Flying at Peak

Like all trips to Oshkosh, in its own way, this year was the best.
2007 was the fifth time to fly the VariEze in.
Maybe a dozen total trips to Big O now.
Two main thoughts; spending the first cool evening sitting with Steve Wright in his shared camp ground front yard, and second, flying home at peak.
Including holding on the way up and maneuvering around weather on the way back, the average fuel burn for this Oshkosh trip was 4 gph. Gluttonous compared to some.

The next thought is Schubert and Hertzler’s cooling and drag forum. Kinda like a home team pep-rally with the coaches replaying film of our last winning game. A few great plays, some good plays, some not so good. You definitely feel at home, but you might also take a hit.
Afterward several EZ buddies agreed that it was in fact the best forum ever at Oshkosh, bar none! But there was a non-EZ fellow sitting near me that left in a huff saying “it was a waste of time, they didn’t talk about nothing new”. I think that was the idea, and what made their presentation of such value. As you know, it is available on ez.org.

The trip up to Wisconsin was flown at LOP, lean of peak, throttle wide open and RPM aggressively reduced with mixture. This is now fairly routine after the last two years of testing and tweaking toward optimum efficiency. During that time only one cruise flight was flown at higher power settings, coming back after a hundred dollar fajita, described in the EZ Chron What Flying is Really About. On that trip things were pretty exciting outside and not much time was spent inside the cockpit figuring data. Otherwise, all of the recent flights had the throttle full open with aggressive leaning to low rpms, between 2200 and 2000. So until now I had not looked at max cruise.

You can notice lots of folks talking LOP. Several of the local spam can drivers say they have been doing it for years. Cool. Listening further, it seems they might be talking about something a little different. They are in fact “leaning lean of peak”. However they are first setting RPM with throttle, the normal practice. But there is a difference in flying with the rpm set with throttle and then leaning LOP, versus putting the throttle wide open and then reducing rpm to 2000 with mixture. Not earth shattering. But interestingly preferable if one can do it. Probably could use a better term for the more aggressive leaning practice.

Enjoying the Chase
Life's good when you have something interesting and not too profound that you might go to sleep thinking about and wake up early thinking about, and can’t wait to get busy on.
In the early Eze years it was great fun just getting all the airplane ducks in a row at the same time. Then cooling became an opportunity. Recent years my attention gravitated to the intake limitations and challenges, now pretty well proven and a very good thing.
So now the hunt has evolved to another interesting element of efficiency that I first paid attention to during the 1986 Voyager flight. Probably everyone knows this and totally uses it to fly their planes but me.

Anyway, with all the variables, they flew Voyager for nine days aggressively holding one constant angle of attack. To hold that specific AOA they initially flew at 130 kts using full power on both engines. They reduced power over time, finally slowing down to 90 knots using partial power on one engine. They landed with 12 gallons of fuel.

Based on his record setting flights, I am assuming Hertzler’s best AOA is at some point attained at around 2200 rpm. But I know little about why that rpm was selected or how much attention he or others pay this AOA aerodynamic element on our short flights.

On the non stop 1400 mile flight to Reno, my main shade tree focus was basically finding the cruise speed with the lowest rpm with the least speed loss. Preparing for the flight, reducing the 0-235 cruise rpm at 50 rpm increments, below 2400 there was a significant sag in attitude and speed. 2400 it was. Looks like I had 200 rpm more drag than Hertzler.
The attitude sag was as close as I got to considering AOA back then. The 1400 miles were made with no problem with over an hour’s fuel remaining. If making the trip again, now the intriguing challenge of best AOA would at least be on my mind. A few more little airflow molecules to go out and chase!

Flying Home At Peak
Maybe the AOA thing created a temporary distraction from LOP and is partly responsible for the great trip home from Oshkosh. Leveling at 10.5K my finger habitually started to curl back the mixture lever. But curiosity crept in. With the throttle open the mixture was adjusted to peak for a change. Starting building the plane late and with some interim delays, I have a lot of my share of fuel to burn to catch up with you guys. There was plenty of fuel on board and average fuel burn so far was below 4 gph. So why not just let the steed open up.

She opened up. WOT and leaned to just slightly below peak, after 5 minutes, then 10 minutes, then 30 minutes, the TAS was holding over 220 mph. Up over 5 gph here but who cares. Adding to the fun, the CHTs were aligned at 360 and the oil temp was about 195 degrees. The CHTs also match wide open down at 2000 feet, but not in all other situations.

Hertzler had projected his prop would result in 221 mph and 2700 rpm with my setup. At just over 2600 rpm here, I still have some filleting and finessing to do.

Schubert’s always asking the question - what have all the changes wrought? Well, I got a pretty good indication today. In eleven years, with lower temps and better fuel burn, flight in this regime has gone from about 185 mph to over 220. That’s about all I know for now Terry : )

But like running wide open at 2000 feet on a hundred degree day, max speed up there is not something one will need to do very often. Unless you are in a group headed for that $100 burger. Then that’s all that matters.

Anyway, the chase is fun. And as usual the point has changed some. The previous cooling goal with the 0-235 was simple... the ability to run wide open at 2000 feet on a 100 degree day with good cylinder and oil cooling. While relatively few folks can probably do that, or even need to, you feel pretty good about having accomplished it.

The other part of the hot day goal, unlimited climb at full power, was and is very practical. And its great fun in a group not to be temperature limited. But at altitude, specifically at LOP reduced rpm, the requirements are less and optimization here may lead to different shapes or components.

This time around with the 0-290, the cylinder cooling was good from day one. But with oil cooling, planning on a couple of upcoming trips, rather than messing with the wide open hot low level 2000’ goal as with the 0-235, the criteria became cruise climb to 12K with the oil temp under 216. You smarter folks have skipped the more stringent low level stuff that I played with and just did this cruise stuff in the first place. Good for you.

So flying home at peak was one fun part of Oshkosh 2007. Other thoughts to come.
While waiting out the weather in Oklahoma, it dawned on me that a significant long term goal has been met, and then some. Because of an early bureaucratic interlude, another story, there has been a respectful but subversive intent to achieve cruise at 210 mph or 181 knots. That means 12 inch N numbers. However, the criteria is actually normal cruise above 180 knots, not max cruise. And knots, not mph. And good news, normal cruise on my plane has been empirically determined to be 179 knots. The three inch numbers are OK.

For now. Schubert and Hertzler, we’re counting on you to finally come up with something new!
Bill James, Fort Worth VariEze