That should be reasonably easy. I lost 380 lbs with the full upgrade sans AP (but with dead wire removal, insist on that), and the AP would allow me to drop another 100 lbs easy (it would allow me to remove the AC inverters, for example).

Also, with the SPZ500 gone, you can pull the radar altimeter and just use the GPS derived AGL readout on the G600 TXi. That saves more weight.

The less stuff you have, the less weight it takes, and the less it costs to maintain. A digital AP would really help in this regard, I can remove 13 boxes and associated wiring from my setup if I had one.


The battery wires are 00 gauge and for that length might need to be 000 gauge to avoid excessive voltage drop. You probably cannot use the fuselage as the negative return for starting currents, either, so there are two wires to the nose battery from the J box. Using 000 gauge, you will have 1.1 lbs per ft for a pair, so that works out to around 30 lbs of wire, plus you have to penetrate the pressure vessel 4 times with this high current cable. There is a reason the battery is right between the engines.

The vapor cycle AC being up front is more reasonable at 100 amps, but quite a lot of rework to do that. Mainly you need a fresh air source and exhaust air dump. I believe some after market AC units did go into the nose.

Mike C.

The a/c system in these are stupid simple. Relocating it to the nose would not be hard to do. The exercise in paperwork and approvals to make it legal would be much more work, IMO.

Is there an STC to move the battery and AC? What’s the paperwork route for that?

I've thought about this for my plane and there are some subtle things to get right.

For exhaust air, the grille it has in the back works up front, so just relocate it.

For intake air, however, you can put a grille up front you think is going to suck in air and it actually blows out due to the curvature of the skin. It takes some careful aerodynamic design to make sure the air flow is inward.

Structurally, the compressor, motor, condenser is about 60 lbs, so you have to find good means to mount it.

You have to move the refrigerant lines from the rear bulkhead to the front.

You have to pass the 100 amp wiring to the front.

Moving it up front would probably steal space from the baggage compartment.

Servicing it would generally be easier up front, and its absence in the back would make things easier there, too.


Maybe. Not sure.

I have seen some drawings from FWA that are for a forward compressor nose install, maybe that helps, but perhaps not since I think you would need more than this. Maybe Enviro has more drawings and they would help?

I'd love to see someone do this and see what the results are.

Mike C.

The 501 IPC has all of the drawings for Freon air-conditioning in the nose. I’ve seen an airplane with that install briefly in person but I haven’t spent any time exploring the installation in detail yet. When he comes in for maintenance, I’ll have a chance to take a closer look. It definitely takes up half of the baggage area and I believe there’s only one set of louvers.

Was it N70CG? Here is a picture from CJP showing the vent just above the nose gear:

The previous owner said that the AC did not work very well in this plane - he said that it cooled the flight deck but not the rear of the cabin. Could have been an issue with his plane though. It looks like Tarver bought it from that owner and then resold it in the past month. Maybe he found and fixed something with the AC or if it's an issue with the nose AC.

My AC works fantastically so I am loathe to change it. I'm currently flying with 120lbs of rocks in the nose for most flights in order to maintain CG (full Garmin panel in my plane). If I went digital autopilot that would aggravate the aft CG. I already have O2 in the nose.

Yes it was 70CG!

That’s interesting because the IPC shows the evaporator(s) on the aft bulkhead. I would expect the higher volume of colder air to be delivered to the cabin. That’s something to check out!

I am in the process of rebuilding my a/c. Lots of fun! We are converting to R134A.

I have to fly with 200 lbs in the nose when I am solo. I also have a garmin panel.

This is almost certainly an issue with the plane. The tricky part is the expansion valve settings to balance the front and rear evaporator performance. It sounds like the rear expansion valve is set too tight, causing little to no flow. I had to play with mine a bit to get it "just right", it was very badly setup when I got the plane.

I very much doubt this is an issue with the nose location for the compressor. The nose compressor will work better than the one in the tail since it will be drawing in colder air than the compartment that has the air cycle machine and bleed air stuff in it.


Someone set up your expansion valves and charge just right, then.


I fly with 100 lbs rocks and 100 lbs tools and spares, 200 lbs total, in the nose. I need that to fly solo. I need only 50 lbs total if I fly 2 up front. With anything else, no nose weight is needed. This is ideal since the plane gets lighter as I add people. Previously, the plane was nose heavy and the prior owner complained about having to through weight in the back if they took a lot of passengers, which is bad. Plane flies faster if you are at the rear CG limit.

I am looking to move oxygen to the nose during my phase 1-5. That will let me drop about 50 lbs of rocks.

Moving the compressor is a bigger job, but would come with bigger benefits.

Even if you have to add ballast, the digital AP will save weight. For example, you can then get rid of your inverters which are behind the CG. Also, the ballast can be far forward so 1 lbs of AP weight savings is less than 1 lbs ballast.

SB500-21-15-R02 deals with the nose AC install in 500/501 planes, too big to attach (1 MB limit, what is this, 1995?).

You can download it for free here:

https://ww2.txtav.com/TechnicalPublications/SI

Mike C.

A concern I would have with that mod is RVSM issues since the vent is directly in front of the static ports:

It seems like the vent air flow would cause some sort of static disruption and could affect RVSM accuracy.

Ideally one finds a way to vent the air not directly upstream of the static ports.

Mike C.

It's hard to believe but a properly functioning ACM (and I've only seen 2 of them in my life in Citations) spits ice out and you don't even need a freon system.

Perhaps a better solution is getting rid of the freon all together and work on improving the ACM/blowers. That would yield a 75lb savings in weight.

My next dream list is making modern carbon fiber seats. The seats in these airplanes are outrageously heavy.

I suspect your two very cold examples were due to a stuck mixing valve in max cold. The Citation controller tends to operate quite far from the freeze point to avoid freezing up the separator sock. It is a bit too conservative, especially compared to what my MU2 did. Maybe we just need a redesigned controller.


Maybe, but it sure is nice to turn on that freon with GPU and/or right after engine start to get cold air moving.


They are outrageously heavy, like 45 lbs each for mine with the lateral translate option.

But this will make the tail heavy tendency worse, alas. Still a win since you can save 200 lbs in seats and replace that with about 60 lbs in ballast.

Now about that 110 lbs galley cabinet I have up front that I don't use, I'd love to get rid of it and just have a baggage bin or empty space.

Sadly, the majority of these changes make the plane more tail heavy.

Mike C.

The military Citations I chopped up had two air cycle machines. The primary purpose of the second one was to cool the F-16 radar up in the nose.

We took out my beverage bar and put in a barrel seat.

Mike

Your interior looks great! I wish I didn't give that left side barrel to you; I haven't seen another one since! It's a very rare seat.

Yeah that was a score. Haha thank you.

It also allowed me to move the partition back. Then with modified seat cushions got a lot of extra room in the pilot seat. Had to figure out some way to my my 6’5” 270lb but up there.

The other thing that spoils my family is the huge area in the back. The distance between the rear bench and rear facing seats is massive.

The interior is one of the things that makes my plane so hard to replace.

Mike