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Speed Question

ebackscheider

Active Member
Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com
 
To measure cruise speed you need to specify altitude. Do you mean 142 kts true or indicated?

2300 rpm cruise for a FP is very low. I cruise at about 2550 rpm.

You're bleeding speed by pulling throttle back too far.



Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com
 
What are your TAS numbers? All the published numbers are true, not indicated, so that is the first place to start your comparison. Go up to 8,000ft density altitude. Run it wide open, note the RPM, TAS, FF and post those up.

EDIT: I see everyone beat me to it while I was yapping on the phone. I am a little slower than I would like, think my prop is a bit underpitched. I see 168kTAS at 8,000DA 2750 RPM. (O-360 FP Catto). I would expect about 172-3.
 
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Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com

shouldn't compare speeds without considering fuel flow and altitude, if looking to compare. I get 159 knots (TAS) at 2730 RPM at 8.1 GPH at 8-9000' with my IO-320 (EI) and FP prop. Your numbers seem low. Make sure you have accurately calculated TAS. Also need to do a 4 point GPS test to verify your static setup. Mine was off by 10 knots until I made a static port fence.

with an FP prop, you need to be turning much closer to 2600 or 2700 for higher speeds. 2300 is way too low. If that RPM is achieverd with WOT at 8000', you are WAY over pitched. Just my opinion, but a properly pitched prop should turn 2700 somwhere between 8K' and 12K' (based upon your goals) when WOT and 100* ROP.

Larry
 
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Thanks!

Thanks all!

I will go do a test, maybe even later today. 8000 ft density, wide open and report back on the speeds I see.

I guess my old days of 23 sq with CS are hurting me :(

Eric
 
Thanks all!

I will go do a test, maybe even later today. 8000 ft density, wide open and report back on the speeds I see.

I guess my old days of 23 sq with CS are hurting me :(

Eric

Just be sure the speed you are looking to see is True Air Speed, not indicated (as already mentioned)

Indicated air speed is nearly useless for doing speed comparisons.

Using my fixed pitch O-360 powered RV-6A as an example - At 11,500 ft and a fuel flow of 7.8 - 8.0 GPH I can get true air speeds of about 195 MPH but my indicated airspeed is often 160 MPH or less.
 
Some data

Did a short flight tonight

8,000 ft Density Alt
Turning about 2650 RPM

TAS right at 160 KTS - 184MPH

I don't have a fuel flow yet, so I have no idea where that was. The spike was some issue with the data.

Y1T9tRu.jpg


Thanks for the help, I just need to push the throttle forward a bit more I guess.
 
That sounds about right for old-style wheel pants and fairings. You would pick up a few knots with the newer stuff.

Glad you have unlocked the potential of your -6. ;)
 
You're in the right ball park. Look carefully at the cowling & baffling, do you have blocks on the sides of the cooling air intake ramps on the upper cowl? Is the baffling working well with few leaks? Drag reduction will get you as many knots as power increases or playing with the prop.
 
cowling

Yes on the upper part of each side. The left side was all cracked out, but I repaired it. How would you check for baffle leaks?
 
Yes on the upper part of each side. The left side was all cracked out, but I repaired it. How would you check for baffle leaks?

Look along the baffle seals and along the underside of the cowling where they rub. You should see evidence of continuous contact all around the perimeter, with no "folds" in the baffle seals that would leave an opening where air can get through.
 
Hey All, I'm new to an RV6 and I have a FP prop with a O360 power plant. I don't know the specs on the prop, but I will get that when I go to the airport next. I also have the old wheel pants and landing gear fairings.

At 2300 rpm I'm getting about 142kts indicated. I hear stories of 160+ kts in a 6, and talked to a guy yesterday that is getting 155 with an O320.

What do I start with to find where I'm bleeding speed from?

Thanks in advance for your thoughts!
Eric
eric at StopFlyingScared dot com

A good reference to compare your RV6 is to compare it to actual tested data from the CAFE foundation. They tested an RV6A and published the data on their website.

https://cafe.foundation/v2/research_aprs.php. Click the RV6A from the list. The test report is in PDF format.
 
Thanks

I appreciate all of the input on this one!

Just to finish off with my prop, I have a Sensenich FP 72M8S9-1-83, but looks to be converted to an 86. So a 72/86 for mine.

I'll be checking the baffling with the next oil change.

Thank You!

Eric
 
Did a short flight tonight

8,000 ft Density Alt
Turning about 2650 RPM

TAS right at 160 KTS - 184MPH

I don't have a fuel flow yet, so I have no idea where that was. The spike was some issue with the data.

Y1T9tRu.jpg


Thanks for the help, I just need to push the throttle forward a bit more I guess.
It is also worth testing and calibrating your TAS calculation. It is not clear if you are doing it manually or thru your instrument. There is an easy 3-way GPS run that will calculate your TAS and confirms its accuracy.
 
My numbers were direct from my Dynon HDX. Would that have done my TAS calibration?
TAS is calculated by the EIFS which uses a few input such as OAT, Density altitude and IAS. The most common source of error comes from IAS. If your static port is at the standard location with the standard VANS provided port which is the head of a pop rivet, then great chances yours is accurate.
But testing with the 3-way GPS method will firm that up.
 
One thing you may want to check Eric ;
Is there an RPM restriction on that propeller , I know my CM 70 prop on my RV 6 has a 2600 RPM RED LINE !!
 
Seems like i have much room for improvement, but not sure where to start.
IMG_44681.jpg


Gear leg fairings and wheel pants installed.
Ground Adjustable Sensenich Prop on Pin setting 4. Gets right at 2700 rpm with full throttle and leaned.
Lycoming 0-320 E2A 160HP
 
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With those CHTs on #1 and #2, I'd start looking for baffling improvements. Also, the #3 and 4 EGT and CHTs are very different than 1 and 2, likely due to poor fuel/air distribution but might also be an induction leak or leaks in play.

Suggest uploading your Dynon data to Savvy Analysis for others to review. They also have a flight test you can run to help determine your spreads and ignition health.

Also, you have your volts in the yellow at 14.3. That is where it should be and ought to be green up to 14.6 or so.
 
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When my RV-6 still had the Sensenich 72FM prop, pitched at 85", O-360 180 hp, I could get 179 kts TAS at 8,000' DA. The IAS has been calibrated and reads about 2 kts high at that speed so let's say 177 kts (204 mph) TAS. Van's currently claims 210 mph with the current fairings. That was wide open at about 2710-2720 rpm, leaned for best power. I still have the old style wheel fairings and Whelen nav/strobe lights hangin' out in the breeze. You should be able to do a little better than what you are seeing now. To check your IAS accuracy you can use your GPS and this website: http://www.csgnetwork.com/tasgpscalc.html. Kevin Horton found this years ago and felt it was accurate enough for our needs.
 
Just flew formation at 5500 feet yesterday in my RV7 (180 w/CS prop) with a RV6 (160 w/FP 80" pitch metal Sensenich).

I could easily out climb him but when level at 5500 we were both using 7.9 GPH at a TAS of 159 to 161 knots or give or take 185 MPH.

The 6 with his 80" pitch was turning 2350 RPM. The 6 is a very efficient airplane! Pitch makes a lot of difference in the RPM needed for a given speed.
At 8000 feet you may need to turn past redline to get to 75% if you have a climb pitch prop. What that pitch is, for climb,standard or cruise; may be very different from prop maker to prop maker, to achieve the same results.
 
Just flew formation at 5500 feet yesterday in my RV7 (180 w/CS prop) with a RV6 (160 w/FP 80" pitch metal Sensenich).

I could easily out climb him but when level at 5500 we were both using 7.9 GPH at a TAS of 159 to 161 knots or give or take 185 MPH.

The 6 with his 80" pitch was turning 2350 RPM. The 6 is a very efficient airplane! Pitch makes a lot of difference in the RPM needed for a given speed.
At 8000 feet you may need to turn past redline to get to 75% if you have a climb pitch prop. What that pitch is, for climb,standard or cruise; may be very different from prop maker to prop maker, to achieve the same results.

2350 sounds low, probably about 50-60% power at that altitude. I would expect at least 2500 rpm for 160kts true with 80" pitch.
 
Just flew formation at 5500 feet yesterday in my RV7 (180 w/CS prop) with a RV6 (160 w/FP 80" pitch metal Sensenich).

I could easily out climb him but when level at 5500 we were both using 7.9 GPH at a TAS of 159 to 161 knots or give or take 185 MPH.

The 6 with his 80" pitch was turning 2350 RPM. The 6 is a very efficient airplane! Pitch makes a lot of difference in the RPM needed for a given speed.
At 8000 feet you may need to turn past redline to get to 75% if you have a climb pitch prop. What that pitch is, for climb,standard or cruise; may be very different from prop maker to prop maker, to achieve the same results.

2350 sounds low, probably about 50-60% power at that altitude. I would expect at least 2500 rpm for 160kts true with 80" pitch. I've been flying the metal Sensenich 80" for nearly two decades (RV-6, 160 hp).
 
I run my 160hp O-320 on my RV-3B at 2650 rpm with a Catto three bladed prop. The design redline on the prop is 3300 rpm. At 2650 rpm I get 200mph smooth as a sewing machine. At 2300 rpm (like your test) I get 165 mph. When i started flying the 3 I thought it was slow. After talking to other RV owners and Catto I discovered I was operating the engine way too slow. I was treating it like a Cherokee or Cessna trainer rather than a balanced sport plane. My O-320 loves 2650 rpm and it really comes alive above 2600. I have no idea what kind of fuel burn I get. I have a totalizer but rarely check it.
 
My speeds for my 6A with 180 hp and FP Sensenich 85” pitch prop are found in this thread
 
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Did a short flight tonight

8,000 ft Density Alt
Turning about 2650 RPM

TAS right at 160 KTS - 184MPH

I don't have a fuel flow yet, so I have no idea where that was. The spike was some issue with the data.

Thanks for the help, I just need to push the throttle forward a bit more I guess.
Get a MAP gauge as well as FF. MAP is cheaper. Yes new gear leg fairing, wheel pants and intersection fairings will help. COOLING DRAG. Make sure the baffles are well sealed.

My old RV-4 cruised at 190 MPH (165 Kts) with 150 HP O-320 and Hartzell CS Prop. Top speed was 205 mph (178 Kts).

Next time you go do flight test.... Fly three leg triangle 120 degrees apart and record (record IAS, TAS and GPS, RPM, MAP). Record each leg separately then average.
 
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I appreciate the feedback. I replaced the intake gaskets and tube boots. Decreased the size of the air ****. Plugged all the air leaks I could find in the baffling. I did fly 3 legs today but only grabbed my phone on the last leg for a picture. I will repeat and grab the data for a savvy analysis. Seems like I'm heading the right direction. Any other tips are appreciated.
IMG_1496.jpg
 
Still in need of more cooling but CHTs are a little better. Oil temp is too high for my comfort. You'll need to improve some there too. Make sure your mag timing is not advanced. If you have electronic ignition, it may need some tuning.
 
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