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Break-in period - Spats or no spats

Janekom

Janekom

Well Known Member
Patron
I am used to the fixed pitch 2 seaters and leaving the fairings and spats off for the first few hours. Mainly to induce drag and be able to run full throttle without over revving.
Now I am wondering if it is necessary on the RV10 with the CS prop. In my mind you can put the spats and fairings on with the 10 as you can control the RPM?
Advise will be appreciated.
 
I've done it both ways, Jan...

...and you simply just go faster. I recently did the first flight on an immaculate -7 and ran the engine wide open, per his request and also the recommended procedure from Lycoming. The -7 chase plane could barely keep up with the -7A.:)

On my -10 that I raced this Spring, WOT and slightly less than full revs...around 2640 as I recall, yielded 211 MPH TAS, according to the D-100, for 45 minutes..(BTW, I took top time of day and 1st place!)

Best,
 
The accepted recommendation is to induce as much drag as is reasonable. Regardless of the RPM, the idea is to "load" the engine as much as possible. The more the drag, the more the load.
 
Why I am asking this is that I reckon that the "go faster" will provide better flow and cooling as it is so hot here right now.
 
Last edited:
You're probably looking at another 17 MPH..

...or so and that will help the cooling as well. Our -6A gained 16 MPH with gear leg fairings and wheelpants/spats.

Regards,
 
I'd say that engine cooling takes precedence over "loading" of the engine (which I suspect is an OWT)... and added speed will help with better cooling... at least it did for me and several other that I personally observed during the first 40.
 
I have never "done the math" on the concept of loading the engine by creating more airframe drag, but my intuition says this doesn't make total sense. It seems to me that if you take the engine to full throttle, it is going to work at accelerating the airplane until the drag equals the thrust. the engine doesn't know what speed this is - it is workign as hard as it can, regardless of what sped it is going through the air.

I personally subscribe to getting better cooling from more airflow - I would have to go back and re-read the excellent break-in write-ups by Mahlon Russel, but I don't think think that you want to limit cylinder cooling during this period, so faster for more cooling would be good.

Again, no science here, just my take on it. I'd love to see someone definitively answer this one with some analysis or test data!

Paul
 
Ironflight said:
I have never "done the math" on the concept of loading the engine by creating more airframe drag, but my intuition says this doesn't make total sense. It seems to me that if you take the engine to full throttle, it is going to work at accelerating the airplane until the drag equals the thrust. the engine doesn't know what speed this is - it is workign as hard as it can, regardless of what sped it is going through the air.

I personally subscribe to getting better cooling from more airflow - I would have to go back and re-read the excellent break-in write-ups by Mahlon Russel, but I don't think think that you want to limit cylinder cooling during this period, so faster for more cooling would be good.

Again, no science here, just my take on it. I'd love to see someone definitively answer this one with some analysis or test data!

Paul
Click to expand...

I was thinking the same thing!
 
My input here is that Vans says to fly sans fairings, if you are breaking in a new or rebuilt engine.

This was in the documents that talk about first flight issues.

Sorry, dont have it in front of me so I can give the actual name-----
 
I agree but--

Ironflight wrote-
It seems to me that if you take the engine to full throttle, it is going to work at accelerating the airplane until the drag equals the thrust.
Click to expand...

I agree but remember that with a fixed pitch prop and spats and fairings on, you get the motor to over speed. Hence the removal of these in order to create more drag.
I have seen this on a number of new RV7's with fixed pitch prop.
No spats and no fairings you are lucky if you see 2550 RPM
Put on the spats and fairings and you will easily see 2800 RPM :eek:
 
Very good point Jan - it might be that the difference is Constant Speed versus Fixed Pitch. Since most of the original RV's were fixed pitch, it might be that the thinkng carries over from that (and is valid in that case).

For a Constant Speed, it might be different, since the prop can just flatten out to allow the engine to reach full power.

Paul
 
High manifold pressure loads the rings and allows them to seat. High rpm may not mean full power. The more drag you create, the higher the manifold pressure. If you don't have a manifold gauge, you don't know how much power your motor is putting out.

Load the motor in a climb and then push over and cool it in a cruse when the temps reach the limit.

The idea is to have cyl pressure by-pass the compression ring and expand the oil ring so it will seat first. When this happens, the compression ring will then seat next.
 
gasman said:
High manifold pressure loads the rings and allows them to seat. High rpm may not mean full power. The more drag you create, the higher the manifold pressure. If you don't have a manifold gauge, you don't know how much power your motor is putting out.

Load the motor in a climb and then push over and cool it in a cruse when the temps reach the limit.

The idea is to have cyl pressure by-pass the compression ring and expand the oil ring so it will seat first. When this happens, the compression ring will then seat next.
Click to expand...

But if you DO have a manifold pressure gauge and know how much power you're putting out, then I still don't think it matters how you load the engine - right?
 
I'm with Paul.

As for spats or no spats, my recent break-in was done with the airplane fully faired. The only "problem" was a practical one.....full power means staying low and staying low can mean rough air. It can get pretty rough running at the higher, fully faired speeds.
 
For what it's worth

Can't say as I've ever seen a certified plane delivered without all that stuff installed from the factory. I assume the new owners get the engines sucessfully broken in somehow. ;)
 
DanH said:
I'm with Paul.

As for spats or no spats, my recent break-in was done with the airplane fully faired. The only "problem" was a practical one.....full power means staying low and staying low can mean rough air. It can get pretty rough running at the higher, fully faired speeds.
Click to expand...

I concur. It is tough to keep it WOT. I've been running mine up higher due to the terrain, geese and turbulence.
My trusted A&P said run it hard, but keep it cool. He said 24 squared will be fine for seating the rings. I haven't seen over 350* CHT's, 190* oil.
 
We have been lucky with a few cooler than normal days here. I have installed the spats now and the test flying is going well. CHT's are about 400 and under with oil running at about 190. I suspect that will drop slightly as the rings seat.
 
In an earlier thread....

....you mentioned a fixed-pitch prop. Is that what you have?

If so, kindly give us some performance numbers.

Thanks,
 
Another consideration:

Flying without wheel pants and fairings, you get to determine what, if any, rudder trim might be needed. Once the plane is flying "in trim" and the engine is broken-in, then install the pants. If you then end up with a heavy wing, you at least know the "naked" plane flew in trim without them and further flights can concentrate on which fiberglass part(s) are causing the issue.

Once the heavy wing is corrected, then look at fine tuning the rudder trim.
 
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