smitty9969

My Feedback: (7)

Fella's
Got a question about RPM's.
Nelson turning 21.4.. 95 degress outside w/ 85% humidity. Sea level (matter of fact, the gulf is about 400 yds away). Prop CF 7.4 x 8 (standard APC Q-40 prop). Plug burning a nice color brown after run.
Is this the performance I should expect under these conditions?

Smitty

luv to race

My Feedback: (1)

Not good. You wrote the 7.4 x 8 ?? If that prop is truely the 8, and not the 8.0..? then that 8 should turn close or over 24K...easily. If your "8", is actually an 8.0... then it would depend on what version 8.0 you have. I know that sounds confusing, but APC hasn't made the prop stamped with 7.4 x 8 in many years. They all read 7.4 x 8.0 ....

If a Q40 engine only turns 21.4, you shouldn't fly it. It will just burn itself up. Don't fly unless that tach reads 23K, on the pinch up.

RB

daven

My Feedback: (1)

No that is not good.

The APC Carbon props are confusing as Randy pointed out.

Not only are their different versions:

Version 1 labeled 7.4x8
Version 2 labeled 7.4x8.0
Version 3 also labeled 7.4x8.0 but has slight witness marks around outside edge of prop
Version 4 also labeled 7.4x8.0 but made out of a slightly different material.

But the pitch tends to vary slightly from prop to prop. I like to put my CF props on a pitch gauge and check them at station 7, its also a good idea to check both blades because they can vary slightly from side to side.

Back to your original question, you need to turn more rpms. If that prop isn't doing it, trim 1/8" off each tip, balance, and retune. You should be getting 22.5 - 23k on the pinch, you need a smaller prop.

garys

Version 4?? I must be out of it...when/where did that come from?

diggs_74

I was wondering the same thing Gary.. It's as bad as trying to keep up with Microsoft

daven

My Feedback: (1)

Yep, there is a new version out. You can see the difference between a Version 3 and 4 by looking at the hole in the front of the prop. On a version 3 you have about a 1/8" step before the diameter of the inner hole changes. On the version 4, the step is only about a 1/16". I believe the material was also changed.

garys

Interesting...when did it come out? Are the others available? I guess I haven't paid much attention since I've been running the 7.4x7.8 since Phoenix.

diggs_74

I haven't had a chance to try one of those 7.8... How are they working for you?? I have a couple, just haven't put one on yet.

garys

The 7.8's have been working great for me. At Phoenix, Jim Allen and Dave Shadel had both tried them and said they felt they were faster than the 8.0, so I bolted one on Friday morning, flew one test flight, it seemed fast, so I went to the NHRA drag races. Other than a few heats at a Basin race where I played with a couple wood props, I've only been running the 7.8.

daven

My Feedback: (1)

I heard about them in Muncie from Darrol. I think he had some of each.

7.8 works good, better than the 8 in my opinion.

diggs_74

Well, I guess I'll have to throw one on for the race this weekend.. Hopefully the old Dago can handle the extra speed

smitty9969

My Feedback: (7)

Thanks Fella's. I didnt do the pinch test. Just tached it before take off. I'll trim the props down to that 1/8.. I also have some 7.8. I'll run those and check the differences.
Again, thanks for the help..

Smitty

daven

My Feedback: (1)

Are you sure the engine was fully up on the pipe? There are a couple stages, its tough to know for sure unless you pinch the line slightly.

daven

My Feedback: (1)

Are you sure the engine was fully up on the pipe? There are a couple stages, its tough to know for sure unless you pinch the line slightly.

smitty9969

My Feedback: (7)

Positive,
Plane flew great. Good speed. Engine unloaded nicely in the air. Especially coming off of pylon 1. Love that sound. Reason why I'm asking because the engine was brought used. And the air is so heavy here with the humidity.
Next question, I thought you couldn't modify a prop if your at a race. Could I enter a sanctioned event with a prop clipped?
Just a thought, maybe I'm not gettin the rpm's on the ground because I didn't pinch, so it's not coming up fully on the pipe until it's airborne and unloads.

Smitty

daven

My Feedback: (1)

No you could not enter a contest with a clipped prop. No modifications are allowed to the black props, that is why I check the pitch of them and mark them accordingly.

smitty9969

My Feedback: (7)

Thanks fella's. That pinch really makes it easier to needle.

My Jett came up to 24.8 as soon as i pinched it, brought it down to 22.5 to fly. It's a new engine and I wanted a very rich flight to trim and get some air time on the engine. Flew with a 7x8 wood prop. After 2 runs, the plug still looked like new.

Will run the Nelson's in a couple of days.

Thanks again for the quick responces.

Smitty

luv to race

My Feedback: (1)

All sounds good, you have no worries then. And running wood should allow the motor to unload even better than the carbon. The wood will tend to flex more under load, actually depitching the tips. However, 7" is much shorter than guys normally run. You normally see 7.25 to 7.60" in length...

NOTE: To try and clear up the carbon prop thing. The version #3 of the 8.0 is NO longer in production, this was the one everyone liked. It had the "witness" marks on the top of both blades, and seem to rev up the most of all the carbon props..gone. The newest version #4 of the 8.0 is basically the same as the version #2, only Fred is using the newer materials. And I have no idea what is better/worse with the newer materials? Probably doesn't shrink and move as much during the cooling stage...beats me.. So, if you like the old version #3. I suggest you hang on to them.

happy flying...
RB