4-place Cruise Speed Survey

[MattS]

BH 4PL with Clamar amphibs. Cont IO-360 recently overhauled with CS McCauley 86".
2500rpm / 26MAP IA = 112 mph, TAS calculated to 117 mph. Burning 43L / hour ROP.

[rodsmith]

That is impressive on amphibs.

[Bcone1381]

43L is 11.36 gallons

[kestrel]

Did a small amount of data collection today by flying 4 sides of a box and averaging GPS speed

Density altitude 10,500, 2300 rpm, 21-22 inches (didn't remember to check carefully, WOT) 124 kts
7,500, 2300, 23 119 kts
4,500 2300, 23, 113 kts

I'm on 31 inch bushwheels, carburetted O-540, probably around 11 gal/hr. Probably a bit less for the 10,500 data.

[whee]

Whee,

What does ~370943FF TAS at 0.00002793AFH mean. I was hoping I could figure it out without having to ask but I'm drawing a hard blank. Thanks!

That was me being dumb. Furlong per Fortnight and Acre feet per hour

I’m still seeing the same speeds mostly at 7000ish msl.

138mph TAS and 9gph.

DA changes significantly around here and I don’t have a OAT hooked to my EFIS so I don’t know what the DAs are.

[JimParker256]

It's a rainy day with low overcast, and I was wondering how Whee came up with those numbers... So I Googled it, and there are actually converters for "furlongs per fortnight" to "MPH", as well as "Acre Feet" to "Gallons"... Who knew? (And yes, I know Whee can't see this, but then, he already knew about the converters, didn't he? LOL)

[Battson]

For 9 gph that is not a bad speed, Jon. I think I would see similar speeds if I reduced fuel flow to 9.

[Battson]

Did a small amount of data collection today by flying 4 sides of a box and averaging GPS speed

Density altitude 10,500, 2300 rpm, 21-22 inches (didn't remember to check carefully, WOT) 124 kts
7,500, 2300, 23 119 kts
4,500 2300, 23, 113 kts

I'm on 31 inch bushwheels, carburetted O-540, probably around 11 gal/hr. Probably a bit less for the 10,500 data.

I presume those are 'effectively' true airspeeds, when you say averaging GPS speeds around a box. Just confirming how your math worked. Very, very similar to what I would expect to see in my plane, if *ever* so slightly more fuel consumed - assuming you are talking 11.0gph

[zkelley2]

That was me being dumb. Furlong per Fortnight and Acre feet per hour

I’m still seeing the same speeds mostly at 7000ish msl.

138mph TAS and 9gph.

DA changes significantly around here and I don’t have a OAT hooked to my EFIS so I don’t know what the DAs are.

40 Rods to the hogshead?

Did grt not include an oat sensor? It comes with the eis.

[kestrel]

I presume those are 'effectively' true airspeeds, when you say averaging GPS speeds around a box. Just confirming how your math worked.

Yes, true airspeed derived from GPS using an average speed of 4 orthogonal headings to cancel out winds aloft.

Very, very similar to what I would expect to see in my plane, if *ever* so slightly more fuel consumed - assuming you are talking 11.0gph

I'd expect mine is a bit slower, or higher fuel burn. My CHTs run about 300F in cruise once leaned out, I and I have no cowl flaps to close. I'm carburetted with the air filter chin sticking out. I also have a couple of small scoops sticking out of the cowling for cabin and carb heat intakes. All of this is how the original builder configured it.

I'm guessing the 11 gph because I have no fuel flow meter and can only base it on the ad-hoc data I've collected on longer trips. My data there is sparse. I lean pretty aggressively and see both EGTs and CHTs fall as a result.

[whee]

For 9 gph that is not a bad speed, Jon. I think I would see similar speeds if I reduced fuel flow to 9.

I was hoping to see more speed at higher fuel burns but I haven't seen that yet. We need to do more testing after we get the rigging issue solved but so far increasing prop speed just increases noise and burns more fuel with little or no change in speed.

[rv8bldr]

I was hoping to see more speed at higher fuel burns but I haven't seen that yet. We need to do more testing after we get the rigging issue solved but so far increasing prop speed just increases noise and burns more fuel with little or no change in speed.

An acquaintance of mine used to fly Beech 18's. He said that the throttle was essentially a volume control because the airplane only seemed to fly at one speed regardless of how much power you put on :-)

[Bdflies]

Whee; There’s no way for us to know how much force you’re using to correct for the heavy wing, but applying one aerodynamic force to overcome another, is contributing parasitic drag. You might be surprised when you get her trimmed to fly hands-off.

Bill

[Battson]

I was hoping to see more speed at higher fuel burns but I haven't seen that yet. We need to do more testing after we get the rigging issue solved but so far increasing prop speed just increases noise and burns more fuel with little or no change in speed.

Sounds like big tires syndrome, no matter how much I open her up I can't see the high cruise speeds we used to get. It is a good thing though, it used to feel like a wheelbarrow roaring along at 80% power and 140 KIAS. Really low nose angle, awful rough ride, twitchy on the stick. Much cruisier at 120 KIAS speeds.

[PaulSA]

Sounds like big tires syndrome, no matter how much I open her up I can't see the high cruise speeds we used to get. It is a good thing though, it used to feel like a wheelbarrow roaring along at 80% power and 140 KIAS. Really low nose angle, awful rough ride, twitchy on the stick. Much cruisier at 120 KIAS speeds.

Eeerrr ...... Couldn't you just have wound it back to 70% and cruised at 120kts?

[Battson]

Eeerrr ...... Couldn't you just have wound it back to 70% and cruised at 120kts?

Oh that was just something I tried to see what it was like. Not a normal thing, but my point was once Jon fits the big tires, high power high speed cruising will not be something he needs to worry about. Just sit back and enjoy the ride.

[Helidesigner]

Configuration:
260 shp IO-540, low loss K&N air filter, One Electronic ignition, 3 bladed composite prop, 8.5x6 tires, VGs, lots of bug splats.

Typical Cruise Performance;
125 KTAS around 6000 ft, 65% power (MAP~23 in) 2150 RPM, 10.1 GPH, average 35 deg LOP.

I have a Grand Rapids EFIS with full engine instrumentation and TAS calculation.

[schu]

Configuration:
260 shp IO-540, low loss K&N air filter, One Electronic ignition, 3 bladed composite prop, 8.5x6 tires, VGs, lots of bug splats.

Typical Cruise Performance;
125 KTAS around 6000 ft, 65% power (MAP~23 in) 2150 RPM, 10.1 GPH, average 35 deg LOP.

I have a Grand Rapids EFIS with full engine instrumentation and TAS calculation.

That's a bit of manifold pressure at that altitude, do you have a horizontal fuel system like Battson?