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08 Aug 2020, 22:11 [ UTC - 5; DST ]


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 Post subject: T303 alternate air door spring tension
PostPosted: 25 Jul 2020, 14:03 
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Company: Skyhaven Airport Inc
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I’ve got a T303 here in the shop which I’ve been working on for about 10 years. With the really hot weather we are having lately I’m working down through the list of possibilities for low power on takeoff which clears up about rotation. We are near sea level at 640ft.

Cooler weather no problem getting to 32.5 and 2400RPM. Fuel flow is normal.

If it flies and lands in the very hot weather we are having. Then sits and heat soaks on the ramp about 1/2 hour the next takeoff will be low manifold pressure 31” Low RPM 2200 to 2300 static and lower fuel flow. 24.6 gph per side.

The indications will come up as the takeoff roll progresses and then after the gear is up and normal climb out everything settles in to normal indications.

The prop governors, engines, props are not matched for hours but the problem seems to affect both engines. I’ve gone down the usual list of timing, compressions, plug resistance, filters, oil change, injectors, unmetered flows, idle speed, idle mixture, flushed turbo bearings, back flushed controller, borescope cylinders and waste gate, mouse milked waste gate, Lines to controller clear, pressure tested intake system, upper deck and exhaust system. Instruments are now a new Garmin G600 monitor. TIT, EGTs and CHT’s are all together and normal. Engine controls all hitting the stops. Pulling governors they feel close to each other in rotation. Pulling one prop it’s not sludge behind in crank

I’m using Phillips XC20-50 and cam guard. Oil temp is high after sitting but normal in flight. Near 220 on shutdown after a few min. No real way to get any cooler due to high OAT about 95F. oil after sitting was 180 on startup.

Oil too thin for the governors to make enough pressure for the props to go to the low pitch stops?

Prop low pitch stops set too high? One prop is marked at 18.47 degrees which is too low but the sticker could be old since the props were apart to reseal a couple times since the overhauls.

In looking around the engine compartments the alternate air doors on the back of the air filter boxes seem very light. It feels about the same moving the door on each box but could it be sucking hot air out of the engine compartment near the turbocharger at the start of the takeoff roll and once the airplane gets enough airspeed the pressure from the external intake scoop is high enough to close the alternate air door fully.

Does anyone know if there is a minimum spring tension on Cessna spring loaded alternate air doors? I have not found any T303 specific info but possibly there is for another model that would be something to compare. Thanks


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 25 Jul 2020, 20:16 
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Location: Columbus, Ohio
Aircraft: Baron 58, Lear 35
Not making static RPM and having it slowly spool up to normal RPM and FF during the takeoff roll sounds like a prop/governor issue. Maybe call your friendly neighborhood prop shop and pick their brain a bit. One thing I can think of which would be very unfortunate would be if the transfer collar clearance is too large. That could make the prop very slow/unable to reach the low pitch stops if the oil is hot. If that is the problem, it will eventually get worse and the prop won’t make TO RPM even with cooler oil. It should work fine even with the temps in your post.
If the oil pressure is in the green, a properly functioning governor should have no problem creating enough pressure with the hot oil. That, of course, assumes it’s not all dumping out of the transfer collar and back into the sump.
If you think the alt air spring could be the issue, fly it, land and safety the door shut, then do a ground run and see if you make static RPM.


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 25 Jul 2020, 21:26 
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Joined: 08/10/12
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Location: KTKV KBKV
Aircraft: Cessna T303
Hey Charlie,

Take a look at the “Hot Day Takeoff Checklist” in Chapter 4 of the AFM. I love my 303 but she does have her flaws. What you’ve described is very common on hot, humid days after heat soaking.

Kirk

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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 04:22 
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Username Protected wrote:
Hey Charlie,

Take a look at the “Hot Day Takeoff Checklist” in Chapter 4 of the AFM. I love my 303 but she does have her flaws. What you’ve described is very common on hot, humid days after heat soaking.

Kirk


This was, honestly, the only bad thing I had to say about the 303. Fantastic platform, but a massive pain whenever it would get very warm and humid.

I ended up burning a starter in Lithuania on a hot start, having just landed to refuel quickly.
Or cancelled more than one mission in Luxembourg in the middle of summer trying to get a quick turn-around.

And there's also the sky-high CHT when you fly 5hrs, land/refuel/manage to restart in less than 30min when the temps are higher than 28degC. Stupid engine covers.

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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 06:56 
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I’ve got a copy of the warm day takeoff checklist. It has been a problem for a while but it seems a lot worse than other TCM installs and I’d like to know why.

Working down through my fuel flow K factor seems accurate after about 60 hours since the install of the G500. End of trip fuel used matches very close with what is pumped to top off the tanks.

The lower RPM / MP will not let the fuel flow increase up to the minimum 150pph or desired 160pph (I’m looking for 25 gph per side) until the rpm comes up after liftoff and the gear is up. Then we are looking close to normal.

I did try disabling the fuel pressure regulators and also tried increasing HP pump pressure slightly (1/8 turn) with no change in performance.

Boost pumps on brings fuel flow up slightly but also no change in RPM increase time.

Transfer collar is a possibility but with one engine and governor having 1700 hours and the other having 400 hours it seems odd both engines have exactly the same trouble. Almost like it’s an installation issue (alternate air doors?)

CHT has been within limits I try to stay 380 or below. TIT and EGT are normal as well. I have the TIT alarm set at 1650
TCM shows 1650 max and 1750 allowed for 1 min while leaning to find peak.

Current plan is send both governors out Monday. Oldest will get overhauled and newest bench checked and checked for SB compliance. I’d like to get them both on the bench together to see how they look before teardown. The higher time governor has noticeable wear on the splines and I do feel more rotational freeplay in the governor drive on the higher time right engine.

Disabling the alternate air door for testing is also on the list. Hopefully I get the governors back before the hot weather is gone.

It has been a trouble for a while but when you need the performance most it’s not there. Later in the flight no problem which is frustrating.

On a side note I pulled my left propeller. I had removed them a couple years ago because the engines stopped with left propeller clocked one blade sticking up and right propeller one blade sticking down. We have had a vibration in the left engine that could not be balanced for years. The left engine has been overhauled due to metal from the starter adapter failure and the vibration remained.
I thought the shop that installed the engine at that time had not installed the propeller correctly. So I removed both props to verify the single blade was over the TC mark for each propeller. The deice rings which cover the crank flange markings have stamps on them but it’s not always in the right spot during installation.
Darn if after that they were still one blade up and the other down on shutdown. I understand phasing and that the propeller clocking affects the vibration level but I have always installed a 3 blade on a 6 cylinder TCM engine so it stops with one blade down and then is in a good position if you ever needed to try to prop it. #1 blade oriented when #1 cylinder is on compression.
This has run smooth on many other airplanes, could be balanced and is how the right engine is setup.

What could the reason be for the left engine to end up opposite when installed to the crank markings? It is the “Correct” rotating engine. Any other T303 owners out there try the propeller both ways on their T303 to see which orientation runs the smoothest? Both stop single blade vertical up or vertical down?


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 08:18 
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Username Protected wrote:
Both stop single blade vertical up or vertical down?


Mine used to stop one up (left eng) one down (right).

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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 08:57 
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Interesting. This one is the same It would be interesting to compare to other counter rotating 3 blade propeller direct drive piston twins. Seneca or Navajo for example.


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 10:23 
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Joined: 08/10/12
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Location: KTKV KBKV
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Username Protected wrote:
I’ve got a copy of the warm day takeoff checklist. It has been a problem for a while but it seems a lot worse than other TCM installs and I’d like to know why.

Do you mean other 303 TCM installs or TCM installs in general? I’ve been down this road. This engine does not run or operate similarly to the other TCM installs. I’ve learned to accept it.

The lower RPM / MP will not let the fuel flow increase up to the minimum 150pph or desired 160pph (I’m looking for 25 gph per side) until the rpm comes up after liftoff and the gear is up. Then we are looking close to normal.

The Hot Day Checklist allows for less than 160pph so that by leaning you can recover some of the lost RPM.

Current plan is send both governors out Monday. Oldest will get overhauled and newest bench checked and checked for SB compliance. I’d like to get them both on the bench together to see how they look before teardown. The higher time governor has noticeable wear on the splines and I do feel more rotational freeplay in the governor drive on the higher time right engine.

It has been a trouble for a while but when you need the performance most it’s not there. Later in the flight no problem which is frustrating.

The fact that the issue is on both engines tells me that it’s the “normal” hot day issues we all struggle with in the 303.

On a side note I pulled my left propeller. I had removed them a couple years ago because the engines stopped with left propeller clocked one blade sticking up and right propeller one blade sticking down. We have had a vibration in the left engine that could not be balanced for years. The left engine has been overhauled due to metal from the starter adapter failure and the vibration remained.
I thought the shop that installed the engine at that time had not installed the propeller correctly. So I removed both props to verify the single blade was over the TC mark for each propeller. The deice rings which cover the crank flange markings have stamps on them but it’s not always in the right spot during installation.
Darn if after that they were still one blade up and the other down on shutdown. I understand phasing and that the propeller clocking affects the vibration level but I have always installed a 3 blade on a 6 cylinder TCM engine so it stops with one blade down and then is in a good position if you ever needed to try to prop it. #1 blade oriented when #1 cylinder is on compression.

Welcome to my world. You may recall you and I discussed this exact situation last year with my props. We reindexed the right prop which had been installed 180 degrees off, and after indexing it properly it still stops opposite of the other prop. Look at some pictures of 303’s, you’ll find most of them stopped opposite.

What could the reason be for the left engine to end up opposite when installed to the crank markings? It is the “Correct” rotating engine. Any other T303 owners out there try the propeller both ways on their T303 to see which orientation runs the smoothest? Both stop single blade vertical up or vertical down?


I suggest you give Tony a call at TAS in Defiance, OH. He’s the expert on all things twin Cessna. Or just head over to the TTCF forum and you can read about all of the issues you’re having. All of them have been covered at one time or another. There’s a 303 specific area.

I’ve come to the conclusion that while some of my thousands of hours of TCM time applies, most of it does not “fit” the 303’s TSIO520AE engines. It’s a totally different animal. As to the let side vibration, it’s inherent in a certain percentage of the fleet. Mine has it too. I don’t like it, but it is what it is.

Best,

Kirk


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 17:00 
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Kirk I mean other TCM installs or turbocharged airplanes in general. I’m in and out of a lot of the singles and twins test flying after maintenance and used to fly/ maintain them part 135.

I don’t remember ever seeing in any other airplane like the T303 with a hot day procedure to run up static and lean to a minimum fuel flow to increase RPM then release the brakes and continue to move both mixtures back towards until rotation speed is reached rich but not far to maintain takeoff power. Then full rich for climb to altitude.

The manual says to abort the takeoff if below 2300 RPM and at 2200 RPM static to lean to 21.5 GPH roughly progressing back up to about to 25 minimum to 26 GPH as the RPM comes up.

If it’s very hot I can’t get to 2300 RPM but since I’m light I’ll take off anyway. Then it will increase up to 2400 and fly away like normal.

It seems to me like it is getting hot air into the induction until enough forward airspeed is reached. The hot cowl air should be expelled pretty fast as the power comes up and with the large cooling outlets on top of the cowl. The only other explanation I have is if the propeller counterweights are over balanced until there is forward airspeed and the prop load changes. But the governors cannot keep up.

I remember your props but I wonder if the left prop installed correctly for this slightly rare odd engine is actually the problem. Did any other airframe use this engine? Could TCM and Cessna have clocked the left propeller 180 out to make the T303 propellers phase opposite of each other between the power pulses and the blade shockwave hitting the fuselage for the base airplane with no sychrophase.

Since we have the optional phase control could we install the left propeller like normal on other IO-520’s which may match up with the engine better for less vibration like the right engine does and then control the phase with the governors. It would be interesting to compare engine construction (crank balancing) and prop installation to a 3 blade on an O-470 U 2400 RPM engine

It’s been discussed a lot of times before but not quite in the context of if the counter rotating propeller phasing problem is worse than any engine mismatch.

viewtopic.php?f=37&t=148972&start=15

With the economic climate and low sales the 303 plus being built in the single engine plant vs the longtime twin factory I think it never quite got all the bugs worked out.


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: 26 Jul 2020, 18:31 
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Interesting tie in between the Brackett filter and alternate air door.
This T303 has Brackett filters. I’m a fan of the filters but in this particular application could it change the airflow volume enough to allow the doors to open?


Beech Engine Air Filter
Model F-35 7160
Bonanza

After installation of a Brackett air filter, the submitter found the
manifold air pressure (MAP) was 2 inches (Hg) lower at takeoff power
than with the original filter installed.

An investigation determined the differential pressure was opening the
alternate air door. The alternate air door began to open at 21 inches
MAP, and was fully open at 23 inches MAP. A new alternate air door
spring was installed, and another operational test produced the same
result. From reading this report, one would conclude the Brackett air
filter was not allowing sufficient airflow to the engine.

This problem was presented to the manufacturer who stated this was not
normal. According to Brackett, "one should normally see approximately
2 inches H20 drop or 1/5 inch Hg." This air filter system has been in
use for many years, and the manufacturer is not aware of this type of
previous occurrences. A review of the FAA Service Difficulty Reporting
(SDR) data base revealed 53 entries associated with Brackett air
filters since 1986. Only two of these reports cited symptoms described
in this article. The cause of one report was attributed to excessive
oil on the filter element, and the other to installing the assembly
"backward." Most of the other reports concerned water or ice saturation
of the filter element during operation and deterioration of the foam
filter element.

The exact cause of this defect has not been determined. If additional
information is obtained, it will be printed in a future edition of this
publication.

Part total time-0 hours.


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 Post subject: Re: T303 alternate air door spring tension
PostPosted: Today, 06:32 
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http://nctc.tk/Cessna/Twin%20Cessna/300 ... 062-60.pdf

Looks like 6-12 lbs to open the alternate air door magnets on the Cessna 320

Both doors on this 303 are much lighter spring force. Less than 1/2 lb force to open the doors fully.

I wonder why Cessna went with the springs over magnet latches other than it’s a progressive opening.

Anyone have a 320? are there springs in the doors also or just magnets?


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