What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Full power run ups for a taildragger?

bobmarkert

bobmarkert

Well Known Member
I've searched the forum for power runs and don't have a good feeling about the way to do a full power run on my RV8.

I consider myself a relatively inexperienced Tailwheel pilot with about 120 hrs of Tailwheel time ( my 12,500+ total time doesn't translate to tail wheels!!!)

I'm configuring my G3X in my RV8 and came across this Statement in the manual concerning an engine vibration test:

"Gradually increase power from idle to full throttle and back to idle over the course of 1-2 minutes, the test data is displayed as the test progresses."

Internal alarms went off as I envisioned a full power run-up putting me on my nose... Even if I held full aft stick.

ok.... No speculation please.... I would prefer to hear from the true masters of the RV Tailwheel community..... What say ye....hold brakes?..... Weight the tail wheel?..... Don't do it?......
Thank You
Grasshopper Bob
 
I would suggest that if you are going to do this test, chock the wheels and tie the tail down. This way it won't go forward and the tail will remain on the ground.
 
One data point. Today I did 10 full power run ups as I was doing a prop balance on my RV-8. Held full up stick and it never even tried to get light on the tail. I did have it tied down, but the rope was slack at the end of the runs. I very much doubt it would go over as long as you are holding the brakes and up elevator.
 
bobmarkert said:
I've searched the forum for power runs and don't have a good feeling about the way to do a full power run on my RV8.

I consider myself a relatively inexperienced Tailwheel pilot with about 120 hrs of Tailwheel time ( my 12,500+ total time doesn't translate to tail wheels!!!)

I'm configuring my G3X in my RV8 and came across this Statement in the manual concerning an engine vibration test:

"Gradually increase power from idle to full throttle and back to idle over the course of 1-2 minutes, the test data is displayed as the test progresses."

Internal alarms went off as I envisioned a full power run-up putting me on my nose... Even if I held full aft stick.

ok.... No speculation please.... I would prefer to hear from the true masters of the RV Tailwheel community..... What say ye....hold brakes?..... Weight the tail wheel?..... Don't do it?......
Thank You
Grasshopper Bob
Click to expand...

Bob,
I can't advance the throttle of my RV-8 much above 2200 RPM without the tail lifting off. Flaps down agitates the situation. I don't recommend ever advancing the throttle to full power without the tail being securely tied down!

I was able to program and operate my G3X without a full power test!
 
When testing propellers for my RV-8 I did multiple full power "run ups" to measure the static rpm. Flaps up and stick back. No problems. I have no experiences of any tendency for a nose over or tail lift during these tests.
 
Elevator should have sufficient authority to hold the tail down if the flaps are up.
Also recommend tying the tail to prevent forward movement.
 
DON'T DO IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

If you run your rpm's high enough, for sure the tail will come up and you WILL have a prop strike. You MUST first tie the tail down securely to one of those rungs in the concrete. Don't ask me how I know:mad:
 
I did the G3X vibration tests on my RV8 and had no problems. Stick was all the way back and I was able to hold still with brakes. CG was close to the middle with just me in it. Battery on the firewall, lightweight Whirlwind composite prop. Just be gentle with the power application, and back off if it doesn't feel right. Make sure you are on an open ramp or taxi-way. If you are not tied down or chocked and you feel the tail start to lift, just gently release the brakes as you reduce power and let the tail settle as you roll forward a little. If you are concerned about nosing over, put a heavyweight pax in the back seat first.
 
new brakes in particular wont hold. Broken in brakes might. Why be distracted by stick, throttle, tail and panel gismos? Tie the tail. Do your tests.
 
tail up?

My RV-8 hasn't flown, but has been run up and taxied. With (less than) full throttle and brakes set, full up elevator, the tail will come up, unlike my Pitts. Keep those conditions and a prop strike is unavoidable. My empty cg is 78.61" aft of datum. Without brakes and at full throttle it just accelerates very quickly and the tail stays down nicely. Since my CG is a little aft, I wonder why other 8's don't do this.
 
When full power testing my RV-8 I tied the tail wheel to my pickup truck, with the aircraft aimed in a safe direction. I DID NOT chock the wheels. If the tail tie got loose, I didn't want the plane to nose over and prop strike. I preferred the idea of rolling forward a bit while I pull off the throttle and apply the brakes.
Still, I don't recall the tail lifting, the tie never broke, and the whole thing was a piece of cake.
Just think it thru, be careful, and be safe.
 
Clearing fouled plugs?

Just curious. How do you tail wheel guys clear fouled plugs without doing a full power run up? :confused:
 
ArVeeNiner said:
Just curious. How do you tail wheel guys clear fouled plugs without doing a full power run up? :confused:
Click to expand...

Never had a fouled plug, that's what the red knob is for.:D If you can't clear a plug at 2000rpm, it should come out to be cleaned properly anyway.
 
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.
 
When we did the first runups on my friend's newly built RV-8 with high compression ECI Titan IO-360 and Hartzell BA CS prop it would easily lift the tail with full aft stick plus the new brake pads would not hold at all. We tied the tail down plus two of us, one on each side of the aft fuselage in front of the tail, helped hold it down for extra measure. My RV-6 with 160hp and fixed pitch prop will keep the tail down at full throttle runups but the brakes don't hold it very well unless it's a hot high density altitude day that reduces the power output.
 
I would concur with the conservative posts above - namely I do not see a good "reason" for a full power test tied down for an RV with a C/S prop?

FP prop maybe, to check static RPM. But at way below 2700RPM, and prop efficiency low, "thrust" is very much below the C/S equivalent.

If you do need to do it, then so be it, but I would have a good think through the "risks v benefits".
 
Be careful.

Sure, it CAN be done, and you might get away with it. But just let one little distraction enter the picture, and WHAM. I know.
It happened to me many years ago when I built my first RV-4. I had a bad Oil pressure sender and wired up a couple of new ones in the cockpit so I could change connections to find out which one was bad. I had my head down in the cockpit and the next thing I know the prop is chewing up the pavement. I had let the stick move forward a little and the tail came up before I caught it. Of course, my reaction was to pull the stick back, as well as the power. Too quickly, unfortunately, and the tail hit the ground so hard that the tail wheel smashed the rudder. I had to rebuild the rudder and replace the prop (wooden).
BTW, I wasn't at full power. The RV-8 I just finished was able to run up at full power AFTER I conditioned the brakes, but I had the tail tied down to be sure. The episode in the 4 still nags at me. :(

Vic
 
Bob,

What Kahuna, Dan, Vic and others have said. Find a pad-eye at BJC, tie the tail down (not back), and have Gringo hold the H-stab down for ya (he needs to mess his hair up once in a while :D). My tail comes up at less than full power, just another data point.

As for clearing slightly fouled plugs (as noted by a slight increase in mag/EI drop), leaning during normal run-up (or slightly higher) usually does the trick.

Pretty cool that you are this point Bob?pictures?

Cheers,
Bob
 
I know what you are talking about on that vibration set up. I did it on the RV 7. You need to either tie it down so the rope/chain is straight up and down and tight or have someone with you. Someone needs to do the set up while the other operates the aircraft. Tied down or not. When the tail comes up either accidentally or on purpose some one needs to be able to control it.
 
My CG is near the forward limit when solo, and the tail will definitely come up. Even if yours doesn't I can't see any reason not to tie it down for this test.
 
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.
 
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...
 
Witnessed Prop Strike

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!
 
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.

Jkf7sCYmzT7UfWhcD3NU-HLJkeHaZlFUesmLUhVksA=w368-h207-p-no
 
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
Click to expand...
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"?
 
Andy Hill said:
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"?
Click to expand...

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?
 
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.....
Click to expand...
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
Click to expand...
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.
 
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?
 
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"
 
DanH said:
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.
Click to expand...

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!
 
Thrust test

I'm required to do a "thrust test" as part of the certification process where I live. Not excited about doing this for obvious reasons, but will have to do it nonetheless.

I don't seem to have a tie-down ring at my airport (that I have found so far, still looking) so my plan is to combine some of the good advice in this thread:

  1. tie down to the top of the gear legs - thankfully I've got the Grove so no gear leg fairings to damage;
  2. run the straps over the elevator to keep the tail down;
  3. flaps up;
  4. connect the thrust testing apparatus to a vehicle.

Thanks for any other hints or experiences that you might have come up with since this was last discussed about 5 years ago.
 
rv8ch said:
I'm required to do a "thrust test" as part of the certification process where I live. Not excited about doing this for obvious reasons, but will have to do it nonetheless.

I don't seem to have a tie-down ring at my airport (that I have found so far, still looking) so my plan is to combine some of the good advice in this thread:

  1. tie down to the top of the gear legs - thankfully I've got the Grove so no gear leg fairings to damage;
  2. run the straps over the elevator to keep the tail down;
  3. flaps up;
  4. connect the thrust testing apparatus to a vehicle.

Thanks for any other hints or experiences that you might have come up with since this was last discussed about 5 years ago.
Click to expand...

#2 concerns me......looks like a good (bad) way to damage elevators. I would find a different method. You need to find or make a tie-down for the tail wheel to keep it from getting very far off the ground.
 
keeping the tail down

Sam Buchanan said:
#2 concerns me......looks like a good (bad) way to damage elevators. I would find a different method. You need to find or make a tie-down for the tail wheel to keep it from getting very far off the ground.
Click to expand...
Thanks Sam, I think you are right. I'll keep looking for a tie down loop at the airport - there must be one hidden somewhere in the grass. On the "ramp" we have tires filled with concrete - a pair of them might be enough to keep the tail down.
 
Hey Mickey, as far as I know LSGY has tie-down rings or cables on or next to the CUST concrete parking spot on the NE side of the apron.
Also you will most probably connect the measuring device to your tail rod or fork, the only thing that could happen is the meter or some in between or at the ends let go... breathe on, slowly apply the brakes and keep the stick pulled to your belly, no sweat :)
 
I used a towing strap wrapped around the tailwheel on my 7. Laid the strap on the ground behind the plane and drove one wheel of my car onto the strap. Still used the brakes and full up elevator. No problem with the plane moving or the tail coming up during full power runs.
 
Scared myself doing a full power pre inspection run up. Tail will float up. Not good. Lesson learned tie down tail. I reacted fast and got the tail back down. Glad I was heads up...
 
Not sure why anyone says it's a requirement, I doubt any FAR requires it, however it gives a sense of security to some. It's a volatile test fixed to a tie down, and I simply sufficed with running to max power on runway and aborting a take-off. Fuel starvation is highly unlikely, and these RVs will easily take off at well below full throttle, so be careful in any non tethered testing. I initially tied my tailwheel spring with a truck tow strap to my truck hitch for first engine run just to validate full travel of the carb..quick, and not comfortable for any length of time.
 
What I've used on a supercharged Rocket & turbocharged RV plus many normal RVs; strong tow ropes attached to the base of a well secured fence post, ropes strung forward over the horizontal stab and attached to the engine mount. On the higher HP planes, also securely stake down the tail wheel. I do this where the prop has a minimum 10 foot radius of clean paved ramp surface under the engine, never on dirt, gravel, or grass to prevent tip damage.
As the modified Rocket was most susceptable to nosing over, partial power run ups were limited to what the brakes would hold and done only in wide open ramp areas and without wheel chocks as if it at all tended to lift it's tail, throttle was chopped and brakes let off to bring the tail back down quickest.
 
tail wheel

Spoke to Van's this evening (morning for them) and they said that tying up to just the tailwheel should be fine for a static thrust test.
 
As another option, I have a big steel sewer grate on the taxi way just outside my hangar. Park the tailwheel on it and Tie down with two cargo straps. Works “grate” because there are multiple places to attach the hooks.

Use it routinely when solo for doing post maintenance run-ups for leak checks and timing checks.
 
tying down tailwheel

Here's how I did it and it worked fine. The strap is about 2" wide. Tied to the frame under the car, and used the wheel to hold the strap down. The part of the strap between the wheel and the frame didn't even get tight.

UNADJUSTEDNONRAW_thumb_5eb6.jpg


Many thanks for the hints and suggestions!
 
Thrust measurement

DeeCee 57 said:
did ya measure the thrust? How much?
Click to expand...
Not yet - I want to do some more tests to make sure that I can actually produce full power on the ground before the tests. Going to make a shroud today to improve cooling during the ground run. In only 2-3 mins #3 got up to 341F, so I'm sure a full power thrust test would get to 400F without a shroud.
 
just had a look at my data... YLL pulled factored 345.1kg @ 2570 static RPM, config see below.
Be sure your weight on strap is good enough ;)
 
My RV-8 will raise the tail at power if the flaps are extended but if not I can go full power with stick all the way back and it'll stay set. Maybe I need more power(bigger engine)?
 
You must log in or register to reply here.
Back
Top