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Loss of Elevator Authority on Landing

K

kkendall2718

Member
When landing my RV-10 with full flaps, only 2 people and 60-80 lbs in the luggage compartment, still a very forward CG, I am at full elevator deflection to keep the nose slightly up before touchdown. I have gotten in the habit of using reduced flap settings unless the CG is farther aft in the envelope. A fellow pilot that helped me with Phase 1 testing of my plane, just flew another RV-10 and called to say that he experienced something similar. Are there rigging mistakes that could be the culprit or are other RV-10 pilots experiencing the same behavior?
 
Are you elevators within the full deflection specs for RV-10's? Meaning, do they have some room left in travel and you can adjust your stops more to get to full deflection? I've seen elevators that did not go all the way up or down when reviewing Van's recommended MAX deflections.
 
kkendall2718 said:
When landing my RV-10 with full flaps, only 2 people and 60-80 lbs in the luggage compartment, still a very forward CG, I am at full elevator deflection to keep the nose slightly up before touchdown. I have gotten in the habit of using reduced flap settings unless the CG is farther aft in the envelope. A fellow pilot that helped me with Phase 1 testing of my plane, just flew another RV-10 and called to say that he experienced something similar. Are there rigging mistakes that could be the culprit or are other RV-10 pilots experiencing the same behavior?
Click to expand...
This is not uncommon although your case seems a bit more extreme (80 lbs in baggage?). I carry 20 lbs of water in the aft baggage area (easy to pour out when the back seats are full). Do you have a light weight battery (eg earthex) in the back? Or an especially heavy prop up front? Is the plane unpainted (paint will move cg aft).
You can check the up elevator max deflection angle, make sure it’s in spec.
Re-check weight and balance measurements.
Have passenger slide his seat back prior to landing.
Do not trim full nose up for landing (this trades more elevator authority for higher control force).
 
Following up to my question -- Before we go chasing angles and rigging I'd like to clarify the actual flight dynamics of your "event"

1. Was the stick all the way aft to the stop and the nose wasn't moving up? Or did it "feel" like the nose wasn't moving up (you could pull on the stick but the nose didn't move)
2. During #1, what was the IAS?
3. During #1, what was the VSI showing?
4. During #1, What was the RPM, MAP.
5. Where was the Elevator trim set and how do you normally configure the elevator trim? Do you adjust the trim to null out stick forces, or do you fly with a little bit of back pressure required so you "feel" the airplane?

Dynamics aside, there is a technique thing also at work - As @BobTurner mentioned, do not trim the elevator full nose up for landing as those big trim tabs (2 of them on the -10) will really quash the available "lift" from the elevator.
 
I typically use half flaps. I also carry ballast most of the time to bring the cg into the middle of the range. I am flying in and out of 2800’ with displaced thresholds and performance hasn’t been a problem. During phase 1 testing, I did the forward cg flights and experience the same thing but not quite as extreme.
 
BobTurner said:
Do not trim full nose up for landing (this trades more elevator authority for higher control force).
Click to expand...
This is true. The RV-10 has unusually large trim tabs. Trimming for full nose up will deflect those large surfaces down. If you leave the trim closer to neutral, you will have to pull harder, but you will get more control authority.
 
VGs on the underside of the horizontal stab did wonders for at least one of my non RV airplanes. Also some tape to act as a gap seal may help if it doesn't already have one.
 
What you are describing is just normal from virtually every aircraft I’ve owned….with a little power…blowing across the elevator, you get more authoriity out of it.

which is demonstrated aptly by the STOL crowd. RV’s aren’t made for gliding in, rather….establish your attitude with trim…add drag with flaps and power up as necessary to fly the attitude to the ground.
 
rocketman1988 said:
I typically use half flaps. I also carry ballast most of the time to bring the cg into the middle of the range. I am flying in and out of 2800’ with displaced thresholds and performance hasn’t been a problem. During phase 1 testing, I did the forward cg flights and experience the same thing but not quite as extreme.
Click to expand...
I don't have flap presets, and have 30 degree max deflection. I generally land with 20 degrees, unless I need to make a steep approach for some reason, e.g short runway with obstacles. The difference in my stall speed between 20 and 30 degrees is two knots, not often affecting rollout in a meaningful way. Partial flaps also reduces the forward stick pressure needed on a go-around, and minimizes (or avoids) the time and effort to reduce flaps to 10 degrees.

Solo, or with just a front seat PAX and nearly full fuel, I definitely need to bring the stick all the way back to avoid landing flat, but it's doable even with some up elevator trim. I do keep a go bag of tools and "stuff" (~10 lb), towbar, tiedowns, etc... in the baggage area, nowhere near what the OP is carrying. Since changing to an EarthX battery, I keep the tool bag against the aft bulkhead. Like others, something seems off--be it elevator deflection, W&B calculations, or ???.
 
I’d guess you did not install the big battery or equivalent aft of the baggage compartment bulkhead (in the per plans location). Did I guess right? It would be helpful if you provided your W&B data.

I mount two PC-625 batteries aft and never had a nose heavy issue as you discribe.
Carl
 
kkendall2718 said:
When landing my RV-10 with full flaps, only 2 people and 60-80 lbs in the luggage compartment, still a very forward CG, I am at full elevator deflection to keep the nose slightly up before touchdown.
Click to expand...
Are you sure the elevator is banging against the stop (and not the stick hitting the seat cushion or your stomach)? I'm not a big guy and I find that with a forward CG, it takes a hefty pull on the stick to flare, but I don't think I've ever hit the stop.
 
Had similar incident recently on the Rv6 but for very different reasons. My son had inadvertently placed a full bottle of water between the stick and seat cushion, I didn’t catch it . Made for a very exciting landing!
My preflight briefings have been amended.
 
I guess it is possible you are out of the front of the W&B envelope? Do you have loading and WB data?
It’s been a while but I seem to remember from testing that at the very front of the envelope I couldn’t trim any slower than maybe about 72-75kts but I still had plenty of elevator authority to flare.
I can’t load out the front of the envelope unless solo with a midget pic
 
Here is a good flight test to do. Do a 1-g power off stall (at a safe altitude so you can recover). Approach the stall as gradually as you can. It is more important to do it power-off than to worry about maintaining constant altitude as you approach the stall -- you are trying to simulate a landing flare flight condition. Now, here is the test: If you get to full back stick and it doesn't stall, then you don't have adequate elevator control authority. You should measure your control deflection and compare to the specs, and verify your c.g. is not ahead of the forward limit.

Having said that, my RV-8 with solo c.g. won't give a sharp nose drop either. At back stick it shutters a little and stays nose up, but the sink rate is over 2500 ft/min. The low aspect ratio wing just does not want to fully stall. But the RV-10 wing is higher aspect ratio. I did work hard to design in a gentle stall break, but it should break.

Some glider trainers, the G-103 in particular, are marginal on elevator power and won't do a full stall when approached this way, it will buck and shutter, but won't give a clean nose drop. So that level of control authority is apparently considered acceptable by certifying authorities, but I would prefer to see enough elevator power to get a nose-drop.

Please report back your results!
 
Aden Rich said:
Are you elevators within the full deflection specs for RV-10's? Meaning, do they have some room left in travel and you can adjust your stops more to get to full deflection? I've seen elevators that did not go all the way up or down when reviewing Van's recommended MAX deflections.
Click to expand...
Elevator travel was checked before the DAR visit. I have been planning to recheck and compare to some other RV-10s.
 
BobTurner said:
This is not uncommon although your case seems a bit more extreme (80 lbs in baggage?). I carry 20 lbs of water in the aft baggage area (easy to pour out when the back seats are full). Do you have a light weight battery (eg earthex) in the back? Or an especially heavy prop up front? Is the plane unpainted (paint will move cg aft).
You can check the up elevator max deflection angle, make sure it’s in spec.
Re-check weight and balance measurements.
Have passenger slide his seat back prior to landing.
Do not trim full nose up for landing (this trades more elevator authority for higher control force).
Click to expand...
Passenger slide the seat back before landing...that is an interesting idea.
I have heard from another pilot that they avoid trimming all of the control force out. When I add nose up trim in the pattern, and acutely aware of the stick moving aft to a new neutral position.

Thanks.
 
Richard Connell said:
I guess it is possible you are out of the front of the W&B envelope? Do you have loading and WB data?
It’s been a while but I seem to remember from testing that at the very front of the envelope I couldn’t trim any slower than maybe about 72-75kts but I still had plenty of elevator authority to flare.
I can’t load out the front of the envelope unless solo with a midget pic
Click to expand...
I have checked the WB data extensively. I have noticed that when I run through theoretical load scenarios, fuel does not shift the CG AFT significantly, this is a nose heavy airplane and it is sounding like I need to use different landing configs depending on the loading.
 
scsmith said:
Here is a good flight test to do. Do a 1-g power off stall (at a safe altitude so you can recover). Approach the stall as gradually as you can. It is more important to do it power-off than to worry about maintaining constant altitude as you approach the stall -- you are trying to simulate a landing flare flight condition. Now, here is the test: If you get to full back stick and it doesn't stall, then you don't have adequate elevator control authority. You should measure your control deflection and compare to the specs, and verify your c.g. is not ahead of the forward limit.

Having said that, my RV-8 with solo c.g. won't give a sharp nose drop either. At back stick it shutters a little and stays nose up, but the sink rate is over 2500 ft/min. The low aspect ratio wing just does not want to fully stall. But the RV-10 wing is higher aspect ratio. I did work hard to design in a gentle stall break, but it should break.

Some glider trainers, the G-103 in particular, are marginal on elevator power and won't do a full stall when approached this way, it will buck and shutter, but won't give a clean nose drop. So that level of control authority is apparently considered acceptable by certifying authorities, but I would prefer to see enough elevator power to get a nose-drop.

Please report back your results!
Click to expand...
I did several power off stalls during Phase 1 testing. There was no problem getting the aircraft to stall. Still, I will recheck my elevator deflection.
 
kkendall2718 said:
I have checked the WB data extensively. I have noticed that when I run through theoretical load scenarios, fuel does not shift the CG AFT significantly, this is a nose heavy airplane and it is sounding like I need to use different landing configs depending on the loading.
Click to expand...
If you ran various scenarios then you should have observed the somewhat unusual behavior that if you takeoff with the CG close to a limit (either limit-forward or aft), then, as you burn fuel, the CG moves closer to (or past) that limit. The effect is larger near the aft limit (I once made a gross weight flight where I knew that I had to land with 20 gal or more of fuel remaining, or be out of aft cg.). But if you take off right at the forward CG limit, you’ll be landing with the cg too far forward. I would hope that Vans padded the numbers a bit to allow for cg measurement errors, but I don’t know.
 
scsmith said:
This is true. The RV-10 has unusually large trim tabs. Trimming for full nose up will deflect those large surfaces down. If you leave the trim closer to neutral, you will have to pull harder, but you will get more control authority.
Click to expand...
in addition, this results in far less drama on a go around. i do not trim for neutral on final and it is still a hard pull if you firewall the throttle before the trim is out.
 
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