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Can't get above 2000 RPM

 
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mt



Joined: 21 Mar 2008
Posts: 19

PostPosted: Sat Nov 22, 2008 9:18 pm    Post subject: Can't get above 2000 RPM Reply with quote

'55 F-35 with an E-225/Hydraulic prop.

On a cold departure (25F) I could not get more than 2000 RPM. It overshot about 200-300 RPM of the final like it usually does but final is now 2000. Switching tanks and using carb heat had no affect either. I looked around and found the governor control cable was free to slide in its clamps and repaired it but this too had no affect. Mags check, and throttle control looks good. When I shut down the engine the propeller is at the high RPM stop. What now?

Thanks in advance.
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bgwells
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Joined: 01 Sep 2005
Posts: 23

PostPosted: Thu Nov 27, 2008 3:38 am    Post subject: RE: Can't get above 2000 RPM Reply with quote

What is the Manifold pressure at during the run up? If prop and governor are all ok, then what about the fuel and air? Got fuel pressure? What about air blockage? The pressure carb can be a tricky device, sometimes you might not be getting full swing on the throttle position arm even though you have full stop from the throttle knob on the control panel. You can check this without firing up the motor, and checking it yourself if full throttle then closed throttle. Also, same for mixture control, look for full swing of this arm. You also have many additional valves and items on the pressure carb that have to be working too. Usually a good shot of spray lubricant on the moving external parts of the pressure carb might help if they are stuck for some reason. But It would have to be in areas of prop or fuel it seems. You can tell if its the prop if you have someone standing out from the side looking at the prop and seeing if the pitch is flat or not on the prop during a ground run up. You can also take off the cheek panels and have someone work the throttle cable and mixture to verify working order there too.
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mt



Joined: 21 Mar 2008
Posts: 19

PostPosted: Sat Nov 29, 2008 2:03 pm    Post subject: Reply with quote

Thanks for your ideas. At a minimum of 20" MP I was able to get 2000 RPM. When I advance the throttle up to another 10" (full), the RPM stays at 2000. I think that eliminates the induction/fuel system but I confirmed the connections you suggested anyway. With this information I think this gets me back to the governor/prop. As far as the low pitch stop on shutdown, since it takes oil pressure to decrease the RPM I think the reason the prop is at the low pitch stops at shutdown is the pressure bleeds off before the propeller stops turning. The fact the prop is able to be governed so low I think eliminates the prop and, while talking to a governor shop, they offered to bench it to assure it was set properly. That said they could not explain the sudden failure however, and strongly recommended to send the T-drive as well. Their fear was there is a fair chance of not getting the coupler installed properly while the T-drive is installed on the engine causing even bigger problems. Seeing that almost requires the removal of the generator, mags etc., and I don't even know what the problem is yet, I gave it over to the local FBO. I'll let you know what he finds.
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mt



Joined: 21 Mar 2008
Posts: 19

PostPosted: Sat Dec 20, 2008 7:15 pm    Post subject: Reply with quote

Almost a month later and little progress. Governor was bench checked and given a thumbs up. It is a pressure-to-increase-RPM system but, with the engine running and despite passing the bench check, the output oil pressure is equal to engine pressure and the RPM is still topping at 2000. They pulled the prop and in a centering cone apparently there was a missing gasket. This part is the one that fits over the shaft to center the propeller and has four channels to pass the oil to the prop plus a slot cut down its length. The propeller shop said they had seen this before and the gasket fixed it. The mechanic however cannot imagine why this would be the problem but trusts the shop and is proceeding with little hope it will work. Hard for me to hear as the aircraft has caused us to miss several holiday trips and we are paying for him to do things he doesn't think will work. Any ideas?
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bgwells
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Joined: 01 Sep 2005
Posts: 23

PostPosted: Sun Dec 21, 2008 4:33 am    Post subject: RE: Can't get above 2000 RPM Reply with quote

Have you already obtained a copy of the Hartzell Manual from the website?

www.vintagebonanza.com/hartzell_for_e-series-engines.htm

And you have verified that ground adjustments for RPM stop limits as per Manual?

Again, I should ask, did this RPM limit of 2000 just start all of a sudden, meaning not after some repair or adjustment, and RPM had previously been just fine before with limits of 2600?


Here is a contact at Hartzell, in the letter it mentions the diaphragm that controls the prop.
Letter from Hartzell
www.vintagebonanza.com/hartzell_propeller.htm
Kevin M. Ryan
Hartzell Product Support.
email: techsupport@hartzellprop.com
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mt



Joined: 21 Mar 2008
Posts: 19

PostPosted: Mon Dec 22, 2008 12:56 pm    Post subject: Reply with quote

Thanks for the links. Good information on the system

This was a sudden thing with the only difference from the norm was it was the first cold start of the year at around 25F. I was in KS on business, flew in a week prior, and this was the return flight.

Today we find out if the gasket recommended by the shop fixes the issue. I went through the document and could not find it but that doesn't mean its not there.
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