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  #1  
Old 08-29-2022, 09:54 AM
cef737 cef737 is offline
 
Join Date: Feb 2022
Location: Logandale, NV
Posts: 5
Default 7A performance

Hello, My name is Chad. I have just finished my 7A and have about 10 hrs on it. my engine is a Superior XP IO-360 180hp and the prop is an ACI 2200.

I'm only able to indicate about 135 kts at 3000-4000' WOT (27.5"mp this morning) and 2650 RPM. ? The density altitude has been 3000-4000 feet at my airport and I'm using 800' of runway to get airborne at 1600lbs. Do these numbers seem about right?

This is the first RV that I have flown and my other airplane is a STOL bird so maybe I'm just used to that.

Chad
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  #2  
Old 08-29-2022, 10:54 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
Posts: 3,945
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Assuming standard atmospheric pressure, ~60 degrees OAT and reasonable accurate IAS, this 135kts IAS equates to ~145kts TAS.

This is slow for an RV-7A.

Do a GPS run to verify IAS. If correct, look for reasons why you are not getting more reasonable speeds. I suggest:
- Rigging. Always room to squeeze out a few more knots.
- Wheel pants. Installed?
- Prop - what do other people see with this prop?
- Is the engine making full power? Your take off roll suggests it is. What fuel flows are you seeing?

Carl
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  #3  
Old 08-29-2022, 10:56 AM
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BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,850
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Nope, seems low. Might check:

-is the engine broken in?
- the ASI calibration in a 3-4 leg run, repair as needed.
- do you have wheel pants and gear leg fairings installed?
- Is your throttle reaching full opening - yes MP is good
- how is the fuel flow?
- flaps all the way up?
- engine timing? CHT EGT should help understand that

Data point - 4-5000 ft for my stock YIO-360 M1B is 170-177KTAS + lean cruise at 8000 DA, WOT, 2500 RPM is 168KTAS, and at peak EGT would be around 173 KTAS Top speed at 8000DA is 177-178 ktas best mixture 2650rpm. Hartzell composite -3-4 kts slower than the BA. I am told it is slow.
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RV-7

Last edited by BillL : 08-29-2022 at 02:56 PM.
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  #4  
Old 08-29-2022, 01:02 PM
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bjdecker bjdecker is offline
 
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Location: Georgetown, TX
Posts: 1,372
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Gear legs and wheel pants faired up yet?
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RV-7 (Flying)
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  #5  
Old 08-29-2022, 02:33 PM
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Untainted123 Untainted123 is offline
 
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Location: Azle, TX
Posts: 197
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Quote:
Originally Posted by Carl Froehlich View Post
This is slow for an RV-7A.
What would be a normal range for an RV-7A? For a RV-6? I have had people make the comment that my airplane is slow for an RV-6, so I am watching this thread to see if I too am missing something.

As a data point:
1997 RV-6
O-360-B, builder wrote in the logbook that they built the engine from an O-360-A4A to an O-360-B1A by using low compression (chrome) pistons and making the case a CS case. My understanding is that made it effectively 168hp instead of the normal 180hp.

Hartzell CS Prop (the old square one, not the BA one)

I consistently get 140-142kts TAS, running at 22"/2400. I can get 8gph or less running peak or slightly less than LOP, CHT's consistently below 395 for the hottest ones at the back.
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  #6  
Old 08-29-2022, 02:41 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by Untainted123 View Post
What would be a normal range for an RV-7A? For a RV-6? I have had people make the comment that my airplane is slow for an RV-6, so I am watching this thread to see if I too am missing something.

As a data point:
1997 RV-6
O-360-B, builder wrote in the logbook that they built the engine from an O-360-A4A to an O-360-B1A by using low compression (chrome) pistons and making the case a CS case. My understanding is that made it effectively 168hp instead of the normal 180hp.

Hartzell CS Prop (the old square one, not the BA one)

I consistently get 140-142kts TAS, running at 22"/2400. I can get 8gph or less running peak or slightly less than LOP, CHT's consistently below 395 for the hottest ones at the back.
I have a 6A with an IO-320 (160 HP) with EI. At 8K, I get 160 KTAS (GPS test verified) on 8.1 GPH (LOP), spinning 2730 RPM (FP prop). CHTs around 360. 140 is way slow for a 6.

Due to static port issues, you need to do a 3 or 4 point GPS run. Search and you will find the spreadsheet to calculate it. I was 8 knots off before I put fences around the static ports.

low compression pistons will cost you a few knots over standard CR at the same GPH flow, but nowhere near 20 knots.

Larry
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N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 08-29-2022 at 02:48 PM.
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  #7  
Old 08-29-2022, 03:01 PM
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jneves jneves is offline
 
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Location: Livermore, CA
Posts: 269
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Data Point:
IO-360 200HP
Fixed Pitch Catto Cruise prop
8500 ft
59 OAT
MP = 20"
RPM = 2450
TAS = 162 kts
8 to 8.5 GPH fuel burn
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N455DM - RV-6A - Bought Flying - 2021
Tip Up Canopy
IO-360-A2B
FP 66" Catta 3 blade Carbon
IFR - 2 Garmin G5s - 430W - Aera 760 - GFC500
JPI EMS-350 to monitor the temps
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2022 Donation Happily Made!

Last edited by jneves : 08-29-2022 at 08:07 PM. Reason: added fuel burn
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  #8  
Old 08-29-2022, 03:07 PM
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Untainted123 Untainted123 is offline
 
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Location: Azle, TX
Posts: 197
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Sounds like step 1 for both Chad (OP) and I is to get the GPS run and know what we what are actually working with re IAS and TAS, and go from there.

I haven't had any other issues with my plane nor engine, and it's my first RV, so I kind of just accepted it as "this plane just flies at that speed, watcha gonna do?" I would love to get closer to 160kts TAS, but I don't want to burn 10-11gph to do it.

I should add that the Lycoming charts (using the James Petty AircraftPower app) shows that is about 65-70% power (depending on altitude of course). Using data from a flight this weekend, I was at 67% power at ~7k DA, and I was getting about that TAS and GPS derived GS was about the same, which I felt was accurate since winds were predicted at almost 90deg XW for this flight.

Looking at the Lycoming fuel flow charts, an O-360-B should flow about 0.51# per HP, and 67% is 113hp, which means I should be flowing closer 9.5gph, but I actually flow closer to 8gph, or a hair lower if I am willing to tolerate the engine running rougher LOP'er. So I am missing about 1.5gph of fuel flow. My fuel consumption on the JPI is spot on (never more than about .5gallons from it shows remaining from what the gas receipt says), so I trust that part at least. Does that fuel flow seem suspect?

I will try to get a speed run in and double check my indicators, but assuming Chad and I both verify instrumentation is correct, what are some of the main gotchas to suffer that much loss of speed?

Last edited by Untainted123 : 08-29-2022 at 03:17 PM. Reason: Fuel flow numbers
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  #9  
Old 08-29-2022, 03:13 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,945
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Quote:
Originally Posted by Untainted123 View Post
What would be a normal range for an RV-7A? For a RV-6? I have had people make the comment that my airplane is slow for an RV-6, so I am watching this thread to see if I too am missing something.

As a data point:
1997 RV-6
O-360-B, builder wrote in the logbook that they built the engine from an O-360-A4A to an O-360-B1A by using low compression (chrome) pistons and making the case a CS case. My understanding is that made it effectively 168hp instead of the normal 180hp.

Hartzell CS Prop (the old square one, not the BA one)

I consistently get 140-142kts TAS, running at 22"/2400. I can get 8gph or less running peak or slightly less than LOP, CHT's consistently below 395 for the hottest ones at the back.
Shoot fire - I have no experience with 6, 6A, 7 or 7A - but I can read Vanís numbers and these speeds appear short of the mark. As discussed, first step is to figure out CAS to IAS doing the GPS runs. As a side note, if using just a Vanís analog airspeed instrument for IAS they can be 7+ knots off in reading (personal experience). I built an simple manometer to check, and then used the same manometer to calibrate two of these instruments over the speed range of 50 to 200 knots.

A 180hp, CS two place RV should be over 160kts in cruise. I have done many data runs in my RV-8 to tweak out the last percentage or two of fuel economy in cruise (IO-360-M1B, Hartzell BA CS prop). Below is a screen shot from my trip home on Saturday.

So back to the OP:
- Wheel pants and gear leg fairings on? Can easiely add 10+ knots
- Rigging out of wack? Can easily cost +5 knots
- Engine running right (timing and such)?
- IAS accurate?
- Other builderís experience with this prop? Prop selection is not trivial and it goes beyond just FP or CS.

Carl
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  #10  
Old 08-29-2022, 03:21 PM
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twsurveyor twsurveyor is offline
 
Join Date: Jan 2005
Location: Ridgetop, Tennessee
Posts: 135
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Quote:
Originally Posted by cef737 View Post
Hello, My name is Chad. I have just finished my 7A and have about 10 hrs on it. my engine is a Superior XP IO-360 180hp and the prop is an ACI 2200.

I'm only able to indicate about 135 kts at 3000-4000' WOT (27.5"mp this morning) and 2650 RPM. ? The density altitude has been 3000-4000 feet at my airport and I'm using 800' of runway to get airborne at 1600lbs. Do these numbers seem about right?

This is the first RV that I have flown and my other airplane is a STOL bird so maybe I'm just used to that.

Chad
RV-6A, 180 hp 0-360, Prince P-Tip
Typically get 155 kts @ 2475, 8-8.5 gph!
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RV-6A, N 350 TW
830 Hrs & "Climbing?!
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