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Anyone have trouble keeping the tail down during runup?

Kooshball

Well Known Member
I’m not sure if something could have changed with prop angle when my prop & hub were overhauled and the governor replaced but I experienced something for the first time last night when I did my run up.

I have a 200hp IO360 with a 3-blade MT prop, Mt hub and MT gov. Yesterday as I was approaching 2000 rpm on my way to 2100 to cycle the prop the tail started to lift even with full aft stick (stick and elevator have full travel and were at the stop). I throttled back, moved the stick, verified visually I was getting full aft stick / elevator and tried it again...same thing happened. I ended up cycling the prop at 1950rpm and as soon as the pitch changed, the tail jumped a little.

I was at 1/2 fuel, solo and I don’t weigh much but the CG was near the middle of the envelope. The air was near standard conditions so my no means exceptionally dense (I’ve flown this plane many times in much denser air without this happening). I normally top off the tanks after every flight so being at 1/2 fuel was something different and of course a new governor and overhauled prop / hub are different.

I have a call in to the prop shop but was curious if this is common with other RV4s given the geometry of the plane and the chosen power plant.

Thx!
 
Did you have a particularly high head wind? It has been very windy here lately. Tail flies on airspeed. Additional 10 knots of wind would make it fly a lot earlier.
 
1800 for me

I use 1800 for run up without problems. 2100 RPM on the ground is a lot of power and dramatically increases the chances of damage to prop and/or tailfeathers due to the increased pebble and debris pick up. I set my "Canopy Open" warning at 1900 RPM as I should never see that RPM on the ground during taxi even considering hills. 1800 RPM seems to provide enough power to detect ignition issues during test and prop governing pressure to move the blades. Higher RPMs have not been needed to detect ignition issues and add a great deal of stress to the blades when cycling the propellor.
 
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~20 deg in this case

And, I believe, therein lies the problem. Flaps should be full up during run-up.

ANY flap deployment can cause the tail to lift.

And, 1700-1800 rpm should be sufficient for run-up.
 
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I use 1800 for run up without problems. 2100 RPM on the ground is a lot of power and dramatically increases the chances of damage to prop and/or tailfeathers due to the increased pebble and debris pick up. I set my "Canopy Open" warning at 1900 RPM as I should never see that RPM on the ground during taxi even considering hills. 1800 RPM seems to provide enough power to detect ignition issues during test and prop governing pressure to move the blades. Higher RPMs have not been needed to detect ignition issues and add a great deal of stress to the blades when cycling the propellor.

1700 for me! for all the above reasons.
 
Agree 100% that the flaps need to be up, stick back, and anything over about 1900 rpm is excessive for run-up on these plans. You will have to figure out for your airplane what the minimum RPM is for the prop to cycle - our four airplanes with C/S props all have different numbers between 1700 and 1900 rpm - and use that. No point in using more!

Paul
 
Thx for the replies folks! Interesting that with the old hub / gov we actually needed over 2000 rpm to get the prop to cycle...now it seems like it will cycle lower which I will implement immediately. Ignition check run up has always been at 1800...maybe I can get the prop to cycle there as well.

Thx
 
prop cycle

Thx for the replies folks! Interesting that with the old hub / gov we actually needed over 2000 rpm to get the prop to cycle...now it seems like it will cycle lower which I will implement immediately. Ignition check run up has always been at 1800...maybe I can get the prop to cycle there as well.

Thx
Another with flaps up, 1700 for mag check, RV-8. I'm surprised you can keep that light RV-4 on the ground at 2000 with that powerful engine and 3-blade MT!
 
I think (just an opinion) that a lot of the RV-4's in the world that are equipped with anything bigger than the 150-160hp that it was designed for are already forward on the CG from birth. The design has had band-aid's added (bigger engine mount weldments, etc) to make it feasible and safe for bigger engines but the end result is still a more nose heavy airplane (or just heavier, if CG is accounted for) than the original design.

I have a O-320, wood propped, short geared -4 and can hold the tail down with a full power runup. Flaps up mind you, I've never tried it with the flaps down.

My opinion: The bigger engine and C/S prop might just be enough nose weight to not allow you keep the tail on ground even with full up elevator.
 
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1800 for me

1700 for me! for all the above reasons.

I was quite startled when during a hot start the engine lit with the throttle wide open. The tail lifted immediately. Thank God no prop strike.
Caught it during the lift.
Phew.
Edited my POA.

Daddyman
 
Our RV7 needs 2000 RPM to cycle it's counterweighted aerobatic prop.

Your new governor may make more pressure than the old one. Your newly overhauled hub may likely have it's low pitch stop positioned flatter, so the blades produce more thrust at lower RPM.
 
Well on Sunday I was able to get it to cycle at ~1850 and had no issues (full fuel and no flaps helped too). Between the governor and freshly lubed hub it seems to respond at lower rpm / oil pressure now.

Thx!
 
No trouble keeping my tail down during runup. I run up to 1800 for the mag check. I have a fixed pitch prop, so no prop cycle. I do have an O-360 lyc, so a little more weight up front, but no issues. I originally had a metal Sensenich, but now have a carbon Sensenich (20 lbs lighter), but no issues with the heavier prop. I recently did a dynamic prop balance and ran my engine up to 2100, but had no trouble with the nose dropping, of course the stick was held full aft. I have the long gear legs, so that may be an issue with an RV4, but I don’t know if that actually makes a difference.
 
late on the wagon... nevertheless, max RPM (flaps up anyway...) before the tail rises on my -6.9 is 2300RPM, therefore run-up is always done at 1800. Into wind if possible. Stick at the back end stop. Parking brake on and brake pedal depressed. Not done on any loose surface, or short stopover, in this case a check of each EI whilst taxiing is good enough for me.
 
Weight a minute...

I’m not sure if something could have changed with prop angle when my prop & hub were overhauled and the governor replaced but I experienced something for the first time last night when I did my run up.

I have a 200hp IO360 with a 3-blade MT prop, Mt hub and MT gov.
Thx!

Dave,
That's alot of weight on the nose of a 4, lots of thrust as well.
Not surprised.
I performed the entire test profile on a 300HP MT propped Bearhawk. I was able to cycle it's MT prop/IO540 at 1500, as its tail was light too. Its a bit slower cycle, but works fine.
Gently cycle the governor at lower RPM and I think you'll like it at much better, just make sure your oil temp is 100F.

V/R
Smokey
 
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