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V speeds for a RV-6

L

Leonard_Smith_nz

Active Member
All,

I'm starting to do some advance preparation work for my test flying and would like to get a 'feel' for the RV6 V speeds. I've looked online at a few POH and noted the numbers shown below.

I appreciate that test flying is all about how YOUR aircraft performs, but as a starting point, do these look in the ballpark?

Vr 55 kts (63 mph)
Vx 65 kts (75 mph)
Vy 75 kts (86 mph)
Vcc 100 kts (115 mph) (Cruise climb)
Va 115 kts (132 mph)
Vno 155 kts (178 mph)
Vne 180 kts (207 mph)
Vs 48 kts (55 mph)
Vso 43 kts (49 mph)
Vfe 90 kts (103 mph)
Vgs 70 kts (80 mph)

BTW, is there a recognized abbreviation for 'cruise climb'?

Regards,
Leonard (RV6 in New Zealand)

Engine: TMX-O360 180hp
FP Prop: Sensenich 85"
 
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The Vx and Vy numbers depend tremendously on whether you have a fixed pitch or a constant speed prop.

I have a fairly aggressive fixed pitch cruise prop and my Vx is probably 80 knots and Vy is over 100 knots. Below those speeds, the engine simply isn't turning fast enough.

At heavy weights, the Vx and Vy are even higher.
 
What is your V speeds?

I have seen 75mph as a Vx in a few POH on this forum but not sure what engine/prop combo that was for. I have a 160hp / FP cruise prop -6A and at 85mph the nose is rediculously high and can't imagine 75mph. What airframe, engine /prop combo do you have and what are you V speed?
 
Corrections

Hi Leonard,
Our best rate of climb is around 135 MPH for 1700 FPM and cruise climbs at 150-160 MPH still yield over 1000 FPM. We weigh 1065 Lbs with a FP Catto three blade.

Regards,
 
Leonard:
Some years ago the CAFE foundation conducted a comprehensive flight test on an RV6A. Typically, these tests are carried out with calibrated test equipment rather than builder installed/non-calibrated hardware and cover a wide range of performance characteristics. You can see this and other RV reports on:
www.cafefoundation.org
Click on "Research and Publications", then on CAFE APRs.
Good luck with your testing.
Terry
 
Here's ours...

AIRSPEED LIMITATIONS
SPEED KIAS REMARKS
VNE Never Exceed Speed 182 Kts Do not exceed this speed in any operations.
VNO Maximum Structural Cruising Speed 156 Kts Exceed this speed only in smooth air.
VA Maneuvering Speed 115 Kts Do not make full control movements above this speed. Full elevator deflection will result in a 6g load at this speed.
VFE Maximum Flap Extended Speed 96 ?20 deg
87 - Full Do not exceed this speed with flaps down
Vy Best Rate of Climb 103 Kts
Vx Best Angle of Climb 65 Kts
Vs Stall Speed Clean 47 Kts
Vso Stall Speed Landing Configuration 43 Kts
 
V speeds

The numbers found on Van's website and in the manual are the ones to use, and verify. There will be some variation depending on weight, CG, but they are close. I would concentrate, initially, more on ensuring the accuracy of the airplane's airspeed indicator, as best as possible, via ground and flight test.

Maybe it's early, but I don't think Vy is affected by prop type. Vy is an airspeed, and is primarily determined by the wing, secondarily by weight and operating CG, while the resultant RATE of climb will certainly vary with HP/propeller. Right?
 
wv4i said:
Maybe it's early, but I don't think Vy is affected by prop type. Vy is an airspeed, and is primarily determined by the wing, secondarily by weight and operating CG, while the resultant RATE of climb will certainly vary with HP/propeller. Right?
Click to expand...
It's early.

The rate of climb is determined by weight and excess power. Excess power is the power available minus the power required to maintain level flight at that speed, weight, etc. The power required for level flight at a given weight won't be affected by prop type. But, the power available will. For a given engine at full throttle, the power available at a given altitude and temperature varies with rpm and prop efficiency.

If you have a constant speed prop, the engine can develop max rpm at any speed. So Vy will probably be very close to the speed where the minimum power is required for level flight (variation in prop efficiency with speed will probably make Vy very slightly faster than the speed for min power required). But if you have a fixed pitch prop, the rpm (and hence the power) will be higher the faster you fly. So Vy will be a faster speed than for a constant speed prop.
 
Best Glide

Best Glide and perhaps some other speeds can only be correct at one point on the lines for density altitude and aircraft weight. I'm not sure that this applies to all speeds, but it does apply to many of them. Angle of attack is a more consistent indicator. I know that POH's use speed, but that doesn't change this.

If you can measure AOA, you can observe the speed and note it. AOA will be more correct over more varieties of situations.

Example (debated in this forum before, but I'm still convinced): Best Glide is about the same as Best L/D in no-wind conditions and giving away some errors from prop pitch, idle vs. stopped, etc. If you can determine the AOA at which you are A. maintaining level flight and B. using the least power then that's IMHO the AOA for best L/D. Why? because total drag is at a minumum as measured by power required for level flight and because the lift is a constant equal to the weight at that moment.

OK, now find the (different) airspeed at which the same AOA happens while engine is not producing power (you choose how realistic to make this). That's your best glide speed under those conditions.

Just a suggestion.
 
hevansrv7a said:
Example (debated in this forum before, but I'm still convinced): Best Glide is about the same as Best L/D in no-wind conditions and giving away some errors from prop pitch, idle vs. stopped, etc. If you can determine the AOA at which you are A. maintaining level flight and B. using the least power then that's IMHO the AOA for best L/D. Why? because total drag is at a minumum as measured by power required for level flight and because the lift is a constant equal to the weight at that moment.
Click to expand...
Not quite. The power required for level flight is equal to the drag times the speed (with the appropriate conversion factors to sort out the units). So, the speed for minimum power required is less than the speed for minimum drag.

For more info, look at the two plots of power vs speed, and drag vs speed in the Maximum Endurance, Maximum Range, and Optimum Cruise Speeds article on the EAA Chapter 1000 (Edwards Air Force Base)page.
 
Oops, but AOA right?

Kevin Horton said:
Not quite. The power required for level flight is equal to the drag times the speed (with the appropriate conversion factors to sort out the units). So, the speed for minimum power required is less than the speed for minimum drag.

For more info, look at the two plots of power vs speed, and drag vs speed in the Maximum Endurance, Maximum Range, and Optimum Cruise Speeds article on the EAA Chapter 1000 (Edwards Air Force Base)page.
Click to expand...
Well, Kevin, I am finally convinced! I only had to read the article about a dozen times. Thank you. It's great to have your expertise on the forum and this is the second time you've helped me understand an aspect of that drag curve.

Now we have a way, starting again with minimum power for level flight (MPLF). It just takes a little more work. and some graph paper. Those of us with PctPwr or FF readouts will have an easier time of this. When you've done the extra work described in the article, you have the speed at which least drag can be found and that's the AOA you want, with or without power. I don't think that the speed for MPLF is necessarily the same as best glide speed. Is it?

With the formula in the article and a little algebra, can we be lazy and just multiply the MPLF speed by 1.316 to get best L/D speed and take that AOA?
 
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hevansrv7a said:
Now we have a way, starting again with minimum power for level flight (MPLF). It just takes a little more work. and some graph paper. Those of us with PctPwr or FF readouts will have an easier time of this. When you've done the extra work described in the article, you have the speed at which least drag can be found and that's the AOA you want, with or without power. I don't think that the speed for MPLF is necessarily the same as best glide speed. Is it?

With the formula in the article and a little algebra, can we be lazy and just multiply the MPLF speed by 1.316 to get best L/D speed and take that AOA?
Click to expand...
The theory is good, so in principle you should be able to take MPLF times 1.316, and call that best glide speed. But, this only works if you use CAS. If you use IAS, the result could be affected by differing airspeed errors at the two conditions. The speed for MPLF will be fairly slow, so it is possible that the airspeed accuracy could be affected by significant static source position error. If you want a reasonably accurate result, you also need to do testing to establish the relationship between IAS and CAS.

The best L/D speed that you get from this method would be valid with prop removed, I think. It should be very, very close to the best glide speed with prop stopped. The best glide speed with prop windmilling will be a bit slower, I think, due to the extra drag from the windmilling prop.

If you measure glide performance with engine at idle you'll get a bit different result, as the effect of idle thrust or drag will vary with speed, and this will pollute the results slightly. But, given the risks of testing with engine stopped, this is probably a good compromise, unless you can minimize the risk by testing right overhead an airfield.
 
Glide Speed (AOA) & Prop Stopped speeds

:eek: 1) I have just installed an AOA on my RV6 (Dynon Skyview) This is new to me. How do I find my best glide speed using the AOA color bars?

2) If the engine quits in flight and the prop has stopped, Is it wise to increase the airspeed from best glide (80 kts?) to get the prop turning for a restart. (Only at a high altitude of course)
 
Bad Sheila said:
:eek: 1) I have just installed an AOA on my RV6 (Dynon Skyview) This is new to me. How do I find my best glide speed using the AOA color bars?

2) If the engine quits in flight and the prop has stopped, Is it wise to increase the airspeed from best glide (80 kts?) to get the prop turning for a restart. (Only at a high altitude of course)
Click to expand...

You do the same flight testing that you would do without an AOA system - i.e. record altitude vs time during descents at a range of speeds. Also record the AOA reading at each of these speeds. Do each speed twice - once with the wind off the left wing tip, and once heading the other way with the wind off the right wing tip.

After landing, calculate the rate of descent (ROD) for each run, and average the ROD for the two runs at each speed. Plot ROD vs speed and draw a smooth curve through the data. Draw a line from 0 speed and 0 ROD and see where it is tangent to the curve - that is the best glide speed.

Look at your flight data, and see what the AOA reading would have been at the best glide speed. That is the AOA for best glide.
 
Thread drifter alert:
Kevin,
How do you re-calculate max range speed and Carson's speed to account for winds aloft? If max range speed is 100mph, and you have a 100mph headwind, you may plow through a lot of air, but you don't get very far. If you have a tailwind, it would seem max range speed would shift toward max endurance speed.
 
fl-mike said:
Thread drifter alert:
Kevin,
How do you re-calculate max range speed and Carson's speed to account for winds aloft? If max range speed is 100mph, and you have a 100mph headwind, you may plow through a lot of air, but you don't get very far. If you have a tailwind, it would seem max range speed would shift toward max endurance speed.
Click to expand...

The easiest way to understand this problem is to consider the graphical method to determine these speeds. To find the speed for max range in the zero wind condition, you plot fuel flow vs TAS (or power required vs TAS, as fuel flow should be proportional to power). Draw a line from zero speed and zero fuel flow that is tangent to the curve. The point where this line touches the curve is the speed for max range. You can see an example in the Performance Charts section on this page on the EAA 1000 site.

If we want to see the effect of wind, we plot fuel flow (or power) against ground speed instead of TAS. If we have a head wind this shifts the curve to the left, and the tangent line hits it at a point which represents a higher TAS than in the zero wind case.

For Carson's speed, we do the same thing, except we plot drag against TAS (or against ground speed if we have wind to worry about).
 
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