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Todd copeland
08-31-2011, 07:26 PM
I just changed the prop on my glastar from a fixed pitch sensenich prop pitched more on the climb side for a hartzell constant speed prop. I have an io320b1a 160hp. My question surrounds the climb performance. While I have a minor adjustment to make on the governor to up the toms from 2610 to hit 2700, the climb performance of my plane is way down. I regularly saw 9-1400 fpm and now the most I can manage is 5-600fpm. The cruise is improved but I could have improved the cruise and sacrificed the climb by have my fixed pitch changed for a cruise pitch. Could that 90rpm adjustment make that much difference? What am I missing, this is really disappointing.Todd

Chad Jensen
08-31-2011, 08:21 PM
Were the conditions the same for comparison? Really hot? 90rpm won't make a huge difference, but may be noticeable...though it won't make a 4-500fpm difference. Where do you pull your rpm indication from? Did something change there? Just thinking out loud here...

Bob Meder
08-31-2011, 09:51 PM
Did you happen to get the manifold pressure being produced by your engine while you had the fixed prop? How does it compare to the MP now? If the engine's putting out the same power, then I suspect that you're not getting the fine pitch you should be getting.

One more thought: have you used a strobe-type tachometer on the prop during a static run-up to verify the aircraft's tach?

FlyingRon
09-01-2011, 05:42 AM
Also, that Hartzell prop weights a lot more than your fixed pitch. If your prop was pitched for climb before, all things being equal, you'd expect to see some decline. Also, if you did nothing else to fix the balance, you're using a lot more elevator down force (and hence drag) to counter hanging that additional weight pretty far out on the arm. When we hang big engines on Navions, we either move the battery back farther in the tail or add a few pounds to the very aft of the aircraft to counter.

Jim Hann
09-01-2011, 08:55 AM
Another out loud thought, what RPM were you pulling in a climb with the fixed pitch prop? Was it greater than 2700?

Jim

Todd copeland
09-01-2011, 04:14 PM
Thanks for the thoughts, the rpms were lower with the fixed pitch prop. We are investigating the cg further. While we haven't added that much to the nose, it is all at the nose! It also feels nose heavy, and if I can feel it it must be a factor. Reading the manual it states the glaster is very sensitive to the forward cg. I weighed the airplane today and I am working it out.Thanks,Todd

Chad Jensen
09-02-2011, 07:43 AM
I'm curious as to the actual weights between the two props, including the governor for the CS...just for an actual data point to be out there.

Howard Handelman
09-02-2011, 07:37 PM
1. Weight. C'mon - 40 pounds makes that much difference? I don't think so.
2. CG - yes, with more weight on the nose there must be more downforce on the elevators, but that sounds insufficient to account for the difference. Gut check, no math.

Let's look at the reported data:
Improved cruise, worse climb. If a CS prop does that when compared to a FP, you have to look at the area and CL of the blades. However, a CS should be able to adjust enough to overcome that. So, is anyone looking at the governor itself?

I took my "transition training" in an RV-6 with CS prop. The takeoffs were dramatic. My 7A with FP prop set up for cruise has a decent climb rate - around 1500 fpm, but that's at least 500 and maybe 1000 fpm less than the -6 on the same 180 HP. These reported results are the exact opposite of what anyone would expect.

And I do agree that you have to compare performance on a similar day. Hot air can make a huge difference. That said, the hot air won't make the cruise any better.

Eric Page
09-02-2011, 10:28 PM
More out loud thoughts...

- I'm not familiar with how CS prop blades are mounted in the hub, but is it possible that one or both blades could be mounted at an improper angle of incidence? is there any vibration that might suggest an asymmetry?
- Was any other work done at the same time that might effect engine performance? I'm thinking of things like carburetor work or throttle/mixture cable adjustments.
- Are you certain that the prop control cable isn't binding? Even if the governor is working properly, a bound cable might prevent it achieving full fine pitch.
- I presume the cowling was off for the installation. Could there be a loose piece of baffling in the induction airflow path? A rag left behind?

Good luck! Let us know what you find.

Todd copeland
09-05-2011, 03:51 PM
CG seems to be the issue. Did a new weight and balance and with the new prop I am at the absolute forward acceptable point in the CG. For a confirmation of results I flew with 50pounds in the baggage compartment to move the CG aft and I climbed at 3-500 fpm better. Also got another 5knots in cruise. Now I will agg some weight as far aft as possible to get a more acceptable range for the airplane. So there you have it, forward CG WILL hurt performance. I should have done a new weight and balance before flying it and shame on me for not doing it. I knew it would shift the weight forward but not that much and I wasn't afraid of a forward CG like an aft one.Todd

Jim Hann
09-06-2011, 03:03 AM
Todd,

Not to sound preachy, but if the performance changed that much with CG shift, I'd recheck all of your numbers for your weight and balance! That is a huge change, be careful!

Jim

Chad Jensen
09-06-2011, 07:32 AM
We'd all love to see more reports of your improved performance after the switch! I think Jim is spot on with the swap you made. Keep the numbers flowing!

Hank
09-08-2011, 08:10 AM
Just be careful adding lead to the tail. Nose heavy flies poorly, but tail heavy flies ONCE! double-check your math, and reweigh to make sure you got it right. And attach it firmly, too.

Bill Greenwood
09-08-2011, 11:41 AM
Todd, Hank is absolutely right. If you are a little nose heavy it just flies slower, climbs slower, and is nose heavy in the landing flare.
If you make a mistake on your cg figures and get it past the aft cg safe limit, it is dangerous. It may fly fast, be light on the stick force, and land easy, BUT IT MAY NOT RECOVER FROM A STALL EASILY AND ALMOST CERTAINLY WILL NOT RECOVER FROM A SPIN. You can't get the nose down to get the airflow over the controls.

So proceed very carefully, perhaps do several test flights and stalls, starting just a little less nose heavy, and slowly move the cg aft. Leave some margin. And maybe wear a chute until you have it worked out.

Todd copeland
09-08-2011, 05:39 PM
Good advice all. I agree with the aft CG worries. Frankly, I wasn't that concerned with the forward gc as it is not nearly as dangerous. The figures I have now with no change is still within 2 inches of the forward limit. Still, there is a lage difference in feel of the plane and the performance as described. There are glisters out there with 180hp and constant speed props that must be moving there battery much further aft than I have it. Hopefully this weekend I get a new set of wieght numbers that I am 100% confident in and the I will keep it on the scales and add the appropriate weight to the tail to get a more ideal CG. My calculations show it will take about ten ponds but I will be absolutely sure and the lead will be well secured. I have read stories about weight moving around in a flying airplane and they never end well. I will post the results here.Todd

drmax
11-17-2011, 01:48 AM
Hello and any updates Todd?

Todd copeland
11-17-2011, 05:17 PM
Now that you ask, I do have an update. I bought new scales to use with the "aircraft scales kit" from aircraft spruce. The design of them is fine but the scales themselves were worthless. We were never happy with the results from them when we did the original w&b as they seemed to be unreliable and inaccurate. The end result is that our glastar is about 25 lbs heavier than we thought it was. As far as the balance issue we were within the forward limit but we were close to it. We experimented with weight in the tail while it was on the scales and ended up putting 12 lbs of lead back there. We are still toward the front on the CG but it gives us a generous baggage weight capacity. Performance is excellent now. Performance takeoff in about 400 feet at gross, climb between 1000-1400 fpm depending on condition and weight. The biggest improvement is in cruise as we hit the book numbers now and can cruise at 132knots. Bottom line is that while we were within CG limits we should have know exactly where it was before testing the new prop. Also, I have learned how much the CG can affect performance in an aircraft even within the acceptable range.Todd

FlyingRon
11-18-2011, 08:23 AM
Hopefully you were doing the weighing inside?
One of the things that bothered me about Cringley's attempt to build a homebuilt (the second time when it was a Fisher) was he did all his weighting outside in a breeze.

Todd copeland
11-18-2011, 02:17 PM
Inside and leveled with the hanger door closed. Easy to watch the different scale readings bushing here lifting there... Yes, outside with even a puff of wind would vary the readings a lot.