Why do 4-strokes often require fuel pumps and 2-strokes seemingly do not?

ITs not the type of engine that requires the pump usually its the placement of the fuel tank. If the fuel tank is far away from the engine and you need extra long fuel lines in an engine that is gravity fed a lot of times there isnt enough vaccume to draw the fuel into the carb at a sufficient rate to keep the engine running. The difference is for an example a YS engine is completly pressurized and the fuel is injected into the engine. Typically you need a fuel tank that can withstand 15 or so lbs of pressure without blowing up. Seeing as though there is a pump in the enigine you can now place the fuel tank on CG (good for 3D flyers) which is typically far away from the engines firewall. Other non pressurized engines need a pump added to it to help the fuel delivery to the carb so it doesnt starve. Then you can put the fuel tank where you want it. Sometimes where a pump makes the difference is when an engine is on its side or inverted and the middle of the tank os way above or below the carb. In that case you would still need a pump reguardless of 2 or 4 stroke type. My personnal issue with adding a pump to an engine is there is more components to worry about and the added weight. A lot of people dont like to use YS's because they are so heavy but by the time you add a pump onto an engine that was a few oz lighter than the YS you are so close to its weight it doesnt matter anymore and YS's really arent that difficult to mess with. So again its not the type of engine 4 stroke or 2 stroke its placement engine to fuel tank.

Twist with Evolution 100 came out to 6.1 pounds, not bad considering...

Because of the way these planes are set up you cannot see the torque twist the plane as you describe. But unlike 2 strokes when you ask for the power there is no waiting for RPMs. The power is right there at your disposal either at 2500 rpm or 10000 rpms and that you can definatly feel. No lag whatso ever in a 4 stroke. it is instantanious. The reason I do not like 2 strokes is that particular difference right there. When I ask for the power I dont want to have to estimate the lag before the response to make sure I can time my manuvers like that. WHen I ask for the power I want it.

Sig Somrthin' Extra with a Saito 91 count? Pics in Teachu2's gallery.

_
That is a Saito 100 poking out the side of that Funtana .40

Well, I'm a convert. I've been flying my Twist with a Magnum .91 4-stroke for a couple of weeks now. For the first 50 feet in a vertical pull-out drag race, the .91 4-stroke wins, but after 50 feet, I think my old G90 2-stroke would win hands down. Like you guys have said, it's not the top end that matters, but the ability to get out of a bad torque roll in a hurry. And while the G90 is a great motor, I like the Magnum better for 3D. The sounds is also better on the 4-stroke and I've noticed slightly better fuel economy. I can hover for 12 minutes and still have half a tank (not sure of the exact size of my tank). This .91 has SO much torque, one click on my radio makes too much difference in the throttle while in a hover. I have an Eclipse 7 (which doesn't provide expo on channel 3 or a throttle curve for the aero program), so I'm running on the heli program now so I can setup a hover-friendly throttle curve. With a 15 x 4 prop and 15% fuel, my throttle mid-point is 30%, which hovers the plane. Not bad. I'm switching to 30% heli fuel but haven't flown yet.

I have/had a YS-140L on mine hovered just above high idle. I thought it was too much. the idle was up a little high and it wanted to land a little hot. when i did get it on the ground the forewrd momentum in the grass. from what i thought was a fairly light landing ripped the landing gear off and sent the wheel pants and wheels through both wings,even came through the top of the wing.Then as it was still moving foreward the gear proceeded to grind the whole bottom off the fuselage. it also dstroyed both wheels pants. I have never seen a landing tear up so much. I would hae to see what it looks like when one goes in.. If i fix it im going with a saito 180 My YS has WAAAAY to much for it

LEt me see if i can get a pic of thebottom of my plane

HERE IT IS

I can see how the 1.40 L would have too much power for it thats why I am using the 1.40 Z sport sligtly lighter and less power. But you got brass ones for trying the 1.40L on it mybe some one should try the 140 Dz next... he he he. Probably would get torn apart in the air. Anyway I am confident that the 1.40 FZ has the same output or close to the Saito 180 and I can put the tank on CG with out an external pump. Given that scenario I should be OK. Mind you I said Should ..... well see.

On my building table right now; 1/4 ToniClark PA18 super cub with ZDZ80..
Intended for glidertowing and fun

Sam

AW .60/.90 Edge, with OS 1.08

Funtana S .40 with a Saito 100 count??

What about .46 size Ultimate with a .61 FX?


:-D

the cap thats in my avitar is a 35% carden cap with a 3w-140.

I just got a GSC 96" Cap 232 with a ZDZ 120. Former owner says it hovers at 3 clicks above idle and comes out like a rocket. Said he had a ZDZ 80 on it at first, but didn't think it came out of the hover fast enough.

I can't WAIT to fly it! [>:]

I have a funtana 40 with a saito 72. It calls for a .70. I figured why not shred the envelope. It hovers at 1/4th throttle on 0% nitro. It weighs 7lbs because of all the expert strengthening mods I did to it. The best 3d bird ever ever (twist close second). It perform all the wild 3d stuff(inverted flying, rolls, hammerheads, and snap rolls)

LOL.

I know what you mean, I have a twist with a Saito .80 on it. When I get into a hover and need a little throttle, it takes off to the moon.

Mike

this is a over powered and over weighted 300 extra.

this is after a kinda bumpy landing the heavy engine just wanted to keep going without the plane

My dads Chris Foss Uno Wot with TT GP42. Far too much power for a trainer, it hovers AND just about pulls out. [&:]

U CanDo .60 with a YS 1.40 FZ. True unlimited vertical performace.

Just finished a 30% Carden Extra 330S with BME Extreme 110 in it.

Previously had a Zenoah GT80 in it and weighed +/- 20 lbs.
Not sure what it weighs now with super light BME 110!!!

Going to test fly it this week-end. Should go pretty well.

I have a Superstar 40 Trainer with a Saito 72 up front spinning a 13x6 only due to ground clearance issues. I am able to hover, knife edge and slightly torque roll with low wind.

DTB

Also have a Four Star 60 with a YS .91FZ, Fat Free Taco (.25 size profile) with a Saito 40

My 1/4 cub with a small OS 1.60 2 stroke. Can you say overpowered? Snapped the wings, now flys better clipped winged.