performance question

[Dennis Madden]

Looking for some approximate (real world) numbers from the 160 hp RV-4 crowd.
I'm wondering what power/speed/altitude combo works out to be long range cruise in the -4. Has anyone flight tested their plane enough to get a sense of what these numbers might be? 75% power and 55% power are published, but is there a combo that gets you further down the road without a stop?
How far can some of you guys stretch a tank of gas?
Looking into aux tanks as well, but that a whole other post... ;-)
TIA

 

[rvator51]

Hi Dennis

2450 to 2500 rpm at 8-10K usually results in 180-185 mph TAS at 7.5 to 8 gpm for us. We try to be on the ground after 3 hrs flight time which still gives us a hour of fuel reserve. We also have the long range tanks (8.5 gal) which can add an extra hour to our flight time if we need it. We tried to do Oskhosh to Phoenix last year with one stop at Ft. Dodge, Kansas (almost exactly midways). The headwinds on the way back put it too close so we did two stops. Our friend in a RV-7 was able to do it in one stop.

 

[Kyle Boatright]

I did a brief search of the Matronics archives looking for information on John Johansen (the 'round the world RV-4 Aussie), but didn't find anything related to the power settings he used. If I recall correctly, his long range cruise figures were 40-45% power.

In my 0-320 powered RV-6, I get 155 knots at 7.5 GPH at a power setting in the 60-65% range. Your RV-4 should go a little faster on the same fuel, and would get better range at a lower power setting.

 

[Kevin Horton]

Looking for some approximate (real world) numbers from the 160 hp RV-4 crowd.
I'm wondering what power/speed/altitude combo works out to be long range cruise in the -4. Has anyone flight tested their plane enough to get a sense of what these numbers might be? 75% power and 55% power are published, but is there a combo that gets you further down the road without a stop?

How slow are you prepared to fly?

If prop and engine efficiency are constant, the absolute maximum range would be achieved if you flew at the speed for best lift / drag, which is much, much slower than most people are prepared to fly. In the real world, the prop and engine efficiency have probably fallen off a bit as you slowed down to that very slow speed, so the speed for best range is probably a bit faster than the speed for L/D max.

The higher you fly, the greater the TAS you will have at the IAS for L/D max. So, you can get the best combination of range and speed by installing an oxygen system, flying at a low IAS at high altitude. Of course, the winds can be strong up high, and a big head wind could make this plan a bad idea. But if you happen to have a big tail wind, you could go a long, long way.

 

[BruceMe]

Best L/D isn't best range...

How slow are you prepared to fly?

If prop and engine efficiency are constant, the absolute maximum range would be achieved if you flew at the speed for best lift / drag

Close... mathematically, best range is a bit ahead of best L/D speed (aka best glide or best endurance). But if you want to go somewhere, you'll use less fuel to get there by going just a bit faster.

It's still real slow by RV standards though! 110 - 130mph would be a typical RV best range speed. I'd throttle my little old RV-3 (just a 25g header tank) way back 1700 RPM and to do these kind of speeds and get much better range. I built my RV-4 to sip fuel at high altitudes and slow speeds. Airworthiness is coming soon.

One thing to keep in mind, these engines aren't designed to run for extended periods at power settings bellow 50%. Be sure to aggressively lean or you'll definitely get fowling.

 

[Kevin Horton]

Close... mathematically, best range is a bit ahead of best L/D speed (aka best glide or best endurance). But if you want to go somewhere, you'll use less fuel to get there by going just a bit faster.

What?? Are you thinking of a jet aircraft maybe? On a jet, the speed for max endurance is at L/D max, but for a prop powered aircraft that is where you will get best range.

Max range is at the condition where nm/(lb of fuel) is at a maximum, or (lb of fuel) / nm is a minimum. Thus (lb/hr) / (nm/hr) is a minimum, or fuel flow / speed is a minimum. If the engine specific power and prop efficiency are constant, then the fuel flow is proportional to the power required. Thus power / speed = a minimum. Power = drag times speed. So, (drag * speed) / speed = a minimum. Thus, the absolute maximum range will occur at the speed where drag is a minimum.

 

[asav8tor]

What?? Are you thinking of a jet aircraft maybe? On a jet, the speed for max endurance is at L/D max, but for a prop powered aircraft that is where you will get best range.

Max range is at the condition where nm/(lb of fuel) is at a maximum, or (lb of fuel) / nm is a minimum. Thus (lb/hr) / (nm/hr) is a minimum, or fuel flow / speed is a minimum. If the engine specific power and prop efficiency are constant, then the fuel flow is proportional to the power required. Thus power / speed = a minimum. Power = drag times speed. So, (drag * speed) / speed = a minimum. Thus, the absolute maximum range will occur at the speed where drag is a minimum.

What Kevin posted is what they taught in Aero. If it's wrong I want my money back.

How does low power settings hurt the engine? Ring flutter? How low can you run without a problem? 15" and 1800 RPM ok?

 

[smokyray]

Reality vs Theory...

Max Conrad flew a 260HP Comanche from Tripoli, Libya to LAX non stop in 62' entirely at max range numbers (105 knots). Having flown my Rocket and RV4 quite a bit (1700 hours) all over the country I tried alot of combinations for speed and range. My RV4 started with a 150HP 0-320 and Sterba wood prop. It trued at 150 Knots at 7GPH at 8500 ft, 160 knots at 8GPH, and would just tip 170 knots at SL and 2800 RPM, 10GPH. The Rocket will do the exact same with 300 ponies up front, in fact a bit less at the higher end. It will go alot faster if you want to burn more fuel. (205 knots true at 12 gph)
L/D max in the F16 is .82 Mach, well below max cruise, the RV4 and Rocket are similar. Both seem to stay on "the step" down to 120 knots IAS at 8500'. Below that they start "plowing through the air and burning more fuel. I have found taking the RV4 or Rocket up into thin air above 15K worked well but cold temps and using O2 makes it tough on my GIB (girl in back). The best altitude for the Rocket is between 8.5 and 10.5 at 20"MP (or 30 degrees advance on my EI) and 2300 rpm. My RV4 The Bandit liked full throttle above 8K, pulled back one knob width and leaned out to 8GPH. Max range was 20"/2350 (FP prop) 6.5 gph 140 knots true. I really like my ER1 tanks in both airplanes, the extra 9 gallons makes a big difference. (RV4 40 gallons, Rocket 54 gallons)

Your mileage may vary...

Rob Ray
RV4ormerly
HR2

 

[Dayton Murdock]

Your Mileage will vary

Hi All
My last trip was an eye opener for me, I went from Carson City to Corvallis in 2.5 hrs @ 8500'
WOT lean to 1430 deg's
TAS 174kts
9.2 gph fuel burn
The next trip I will bring the throttle back to 2500-2600 rpm's and maybe get a better fuel burn without going to much slower

 

[frankh]

Maybe

Remember Dayton that with a fixed pitch prop the only option you have is to pull the throttle back...Trouble is this will increase the pumping losses..Actually the worse thing you can do (for the engine that is in terms of power per unit of fuel) is to throttle the engine.

So while you may do a little better (because less horse power my not make that much difference to speed) the cost of that reduced horse power will effectively go up.

I guess power like anyhing else is cheaper in bulk...

Frank

 

[LAMPSguy]

Anyone ever try any combinations of reflex in their flaps? Don't know how much it would change it...maybe a few knots...but I guess if you do 5 things that each get you 1-1.5 kts, then you've got a few more!!!

 

[smokyray]

Yep, works good...

My buddy Trout out in San Diego has an RV4 built with 5 degree reflex in the flaps. It is good for about 5 knots increase at cruise power. Better though is when he flies at max range speeds 130 knots, it burns less gas. Worth trying...

Smokey
HR2

Myself and "Shrek" in front Trouts reflex RV4 last summer...

 

[Bill Wightman]

Reflex flaps...

Anyone ever try any combinations of reflex in their flaps?

Not a good idea with any of the NACA 23XXX sections. These airfoils are symmetrical aft of about .20 chord. All the camber is up front. In 1931 the idea was to build a zero-pitching moment section with the goal of reducing tail trim loads. That's what Van used on the RV3/4/6/7/8 after reverse engineering a Sti.ts Playboy. Any reflex back there would give you negative camber - sort of a "duck tail" effect.

I ran a 2-d CFD analysis of the 23013 and could see no gains in running negative camber in the aft section of the wing. Just for fun, I did reflex my RV4's ailerons slightly and there was no measurable difference from doing that.

 

[Andy_RR]

What Kevin posted is what they taught in Aero. If it's wrong I want my money back.

How does low power settings hurt the engine? Ring flutter? How low can you run without a problem? 15" and 1800 RPM ok?

Unless I've misread, best range speed is a function of your head/tail wind. If you have a tailwind your best range speed is slower than the still-air best range (or best L/D). With a headwind, it's faster.

I think the above graph kind of describes the situation.

A

 

[smokyray]

Not an aero major...

Thanks for the information, I learn something every day when I pay attention! I'm not disputing the engineering information, I'm just posting what I saw in action while flying the airplane. I wasn't aware of the Reflex anomalies involved with the RV airfoil (similar to my Tcraft 23012, twin beech, bonanza) It does work fairly well on the older Maules, and apparently on Trouts RV4. My Rocket flies just fine and plenty efficient and fast without them...

Smokey

 

[Kevin Horton]

. I wasn't aware of the Reflex anomalies involved with the RV airfoil (similar to my Tcraft 23012, twin beech, bonanza) It does work fairly well on the older Maules, and apparently on Trouts RV4.

Do you know how Trout determined that he has a speed increase with reflex? Is that conclusion based on an observed increase in IAS, or is it based on observed changes in GPS ground speed on several legs on different tracks, with an appropriate method to convert to TAS? If the conclusion is based on IAS, it is possible that the change in airflow caused by the change in flap angle has changed the pressure at the static port, thus causing a change in the error in the airspeed system.

If the conclusion is based on GPS data, is the change in performance repeatable?

 

[groucho]

Unless I've misread, best range speed is a function of your head/tail wind.

For me, best range speed is full throttle...wife bladder range is less than aircraft range.

 

[smokyray]

Amen Brother...

Groucho,

My L/D max formula is: Best Range=GIB tolerance level X time Trouts RV4 showed a GPS groundspeed increase over a given distance on a cross country I was along with last summer. I would have to ask him how consistent it is and exactly how much. Being an Aeronautical Engineer and former Navy Top gun instructor normally he likes using something that works.
I'll get back with you...BTW, Trout is building an RV4 with P-51 style wings, almost completed.

Smokey

 

[pierre smith]

Who did the design?

..BTW, Trout is building an RV4 with P-51 style wings, almost completed.

Smokey

Now that's interesting...tapered wings like a -51? Would they happen to be EVO wings? Pictures?

Regards,

 

[Kevin Horton]

Groucho,
Trouts RV4 showed a GPS groundspeed increase over a given distance on a cross country I was along with last summer. I would have to ask him how consistent it is and exactly how much. Being an Aeronautical Engineer and former Navy Top gun instructor normally he likes using something that works.

Some day when you and Trout are flying together, have him set his flaps to zero degrees on the ground, using some credible method (wing profile template, etc), then leave them there for takeoff. Level off at his typical cruise altitude and have him set his normal cruise speed, with you on his wing in the Rocket. Note the stabilized IAS in the Rocket and the RV-4. Then have Trout fully retract his flaps to the reflexed position without changing power setting and note the new speeds. The change in IAS in the Rocket will be a useful measure of the effect of reflexing the flaps.

 

[tin man]

Doesn't help on an RV3 wing. 23012 series. I rigged my flaps in trail via template and good old eyeball. With manual flap handle I can actually go forward on the handle a bit, reflex maybe 5 degrees or so. Set up side by side flt with well known RV4 all stabilized and that, then reflexed flaps . Airplane gradually lost ground and had a slight pitch change. Not faster on an RV3.
Tom
RV3 x 2
2000+ hours

 

[smokyray]

A Skosh...

Just spoke with Trout on the reflex flaps and laminar flow wing project. His manual flaps reflex TE 1" up from level flight. His test results in 500 hours of flying have netted a consistent "just a skosh" improvement at cruise speed only, max 5 knots IAS. Whether that 5 knots is ASI error due to AOA is uncertain. Now he rarely uses them as he flies around at low cruise and they prove ineffective there. His overall comment: don't bother.
The Laminar Flow wing project is on hold while he finishes a Navy SNJ tail section project. They are complete, custom made landing gear (in his machine shop) installed ready for fuselage mounting. John Roncz helped with airfoil design. My visit showed them as incredible workmanship and the wall blueprint really looks cool. More P-51 than EVO...

Smokey

 

[elippse]

Anyone ever try any combinations of reflex in their flaps? Don't know how much it would change it...maybe a few knots...but I guess if you do 5 things that each get you 1-1.5 kts, then you've got a few more!!!

I've done reflex tests on my Lancair 235. Going from 8 deg to 6 deg gave me +3 to 4k more speed; from 6 deg to 4 deg speed dropped 3 to 4k, and from 4 deg to 2 deg it dropped 4k more. One nice thing is that as you decrease reflex the nose comes down. I have a rec veh bubble-level set to the chord-line at 1/3 span. When it indicates +0.5 deg to + 1.5 deg I get the best speed. The amount of reflex is conditional on CL; at low altitudes / higher speed the required CL is lower and you need more reflex / less camber. As altitude goes up and speed goes down you want less reflex. The drag bucket follows the CL. With more reflex, less camber, the bucket min is at low CL, and conversely, at higher camber the drag bucket moves out to the higher required CL. See Sport Aviation 1983 August issue for the polars on the NLF(1)-0215F airfoil used on the Lancair with and without reflex.

 

[chuckh1197]

RV7A Performance

Just flew from Reno to Oklahoma City at 15.5 and had some time to try different rpm/fuel flow Here is the data.
IO360 200 HP Angle Valve/ Holly Cowl / Hartzell CS prop
Alt MP Temp
15500 17.7 5c
RPM Gal/hr Kts TAS EGT miles/gal Gal/100 Time/100
Nm miles Nm miles(min)
2200 6.9 144 20.87 4.79 41.67
2200 7.6 148 19.47 5.14 40.54
2200 8.2 150 18.29 5.47 40.00
2200 8.5 154 18.12 5.52 38.96
2300 8.1 155 19.14 5.23 38.71
2410 8.3 156 18.80 5.32 38.46
2500 8 160 1410 20.00 5.00 37.50
2500 8.2 160 1400 19.51 5.13 37.50
2500 9 160 1330 17.78 5.63 37.50
2500 10 158 1230 15.80 6.33 37.97
2600 8.3 163 1430 19.64 5.09 36.81
2600 9 163 1380 18.11 5.52 36.81
2600 9.5 163 1340 17.16 5.83 36.81

 

[smokyray]

Hmmmm?

Chuck, Are you using reflex flaps or are you just posting RV7A performance info on the RV4 forum?
Rob Ray
RV4ormerly
HR2

ps: I know, cause I'm guilty of the same posting ROCKET numbers...