Aeromatic Adjustment

D

dtreid

New member
I'm in the process of trying to set up the aeromatic behind my Franklin 165 in my 14-13-3.

I've followed the book and adjusted static rpm without weights...all seems fine.

I've added weights to bring static rpm down about 50rpm or so. When I took it flying the prop doesn't seem to want to shift to coarse pitch. I will overspeed the engine if not careful on climbout and can only get about 100mph out of it at 2600rpm pulling about 15MP.

I added weights so that at full throttle field elevation in flight I don't overspeed the engine, but now I'm about 150rpm under what I'd like for takeoff.

Any ideas? My field elevation is about 4000ft.
 
Remember, you adjust static RPM with the shims at the center of the hub....not with weights.
After that, you should add the previously installed weights, and work from there.
Dan
 
Dan,
I did adjust static rpm with the shims. My issue is that when I get flight RPM adjusted to where I want it (using the weights), I lose 200 rpm at takeoff.
I spoke to Kent Tarver about it and he suggested drilling 2 of the -4 weights off center and have the bulk of their weight pointing towards the blade leading edge. This will have the same effect at lowering the arm angle. I guess we'll see if this makes any difference.

I was just wondering if anyone else had run in to this with their aeromatic?
 
dtreid,
I noticed an interesting page on Kent Tarver's Aeromatic.com a few months ago related to the effect of changing the arm angle. So, Tarver's eccentric weight suggestion here is a very intriguing one since it would make it quick and easy to experiment with arm angle.
Well, I've have had two Aeromatics, and both worked great - right out of the book, with no weirdness whatever.
But I also had heard several Aeromatic stories early on about "sticking" in high or low blade angle supposedly due to the blade bearings wearing slight indents in the races. Maybe. The stories sounded a lot like what you are experiencing. Could be a too small angle with extra weight will produce this "two speed" jump effect, or maybe the reverse as Kent said. You have the experimental Bellanca, so see what changing the effective arm angle does. Maybe after 60 years or so someone will get to the bottom of those stories I have heard about "slam shifting Aeromatics".
r
 
My aeromatic only has about 40hrs on it since overhaul, however, it seems like the previous owner neglected to put oil in the hub after he got it so it ran the first 20hrs with no oil.....Kent Tarver didn't seem to think this was a huge problem but I'm not too sure.

I have been chasing a problem it that I was getting a sudden pitch change right at lift-off. The engine would suddenly pull down about 150rpm as the pitch suddenly coarsened up.

I'm hoping that all my fiddling will provide some answers.
 
David, do you have a fixed pitch prop available to try, just to make sure you are chasing the correct problem? It is possible that your problem could be the engine, and not the prop. There was a long write up a few years ago about a Viking that the owner spent thousands of dollars on overhauling a prop, and then a top overhaul on his engine, all to no success, and then discovered the whole problem was the trim tab vibrating at certain speeds and RPMs. I would also consider measuring the angle on the arms to make sure the previous owner didnt change them. It is a delicate balance between your airspeed, which coarsens the pitch, and the weights which are supposed to allow the pitch to change smoothly. I think Larry L posted a technical review of Aeromatic operation a few years ago. Maybe he could post it again???? I hope it all works out. ______Grant.
 
This seems mighty suspicious to me.. and I will be waiting to hear what you finally discover.
The mechanism should move very freely by hand. Can't you duplicate this sudden pitch/rpm change on the ground - during a full power static run-up ?

If the thing isn't really smooth when you cycle the blade postion by hand... then I would want to open it up and inspect it.
If it is.. I would really be looking at my engine very closely.


There is a "dash pot" as well as a lube function for the oil.
It is really easy to open up the hub to inspect it

Nobody is using anything more exacting than pencil marks when they remove and replace the balance bands..
are they tight ? :oops:

---

Are you sure you don't have a Magneto Fault, or Fuel Problem. :?: :?:

This symptom would freak me out.. and I wouldn't want to fly the plane till I had it figured out.

After I nearly lost an intake manifold in flight.. I can say it is easy to take fundamental things for granted .

Engage a second set of eyes and hands.. preferably an A&P..

engine failure on take-off is deadly serious.
 
I think dan is correct.. and that you need to set it up In Order.. static first with shims... per the manual
and then work with the weights and cruise rpm.

otherwise you will be chasing your tail.

--
what ron said about the bearings getting notchy is interesting.

if you can't feel it, you could certainly see it... and if a lack of lubrication caused a problem.. galling in the bearings would be where I would expect to find it.. so.. maybe a tear down is in order.

Doesn't cost anything... but absolutely slays the dragon one way or the other.

I really don't see how misadjustment is going to account for quirky sudden pitch changes.. I just don't.

So I vote for opening up the hub, and visually inspecting everything.

Kent's son can whip through this fast.. if you pre-schedule .

Worth doing. :D
 
Per Grant's request, I have tried to attach a power point presentation on how the Aeromatic prop works. The site won't let me add it to this message, so if you want it, email me and I will send it...unless Robert can do some magic to let me attach it.
Larry Lowenkron
 
The sudden pitch change has never happened on my first takeoff of the day, only the 2nd or 3rd, after a longer taxi back. It got me to wondering if it was caused by things getting a bit warmer in the prop hub while on the ground. I glanced down at the MP gauge the last time it had the sudden pitch change and I was showing 25" of MP leading me to believe the engine was developing full power.

I set static rpm up as per manual with no weight. I then added weights to get a 50 rpm drop at full throttle with the wheels chocked.

When I took it flying the engine would overspeed on climbout by a bit (but boy did it climb!) In cruise I could only get a bit over 100mph w/o overspeed the engine pulling about 15"MP.
I added one -3 weight to either side and went flying again. Takeoff rpm was good but full throttle near field elevation would still overspeed the engine.
I added one more -3 weight. Takeoff and climbout rpm was about 150rpm lower that I'd like. Full throttle rpm near field elevation was good.

I did NOT have the sudden pitch change while doing any of this experimenting.
 
dtreid,
You obviously know the standard Aeromatic set-up drill as well as any of us by now. In fact, a few more shots at this and you should have your Expert Badge. :) Well, you shimmed to your redline rpm, and went through the range of weights possible without getting good results. Your last results sent have you at fig 3 inhttp://www.aeromatic.com/resources/index.php?category=4 . That diagram shows rpm increasing with airspeed. As Kent suggested, it means adding weight toward the blade leading edge to reduce effective arm angle.
I would start the weighting process by applying a substantial eccentric weight to each side per Tarver, then add normal weights to get results. Hopefully this will get you what is needed with no prop teardown, and we will all learn a little. Good luck.
r
 
David, what weight oil are you using in the prop? I understand that Kent has recommended, up to 90 weight oil in the props, but I once had a bottle of original Aeromatic oil (whatever that designation was) and it was very thin. People often recommended using Marvel Mystery Oil, which is also very thin. If you are using 90 weight you might try switching to a much lighter oil, and see if it makes a difference. I would try that before a major tear down. Just my 2 cents worth. _____Grant.
 
I was running a 75w90 synthetic gear oil, but have now switched to Marvel Mystery Oil.

Weather has been crummy for flying, but I did some high speed taxi tests and am getting an easy 100rpm increase on the ground after moving the -4 weights off center.
It will be interesting to see what it does in the air, but there certainly is a difference on the ground.
 
Had the Cruisair up today with my off-center weight.

With the weighting I had, it would overspeed about 100rpm on takeoff and not coarsen up enough in cruise (I could only get about 90mph without overspeeding the engine)

I added 2 x -1 weights. It pulled the takeoff rpm down a bit but was still too high. Cruise was now up to 100mph without an overspeed.

I put my drilled -4 weight on with the bolt in the center hole again, but turned it so that the hole that I drilled was towards the trailing edge of the propeller blade. My thought being that this would still cause a slight bit more weight towards the leading edge of the blade, effectively lowering arm angle slightly.

Up again, and takeoff rpm was still very slightly high, but I was now pulling 21-22" MP at cruise and getting another 8mph out of her.

Next I will try adding a -2 weight to it and see how things go.
 
David,
Since my nature is on the experimental side, I think you are having too much fun for one guy. But like most others though, you probably just wanta-git-r-done.
So, the engineer side of me offers these observations to that end. ( tune the arm angle to get normal behavior as directly as possible)

1. Fact. Moving the arm forward (reducing the arm angle) will require more total weight
2.Start with a substantial offset weight forward, your -4 or more mounted forward by offset hole.
3.Add regular weights. Total weight required will be greater, maybe substantially more than before.
4. Success will be indicated by similar rpm at t. o. and WOT level flight. Or back to 2. for more or less offset as needed.
5. Stir and enjoy
Again, you may not be out of the woods re blade bearing, etc, but its worth a little time I think.
r
 
I have a question and a statement.........
Question:
Was this propeller operating normally before all these recent "adjustments?"
Statement:
According to David Reid's statement of November 21, "...added weights to get 50 rpm drop at full throttle
with wheels chocked." According to the Aeromatic Field Service Manual, you add or subtract SHIMS at the center of the hub to obtain desired static rpm......NOT WEIGHTS. Apparently, this propeller was not set up properly and unless it is, there is no sense in further diagnosis or discussion.
Dan
 
Dan,
The prop was adjusted with all weights removed and shimmed in order to get the static rpm set.
The manual talks about adding weights to bring the rpm around 50rpm below redline, take it flying and see what weights need to be added in order to achieve flight rpm.

With weights added to bring full throttle rpm on the ground down to 50rpm below redline rpm I was getting an overspeed on takeoff and a very low cruise speed.
 
I can't help but wonder ...I am always suspicious of instrument problems. Have you watched the MAP carefully as the RPM drops? Your initial description of 2600 rpm (?) and 15"MAP sounds pretty strange to me. Since I have had tach problems in the past, I just wonder...?
LL
 
The tach is an electronic one that I've checked with a hand held lazer tach and it reads right on if that's what you're referring to Larry.
 
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