What's new
Van's Air Force

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

New top end, bad ground-run RPM

B

bucaronco

Member
Guys,

I've invested in four new ECI Titan cylinders for my RV6 (O-320-B3B), due to exhaust port cracks.

The A&P tells me that the initial post-maintenance ground-run was good, except that at full throttle, the engine only reached 2200-2250 RPM, instead of the 2700RPM as called for in the Type Certificate Data sheet.

He was careful to keep oil temps and CHT's below levels specified in the manufacturer's info booklet.

My suspicion is TACH troble of some sort, but my question is this:
Does anyone know of another problem which might cause this after a new top-end job?

THX....Ron
 
Fixed pitch or constant speed prop?

If you have a fixed pitch prop the static RPM is good.

If you have a constant speed prop you might need a new mechanic.

Mark
 
bucaronco said:
Guys,

I've invested in four new ECI Titan cylinders for my RV6 (O-320-B3B), due to exhaust port cracks.

The A&P tells me that the initial post-maintenance ground-run was good, except that at full throttle, the engine only reached 2200-2250 RPM, instead of the 2700RPM as called for in the Type Certificate Data sheet.

He was careful to keep oil temps and CHT's below levels specified in the manufacturer's info booklet.

My suspicion is TACH troble of some sort, but my question is this:
Does anyone know of another problem which might cause this after a new top-end job?

THX....Ron
Click to expand...

Full throttle on the ground static RPM you're in the ball park at 2250. You're not going to make 2700 static. What did you see before on the tach static?
 
Were you getting 2700 RPM with your enging/prop combo anytime prior to
just replacing the cylinders?

Something else to check, besides 'get a new mechanic'...
If C/S prop you my check the prop governor. First make sure you have the right one for the prop combo, make sure you are getting full motion stop-to-stop, and make sure it's going high-RPM when it should be and cable is not retreating. It's possible the governor also may need overhaul. Its happened to me but I was only losing about about 75RPM.

The tach can be pinched and not show the right RPM, the cable end can be
worn either on the engine or TACH ends; Another possibility is the cable
is incorrect for the TACH.

If you are not getting what's specified in the TCDS your aircraft is not
airworthy, but you probably already know this.
 
Do not do full power static runups with new cylinders. You will cook them. Run it to check for leaks, , cool it down, cowl it up and get airborne. Airflow is insufficient to break in new cylinders on the ground.
 
Break in rant

Nothing is gained by running on the ground except glazed cylinders. You can check static rpm on your initial takeoff roll. Since the engine is tight it might not make full static rpm with a fixed pitch prop but close is good enough. Run on the ground only enough to make sure nothing is leaking or falling off. Three minutes is enough, including a mag check. Shut down, pull the cowling and look for problems, put it back together, and go have a Coke. Then, taxi promptly to the runway and push the throttle to the stop and leave it there for the next hour while you circle the airport at 3000 feet, then land and pull the cowling again. I ran my 0-290 WOT for the first ten or so hours after OH just like that. About then the oil temp came down and I figured it was mostly broken in, and it was. 500+ hours later it has good, no, great compression and uses about a quart every ten hours or maybe less. To break in an engine you need high pressures on the rings, plenty of airflow over the cylinders, and a rich mixture for additional cooling. In the absence of a test cell this is best accomplished with WOT in flight and at low enough altitude to develop as much power as possible. Minimize ground running as much as possible on a newly overhauled engine. You can find out all you need to know before flight in just a very few minutes. Anymore ground running is counter-productive. (You can tell I am in high dudgeon, it has been a long, irksome day!)
 
I disagree. Yes, it's insufficient to break in the cylinders; About an hour or so
of flight and you'll probaby start seeing the CHT rise and then drop to 'normal' levels; but if you are not getting what's specified in the TCDS you shouldn't fly. A full power runup to check RPM is not going to cook the cylinders.
 
makes sense

Thanks guys, for the replies.

To be honest, I couldn't remember what the static runup value was, since I don't normally do that. Before the new cylinders, I did a mag check and took to the sky (after eng instruments in the green).

My first usual check of RPM has always been after making sure that the centerline is tracking between my legs!... at which time, airspeed was higher, and the RPM that I saw was in the 2500-2700 range. However, the prospect of a "test flight" has me paying closer attention to what's normal and what's not. The A&P did not "squawk" the low RPM, he merely reported the number and left it up to me as to whether or not that was good.

In the mech's defense... he's a young guy, freshly retired from the Airforce, and has grown up on jets. Both he I are on a learning curve with these lil airplanes and recip engines. The difference is that MY learning curve is costing $$$ !
 
brenegan said:
I disagree. Yes, it's insufficient to break in the cylinders; About an hour or so
of flight and you'll probaby start seeing the CHT rise and then drop to 'normal' levels; but if you are not getting what's specified in the TCDS you shouldn't fly. A full power runup to check RPM is not going to cook the cylinders.
Click to expand...


The TCDS make no accounting of the prop installed, only the RPM at which rated hp occurs. Fixed-pitch props will indicate much lower than TCDS RPM, even if they aren't sporting new cylinders. PS : You are way wrong about full power runups, JUST SAY NO!
 
Yukon said:
The TCDS make no accounting of the prop installed, only the RPM at which rated hp occurs. Fixed-pitch props will indicate much lower than TCDS RPM, even if they aren't sporting new cylinders. PS : You are way wrong about full power runups, JUST SAY NO!
Click to expand...


Not so. Read page 7 of the ECI recommended break-in procedures. I didn't say mag-check or extended run at full power, only to verify takeoff power is available. I provided you a link so all you have to do is click ;).
 
fixed pitch

Sorry guys...

I forgot to mention that it's a fixed pitch prop, which is why I was suspicious of the TACH rather than the prop/governor...

I agree that ground time should be held to a minimum on new cylinders, as does my A&P. He has mentioned several times that a "ground breakin" will not seat the rings. The installation instructions directed the A&P as to how the ground run should be conducted, and it said to do a run to full throttle, keeping oil temp and pressure below certain levels.

Thanks to threads on this site, and previous discussions on setting rings, I've already made arrangements to tow the A/C to the runway, crankup, warmup and go, to get the cooling flow over the cylinders.

I'm still reading-for-effect the "Break-in Instructions" which I D'loaded from the ECI website. I'll follow them to a T on the first flight, but first pass over them shows a direction to "keep power at top of the green arc on the tachometer and manifold pressure gauge or 74% power (whichever is higher) for 1/2 hour." ....thus my concern that the tach'd RPM was an accurate number, AND not evidence of a lurking problem that someone on here may have knowledge of.

I appreciate the reassurances of what's normal, as I get ready to exercise my right stuff. :)
 
Static rpm limits vs. max rpm for full power

Agree with John on the undesirability of full power ground operations with new cylinders. Don't do it. At all.

The type data sheet will specify max and min ground static rpm for a fixed pitch propeller, and that is different than the max rpm for full power. For my PA-12/0-290D it is max 2450 static and min 2350 static. Max rpm in flight is 2600 (125 hp) on the data sheet. The metal plate on the engine says max continuous 2600 for 125 hp, five minute max 2700 for 130 hp. I'm not sure why full power is limited to five minutes on this model Lycoming but that is fine with me. I can hit 2700 in level flight but that puts my airspeed about half way into the yellow. I see about 2450 WOT in a 70 mph climb. BTW, when I broke in this engine I had a prop with too much pitch. After the engine was broken in and I had a reading on static rpm and max rpm in level flight, the prop shop took out a few inches of pitch and put me right in the middle of the static rpm range and right at max rpm in level flght.
 
My apologies

Mark Burns said:
If you have a fixed pitch prop the static RPM is good.

If you have a constant speed prop you might need a new mechanic.

Mark
Click to expand...

Ron,
My previous post was meant to be funny, but now doesn't seem so.

I just bashed your mechanic and offered little information.

I'm sure your mechanic is a good one. And now that I've learned he is retired Air Force I feel even shorter.

It looks like the other guys here have given you some good advice.

If I might add one thing, I don't think one full power run-up lasting 10 -15 seconds will glaze the cylinders. That's just my opinion, I have no data to back it up.

Mark
 
Thanks Mark...

I figured that the mechanic slams were BB humor, but felt compelled to defend him anyway. He has been verrry meticulous in his approach to the condition inspection, and I have his bill to *prove it*! However, Tram and I (my son)...he has much more time in it than me... are the fliers of this machine, and we welcome the fine-tooth approach, within reason. The mechanic who did last year's CI didn't even check the ELT batts !

314L's builder did a fine job on the airframe and fit and finish. It flies like a dream, and we're hoping that the new jugs will make it even more fun to fly. Jeff
has interior makeover ideas for it too, but this lil evolution has put those off for a while.

It's good to have this board for hangar talk before the first flight :)
 
Stephen Lindberg said:
Type data sheet will specify max and min ground static rpm for a fixed pitch propeller, and that is different than the max rpm for full power. For my PA-12/0-290D it is max 2450 static and min 2350 static. Max rpm in flight is 2600 (125 hp) on the data sheet.
Click to expand...
Engine Type Certificate Data Sheets (TCDS) won't specify a minimum static rpm, as that depends on the prop that is installed. An aircraft TCDS might specify a minimum static rpm, but there are no TCDSs for RVs, as they don't have type certificates.
 
oops

I was quoting from my aircraft (PA-12) type data sheet, sorry I didn't make that clear. BTW, I think that my 0-290D max five minute rpm is 2800, not 2700 as I previously stated. That's not on the aircraft data sheet, but on the metal data plate mounted on the engine case, and I was going by memory. I don't know, but I'll bet with all the pitch required by an RV to go fast that ground static rpm is pretty low. Maybe 2000? Anybody care to comment?
 
2200

Steve,
Our Catto is pitched for max cruise speed and we only get 2200 static. That's what Craig siad it would do. He also said that with a reasonably good 0-360 we will more than likely exceed Van's numbers and we do, by 4 MPH for a 202 TAS at 2700 RPM.

Regards,
 
Kevin Horton said:
Engine Type Certificate Data Sheets (TCDS) won't specify a minimum static rpm, as that depends on the prop that is installed. An aircraft TCDS might specify a minimum static rpm, but there are no TCDSs for RVs, as they don't have type certificates.
Click to expand...

Kevin..

In aircraft with type certificates, it's true, I think, that the TCDS is associated with the aircraft; and homebuilts have no type certificate. However, my A&P has told me that our O-320 has a data plate on it which states, "TC274", and lacking other guidance to establish engine limits, I have googled-up TCDS no.E-274 (covering O-320-B3B ... our engine), dated 9-13-2005.

This TCDS has no static runup RPM, but it does address rated HP (160) and full throttle RPM (2700) at sealevel.

My question for the DAR's and A&P's out there, is: would this TCDS not be considered as acceptable data for the RV6 even though we do not have a TC for the airplane. Normally accepted maintenance practices would be derived from the manufacturer's approved maintenance Manual, but how do we know that the data we are referencing, is in fact, acceptable data to use in determining the safe operating condition of the airplane?
 
Well, I'm not an A&P, but I can tell you for certain you will not get max RPM out of an engine at full power with a fixed pitch prop without moving. The Lycomings I've flown with a fixed pitch prop won't hit more than about 2300 RPM in a static runup.

Sounds to me like a non-issue.
 
bucaronco said:
Kevin..

In aircraft with type certificates, it's true, I think, that the TCDS is associated with the aircraft; and homebuilts have no type certificate. However, my A&P has told me that our O-320 has a data plate on it which states, "TC274", and lacking other guidance to establish engine limits, I have googled-up TCDS no.E-274 (covering O-320-B3B ... our engine), dated 9-13-2005.

This TCDS has no static runup RPM, but it does address rated HP (160) and full throttle RPM (2700) at sealevel.

My question for the DAR's and A&P's out there, is: would this TCDS not be considered as acceptable data for the RV6 even though we do not have a TC for the airplane. Normally accepted maintenance practices would be derived from the manufacturer's approved maintenance Manual, but how do we know that the data we are referencing, is in fact, acceptable data to use in determining the safe operating condition of the airplane?
Click to expand...

Ron,
There are specific TCDS' for Engines, Airframes, Propellers and Appliances. It's been implied in this thread, but I thought I'd make that clear for you. You'll find the static runup RPMs on the Airframe TCDS not Engine TCDS. The Airframe TCDS specifies conditions and limitations, which includes propeller data configuration and thus includes static runup RPM (as well as limitations such as avoiding continuous operation between 2100-2250 RPM, for example). So when you say 'acceptable data for the RV6', it's not equalivent since you are talking about an Airframe TCDS (and as already pointed out here, there is none for uncertified aircraft).

You happen to google right Engine TCDS revision for that engine, but here's an official FAA link to help you the next time: http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet
The Engine TCDS is the right place for determining *Engine* limits.

I am an FAA certified Mechanic. Officially with only my Airframe license although I'm Working on my powerplant; but I've also rebuilt an O-320 and two IO-360's so far.

I hope this helps you.
 
David,

thanks for confirming that an engine TCDS is, in fact, valid in homebuilts,and for the link. Not exactly the most user friendly one, but maybe I can wade through it.
 
You must log in or register to reply here.
Back
Top