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  #1  
Old 01-26-2019, 07:57 PM
AviatorJ AviatorJ is offline
 
Join Date: Feb 2015
Location: Oklahoma City
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Default Taxi Test Advice

I'm extremely paranoid about having a proper engine break in so looking for some assistance on temps for my one and only taxi test. Truth be told I've done a number of engine starts, most less than 30 seconds. The two longest was a 3 min one and then today a 7 min one. I don't know if this is normal but these were needed to ensure everything that I corrected was indeed corrected.

I cowled her up today and am ready to do the official taxi test, let oil temp stabilize and do my full power run up and prop pitch test. Even though Barrett's did an hour on the test cell, and per the report seems to have been done with various setting per the Lycoming Service Instruction. Between the instruction and various other write ups I'm concerned about glazing my cylinders.

It will be somewhere between 55 - 60F out tomorrow, I'll plugged in my old 172 preheater for tomorrow. If I'm letting the oil get up to 140F, what is a reasonable CHT I should be looking for? I've seen various figures to keep them under ranging from 300 - 350F while staying on the ground.

For Prop pitch test I assume should RPM up to 1700, then slowly adjust the prop to get the new oil in and air out. Do I need to do 3 full cycles or is one recommended as I read some place else?

Finally for a full RPM run up. Is the goal to get to 2700, stay there for a few seconds and then throttle back to 1000? I'm going to use my brakes, but I'll be on the runway if they start dragging so I can throttle down and release the brakes. I did a high speed taxi test in my buddy's old RV-10, I could repeat what I did on his, but would prefer to try the brakes first.

Thanks!
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  #2  
Old 01-26-2019, 08:15 PM
BobTurner BobTurner is offline
 
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I'd suggest a moderate speed taxi run first, to condition the brakes (follow pad manufacturer's instructions). If you don't, I think there's a fair chance they won't hold a full power runup.
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  #3  
Old 01-26-2019, 10:16 PM
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Ironflight Ironflight is offline
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According to the best old-time engineers I know, as long as the CHT’s stay under 300 degrees, the cylinders never know they have been run (in terms of breaking in, or glazing cylinders. Doesn’t make any difference how long you run - just observe the limit.

You could be able to cycle the prop at somewhere between 1800 - 1900 rpm - sometimes a little higher. Cycle a couple of times to purge the air, but don’t deep cycle it - this is hard on the machinery. When you see the first hint of a drop, put the lever forward again.

Be very careful with taxi testing above a normal taxi. RV’s have lots of power, and it is real easy to get goign fast enough to lift off before you know it - and now you’re doing an unbridled flight test before you’re ready to fly. I only do high speed taxi tests (still below predicted liftoff speed) on brand new designs - not anything that is as wel known as an RV.

Paul
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  #4  
Old 01-27-2019, 08:20 AM
Jpm757 Jpm757 is offline
 
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I concur with Paul, many taxi tests, especially the high speed type go awry. Pilots find themselves airborne before they know it, without a plan! I would discourage this practice especially in an RV where you can become airborne in several hundred feet. If all the systems check out, point it down the runway and go flying, there's your engine break in. Don't psych yourself out on this one, most likely everything will go as planned. Never flown an RV? Either get some dual or get an experienced RV pilot for the job. I love first flights, it's a terrific unique experience!
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Last edited by Jpm757 : 01-27-2019 at 08:28 AM. Reason: Sp
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  #5  
Old 01-27-2019, 08:48 AM
AviatorJ AviatorJ is offline
 
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Thanks for the responses, I hadnít thought about conditioning the brakes. Read how to do it with Matcos so Iíll do that today as well.

As I mentioned I did a high speed taxi after I fixed my friends RV-10 nose torque. However in that case he was there to stare at the speed and tell me when I hit 55, also given I had been flying that plane I was ready to take off if need be. As you mentioned Paul it took maybe 2 secs to get to 55 before I shut her down.

So going to condition the brakes, keep her under 300 CHT if I can (Iím guessing on run up though it will go higher for a bit). Do the prop pitch check per Paulís suggestion. Then crank her up to 2700 (assuming brakes hold), throttle back and taxi to the hangar.

Thanks again
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  #6  
Old 01-27-2019, 10:13 AM
BillL BillL is offline
 
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Quote:
Originally Posted by AviatorJ View Post
Thanks for the responses, I hadnít thought about conditioning the brakes. Read how to do it with Matcos so Iíll do that today as well.

As I mentioned I did a high speed taxi after I fixed my friends RV-10 nose torque. However in that case he was there to stare at the speed and tell me when I hit 55, also given I had been flying that plane I was ready to take off if need be. As you mentioned Paul it took maybe 2 secs to get to 55 before I shut her down.

So going to condition the brakes, keep her under 300 CHT if I can (Iím guessing on run up though it will go higher for a bit). Do the prop pitch check per Paulís suggestion. Then crank her up to 2700 (assuming brakes hold), throttle back and taxi to the hangar.

Thanks again
I tied down & chocked my 7 when doing the prop cycle test, but it really squatted when cycling the prop. Even starting at 1900 rpm. The book on my prop says 900 lbs thrust, your 10 will be higher. Just be looking outside when cycling, you probably already considered this anyway.

If you are interested I'll sent the video (if it is not too large).
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  #7  
Old 01-27-2019, 05:54 PM
AviatorJ AviatorJ is offline
 
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Did my run up today. It was about 60F out, the CHTs, especially on 5 & 6 were getting way too high. The brakes gave way at about 2500 so throttle down and decided to go to the hangar because of the temps.

Guess it's time to research baffling efficiencies.
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  #8  
Old 01-27-2019, 06:47 PM
Kyle Boatright Kyle Boatright is offline
 
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Quote:
Originally Posted by AviatorJ View Post
Did my run up today. It was about 60F out, the CHTs, especially on 5 & 6 were getting way too high. The brakes gave way at about 2500 so throttle down and decided to go to the hangar because of the temps.

Guess it's time to research baffling efficiencies.
Can you walk us through your runup? How long did you run it, and how much of that time was at higher than mag-check type power settings?

We have a very limited run-up window at medium to high power if keeping temperatures under 300F is important (and it is).
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  #9  
Old 01-27-2019, 08:54 PM
AviatorJ AviatorJ is offline
 
Join Date: Feb 2015
Location: Oklahoma City
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Quote:
Originally Posted by Kyle Boatright View Post
We have a very limited run-up window at medium to high power if keeping temperatures under 300F is important (and it is).
Notes are in the hangar, it was around 20-25 mins total. Of that about 2 seconds were higher than mag check RPM, maybe about 30 seconds at mag check speed at two different occasions. The rest was 1000 - 1300 with a few pulled back idle around 620.

I don't really see the possibility of doing a ground run long enough to get your oil temp up while keeping CHTs under 300. Loop in run ups and it seems to be a challenge keeping things under 400. For reference if I remember the time it took 7 mins for #5 to hit 300, the oil temp was still sub 100.

Outside of my CHT temps, there are a few items I'm not happy with that I'm going to engage with an A&P on (for example double check mag timing). I'm at least confident enough that she'll run and create power, so my next run will be the first flight. The items I'm going to have double checked I can check on my taxi to the run up area and I can validate a full 2700 RPMs of power on my take off roll.
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  #10  
Old 01-31-2019, 06:05 PM
AviatorJ AviatorJ is offline
 
Join Date: Feb 2015
Location: Oklahoma City
Posts: 735
Default Magneto Timing Important

Just wanted to give an update on my high cylinder temps. Today I worked with some real A&Ps on some of my concerns. What was discovered is my left mag was about 2 degree's or so off but my right was over 12 degrees off. From what I understand the pre detonation can and will cause high temps as well as not allow you to create full power... both very bad things! We didn't run it yet, but I'm anticipating lower CHTs.

Anyhow just wanted to update so if someone reads this in the future they don't think my high CHTs were anything normal.
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