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Taxi Test Advice

AviatorJ

Well Known Member
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!
 
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.
 
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
 
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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Thanks for the responses, I hadn?t thought about conditioning the brakes. Read how to do it with Matcos so I?ll 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 (I?m guessing on run up though it will go higher for a bit). Do the prop pitch check per Paul?s suggestion. Then crank her up to 2700 (assuming brakes hold), throttle back and taxi to the hangar.

Thanks again
 
Thanks for the responses, I hadn?t thought about conditioning the brakes. Read how to do it with Matcos so I?ll 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 (I?m guessing on run up though it will go higher for a bit). Do the prop pitch check per Paul?s 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).
 
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.
 
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).
 
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.
 
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.
 
Brake pads are easily replaceable, engines aren't. I wouldn't worry about them.

Always, always check timing before running an engine for the first time! Even if the engine has been run in a test cell. There is no reason not to do it.
 
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.

Put a couple washers on the back baffle bolts. It will drop the temps down about ten degrees. Unfortunately, that bolt is only on one side.
 
Sounds great, not sure what you mean though. The bolts holding the bracket in?

If you search "washer trick" you will find how to put a washer in the rear screw (between baffle & cyl) holding the aft baffle onto the #5 cyl. The search will show 4 cyl examples, but it is the same for your 540. It allows better air flow around the rear fins of #3/#5.
 
Go - - get ready for a safe first flight and . . .

Don't worry about that washer trick until you have compared your temps with some airspeed.
 
Don't worry about that washer trick until you have compared your temps with some airspeed.

Too late! I did it this morning and a handful of other things. This meant I had to do another run up to test the retiming of the mag, governor adjustments, among other things.

I seriously debated just waiting for my first flight, but too be quite honest I'm already anxious about the first flight and had to ensure (For my own self insurance) that my prop was going to pitch, not hit the ramair cowl and that I was going to be able to make full power. This time I did it on that taxiway right out front of my hangar. Used 3 chocks, parking brake and a winch attaching the tail to the jeep.

CHTs on 5&6 were still higher than the others, but over all noticeably lower than before. My Mags checked out great, it took a bit but got all the air out and the oil into the prop so that was working. Ramped her up to full power for about 15 seconds and she pegged at 2650. Minor adjustment of 25 RPM will be made prior to first flight.

All in all I'm now 100% confident that she'll get up and go and assuming we don't find any structural issues during the pre-inspection inspection then the DAR inspection should go great!
 
Ramped her up to full power for about 15 seconds and she pegged at 2650. Minor adjustment of 25 RPM will be made prior to first flight.

Don't forget that static runup RPM will be lower than when you're actually moving down the runway. I chased what I thought might be issues with my governor or limits on the prop for some time thinking I wasn't anywhere near close enough to the 2700 I was looking for at full power until I did my first high speed taxi and found I'd overcompensated and then had to dial it back.
 
Don't worry about that washer trick until you have compared your temps with some airspeed.

I agree

The cooling system (baffles, etc) functions with airspeed in flight.
Making changes based on what you see with ground runs or taxiing is a waste of effort.
 
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