Author Topic: Geared Lycoming VS direct drive  (Read 317 times)

Gary

Geared Lycoming VS direct drive
« on: October 16, 2019, 09:54:37 AM »
Hi everyone. I’m new to the group and hoping to gain info from all the experienced Helio owners. I presently fly a Super Stinson on 31” BW for all my back country flying but feel a Helio may be a better fit for my needs. My question to the group is how affected is a H295 with naturally aspired engine (GO480) to altitudes or high density altitude. Would a TIO 540 perform better than geared for carrying a load out etc. Thanks.

RCarter

Re: Geared Lycoming VS direct drive
« Reply #1 on: October 16, 2019, 11:19:14 AM »
In my experience the GO-480 makes pretty good power at altitude.  But for the most part I operate at density altitudes of 2000-3000 feet with the occasional forray to density altitudes of the 6000ft realm.  Sure takeoff performance is affected, but it is still pretty good.  My handy dandy takeoff calculator sheet says I should be at about an 1100 foot ground roll at 3800lbs in the 6000foot DA range.  I am sure others who fly in the mountains and in hotter climes will add more.  I have always guessed that a H700 if really gone through and lightened would be a pretty good plane for high altitude work.  Or just put the turbos on a H295 like others have.

Louis

Re: Geared Lycoming VS direct drive
« Reply #2 on: October 16, 2019, 03:55:33 PM »
Between a 700 and a turbo charged 295, i would go for the 295 anytime.  The 700 lacks the angle of attack on it's short gear that a 295 gets.  Particularly when the shock sprigned legs put the 295 on high heels in the first 50 feet of rolling.

The problem with the pressurized carb of the 295 is that it does not easily allow leaning for altitude take-off.  I don't think that the automatic leaning leans at full throttle position.  When i was flying in the west with the Winnebago, some guys showed me how they lean for altitude take-off with injection.  Quite simple but it does change a lot in the power available. 

May be someone could point out that it isn't true and that the carburetor of a 295 will still lean at full throttle position.

But i am not sure.  When we took 011 from Vancouver to Montreal, the plane had a couple of bad ideas that were put on it.  Like a reverse cooling fibreglass cowling.  The engine was running at really too high temperature.  Each time i would pull the throttle, it was getting worse.  Then Neil said to us on the phone to push the throttle all the way.  Bingo, the engine was running with a lot more fuel and was rich enough to do the trip to montreal.  All the small bad ideas were reverted to original design, and now the plane works perfectly.

It is this experience that make me say that at full power, it does not lean for altitude.  But i might be wrong

A hundred years ago, i saw Larry playing with the mixture at altitude take-off.  But i was too young to understand what he was doing. And i don't remember what was his idea. 

Louis
« Last Edit: October 16, 2019, 04:16:36 PM by Louis »

Gary

Re: Geared Lycoming VS direct drive
« Reply #3 on: October 17, 2019, 10:57:33 AM »
Thanks for the info. I didn’t realize the 700 had a different angle of attack. Much of my flying is toward the west coast. Not super high but density altitude would likely be around 6000 for takeoff. Of course departure would be in cooler temps to minimize but cruise would be 9000+ to clear mountains. I haven’t seen many 295 with turbos. Is this simply an STC for the GO 480?  Any issues with that motor operating with a turbo?  Thanks again for any input.

Louis

Re: Geared Lycoming VS direct drive
« Reply #4 on: October 17, 2019, 05:00:35 PM »
Well the angle of attack is the same once you are airborne.  But the gear legs are a lot shorter, and not mounted with oleo that are ready to make the gear spring up. So like any tailwheel, you can't pull to make a rotation.  It is the angle of attack that the gear allow on the ground that will define the angle of attack that it will fly. 

The destroyed turbine Wilga had a spring loaded gear to do what the 391-295 Helio does when starting to roll.  In a much complicated way.  The pilatus pc6 also does gain angle from it's gear at rolling.  But not the 700-800.  They have a fibreglass or aluminium gear that will spring only two or three inches.  And they are shorter than the 391-295 legs

I am sure your super stinson with 31 inches tire does fly a lot sooner than with it's standard tires when you need it. 

Louis
« Last Edit: October 17, 2019, 05:03:03 PM by Louis »

RCarter

Re: Geared Lycoming VS direct drive
« Reply #5 on: October 17, 2019, 09:07:56 PM »
So how much sooner will a helio with out the spacers in the oleos fly than one with the spacers? Mine has the spacers in the oleos that keep the gear from tucking too far under the plane when airborne, good for when flying skis.  It never occurred to me, but I guess they also limit how much higher the nose can lift during the takeoff roll.

Would there be a significant decrease in takeoff roll if those spacers were removed and I got a few extra inches of lift and degrees of aoa?