hsukaria

I know what you mean about the Ultimate Bipes needing to land fast. I have a Seagull Ultimate 46 and I have to land it hot. Last year the engine stalled on me (not a Fox, but an OS) because the high speed needle o-ring tore up. Even knowing that it needed to land hot, I still was not able to flare it before touchdown, ended up ripping the landing gear. It is the hardest plane I have, always needing rudder correction the whole time.

But, back to the Fox engine, I don't mind using FAI fuel if that would solve the problem. I could run the engine at half throttle most of the time except doing verticals. So, if FAI causes a little power loss compared to 15% nitro, that is ok if it means no stalls.

I will try tuning with 1/4 tank and running it tilted up for a while like you said to verify no stalls before flying.

If I really need to change the head button, I might just change to a Davis Diesel. Would that also be an option to solve this problem?

earlwb

A new head button would be a lot less costly than the DDD head.  But you need to break in the engine real good before you use the DDD head anyway.

hsukaria

Last year when I was replacing the piston ring and bearings, I noticed that the cylinder liner was stuck to the cylinder head. Is that going to be a problem for replacing the head button?

Sport_Pilot

Soak them in fuel and it should come apart.  Or heat it in your oven.

earlwb

Just heat up the head a little, it ought to pop loose. Maybe with it heated up and the head screws loose a little so the head has some wiggle room you can gently tap it with a small brass hammer or wood block or something.

hsukaria

Ok, will do that.

Cougar429

My Feedback: (3)

Interesting problem with the Ultimate bipe and one I have never had to suffer so far. Every once in a while my Saito 91 powered Skybolt acts up if I really honk on it and that was traced every time to the clunk falling to the front of the tank on the previous landing, (don't ask). Out of close to 300 flights this has happened 3 or 4 times, early in the series when I tended toward hot dog landing and/or the throttle linkage broke.

I also found they are relatively draggy compared to my other bipe experience, especially the need for lots of throttle if over anything more than a 60 degree bank.

I'm surprised the pump did not cure it except to say they will not pump air if the pickup gets exposed. Did the direction of rotation have any effect?


I was able to put a couple more tanks through the engine before heading back to the build table to finish the pump compartment and this caused some unexpected problems. The edge of the opening was well ahead of the exhaust, yet became oil soaked and is currently bathed in baby powder to help dry it out, (or the covering will not stick). I suspect this must have come from the front bearing.

I was happy with the muffler adapter as despite the fact the engine does vibrate the airframe quite a bit when 4-stroking, (no wing does make quite a difference) that much longer muffler shows no signs of coming loose, nor does the 2 piece adapter setup have ANY indications of leakage.

earlwb

I think in hindsight now that  the clunk wasn't heavy enough, so it tended to lag in response time to the roll, this it got exposed to air as the plane rolled.  It was some time later that I discovered heavier clunks that I could get. At the time I never thought about it or I would have added more weight to the clunk or made a new heavier clunk.
But I never pursued it after I sold it to someone else.  I do have another Ultimate bipe but I haven't put it together yet.
Hopefully it won't have the same problem.

It was one of those odd things. I could fly the plane numerous times, just avoid the faster rolls etc. Do them slow and it worked fine. If you do a nice slow four point it worked fine too. But every once in a while I would forget and sure enough the engine would quit on me.
Fortunately I never crashed it or had a hard landing.  I had gotten pretty good at dead stick landings flying 1/2a planes years ago, so dead sticks usually aren't a problem, unless the plane is in the worst place in the air to have the engine quit on you.

I usually prop my planes up against the wall nose down. So I got used to jiggling and rapping on the plane to make sure the clunk wasn't stuck up in the front of the fuel tank. But I have had that problem before too. A clunk stuck at the front usually shows itself right after take off when you pull up to climb on out. Worst possible time to have it happen too.

hsukaria

Earlier this evening I was addding some castor oil to my 5% nitro fuel in preparation for running the Fox 74 this weekend. As I was pouring the castor oil out, I noticed how viscous it is. Then I remembered the problem you had with your old Ultimate biplane. Could it be that you had a lot of castor oil in the fuel, and that increased the fuel viscosity? That would have potentially caused the fuel clunk to move slowly during the rapid maneuvers, as you mentioned. Just a thought.

earlwb

Interesting thought, thanks.
I doubt it was the problem as I had the plane for almost a year through winter, spring, summer and fall. The oil tends to thin out quite a bit when mixed with the fuel. I suspect it was the silicon fuel tubing at the that time was a bit more stiff than it is today, so it really needed a heavier clunk on the end. Another thought would have been to use a Jett Bubbleless fuel tank, but they weren't out back then yet. Using a bladder would have been too much fuel pressure though, but I didn't think of it at the time.

hsukaria

I'm fired up about tuning/testing/flying my Fox 74 tomorrow (weather permitting, this is Michigan, you know). Meanwhile, I was doing some simple math and started looking at the bore and stroke of the 60 and 74 (these are estimates, some of you will know the exact figures).

60: stroke = 0.94 inch, bore = 0.9 inch

74: stroke = 0.94 inch, bore = 1 inch

'hypothetical' 90: stroke = 0.94 inch, bore = 1.1 inch.

Would be nice if Fox produced a .90 cu.in., only 0.1 inch bore difference, could be achieved by thinning out the cylinder liner, new piston and ring.

ok, ok, I'll get back to the real world now.

earlwb

There is maybe room for it, but they usually keep the cylinder liner thickness the same (prevent heat distortion when running) and bore out the cylinder a little bit more. But a tenth of a inch is quite a bit, so I don't know if they really have enough metal to do that or not. I haven't looked at a cylinder in quite a while along with the cylinder sleeve to be certain. Then are the cylinder head bolts in the way or not if you go that big? So it may not work even if they make a new cylinder casting to hold the larger sleeve, if the screws are in the way. Hummm, if the screws are close maybe some notches in the top of the cylinder sleeve to clear it might work.

hsukaria

Well, it's always more complicated than it seems. Looks like the weather won't cooperate tomorrow for testing my engine, it is raining.[]

earlwb

FYI: I found someone with a K&B 61 engine and when I weighed it without the muffler, it weighed about 406 grams. One of my Fox Eagle I engines weighed in at 407 grams sans muffler (but with the MKX carb). The Eagle I with the old butterfly carb weghed 395 grams with a MKX carb on it. The Fox Hawk .60 engine weighed in at 424 grams sans muffler with a butteryfly carb on it. The Fox Hawk weighed about 436 grams with a MKX carb on it. I found it odd that the Lee Custom .61 weighed the same as the Fox Hawk with a MKX carb. But maybe that was because they removed extra metal for the PDP porting. The slight difference in weight could be the after run oil used inside the engines too. A Fox Eagle IV early style with MKX carb sans muffler weighed in at 543 grams, but it is a bigger engine though. The K&B Twister .61 engine weighs in at 418 grams sans muffler, including the remove needle valve, or 403 grams without the remote needle valve. Using a screw on cylinder assembly instead of head screws can save a fair amount of weight.

What is really cool though is the modern Evolution .60 NX engine weighs about 395 grams which is slightly less than the Fox Hawk .60 engine. So that is why I have a interest in possibly running a Fox Hawk .60 engine in a Jackal plane myself. The engine is only slightly larger in width than the Evo .60 NX engine, so besides being somewhat taller (longer stroke) the engine should plug right in OK. A modern OS 55AX sans muffler weighs about 405 grams as well. The modern OS 65 AX weights about 497 grams sans muffler. The Jett 60L or 60LX engine weighs in at 497 grams too.

The K&B .61 ran about the same as the Fox Eagle I engine did, not really any difference in performance. But the K&B 61 Pumped engine with PDP porting ran almost as good as a Fox Hawk .60 did. But the K&B engine with the pump was much more consistent in running as you could lean it out to get max power.

earlwb

I took a look see at a Fox Eagle III .60 engine and there maybe possibly be enough room for boring it out another tenth of a inch. But the flange on the cylinder sleeve would have to be notched for the head screws in order to have room for it. The other problem is whether there would be any intake port passages left for the air/fuel charge to get into the combustion chamber. Then there is the question of the cylinder jacket being strong enough too.

I think it might work if someone made a new cylinder jacket and head to fit the larger bore cylinder and thus they can move the head screws farther out then too. So in that case it looks quite probable that it could be done. But it depends on the cylinder base area and whether the cylinder would be too thin to be strong enough to hold up Ok in that area, as it is getting a tenth of a inch more thin there. But one could inset the four cylinder base mounting screws to help reinforce it there too.

DougB1

My Feedback: (11)

If any of you Fox guys are interested in buying my Fox 74, I'll post a picture on here of it. If not I'll just keep it in the drawer till next falls swap meet.
Thanks
DougB1

hsukaria

You can also put a sale ad for it here on RCU and let us know when you did it so we can look at it there. More people will see it there.

DougB1

My Feedback: (11)

I have put items on there before but thought I would let you guys that really like them here have first shot. I'll get it put on here later this weekend.

hsukaria

Yeah!! You just want to temp us with more engine pictures!!!

Tarasdad

Added a Fox .19 BBRC Schneurle to my inventory today, now I just need to figure out what to do with it....

earlwb

yeah I have one too, that I haven't used either, They are great engines. But it is hard to want to use it when I have some .25bbrc engines I can use instead. This example is from Duke Fox's first production run. Someone had mistakenly drilled and tapped the muffler screw holes about 2mm off so that the mufflers didn't fit or vice versa. So Fox had to thread in some aluminum rod and use permanent thread lock on it. Then re-drill and tap the holes in the correct place to match the mufflers. Subsequent production runs didn't have the issue.

Tarasdad

My .25 is the bushed version. Bought it because it was dirt cheap at the time. The club I was in had decided to use a certain inexpensive trainer for a club fun fly plane. It was rated or .25 to .40 for power and I couldn't afford th larger engine so went with the .25 - and never used the darned thing in competition! IIRC that engine has a total of maybe 30 minutes runtime. Not bad for an engine I bought in 1989, eh?

Cougar429

My Feedback: (3)

Tarasdad, I may have one close to that. My 50BB was bought new in '87. Bolted it to the firewall on the Seamaster and after break in, promptly wonked it into the water on the day of the maiden, (found out later there was an issue with the tail design-since resolved). It was stuffed into the corner and the engine pickled. I left almost immediately for a career in helis so it sat for over 20 years. It has been resurrected and I like the motor so much picked up one as a basket case for rebuild. As some may have figured out by now, I love taking discarded, worn out or old monsters and bringing them to life again.

Hopefully someone with some experience with your 25 can point out if that one was designed to run on FAI fuel.

earlwb

The old loop scavenged Fox ,25 engines are great, They have a small baffle on the piston crown. Sometimes they take a while ot longer to break in, but they last almost forever barring a nasty mishap. They aren't as powerful as the bigger Schnuerle Ported engines though, but they can still be used for lots of purposes.
Here is one of mine on a Spad Pizza Box flyer plane. You can get a Mac's muffler to fit OK on it too.
I still have several of these engines from when I was using them before the Schnuerle engines became popular.

fujiman

My Feedback: (133)

we just have to see that pizza thing fly. any video of it?