Xkuzme1

Xkuzme1

Well Known Member
I have an RV-4. I did not build it. I am not sure I agree with the VX and XY speeds that the builder had attached to it.

Are there Reccomended speeds from Vans?

What are some of y'all's speeds gathered from flight testing?

If I disagree, as the owner (not the manufacturer) can I just make changes to the limitations/specifications? I thought that I read someplace that only the builder could change the limitations/specs?

Thanks.

X
 
Van's recommendations for V speed markings are in section 15 of the construction manual. They now supply that on CD at very little cost.

Those are:
White arc 54-100 MPH (110 for partial flap)
Green Arc 58-180 MPH
Blue line 134 MPH
Yellow arc 180-210 MPH
Red line 210 MPH

Vx and Vy need to be determined for individual aircraft.
Because they are sensitive to the propeller type, power output, aerodynamic cleanliness etc they can't generalise.

It explains how to do that in the manual, but basically you need to measure rate of climb at different airspeeds and aircraft gross weights.

I'd expect to see Vx in the 75-100MPH range and Vy in the 100-140 range at normal gross weight.

And, as Bob said, they are not limitations, just good to know.

Even the other speeds are not limitations as such. You could in principle determine new values and demonstrate them in phase 1 flight testing, but you'd be ill-advised to ignore Van's recommendations.
 
In my RV6, Vx is about 85 mph IAS and Vy is about 105 mph IAS just like Vans predicted. I prefer to climb about 120 mph indicated for cruise climb. That's about 2450 rpm for fixed pitch (well ground adjustable) prop and 160hp O-320 engine.
 
Last edited:
V Speeds

Todd,

Mark lays it out very well. If you want to peel the onion back farther:

The V speeds that are defined by the designer and typically addressed for most aircraft are listed in the limitations section of the RV-4 handbook for our airplane that is posted in the POH section of this site--they were obtained from the builder's manual (you can buy a set of preview plans with the manual from Van's if you don't have a copy). Performance data for our plane is in the performance section as well (fixed pitch Catto/160 HP). As a rule of thumb, you can take Van's published numbers to the bank as long as you allow for weight/configuration differences (generally how the airplane is propped). This assumes that proper pitot/static ground and flight test as been accomplished and aircraft specific system performance has been validated (i.e., CAS vs IAS so you can do an apples to apples comparison). Not everyone takes the time to dial in their system or test for error.

The flat drag curve for RV's yields good cliimb performance over a wide speed band, so for typical operation, engine cooling (CHT) can take priority during normal cruise climb. Vref is 1.3-1.4 Vs, L/D max is about 105 MPH and Carson's Number is about 140 MPH for an RV-4. I put some rules of thumb and other info in the transition training syllabus over on the safety page (Part 3 and appendixes). There is also discussion regarding maneuvering speed as it applies to RV's if you're interested.

You could utilize bootstrap techniques for deriving specific climb and glide performance data with your fixed pitch installation or conventional techniques described in AC 90-89B. Google "bootstrap flight test" for more information if you are curious.

As owner/operator, you may now experiment with the airplane in accordance with your operating limitations. They may be amended by a DAR or FSDO, and proper testing and documentation can superceed any entries in your airframe log. Similar validation/modification logic applies to checklists or handbooks (if they exist) for your airplane.

Cheers,

Vac
 
Last edited:
Your mileage may vary...

Xkuzme1 said:
I have an RV-4. I did not build it. I am not sure I agree with the VX and XY speeds that the builder had attached to it.

Are there Reccomended speeds from Vans?

What are some of y'all's speeds gathered from flight testing?

If I disagree, as the owner (not the manufacturer) can I just make changes to the limitations/specifications? I thought that I read someplace that only the builder could change the limitations/specs?

Thanks.

X
Click to expand...

Todd "X",
As mentioned above, The RV4 speed range is wide and allows a great range of maneuvering. I recommend you treat it like any airplane at first. Learn, then do. Once you start really flying it you can takeoff, climb to a safe altitude and practice slow flight, stalls and maneuvers, then get into more fun stuff. My initial test flight on my RV4 was my first RV flight. The book numbers were close, but as you will find, every airplane is slightly different. Remember, these are Experimental...I don't recommend changing the operating limitations, but learn your personal limitations.
I'm not fond of V speeds, unfortunately I have to use them every day at work. I'd rather talk AOA or even more simply, "butt" speeds.

These are by no means hard and fast RV4 numbers, your mileage may vary. This works for a FP prop, 160-180HP. CS numbers are slightly different depending on prop.

Takeoff: 60 Knots
Initial Climb( for obstacles) 80 Knots
Best climb 100 Knots
Cruise climb (for extended climbs) 120 Knots
Acro entry 130-180 (150 best IMHO)
Stall with flaps 45-55 Knots depending on indicators, EW and HP. Docile stall.
Final Approach speed full flaps 60-75 Knots depending on strip length.
I operated mine from a very short strip (900') for many years and practiced flying final at 60 Knots, every landing

Practice makes perfect...
V/R
Smokey
 
Last edited:
You must log in or register to reply here.