gunny11

My Feedback: (6)

I did a search and could'nt find any info if people are experiencing any vibration problems. I cant seem to pinpoint exactly where it's comming from. I get the vibration only in the 6,000 rpm range. Above and below this, it's smooth. I tried everything. Everything I could possibly imagine. May be this is normal for this engine? But the vibration is unscrewing canopy and cowl screws only in this 6,000 to 6,800 rpm range.

Has anyone else noticed this?

Gunny

Tired Old Man

My Feedback: (1)

What prop are you using? The vibration could be caused by propeller tips at that rpm if the blades are not stiff enough.

AirWizard

My Feedback: (3)

I haven't had any problem with vibration.

gunny11

My Feedback: (6)

The props I tried are: TF power point, Bambula, Master Airscrew wood and Zinger. I have ordered more props. 3W, Bolly and Menz. I'll have to try these. It vibrated right out of the box. lol [X(] Even on the test stand.

Gunny

AirWizard

My Feedback: (3)

I'm using a Menz

Rcpilot

My Feedback: (78)

Whats that fan thing on the hub? Obviously, it's intended for cooling. Is that a stock item on the engine? Did you make that?

Details!!

dasintex

My Feedback: (10)

The Fan Unit comes from the Engine Manufacturer; designed specifically for this engine when used in the TF Giant p-51; comes with a shroud that attaches inside the cowl.

Bass1

I guess the next obvious question is.. Is the vibration still present with the optional cooling fan removed?

Tired Old Man

My Feedback: (1)

I was wondering the same thing. Next question, does it really do anything?

gunny11

My Feedback: (6)

Hi guys.
Yes, I've tried it with and without the fan. I've tried it with and without the True Turn spinner. I even put a dial indicator on the shaft and found it to be "within their tollerance" under 3,000th of an inch out. I dont exactly remember what mine was, but I think mine was about 1,000th out. And yes, the TF P-51 needs this fan because of the small inlet area to prevent overheating.

We shall get to the bottom of this. I will try these new props.
Keep the ideas comming and I'll keep you guys updated.

Thanks,

Gunny

rcacro

Hi
Well here's my $.02 on the subject. I have seen some engines tend to shake or vibrate when mounted on Long metal standoffs like the type you are using. Do your engine mounting bolts stay tight? The end of the standoff will sometimes compress the wood they are mounted on and as a result the overall mount is not very rigid. If this is the cause, then the solution is mount the engine on a block or box structure to keep it from twisting.
JohnW.

gunny11

My Feedback: (6)

Very good .02 cents. I did notice that after a couple of runs I had to re-tighten the bolts. The p-51 fire wall comes laminated together with a few sheets of lite ply and not of aircraft birch ply. I'll have to keep this close in mind and re-check this, because I believe the fire wall is on the flexy side of cheesyness.

Good point.

Gunny

Bass1

.Good stuff!

dasintex

My Feedback: (10)

Gunny;

Sorry to hear about the vibration problem you are having, In reading the reply or 2cents worth from John W(rcacro) makes some sense, since I haven't gotten to the point in mounting my Revo 50 in my build, I recall, that per recommendation from Top Flite and you had followed, that the engine mounting was extended 1/4", right?; you had used longer standoffs over the stock ones provided, you have also stated and I agree that the firewall does flex, which may be the source, so what I think I will do with my build is to use the the standoffs or the length that came with engine, and increase the thickness of the firewall 1/4" using Aircraft Plywood, with a cut out for the carb if needed, this would accomplish extending the engine mount and making the firewall a little stiffer.

Dasintex

gunny11

My Feedback: (6)

Yeah, sigh . I could still do the same thing of what your talking about. Shortening the standoffs and adding real plywood to make up the 3/8" inch difference. But not to jump to conclusions yet. This engine was mounted on my test stand which had 1 1/2" thk. backboard of layers of ply and vibrated too. But come to think of it, it did'nt seem so bad untill it was bolted into the mustang. Hmmm

Gunny

dasintex

My Feedback: (10)

Gunny;

I can see your delema, little tricky now to put in another layer of Ply on the Firewall and hope it solves the problem; I plan on going ahead and putting another layer of ply on the firewall, needs extra weight up front for one and would stiffen it up; I thought the recommended lengthening was 1/4" you mentioned 3/8", I have the tech notice somewhere, 3/8" sounds familiar, I will just add that thickness of ply to the firewall.

Doug.

ec121

My Feedback: (2)

Almost every structure has a resonant frequency. If the firewall is flexible, the framework of firewall and standoffs could be resonating at that 6000rpm freq.

Kweasel

My Feedback: (29)

I think you are experiencing airframe resonance since it happens at a fixed rpm.

gunny11

My Feedback: (6)

Well you'll never believe what I found. The prop hub does not seat onto the tapered cone part on the crank shaft. It bottoms out on the bearing first. I was wondering why the hub always fell off when I changed props. Usually you need a gear puller to get these off. So I releived the back of the hub on my lathe to make the mating cone and taper fit. So now it's seating properly and now it does'nt fall off the crank shaft. I put the dial indicator on the hub "circumferentially" and it's right on now. I then put my tru-turn spinner backplate on and set up the dial indicator to run onto the back surface and noticed it was out quite a bit. I noticed the knuling is not at a uniform depth on the face of the hub. So back to the lathe. I got it as close as I possibly can. I ran the engine and HOLLY COW I eliminated about 50 to 60 percent of the vibration. Instead of the horizontal stab vibrating at a resonance of 1" it feels like about a half of an inch. The vibration of the stab is measured between my thumb and forefinger, thus the "feel". BUT, I'm still not happy with the remaining vibration. Still at the 6,000 rpm range and screws are still comming out but not as fast as before.
I called Bill Jensen "Tech service for this engine" and explained what I came across. He agrees that this hub definetally sounds like a manufacturing defect. So I asked him to mail me a new prop hub to see if it will: 1.) seat properly on the crank and 2.) see if the horrific vibration goes away.

Gunny

dasintex

My Feedback: (10)

Gunny;

Thats good news, I hope it solves the problem; I checked my engine and the prop hub doesn't fall off, it appears to be seated soundly; I wonder if I should still go ahead and use shorter standoffs and increase the thickness of the firewall 3/8 with some aircraft ply; it wouldn't hurt I guess, what do you think?

Dasintex.

gunny11

My Feedback: (6)

Well, since I'm already finished and knowing now what I know, the answer is yes I would definetally do it and I might still do it because it is a flimsy fire wall. Bill Jensen said the same thing as rcacro mentioned about using long stand-offs.
Also I recieved my replacement hub today. I noticed the knurling on the face of this new hub is of uniform consistency and depth. Tomorrow I'll hope to get around to install it, but I dont think I'll be able to test run it considering it's going to snow...

Yeah, I hope this solves the problem too.

Gunny

gunny11

My Feedback: (6)

O.k. I installed new hub and it pressed on perfectly with the prop and did'nt fall off. I also double checked it with a dial indicator and this one is absolutally perfect.

Now I wait for good weather to test run.

Gunny

gunny11

My Feedback: (6)

O.k It's all fixed.

I ran the engine with the original prop which i was testing it on the ground when first got the engine. Bambula 20x10. The vibration level went way down. Remember, my original hub was 3,000 th out [X(] and not seating properly. Shook like the dickens. After machining the original hub to seat properly and trying to tru it up, I was out about 1,000 th of an inch. Still shook, but only half as bad. [>:] The new hub again was absolutellaly perfect. 0,000 out. Shook even way less. Aceptable, but not perfect []. So now I am dealing with the resonating vibration of the airframe. I then tried all the props I had ordered (ballanced of coarse in the X and Y directions.) I first removed the Bambula prop and tried the Mens, 3w, Bolly. Still the same tollerable shake. O.k. I decided to try some of the lighter props like the Top Flite Power Point (22x6-10). Low and behold the shaking completely disappeared.
Here's my theory of what I learned or discovered. 1. The original prop hub definitely had a machining error. Just my luck. 2. By using a lighter prop out on a long crank shaft engine on a 3/8" to 1/2" longer engine standoffs on a flimsy lite ply flexing fire wall does not create or induce a type of gyroscopic (amplified) vibrating resonance throughout the entire airframe.

That's my theory and I'm sticking to it. Unless someone else can shine some light on it.

Vibration is gone![8D]

Gunny

AirWizard

My Feedback: (3)

Glade you got it fiqured out.

gunny11

My Feedback: (6)

Me too! I even called Bill Jensen and thanked him too for his help.

gunny