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Vx, Vy rates

rjcthree

Well Known Member
I've done some searching and found a little bit on information, but directly not related to RV-9/9A.

For those of you flying, can you provide:
Vx and climb rate at solo/light weight
Vy and climb rate at solo/light weight
An estimate of what that solo/light weight is
Your engine (HP) and prop combination

From this we should be able to generate a deck angle for fuel flows, and I can put estimates into my program schedule for my prelim POH ;). I'll summarize and report back for future travellers. Even partial information would help. Either response here or IM works.

Thanks in advance. Rick
 
good idea....please publish!

Great info to see,
so far, I'd say not a lot of replies as a good chunk of folks don't have real hard data except for the initial test flight or two...you just never get around to correcting for temp, and repeating at all different weights and loading ( I suppose most just test at gross???)
Once you see that the -9 climbs at this or that IAS, that's as far as most of us go. More elusive even are takeoff & landing DISTANCES!

I'll dig mine up and send to you.
thx for doing this!
 
My starting point . . .

This was a starting point i used on my RV-9A and adjusted after Phase 1 testing.

Configuration:
IO-320 (165HP)
F/P Prop

Your numbers must be verified during Phase 1 testing:

VNE Never Exceed Speed 182 kts
VNO Maximum Structural Cruising Speed 156 kts
VA Maneuvering Speed 102 kts
VFE Maximum Flap Extended Speed 78 kts
Vy Best Rate of Climb 81 kts
Vx Best Angle of Climb 70 kts
Vs Stall Speed, Clean 50 kts
Vso Stall Speed, Landing Configuration 43 kts
 
If it is not too much trouble, Sir: Frederic.magare "at" gmail.com

Thank you for your time and consideration.
 
I would like a copy of that report also please - greg dot niehues at ngsgi dot com.

I'm curious what this means, could you expand on it a little?

I think he's talking about testing the fuel flows on the ground before first flight, making sure the flow is adequate with high nose-up angles where the fuel is pumped "uphill" to the engine.
 
For fuel flow deck angle you want the worst case (highest angle) which is Vx at light weight. But since the target fuel flow for the test is usually 150% of max fuel burn of the engine the deck angle doesn't have to be very accurate.
 
So.. we are talking about calculating path through the air PLUS angle of attack plus or minus incidence angle in order to measure attitude at top surface of canopy rails.

Gas tanks should be nearly empty (for minimum head).

I think this test has little relevance to a fuel pumped system other than a yes/no answer on fuel flow which would mean there is a fuel system problem other than deck angle. The change in head requirements will be small compared to pump output pressure.

OTOH, This test is critical for gravity fed systems and the flow rate data would be much more variable and relevant.
 
So.. we are talking about calculating path through the air PLUS angle of attack plus or minus incidence angle in order to measure attitude at top surface of canopy rails.

Gas tanks should be nearly empty (for minimum head).

I think this test has little relevance to a fuel pumped system other than a yes/no answer on fuel flow which would mean there is a fuel system problem other than deck angle. The change in head requirements will be small compared to pump output pressure.

OTOH, This test is critical for gravity fed systems and the flow rate data would be much more variable and relevant.

A yes no answer on fuel flow is pretty important if you want to survive your first flight. And there are any number of construction errors that could reduce fuel flow for a pumped system.

A friend of mine bought the wrong electric fuel pump. There is one kind that has a bypass and one that doesn't. He didn't bother to do the fuelflow test and found out in the air that when he turned off the boost pump the engine quit. It could not run on the mech pump alone.

So this test is fundamental for first flight safety for any type of fuel system.
 
You completely missed my point. Of course a fuel flow test is important before first flight. My point is that to expect a measurable fuel flow rate change due to attitude on an RV is not realistic.
 
Interesting how much discussion there is on an assumed test protocol wwith an assumed test objective. Unless that test is documented, then one can not effectively engage with the usefulness of the test. RZBill is right, flow is not a pass fail criterion, at least vs gravity vector angle. It is valid for pass/fail of a pump. 125% of TO fuel flow at minimum supply pressure to carb or FI is the tipping point.

Dave Prizio did an EAA webinar on unusable fuel testing and it was better than the AC to which it referenced. Having participated in a ground test, it is good to see if there is air in the system being pumped to the carb or to the injection system, and if there are any fuel leaks. A static 30 pis air pressure test is best for finding a leak, but it is prudent to enable an observation of same during a unusable fuel test. Neither Daves, or the AC, should be followed blindly. One should consider the location and effects of fuel pickup points in the tank to fully develop conditions for a model/plane specific test sequence.

A nose up, nose down test at minimum pressures, measuring fuel flow for cruise and max TO is simply a test condition for the unusable fuel. The suction test needed is to measure the absolute pressure to the inlet of the mechanical pump under the power stall nose up condition. Then using vapor pressure, one can determine if cavitation is likely to occur for the fuel selected. It may be fine for 100LL, but fail for 100% auto gas. Slip testing is also needed to complete the unusable fuel testing, but it will be a flight test, tricky as it is.
 
For fuel flow deck angle you want the worst case (highest angle) which is Vx at light weight. But since the target fuel flow for the test is usually 150% of max fuel burn of the engine the deck angle doesn't have to be very accurate.

Agree, and I'd add that the worst case is actually full power, nose-high stall. That will have a significantly different deck angle than would a full power Vx climb.
 
Here are my numbers.

xo-320 RV-9

Vne
Never Exceed Speed
182 KTS
210 MPH

Vno
Maximum Structural Cruising Speed
156 KTS
180 MPH

Va
Maneuvering Speed
102 KTS
118 MPH

Vfe*
Maximum Flap Extended Speed
78 KTS
90 MPH

Vglide
Best Glide Speed
82 KTS
95 MPH

Vy
Best Rate of Climb
82 KTS
95 MPH


Vx
Best Angle of Climb
71 KTS
82 MPH


Vs
Stall Speed Clean
50 KTS
58 MPH


Vso
Stall Speed Landing Configuration
43 KTS
49 MPH
 
Hint

Before you do the V testing make sure your airspeed has been calibrated. Spent some time with stall and AOA before I established my airspeed indications were off.
 
AOA

For those of you with AOA, assign a specific angle to each Vspeed. Hold that AOA and the Vspeed will follow. For example if Vx is 8 deg AOA, go to and hold 8 deg, and the airplane will settle at Vx some moments later and there's no under shooting or over shooting the airspeed. Very handy at a short field with trees at the end. This is really what flying AOA is all about, not just for stall warning.
 
N183RC results

Thanks everybody for the help/info.

After IAS calibration and halfway through Phase 1, N183RC V speeds are as follows:

Vx = 75kt
Vy = 95kt
Vg = 80kt (Best glide defined as best distance)
Vg, 10 deg flaps = 75kt
The slope of the curves is very shallow around the respective optimal number, +/- 5kt on most V speed is within 10% of optimal. Based on the data, I could call Vy anywhere between 89kt to 98kt, because the curve is dead flat in the range, for operational purposes, I like the higher speed for cooling reasons. Coming out of a Warrior, the deck angle vs horizon at Vx is pretty mind boggling. AC is RV-9A, 1113 empty, o-320/160hp, fixed Sensenich.
 
Last edited:
6 years flying my 9A
0320 dual lightspeed, fuel injected, catto 3 blade

VNE Never Exceed Speed 210 mph
VNO Maximum Structural Cruising Speed 180mph
VA Maneuvering Speed 124mph
VFE Maximum Flap Extended Speed 95mph
Vy Best Rate of Climb 90mph
Vx Best Angle of Climb 80mph
Best glide speed 75-80mph
Vso Stall Speed, Landing Configuration 54mph
 
I'm sure I'll be corrected if I'm wrong, but my recollection is that Vy equals best glide ratio and Vx equals minimum sink speed as well as being best angle and rate of climb speeds respectively.
 
I'm sure I'll be corrected if I'm wrong, but my recollection is that Vy equals best glide ratio and Vx equals minimum sink speed as well as being best angle and rate of climb speeds respectively.

You are wrong, but correct me if I'm wrong
 
The best climb/best glide and best angle/min sink are starting points.

FAA sez:

"This is often referred to as best glide speed and, on most airplanes, it will be roughly halfway between Vx (best angle of climb speed) and Vy (best rate of climb speed). Keep in mind that this speed will increase with weight so most manufacturers will establish the best glide speed at gross weight for the aircraft."

https://www.google.com/url?sa=t&sou...WBNoQFggkMAA&usg=AOvVaw0kwH91JS_D_osCZnW3dTaV
 
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