EJWash1

My Feedback: (3)

Duplicate post. Disregard...

EJWash1

My Feedback: (3)

Zor

Hello Fly_24_7,

The scheme in the link you posted looks very nice with a white base.

In the end your best satisfaction comes from a unique scheme of your own imagination.
Use the ideas to design your unique scheme.

There is too much duplication here. Make that final color combination and pattern your very own exclusive creation.

Zor

Zor

I did.

flygilmore

Scored me a very nice NIB GP Skybolt the other day that came in yesterday!! Looking throught the kit, reminds me of how the Giant Aeromaster looked (in its kit form) that I built a couple years ago-lots of wood! This one will be put up for a while until the mood hits-too many planes flying now to add another to the flying fleet.

Cougar429

My Feedback: (3)

Had a chance to run up the Saito again. Did a short vid of the motor running to show the throttle linkage.

Anyway, this is getting annoying. Threw a prop again when I throttled up to do a tach reading.[:@][:'(] Nice new hub is gone the way of the nut and washer. Have been all over the lawn and can't locate it anywhere. For all I know the prop catapulted it into the next postal code.

Wish someone could tell me what the hell is wrong. Motor idles and transitions fine, just if it sits low throttle for a bit and I rev it up it has this bad habit. This is my first 4-stroke, so would like some advice if I'm too rich or lean.

[link]http://www.youtube.com/watch?v=m_J2O0f0wts[/link]

Zor

Cougar429,

I had the same prpblem and solved it.
I was and am using a spinner.

It is too long to fully explain here what the reason and solution was.

Let me just say it was due to a lack of friction between the prop rear face and the front face of the spinner rear disk and the spinner disk rear face and the engine flange.

The radial ridges are not the same and the contact is only on the top surfaces of the ridges.

Count the ridges and see the difference.

No time right now to go in all details that would bore most readers anyway.

Send PM or email if it is not now evident to you.

Zor

Edited for s;pinner to become spinner.

I also notice in your video that you do not have a spinner (hub???).
When I read in your posting "Nice new hub is gone the way of the nut and washer" I assumed that the hub was a spinner.

My spinner made of plastic went into many pieces to the grass. I was lucky to find the two nuts and the thick washer in the grass.

Zor

Jaybird

Do you have a "jam" nut as well as the prop hub nut? I can't tell clearly from the picture or video. If not that may be why it spits the hub off when it backfires. As to why it's backfiring I'm not sure, but it may need some bench run time to get it tuned up properly. You certainly don't want to try and fly it this way with the possibility of loosing the prop in flight.


Jaybird

Cougar429

My Feedback: (3)

No jam nut as this was the Higley's alloy hub nut. Had a dab of loctite on the threads, but that obviously did not work.

Jam nut on order, but not here yet. Still would like the hub for the looks.

EJWash1

My Feedback: (3)

The stock 4-strokes come with double lock nuts. When you add a spinner or a hub, the game changes and the stock nuts may not work.

On Harry's site, you'll see a double-lock hub:

http://www.harryhigley.com/EngineAccessories1.htm

This arrangement will solve the loosening of the hub/spinner during a back-fire.

EJWash

Jaybird

Yes, the hub you have will go on after the the flat jam nut (the link above shows a great picture) and jam against the flat nut which is against the prop hub. I use them on all my four strokes. When I've needed to add nose weight, I use the heavy brass ones as it adds needed weight to the farthest point ahead of the CG if moving the battery doesn't help.

Jaybird

ejmorgan

My Feedback: (1)

Hey Cougar429

I think you might have the IDLE mixture set a little on the LEAN side. Then, when you open the throttle quickly, it creates an even leaner situation causing pre-ignition and backfire which throws your prop. Prop lock nuts are nice to have, for sure, but you should still fix the problem causing the backfire in the first place. I would try opening (richer) the idle fuel mixture needle about 1/8 of a turn, at first, and see if that helps. Good luck with your Skybolt!

Ed

Zor

ejmorgan and cougar 429,

Just letting cougar know that I am in agreement with you.

Four strokes back firing is also often due to a loose prop that slips and cannot carry its inertia past the TDC (Top Dead Center).

Often the prop does not appear to be loose but does not have enough friction area.

Zor

Cougar429

My Feedback: (3)

As mentioned, I'm waiting for the stock locking nut and washer setup. Did not realize Higleys had the same rig till I looked tonight.

Next time I order that will be included.

Zor

While this thread is mainly dedicated to Skybolts, I find it useful for various general knowledge useful to everyone.

I wonder how many realize that lock nuts are not always "lock nuts" .

They often are single nuts just pressing on a thick washer (the first nut put on).
This can be easily explained and visualized by considering the axial tolerances of the threads.

After tightening the lock nut (the second one installed even if it is a so called "hub", just put your wrench (British "spanner") on the first installed nut and force it in a removal direction.

You may find it very easy to unscrew both nuts.

Just visualize what happens at the thread contacts keeping in mind the axial play of the threads. How much distance (gap) is needed for the thread friction to become very small?

Visualize the grab (friction) of the thread faces.

The second nut installed may be tightened just so the axial play of the first nut is just pushed half way (or so) and the first nut put on becomes a thick washer with negligeable grab to the shaft threads.

The maleability and hardness of the shaft threads and the nut(s) thread and their surface finish also has contribution to how mcuh a lock nut is a lock nut.

It is preferable to use a pair of nuts such that the first nut that goes on has a female cone in which the socond nut has a male cone with axial splits that allows that second nut to press inward in a radial direction and insure a better thread grab. A typical double nut supplied with some engines.

Of course those nuts are aimed at creating a high friction at the front and rear faces of the prop hub (prop center) but here we have to consider the surface area being pressed together and the resulting friction necessary to avoid slippage.

If the prop torque comes from an electric motor, there is less of a problem because the torque is distributed more evenly around a prop rotation snd there is no tendency to reverse the rotation of the motor.

In an engine installation (IC glow fuel engine) the torque is an impulse from the repeated firing that occurs before the TDC (Top Dead Center of the crankshaft) and the mass (inertia) of the prop becomes necessary to carry the rotation pass the TDC so that the firing pressure does its job during the downstroke of the piston. If the prop does not have enough friction as well as mass and inertia to carry the engine shaft pass the TDC we then have a problem.

On a practical viewpoint, the engine shafts are hardened steel and so are the nuts to be used.
On a 5/16" dia shaft I use a six inch wrench on the nuts and a thick rag on the trailing edge of a prop blade and thighten to the full strength of my arm muscles. I am not afraid of stripping the threads and they do not strip.

Hope there is some valuable information here for someone to benefit.

Enjoy a well tuned engine that does not backfire and a prop that does not slip (that has enough fricttion to the shaft and engine flange).

Zor

P.S.: A problem can exist if a spinner rear plate has hard plastic ridges that contact only on their top with the top of the engine flange ridges due to a different number of ridges.

That is a different source for prop slippage and there is a solution not part of this posting.

End

Cougar429

My Feedback: (3)

Saito lock nut came in today, along with a few other packages to sort. In the meantime I went and corrected a couple of minor boo boos, (remote glow adapter came loose), so now it's just reassembly and test.

Only wish the weather would cooperate so I can get the motor sorted and give some kind of maiden flight report. Think I'll need a canoe to leave the house if this keeps up.[sm=drowning.gif]

Zor

Further to the discussion on lock nuts.

The attached drawing shows what happens when a lock nut is not thight enough.

The nut closer to the part being held becomes a thick washer and only the lock nut (jam nut) is doing any retaining. That is not better than a single nut.

Admittedly, perhaps, it is tightened harder than a typical single nut and that helps.

If the jam nut is tightened enough to gain all the axial clearance and make the first nut in contact on the left side we then have a larger friction area at work.

The most important consideration is to have no slipping between the rear face of the prop and the ridged face of the engine flange.

If the engine flane is in contact with the rear face of a spinner disk, check the ridge pattern of both (engine flange and rear face of the spinner rear disk) and see what the differences are.
You may notice the ridges only touch on their upper surface (a few point contacts) and the prop and nut (even double so called "lock nut" may spin out on a back fire.

It happened to me and broke the spinner to pieces.

I was fortunate to find the front washer and the two nuts in the grass.
In reality I did not find the two nuts; a powerful magnet did it for me in a systematic scanning process.

Zor

Jaybird

Yes, nothing like having your nuts locked together to make for an exciting flight!

Jaybird

Zor

[X(]

DGrant

My Feedback: (4)

I've had this experience with Saito engines too. If they are even the slightest bit lean they will lock up, instantly. With seemingly no damage to the engine, although I'm sure it doesn't do it any good. A tachometer is an essential tool for tuning a 4-stroke engine, usually for the high speed needle. After the high speed needle is set, then the low speed needle is set based on transition.. and in your case Cougar, I'd say your low speed needle is lean(someone else said that too I saw). For the high speed needle, you tune the engine to peak RPM(be careful, it could sieze again), from peak RPM, richen the mixture until the R's drop about 400-500 off the peak(rich). From that point, your high end should be set decently and very runnable. Again, now comes the low end which is set to transition.. which is somewhat tricky as you have to listen for a slight blubber right when throttle advances.. once you here a slight blubber, your just slightly rich..turn the low needls in 1/16(to lean a touch).. and you should be right there. Every 4-stroke I've had has been tuned like this, and runs consistently. It might take some time to get it exact, and other folks might have some more ideas, but this is your basic 4-stroke 101 you might say. I hope it helps.

Cougar429

My Feedback: (3)

MAIDEN COMPLETE!!!!!!
And I come home with the plane still in one piece, so I guess it was a great day[sm=bananahead.gif]

Took the Skybolt and Eagle 2 out to our local club season opener today. Entered a couple of contest with the Eagle first, something I would definitely NOT recommend for a brand new engine and prop combo. In fact, firing the motor up for the first contest is also the first time the motor has run since I replaced the bearings, so had a lot of tuning to do. There was an ulterior motive to flying this one first, as I had not been airborne due to weather for at least 3 weeks.

Anyway, back to the Skybolt. I richened up both low and high speed needles and can happily report the prop is still attached. We did a few minutes of this to guarantee the motor was running slightly on the rich side and then waited for the contest results from earlier to get up enough nerve to try it out.

Hoo Boy! Have I got a lot to learn. For one thing, the plane does not like crosswind takeoffs. Regardless of rudder it cranked around into the wind. I also was slow on the throttle, as the Saito swinging that 13/6 prop will create a lot of torque, so the rudder may have been a bit ineffective.

Once in the air I found quite a bit of down elevator trim was necessary. I suspect this is due to no down thrust in the mounting. Also had to add a bit of right aileron trim. Once accomplished it seemed to track pretty well, despite the wind.

I have to thank my friend, Pete who was spotting for me for his advice as I seriously think the plane would have rolled into a ball on landing. I found anything less than half stick deflection for ailerons was virtually useless. Never having flown a bipe before did not know till he mentioned it that rudder seems mandatory in this plane. Once I had that things were a lot more responsive and predictable. That lack of aileron would likely have come out to bite me as I slowed down for landing as any excursion would have been a ***** to get back.

I also followed his advice to keep the power on for landing. Lots of drag there.

All told, did pretty basic flight maneuvers for this initial try, just adding one loop to see how it felt. Most of the flight was at 1/3 throttle, jumping up to perhaps 1/2 in the turns. Same with the loop as I did not require any more than that to climb like a bear.

Once the knees stop shaking this should end up lots of fun. Time to do some mixing in the Tx for aileron/rudder. Will have a few more flights under the wheels before the cowl installation is started, as well.

The first pic is just after arrival and unpacking, the two planes mentioned in the foreground. Unfortunately the second gives no hint of the smile on my face, (nor the drying sweat on my brow) but it does show the plane coming home in the same number of pieces as it left this morning.

EJWash1

My Feedback: (3)

GREAT news, CONGRATS!

EJWash

Zor

Joining with CONGRATS.

Well done.

Zor

whatwind

My Feedback: (1)

A question for those who have had the sig skybolt. would a 70surpass be enough to fly one well/

yel914

Mine flies very well with an ST .61 2 stroke on it. I suspect the .70 4 stroke would be a little marginal, but then, I haven't tried it.