bako

i used this kind of setup on mag91fs. if there was increase of power, it was little. but my pipe isn't bent it's straight. it's backfiring sometimes when dropping throtile from wot to idle. i like it.

zvika

flying with the new arrangment including the perri pump and a new 90 deg pipe silver brazed to exhaust outlet had some impruvment but not all was fine.

engine was working good but wot rpm was lower thane expected at about 8900-9000, might be that the coupler was restraining the flow (coupler and pipe shown in pic 1 right) or an addition of 3% castor oil to the fuel made some changes.

after about 5 flights the coupler had changed color due to the high temp of the exhaust (see pic 2)

Pic 3 shows the flight setup.

TManiaci

My Feedback: (6)

zvika,

Your pipe looks awesome. Nice work! Looks like a header pipe on a top-fuel dragster [8D].

Dude, I ran some prop calcs on your setup. You are just not getting the most from your setup. You appear to be over prop'ed. I show that if you were to put on an APC 16x4W, you could probably turn over 10,000 rpm with your setup and increase thrust BIGTIME!

Here are the numbers:
Master Airscrew 16x6, 9000 rpm, 2.05 HP, 12.6 lbs thrust
APC 16x4W, 10,200 rpm, 2.00 HP, 17.1 lbs thrust

Note that I adjusted rpm till we matched HP output (assumed to be consistent), that yields a static thrust rating. This is a 36% increase in thrust with just a simple prop change.

There is a group of guys here on RCU and otherwise that have been doing tons of prop-thrust work gathering data and learning about this stuff. What we are finding is that two key things are evident: prop thrust efficiency goes up exponentially with rpm - and - APC props are far-and-away the most efficient for generating thrust at a given rpm.

I know you love the Master Airscrew props, but this warrants another look IMHO.

zvika

Hello TMan

Thanks for the check and the replay. I'll check the local RC store to find 16x4W APC (although it may take time to find).

right now we're less concern about the engine and more about the ShowTimw airborne behavior as we started some vertical maneuvers and found a nasty snap stall lurking for a small elevator movement. we are looking for a twist in the wings that may have initiated it.

I tried to thread a duplicate exhaust pipe used in the last flight but due to the thin wall i was un able to thread it. (i'm trying to overcome the suspected choking in the outlet...)

anyway, silver brazing seems to hold the exhaust gas temp.

the best
Zvika

TManiaci

My Feedback: (6)

zvika,

Not to get too off-subject here. I watched a Showtime maiden yesterday. Flies GREAT, no snap at all in any manuver. I noted that the two elevator servos are rigged just like my Funtana 90, and I was having similar problems with a snap tendency.

What I found was that the two elevators were not perfectly matched mid-throw, yet were perfect at the endpoints. I found that the geometry of the control horn connection points (relative to the hinge-line) and servo arm neutral angles were not exactly the same. Once I made all the geometry pefectly matching on both sides so the sticks remain parallel, the snap went away completely. Believe me, it was a very small error that resulted in a really big problem.

I attached long straight pieces of balsa stock to the two control surfaces, and looked for perfectly parallel positioning of the two extensions thru the entire throw. This magnifies small errors in match and makes it real obvious where the problem lies. A mis-match on the two elevator surfaces acts like you are mixing in aileron when you pitch the plane. It looks just like a snap, but the Showtime does not appear to have this problem.

zvika

TMan

Thanks again. we are going to check it, and will keep you posted on the prop and the snap.

following is a picture of the old setup including the stock muffler with the 90 deg elbow.

zvika

Hello TMan

we found 16x4W APC prop and wow... the plane hanges on the prop as it was nailed in the sky, getting out from tail falling is easy and powerfull.

Engine works great at about 9900 RPM (can go to 10100) no hicks or sudden death. due to lack of thread in the pipe i made we are back to the stock coupler with the silicon deflector.

following is the last flight with the SFG on

TManiaci

My Feedback: (6)

Zvika,

Wow, that's cool... you nailed the rpm right where it should be with that prop. So, can I assume the pullout is much stronger with the APC 16x4W prop?

How about your snap problem... cure that yet?

zvika

TMan

Pull out is swift and steady with a lot of power, top speed is slower (as supposed to be at that pitch)


The snap is still there, looking again at the setup yield a small twist in the right elevator. i suspect that such a small inaccuracy cant make such a nasty snap. we will try to fix it and may apply more exponential (is about 40% will go up to 55-60%).

what type of servos do you use for the elevator / Ailron / Rudder ?

we are using hitec 645MG with 6V battery but the backlash we are getting scares me a little. ( aileron play is about 1mm -1/16")

have fun with the funtana, we enjoyed it a lot.

TManiaci

My Feedback: (6)

I am using 6635 Digital Karbonites... REAL tight drive, no measureable slop there. The HS-645MG's are notorious for slop. The metal geared servos are generally loose like that.

The best remedy for the slop is to maximize mechanical advantage. Move out on the control horns and in on the servo arms. Give up a little on throw, but reduces the magnification of the freeplay in the servo.

Warped elevator, that will do it. To fix that, bend it and hold it bent just past flat in the other direction, then shrink the Ultracote with a blow-gun. Should find a spot where it is flat. and it will stay there.

zvika

thanks TMan, going to try and solve the elevator wrap....

Harrymntncs

Hi everyone, I know this thread has been inactive for almost 20 years, but I bring it back because I have 2 questions:

1) Will the Perry VP-20 pump on its own, with the stock exhaust, make any difference on my Saito Fa-220A in terms of extra top end power?

2) If the above applies, and I decide to fit one, do I have to disconnect the muffler pressure vent and leave it open in the atmosphere? I think I saw just this mentioned in one of the posts above.

Thank you in advance,

Harry

1QwkSport2.5r

A fuel pump isn’t going to increase top end power. It might even things out from full tank to empty, but that’s about it. If you need a boost in top end power, dump the Saito and get a YS.

J330

My Feedback: (3)

Yes.

the Wasp

My Feedback: (1)

More Power: I can't say. I will say, these glow engines are so finnage it may or may-not make more power. specially if your tank is mounted low. but I would think you may need to tune a bit leaner for of the higher fuel pressure.

as for setting up the fuel line, Google Images is you friend. click my link.
perry punp setup diagram - Google Search

Harrymntncs

Thank you all for the answers, I must clarify 2 factors, one I am certainly not getting rid of the big Saito, it's a gorgeous engine and really not that thirsty for its cc, two my fuel tank is mounted in the center line of the carb.
The engine still performs quite decently, I was just wondering if I could get any extra performance by the VP-20 pump that I have - not absolutely necessary, but welcome if it happened.

1200SportsterRider

https://www.rcspecialties.net/
The Turbo Header is good for 240 rpm on the Saito 100

The Turbo Headers are good for between 100 and 360 extra rpm, depending on which Saito they're on. Gary made me an adapter to install a TH on a little FA 30-s, I shortened a 40 sized TH by what I guessed was 10% and it was good for 100 rpm on the 30.

PS, they have an awesome sound and have the poit, poit, poit at idle.

Harrymntncs

Thank you for the feedback, however I am aware of the existence of the Turbo Headers, but unable to use such a header because there's a very specific way the stock exhaust is mounted with the original Saito manifold; that is all done to preserve the lines of the engine cowling. I didn't want to "butcher" it and it has worked, the exhaust is practically invisible from every angle - the factory setup, after some experimentation, was ideal for this solution. If the tuned exhaust was available for pairing with the stock manifold I might have given it a try long before.

1QwkSport2.5r

If more power is what you’re after, I’d suggest doing some testing with your fuel, glow plug, and prop. Adding nitro, reducing prop load, and cooling the plug down will usually net more power, to a point. Cam timing and compression ratio adjustments can net some results.

Chuck the fuel pump idea. It’s not going to help you since your setup is already optimal. The engine should be able to suck a golf ball through a garden hose (fuel draw should be excellent).

Harrymntncs

Already using Optifuel 12% Nitro, 18% fully synthetic oil & the rest methanol, OS F plug, APC 19x8W or APC 18.1x10 prop (almost identical RPM, which means almost identical load). It does draw fuel quite well - only thing I'm not too sure about, you mentioned "cooling the plug". Do you mean going for a colder plug? As far as I know 4-strokes are the happiest with hot plugs.
Compression, what about that, I know increasing it will yield a bit more power, but how could that be achieved safely without compromising engine reliability and longevity? It was easy in one of my other engines - namely a lovely Irvine 72 2-stroke - just removed the gasket from the cylinder head (no leaks whatsoever afterwards) and that alone gave me an extra 300+ rpm, but that's running 10,800 on the ground. What could be done -in a safe way- with the big FA-220a?

the Wasp

My Feedback: (1)

Harrymntncs. we need to know the RPM numbers for each prop. at peak RPM.

Harrymntncs

Using Optifuel 12% Nitro, 18% fully synth oil and OS F glow plug:

1) APC 19x8W reaches 7,600 rpm peaked out

2) APC 18.1x10 reaches 7,730 rpm peaked out

My engine's only opened up once before for a main bearing and valve spring change. It has about 30 running hours on it. Now it will be opened again for both a new front bearing (it's got the original one still but leaks oil all over the aircraft's nose) and - as an opportunistic change - one more main bearing. Should the person undertaking this process need to watch out for anything else? I don't have the expertise and / or necessary tooling to carry out such jobs myself, sadly. I only deal with 2-strokes on my own.

Thank you all in advance,

Harry

the Wasp

My Feedback: (1)

​​​​​​​ I'm impressed. that's a big prop. you said you want "more Power" that tells me you want a bit more throttle responds. try an APC 19x6w. it won't go faster. but it may have more throttle responds.

Harrymntncs

I can't go any lower than an 8" pitch, because the aircraft hasn't got enough speed with such low pitch - it's got high wing loading and speed is its "best friend", so to speak.

I was mainly looking forward to somehow get a little bit more max RPM, the throttle response is just fine.

the Wasp

My Feedback: (1)

Harrymntncs. you know I have heard flyers say, Saito engines get a bit more power with CH spark ignition (glow fuel).