More turn and bank

[jmvolpp]

Being another who desires at least one gyro attitude instrument in the panel, I purchased the venturi driven turn and bank kit offered by Aircraft Spruce and installed it, top and center, in N44305 last week while down for annual inspection. The AN 5280-1 T&B has 3 threaded ports on it - 1 on the top rear at an angle, 1 on the back and 1 on the bottom rear, none of which are labeled inlet or outlet. Included with the kit were 2 straight nylon 1/8" NPT with 1/4" straight barb fittings, plus a length of 1/4" tubing better suited as an undersized, very stiff hula-hoop. With the limited room between panel and gas tank, a straight fitting won't work on the back of the instrument. I consulted an avionics technician about which was in and which was out and whether the ports on the back and bottom were interchangeable (we had already determined that the combination of brass elbow with straight barb was several millimeters too long to add to the length of the instrument). That done, I removed the plug from the bottom port so it could be used, plugged the port on the back and hooked everything up, with a piece of gauze on the end of the inlet tube until a filter, not included in the kit, arrives. With the first turn away from runway heading on the way home, it was apparent that the inlet/outlet information was wrong since only the ball worked. That was confirmed with a call to the instrument overhaul shop; the technician also said the port on the back should be used, but couldn't say what the port on the bottom is for. It's hard to argue with the expert, but I do have two opinions and it sure looks like both ports empty the same chamber. I can't find any nylon fittings locally, but have found a one-piece brass elbow at NAPA that I hope will be short enough to clear the gas tank, unless one of you has already determined that the bottom port does work OK.

As an added bonus, the vertical card compass, sitting atop the panel above the T&B, which is in the hole formerly occupied by the tach, now is 30 or 40 degrees out of kilter. (?)

Any comments from those more knowledgeable will be welcomed. Thanks in advance!

Mike Volpp

[NY86]

Re: More turn and bank

Is this what you need?

[jmvolpp]

Re: More turn and bank

Yes, I think so. That looks the same as what I picked up at the local NAPA yesterday, but with a longer barb. Hopefully this weekend will afford a chance to try it as well as to see if the bottom port works. Sure could have used your snow blower around here a month ago!

Mike

[Len Petterson]

Re: More turn and bank

If yo need a vaccuum source, use a Shop vac , or 12 volt car vaccuum. whatch so you dont PULL TO MUCH VACCUUM!
Stick the small hose inside the big one 3- 4 inshes and and you should have enough for a short trial.
Fitting can aslo be had at your local Parker dealer or other hydrualic shop.
Len

[flyguy]

Re: More turn and bank

Mike,
I have 2 disassembled turn gyros in front of me just now. Both the back and the bottom outlets are open to the case and should (and on mine do) work just fine for exhausting the case.
If you have the filter assembly off you may want to check down the inlet bore and see if there is a "plug" with a small hole in it threaded in. This is a nozzle that directs the incoming air onto the rotor. Not there, will not function. Len's suggestion for using a little of the vacuum from a vacuum cleaner hose is a good one--it works.
Good luck,
Darryl

[Howard Wilson]

Re: More turn and bank

I have read that vertical card compasses can be 'wrecked' by a magnetized screwdriver in the vicinity....................? Will look for source, think it was Cessna Pilots Assoc.??? Howard

[Hank Jarrett]

Re: More turn and bank

Not exactly "wrecked" but it certainly won't work with it anywhere near. If you manage to magnetize the structure (or more likely a steel screw) it can cause some problems till you get the screw out but my first plane had a compass that always had pointed in the same direction when I bought it. The prior owner just parked it so it read correctly when the annual was done and said the inspector never noticed. Left me shaking my head but not enough to not buy the plane. When I took one of the mounting screws out it swung around and worked great. He had mounted the compass with steel screws (DUMB!) and one of them was REALLY magnetized. He had flown it for years like that and all he needed was to put the right screws in. There was NO permanent damage to the compass. I still have it and it still works fine.
Hank

[jmvolpp]

Re: More turn and bank

Today's short XC confirmed the T&B works great using the bottom port instead of the rear port as I found the shorter elbow was still long enough to rub the gas tank. But the compass is still off 20 degrees or so.

Thanks for the tips about the magnetized screwdriver, which I used in the vicinity but not for the first time, and the steel screws, 2 of which have been used to mount the compass but up to now haven't been an issue. I'll be sure to replace those before swinging the compass.

Mike V.

[astjp2]

Re: More turn and bank

I use the airbrake style push locks that McMaster/Grainger has with poly tubing and they are Awesome!

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611745533

[Howard Wilson]

Re: More turn and bank

Finally refound the link to "wrecking" vertical card compasses. It is an article by Tom Rogers. Try: http://www.avionicswest.com/articles...etic%20compass!

[Howard Wilson]

Re: More turn and bank

Mike, don't know whether you figured out what the third hole was on the T&B. It came back to me as I was changing out all three gyros on the '56 172... !! The third hole (sharing the chamber) is for attachment to a vacuum gauge. Sounds like you figured out the other option...leave the plug in it. I've also seen it used to carry vacuum to (from?) another instrument. You may want to look into a vacuum regulator also; installed between the venturi and the instrument, it allows you to adjust the vacuum to the optimum "Hg for the gyro. The new AI and DG in the 172 require 4.5-5.4" Hg. Cessna wanted over $500 for one, Wag aero has a PMA'd one for ~$200. howard

[jmvolpp]

Re: More turn and bank

Howard, thanks for the additional info. My current quest with this T&B, with makeshift gauze filter on the end of 1/4" tubing, is to figure why a 2-minute turn takes only 1:00 to the left and 1:20 to the right. The 2" venturi (no gauge, so I don't really know how much suction it makes) is mounted on the left boot cowl - I've seen varied opinions as to best location, but holes were already there - which probably accounts for the left/right discrepancy. I've since come across an original disk type filter that fits on top of the instrument but have yet to get the weather and my work schedule together to see if it makes any difference by creating more resistance in suction through the instrument. I can understand slower performance in the case of less than optimum suction (2"), but am not sure whether higher suction would actually make it work faster. At worst, I may just have to note where the needle produces the 2-minute turn and be done with it, although that somewhat insults my IFR sensiblities!

Mike

[Howard Wilson]

Re: More turn and bank

Hmmm, maybe higher suction would make it closer to the correct 2 min. turn by giving the gyro enough inertia to compensate for the turning moment??? Or maybe you've got one of those gyros where when the guy inadvertantly flys into IMC he says "we'd better do a 360 and get the H out of here!"