gereed75

Well Known Member
I have been very curious about actual best range performance of my RV-6. Ever since last fall when on an IFR cross country when poor weather made me begin to contemplate “If I can’t get into here because of extreme low weather, how far could I go to get to better conditions and where would I have to operate (power settings vs performance) to get there“???

I have read all the posts about LOP and best range and min glide and L/D max and Whozit’s speed. But no where in there did I find any definitive data. So I decided to let my airplane tell me.

Today was smooth with light winds. I devised a flight plan to fly multiple race track patterns above a known landmark and use the GPS and fuel flow equipped EIS4000 to turn the plane into a calculator. I chose a distant direct to waypoint - TPK, 735 miles distance. Each pattern I crossed the same point, on the same heading, same 8000’ altitude, GPS tracking direct to TPK. On the “downwind leg” of each race track, I adjusted power to a new setting and stabilized the engine. Then turned onto the track. As I crossed the 735 mile away point, I reset the fuel onboard to 38 gallons. Then I recorded all of the data. They are spread sheeted below.

Best Range 3/26/10 N1024R KVVS to KTPA 735 mi 8000' 32F oat
RV-6 IO-360 RV200 Prop 1 Mag/1 LSE Plasma 2 ES4000 with fuel flow

reserve max set tot fuel
ETE Range mins Map/RPM EGT/EGT KIAS GS FF Used
4:32 3:39 -44 23.4/2200 1500/1350 165 163 10.5 46.1
4:57 5:12 15 23.4/2200 1485/1460 150 149 7.3 36.14
5:11 5:45 34 23.2/1900 1425/1400 143 142 6.6 34.21
5:21 6:19 58 22/1900 1440/1410 139 137 5.9 31.5
6:48 8:05 77 19.7/1900 1440 110 108 4.7 31.0
6:48 8:50 132 16.7/1900 1400 110 109 4.3 29.24
7:41 10:44 183 96 93 1405 96 93 3.7 28.42
11-12/1900 1400
Notes:
Run 1 - WOT, 125 ROP, slightly less than my normal 2400/WOT best power x-cnty cruise
Run 2 - WOT, 25 LOP
Run 3 - WOT, 25 LOP 1900 RPM, CHT 285, 145 oil temp with my oil cooler door closed
Run 5- CHT 250 LOP for smooth running Run 6 - CHT 230, LOP for smooth running
Run 7 - Oil temps rising, 171 with door cracked, CHT’s rising 275
Run 8 - Things getting unstable - hard to hold A/S, Can’t recover altitude, performance totally dependent on fuel flow - ain’t gonna happen in real life

Wow I learned a lot. First of all, I could make it TPK from KVVS (east of Pittsburgh) non stop if I wanted to!!! My LOP operations have always shown an unsettling EGT rise at about 50 LOP as engine roughens. This was uncomfortable and still is. As percent power goes down, peak becomes less distinct and just setting up for smooth running LOP is easiest. As airspeed and power goes down, performance can be controlled by fuel flow. Much below 12.5 inches and LOP, things just get squirrelly all around. Temps begin to rise (reduced airflow probably), prop is about on the min stops - it is just all squirrelly.

What did I learn about efficient cruise and max emergency range?? - Just going LOP is a quantum leap in efficient cruise (I think we all knew that). If I was in a real pinch, 20”/1900 LOP looks like great place to be while 16.7“/1900 could really stretch it in an emergency (lost over the north atlantic).

These are some incredible airplanes. Now maybe I understand the -9 better.

I welcome anaysis by the aero and graph/math guys. Very interesting and finally some numbers with confidence for the POH.

Still having trouble tabulating the data - first colum is ETE, second is endurance, third is minutes in reserve, the fourth is map/rpm, the fifth is max EGt/set EGT, sixth is IAS, seventh is GS, 8th is fuel flow, last is total fuel used to get there. Hope it helps someone else. Thanks
 
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Best Range Speed IAS

That's good work. You may also want to see the CAFE report on the 9A for similar findings.

Independent of engine & prop performance, the best range speed (ignoring wind) is the speed for maximum L/D. It has been demonstrated, however, that it is difficult to find that speed because it is not the best glide with engine out speed. It is not even close. On older engines, you could make your own Zero Thrust device as described by Jack Norris and Andy Bauer. On newer engines with less or no fore-aft movement in the crankshaft, it can't be done.

The next best approach, a good one, is one I developed, published in EAA's Experimenter and then improved. It will probably get you within 1 mph.

The best range speed is a CAS, not TAS and not IAS. My latest publications give you an easy way to resolve that factor, too. That means that your TAS will vary with altitude. In many cases, the accuracy of the ASI varies with airspeed; it's not a single error or a single %.

This link: http://home.cogeco.ca/~n17hh/Models/models.html will get you to a page containing a number of spreadsheets and other publications which covers all of what I said above.
 
I have read through your fabulous site at some point in the past. An invaluable asset for anyone serious about efficiency. My effort was to gain more insight into how it translates into useable info relative to a particular aircraft/engine/prop combo. Now that I have done that (at least for a single condition), I think I will go back to study your work for more insight. Thanks for the feedback
 
Thanks

I have read through your fabulous site at some point in the past. An invaluable asset for anyone serious about efficiency. My effort was to gain more insight into how it translates into useable info relative to a particular aircraft/engine/prop combo. Now that I have done that (at least for a single condition), I think I will go back to study your work for more insight. Thanks for the feedback
Thank you for the kind words! I totally agree that the best practical speed will ultimately depend not only on the VL/D but also on altitude, engine & prop. Mine, too, operates LOP much better at power settings above 7.5 GPH. Our Lyco-types are not designed to run at 30%. Keep up the good work.
H.
 
Today was smooth with light winds. I devised a flight plan to fly multiple race track patterns above a known landmark and use the GPS and fuel flow equipped EIS4000 to turn the plane into a calculator. I chose a distant direct to waypoint - TPK, 735 miles distance. Each pattern I crossed the same point, on the same heading, same 8000’ altitude, GPS tracking direct to TPK. On the “downwind leg” of each race track, I adjusted power to a new setting and stabilized the engine. Then turned onto the track. As I crossed the 735 mile away point, I reset the fuel onboard to 38 gallons. Then I recorded all of the data. They are spread sheeted below.

Best Range 3/26/10 N1024R KVVS to KTPA 735 mi 8000' 32F oat
RV-6 IO-360 RV200 Prop 1 Mag/1 LSE Plasma 2 ES4000 with fuel flow


reserve max set tot fuel

ETE Range mins Map/RPM EGT/EGT KIAS GS FF Used
4:32 3:39 -44 23.4/2200 1500/1350 165 163 10.5 46.1
4:57 5:12 15 23.4/2200 1485/1460 150 149 7.3 36.14
5:11 5:45 34 23.2/1900 1425/1400 143 142 6.6 34.21
5:21 6:19 58 22/1900 1440/1410 139 137 5.9 31.5
6:48 8:05 77 19.7/1900 1440 110 108 4.7 31.0
6:48 8:50 132 16.7/1900 1400 110 109 4.3 29.24
7:41 10:44 183 96 93 1405 96 93 3.7 28.42
11-12/1900 1400​
Notes:
Run 1 - WOT, 125 ROP, slightly less than my normal 2400/WOT best power x-cnty cruise
Run 2 - WOT, 25 LOP
Run 3 - WOT, 25 LOP 1900 RPM, CHT 285, 145 oil temp with my oil cooler door closed
Run 5- CHT 250 LOP for smooth running Run 6 - CHT 230, LOP for smooth running
Run 7 - Oil temps rising, 171 with door cracked, CHT’s rising 275
Run 8 - Things getting unstable - hard to hold A/S, Can’t recover altitude, performance totally dependent on fuel flow - ain’t gonna happen in real life

Not sure I understand. You did not actually fly all 735nm each time. That would be a lot of miles (>5000nm) in one day. I assume you set up the leg to KTPA and then flew for a bit to stabilze fuel flow and then calculated total fuel used to get to destination. How long did you fly the leg before starting the turn back on the race track pattern?
 
I fly high. Near full throttle (2550-2600 RPM on FP prop), lean as best possible considering it is carbed, but with one EI and cylinders ported and flow matched, then sit back and await the next ATC flight following frequency change.

I need to review the data closer but I am not going to extend my flight duration by 50% or more just to save a bit of gas.

I seldom fly as low as 8000' and realistic legs are three hours...plus or minus, regardless of fuel.
 
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plehrke - only flew three or four miles on track to KTPA. Long enough to stabilize altitude, heading/track, airspeed and power settings. Flew over the same geographic point on the ground each time, stabilized on track long enough to record data, then back around at a new (reduced) power setting.

Ron - I also fly pretty much WOT/2400, best power EGT (typically 10.5 gph or so). From this data, I can see LOP to extend legs if needed to avoid a fuel stop, or make it to your destination if winds are worse than planned for, or turning a three leg day into a two leg day.

The low power, high efficiency data would be used for that time when you get to the end of a 2.8 hour leg with 10 gallons of fuel left and you have to go to your alternate or somewhere else to get to better weather. Hopefully good flight planning/weather following would avoid this, but if you had to do it, do you confidently know your most efficient cruise when your down to 10 gallons and you have to cover some ground and have some gas left when you get there and your rectum is puckering?? That was the real data I wanted to have in my knowledge base.

Thanks and again hope it proves helpful.
 
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