JeffH

My Feedback: (43)

Maiden flight on the Whiplash Generation 1 yesterday.
It is set up with a K&B 7.5 DF with full length pipe and turning an 8x8 prop. It was cruising pretty good...Guessing about 180, and I still need to do some pipe tuning.

I have 2 issues...one is severe fuel foaming. I added Armor All, and the prop is VERY well balanced..HELP!!

Issue number 2, is throttle servo. I have killed 2 standard servos in 2 days. The first one died while test running the engine, but I wrote it off to being old servo. The 2nd one died while in the air @ full throttle. Makes for some interesting times!!
Why is this thing eating servoes? They were both 148's. The elevons are JR 2721 MG 120 oz servos.
It finally brought the throttle back to about a 1/3 and I landed it like that with no problems other than prop breakage.
I hate to put a good servo on it and have it beat that one to death as well. My thoughts are to go with a nyrod type linkage and make a full length support bracket for it---easy to do really. I am thinking that this will take some of the shock out of the pushrod and prevent the vibration from beating the servo innards to death.

BAGOSTIX

My Feedback: (178)

Engine resonance is notorious for vibrating servos to death.. a soft linkage would help.. perhaps a cushion mount would do too.. a rubber padding under the servo mount..

Bubbling?, if you find the solution to that problem, let us all know..

the only thing I think would work is a collapsible tank, similar to a baby bottle liner, something that collapses as the fuel drains..

JeffH

My Feedback: (43)

Those tanks will not fit in the tank hole will they? How much of that tank recess can be cut away to get padding around it? I am willing to try just about anything. Once I get below one half of a tank, the air gets severe and the motor start to surge or quit.
The rubber pad under the servo is not a bad idea at all....
That combined with the softer linkage might do it.

ChuckAuger

My Feedback: (12)

Tetra makes several different sizes of bladder tanks. I think the 5 1/4 oz will fit in the Whiplash tank bay, but that's not a lot of fuel.

jlong34016

My Feedback: (1)

I use a simple soft linkage. i put on a wheel collar, then inch or so of fuel line, then ez link without set screw, then inch or so of fuel line, then wheel collar. I put lock tite on wheel collars and have not had one come off yet. Could bend rod at the end to ensure nothing comes off and you can throttle down.

As far as fuel problem. I am having same issue now that im using bigger prop with the nelson q500. Its not foaming but more sloshing around gulping air. If anyone finds a tank that fits please let everyone know. Or if someone wants to custom make a few count me in for a couple.

Rudeboy

Your fuel foaming and broken throttle servo is caused by the same problem: engine vibes...

That plane is very rigid... "...it is so rigid it will survive all but the most destructive crashes...", I believe I read somewhere...
Well there you have your problem!

Seeing you can't do much about the rigidity of the plane there's only one solution: isolating the affected components from these vibrations.

The Tettra tanks are a viable solution if you have the room for them. If not, foam padding will be your next alternative. An anti foam agent in your fuel might prevent foaming, but it will not prevent your tank from vibrating. Focus on padding, then if you are out of options, grab the Armor All bottle.

As for the servo dying... I don't think it's the vibes transmitted from the carb, through the linkage, into the servo that are kiling your servo's, it is the vibrations of the plane-engine combination that are killing them...
I've had this happens before and there are only 2 solutions; first, try to move the affected servo to a different location, and/or two, try to mount the servo isolated from airframe vibrations.

S3HD

My Feedback: (1)

JLONG,
Can you post a photo of your linkage here on RCU?

splatt

Use a Tetra or Jett Tank to prevent fuel foaming. Once you do it, you'll never go back. Don't have to worry about padding. I use them with my Nelson equipped quickees and they go,go ,go

Jett has a couple different configurations of tank shapes

and maybe a plastic rod for the linkage, never had a throttle servo go like you say in my racers

JeffH

My Feedback: (43)

the fuel line idea does seem like a good one! It will keep the rod from being directly hooked to the servo, but yet still provide good precision.

I need to check the dimensions for the other tanks as there is zero room for padding. The tanks in these are glued to the airframe directly.

Ya'll are right, it fuel slosh and bounce rather than foam....

daven

My Feedback: (1)

The Tetra 5 1/4 oz tank does NOT fit. I was hoping to use one, but its just a bit too big, and I didn't want to set it in all cock-eyed.

The fueltubing on the throttle linkage works good, a local racer uses that all the time (Pat G.).

Basically, you cut a 1" gap in your solid pushrod, and bridge the gap with fuel tubing. You can either glue the fuel line with silicone Adhesive, or use wheel collars on each side. The fuel line is plenty stiff enough to keep the pressure on the carb, but absorbs most of the vibration.

MMallory

My Feedback: (1)

Jeff,

I too ate up 2 servos before I caught on and put a "soft" linkage. I used a Dubro (I think). Anyway the car guys use the same setup for brakes. A spring on both sides of a quick connect. The K&B just seems to like to shake. Also balance your spinner/propnut with the prop.

Mark M

ChuckAuger

My Feedback: (12)

The DuBro servo saver is #120 if you want to have a look at it.

jetsett

My Feedback: (6)

I also had all of the above mentioned problems. Here's what I did.

I soft mounted the engine. I put 1/8" rubber under the engine when mounting it to the whiplash. You could probably use thicker rubber. The more the better.

As for the gas tank, I put Sig foam under and around (yes! Around) the gas tank. Then a couple of beads of silicon to seal it in. Before every flight, put in a couple of drops of Armor all into the tank before filling it. All of this, with the soft mounting of the the soft mounting works great.

I am running a K&B 7.5 and the vibration was horrible. I had more air bubbles than gas in my tank. After the modifications, smooth sailing,no bubbles at all, even over 19,000 rpms!!
Unbelievable.

Don

Dustflyer

My Feedback: (13)

Here's what I did on my Jett FIRE 50 powered Dust:

Take about a 2 inch piece of the INNER part of a nyrod. Thread some fully threaded pushrod into both ends, cut to proper length for your setup. Use nylon clevises on both ends. This will isolate the servo from vibration.

I must have close to 200 flights on my Dust and the cheap FMA mini servo I use on throttle still works perfectly! I am using the same setup on my Whiplash.

Dustflyer

My Feedback: (13)

Here's a close-up photo of the linkage:

MR Flyer57

Just my 2 cents, but I read a long while ago about a cure for foaming. It was to use a foam type tank filter.
Looks a little like fish aquarium bubbler.

I haven't used one but the idea was that air bubbles were to big to get through and the fuel came through with out them.

They also were saying that a filter with a really fine screen would do the same thing.

I have not tried these out, and only read about them. They were just a few tricks that I put away in the brain file until they might be needed.
Just a thought,
MR Flyer57

ishu4u

My Feedback: (9)

the filter idea is right on.. but we use them in giant scale 3d machines as a clunk inside the tank..they are a walbro item and you find them as a clunk inside weedeaters and chain saws....i don't know about an inline filter that will do the same. i think the clunk is the only way to go, as this can filter the fine air bubbles at the start of the line not in the middle......i have a bladder tank i bought from dub jett at toledo last year and never used. it is a 6 oz and round. but if siliconed to the tank floor should work great. i am waiting on my extreme to arrive any day now.
joe in ky