STC needed for c-65 to c-85 engine upgrade

[VictorBravo]

Re: STC needed for c-65 to c-85 engine upgrade

I have the standard Sensenich wood 72CK42 prop on it. As for how it is rigged etc, I wouldn't have a clue as to how to address that.

Your problem is either in the propeller or the rigging. If you have a "dirty" prop, and low pitch, that will account for a lot of it.

As far as the rigging, you can use the factory method with a piece of wood and a level, which will tell you a lot. You can find that under "rigging" in a search.

If you happen to have an old "free flight" (or OLDER experienced R/C) model airplane builder nearby, just roll the airplane out of the hangar and have him look at it. He will tell you if it is rigged straight or not in about two minutes. Tell the model airplane guy the following:

• You only need about a degree of wash-out in each wing
• The fin is factory offset a degree or two for torque
• There is not supposed to be any thrust offset
• The ailerons should not have any reflex with flight loads, but not a lot of droop on the ground either

If you have a standard certified wood prop, you will get less performance on both climb and cruise. A wood prop, too much washout, some differential twist, etc. and you can easily lose 10 or 12 miles an hour off of what the airplane should be capable of.

Look for any externally mounted thin metal bent trim tabs on the ailerons or rudder. There are not supposed to be any on the ailerons, having one on the rudder is optional. If the one on the rudder is bent more than 5 degrees, and/or there are ones that were put on the aileron that are bent, that is indicative of some kind of rigging issue.

Look up at the two big "X" tubes above the pilot seat inside the airplane. Have they been patched back together with other tubes? Are there any bent tubes?

[Pearson]

Re: STC needed for c-65 to c-85 engine upgrade

Tim/GEO6,

Ahha!! A 42 pitch prop. I bet you would beat me on the take off roll and climb out, but I would pass you up in cruise. I don't have any experience with anything but my metal 45 pitch McCauly, but I suspect that with the prop you have you are going about as fast as can be expected.

I don't think having a less than perfect fabric job would slow you down much. I take of with dust on top of my wings all the time and it is still there when I get back.

But Bill Berle is right, rigging will certainly cost you a few mph. After replacing my lift struts I used the rigging proceedure in the Service Manual. But even then I still had one heavy wing. It took about three flights with a tweaking of the strut adjustment screw each time to get it to fly perfectly straight.

If your plane flies straight and level with no aileron input and only using rudders to keep the ball centered, you are probably rigged pretty good. I think the ultimate test is to do a straight on stall with the ball CENTERED and see if it stalls wings level. Do several and if you keep dropping off on the same wing each time, you either aren't keeping the ball centered or you are out of rig. Just be sure to not try to use the ailerons to pick up a dropped wing. I did that with my wife onboard once and we went around for about a one turn spin. She said, "well that was interesting". I got a laugh out of it, but was mad at myself because I know better.

Maybe someone else on the forum has a 42 pitch prop and can share their performance numbers with you.

[N95645]

Re: STC needed for c-65 to c-85 engine upgrade

Gents,
Thanks for the great input. The bird flew fine at cruise hands off and trimmed up when I got my tailwheel endorsement in it. The rudder has a metal trim tab on it which seems to work fine at cruise. Need a touch of rudder climbing out which is normal.
Yeah. On a cold day I can get off the ground in about 300 feet or less off of grass and dirt. It climbs out at a routine 500ftm in the summer, usually no more than 20-25 degress above Standard (hey its Vermont!) This time of year and about 100 lbs below gross I am getting up to 700 ftm on the VSI and confirmed on my Garmin 196.
Maybe a new prop is what I need. Is metal the way to go?

Tim

[N95645]

Re: STC needed for c-65 to c-85 engine upgrade

BTW, Unable to see the X tubes as the headliner was fabric like the rest of the plane. Wouldn't have known the diff before.

[N95645]

Re: STC needed for c-65 to c-85 engine upgrade

I'm afraid I bought the first LSA T-Craft I saw. It was an excellent mistake.
As for the dirty prop, if you mean bug guts and crud on it, I keep it cleaned up. Pledge is the best stuff I have found to do that and I do the windshield with it to boot. Not too many bugs this time of year though.

[VictorBravo]

Re: STC needed for c-65 to c-85 engine upgrade

No, by "dirty" I mean aerodynamically dirty... brass leading edges, rivets, thick tip with a rounded shape, that huge drop-off behind the brass leading edge down to the wood, the extra thickness of a wood prop to be strong enough, the large transition area between where the prop blade is an airfoil one place and a tree stump a few inches away, etc.

Metal is a noticeable improvement as soon as you bolt it on. You lose a few pounds of legal useful load but it gives you back all that and then some in performance. The big downside is dollar cost.

[N95645]

Re: STC needed for c-65 to c-85 engine upgrade

Bill,

So the prop seems the culprit then. Yeah. Pricy when I looked it up.

Tim

[Pearson]

Re: STC needed for c-65 to c-85 engine upgrade

Tim,

Unless you do a LOT of long cross country flying, I would just keep what you have. Being able to take off short and climb out quicker are worth a 6-7 mph if all you are doing is going an hour out & back for a hamburger.

Also with a wood prop you have an advantage if you ever do a ground loop, less chance of engine damage.

[N95645]

Re: STC needed for c-65 to c-85 engine upgrade

Richard,

I have started to do more XC flying and want to be able to head to Maine to visit family on nice weekends. For me, that is about a 150 mile trip one way. That also entails some mountain flying but that is another story.
The grass fields I fly out of here are all 2100 feet or more so even a high density altitude day isn't problematic. I think a partial solution, which presented itself this evening, is that one of the members here would like to swap wooden props to try out a change, 44 for a 42. I am game.
As for the wood prop, that was one of the reasons I liked this aircraft enough to buy for the very reason you mentioned, the prop will shatter and prevent engine damage. Out of about 150 landings I have logged in this airplane, I only scared myself once and that was just after I got my conventional gear endorsement. (Hope it stays that way). I was leary of landing on asphalt runways for several months as they are less forgiving than grass or dirt as I am sure you know but now do it often. Also, my best asset is using my superior judgement so I don't have to use those superior skills i.e. if conditions put me at the edge of my personal envelope,
I don't go up. Thanks for the input.
Best,
Tim

[astjp2]

Re: STC needed for c-65 to c-85 engine upgrade

Do they have mountains east of the Mississippi?
I have flown through 2 mountain ranges going from Delta to Anchorage, 10 below the fog that was 20' above the ground....until the sucker hole got me up to 14.3k before I was able to clear the pass.....and that was the trip there, you should have seen the trip home!

[N95645]

Re: STC needed for c-65 to c-85 engine upgrade

Only mountains just big enough to kill you if you are ignorant, careless, complacent , stupid or unlucky.
My hats off to you guys doing that kind of flying up your way.