Quikturn

My Feedback: (12)

Hmmm. Well, that's what I didn't want to hear.

I did cut the cowl flaps and fiberglassed them in the open position to aid in cooling. My guess is the cowl flap opening is the size of the intake area. Perhaps I should completely cut out the area where the holes are drilled.

Hobbsy

My Feedback: (102)

Roto, here is a hint that will help eliminate the midrange wandering, set the LS needle with the HS needle at the 9,850 peak. 400 rpm rich of peak is mighty wet, you need onboard glow power to get that to work. The two needles effect each other somewhat, peaking the HS needle eliminates one variable. If you try to set the LS needle at 400 rpm rich of peak setting you'll chase the LS needle forever and never be satisfied.

earlwb

Quikturn, I agree with the others in that you need more airflow through the cowl for the engine. The rule I followed was that the air outlet has to be about twice are large as the inlet. Now some guys fabricate internal air ducts to help guide the air over and around the engine, so that no air flow is wasted.

Quikturn

My Feedback: (12)

Thank you everyone for your input. Looks like I'll have to open up the bottom area of the cowl and see how that works. I guess it won't be very noticable in flight.

FNQFLYER

I have said this before but you can have a situation where you have to much air coming in and not enough outlet area thus hot air is trapped with the resultant overheating effect.  I have successfully "fixed" this problem by restricting the inlet airflow thus reducing the build up of inlet air.  Consider the inlet as the two ends of a venturi with the outlet of a lesser diameter than the inlet and the choke area as the engine cylinders should help to explain the o/heating problem

blw

My Feedback: (3)

#720 dalemilam58

Sorry about the delay. I moved recently and a few things were hard to find, such as the list of club members. Welcome to the club.

Quikturn

My Feedback: (12)

FNQFLYER, Originally I cut out all the air inlet openings and later fiberglassed in the top and the bottom of the cowl to restrict the inlet area as you have said. Apparently it wasn't enough.

earlwb

This weekend I was bench running a couple of Fox engines to use later in some airplanes, and I noticed that as the fuel/oil oozed out of the front bearings, the droplets would get sucked forward into the spinning propeller. There the droplets wind up getting slung off as a fine spray behind the prop. So anyway if any oil or fuel residue gets down near the front bearing or thrust washer it can get sucked into the prop and flung off and back to the engine and airplane. Granted the 4 cycle engines don't ooze oil out of the front bearing much, but it does help explain some of the air vortices and airflow off the propeller on the engines.

interestingly also, the oil would ooze out from the left side ( at about 270 degrees) of the crankcase front just behind the thrust washer and as the drops broke free, they would get sucked forward. it looked like the oil would ooze out around the bearing periphery but the airflow would push it all to about the 270 degree point on the front bearing housing part.

You would think that someone had posted some articles about it on the internet someplace, Especially some flow diagrams or video of smoke being passed through the spinning propeller. But I didn't run across any though.

Rudolph Hart

Hello all i've heard about people mounting old 35mm film canisters to the firewall to collect engine oil blowby.Whats the neatest system you have seen or used so far?

earlwb

I just look at the airplane after each flight and you can see the interesting oil patterns on the wing and fuselage.
You can see some swirls around the fuselage as the air flow spirals back. Granted with 4 stroke engines you don't see as much as with a messy two stroke engine. But I find it interesting, when you do a bunch of aerobatics with the plane how the oil residue is on both sides of the wing, top and bottom and on the Horizontal stab both sides and top and bottom, along with residue on the fuselage. As someone else mentioned the back of the prop blades tend to collect a tiny thin oil film too.

earlwb

In your original pic you show a small air inlet and small air outlets. You need a larger air outlet so that positive pressure doesn't build up inside the cowl reducing the airflow. Now the air inlet is pretty small, but it might be Ok, but you may have to make the air inlet larger too, hard to say at this time. What you can do is run the engine more rich so that it gets more fuel which helps to cool the engine. Since it flies for a while before it overheats, maybe opening up the air outlets more and running the engine more rich would do the trick.

Here is a old RCU thread on cowls, cooling and baffling to control the air flow for keeping the engines from overheating.
http://www.rcuniverse.com/forum/m_79...tm.htm#7942738

FNQFLYER

Cooling of "air cooled engines, that is ones without radiators and glycol is all about airflow in particular airflow away from the engine.  On 1:1 a/c if one wishes to heat the engine up one closes those flaps at the back of the cowl if one wishes to cool same one opens them up.  It is the same with models, on the Reliant I am building the radial cowl will not touch the fuselage at the back of the cowl (First point of exit airflow), secondly I will be using the exhaust pipes (sale exhaust) as the second point of exit air (with small actual engine pipes inside) then I will "restrict" the airflow into the cowl so as to quote another poster I will have positive airflow through the cowl and thus around the engine.
I will first fly the model without the cowl to ensure that all systems "are go" then install the cowl probably richen the engine until I have a positive smoke trail on the ground out of the exhaust and then fly it to confirm all hings on the a/c are ok. Then lean the engine stightly and operate.  If the engine o/heats (cuts) I will first restrict the airflow through the cowl slightly (easiest correction at the field) if ok mkae the restriction permanent at home if not I will open up the front (major workshop item) and run tests until a satisfactory result is obtained.  BTB a satisfactory result is consistet 10 minute flights without o/heating.  My formula for airflow is twice the outlet flow to inlet but if I get a 1 to 3 ratio I don't worry and I find each engine install is different (my engines are usually inverted or upright)  Also I try not to use baffles they are to me an unnecessary complication.

And just to put a twist on things if I cwl an O/T engine (YS, Nelson or Dubbjet or similar) I usually don't bother about any of the above just inlet and out let (which is always bigger) why because they usually only run a max of 30 seconds.    

FNQFLYER

With regards to the 35mm film canisters as oil collectors, been using them for years (and have a stock for future use the SD card holders for digital camersa are not quite as good).  The clear Fuji  ones are the best I find but any will do and make sre you have an additional pin hole in the lid beause you will blow it off if the drain tube is a tight fit. 

RC-CAKES

My Feedback: (4)

Well my parts came in for my update on the 72. Giving the engine a good looking over, I noticed I can see the o-ring in the top where the intake tube comes out of the carb. I already replaced the mainfold/head o-ring & flat washer (yep- she's worn!). After looking at my SA100 & 125 - There is no sign of any gasket peeking out from this location.

Does any on the o-rings that come with the carb kit ( SAI8091B & SAI91590 ) fit this ? Unfortunately my buddy was looking it over and pulled the manifold out of the carb.. now exposing the o-rings. There are two; they are worn and a little deformed. One of them is appears to be the same size as the head o-ring and the other about the size of the pipe itself.

Is it possible to match o-rings at the hardware store to fit?? OR order a different rebuild kit?

I am cutting out a gasket for the rear back plate and also considering some hi-temp RTV as added insurance.

Thanks for the help

w8ye

My Feedback: (16)

I have used O rings from the hardware

The O rings that fit the 72 manifold were originally for the Saito 80 and will have a part number starting with SAI80???

In the package of O rings, there is one in a separate package with a little paper inside that says "Viton" and this is the one that goes on the intake manifold at the head.

There is only the metal washer and one O ring that belongs in the position where the intake manifold goes into the head

The correct part number for the O ring that goes into the junction of the intake manifold and the head is

http://www.horizonhobby.com/Products...rodID=SAI8091B

RC-CAKES

My Feedback: (4)

Thanks! I have the o-ring installed in the head/manifold connection. Perfect fit. Now for the bottom where the manifold/throttle body fit. When he pulled it out, there were two different size o-rings that came out. They were a little chewed and worn. In addition, there is one remaining recessed in the body as well (see pics). Seems like a lot for such a small area.
Will any of the new o-rings in the pack fit here? Is there supposed to be one in the upper recessed area and one at the bottom of the throttle body? I am sure there needs to be something here to keep the vibration from causing metal/metal rubbing.
The exploded view in the book doesn't cover this.
I bought this engine low time at an auction (came with the plane) a couple of years ago... maybe the original owner made some repairs because before I started I always noticed you could see the outline of an o-ring where the manifold tube & carb mate. My FA100 & 125 are shiny/clean with no o-ring showing. Also, will Permatex RTV black hi-temp silcone be ok to use to seal exhaust threads and manifold/carb joints?
Suggestions?!

-J

w8ye

My Feedback: (16)

At the junction of the intake manifold and the the carburetor, there is just one O ring and it fits in the groove of the carburetor body. Any of the other O rings from the SAI8091B packet should fit in this position.

After removing the old O ring, and it usually takes a big modeler's Tee Pin, I use the pin to get the new O ring into the groove.

The Manifold should then slip into place.

There's a little white Teflon flat washer in that gasket pack that is used with the choke. Since you do not have a choke, it is thrown into the junk box.

triumphman49

My Feedback: (149)

Hi, Have a NIB Sig Mini Plane, am contemplating engine to use & looking for "input". Have a FA60T just looking for a home, altho installation would require modifications. Seems the consenus to be FA56 - some even up to FA82 - but the OS 52FS suggested "to be lacking". Do have an FA50, FA56 & FA60T & my question is how would you rank the OS52FS & the 3-Saitos for use in the Mini for average plus aerobatics (by that I mean limited pilot skills, looking towards moderate improvement)? Would anyone consider a 2-stroke, as also have a 40FP, K&B 45, 48 & 61? Thanks for your thoughts

Mike Brennan

w8ye

My Feedback: (16)

I have or have had most of these engines.

The 60T was brought out for use in the 1/5 scale Cubs and it works very well in these planes.

The 60T has a lot of low rpm torque. It will not swing a 12 X 6 as fast as a Saito 56 but it will rev it up faster. The 60T also weighs a lot more than a Saito 56. In the Cub I consider the APC 13 X 6 for the 60T but it doesn't turn it very fast which works well on the Cub.

I have four of the OS 52 four strokes and they tend to have mixture problems at part throttle in that they will run correctly for a while and then slowly get rich and slower and then will pick up and run correct for a while. I've often thought that the carb was building up ice inside? If run full throttle this problem does not occur.

There's not much difference in the total power output between the Saito 50 and the OS 52. But the Saito 50 does not have any problems with the carb.

With the drag of a biplane, I would use the the bigger engines 56 or 60T.

http://www.sigmfg.com/IndexText/SIGRC38.html

Quikturn

My Feedback: (12)

earlwb,

I could be wrong but I think the inlet size is OK. I've seen mustangs with smaller inlets that seem to work. I'm going to open up the bottom a bit more by cutting out the area I drilled and see how that works.
Thanks for the link!

triumphman49

My Feedback: (149)

Hey W8YE, & thanx for the valued response, am wanting to use the 60T, but was afraid it would be more comparable to the OS 52 (don't have one of them) in service on the Mini. Your input does help to put the 60T in perspective - plan to use a 12X5, & the FA56 has a tentative home, replacing the FA50 in a Kyosho Ag-Wagon. Don't think the extra weight will hurt the DSA Mini flight charecteristics to much, as some have had to add lead to the nose & indications are good flights with weights from 5-1/4# even up to 7 lbs. Thanx again, your friend in Alabama

Mike Brennan

w8ye

My Feedback: (16)

I've run the Saito 50, 56, and 62 quite a bit.

These are all about the same size and weight and fit in the same holes and with the same throttle connection.

You do notice the difference in fuel consumption between these engines in spite of them all having the same carb.

You also notice a difference in power output.

I've run a APC 12 X 5 on the 60T and it seems like it is not enough prop for the engine. Yet the 60T will not swing a 12 X 6 as fast as a Saito 56 will. The problem is the extra drag of the extra mechanism is the 60T and the seven ball bearings inside.

blw

My Feedback: (3)

The Saito 72 should have an RTV seal under the metal washer. The problem is with the plastic backplates. They weaken and vibrate, causing the manifold to cylinder head joint to leak in air. I don't have the new metal backplate yet, but my 72 ran great only after I used something to lock the backplate screw threads. They would back out in just a couple of minutes of running, and then the backplate would be loose.

RC-CAKES

My Feedback: (4)

Well I think I figured out why I am having so many issues with a simple seal replacement... I pulled the carb off my SA100.. and they are both the same! This is not the original carb on my 72!! The bore to receive the manifold is waaaaaay too big for the 72's tube. That's why there were several o-rings taking up the gap. I knew it couldn't be this hard.
Its no wonder why I have been having realibility issues all along. I am sure the plastic backplate doesn't help. This carb doesn't look like any of the online 72 carb pics I find. Does the 72 have a screw/spring on the body? Right?

So do I reseal the manifold into the body ?? Or just order a new complete carb for about $50.?

I have been attempting to post some pics but the forum has been acting goofy all day and wont let me. (barely can even read it!)

w8ye

My Feedback: (16)

In your case. I would order a new carb and I think it is fortunate that you had the 100 setting around to compare to.