Hi Folks.
Here is my situation:
I have a Magnum 91 XLS four stroke engine that is not yet fully broken in. It was in a Seagull Decathlon that I crashed, and is now awaiting repairs.
In the meantime, I bought a GP .60 size shoestring racer, and on a whim bought the Tower Hobbies .75 two stroke engine. I originally intended to put the Tower 75 in the Decathlon after repairs, and put the Magnum 91 in the Shoestring.

However, it crossed my mind that perhaps they should be the other way round; i.e the tower 75 in the shoestring and the magnum back in the decathlon.

What would you do if you were in my shoes?

I would like the shoestring to be as fast as possible, and i know the decathlon is really not a speed model, but I want engine enough for decent aerobatics.

Please let me know what you'd do, and most important, why.

Thanks!

Here are four of my planes. The first three have Magnum .91 FS engines.
The last one has a Tower .75 in it....

....does that tell you anything ?

FBD.

Good answer FBD! I thought so myself. What prop do you have on the .75? Thanks

The Master Airscrew 11-7 1/2 is the best prop for speed. I've tried the others.
The .75 will turn 14 grand with that prop. Make sure everything is balanced to
the "enth" degree for best results.

FBD.

The Tower .75 will be the best for speed. I have a 60+ size Morris Knife that I scaled up from 40 size plans. The Magnum would not hover it well, the Tower turned it into a rocket and hover machine

Seriously folks. If you need a .61 size engine buy the Tower .75 before Tower realizes what they have and raise the price. I have 45 flights on mine now and it just keeps getting better.

Dave is that beach sand or desert sand you fly off ? Looks like you would need air filters!!!!!!!!!!

ROFL!! Good one FBD! I agree, go with the 75 in the speed plane. I have one on a Four Star, and blew a chunk of the covering off the other day. That 75 makes my 4* look like a freakin Shrike. Never knew a 4* could fly that fast.

The surface is a dry lake bed, mostly clay. It varies from year to year depending
on the amount of water it gets over the winter. Here it is just like concrete. That
day we had to fly just off the edge of the lake. It was kinda "pebbley" around the
edges, but was smoother as you moved forward. Dirt is not usually a problem.

Dave.

Dirt does become a problem when we get one of these "dirt devils" coming
by....time to cover the potato salad.

Dave. [sm=bananahead.gif]

Generally speaking:

4-stroke for scale--slow flying.

2-stroke for speed.

I use 2-strokes in my 3D planes. I know this goes against the grain and people will swear that the only way to 3D is with a 4-stroke, but thats BS. A 2-stroke is your best power/weight ratio. They generally turn more RPM than a 4-stroke--so if you want speed--then you put a smaller diameter prop on it and more pitch. Let 'er rev.

Thats why Dave is using an 11-7.5 on his rocket ship. I use a 13-5 on the same engine for 3D.

Dave, is that a Patriot? If so--could you advise on your setup? I've been wanting a go-fast airplane, but don't know what servos to use. Retracts? Hobbico mechanical?

BTW--one of my TH .75 engines pooped the bed last weekend.[X(] It's about 1.5yrs old and has about 10 gallons of fuel through it. I had to set my low end again because I changed tank location, prop and plug. I had my low end set up and i went to full throttle and re-checked the high speed needle again. Set it about 1/4 turn rich and went back to low end again. All was well---plane was at idle. I picked up my TX and the plane and took a step towards the runway when BANG!! The engine loet out a loud noise--but kept idleing. I shut it down and went home. Removed the backplate and saw that the crankcase was full of metal shavings.[X(][&o]

I got it boxed up. Need to send it to Hobby Services. I'm sure they will just give me a new one. I'm a Super Club Member at Tower--so it's under warrenty for 4yrs from date of purchase.

Too bad though. I like this engine. Good thing I had 3 NIB engines (all TH .75) sitting on the shelf. I just pulled one outta the box and dropped it in the plane. Took 5 mintues. I have 6 of the TH .75 engines--altogether.

That is somewhat of a generalization, often based on the fact that a 2-stroke of any given displacement, will rev higher than a 4-stroke.

However, there are plenty of *very* fast 4-stroke-powered models which rival or exceed the speed produced by similarly powerful 2-stroke engines, particularly when it comes to scale(ish) aircraft.

My P51 with a 4-stroke 91 is slightly faster than a friends exact-same model with a 2-stroke 90 engine.

The difference is that he's running a 13x8 prop and I'm running a 12x10.

He pulls about 12,000 RPMs and I pull about 10,500 or so -- which means our top-speeds are pretty damned close. Of course mine sounds liike a tractor and his sounds like a demented blow-fly. We each like the respective sounds of our engines however, and the realityh is that both planes fly just fine.

Of course I also get almost twice the flight-time from a tank of fuel (gloat).

No, Rcpilot....it's an F-20 Tigershark. Here's a look at the F-20 and the Patriot
together. They are both currently out of production, although Hobby People
recently sold the .40 size (like this one), and I believe Kange still sells theirs
as well. The Patriot is narrower at the fuse, and should be a bit faster.

My .60 size F-20 came with the Hobbico mechanical retracts....they are in the
scrap heap now....I use the Robart 609HD mechanicals. Standard servos are
OK on all the flying surfaces on all three planes, however I use a metal gear HD
ball bearing jobber in the big F-20 elevator.

These planes are genearlly flown in circles at high speed....jet style. I wouldn't
recommend yanking one into a snap-roll at a buck and a quarter.

Tower sells a nice retract servo for around thirty five bucks.

FBD.