Approved Data P-Series/JPI Instrument Installation and Use

[Dave Underwood]

Have any P-series owners had to provide "Approved Data" to put holes in the firewalls to pass wire bundles for the installation of a JPI GEM.

I can see in the service manual Page 16-13 section 16-35 describes doing it, as does chapter 13 of AC 43.13-2A, but has anyone had to provide beam strength calculations or similar to "assure that the strength of the structure is maintained". Are there any recommendations from Cessna in this regard for the 337.

Any input would be appreciated as it was suggested today by my local FAA friends that I would require a DRA to approve putting a half inch hole in each firewall. That would seem over kill to me. If anyone has had this before, or has any "approved data" could they let me know.

Regards - Dave Underwood

[Bob Cook]

Dave

I had a JPI installed in our "P". I believe there was a hole behind the engine and about the middle of the firewall that was used rather than drilling a new one. Besides, they used a type of feed thru that was "split" and then it was cherry riveted to a backing plate. There are in the spruce catalogue as fireproof feedthru's. Make sure you seal from the inside carefully to insure no leaks and use fire proof sealant on the engine side of things.

Ideally it would be best to put a CANNON type feed-thru connector, however, this is not the best idea since the type of wire (nichrome) should not be cut or altered.

The wire JPI uses is rather small and I think the size of hole recommended is too large. I would think the hole for the front engine is about 1/2 to 5/8 inch. The hole for the rear engine was in the top left corner of the rear (looking from the inside) bulkhead and there is a lot of support in that area where other wires pass thru. There is quite a bundle of wires including the spoiler hydraulics and I don't think there should be a support issue. Running the wires up the window channel will be a chore as there is not much room.

I could take some pics the next time I am at the aircraft.

Two words of caution (then some)

1) keep the wires routed AWAY from any of the ignition wires.
2) use the CHT WELL probe where existing cht probes are located. The sparkplug probes are not as good as the well type.
3) Be careful where you drill the holes for the probes on the front engine exhaust. make sure they are uniform length from the exhaust flanges and I think we could only get them about inch away rather than the specified length. You will not get the TIT far enough away on the front engine so it will read somewhat different to the rear...... it is more a relative indication anyway.
4) be sure to add the oil temp sensors. they are very important.
5) I use the OAT probe to measure the intercooler exhaust temp so you can get a handle on boost limits.
6) Reset the limits so that CHT is 400 for the alarm.
7) take the alarm output and feed it to a LED on the eyebrow to get your attention. It is a great alarm system.
8) do install the jack for the computer serial port. Best location is down under the glove box on the lower right side.
9) connect the wiring close to the battery as possible as it can pick up interference on the radio bus. (my experience).


It is a great instrument !!!! Now you will find out how bad the Cessna instrumentation really is...... ARG!

hope this helps

now for your question. YES= it had to be approved by an Engineer and a 337 drawn up.

bob

[Dave Underwood]

Thanks very much for your comments and advice, all noted with interest. And yes, can't wait to fly with the GEM and find out what is actually happening with the engines during various phases of flight.

Do you think the FAA would accept my engineering calcs as to web strengths and safety factors of the half inch holes? No, I didn't think so.

Could I have the name and contact details of the DER who did your work on the basis he could do the same for me by just pulling out the file records?

Nothing is easy, but at least it will keep the FAA happy.

Regards - Dave Underwood

[Mark Hislop]

Dave:

My 73 P337 has a GEM 1200 unit. There was no DER involved. The GEM came with an STC. It was installed by my shop and signed off by the AI at the shop. I don't remember the pathways used to run the wires, but I am going into annual inspection in February, and I can check then if you need me to do so.

I also installed a Shadin Fuel Flow system. Same deal...just installed in under the accompanying STC. I know that on that installation, the mechanics were able to get the transducer wires through an existing grommet hole with other pre-existing wires.

I'm not too familiar with the JPI system, but I would assume that it also has an STC. If so, I would think that all of the calculations have been done as part of the STC.

Mark

[Kevin McDole]

My experience with the JPI 760 installation was the same as Mark's. The STC covered it. No DER required.

I would encourage you to consider using two JPI EDM-800's instead of the EDM-760 model (albeit at a significant cost increase and additional panel space). While the 760 does 90% of the job, there are a few extra probe options available for the 800 model. I think most notably the 800 has a digital RPM (which is missing from the 760).

The 800 also has MAP, Oil Pressure, % HP, IAT & CDT (the difference indicates the cooling drop across the intercooler).

Regardless of which unit you choose, I strongly recommend the optional oil temp prob. The competition from Insight is the GEM and to my knowledge it has not Oil Temp option.

Check out JPI website and see if the extra probes are of interest to you.

http://www.jpinstruments.com/main_Frame-2.html

[Bob Cook]

Kevin

If there is a modification to a pressurized hull then there needs to be an approval. The 337 does not cover structural modifications... only electrical and physical such as mounting. In this case there is an increase in hole size or an additional hole required.

re 800

If you have a shadin the diff isn't worth it. It still needs to be "calibrated" and once you fly for a while the power settings become rather automatic. Then there is LOP (oops).

Using the temp probe to monitor intercooler output on the 700c can give you a good indication of boost but is not really advantageous.

Having both engines on the same display is a real bonus with the 760C.

imho

Bob

[skymaster]

what tit's are you showing for climb and cruise ? J

That's just too easy.
________
KinkyViolet

[Bob Cook]

are you refering to the ones up front or the "hind" ones?

There is a difference.

Bob

[Kevin McDole]

Bob,

Since my aircraft was a Riley conversion, I replaced those old engine monitors and I assume that no new holes were needed. Sorry I don't have more details on that point.

I agree with your point about the Shadin - the %HP is not essential. However, it's the digital RPM that I miss the most.

Let me offer a case fo why two different displays could be handy. My rear engine cyl #5 is the hot one, and the front is #2. I don't use auto-scan, so I always set it to the probe I want to watch. On the 760, you have to watch the same probe on both engines (meaning both have to display #5, or both display #2). Two separate units would let me independantly display these. But there's a significant price to pay for this "benefit."

[Dave Underwood]

An update for you all and a thanks for your input.

The FAA does require a DER signoff for a new hole in the firewall of a P-series as none of the existing holes appear usable.

Mind you any time you meet a nice FAA inspector and he agrees to the Field Approval, I think you should be thankful.

If anyone is interested, in the future, I will have a data package and a signed 8110-3 that will allow half inch holes to be placed in the upper passenger side front firewall and upper pilot side rear firewall with approved data and installation instructions.

As I mentioned, he was a very nice fellow and made a number of very good and sensible suggestions about paperwork and the aircraft.

One that was of particular interest was his strong suggestion to install a CO Detector on the panel. (Janitrol Heaters being the reason)

In researching what is available, I see Aircraft Spruce has an Areo-352, P/N 13--1642, a small panel mount unit that looks good. I know AvWeb did a report on some units, but has anyone had any experience with the Aero-352 units?

On the discussion about graphic engine monitors, I took the JPI 760 w/fuel flow as it was a direct replacement for the Shadin and minimizes the use of panel space, already tight. It also gets the gauge right in front of me (above the IFCS) so I can see what is going on.

The note about the OAT is interesting. Here in England in the winter you can be flying along IFR in cloud, in well above freezing temps and then hit a cold pocket and get a lot of ice very quickly. That happened to me on a recent night flight with the boots U/S at the time. There was some excitment as I had already decended to the sector MSA in prep for the approach. We were close enough to the airport to get vectors direct and a decent to get into warm air. I am going to use the OAT and alarm it so at least I know when it is about to happen.

Regards - Dave Underwood

[Bob Cook]

Dave

CO2 monitor will not do any good unless you run around unpressurized. The "fire" is at atmosphere so any leaks in a chamber the cabin air will be exhausted thru the leak.

Why waste your money?

the alarms work really well including the over and undervolt alarm. I alarm the oil for 95 degrees and do not move until the flashing quits (on startup).

fwiw

Bob

[skymaster]

curious if my tit temps are close. 73 p cruises 1440 degrees climb below 1500. book temp tit limit 1650 degrees. engines running well within ranges est 60-65 % power. latley rear engine running higher tit. last annual i scorched three cylinders/valves operating lop. my gem 603 tit number is easier to read than the bar graph. probably accurate too? what tit ranges are you running cruise /climb. j

[Bob Cook]

Skymaster

The TIT has never been a concern. Running 1450 up to 1525 depending on power etc. Never had them close to 1600 as I only lean DURING CRUISE or DECENT, otherwise mixture is to the wall.

If you are running 65% power or less then I do not see how you can burn valves. You must have been running higher power.

Do you have intercoolers?

The TIT will drop when going LOP. If running LOP (heaven forbid) you need to insure your last cylinder (to peak) is 50-75 LOP otherwise you can/could burn valves but more likely 0-40 ROP. I am more concerned with EGT's that TIT. In the 337 the TIT is more likely to be the EGT of the last cylinder UNLESS you are wasting fuel and the unburned fuel is igniting in the exhaust stack (burning)... then the tit will be higher.

Some people will use the PEAK on the JPI/Gem to determine peak but there are *5* more cylinders to LEAN before you are LOP.

The other good test is to roll back mixture until the engine starts to "baulk"... richen till smooth... then look at your fuel flow. Then slowly richen and monitor EGT. All cyl should go UP then start to FALL OFF. If one starts to fall off then that cylinder never did reach "peak" and it is still on the ROP side. Depends on how close the cylinders and injectors are matched.

You are more likely to burn valves running lean at higher power settings especially in the climb. Always important to monitor full rich / full power fuel flows to make sure they are in spec.... rest should track.

How do you calc your power if you have intercoolers? Is the tachometer been calibrated recently? and--- what is the fuel flow at 65% power?

I always have found CYL2 running hotter than the rest. I have found the TITs closely matched when the engines are running same fuel flow during cruise to within 5 degrees.

There was a baffling change on the engines around s/n 225 and higher (around '75 or later and the temps improved somewhat.

bob

[Kevin McDole]

Originally posted by Bob Cook Some people will use the PEAK on the JPI/Gem to determine peak but there are *5* more cylinders to LEAN before you are LOP.

Bob,
Agreed. LeanFind mode tells you the first to peak - and for LOP operation you need to know which peaks last (i.e. the richest cylinder).

Here's two thoughts about how to deal with this:

1) Use the LeanFind mode "in reverse." If you use LeanFind beginning from LOP and richen the mixture, the first cylinder to peak will be the richest - so you can use that as the reference, and lean out the misture until you've hit your desired delta LOP temp.

2) Or, JPI offers a $100 update to the EDM-760 to give it the “Overlean” feature, which is an icicle display that helps you setup LOP.