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Elevator control

Barbeau

Barbeau

Member
I just got a RV6A, and it seems performances are a bit far from Van's data.
I did some tests and what I found is the following
AT 65% power (engine is O360), aicraft leveled, cruise speed is about 140kts at 3000Fts :(
Cruise speed seems a bit low, and what I saw is the elevator control a bit pitch down, counterweight is about 1/2' over top surface.
So it means more drag.
First of all I thing that the elevator control should be perfectly straight with elevator.
Do you thing it has small or great impact on cruise speed ?
How to fix it? (engine or elevator)
Many thanks in advance
Bernard
 
I think most of us have a small amount of counter weight showing. I shimmed the HS up some for a little help. Made no difference in speed.
IF you have a problem I doubt that will be the place to fix it.
 
Vans wants a small amount of down elevator in cruise. I think I read that his theory is that it maintains a load on the elevator system and reduces the chance of inducing flutter. Some guy remove all of the down elevator and they haven't vibrated out of the sky yet.

Barbeau said:
I just got a RV6A, and it seems performances are a bit far from Van's data.
I did some tests and what I found is the following
AT 65% power (engine is O360), aicraft leveled, cruise speed is about 140kts at 3000Fts :(
Cruise speed seems a bit low, and what I saw is the elevator control a bit pitch down, counterweight is about 1/2' over top surface.
So it means more drag.
First of all I thing that the elevator control should be perfectly straight with elevator.
Do you thing it has small or great impact on cruise speed ?
How to fix it? (engine or elevator)
Many thanks in advance
Bernard
Click to expand...
 
TAS or IAS

Bernard, is your reported speed True or Indicated? Depending upon temperature, if it is indicated you are not that far off. Have you calibrated the Airspeed indicator using GPS to know it is accurate?

Vic
 
vic syracuse said:
Bernard, is your reported speed True or Indicated? Depending upon temperature, if it is indicated you are not that far off. Have you calibrated the Airspeed indicator using GPS to know it is accurate?

Vic
Click to expand...

Hello Vic
It's true air speed, calculated by AFS 3500. I did some cross check With GPS and KTAS is rearly accurate.
 
Stab incidence and elevator position can help with a couple of Kts.
Your are ~ 15 kts slow.... You need to be looking for other causes.
 
Do you have all the upper and lower intersection fairings installed? Late style pressure recovery wheelpants?

Also try 75% power at 7,500' where they are fastest.

Best,
 
how do you know you have 65% power? Are you basing that on MAP? Do you have constant speed prop? If not what prop? Vans numbers are only applicable for a specific engine/prop combination. Elevator is not going to make any significant difference. In fact, if the stabilizer load is high, a slight elevator deflection will be more efficient, because at higher CL a cambered airfoil is more efficient.

The things that slow you down are things that have a wake. Antennas, things sticking out, bad seams, poorly faired landing gear, anything that is going to have turbulence behind it. A slightly deflected elevator is not going to make any significant difference.
 
I'd start off by trying to verify 65%..

If you go to 8000' density altitude and run wide open that should be around 75%. Get your true air speed from that using the GPS. If you only gain 5 kts true at 75% then your 65% numbers are probably correct and you can start looking for issues. Drag or power/propulsion.

If you true at 170 kts at 8000 DA and WOT then your 65% numbers are just wrong and you don't have anything to fix.
 
Clean the Airfilter

Hello,

we recently cleaned the airfilter and gained about 50 RPM!

It was not really dirty, but had too much oil in the filter (from the supplyer).

Check this! Maybe you gain a bit.
 
Hello
I'm back with much more accurate performances of my RV6A

First of all, my RV6 is fitted with:
O360, Presicion carb M-A 4-5, Lasar ignition, propeler MTV 12-B /183-59, Exhaust pipeVetterman Cross Over, Exhaust silencer Liese76x150-L
All fairing, wheels pants installed, slide canopy.

Tests have been done with 4 legs at 90?

First test: 2500 Fts, temp:19? C, QNH 1018
RPM 2300 MAP 22.5 (65%), FF 8.7G/H
4 legs Average values
IAS 136Kts KTAS 143Kts GPS 143Kts

Second test:4500Fts, temp 17?C, QNH 1018
RPM 2300 MAP 22.5 (65%), FF 8.4G/H
4 legs Average values
IAS 133Kts KTAS 146Kts GPS 147Kts

What do you thing about those figures?
I thing it's a be low.
Bernard
 
More power

You really ought to go to 7,500' and run it wide open, full throttle. You'll be making around 75% power and that's where Van's numbers come from, not 2300 RPM and low altitudes.

Best
 
Ahh, Exhaust silencer Liese76x150-L

Describe what this is.
Many of them used in EU are huge and mounted on the belly. It could be causing a large drag penalty (as well as some HP loss)....


Barbeau said:
Hello
I'm back with much more accurate performances of my RV6A

First of all, my RV6 is fitted with:
O360, Presicion carb M-A 4-5, Lasar ignition, propeler MTV 12-B /183-59, Exhaust pipeVetterman Cross Over, Exhaust silencer Liese76x150-L
All fairing, wheels pants installed, slide canopy.

Tests have been done with 4 legs at 90?

First test: 2500 Fts, temp:19? C, QNH 1018
RPM 2300 MAP 22.5 (65%), FF 8.7G/H
4 legs Average values
IAS 136Kts KTAS 143Kts GPS 143Kts

Second test:4500Fts, temp 17?C, QNH 1018
RPM 2300 MAP 22.5 (65%), FF 8.4G/H
4 legs Average values
IAS 133Kts KTAS 146Kts GPS 147Kts

What do you thing about those figures?
I thing it's a be low.
Bernard
Click to expand...
 
Hello
here is my muffler. I took of from the Liese site
F-PSAK-3.jpg

F-PGAK is my RV6
 
Listen to Sid and Pierre

Post #10 and Post #13 should be your starting point. Pierre and Sid are spot on with the right advice.
 
Thanks a lot for advises.
As you say, I'm gong to test at 7500 Fts with mufflers and without. It Could be a tiny improvement
Have a Nice WE
 
Hello
I took away the silencers LIESE, replaced by turndown pipe from Weterman.
A quick test report.
Climb ratio improvement by 300 Fts/mn. I felt improvement as soon as I put full throttle.
Cruise speed at 65% (MAP 22.5 RPM 2300 FF 8.5 USG/H) improved by 7 KTAS (150 KTAS)
I'l come back soon with a much more d?tail report.
For sure the silencers are drag producer, but the main impact is on engine torque loss and of course on output power
An other unexpected effect is CHT lower and much better balanced
Thanks to all of you for advices
 
Cruise speed

Part of your problem is your RPM.
If you have a constant speed prop, you really should be running around 2400 to 2500 rpm.
This should get you several more KTS out of your bird.
I have had several 180hp engines and they really seem smoother at 2500 range.
A decent 6A with a 180hp should be cruising in the 165KTS range down lower and up to 170-175 up higher.
Running down in the lower rpm range saves gas but does not make you go faster.
My RV-6 WOT and 1500ft would top out at 190kts, doing at 4 way speed test.
You should have a 1/8" shim under the front Horz stab spar. IF you don't then the angle of incidence might be off and causing some slight drag.
A Harmon Rocket gained 17mph by getting his AOI correct on his horz stab. He was dragging his tail through the air......
 
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