P-Force with Saito 30

LAST EDITED ON Oct-20-03 AT 11:39 AM (CDT)
 
Here are some picture of my P-Force with a Satio 30 4S mounted.
Initial flights were very disappointing. Apparently a 4 stroke vibrates differently than a 2 stroke. Had a couple of 2 strokes on this plane before and no problems with the fuel. The vibration on the nose caused the fuel to foam, I mean like bad, almost looked like shaving cream at times. The fuel did have Amour-All in it. Changed to a metal tank and that helped a little. Putting my hand around the fuse and gripping it made the bubbles go away so it will need the nose reinforced. Will place a corner crutch between the wing and fuse this week.

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Notice that the uniflow tank is plumbed with the uniflow vent blocked and pressure to the overflow.

During the 30 to 40 seconds that the plane was in the air and running properly, it seemed to fly well. Doing 5.15 lap time with a 10/5 APC prop. Had good line tension. Did two loops and thought I noticed that the was little to no speed up on the down leg, but that may have been just wishful thinking 'cause the engine started coughing again and had to run the tank out with no other maneuvers.

Jerry

Jerry,

It sounds to me like your engine may be running too rich. Is that potentially the problem? I haven't seen the same issue you are talking about, but when mine are too rich, they tend to vibrate more.

Good luck.

Paul,
Will try to make it leaner, but with the foaming problem, it just made getting a true setting difficult at best, if not impossible.
I peaked it while holding the nose firmly, and there were no bubbles in the line, then, when letting go, the bubbles came back immediately.

Ok, stupid question, the prop is balanced isn't it? I flew a Saito 30 on a modified Twister, and in that case I had no problem with vibration. I understand that it may just be your front end that is resonating at the running rpm of the Saito. I have put a thin layer of foam under some of my tanks to try and cut down the foaming.

LAST EDITED ON Oct-20-03 AT 03:06 PM (CDT)
 
Yes they are, and it was tried with 3 different props. If you look closely there is foam under the metal tank.

FWIW, wouldn't the brass tabs and screws negate the effect of the foam under the tank?

I would tend to agree that you have a resonance problem and bracing the nose should chase it away.

>FWIW, wouldn't the brass tabs and screws negate the effect
>of the foam under the tank?
>
>I would tend to agree that you have a resonance problem and
>bracing the nose should chase it away.

You can try it, but I am not convinced that bracing the nose is going to help you or that it is even part of the problem. I have a test stand made out of 3/4 inch plywood for a base, two 2 x 4 uprights on which are mounted the Tatone test stand itself. There is a plastic tank rigidly affixed to the whole assembly. I weight the stand down with two concrete blocks. Everything is solid. Yet when I run certain engines on the stand, even using defoamed fuel, the tank will foam up and the engines will go lean. All I need to do is touch the tank. I don't need to grab the tank, press down hard, or anything. Touching the stand doesn't do any good. But if I just touch the thank, the foaming stops. I think it has to do with a resonance inside the tank. (I never did like plastic tanks, anyway, but, on a test stand I will tolerate them as I can see the fuel and know what is happening as it is consumed.

Sunday we were breaking in a new 65 for Matt. With this engine there was no foaming problem. But, then, it was running at a higher rpm.

Along the line of thinking that Len is going, why not try the addition of rubber bands to your existing tank mount,(keep using the tabs too)and see if it changes the tank resonance.

With the Saito 72, I am a fanatic when it comes to prop balance. The "Big Block" makes a VERY big bang every other stroke. The nose of my Backfires are especially engineered to deal with this. Consequently, I find my 72 to run very smoothly in actual use.

Ahhhh! Choices, choices, and choices.

Well adding a stiffener to the wing/fuse joint is not the easiest but would only take an hour or two, especially if the Yankees keep winning.

Floating the tank off the fuse is probably easier using some RC foam (argh, cough, cough) and rubber bands. Might try just putting some rubber bands around the fuse/tank to see if that has any effect.

Note the screws on the metal tank are not tightened down all the way. Was trying to make the foam behind the tank more effective. Maybe I’ll try that real soft RC (there’s that word again) foam. (well it’s not really a word)

The engine ran perfect on the stand, no foaming at all, of course it was upright and very secure.

Well, better get to it, only 8 months ‘till Brodak’s.

Ready for a 'physics hint'? The limited weight of the tank has no resistance to the mass of the fuel resonating. Rubber band a small 'U' shaped bracket that stands off from the extreme outboard of the tank, with a 1/2 oz. weight attached. The dampening effect will be immediately noticeable, and the weight can then be moved inboard (to the tank) where it can be 'streamlined'.

"Life's largest battles are frought with inertia." Erwin Rommel

Jerry - for what it's worth, we have had the SAITO .30 on three different profile planes. We used an old Veco metal tank, rigidly attached to the fuselage. The engine is now in my Little Cherokee, mounted inverted, also with a solid-mounted tank. In every case, the runs were PERFECT. We tried a number of different props, finally settling on a Master Airscrew plastic 9 1/2-6. The exclusive fuel of choice is Powermaster, 5% nitro, 22%, 50/50 lube.
Bob Z