4-place Cruise Speed Survey

[Helidesigner]

I am not sure what you mean by a horizontal fuel system.

[Battson]

I am not sure what you mean by a horizontal fuel system.

I guess he means the air induction system, are you getting ram-air to boost the MAP?

[TimTall]

Here's another data point for this discussion...

I've got about 40 hours on GGUB now. I've been taking photos of my EFIS regularly in different configurations so I can learn what works best for me and for the engine. (I know I could download the data from the Dynon and look at it on a graph but this seems simpler to me.)

I've settled on this configuration for a good cruise set up.... A good combination of speed, fuel efficiency over the ground, and happy engine temps. I figure if I'm getting 16.4l/100km (14mpg) I'm getting close to what I get in my pick truck so I'm doing pretty well, especially where I live - it's typically 2 or 3 times as many road miles as air miles to get around the mountains.

I'm not sure how accurate my percent power reading is. The LOP/ROP indication (below the fuel flow gauge) isn't correct and that is tied to the percent power meter through Dynon's algorithm based on generic fuel flow charts from Continental. I can make adjustments to make it more accurate but it sounds like it's bit of trial and error process so I haven't gotten around to it yet.

Continental IO-470 with 26" Goodyears. With newly installed VG's on the wing and on the horizontal stab. No change in cruise speed with that addition.

IMG_6406.jpg

[Nev]

Nothing wrong with those numbers Tim !

[whee]

Wow TimTall! 146mph TAS on 9.5gph Can’t complain about those number at all.

What prop are you running?

[TimTall]

84" McCauley 2 blade. With the obsolete screw on style blades. I was looking at composite replacements at Oshkosh this year. Definitely on the list of upgrades. It would be nice to take 30lbs off the nose.

[whee]

Thanks Tim. 84” is probably the ideal size for a two blade metal McCauley. My 88” is too long and costs me some speed but I can’t bring myself to cut it down.

Where did your empty CG come out at? I keep wishing my FWF weighed 40lbs more.

[marcusofcotton]

US or Canadian gallons???

[TimTall]

US. I've never actually used Canadian gallons for anything.

[Battson]

Wow TimTall! 146mph TAS on 9.5gph Can’t complain about those number at all.

125 KTAS at 37L/hr at 9,000ft DA, (~peak power output).

With 26" tires those are the standard 6-cyl Bearhawk numbers aren't they?? Certainly nothing to complain about. Very interesting to see the 470 delivering the same airspeed per fuel burn in more than one case now.

With 800x6 tires that would normally be 130 KTAS at the same fuel flow.

[Bcone1381]

37L is 9.77 us gallons

[Enewton57]

Sorry, this report is not very scientific and it uses MPH instead of knots, but it will give you a comparison for how a 4-place with an O-360, with fixed pitch performed. Here is my 25-hour report.

http://mybearhawk.com/flying/25hours.html

Eric Newton
Bearhawk Tailwheels LLC

[Bcone1381]

Lyc O-360 with a Climb Prop
@8000', 18.0" map, 2700 rpm, 65% power, 135 mph @ 8 gal/hr
@2000', 21.5" map, 2650 rpm, 75% power, 137 mph @ 9.5 gal/hr

[whee]

125 KTAS at 37L/hr at 9,000ft DA, (~peak power output).

With 26" tires those are the standard Bearhawk numbers aren't they?? Certainly nothing to complain about. Very interesting to see the 470 delivering the same airspeed per fuel burn in more than one case now.

With 800x6 tires that would normally be 130 KTAS at the same fuel flow.

Could be for a big engine BH. Mine won’t go that fast at the power levels I can achieve with my smaller engine and highish cruising altitudes. 9000DA is about a low as I can cruise and 9gph is about an much as I can burn giving me 120KTAS on 8.50s. 31s cost me about 5kts.

[Battson]

Good point, I have added that qualifier. It does seem that the lazy 6 is more fuel efficient, when run in economy mode

[whee]

That qualifier covers it aside from us small bore 6-cylinder Continental guys

[Bcone1381]

37L is 9.77 gallons

[Utah-Jay]

Sorry, this report is not very scientific and it uses MPH instead of knots, but it will give you a comparison for how a 4-place with an O-360, with fixed pitch performed. Here is my 25-hour report.

http://mybearhawk.com/flying/25hours.html

Eric Newton
Bearhawk Tailwheels LLC

Eric

Great testing write up. I am very encouraged to hit my cruising goal of 135mph with my 200hp O-360 after reading your test results.

You might want to look at the Sensenich ground adjustable prop. I’m hanging the 82” on my Companion. 15 minutes to change pitch and has 6 different pitch settings. Light and inexpensive, so a win-win in my book. 82” is a long prop, so depending on tire size and TW diameter you might look at 80”. Certainly the 82” will hurt me a bit in cruise.

I’m out here in the land of high DA’s, so I need the climb pitch at times for backcountry fun and games.

Ok, glue is dry, time to slap on some oratex

[Battson]

I have to say performance does vary from day to day. Some days are fast, others are slow. This isn't about weight / CG, it's ambient conditions.

This was a good day, 121 to 122 KTAS for 38 to 39 L/h, 3000 ft DA, from the IO-540 with dual EI, dragging 31" bushwheels...

Sorry about the photo sharpness, I had difficulty getting a nice picture with the glare.

EFIS.jpg
EMS.jpg
I would have loved to settle into a cruise at 8k or 9k feet DA and see what kind of speed this would have allowed, time didn't allow.

[whee]

I have to say performance does vary from day to day. Some days are fast, others are slow. This isn't about weight / CG, it's ambient conditions.

I find it pretty interesting how much the performance varies with ambient conditions. I do enjoy the days when the plane scoots along at 120kts while burning 9.5gph and dragging 31s along.

[whee]

Today was a slower day but it was fun to try out my newly installed OAT probe and see all the feature I’ve been missing on the EFIS.

113KTAS @ 9.5gph cruising at 7000msl going.
105KTAS @ 7.5gph cruising at 8000msl coming home.

[Nev]

Nothing wrong with those speeds at those fuel burns Whee !

[whee]

Your right Nev, I can’t complain. I do wish my little 6 cylinder Continental could put out more power and burn more fuel so I could go faster. Oh well, I’ll have to learn to enjoy the ride even when I’m in a hurry.

[Nev]

I find it pretty interesting how much the performance varies with ambient conditions. I do enjoy the days when the plane scoots along at 120kts while burning 9.5gph and dragging 31s along.

It's likely the effects of temperature and air pressure. At a given altitude on a low temp / high pressure day the IAS will read higher (and the resulting TAS is lower than normal). The aircraft feels fast. The engine is capable of putting out more power (higher manifold pressure at full throttle) and the prop is more efficient.

Conversely for a high temp / low pressure day the IAS will read slightly lower, and the resulting TAS will be higher. Effectively a higher density altitude, as though you were flying much higher.

Actually I see Jim gives a good explanation in post #6 of this thread.

[Battson]

I always use TAS, IAS is not that interesting in terms of real performance on this subject. The AOA probe renders IAS uninteresting in other flight phases too, so generally the IAS is not a number I use. I normally talk in terms of TAS, although sometimes forget to be clear about it.

[whee]

Went out scouting for a hunt, looking for animals and a landing zone. Found neither. But on my way there and back I played around with some power settings and such. The amount of speed lots due to cooling drag was pretty interesting. Closing the cowl flaps gave me an honest 4 knots.

[Battson]

Went out scouting for a hunt, looking for animals and a landing zone. Found neither. But on my way there and back I played around with some power settings and such. The amount of speed lots due to cooling drag was pretty interesting. Closing the cowl flaps gave me an honest 4 knots.

That is really interesting.
I can't measure any - but I am sure they have some effect. The cowl flaps make a huge difference to pressures in the cowl, which must affect drag somewhat

[TimTall]

Same. My top cowl gets pulled down in the center. There's no question there is suction happening!. I'm having zero issues keeping the engine cool. Definitely glad I took the time to install the cowl flaps. Now that winter is coming, I'm going to have to close up the outlet more. During the hottest part of summer I could easily end up in the 320F range in cruise if I was throttled back and leaned out. That's going to be an issue when the temps are closer to freezing.

[whee]

I was surprised. I thought I might see 1 knot, maybe. When I saw 4 I was sure it was an error so I opened and closed the cowl flaps many times, to the point I commented to my passenger that I was going to wear out the servos and switch, and the result was the same each time. Academic papers show that cooling drag can have a significant effect on speed but mostly on fast airplanes. I didn't expect my BH to be fast enough that cooling drag would have a 4 knot effect.

My cowling outlet is tiny compared to most others and is significantly blocked by the muffler. Unless the OAT is pretty cool, I keep my cowl flaps partially open most of the time which easily keeps the temps in check.

[Battson]

I recall when I was starting our build, nobody was really using cowl flaps and there was no real information or data available. Almost everyone recommended against installing them! How that's changed for the better in the last decade. This community is such a great resource.