. This is at 1000' MSL. The great thing is that the error was greater at high airspeeds, due to the higher pressures, so I still touch down about 40 MPH. When the weather behaves a bit, I'll go higher and get some speeds at altitude, and a top end run. But I can now say that my Patrol can cruise at an honest 150 MPH! Not bad, huh? 10 MPH more speed and no increased fuel burn!

Bill

[John Bickham]

Hey Bill,

Sounds like your gaining ground on the "smarter than me types"!!!! Get up there to altitude so you can come visit here in New Mexico. This DA flying is different than south Louisiana. I'm learning a lot while grinding away on the BH. Thanks for the all the helpful post. It helps those of us that are trailing farther behind.

I'm looking for an old post you may have made on control cable brackets. Struggling to find it. That on me and my less than adequate computer skills.

[Bdflies]

Good hearing from you John! I know what you mean about DA over there. A while back, a couple of us flew an R22 across the southern tip of NM. It was hot and calm when we stopped for fuel in Las Cruces. I’m here to tell you that it IS possible to cross ETL with skids skimming grass!!
I don’t remember the cable bracket post, but if you give me an idea what you’re looking for, I'll be happy to post pics or part numbers.

Bill

[jaredyates]

My avionics shop found a pitot leak caused by a cracked flare a few years back. I didn't quite get 10 knots, but otherwise it's a very similar story.

[Bdflies]

It’s been 'one of those weeks'. Monday morning, I pushed the Patrol out of the hangar to do some runs at altitude. Before unhooking the tug, a friend landed and taxied up, to visit. He immediately commented about the poor visibility. No clouds or ceiling, just a lot of dust and haze. "Not an inch over 3 miles." Well, planning to go to 4,500 for a 75%run in visibility like that just didn’t appeal to me. I pulled her back in and cut some grass... Tuesday morning looked a lot better! No clouds, at 8:30 and the vis was much improved. Pushed her back out, grabbed a cold water and hopped in. Fuel on 'both' mixture to 'full rich' master and alternator 'on'...... but wait! Those switches were already 'on'.... yep, I'd left the master on, last time I flew... last week... Hooked up the tug and pulled her back in. Charge battery. Cut grass. Today, the stars aligned. No ceiling, visibility was probably 8 miles and the battery was just fine. Up to 4,500, where I could still see 75%, set up a course and let the autopilot hold it. I saw 153 mph tas for a bit, but it stabilized at 152. Picture attached. I’m just as pleased as can be! Upon landing, I glanced up at the speed tape on touchdown and noted 40 mph indicated. I'd have taked a picture of that too, but I was kinda busy..

Bill

[Mark Goldberg]

Bill, I have always been told that the "sweet spot" for getting best TAS is a little higher - 6,000 ft - 7,000 ft. If that is true maybe you would see a little more TAS at a slightly higher altitude. Mark

[Bdflies]

That sounds like a reason for another flight! My Glasair peaked at 8 to 9k, but that was a much different aircraft. It’s a bit unfair to try these speed runs in such hot weather, but at least it’s a comparison point. I got to fly my old Husky this evening. Almost forgot what it’s like to look at a bunch of needles!

[JimParker256]

I agree with Mark. Most POH for normally aspirated, carbureted aircraft show the highest cruise speeds occur at the maximum altitude where you can still obtain 75% power from the engine. That's typically right around 8,000 feet (though some of those manuals do show 75% power may still be available at 10,000 ft when OAT is 20ºC or more below ISA standard temps).

[Bdflies]

Judging from the last couple of weeks, I'm expecting lots of big buildups and scattered thunder showers by noon. But it was nice at 8:30, so I figured it would be a good time for a higher run. Crossing 7,000' I was no longer able to maintain 75% power. As before, autopilot engaged holding altitude and heading. Picture attached. I have my theories, but I'll wait to hear others'.

Bill

[Bcone1381]

Curiously watching. How do you lean, Bill? What would your % power be at 7000' if you had 2500 RPM set?

[JimParker256]

Bill,

According to the" Full Throttle HP at Altitude" chart on pg 8-4 in the Lycoming O-360 Operator's Manual, your engine should produce 78.9% power at 7000 ft, 76.2% power at 8000 ft, and 73.5% power at 9000 ft. So the max altitude for 75% power should just below 8500 ft. Of course, that's in "standard atmospheric conditions" which your situation was definitely NOT...

But taking the numbers you provided (7100 ft, 62ºF, 29.99 altimeter setting) I calculate the DA at that altitude as 8910 ft. That is, in fact, above the max altitude where the engine could be expected to produce 75% power, and the 73% your EFIS is reporting correlates pretty darn well with the 73.5% at 9000 feet that the "book" calls for... (I'm guessing the EFIS is either rounding off the number or you've got a slight loss from induction "friction"...)

I think your figures are correct, but that you just forgot to account for the higher-than-standard density altitude caused by the warm temperatures and higher than normal barometric pressure (altimeter setting). The fact that you're getting 153 TAS at a DA of 8900 feet is pretty impressive!

(And oddly enough, your previous flight at 4500 ft, 70ºF, and 30.03 altimeter setting comes out to 6200 ft DA, The "Sea Level and Altitude Performance" chart shows that to be almost exactly 72% power as well, so the fact that you got 152 TAS under those conditions pretty well correlates to today's numbers. Still very impressive!)

[Bdflies]

Hi Jim, in my first comment, I suggested such runs really weren't fair in such warm weather. I'm just as pleased as I can be with these numbers! Mine isn't the lightest Patrol, nor is it the cleanest. I'm running 8:50's as well. Even in this situation, my numbers validate the advertised specs. Still thinking about 31's, so all this will be for nought.

[n302jw]

Thanks Jim ,

[Bdflies]

Hi Brooks! I was waiting for someone to question leaning. In the pic at 4500 I hadn't leaned hardly at all. At 7,000 I'd leaned a bit as I climbed. The G3X has a leaning function that alerts which cylinder peaks first and then displays the delta as leaning continues. At 7,000 I leaned to peak and switched out of that page to take the pic. I don't fly at peak, but wanted to be sure I wasn't too rich. Don't read too much into temps or fuel flows. The mission was to get to altitude, check speeds and come down. Can't say exactly about 2500, but I can guess that I'd see 60-65%. And it would consequently slow down. The MP available at 7,000 is the limiting factor. That's why I was running 2700 rpm. Lower rpm at 22.3" would drop the power noticeably. As a FYI, I'd never cruise at 2700 rpm. I'm more of a 2300 kinda guy. It's just a whole lot louder at high rpm.

Bill