function of load on the eng.

[dwilfong]

I am posting here to try and get a better understanding of the function of the load on are engs.

In my testing I have bin finding that some props will rev to the moon off the conner. but at half track will peter out and the RPM will drop.

Now get back in the conner and it will lite up and launch like a missile to half track.

the other prop will keep loaded and good RPM all the way around the course but never get that killer over rev off the conner.

How do you over come this problem?

Is it all in the prop?

I have made BIG carbs and BIGGER carb.

Spray bars larger and larger.

Pipe shorter and shorter.

It just Reeves higher but still Peters out at half track.

What is holding it back at half track?

To little load?

Why do the RPM's drop after thy peek?

Have a good 6.9 H50 prop that is loaded all the way around the track.

But then there is that tease of the Prop Shop 7022/3 prop that will gust revvvvvv and pull like a monster till half track.

What gives?

What is it with nitro and load?

Could use a little help from those that have bin down this road.

 

[steve wood]

maybe increased blowdown for more rev after peak.don't know,i've run into this also

 

[shoboat]

David,

You need more pitch.

The turn is loading the motor, but you run out of propeller at half track.

When you get the fuel to work very well, the motor will step up to more load.

You need to find more load for your motor. You may think about putting the Eagletree

system back in the boat? It will give you the info you are missing.

Enjoy Testing,

Mark

 

[bermudadude]

in my experience prop shop props r no good.

but if u are reving in the corner the hull is unloading the prop then loads it back up and the engine slowly dies out -> lack of power? lengthen pipe.

also makes a diff what hull u r using. i imagine a rigger but still makes a diff which type. a "piggy" rigger(my own slang ) with side tub mounted large rear sponsons will require a larger prop like 1667,1475 cut down to 70mm stuff like that to keep it hooked up . while a slim,rigger with rails under will use a smaller prop 67mm down to 63 with more cup. then a center/single rail will need a prop in between size because the rail will b blocking half the water from entering the prop.

generaly speaking a 6.9 h50 is over cupped the dia is now too small, if this is the blade ur talking about then surely this is ur problem. 6.2-6.4 max

if u r unloading in the corner->need more blade

overloading in the straight-> need less pitch

jus some stuff i figured out over the years of experimenting and getting all the props not done by me from andy brown. hes the 1 told me about the "over" cupping. i got a h50 at 6.5 and it was pretty useless on my 100 rigger(sg) but works ok on a gas cat or canard with a quickdraw. the gas engines have an almost non existent high rpm power band that seems to like it.

 

[dwilfong]

It is not unloading in the corners it is loading and the boat will go faster under the load.

It is when it unloads the RPMs drop off that is the problem.

I have tried many props 1475 from Andy 1475 cut down from Mark and Canto 66mm H50

Many 1667 and a H767. thy all have there own quirks.

the H50 is by far the best over all of them.

But the PS 7022/3 that Mark did is the best at top end.

It is when the load drops it stops Reeving and the RPM drops.

I have lowerd the CR and bumped up the timing a tad to let it spool up and spool up it dose.

The boat is the newest design SGX with no center ski and the rear sponsons .100 higher than before.

Spent time changing the rear wing set up after talking with Andy and it floats real nice and handles killer.

Use the Octura ss skeg strut with the skeg cut off.

The new set up runs the props much different than the old SG ski and CMDI strut did.

The props are much more efficient using this setup.

The boat is over 90MPH with the H50 and with the 7022/3 its top end is well above that but only to half track.

The question is with the 7022/3 why dose it stop making RPM and slow down when it unloads?

Seams it should go higher or maintain RPM with less load not go backward..

 

[David Murany]

You actually unload the prop in the corner because when you turn you are basically letting the prop pull itself sideways which is easier on the motor than pushing straight forward. Same reason you always see people turning to get the boat up on pipe. Too much cup kills RPM. I would drop the cup off and try to keep the same pitch.

 

[moparbarn]

because load = heat. when it spools up it is unloading, the combustion chamber heat drops, & you can't burn the fuel. the burn temps change almost instantly, so the drop off is just as quick. more load, imho. your best prop may not be the fastest.........

 

[dwilfong]

because load = heat. when it spools up it is unloading, the combustion chamber heat drops, & you can't burn the fuel. the burn temps change almost instantly, so the drop off is just as quick. more load, imho. your best prop may not be the fastest.........

Thanks Robin that is what I was looking for.

It explains what I am seeing.

Now if I just get the time to build the fuel management system controlled by ex gas temp this will change every thing.

O well some thing to look forward to in my retirement.

 

[dwilfong]

Ok so let me ask this .

If you lower the nitro content and make the eng work harder will it stop this?

I ask this because at this point a bigger prop will not launch or throttle good.

Can a lower nitro content work to a advantage?

I know that I have bin told over and over. RPM is where it is at as far as speed.

Have swung a sledge hammer at it for some time now and have always hit a brick wall.

So with CID on my side maybe high nitro is not the answer?

 

[moparbarn]

you might try lowering the compression some. not the squish, but bowl volume. i've had a few small engines (.21's) that this helped them keep pulling on top. not sure if it would help one your size, though. or maybe, like you say, lower nitro (& more compression)? that has also worked on some of my .21's. just more stuff to spin your brain some.

 

[DickJones]

Ok so let me ask this .

If you lower the nitro content and make the eng work harder will it stop this?

I ask this because at this point a bigger prop will not launch or throttle good.

Can a lower nitro content work to a advantage?

I know that I have bin told over and over. RPM is where it is at as far as speed.

Have swung a sledge hammer at it for some time now and have always hit a brick wall.

So with CID on my side maybe high nitro is not the answer?

2 strokes, "no load" = no RPM's, open the throttle on any 2 stroke without a load and it will not rev to peak.If the prop U are testing with launches and accelerates very easily, it may need some pitch tweaking to keep the load on the engine thru top RPM's. I like to see top RPM's just pass the half track.

JM2CW

dick

 

[Terry Keeley]

You're not over-cooling it RU?

 

[henry velasco]

David

Years past I ran a lot of Prop Shop props -- I could never figure out why the 22 style (7022) would not work as good as the 7020 or 7024 -- have you try,ed them

 

[dwilfong]

Well after three mounts waiting and $100 to the door.

I don't think I will be trying any more just yet.

Have S40 Andy ruted out of his tool box to try next.

 

[Jim Caldwell]

High Nitro slows down the flame front across the piston which will limit your rpm. Drop the nitro and try it, easy test with the Eagletree.

 

[David Murany]

David,

I came across an article from Marty Davis that talks about tuning the water. It describes the same thing you are experiencing. Reving in the turn and flattening out in the straight. He equates it to the engine cooling too much in the straightaway hence the tuning your water.

Dave

 

[shoboat]

Dave,

Good point to make there. I was out testing yesterday with no water

on one of my 12 JAE's and it was unbelievable how much propeller

and fuel you can burn with the right engine temperature. I was aprox.

at 250* head temperature, 60 on the Boris Meter, and running high 60's

maybe even low 70's on 70% fuel and a Great 1440 L/C @ 3.21" cup

2.73" of center of blade pitch and at 38.85 mm diameter propeller.

Hopefully going out later today before dark and trying some different

pipes and propellers. Oh, the air density yesterday was 106 and the temp.

was 38* to 41* outside around 4PM. Motor was a Nova 12-3C-SCT modified

With a 12 Squarewave pipe set at 6.5". Going shorter with the pipe today and

More Propeller Of Course! The boat had just about the perfect load for the motor

And pipe combination. Plug was a ODO-77T. I ran out of battery power on my

Stalker Pro or I would have the MPH for sure. I need new batteries for the radar gun.

No BS here, this motor is the real deal, it gets better and better as it is getting broken in.

The Boat Was Strolling For A 12 Hydro!!!

AWESOME SET UP!

Mark Sholund

 

[Terry Keeley]

David,

I came across an article from Marty Davis that talks about tuning the water. It describes the same thing you are experiencing. Reving in the turn and flattening out in the straight. He equates it to the engine cooling too much in the straightaway hence the tuning your water.

Dave

He never answered post 12...

 

[dwilfong]

I have gone to extreme measures to limit the cooling on this 1.01.

I run my own cooling cap that just sits on top of the bras button. this cap has only a 3/16" grove cut in it for a cooling chamber. Also the output hole is .080 I have also drilled a hole in the fitting in the ruder to bleed off excess pressure to the system.

Have tested bigger and bigger holes in the rudder fitting to limit the water pressure in the system.

I don't think it is a cooling problem.

I have spent some time talking with few people about this. Andy and my buddy Dick this weekend at the race.

It seams it is a function of the pipe at this point.

I touched on this in another thread.

I will trow it out here for some input. Good,bad or indifferent dose not matter.

It is all good to me.

From what I have gathered is that when the boat loses its forward momentum in the strait and the RPMs reach the pipe usable limits as to length. The pipe will draw to much fuel and over richen the eng.

As Robin stated it drops the EX gas temps quick. To a point that the eng will not recover till load is put back on the eng. at this point the over rich mix is burned and the temps come back up.

The front section of the pie is the controlling factor in this scenario.

A smaller angle will give good RPM but it will not react to a load as good.

The second and in some case the third angle is the load scavenging part of the pipe.

It is a balancing act with this sections that will give the result I am looking for.

Now this all changes with the boat and prop used.

So you tune the boat and prop to the pipe that is available. What else can you do.

Make lots of pipes and give them a try.

This can be a endless circle.

It is funny that programs will get you close then it is how good can you tune to that pipe.

Smaller eng are not as critical as a very large eng as the prop selection is limited at this point.

Props will be the key in finding more power.

The search continues for the magic blade and the pipe with all the right angles.

I will keep hammering on this 1.01 till I find all I can as now I have a reliable eng to work with.

Heat racing is the agenda at this point not a point and shoot.

I am getting closer as testing at the race this weekend was very good.

Lead a pack of twins and one killer JAE .91 boat around the track.

Now If I can only learn to drive at this speed.

Time to patch the Eagle up and hit the pond.

 

[dwilfong]

To add a foot note to my last post.

I have found a group here in Orland that has classes and many people interested in Arduino systems.

As time permits in the coming year. I will start my design and testing on a eng management system.

Based on ex gas temp, head temp and fuel delivery.

Will learn code and start a program to investigate what this might do for are little engs.

All I need now is time.

Will see if I get the time to explore my ideas in the coming year.