Full power run ups for a taildragger?

[Yen]

I agree about brakes causing a nose over. What is really bad from that point of view is the reflex action to stab the brakes on if they have slipped a bit. that will just about guarantee a prop strike. Full back stick should keep the tail down, but I wouldn't rely on it.

[Ralph Inkster]

Recently did a series of high power run up testing on a supercharged Harmon Rocket. This application would start lifting it's tail anything over 2200rpm because of it's rather forward balancing on it's landing gear. Truely a sickening feeling when that occured. What we did to prevent this during static tests was to tie the Upper engine mounts (both sides) back to the base of a chain link fence post, the rope passed over the Horiz Stab, as well strongly tieing down the tail wheel. We were able to get full throttle (fine & course pitch!) testing done this way. We sure raised some impressive dust plumes across the gravel parking area behind the plane.
Some partial throttle testing was done without chocks or being tied down. These run-ups were done in an appropriate open area of course. With it being very easy (& quick) to get to the 2200rpm barrier & if the tail started to get light, we Cut Throttle (natural) & LET OFF THE BRAKES (not so natural) & the tail would settle immediately. We found that when only cutting the throttle the tail would continue to come up because of residual thrust & fuselage tipping momentum, so we'd trade tipping momentum for some forward motion. - I mention this throttle/brake technique as it may come in handy to you someday during a run-up gone wild...

[WSBuilder]

I flew my friend's RV-6 last Sunday (holy cow, what a machine!), ending with a RTB because of regulator failure. He is medically grounded and hasn't flown for over a year. Once called, he arrived and wanted to check it out with a ground run. He flooded it on restart and against advice, had the throttle full open when it finally lit off. His throttle is the locking, button type. I saw him from the wing tip with both hands desperately pulling on the locked throttle as the tail went skyward and high-velocity dirt sprayed on my sandwich. Then the tail slammed down and the castor rotated 90. It was simply amazing how fast it happened and the subsequent quiet was deafening ....until the cursing started. God bless insurance, but curse those locking throttles!

[MikeyDale]

I just test ran my engine (1800 RPM max) and tied the tail down to the front bucket of my John Deere. The hitch on my Pick Up Truck is too tall in my opinion. I will do the same later for a full static test if I can find a grassy spot on this drought stricken West Texas farm.

[Andy Hill]

I will do the same later for a full static test if I can find a grassy spot on this drought stricken West Texas farm

From your pic Mike, you seem to have a Hartzell VP Prop. Out of interest, what do you intend to gain / understand / value from a "full static test"?

[MikeyDale]

Originally Posted by Andy Hill

From your pic Mike, you seem to have a Hartzell VP Prop. Out of interest, what do you intend to gain / understand / value from a "full static test"?

I would like to know what the static rpm of my prop is at full throttle but a few high speed taxi test may reassure me that I will not over speed my engine on that first takeoff.....But most of all, I would like to know for sure, my engine will produce full power for as long as it will take me to get to a safe altitude. I bought a used engine with 75 hrs SMOH and have no reason to doubt it, but it would still make me feel better to have a few full throttle runs on it. I will do it on a very cool morning and monitor CHT's very closely. ....Maybe I have been flying two stroke engines for too long?

[Andy Hill]

I would like to know what the static rpm of my prop is at full throttle but a few high speed taxi test may reassure me that I will not over speed my engine on that first takeoff.....

The way I do it for new RVs is 1 "aborted takeoff" to make sure engine / airframe / controls all feel good while removing the "go/no-go decision". How fast I go will be balanced against strip length.

Your engine will almost certainly overspeed slightly. However, as per the manual, you are allowed 10% (2970RPM!) for 3s. I would suggest over the initial flights you note the Max RPM before the governor cuts it back, and then adjust the FPS after the flight. After 2-3 goes you'll likely get it to about 2600RPM e.g. new RV-8 last weekend: RPM peaked 2750, 2710 2590 RPM (for about 0.1s) with ~3/4 turn adjustments of FPS between. If you are really cautious, for the average RV Hartzell / Engine, you could start by screwing in the FPS say 2 turns and work the static RPM up (not down).

But most of all, I would like to know for sure, my engine will produce full power

Trouble is, with a VP prop, you have no idea if you do have max power. You might have ~2700RPM, but you can get that with say half "power". Your MAP gauge might say 29", but that is just measuring air pressure. Unless you know what angle the blades have gone to to "absorb" the HP you are guessing somewhat.

I'm not suggesting you follow my techniques blindly - it's all a risk balance. I just have seen / heard of too many horror stories from high power static run-ups (risk) for my liking so do as above. To be fair, the Hartzell manual does call for a tie down, turning governor up and progressively adjusting FPS - by implication via short overspeeds.

[MikeyDale]

Thanks Andy. I will take all that into account....... I have a 2" tow strap that I looped over the fuse just in front of the vert stab and then ties down at ground level so I am very confident about the plane not tipping over or coming loose. I wonder how much static thrust an IO 360 with a CS prop produces?

[Wallbangar]

This discussion sounds like the "VFR-ONLY' Pilot who flies at 5000 feet on solid instruments. "What's wrong with that ? I've done it before"

[bsacks05]

Originally Posted by DanH

Don't use chocks, nor depend on brakes. Both are pro-noseover.

Tie the tailwheel to a good ring in the ground if you have one available.

No ring? Yoke (two ropes, or a very long cargo strap) the top of the gear legs to the tow hitch of a full-size pickup truck. Do not run a rope from the tailwheel to the hitch. The hitch is above the tailwheel, again pro-noseover.

One of my fondest RV memories is when I flew to Alabama to visit Dan and the RV1 when it was on its trip around the country.

I got to sit inside and run it up while Dan held the tail down. He was listening for a suspected fuel flow issue which turned out to be a rather nasty blockage of some sort at the selector.

Thanks, Dan!