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What does an "out of rig" airplane mean?

Lemos

Active Member
I am still very actively shopping for an RV. I was talking to a builder today who was saying that his RV-9 goes 150 knots at altitude "because it's probably out of rig." I accepted this statement, and it wasn't until I hung up the phone that I got to thinking; can an "out of rig" RV be fixed? What exactly does "out of rig" mean? Does it sound right that an out of rig RV-9 (tailwheel) would go 150 knots at 10,000'?
 
My RV-9A goes 150 Knots and it isn't out of rig!

With a prepunched kit, you'd really have to screw something up to be very far out of rig. There's only so much room to mis-rig the wings to the fuselage, or the tail to the fuselage, or the ailerons/flaps, or twist in the fuselage or wings.

Van's gives really good guidance in the plans for how to mate up these parts and keep them within tolerance (which is small fractions of inches). For example, I have a heavy wing, and I messed around with the positions of the hinges for the ailerons, among other things and it really made no difference. I have a small wedge on the right aileron and it flys straight now. If you have to dial up a lot of rudder or roll trim, then maybe something isn't rigged correctly, but there might be simple solutions.
 
It refers to the alignment of all the parts ------wing incidence from side to side, tail incidence vs wing.

All the control surfaces also need to be properly aligned with respect to the rest of the airframe.
 
Thank you both for the replies.

Very interesting that an "in" rig airplane goes 150 knots as well. I am having a hard time figuring out just how fast the RV's go. It seems the Vans website says one figure, and the owners of these airplanes say they go 150 - 180 knots. It's quite a large spread. Is some inflation involved? :)

To Bruceh, I still need to make it down to Ramona. Congratulations on 800 hours. That is quite an accomplishment.

One thing that this website has helped me to learn is that I want to fly not build. I mean I'd love to build and I am sure that it would be educational, but I am not sure that I have the patience. I am somewhat debating buying a flying RV and then simultaneously buying a tailkit and see if I take to building. It is an odd time right now because I'd like to take a building weekend course but there aren't any running.
 
I am still very actively shopping for an RV. I was talking to a builder today who was saying that his RV-9 goes 150 knots at altitude "because it's probably out of rig." I accepted this statement, and it wasn't until I hung up the phone that I got to thinking; can an "out of rig" RV be fixed? What exactly does "out of rig" mean? Does it sound right that an out of rig RV-9 (tailwheel) would go 150 knots at 10,000'?

What does 150 knots mean? 150 KIAS, KTAS, KTGS? Has the pitot-static system in the plane been calibrated?

Also, what does "at altitude" mean? Pressure altitude, Density altitude, 7,500' MSL, or 11,500' MSL?

What engine? What prop? What power setting? What fuel flow?

Way to many variables and unknowns to even begin to answer the question.

IMHO, rigging will be a very minor issue, if one at all.
 
An out of rig a/c will lose a few knots. I bought rather than build so got to test got the plane first which showed no issues.
Whilst not a Vans I used to fly (commercially) some years ago several of the same type of machine. EG.the AC50 (Shrike) no 2 airframes where the same, diff in speed could vary as much as 10 kts, miss rigging was often the issue.
Most things are fixable on any plane especially a Vans machine as they are very basic (almost crude to some degree) and metal, an easy medium to work with:)
 
In addition to the big pieces, rigging on an RV can also refer to wheel pants and gear leg fairings - potentially worth a significant number of knots if they aren’t lined up with the airflow!
 
They can also introduce trim changes that the owner can "correct" by trim tabs. That's part of the speed loss.

Dave
 
What does 150 knots mean? 150 KIAS, KTAS, KTGS? Has the pitot-static system in the plane been calibrated?

Also, what does "at altitude" mean? Pressure altitude, Density altitude, 7,500' MSL, or 11,500' MSL?

What engine? What prop? What power setting? What fuel flow?

Way to many variables and unknowns to even begin to answer the question.

IMHO, rigging will be a very minor issue, if one at all.

#1: 150 knots true airspeed. The aircraft is maintained for IFR, so I'd say yes the static system was calibrated.

#2: Engine is an 0-320. Not sure what prop but it is fixed pitch. Power is 2650 RPM. Fuel flow is 9 gph.

Do these specs match up with say, an average RV-9? If I take this to pre-buy should I check the rigging as part of the pre-buy?
 
The 2 year certification for the altimeter / transponder is performed on the ground with calibrated test equipment. It is attached to the static ports on the aircraft (and depending on the equipment, also the pitot tube). When the aircraft is flying through the air, the static port can give an "incorrect" pressure to the aircrafts instruments based on the shape and placement of the port.

This static port error can not be duplicated with the "on ground" test. There are numerous post on this forum that discuss how to discover and address this issue.
 
#1: 150 knots true airspeed. The aircraft is maintained for IFR, so I'd say yes the static system was calibrated.

#2: Engine is an 0-320. Not sure what prop but it is fixed pitch. Power is 2650 RPM. Fuel flow is 9 gph.

Do these specs match up with say, an average RV-9? If I take this to pre-buy should I check the rigging as part of the pre-buy?

My 6 has a 320 and I fly at 160kts on 8.1 GPH at 8K'. I would expect the 9 to be similar. However, until you confirm the IAS reading wiht the GPS box run, the 150 number doesn't mean too much. Just do another test flight. It only takes 20 minutes to do the test, if you have an A/P. Calibrated static has nothing to doe with dynamic static error from source location. That can only be addressed by the GPS box run or similar tests.
 
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What does 150 knots mean? 150 KIAS, KTAS, KTGS? Has the pitot-static system in the plane been calibrated?

Also, what does "at altitude" mean? Pressure altitude, Density altitude, 7,500' MSL, or 11,500' MSL?

What engine? What prop? What power setting? What fuel flow?

Way to many variables and unknowns to even begin to answer the question.

IMHO, rigging will be a very minor issue, if one at all.


The definition of calibrated airspeed is indicated airspeed corrected for installation errors. In my case, my AS indicator was in error by 5 knots. I thought it was my static port installation until I bought a couple of G5's and that solved the problem.

Just because the static system has had its 24 month inspection, it does not mean your airspeed indicator is accurate.

"At altitude" usually means 7000 feet or above because this is where the engine power can be set at full throttle. Most manufactures set max cruise at an altitude of around 7000 feet because this will give you 75% power, maximum cruise speed and less dense air. Most engine manufacturers will not recommend cruise powers above 75%.

The only way to determine your max cruise true airspeed is to climb to 7000 feet and fly two directions 180 degrees difference and note your ground speed then add them together and divide by 2. I have tried flying up to 4 directions 90 degrees apart and came up with a difference of less than 1 knot. Probably more accurate but not worth the effort.

150-155 Knots seems about right for a 0320 with fixed pitch prop. You could check for drooping control surfaces. You can raise the ailerons and get a few more knots of speed but once the plane is built, not much can you do with rigging because unlike some certified airplanes, they don't have any adjustments. Wheel pants, leg fairings and cooling drag are the major areas of improvement for the average RV IMO but take a substantial amount of work for the results.

If I am on a cross country of more than 150 miles, I will usually fly at above 10K feet because that gives me 179 knots TAS and less than 7 GPH in my 0360 180HP Superior with fuel injection and electronic ignition.

Getting to excited about cruise probably is not worth the effort. I was at Oceano, CA the other day flying to Fresno with a friend in a 182 Cessna. I took off probably 5-10 minutes after he did and passed him about half way. I climbed to 8500 and he stayed down at 6500. I was putting my plane away in the hanger when he landed. Other than burning a lot less gas, the time saved was insignificant.
 
#1: 150 knots true airspeed. The aircraft is maintained for IFR, so I'd say yes the static system was calibrated.

#2: Engine is an 0-320. Not sure what prop but it is fixed pitch. Power is 2650 RPM. Fuel flow is 9 gph.

Do these specs match up with say, an average RV-9? If I take this to pre-buy should I check the rigging as part of the pre-buy?

Varies but for a comfortable/economical cruise (around 60 to 65% power) you would expect a 9A with an 0-320 leaned out between 8,000 to 10,000 feet to TAS around 150 kt and burn about 6.5 to 7.5 g/hr. The most economical accurate figures I have seen are Pete Howells 9A
He uses the NTPS GPS PEC Spreadsheet to accurately determine TAS. It can be downloaded here (at the bottom of the page).

Fin 9A.
 
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#1: 150 knots true airspeed. The aircraft is maintained for IFR, so I'd say yes the static system was calibrated.

#2: Engine is an 0-320. Not sure what prop but it is fixed pitch. Power is 2650 RPM. Fuel flow is 9 gph.

Do these specs match up with say, an average RV-9? If I take this to pre-buy should I check the rigging as part of the pre-buy?

As already mentioned, IFR certification means nothing regarding the assurance that the ASI is calebrated.

Stating a power level with just an RPM indication has little value in determining what the power output of the engine is. If the prop pitch is less than ideal, the throttle setting may be pulled back to a MP value that would equal much less than 75% power to attain 2650 RPM at 8000'. If that is the case, then 150 kts might be doing very well.

An RV-9 whose engine is actually producing ~75% power at 8000 feet, should easily achieve 160 Kts and cleanly built ones will be closer to 165 kts. An O-320 actually producing 75% power will be burning about 8.5 GPH. If someone claims lower fuel burn and also slower speeds, that is to be expected.

The variability you see in quoted speeds is fairly often cause by airplanes that don't have a well matched propeller and/or pilots flying them that don't understand the variables involved in power settings (By my experience it is often quite a bit of both).
 
A bit of trim drag is going to cost 2 or 3 or 4 kts, as a rough order of magnitude, not 10 or 20. So you can to tweaks to squeeze a couple more kts out, but not much more. Speed comes from good tight fairings and elimination of gaps and anything that could cause turbulence.

Of course being a homebuilt ever rv has a different engine and prop. The prop choice might not be optimal or the engine might not be running well or the throttle might not be properly adjusted.

Airspeed errors are a whole other thing. They can be caused by leaks, a poorly calibrated instrument or static source error.

So if an rv is flying 10kts faster or slower than one would expect, there is some detective work to do. It’s very unlikely to be due to rigging and it may or may not be real.
 
A bit of trim drag is going to cost 2 or 3 or 4 kts, as a rough order of magnitude, not 10 or 20. So you can to tweaks to squeeze a couple more kts out, but not much more. Speed comes from good tight fairings and elimination of gaps and anything that could cause turbulence.

Of course being a homebuilt ever rv has a different engine and prop. The prop choice might not be optimal or the engine might not be running well or the throttle might not be properly adjusted.

Airspeed errors are a whole other thing. They can be caused by leaks, a poorly calibrated instrument or static source error.

So if an rv is flying 10kts faster or slower than one would expect, there is some detective work to do. It’s very unlikely to be due to rigging and it may or may not be real.

As I dig a bit deeper into the pitfalls of an RV purchase, I find after reading your message that I need a little help. You say that the engine may not be running well. How can I, as a pilot and potential purchaser know this? The cockpit photos that I've seen indicate 2600 RPM at 13,500 going 148 knots at 68% power. Oil pressure is 88 and temperature is 201. Fuel pressure is in the green at 5.5 PSI. Last compressions in June were in the mid and high 70's according to the signoff. This looks healthy to me, but how can I tell? What inspection should I do in a pre purchase to catch an engine not running well?
 
As I dig a bit deeper into the pitfalls of an RV purchase, I find after reading your message that I need a little help. You say that the engine may not be running well. How can I, as a pilot and potential purchaser know this? The cockpit photos that I've seen indicate 2600 RPM at 13,500 going 148 knots at 68% power. Oil pressure is 88 and temperature is 201. Fuel pressure is in the green at 5.5 PSI. Last compressions in June were in the mid and high 70's according to the signoff. This looks healthy to me, but how can I tell? What inspection should I do in a pre purchase to catch an engine not running well?

It sounds like you’re reading off of an EFIS - is that indicated airspeed, or true? If its indicated, the TAS is probably around 180 knots!! In that case...nothing wrong with that engine....:rolleyes:
 
It sounds like you’re reading off of an EFIS - is that indicated airspeed, or true? If its indicated, the TAS is probably around 180 knots!! In that case...nothing wrong with that engine....:rolleyes:

Correct, reading off of an EFIS. The pictures show 118 knots indicated, and 148 knots true airspeed. I have very mixed responses, some saying that's normal, and some saying it's 10+ knots slow. Just wondering how I can tell for certain? Again this is a RV-9, with a tailwheel.
 
Getting 68% power at 13,500' seems curious to me.

Looking back at some flight data for a cross country trip I took from Ramona to Salt Lake City, I spent most of the flight at 11,500' and was only seeing 57% power (TAS was 150 Kts). I climbed up to 15,500' and was getting 46% power (TAS was 145 Kts). This is all at LOP, and Fuel flow was 6.3 Gph at 11,500' and 5.5 at 15,500'. It will go faster if you push more fuel flow, but I like saving gas.
 
Rigging

Many of the key points have been discussed. Not much you can do on the initial mounting of the stabilizer and vertical fin. Where you want to get accurate is getting your wing incidence and lead/lag right. The incidence is critical. You want each wing the same!!!

From there, wing tip alignment is also important. Without you've got a huge non adjustable trim tab!!

I've also seen RV's with misaligned ailerons. One might be neutral the other up or down. You can adjust the heim joints a half turn at a time to get things absolutely perfect.

Finally, the gear leg fairings must be aligned properly. Again, a huge trim factor if off.

It's all in the details. Take your time. This is one of those things, "do it right or you'll be doing it over."
 
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