F-4C Phantom - Pavel Bosak
10-10-2007, 05:57 PM
#126
RE: F-4C Phantom - Pavel Bosak
The Phantom is now ready to fly again.
The pics below show the HS81MG micro servos used to actuate the air brake valve and the retract valve. Both valves are Robart #174 gear door valves, which have a spring loaded stem. When the stem is pushed in, air pressure is connected to the cylinders. When the stem is released, the pressure is cut off and the air in the cylinders is vented. (Pic 1)
The brake servo is "y" cord connected to the elevator servos, such that full down elevator applies the brakes. (Pic 2)
The retract servo pushes the stem of the retract valve in when gear retract is selected. (Pic 3) The gear works better than it ever has. I always had trouble with the Robart retract valve binding.
Channel 6 is now used for the left aileron servo, and Channel 1 for the right, so I have flaperons with about 40 degrees deflection.
I'll be doing some more flying in St. Louis later on this month, weather permitting.
The pics below show the HS81MG micro servos used to actuate the air brake valve and the retract valve. Both valves are Robart #174 gear door valves, which have a spring loaded stem. When the stem is pushed in, air pressure is connected to the cylinders. When the stem is released, the pressure is cut off and the air in the cylinders is vented. (Pic 1)
The brake servo is "y" cord connected to the elevator servos, such that full down elevator applies the brakes. (Pic 2)
The retract servo pushes the stem of the retract valve in when gear retract is selected. (Pic 3) The gear works better than it ever has. I always had trouble with the Robart retract valve binding.
Channel 6 is now used for the left aileron servo, and Channel 1 for the right, so I have flaperons with about 40 degrees deflection.
I'll be doing some more flying in St. Louis later on this month, weather permitting.
07-02-2008, 08:28 AM
#127
RE: F-4C Phantom - Pavel Bosak
Finally bit the bullet this week and made the decision to install a Perry pump, above the nose gear behind the firewall.
The engine never has run really right in this bird. I was using a "jumper tank" system. I guess I never really believed it would work, and it didn't. The engine always wanted to "sag" when the nose was lifted past about 35 degrees on the ground, and no amount of adjustment would cure that. The laws of physics also say the jumper won't work: in order for the engine to get fuel from the jumper, an equal amount of fuel must be transferred from the main tank, so the system is working under the same disadvantage regardless of the presence of the jumper. Sorry, Bob, but I have to disagree on this one.
The back plate on the OS 91 FX is way too thin (about 0.10", max) to be boring a hole in it for the pressure fitting, so I'll have to put a 90 degree fitting on the left engine mount tab. Very ticklish operation, measuring everything to insure that the hole comes out centered on the con rod, and drilling the hole without breaking the drill bit.
Too far aft, and it gets covered by the recessed back plate. Too far forward and it comes out under the crank cheek, and it would be impossible to clean out the few chips without disassembling the engine.
Truthfully, last year I mistrusted any kind of "add on" fuel system device, after that horrible experience with Cline's setup. It took a whole season of flying my DR-1 with the Perry shaker pump on my 91 four stroke to convince me that anything would work right. I had no choice on that bird. The tank on that ARF was way too big for the engine, and it wouldn't run reliably below 2/3 full. (A lot of ARFs seem to have tanks that are too big for the application) There was a monster 17oz+ tank in my Hangar 9 Camel. I tossed that thing in the tank box, and put a 12 oz in for my Magnum 91 two stroke. Works great.
The objective, here, is to get the Phantom running really well so I can take it to the fly in at Roben Hood airport in Big Rapids, MI on the 26th of July.
The engine never has run really right in this bird. I was using a "jumper tank" system. I guess I never really believed it would work, and it didn't. The engine always wanted to "sag" when the nose was lifted past about 35 degrees on the ground, and no amount of adjustment would cure that. The laws of physics also say the jumper won't work: in order for the engine to get fuel from the jumper, an equal amount of fuel must be transferred from the main tank, so the system is working under the same disadvantage regardless of the presence of the jumper. Sorry, Bob, but I have to disagree on this one.
The back plate on the OS 91 FX is way too thin (about 0.10", max) to be boring a hole in it for the pressure fitting, so I'll have to put a 90 degree fitting on the left engine mount tab. Very ticklish operation, measuring everything to insure that the hole comes out centered on the con rod, and drilling the hole without breaking the drill bit.
Too far aft, and it gets covered by the recessed back plate. Too far forward and it comes out under the crank cheek, and it would be impossible to clean out the few chips without disassembling the engine.
Truthfully, last year I mistrusted any kind of "add on" fuel system device, after that horrible experience with Cline's setup. It took a whole season of flying my DR-1 with the Perry shaker pump on my 91 four stroke to convince me that anything would work right. I had no choice on that bird. The tank on that ARF was way too big for the engine, and it wouldn't run reliably below 2/3 full. (A lot of ARFs seem to have tanks that are too big for the application) There was a monster 17oz+ tank in my Hangar 9 Camel. I tossed that thing in the tank box, and put a 12 oz in for my Magnum 91 two stroke. Works great.
The objective, here, is to get the Phantom running really well so I can take it to the fly in at Roben Hood airport in Big Rapids, MI on the 26th of July.
07-02-2008, 09:31 AM
#128
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RE: F-4C Phantom - Pavel Bosak
I was just wondering about this project.... good timing.....
Well, it was a good experiment with the application. Usually this works well. The dual tanks rely a lot on the muffler pressure developed.... and that last half of a PSI sometimes can make or break ya. But for some installations, there is no substitute for positive pressure I guess.
As for the pressure fitting, usually you can install a pressure fitting as replacement of the upper left backplate bolt. I believe on the OS91 that bolt hole is drilled through into the crankcase. If not it is darn close and can be broken through.
The backplate pressure port is used on the OS140 and also on the 160 fuel injected versions. I THINK this one will fit on the OS91 as well.
I installed the fitting on my OS160 engine when I was playing with the Iron Bay regulator and the Perry Pump
OS part: 29407300 Pressure Fitting
http://www3.towerhobbies.com/cgi-bin...ARCH=29407300+
Take a look....
(OPPS! EDIT..... wont work. The 91 backplate is 3.5mm ........ this fitting is 4mm. Sorry ..... arggggg)
(But see if you can find a long, vented 3.5 mm set screw or SHCS ..... does the same sorta thing installed in the same place)
(Your engine lug location will work just as well anyway)
Well, it was a good experiment with the application. Usually this works well. The dual tanks rely a lot on the muffler pressure developed.... and that last half of a PSI sometimes can make or break ya. But for some installations, there is no substitute for positive pressure I guess.
As for the pressure fitting, usually you can install a pressure fitting as replacement of the upper left backplate bolt. I believe on the OS91 that bolt hole is drilled through into the crankcase. If not it is darn close and can be broken through.
The backplate pressure port is used on the OS140 and also on the 160 fuel injected versions. I THINK this one will fit on the OS91 as well.
I installed the fitting on my OS160 engine when I was playing with the Iron Bay regulator and the Perry Pump
OS part: 29407300 Pressure Fitting
http://www3.towerhobbies.com/cgi-bin...ARCH=29407300+
Take a look....
(OPPS! EDIT..... wont work. The 91 backplate is 3.5mm ........ this fitting is 4mm. Sorry ..... arggggg)
(But see if you can find a long, vented 3.5 mm set screw or SHCS ..... does the same sorta thing installed in the same place)
(Your engine lug location will work just as well anyway)
07-19-2008, 08:47 PM
#130
RE: F-4C Phantom - Pavel Bosak
Got it all plumbed up, and made some run ups this past week. I must have left a speck of aluminum in the crankcase, for after about 5 minutes on the first run, she quit and wouldn't restart. Glow plug was fried. Put another #8 in, and there have been no repeats of that. [:-]
I put some better nose wheels on the bird so that I could safely use a 12x8 3 blade prop, and that was the final touch in this engine tuning project. The 91FX runs better than it ever has. The Perry pump gives consistent performance across the RPM band regardless of attitude and she pulls hard right to the end of the tank.
Can't wait to fly next Saturday.
I put some better nose wheels on the bird so that I could safely use a 12x8 3 blade prop, and that was the final touch in this engine tuning project. The 91FX runs better than it ever has. The Perry pump gives consistent performance across the RPM band regardless of attitude and she pulls hard right to the end of the tank.
Can't wait to fly next Saturday.
07-20-2008, 10:59 AM
#131
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RE: F-4C Phantom - Pavel Bosak
WOOHOO!!!!
Way to go, Bob. Just finished reading this whole post and want to say you did a super job on the F-4 and figuring out the various problems along the way. You really need to consider bringing this plane to the TRAMPS airshow next June. Also....maybe a float or two on the.....
Soft landings.
Joe
Way to go, Bob. Just finished reading this whole post and want to say you did a super job on the F-4 and figuring out the various problems along the way. You really need to consider bringing this plane to the TRAMPS airshow next June. Also....maybe a float or two on the.....
Soft landings.
Joe
07-26-2008, 04:43 PM
#133
RE: F-4C Phantom - Pavel Bosak
Well, for the first time, I didn't have anything to redesign, correct, refit or scratch my head over after landing the Phantom. The engine ran great, and the gear and brakes worked the way they should, and nothing fell off.
The Phantom is now ready for prime time. She'll fly at the SIR/CM Scale Classic northwest of Louisville on Sept 14.
The Phantom is now ready for prime time. She'll fly at the SIR/CM Scale Classic northwest of Louisville on Sept 14.
09-10-2008, 03:56 PM
#134
RE: F-4C Phantom - Pavel Bosak
The Phantom is no more. She got too heavy along the way, and snapped out on takeoff today from a runway that wasn't quite long enough. I decided I'd had enough after two years, and removed all my stuff. She's in the trash can at Buder Park outside St. Louis.
I think this experience is enough to convince me that prop in the nose jets are problematical, mostly due to balancing issues, but also prop clearance issues and difficulties with grass fields. I have a NIB AK Models SU-27 that I have never even touched. $70 plus shipping if anyone's interested, PM me.
I think this experience is enough to convince me that prop in the nose jets are problematical, mostly due to balancing issues, but also prop clearance issues and difficulties with grass fields. I have a NIB AK Models SU-27 that I have never even touched. $70 plus shipping if anyone's interested, PM me.
