DanH

DanH

Legacy Member
Mentor
Need to pick a run-up and prop exercise RPM.....and I'm gun shy when I jump in a new-to-me taildragger. Sure would hate to stand one on the nose.

What seems to be a safe RPM for an RV-8 in the forward third of the CG range? I'm guessing elevator authority exceeds the ability of the brakes to hold in place, but I'd hate to be wrong.
 
My prop cycles just great at 1800 RPM Dan. And while I do hold the stick back, I have (cautiously) experimented with wagging the stick around while at that RPM, and I can go full down without raising the tail at that setting, solo. I sure wouldn't do that if there was a gusting wind or anything, but it's nice to know the margin.

Our RV-6 prop doesn't cycle well below about 1875 or so - just a little different, I guess.

Paul
 
No issues at 1700 either. You can run it up to much higher RPM, but keep the flaps retracted!!
 
Hey Dan,
I just did my first engine run last week. Ran the IO360 up to 1760 RPM to test prop cycling and check for leaks. The wings weren't on the airplane at the time, so weight on tail was substantially less. I had the tail tied to the rear axle of a 1/2 ton Chevy pickup so it wasn't gonna go anywhere. With the wings on, the airplane won't nose over at any power setting with the stick back.
 
Same here

Ironflight said:
My prop cycles just great at 1800 RPM Dan. And while I do hold the stick back, I have (cautiously) experimented with wagging the stick around while at that RPM, and I can go full down without raising the tail at that setting, solo. I sure wouldn't do that if there was a gusting wind or anything, but it's nice to know the margin. Paul
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My experience is the same as Paul's even with a heavier angle valve IO-360 on the nose.

John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
 
MauiLvrs said:
Didn't you read where that isn't always such a good idea?:eek:
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I think that's putting it mildly, it's a REALLY BAD idea to do this! I remember seeing a youtube video of this once, turned out really ugly! It would really stink to roll your new airplane on it's side and have a prop strike on the first run :eek:
 
For full power run ups, definitely tie your tail down. Mine is a constant speed prop, and above 2500 RPM, the tail wheel is dancing in the air trying to go straight up. At 1800 RPM, prop & Mag checks are no problem.
 
Something not quite right here.

donaziza said:
Mine is a constant speed prop, and above 2500 RPM, the tail wheel is dancing in the air trying to go straight up.
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At 2500 RPM you should have enough elevator authority to keep the tail on the ground. Unless of course you have the flaps down.
 
DanH said:
The tail gets light with the flaps down?
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Yes - it does! Partly because you're blowing all that air right at the bottom of the flaps, giving you a nose-down pitching moment. Not a particularly efficient one, but it is effective.

Oh, and once you have the great paint job that I am expecting from you Dan, you'll chip the heck out of the bottom of the flaps....:(
 
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We use 1800RPM for Prop and Mag checks.

From 2nd hand experience / feedback, it is important to be very close to into wind. Any crosswind, or worse quartering tailkwind, can blow the propwash away from the tailplane... the tail lift to propstrike I witnessed was a slight quartering TW and lots of power :(

As an aside, Bulldog I fly (200HP IO-360) uses 1800RPM for Prop, 2100RPM for Mags. Extra 300 (IO540) 1800RPM for each.

Clearly Flaps Up unless you are trying to remove the paint/smooth surface deliberately ;)

Andy
 
WRT the prop what is one trying to achieve with the cycling?

a) Clearly you want to know it works.
b) I have always understood there is an element of moving colder oil out of the mechanism in exchange for warmer oil.
c) So what does it take to do that? Is a slight drop at say 1700 to 1650rpm adequate? Perhaps a couple of times?
d) Anything else?

PS In cruise flight what rate of change is going on of the oil in the prop mechanism? Is there a built in 'leak' so there is continuous exchange?
 
Steve...

WRT the prop what is one trying to achieve with the cycling?
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As ever a good qu! Largely as you say I would suggest.

From UAS days / other "rumours" / checklists I try for:
  1. 1st cycle of day is minimal change in RPM e.g. as little as 50RPM if you can do it,
  2. 2nd/3rd cycles are ~300RPM, Max 500RPM [NB less during engine break-in]
  3. 1st Flight of day only does 3, subsequent flights do 1
  4. When you advance the lever again, do it gently to the set RPM, let RPM settle, then advance the rest of the way. RAF taught this in a bid to stop damage to the FPS...
Re "getting warm oil" to the prop, and the prop "surging" some had experienced (usually because the FPS had not been setup), it was stated, and I think we observed, cycling RPM downwind did reduce the surging, so it would seem the oil in there can get cold / is not continuously cycled?

ATB
Andy
 
Thank you gentlemen. You figure 1800 is safe even with forgotten flaps? When possible I prefer SOP with leeway for pilot error.

Andy, good point about off-angle relative wind. It is also very hard on crankshafts and prop blades due to asymmetrical disk loading.

Thank you Paul. I'm real tempted to take a screwdriver and scratch the paint just to get it over with ;)
 
You figure 1800 is safe even with forgotten flaps?
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The "Hazard" with forgotten flaps is presumably tail rising? I don't think the flaps have much of an effect, else they would cause all sorts of trim issues on finals/takeoff... e.g. I use the same trim setting for takeoff with Flaps Up and Down (and Half down) and cannot feel a difference.

Andy
 
Don't

Don't worry Dan. The paint Gods will scratch it for you before you know it.
Good Luck.



DanH said:
Thank you gentlemen. You figure 1800 is safe even with forgotten flaps? When possible I prefer SOP with leeway for pilot error.

Andy, good point about off-angle relative wind. It is also very hard on crankshafts and prop blades due to asymmetrical disk loading.

Thank you Paul. I'm real tempted to take a screwdriver and scratch the paint just to get it over with ;)
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Andy Hill said:
I don't think the flaps have much of an effect, else they would cause all sorts of trim issues on finals/takeoff... e.g. I use the same trim setting for takeoff with Flaps Up and Down (and Half down) and cannot feel a difference.
Andy
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I have to respectively disagree. I have seen several props-in-the dirt from doing run-up with flaps down. All required engine tear-down.
My trim tab differs approximately 3/8" at trailing edge between no flaps and 15* flap take-off.
 
DanH said:
........ I'm real tempted to take a screwdriver and scratch the paint just to get it over with ;)
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:D I know the feeling. working around all that nice paint is surely adding hours to the build. Also it has postponed any thoughts of dirt strips for a while after first flight.
 
Good info to know. I've always used 2000 rpm (not sure where I got that advice, but it was suggested and I just used it), without any issues. However, the other day I just ran it up to 1800 and the prop cycled just dandy. I think 1800 is my new run-up target.
 
I have to respectively disagree. I have seen several props-in-the dirt from doing run-up with flaps down. All required engine tear-down.
My trim tab differs approximately 3/8" at trailing edge between no flaps and 15* flap take-off.
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No probs Mel, I'll add it to my experience database. To date I have not (knowingly!) done the run-ups Flaps Down ;) I'll take a look at the takeoff trim.. never thought to do it before.

Andy
 
Well, I must have most of the dumb mistakes by now.

I can confirm that 1800RPM power checks with full flap is ok :eek::eek::eek: but I do hold the stick back (with my knees) and I do make a point of being as into wind as possible.

No doubt there are still a few big goofs to get out of the way.:D

Chris
 
Flaps up, full aft stick--maybe it's more like 2650 RPM. I've watched my mechanic do full power run ups. Tail has to be tied down.
 
Walt said:
I think that's putting it mildly, it's a REALLY BAD idea to do this! I remember seeing a youtube video of this once, turned out really ugly! It would really stink to roll your new airplane on it's side and have a prop strike on the first run :eek:
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I did an extensive amount of researching this issue before running the engine with the wings off. Yes I did see the video of the turbine Lancair IV. The MG legs both bent/failed rearward with the turbine at high power.

Running the little O360 at idle to 1800 rpm while tied down was a total non event. Lateral stability, wings off was no problem.
 
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Bill Wightman said:
I did an extensive amount of researching this issue before running the engine with the wings off. Yes I did see the video of the turbine Lancair IV. The MG legs both bent/failed rearward with the turbine at high power.

Running the little O360 at idle to 1800 rpm while tied down was a total non event. Lateral stability, wings off was no problem.
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I recall a previous discussion -- the wings keep the fuse from vibrating too much during start-up and shut down. Of course, this is not their intended purpose, it's only a benefit of their added weight and arm. The startup, idle, or shut-down vibration can cause damage to the elevators in the counterweight area, and possibly the rudder too, as the fuselage rotates along its length around its center of mass.

If you had the machine tied laterally too, I suspect this would be a non-issue. If not, you might want to have a look at the elev skins just inboard of the counterweights. A slight kink in the TE about 6-8" inboard of the tip would be the 1st indicator...

Any doubts about this will be dispelled if you stand by the tail of a Lyc powered 172 when it shuts down. It ain't pretty!

Carry on!
Mark
 
I recently had that "Lyc powered 172 when it shuts down" explained to me in very succinct terms. The fellow doing the explaining had spent far too many hours in uncomfortable positions replacing cracked parts in the tails of Grumman AA5 airplanes. He refered to the wicked shaking of the tail on engine shut-down as "the wet dog shake". In retrospect I can't think of a more appropriate description of what happens to the tail as the Lycoming comes to a stop. All that's missing is the flailing dog ears!
 
Hmmm... hadn't thought of the fuselage torsional issues. No problems and no visible damage during my run.

I'll wait until I get the wings on for further engine runs. Thanks all...
 
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