noahb

My Feedback: (67)

Well, from my experience... it does not look like it got hot. The head bolts were still tight. The only part of the piston that got hosed was around the exhaust port. It actually pulled chunks of metal off the piston and deposited them on the sleeve. The alum. seems to be on the sleeve pretty good. I am going to send it in to Dubb and have him look at it. See what he says and see if he thinks it was a severe lean run or forigen matter that got in there. Then I will see if he can fit a new piston to the liner. That way, i will have an extra one for just in case.

I am using Magnum Fuel 15%. I use to run Morgan fuels, but I can pick up the magnum fuel for much cheaper as long as I am willing to buy in bulk. I have run it in just about everything I own and have yet to have a problem with it.

Funny thing is, most engines when they get lean you can hear them go lean, sometimes they will drop RPM at high throttle settings, or even die. But this one gave no indication, it was just flying along and BAP... it just dies. I figure it was air in the fuel line as there was air in it when I landed.

I will keep you updated.

noahb

My Feedback: (67)

Here is some pics of the sleeve, piston, and plug. I downsized them as much as possible and still have some detail in them.

The head button is a slight brown color which i would assume is normal. The glow plug has some castor stains and does show some minor signs of getting hot. However, I would assume that it's from the piston taking a dump causing it, and not from a lean run. But I am not sure. the plug seal still looks good, holds compression and the plug looks good and still works. No, I am not going to re-use it! hehee

bob27s

My Feedback: (19)

Yeah, send that in.....

It ate something

Flyboy Dave

My Feedback: (21)

....it looks like a straight siezure to me.

noahb

My Feedback: (67)

Yeah I will. He said he wanted to see it so that he can check it out and he said sometimes there can be improvements made. However in this case... nothing in his design would have prevented it. It was running so sweet too.

Bob27's.... should there be a shim between the head button and the sleeve? When I took it apart, there were not any shims.

bob27s

My Feedback: (19)

Umm.... usually there is at least one head shim in there. Depends on the fit-up. The seal does not rely on the shim though.

Dub does like to inspect any kind of failure first hand. It does help with continual improvements.

MyWay

My guess is that its not an engine problem, its a plane design problem. The engine is overheating because it is not getting enough cooling air. Pushers tend to overheat even when the engine is exposed. The body of the plane is blocking most of the incoming cooling air causing over heating or uneven heating.

Flyboy Dave

My Feedback: (21)

Lemme explain why it looks like a seizure, a classic overheating seizure. See
where the damage goes front top to bottom where I have placed the marks ?

If you look inside the piston, up near the top, this is where the wrist-pin bosses
are located....this is the area with the most aluminum is. When the piston overheats
these areas expand the most, and this is where the tightening up, or "seizure"
starts, usually on the exhaust, or "hot side" of the piston.

If there are no dents on the top of the piston, or dents in the head, it probably
wasn't damaged by FOD. (foreign object damage, Air Force term).

Notice also that the damage is greater at the top of the piston. This is mainly
because the top of the piston has the most metal....it expands the most, and
gets the worst of the damage.

There are different type of siezures....they leave different patterns that are helpful
in determining what the problem was that caused the failure. I did this type of
diagnostic work and repair for 20 years at the m/c shop. You have to know what
the problem was, and correct it....not just replace the parts, or the engine will
fail again in the exact same manner.

Are there dents in the head, and on top of the piston ?

FBD.

bob27s

My Feedback: (19)

Could be possible. Usually if that is the case, only the piston gets damaged on these engines. The hard chrome on the liner is hard to scratch with AL. A scratched liner usually means something more solid got in to the works. I will let the resident medical examiner figure it out

noahb

My Feedback: (67)

Well, it could have been heat. Truthfully, I don't know. I do know that I have ran just about everytype of motor out there and have never done this. Does not mean I am not capable of a brain fart...which in this case is very likely..hehehe

I just know that in all the times that I had an engine overheat badly, it died way before anything like this happend. Ihave ran car, boats, helis, airplane motors, both glow and gas. Oh well, I will have it fixed shortly and the potential problem of fuel foaming fixed. I will also take off richer then I did before. Using the 11x7P prop, it could have been that it was not rich enough when I took off, but I doubt it. If it is heat damage, it was casued from air in the fuel line.

No, I have not seen any dents in the top of the piston or the head button. If it was FOD, it came from the muffler. I had run this motor on the ground before I ever put it in the air and it was just fine.

I just got my other two Jett 90'Ls from the guy in FL. They are brand new. I got both of them for the price of one. Killer deal.


I was hoping my sleeve/piston would show up today... but it did not.


I will keep everybody posted.

Flyboy Dave

My Feedback: (21)

Yo, Bob....I didn't look closely at the cylinder, I looked carefully at the piston.
The cylinder wall shows conclusive evidence of a massive seizure. When the
seizure is in progress, the transfer of metals takes place, that is why there is
aluminum stuck on the cylinder wall. I noticed also, that yes, this is the
exhaust side (hot side) of the cylinder.

Normally with a ringed engine, a technician could dissolve that aluminum off
the cylinder wall with sulfuric acid, hone the cylinder to smooth it out, and
replace the piston and rings. As you know, the ABC engines use a pared cyl
and piston combination, so the set will have to be replaced.

That was one hot engine....look at the plug....another clue.

FBD.

bob27s

My Feedback: (19)

anyone have any more time and experience with these yet?

I know there is a pretty active thread in the jet forum... just figured Id ask around here.

Bob

AGR413

My Feedback: (1)

Nope not really I weighed all the parts the other night I am still considering going electric..but I think the issue is dead. I did not like what Moto-Calc had to tell me. The plane and hardware came out to 66.7oz. My latest theory has me considering a tower .61 motor.

Flyboy Dave

My Feedback: (21)

I saw an electric version fly this past weekend at Revver's II. It flew good, he
said the balance was at 10".

I didn't get to fly mine, the front wheel steering broke, and I guess it was too
nose heavy to boot....it wouldn't rotate. I tried to raise the front end an inch
to get a better angle of attack....but the collar in the steering arm started
turning, and I couldn't tighten it back down....I was bummed. []

FBD.

AGR413

My Feedback: (1)

I would really like to see pictures about how others have re-engineered securing the booms to the main body of the plane. I looked this part over and did not like it. I am contemplating placing fiberglass/epoxy reinforcement around and on where the nuts are on the booms. On the wings I want to do somthing similar to what they are doing on the large 3D models know where a nut is installed and a poly wing bolt is used to secure the wing to the plane. I would love to be able to break the plane down.

Kmot

My Feedback: (24)

Dave, you did a super nice job on your Bobcat! The polished and waxed airframe, the shiny hardware, the varnished plywood mounts. Just truly awesome.

However, I wonder if the prop had anything to do with your problems?

Flyboy Dave

My Feedback: (21)

Thanks, Tom....

....A couple small changes, and I should be in business.I have to move the gear forward
a bit to make it easier to rotate, and I'll put a heavy hub on to help move the balance
rearward. I'll also run the engine on 20% next time, instead of 15%, and wind that YS .63
up for everything it's worth. If that's not enough change on the balance, I'll have to hack
the nose off, and remove some of the lead balls I coated with epoxy, and dropped
up in there.

The Guy with the electric Bob-Cat said his balance was all the way back to 10 inches.
Mine is like about 8".

AGR413....I drilled my wing bolts straight through, and through bolted the booms on.
They could be removed easily. Inside the booms are hollowed out, so connectors
could be unplugged, and the rear of the plane removed for transport if necessary.

FBD.

Razor-RCU

My Feedback: (50)

That YS-63FZ has a ton of power! I am pretty sure Dave's Bobcat is a bit nose heavy, as he mentioned, and the gear are a bit far back to prohibit rotation.

I sure miss my 63FZ []

I bet a Byron fan/ OS-91VRDF (Think Byro-Enforcer) would kick butt in the Bobby-Cat

MMallory

My Feedback: (1)

I'll state the not so obvious. The prop is on backwards. That will kill most of the performance. The lettering should face the front of the plane.

Mark M

mcdonald77

I will state the obvious LOOKS LIKE A PUSHER PROP thats the way the writing is supposed to go on a pusher prop

bob27s

My Feedback: (19)

I figured Dave would figure it out... the curved side of the blade with the lettering/markings faces foward into the direction of flight. Flat side faces aft. Just like with a tractor setup.

MMallory

My Feedback: (1)

Bob,

Yes, I know. I built a Sig Tri-star and found out the hard way years ago.

On another note, it would be great if you could help convince Dub to build a pusher pipe for us. I'll put it here in writing that I will pay my $50 - $100 bucks for one.

Mark M.

bob27s

My Feedback: (19)

We just have to figure out how to do it first And so it does not cost $200.

MMallory

My Feedback: (1)

Bob,

I think R/C cars and Helis have already figured out the configuration. I wish I had the skill to machine an adapter for the .50 sized Heli tuned pipes. I would settle to a Turbo-Jett with an adjustable exhaust angle. Think a 90 degree curve with an extra long length so it could be cut to clear the rear parts of the plane.

Just my ideas,

Mark

R/C Foolish

My Feedback: (6)

Maybe I have missed it, but does anybody know what size prop I should use for an OS 61 FX? Too bad we can't put retracts in this plane but I am going to try the new Fults Scorpion gear, they look much stronger than the stock wire and I think there is enough hard wood in the wing for mounting. Also what is everyone else doing, gluing the rear stab or just using the 2 bolts?

R/C Foolish