Flap/Gear Warning Mod  Developed by senior Swift mechanic Buzz Winslow

From: Bob Runge (
Subject: Flaps and Windows
When I'm done flying for the day, I leave my flaps up. Next time I get there, they are either somewhat down or down completely. When I turn on the master, the hydraulic pump comes on and puts them up. Is this an indication of a leak somewhere or a bad hydraulic flap actuator?

If the flaps go down without any external hydraulic leak that is an indication of internal leakage from pressure to return. This can happen in the actuator, or in the hydraulic package on the firewall. The actuator is a simple fix, usually an "O" ring. If its in the hydraulic package its usually the brass plates which are in there leaking, which requires lapping the plates for a perfect seal. Usually, when I've tried to lap them I end up making them leak a lot worse! Joe Ranson does a good job on these.

Subject: Re: bearings
In need of a source for the bearings that press into the flap and aileron wing fittings.

Those are K3L and K3SL bearings. The "S" denotes "swivel", the tail surfaces have plain K3L and the flaps and ailerons have K3SL. I would imagine Joe at Swift parts has them. I see Aircraft Spruce has them also in their catalog.   -- Jim

Subject: Re: Need part number
From: Eddie Shields <>
Do you know the part number to the conical washers that go around the flap bearings at the attach point?? Is that the same ones that go at the aileron attach point also?? Thanks, Eddie Shields

Those washers go everyplace a KS-3L bearing is used. (At the flaps and ailerons on a Swift) I don't know of a p/n but Swift Parts has them. The DC-3 used them and we used to have them in stock at the airline, but Swift Parts is the only source I know of these days. Missed you at the fly-in. -- Jim

Subj: Bleeding Flap Cylinder
From: Bob O'Dell <>
Greetings Jim,
I have gone ahead with installing a wing leveler in N80881. I had thought that only the Century units were STC'd, but Bill Harris pointed out that there was also one for the Brittain system. Bill had one that he wanted to sell, but since it was use, unused for an indefinite number of years, and didn't have all the bits and pieces, I've ordered one from Brittain. Right now the patient is opened up on the operating table and ready for installation of the new component. This preparation of the belly area (second bay, where the aux fuel tanks are located) required pulling the hydraulic lines to the drive cylinder for the flaps. I didn't cap the connections, so must assume that most of the hydraulic fluid in the cylinder (and of course the lines I removed) are now mostly filled with air.  When I reach the happy state of having completed the installation of the servos and am closing up the plane (I'm working under the supervision of an AP/AI), do I need to worry about air in the cylinder and lines? If so, what can I do about it?

You can minimize fluid loss by positioning the flap selector to a position halfway between "up" and "down", and/or get some AN4 caps and cap off the lines. The system will bleed itself. When selecting flaps down, the up lines become return lines and when selecting flaps up the down lines become return lines. Just be sure to replenish the reservoir several times. -- Jim

Subject: Re: Flap Travel
From: Ed Lloyd <>
Hi Jim, it's been awhile.
Stumbled into something the other day concerning rigging differences between GC-1A and GC-1B wing flaps. There is a stop bushing in the flap actuator on the 'B' models that limits flap down travel to 30 degrees. I'm told that you remove this on the GC-1A so you get 45 degrees flap travel. Would seem that you would want 45 degrees flap travel on the GC-1B as well! What's the difference between the two aircraft models that dictates different flap deflection? Just curious. Thanks ..........Ed

The GC-1A's had 45 degrees of travel as built. One of the requirements when converting from GC-1A to GC-1B is to change the degrees of travel to 30 degrees. The reason may be some certification requirement. I have flown big engine Swifts with 45 degrees of flap and whatever the reason, 30 degrees is more comfortable. -- Jim

Subj: Re Skinning A Flap
From: Bob Runge <>
Hi Jim:
N80528's right flap has had a slight crease in it since I've taken over its care. Some klutz must have either stepped on it or dropped a 2x4 on it at some time. The crease traverses the flap from upper left corner to lower right corner. How intense of a job is re skinning a flap and what would be the most difficult part of the job? Thanks Jim. -- Bob

I don't think reskinning a flap is very hard, but for a person who has never done aircraft sheet metal work it may be different! A basic primer - for aircraft purposes there are 4 basic rivet diameters, 3/32", 1/8", 5/32" and 3/16". These take 4 drill sizes - 40, 30, 21 and 11. There are several type protruding head rivets, in 1946 the Swift used AN356 and AN355 Brazier head rivets, nowadays we use the AN470 Universal head rivet. The flap has mostly 3/32" rivets which you will drill out with a #40 drill. 1/8" rivets you will drill out with a #30 drill. After you get the skin off, you mark the bend radius on a pattern, then flatten out the skin. Back drill the new skin using the old skin as a pattern, scratch around the old skin and cut the new skin to identical size. Drill from one corner to the other. Bend the new skin to match the removed skin. Cleco the new skin in place. The rivets will be something like AN470-3-4 or 5 AD. The -3 means 3/32 dia. , the -4 or -5 means the length in sixteenths. The AD means the aluminum alloy is soft enough to drive without heat treating. Drive in the top skin rivets. Drive in the bottom skin rivets. On the bottom skin you will have to use 3 blind rivets near the trailing edge in the ribs where you can't get in to buck. The final trailing edge row is easy to shoot but a rivet squeezer may do a prettier job. There could be much more said, but I can't relay years of experience in a short note! Find someone who knows sheet metal work for your first such project, watch, then ask yourself, can I do as well? -- Jim

Subj: flaps
From: Mark Oltjenbruns <>
Hi Jim ,
A day of flying a Swift is better then any day at work ...but we have to pay for them! My question is that my flaps works most of the time . I have replace the solenoid with the one that is listed on the site . Is there any contacts or wiring that can be loose that I can look for . Happy Flyin’ , Mark

The flaps do not involve that solenoid - the solenoid is in the gear circuit only. I had a similar problem once and it was just a loose wire on the switch under the panel at the flap selector. Or it could be a bad switch - after all it is probably over 50 years old! The solenoid on the gear circuit takes the starting load off the switch - the flap switch is not so lucky! Not the best way to design a circuit, but it has worked that way for over 50 years. It's pretty hard to argue with that, but perhaps your switch has reached the end of it's life. -- Jim

FLAP FLAP...(030402)
Subj: flaps ...
From: Mark Oltjenbruns <>
Hi Jim ,
I found out that one of the center wires were broken on the flap switch under the instrument panel . I put on a new connector, then I added the new switch ( center off position switch from Swift parts ) . when I connected the new switch . The flaps would only go up and not down. Then I put in the old switch and the flaps would work only if I went opposite direction first then back to the direction of flap travel. Then the pump would keep on running. I then would try the opposite direction, The flaps again would not work unless I would turn the flaps opposite direction first then to the direction of travel, the pump still running ... I'm puzzled! Any help would be appreciated. Thanks, Mark 78311

It sounds like you got the wires back on wrong at the switch. First of all, the switch should be an AN3022-3. I don't like the replacement that requires holding the selector "down" to get the motor to operate. If you can still read the numbers on your wiring, wire #40 goes the the up side, wire #37 goes to the down side and wire #41 and #22 (amber light) go to the center contact screw. Do you have a VOM? Try studying the diagram on pg. 34 of the Swift Maintenance Manual and check things out with the Ohm scale. -- Jim

FLAP FIXED...(030402)
Subj: flaps ...
From: Mark Oltjenbruns <>
Hi Jim , You were right the wires on the up and down postition were on the wrong terminals ! Thanks , Mark 78311

FLAP RIGGING...(060102)
Subj: Rigging info ?
From: Joe Sills <>
Can you tell me the reason for reducing the flap rigging to 30 degrees from 39 degrees when converting from a GC-1A to the GC-1B ? I am trying to rig N80737 S/N 140 and have run out of travel on the adjustment. I also wonder if you have a set procedure you follow when rigging the ailerons. Thanks: Joe Sills

The aircraft will be OK with 40 degrees, but it should be changed to 30 to be in conformity with the GC-1B specs. It tells how to do it in SB #27 -- conversion of GC-1A to GC-1B. It is simple to do, you just relocate the down microswitch 3/4" aft. Just drill off the bracket for the fwd. microswitch and drill holes 3/4" aft then re rivet it back in. The aileron rigging is covered quite well in the Operators Manual. Tape the control wheels in neutral to a yardstick or other straight piece of wood or whatever, then adjust the aileron cable turnbuckles to get the bellcranks 90 degrees to the rear spar. (use an inspection cover for a 90 deg measuring protractor) After you have the cables rigged, adjust the push/pull rod to neutral. Check the travel with a swinging protractor. -- Jim

Subject: Re: flap conversion
From: Ron Williamson <>
I don't have the service bulletin in front of me, but the most important thing is to put that spacer in the flap cylinder. True, the flaps will shut off when the microswitch is reached, but when the gear is cycled or anything else runs the hydraulic pump, the cylinder will continue to travel and will rip that little bracket right off the rivets. Trust me, I've seen it done. -- Ron

You are right, I don't know why I didn't remember that, I converted several GC-1A's to GC-1B's in the 60s and 70s and have no recollection of installing those spacers in the flap cylinder. Perhaps Univair furnished flap cylinders with that spacer already installed at that time and I used a cylinder from Univair. The Commings hydraulic manual shows that spacer. -- Monty

Subj: Re: flap conversion
From: Joe Sills <>
This is what I have figured out. I placed the flaps at 30 degrees, I marked the actuator shaft with a felt marker, I removed and disassembled the actuator. I measured the length of spacer I needed and had a machine shop buddy make one up. I reassembled everything and all works good. The spacer is 1 1/8 " OD X 1 3/4" long. and the wall is .060 " . I believe the spacers to be different for a GC1A vrs a GC1B. This actuator had a spacer in it but was too short, only 1" long. The Service letter for the conversion doesn't mention the spacer , only relocating the micro switch . Thanks for bringing this to my attention. This is just the sort of "gotch-ya" that ruins a first flight after restoration. Thanks: Joe Sills

From: (Mike Bell)
Except for the landing gear actuators I can't find the part numbers for the O-rings in any of the manuals, just a reference to service kits. My flaps "droop" down and the pump comes on every minute or so when the plane is on the ground. I don't notice it happening in the air. From reading some on Denis' website it sounds like that means an internal leak in the flap actuator. I may be getting a dribble out of one of the downlock actuators too. Do you have the O-ring part numbers for the other actuators? Thanks, Mike Bell

It could be the "O" ring in the flap actuator or an internal leak in the power pack. (Probably the actuator.) That's not too bad a job. Sorry, I don't know those part numbers. I have a Parker kit with all the common "O" rings in it and I just grab one the same size. AC Spruce has those kits for $98.95 in their 2001-2002 Catalogue. -- Jim

(Editor says... I think you can buy specific "O" ring kits from the Swift Museum Foundation too.)

Subj: Flap problems
From: Mick Supina <>
Jim, I recently flew to a nearby airport for gas. After I was in the pattern and had the gear down successfully, I activated the flaps. They only deployed about 5 degrees and then stopped. I moved the flap selector switch to both the up and down positions and the pump would run, but the flaps were frozen. I aborted the landing, left the gear down and returned to Lake Elmo at 90 mph. At first, I thought the mechanism on the cylinder shaft to operate the micro-switches had broken or come lose. It was in place, but was not rigidly mounted. I fixed it so it is well aligned to the switches and adjusted properly. However, the cylinder still will not move when the flap selector is activated. The pump runs but nothing happens. I jacked the plane up and tried to operate the landing gear. It moved a few inches toward retract, but then would not move further. So I am stymied! I know the hydraulic system should be self bleeding, but the system acts like there is an air lock. Any ideas and advice you have would be greatly appreciated. Thanks a million! Mick Supina

It sounds like there is something wrong inside the flap actuator. Get some caps and fittings and cap off the hydraulic lines to the flap cylinder. Then with the airplane on jacks, raise the gear. If the gear operates, you know the trouble is in the flap actuator. -- Jim

Subj: Flap problems
From: Mick Supina <>
OK, I slipped over o the hangar and disconnected the two hydraulic lines to the flap actuator. Then I capped both lines. Next, I filled the hydraulic reservoir back up and jacked the plane up again. Finally, I ran the gear and, bingo, the gear retracts and extends perfectly. So, now I know I have a problem with the cylinder. Do you think an O ring is blown out or torn apart? Thanks for helping me with this mystery! I will remove the cylinder tonight and maybe we can tear into it sometime this week! Mick Supina >>

I would presume the "O" ring on the actuator piston has failed. All your hydraulic pressure was lost -- going from pressure to return, that's why the gear didn't work either. Next step is to remove and repair the flap actuator. -- Jim

Subj: Flaps - the rest of the story!
From: Mick Supina <>
Well Jim, the flap issue is resolved - thanks to your ideas and guidance. We tore the flap actuator cylinder down and one of the snap rings had broken - $0.26 at the local hardware store. During restoration, we had torn the cylinder down and put in all new o-rings, but re-used the old snap rings. There is a lesson in there somewhere! Anyway, the piston could slide back and forth on the shaft and everything became inoperative because all the pressure flowed directly from pressure to return in the cylinder. Everything is back in place and I am flying again! Thanks again for all you help! -- Mick Supina

Subj: Flaps
From: Ed Lloyd <>
Howdy Monty. Was working on Wilfong's Swift yesterday and had a strange situation develop with the flaps. He installed a momentary flap switch which he got from Swift parts. Once the switch was installed the flaps would not operate normally. I checked power with a test probe and power was on the terminals of the switch that should have power. The flaps would operate to the down position if you put some downward pressure by hand on the flap itself. Thought I had located the problem, up / down micro out of adjustment in the belly. With Dick operating the flap handle, I could put some pressure on the tab that operates the flap limit in the up/down position and the flaps would operate. What I was doing was opening the circuit of the up/down flap limit switches. Wound up removing the two limit switches from their brackets (all wires remained connected) and the flaps work "normally" with the incremental switch installed under the panel! The thing we don't understand...... by changing the flap switch under the instrument panel, being careful to change the wires one terminal at a time, why do the limit switches in the belly panel now keep the flaps from operating? Do you know if there is something different internally about the incremental flap switch? I studied the wiring diagram for the flaps in the Commings Manual and that is the way the flaps are wired! Cheers........Ed

Are you holding pressure on the flap switch to the "down" direction? (Or the "up" direction?, when going that way.) Go thru everything on the flap circuit again making sure there is good contact at every wire and no wires or terminals are broken. -- Jim

Subj: Flap Hydraulic Actuator
From: Pat Waters <>
Old age has its problems. I have pulled my flap actuator to replace the O rings. In the course of things, I do not remember if the internal stop ring (+/- 1.5 insert) goes in so as to stop full movement of the push rod when it goes in or when it comes out. (if that makes sense) Another words, when put back together, will I see about 1.5 in of the push rod when it is fully retracted (pushed into cylinder, or will it restrict my pulling it all the way. I hope this is clear. Another way of asking is which end does it go in, where the hole is or the sealed end. Thank you and I am sorry to bother you but my books do not show it clearly. Merry Christmas. Pat Waters

The stop spacer was put there on the GC-1B's to restrict flap travel to 30 degrees. If the spacer is not there (and the microswitch is adjusted accordingly) the flaps go down 40 degrees. The spacer must be installed to limit the full travel. -- Jim

Subj: Flap Actuator
From: Austin Smith <>
Mr. Montague,
I recently removed the flap actuator from the center section to replace the O-rings which had begun to leak after 25 years. When I took the cylinder apart there appeared to be two substances: First, the red hydraulic fluid, and second, some sort of dark oily lube inside the cylinder. My question concerns the second lube. What type lube should I refill the cylinder with, and what is the best way to go about doing this? I have consulted the operators handbook, the blue book and the online archive and haven't found much, if anything, on this. Your help is forever appreciated. Swift Flying, ---Austin

The only lube that is there is MIL 5606 hydraulic oil. 5606 deteriorates over time and assumes the appearance of dark oily lube or something that has been described as Jell-O or even a yellow watery goo. When you assemble the "O" rings coat them with Vaseline, the Vaseline is compatible with 5606 and will be absorbed into it. The actuator will fill itself and bleed itself out after a couple of cycles when everything is reassembled. -- Jim

From: Ed Lloyd <>
Subject: Dick Wilfong’s Flaps
Jim. The flap situation I told you about on Wilfong's Swift about a month ago is cleared up finally. Nothing made any sense in the whole deal. We could not make the intermittent flap switch work unless the up / down limit micro switches made no contact with the limit tab on the flap actuator push rod. Now that is what made no sense. Dick finally went to a supplier in San Antonio and asked for a AN 3022-3 switch like the original and they happened to have five of them. We're going to try and find out who their supplier is and will pass it on to Bo Mabry. Swift parts only had the momentary switch and Pam said we were not the first ones that had a problem with the switch! Anyhow......we installed the new switch, reset the flap up/down limit micro switches, and the system operates the "Mr. Swift" designed it. to operate..........go figure....... I noticed a couple times in checking power to and from the momentary switch while it was installed the power out lug was dead when it should have had power so I think we had a bad momentery switch. Cheers.........Ed

Subj: Flap Limit
From: Ed Lloyd <>
Hi Jim. Understand Dick Wilfong needs to know the length of the restrictor for in the flap actuating cylinder. I suppose I'll turn one out on the lathe for him. For some reason Duane Golding checked the extension and movement on all the controls and found the flaps went to 40 degrees instead of 30. I have flown 3313K probably close to 50 hrs. and I couldn't tell any difference between his Swift and mine in landing. We checked mine and the flaps have the limiter that only permits 30 degrees. Probably was set that way by Buzz Winslow when he was on the coast. Dorothy said Buzz related to her that he has both their Swift set to 40 degrees. Cheers.................Ed

Wouldn't you know, I just had one apart last fall but did not measure the spacer. I looked a the "Answer Man" page and Joe Sills figured out it had to be aluminum tubing, 1 1/8" OD, .060 wall, 1 3/4" long. You can also do the same thing without disassembling the flap actuator by making a clamp which you install on the actuator shaft, limiting the travel in to the actuator. I think the actuator piston is 3/8" dia. (.312) Make an aluminum slug about 1" dia. Drill a 3/8" hole in it. Cut it in half. Drill two holes for 6/32 or 8/32 clamp bolts. After cutting, redrill the 3/8" hole leaving it at least .002 tight on the actuator shaft. Manually move the flaps to 30 degrees, install the clamp on the actuator shaft. Adjust the micro switch to cut off power to the hyd motor at the right time. Jim

The aluminum slug should be 3/8" to 1/2" thick - wide enough for the clamp bolts to have enough "meat'.

Subject: Flap Cylinder-Internal Spacer
It was very good to hear from you! In reference to the Hydraulics Manual (Commings) I noticed the position of the internal spacer was shown located at the end of the cylinder (head) that is attached to the fixed bracket. What is the purpose of the spacer? Is that the proper location? When dis-assemblying last night I could have sworn the spacer was at the end where the piston rod passes through... By the way..the major cause of the leak was failure of the threaded tie-rod which allowed separation of the "head" of the cylinder. Looked like the nut had been over torqued stripping the threads. The other cause was the possibility of water collecting in the cylinder and freezing/expanding during the extreme cold weather this winter...stripping the threads and allowing separation of the head from the cylinder. Thank you for your response..... Warmest regards.... Bob P

If the spacer is not in there the piston travels too far and will break the micro switch bracket or at least push it out of the way. It must be installed to limit the piston travel. -- Jim

Subj: Sagging flaps
From: (Harry Fenton)
Hi Jim,
If you recall, about three weeks ago the seals in my flap actuator blew, and I replaced them. No problem, the new seals went in with no problem and the flaps have worked perfectly with no leaks. But, now the flaps sag about three inches after a few days of inactivity. I never had this problem previously with the old o-rings. I can't find any external leaks to the system and I really don't want to open up the power pack to lap the plates. Is the flap sag something to worry about or is it something that I can just live with? -- Harry

I would just live with it. That problem is usually worn "O" rings in the actuator or leaking brass plates in the hyd package. The thing that puzzles me is why it started after changing the "O" rings. I like to avoid fooling with those brass plates. They usually leak worse after I lap them! However, on the second or 3rd try I have succeeded. -- Jim