What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

7A performance

cef737

Member
Friend
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
 
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
 
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.
 
Last edited:
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.
 
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
 
Last edited:
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
 
Last edited:
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:
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 Van’s 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 Van’s 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 builder’s experience with this prop? Prop selection is not trivial and it goes beyond just FP or CS.

Carl
D1290-ED1-964-F-49-C3-BBA4-DBA29077-DE27.png
 
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!
 
RV-7A, IO-360-M1B, injected, Hartzell BA prop. 170 KTAS in the 7000-9000 MSL range, leaned to best power.

OP needs to make sure his ASI is accurate before doing anything else.
 
The engine is new and still being broke in. I have no wheel pants or gear fairings yet. The ASI seems to be accurate as I have checked the GPS ground speed
to my TAS. The engine is making good power MP 28” but RPM on takeoff is only 2650. I need to adjust that. Fuel burn is around 15gph at WOT and 2600rpm full rich at 3000-4000msl. Probably 7000DA The airplane also rolls to the right significantly. I’ve double checked A of I and sweep and they check good. My right wing had been painted but nothing else. I took this project over at 90%.
 
Gear and wheel fairings really work. Without them you’ll lose of order 10 knots.
Search for ‘heavy wing’. Check the vertical height of the two ailerons, they need to be exactly the same. Then move on to slight adjustments (‘pinching’) of the trailing edge.
 
That's doesn't seem too far off if you don't have any fairings installed. The wheel pants and fairings should be good for around 10 knots, and 145 indicated at 3000 ft is equivalent to 170 true at 9k.
 
I went and did speed runs this afternoon, plugged them into the kitplanes spreadsheet, I have a calculated IAS correction of +3.9, so that’s part of the answer.

But I discovered something else doing research on MAP gauge calibration. Reading this thread here, I calculated that my MAP gauge should be reading 28.95 with the engine off. Turns out it’s reading a hair past 30.00 with the engine off, so I have been thinking I have been flying around at ~65% power, instead it been closer to 58-60%.

So OP, double check your manifold pressure is reading correctly, and from several other posts, just cause it’s electronic sensor or EFIS doesn’t mean it’s any more accurate or calibrated than a mechanical one.
 
Back
Top