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Speed test on RV-4

B

britt fincher

Member
I'm going to look at an Rv 4 with a three blade Catto, XP-360 engine, aprox. empty wt. 1040 pounds. I would like to see if the aircraft will come close to Vans cruise performance numbers. Anyone know a good way to do an accurate speed check on a short test flight? What are some IAS numbers I should see at what altitude and RPM settings?

Thanks
 
Just fly 3 or 4 headings 90 degrees apart at the same altitude and power setting and then average the ground speeds. That will give you true airspeed.

I.E. 360 = 167 kts, 90 = 164 kts, 180 = 162 kts, 270 = 160 kts

That averages out to 163.25 kts.
 
7500'

Britt, Van's numbers are obtained at 7,500' or so. Down low will be way off. Top speed is usually also WOT.

My RV-10 picks up 15 mph up high.

Best,
 
ASI readings can be significantly different from airplane to airplane. I would recommend flying beside another RV and comparing notes. If possible find an RV that has flown a lot, and has a calibrated ASI system.
The three/four turn gps works well but power levels vary significantly based on air temperature. Using this system, to three or four reps, you can work backwards to compare true airspeed to what your ASI is reading.
Another quick and dirty test of your ASI system is to do a low pass over your runway and compare the altitude reading with what you are actually flying. This will show static error.
 
Britt,
If the -4 has a GPS or you have a portable, the ground speed may give you a more accurate indication of top speed.

As for the other speeds, you'll need to do flight testing and compare Van's numbers (a good Benchmark) to what the ASI shows get a sense of how that ASI/Static Sys compares to others' results. It's fairly relative.

You would also enjoy reading an article Van wrote years ago about the ASI.
I think he called it "The Instrument That Lies", its probable on VAF.

Good Luck,
Glenn Wilkinson
 
Unless severely "mis-propped" it's hard for an RV-4 not to make Van's numbers under similar conditions--doubtful that would be the case with a Catto. Craig generally has a design point for maximum performance (MPH/Knots at XXXX feet, engine at max RPM), there may be a sticker on the propeller hub with this information. If the airplane has MAP and tach, the following rule of thumb will help: MAP (inches) + RPM/100 = % power. When the total is 48, you're at 75%; 45 65% and 42 55%. You can interpolate, with 3% ~ a difference of one in the sum. Since the engine produces roughly 75% power at WOT at 8000 feet, a quick speed run at that altitude will give you a rough hack. The 3 knots/MPH per 1K altitude TAS ROT is very conservative at low altitudes, so that will help you with a WAG adjustment if you don't check at 8K'. RV-4's are capable of exceeding Vno in level flight, and can even exceed Vne (especially at high altitudes) with the right prop. As I'm sure you're aware, red line is a function of equivalent (de facto true) airspeed. Individual airplanes will vary in the quality of airspeed calibration testing, however; but regardless, unless there is a serious deficiency, it'll probably be fine (in terms of CAS/TAS corrected to standard atmosphere).

Cheers,

Vac
 
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Rv 4 speed test

Thanks for the reply. Did the speed test yesterday. 8000 MSL, 2400 RPM, no MP gauge, little warmer than standard day. Four heading method on the GPS ground speed average speed 171 MPH, 2% method around 181 MPH. We were a little below max gross of 1500. Speeds seem a little slow for a 180 HP RV 4. Any thoughts?

Thanks
 
Was it wide open? If so it is propped too coarse.

My 2600 RPM limited prop will give me 190MPH TAS at 8000. O-320 with 160 HP at 2700.
 
It was not wide open. Max RPM would have been more like 2750 RPM. IAS only around 136 knots. Four ground speeds in MPH were; 173, 173, 163&178.
 
Vac is correct that there is simply not enough info to give you any accurate feedback. Edit: What happened to Vac's post?

I will say that on the surface... It looks like you were cruising around at about 60% power and the speeds would agree.

75% at 8000 DA is wide open for the most part RPM isn't a factor in that 'rule of thumb'. That's where Van's numbers come from.

Is this airplane painted silver with stars and bars? If it's the airplane I'm thinking of then I'm betting you were just running at 60%.
 
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Your GPS observed average speed is a rough approximation of TAS (i.e., no conversion required) and if you observed 136 knots IAS, then the airspeed system does seem to be roughly in the ballpark, i.e., a TAS of 175 MPH, standard atmoshpere requires a CAS of about 136 Knots.

Unfortunately, without MAP, it's not possible to determine the amount of power the engine is producing. If you have access to the Lycoming curve and the engine is configuration for which data is available, you can somewhat "reverse engineer" a ballpark number that may help, based on the limited data you have available.

The purpose of the WOT throttle @ 8K' test is simply to WAG 70-75%--a known point. If engine red line is 2700 and the prop is capable of turning 2750, it's likely pitched about right for cruise; but it's difficult to determine unless you have the prop data. If it's not on the sticker on the hub or in the logs, then a S/N for the prop and a call to Craig may help sort things out.

Unfortunately, without proper flight test you just don't know. What you're seeing may be reasonable performance based on engine configuration/rigging and prop.

If you have any questions, don't hesitate to drop a line or PM.

Best of Luck,

Vac

P.S. Sid--I had to do a quick edit when I saw the new data pop up! I think you are correct, and it's likely the engine is producing about 50-60% power.
 
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rv-4 speed

Hello James

I just did a WOT speed test as per Craig Catto recommendation to find the max RPM of my prop due to a porting & balancing job.

At 7500, ( DA 6500, ) WOT , 2800 RPM, 174 KNOTS, still increasing when I pulled the power back.

The aircraft is an RV-4, O-320 E2D, 160 HP +, 8.5 to 1 pistons. Catto 3 Bladded prop .

YMMV

Bruno
 
RV-4 said:
Hello James

I just did a WOT speed test as per Craig Catto recommendation to find the max RPM of my prop due to a porting & balancing job.

At 7500, ( DA 6500, ) WOT , 2800 RPM, 174 KNOTS, still increasing when I pulled the power back.
Click to expand...

Weird that he would “recommend” a WOT at 6,500 DA. I have been testing his next generation 3 bladed prop for about 2 months now. He has asked me to evaluate it at WOT between 7500-8000 DA. I have been doing all my level testing at 8000 DA.

This is the data he likes to look at:
Max RPM on ground.
Climb at 110kts and collect the RPM
RPM TAS
2100 ?
2300 ?
2500 ?
2700 ?
WOT ?
 
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RV-4 SPEED DATA

Hi Axell

''Weird that he would ?recommend? a WOT at 6,500 DA''

Well that is what he asked for..A flight at WOT at a 6500-7000' DA..

I'm going flying tomorrow and time permitting I will redo the test using your specs and will right them down in case Craig needs them..

Are you flight testing his new Carbon Fiber 3 bladded prop?

If so, if possible, could you share your feelings about it as I'm thinking of getting one to replace the one I have now..

I will like one with the nickel leading edge so I can fly it in rain if require .

Thanks

Bruno
 
Your mileage may vary...

britt fincher said:
I'm going to look at an Rv 4 with a three blade Catto, XP-360 engine, aprox. empty wt. 1040 pounds. I would like to see if the aircraft will come close to Vans cruise performance numbers. Anyone know a good way to do an accurate speed check on a short test flight? What are some IAS numbers I should see at what altitude and RPM settings?

Thanks
Click to expand...

Britt,

As you and I previously discussed, people tend to inflate several items, ego and TAS are in the top five! :)
A properly propped rigged and faired 180HP RV4 should easily achieve 150 Knots below 5K at 2400 RPM. WOT at 5K should be close to Max engine RPM (2700) and 170 KIAS. Above 8500' WOT should be 170-175 KTAS. Most 4's exceed these numbers and a well tweaked 0-320 RV4 will nearly match all of the above.

The Fastback RV4 is faster, by definition...

V/R
Smokey
 
RV-4 SPEED CHECK

Hi Axel

Thanks for the link, I will have a look at it.

Yesterday I did another speed test with my -4 using your parameters but I left my notes in the a/c..I will pick them up tomorrow and post them .

I remember my WOT RPM to be around 2760-2770..So it might be slightly underpitch now ..

Bruno
 
RV-4 SPEED TEST

Hi Axel

Here's are my numbers, slightly slower than yours but about the same at WOT.

0-320 E2D 160 HP 8.5 to 1, Ported & flow balanced by Lycon.

Alt: 9000' / DA 8120 / Temp : -3 C Alt : 30.66
RPM/TAS
2100 : 121
2300 : 134
2500 : 148
2700 : 161
WOT : 165

MAX RPM : 2770, I'll see what Craig thinks of these numbers and if they can be improved..

The rate of climb at 110 Kts was amazing : initial 2350' / min.

Really amazing what these machine can do..

Bruno
 
I went up and collected some (non inflated) data with my similar set-up.

RV-4 O320 E3D w/8.5:1 pistons. PR wheel pants

Catto 3 blade w/stainless leading edges. 68" dia X 71" pitch

8000' DA. 41 degrees F

WOT 2820 RPM / 22.2" mp / 163 KTAS / 9.5 GPH

2600 RPM / 20." mp / 148 KTAS / 8.0 GPH
 
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Hmmmm???

Spike,

I have recently started testing my RV4 after a 20 year build and have a similar engine set up to you E2A with 8.5/1 pistons and a lightspeed ignition.

Differences are that I have made my own sealed plenum and am running Sensenich metal prop, and I have the old style pants, but latest leg fairings.

Now whats making me go Hmmmmm?

I am keeping the RPM up to 2400 as am breaking in the engine and have only flown to 3000 ft...... but am seeing 175mph/ 152 kts which appears to be verified by the GPS. I say appears to be because I have not actually run a box speed check yet although I have flown down/up/and crosswind legs which tend to make me believe the speed is accurate. However, when I look at the speeds AX-O got on his tests with the Catto I think my ASI might be optimistic!!

I will try to run proper tests in the next few days but the WX in the UK is really poor in the UK at the moment.
 
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My -4 speed today

I was fly to TCY for some formation work so I wrote down the speeds
Alt 9500 OAT 40F BAR 30.19
110kts climb 2130rpm 1350fpm starting at 4700' msl
WOT Static 2100 rpm
RPM TAS IAS
2100 138kts
2200 147kts
2300 153kts 129kts
2400 162kts 138kts
2500 171kts 145kts
2590 177kts 152kts
 
Engine

It is an O320-E2D with 8.5/1 pistons, E-Mags,Catto 3 blade prop
My airplane is straight and light, 945# ready to fly and the RED paint has a lot to do with speed:D
When I built the wings I raised the ailerons flush with the bottom of the wings, There is a 3/8" spacer under the horizontal spar, I have the new wheel pants.
 
More data for the list...

Stock O-320-D2J (160), two-blade 2nd generation Catto (68x72)...no red paint, so that definitely costs some knots!



Cheers,

Vac
 
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AX-O said:
Thought you had 10/1 helicopter pistons :confused:
Click to expand...

After overhauling #2 cylinder of late I am not sure, I will ask my engine builder and get back to everyone, During my initial engine overhaul we had talked about the benefits of 10/1 at our altitude now I am not confident he installed them
 
AX-O said:
Thought you had 10/1 helicopter pistons :confused:
Click to expand...

Dayton Murdock said:
I was fly to TCY for some formation work so I wrote down the speeds
Alt 9500 OAT 40F BAR 30.19
110kts climb 2130rpm 1350fpm starting at 4700' msl
WOT Static 2100 rpm
RPM TAS IAS
2100 138kts
2200 147kts
2300 153kts 129kts
2400 162kts 138kts
2500 171kts 145kts
2590 177kts 152kts
Click to expand...

Well after tracking down my engine builder it has been confirmed that my O320 E2D has 8.5/1 pistons and is flying theses number
 
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