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Rudder Replacement Phase I Testing

scrollF4

Moderator, Asst. Line Boy
Ambassador
Merry Christmas to all.

I am replacing my longer/taller RV-7 rudder with a new RV-8 rudder (see other posts associated with this subject to learn the 'why'). KELLI GIRL will go into 5 hours of Phase I.

As I form my test plan, I welcome any inputs/suggestions on what I should test and how. Things like:
- Low and high-speed taxi characteristics
- Takeoff run rudder effectiveness
- Normal flight: Climb, cruise, descent
- High and low speed flight characteristics
- Slips

Please let me know any specifics you may recommend.
 
I'm excited to hear your feedback on switching to the 8 rudder. I built the 9 rudder that came with my 7 kit, but after reading the ongoing thread on this topic, I'm planning to order an 8 rudder and use that. Please keep us posted!
 
Merry Christmas to all.

I am replacing my longer/taller RV-7 rudder with a new RV-8 rudder (see other posts associated with this subject to learn the 'why'). KELLI GIRL will go into 5 hours of Phase I.

As I form my test plan, I welcome any inputs/suggestions on what I should test and how. Things like:
- Low and high-speed taxi characteristics
- Takeoff run rudder effectiveness
- Normal flight: Climb, cruise, descent
- High and low speed flight characteristics
- Slips

Please let me know any specifics you may recommend.

Please post the result when done. There are others like myself that will be using the original rudder from first the flight on.

For others that are interested, the Vans service bulletin SB-2-6-1 details the two rudders and the aerodynamic differences very nicely.
 
If you have any acro figures signed off for your 7 from the original flight testing and you want to continue be able to perform them in the future you need to test them all again.

At least that's the way I read my ops limitations and what I did after getting a new prop... .

I would in particular focus on spins and hammerheads when changing the rudder.

Oliver
 
I wanna watch/record the 'High speed" taxi tests :eek:

Yah, I'm not sure I meant to include "high speed taxi" in that list. That would make an entertaining video, wouldn't it Walt?

I was thinking about rudder authority and response during the higher-speed portions of the takeoff and landing rolls.
 
Yah, I'm not sure I meant to include "high speed taxi" in that list. That would make an entertaining video, wouldn't it Walt?

I was thinking about rudder authority and response during the higher-speed portions of the takeoff and landing rolls.

Personally I would not and did not just recently with my 7, too sketchy with a tailwheel (assuming you have that). Based on what I've seen so far if you got the tail up you would be very close to liftoff speed and slowing down would be "fun". Decided it was too risky and low benefit. I now have 26 hours and loving it, amazing plane!
 
I think the list you have, plus spins, is a good one. You already know that the design is airworthy, you just need to show airworthiness of your new rudder as built and get yourself comfortable with the airplane's new handling qualities.

Dave
 
I agree with several other posters - High Speed Taxi is risk for no reward, and I’d retest ALL aerobatic maneuvers, just for good measure.
 
Thank you, Gents.
Great comments. My test card is coming together. The 'high speed taxi' part was mindless typing on my part. I have no intention of adding that to the profiles. I wouldn't want to distract Walt unnecessarily...he has such a great view of all the takeoffs and landings at 52F as it is.
 
Thank you, Gents.
Great comments. My test card is coming together. The 'high speed taxi' part was mindless typing on my part. I have no intention of adding that to the profiles. I wouldn't want to distract Walt unnecessarily...he has such a great view of all the takeoffs and landings at 52F as it is.

I’ll be watching this closely. Definitely get some spins, stalls in all regimes, crosswind performance. I think you’ve done some YouTube stuff if I remember correctly. I’d be very interested in seeing this progress on there as well. Thanks for getting us the info.
 
Swapping Rudder

Planning on making the change to the RV-8 rudder for my RV-7A and doing the planning for doing the necessary flight testing. Before removing and replacing the existing kit RV-7/RV-9 rudder I plan on rerunning some of the phase 1 test sheets I did during the original phase 1 just to have a current baseline comparison.
No high speed taxi tests.
Probably going to do first flight at a nearby field with wider and longer runway.
High power, low speed testing at altitude to determine rudder authority limits.
Higher speed level flight rudder kicks at various CG positions to determine stability margins.
Crosswind landings at various weights and CG positions to confirm crosswind landing performance limits.
I dont plan on doing any fully developed spins - no more than half turn insipient. I have reached that stage in life where experiencing more than 2 G and lots of excitement is best left to others.
Until I make the change to the RV-8 rudder I have lowered placarded top speed to 180 kts TAS with particular emphasis on descents from higher altitude - way too easy to get the speed up in the descent and be right up on red line TAS.
I dont see an urgent rush to complete the change so will continue to fly with the existing configuration until the days are longer and all the pieces of the puzzle are in place. I see this as a “good to do” change rather than a “must do”. Limiting top speed until it is done is just prudent.
KT
 
Phase 1 has begun

The rudder build went well. Solid blue paint from GLO Aircraft Paint (52F) closely matches the existing vinyl wrap (and gets us another year, when GLO will replace the vinyl wrap with basically the same aircraft scheme in paint).

Many thanks to all of you for responding to this thread. I've flown two flights/1.6 hours on the Phase I and have initial reports. Overall, going from the RV-7/9 rudder to the RV-8 rudder yields these results.
In all ground flight regimes and on the ground:
- I have slightly less yaw response for the same amount of rudder deflection, meaning I have to just press a little more pedal to get what I want.
- I have slightly less loading/resistance in the rudder (as if it was on power steering).
- I have FULL yaw authority from that rudder, meaning I can get everything I want, and still have more rudder available.
- Note: When I say slightly, I mean just barely noticeable.

The test cards, and results:

Sortie #1, 0.9 hours
- Low speed taxi: I have slightly less directional authority from the rudder. I had to tap a tad more brake for directional control and turns. This may be an issue if you use stock Matco or Cleveland brakes with the single puck...I have 2-puck Groove brakes, thankfully.
- Takeoff Rudder effectiveness: Excellent performance for P-factor, etc.
- Low speed trim and turns: Excellent performance, at all flap settings. I'm saving stalls for later.
- Max Demo XWind for takeoff and landing: Great day for it. I demonstrated 20.68 mph right-to-left crosswinds today, and had rudder to spare. KAFW Rwy 16R, winds 210/27.

Sortie #2, 0.7 hours
- Vx climb at takeoff: Excellent performance. She tracked straight and true.
- High speed/cruise trim and turns: Excellent performance
- Stability at VNE minus 1 knot: Excellent performance
- Slips at altitude and in pattern: Excellent performance, almost the same level of yaw authority as the 7 rudder. I needed just a smidge more top pedal, but I had plenty of rudder available to achieve my frontal drag goal in the base-to-final turn. These were accomplished in both directions.

So far I'm loving it. Big bad winds tomorrow, so I'll delay the 3rd hop until Friday. Sortie #3's card includes:
- Stalls: Clean, Flaps half, Flaps full
- Aerobatics
-- Aileron Rolls
-- Barrel Rolls
-- Horizontal 8s
-- Lazy 8s
-- Loops
-- Immelmanns
-- Split-S
- Spins

Will report results.
 

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The rudder build went well. Solid blue paint from GLO Aircraft Paint (52F) closely matches the existing vinyl wrap (and gets us another year, when GLO will replace the vinyl wrap with basically the same aircraft scheme in paint).

Many thanks to all of you for responding to this thread. I've flown two flights/1.6 hours on the Phase I and have initial reports. Overall, going from the RV-7/9 rudder to the RV-8 rudder yields these results.
In all ground flight regimes and on the ground:
- I have slightly less yaw response for the same amount of rudder deflection, meaning I have to just press a little more pedal to get what I want.
- I have slightly less loading/resistance in the rudder (as if it was on power steering).
- I have FULL yaw authority from that rudder, meaning I can get everything I want, and still have more rudder available.
- Note: When I say slightly, I mean just barely noticeable.

The test cards, and results:

Sortie #1, 0.9 hours
- Low speed taxi: I have slightly less directional authority from the rudder. I had to tap a tad more brake for directional control and turns. This may be an issue if you use stock Matco or Cleveland brakes with the single puck...I have 2-puck Groove brakes, thankfully.
- Takeoff Rudder effectiveness: Excellent performance for P-factor, etc.
- Low speed trim and turns: Excellent performance, at all flap settings. I'm saving stalls for later.
- Max Demo XWind for takeoff and landing: Great day for it. I demonstrated 20.68 mph right-to-left crosswinds today, and had rudder to spare. KAFW Rwy 16R, winds 210/27.

Sortie #2, 0.7 hours
- Vx climb at takeoff: Excellent performance. She tracked straight and true.
- High speed/cruise trim and turns: Excellent performance
- Stability at VNE minus 1 knot: Excellent performance
- Slips at altitude and in pattern: Excellent performance, almost the same level of yaw authority as the 7 rudder. I needed just a smidge more top pedal, but I had plenty of rudder available to achieve my frontal drag goal in the base-to-final turn. These were accomplished in both directions.

So far I'm loving it. Big bad winds tomorrow, so I'll delay the 3rd hop until Friday. Sortie #3's card includes:
- Stalls: Clean, Flaps half, Flaps full
- Aerobatics
-- Aileron Rolls
-- Barrel Rolls
-- Horizontal 8s
-- Lazy 8s
-- Loops
-- Immelmanns
-- Split-S
- Spins

Will report results.

Great information! Can’t wait to hear more.
 
... Solid blue paint from GLO Aircraft Paint (52F) closely matches the existing vinyl wrap (and gets us another year, when GLO will replace the vinyl wrap with basically the same aircraft scheme in paint).
...

Wow - you're not kidding - those photos look like they are identical colors.
 
Do you have the weight difference? My -7 will likely be tail heavy and this could be a cool solution.
 
Do you have the weight difference? My -7 will likely be tail heavy and this could be a cool solution.

Hopefully Scroll will weigh in with the differences

I just built and installed the -8 rudder on my -7 but didn't weigh them. I'm just getting ready to do my initial weighing but expect it will effect my CG favorably.
 
I just read through the SB posted - two questions: How does the -8 rudder compare to the original -6 vs original -7 vs -9? And why switch? What is the complaint with the -9 or the desired improvement with the -8 that is initiating the switch?
 
I just read through the SB posted - two questions: How does the -8 rudder compare to the original -6 vs original -7 vs -9? And why switch? What is the complaint with the -9 or the desired improvement with the -8 that is initiating the switch?

Larger flutter and strength margins with the -8 rudder installed. See this thread:


And this one:

 
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Hopefully Scroll will weigh in with the differences

I just built and installed the -8 rudder on my -7 but didn't weigh them. I'm just getting ready to do my initial weighing but expect it will effect my CG favorably.

Yep, I'll have those numbers tomorrow.
 
RV8 Rudder history

Hi All, The original RV7 was using the RV8 Rudder , but as I recall Spin Testing by Bob Herrendeen said it was not easy to stop spins, they made the bigger RV7 Rudder to fix this and testing was made (good Result)

I have a RV6 with the RV8 rudder and on the 6 it spins and stops on point (remember avoid more then 2 turn spins as they wrap up in the 6 and take a while to stop)

Cheers

Peter

PS I did not balance my RV8 rudder just added the Vans supplied depleted Uranium weight
 
Hi All, The original RV7 was using the RV8 Rudder , but as I recall Spin Testing by Bob Herrendeen said it was not easy to stop spins, they made the bigger RV7 Rudder to fix this and testing was made (good Result)

Just to be clear, the 'the bigger RV7 Rudder' you mention is just the stock RV-9/9A rudder. All RV-7/7A kits after 5/20/2002 were shipped with the RV-9/9A rudder. This and the spin characteristics are documented in Van's SB 2-6-1:

 
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Depleted Uraninum??

Peter

PS I did not balance my RV8 rudder just added the Vans supplied depleted Uranium weight

OK you got my attention - tell me more about this. I may missed this availability somewhere along the line. All I ever have know about are the lead counterweights.
 
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OK you got my attention - tell me more about this. I may missed this availability somewhere along the line. All I ever have know about are the lead counterweights.

They are lead -- also known as unmachineableibnium ;)
 
Hi All, The original RV7 was using the RV8 Rudder , but as I recall Spin Testing by Bob Herrendeen said it was not easy to stop spins, they made the bigger RV7 Rudder to fix this and testing was made (good Result) ....SNIP.....

After 6 turns according to the Service Bulletin. Otherwise the spin characteristics were good.
 
Well I have read all of this and the SB...is this a little like primer?

how many unintentional spins have caused loss of hull on any rv?

the SB states that a 20 to 40 degree wing drop might occur on a stall and if recovery is initiated at this point recovery is almost immediate. full back pressure and rudder will initiate a spin meaning you have done that deliberately. immediate recovery stops the spin within 90 degrees. A 6 turn spin requires a half turn extra recovery over the standard 6 rudder. Who is doing those and did you buy the right aeroplane for that?:(

so it figures that its a big nothing...the flutter margin has anecdotal evidence to be better on the folded trailing edge rudders...either that or the construction is stronger

that being said lots of 7 aircraft out there with the 9 rudder flying successfully.

still think ill build my 7 and throw the 8 rudder at it.;)
 
For me it’s all about the aesthetics.
The smaller tail in my opinion, has better proportion to the rest of the airframe, and is easier on the eye in my mind. 😉
 
Hopefully Scroll will weigh in with the differences

I just built and installed the -8 rudder on my -7 but didn't weigh them. I'm just getting ready to do my initial weighing but expect it will effect my CG favorably.

Michael,
My 7 rudder with tips, bearing ends, and vinyl weighed just under 13 lbs. The new 8 rudder with tips, bearing ends, and paint weighs right at 12 lbs. I figured it'd be close since they both use the same lead counterweight. These weights are derived from a bathroom scale of dubious accuracy.
 
Final results: Excellent performance on Sortie #3. Maneuvers and their results:

- Stalls, including clean stalls, half-flaps, and full-flaps: Zero change in performance. My stall speeds are unchanged. I had no trouble maintaining my heading.

- Aerobatic maneuvers, including Aileron Rolls, Aileron/Rudder rolls, Barrel Rolls, Horizontal 8s, Lazy 8s, Loops, Immelmanns, and Split-S: Zero change in performance, excellent results.

- Spins: This was the day's surprise. I executed two spins in each direction, and allowed them to develop 3 full rotations before applying the corrective rudder input. Recovery was immediate. I could have selected a compass heading to recover on.

Weight/balance: No real benefit from the slightly lighter rudder (it's really only a 1 lb difference). I've got other problems swelling my aircraft's empty weight, so I'll work on that later.

OK, Phase I complete, I'm done. Very happy with this change. Frankly, I just don't see what the problem was...my RV-7A flies perfectly fine with this rudder. I'm happy with the change, and feel more comfortable with its more-robust construction.
 
- Spins: This was the day's surprise. I executed two spins in each direction, and allowed them to develop 3 full rotations before applying the corrective rudder input. Recovery was immediate. I could have selected a compass heading to recover on.

Excellent results - Thank you for flying and posting!!
 
Good report. It’ll be interesting to see if you pick up any cursing speed. I’ve always heard that the 8 rudder will give you a knot or two, but this could just be an old wives tale. The 14 also uses the 9 VS and rudder and I’m considering using the 8 rudder on my 14 build.
 
Michael,
My 7 rudder with tips, bearing ends, and vinyl weighed just under 13 lbs. The new 8 rudder with tips, bearing ends, and paint weighs right at 12 lbs. I figured it'd be close since they both use the same lead counterweight. These weights are derived from a bathroom scale of dubious accuracy.

Thank you're for the specifics on the delta between the two rudders weight wise. Not much difference but a pound is a pound...I'll take it ;- )

Final results: Excellent performance on Sortie #3. Maneuvers and their results:

- Stalls, including clean stalls, half-flaps, and full-flaps: Zero change in performance. My stall speeds are unchanged. I had no trouble maintaining my heading.

- Aerobatic maneuvers, including Aileron Rolls, Aileron/Rudder rolls, Barrel Rolls, Horizontal 8s, Lazy 8s, Loops, Immelmanns, and Split-S: Zero change in performance, excellent results.

- Spins: This was the day's surprise. I executed two spins in each direction, and allowed them to develop 3 full rotations before applying the corrective rudder input. Recovery was immediate. I could have selected a compass heading to recover on.

Weight/balance: No real benefit from the slightly lighter rudder (it's really only a 1 lb difference). I've got other problems swelling my aircraft's empty weight, so I'll work on that later.

OK, Phase I complete, I'm done. Very happy with this change. Frankly, I just don't see what the problem was...my RV-7A flies perfectly fine with this rudder. I'm happy with the change, and feel more comfortable with its more-robust construction.

Great news on the completion of phase 1. The results seem to verify the information in the service bulletin, which is comforting.

Stronger rudder, great aerodynamic performance, looks good....whats not to like.
 
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...the flutter margin has anecdotal evidence to be better on the folded trailing edge rudders...either that or the construction is stronger

For the reasons given below, the -8 rudder would provide larger strength and flutter margins in case of an inadvertent excursion outside the published flight envelope:

- The -8 rudder has thicker skins (0.020") than the -9/-7 rudder (0.016"), making the -8 rudder stronger and stiffer.

- The -8 rudder has a folded trailing edge, which makes the -8 rudder stiffer and stronger than the riveted trailing edge of the -9/-7 rudder.

- The -8 rudder has less area than the -9/-7 rudder, creating smaller unsteady (oscillatory) aerodynamic forces (which are an important item in the flutter equation) than the larger -9/-7 rudder.​

Note that the -9 rudder was designed for an airplane that has a Vne of 210 MPH, whereas the -7 has a Vne of 230 MPH. Now, of course, those speeds are designated as TAS values.
 
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PS I did not balance my RV8 rudder just added the Vans supplied depleted Uranium weight

OK you got my attention - tell me more about this. I may missed this availability somewhere along the line. All I ever have know about are the lead counterweights.

Depleted Uranium was used for mass balance weights on commercial airliners up through the early 747s. Depleted Uranium is very dense and heavy for its size, thus minimizing the physical size the balance weights needed to be. At some point the Government realized that depleted Uranium could be used for nefarious purposes and Boeing switched to sintered Tungsten for mass balance weights.

I am sure Van's never used depleted Uranium for mass balance weights!! :eek:
 
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Final results: Excellent performance on Sortie #3. Maneuvers and their results:

- Stalls, including clean stalls, half-flaps, and full-flaps: Zero change in performance. My stall speeds are unchanged. I had no trouble maintaining my heading.

- Aerobatic maneuvers, including Aileron Rolls, Aileron/Rudder rolls, Barrel Rolls, Horizontal 8s, Lazy 8s, Loops, Immelmanns, and Split-S: Zero change in performance, excellent results.

- Spins: This was the day's surprise. I executed two spins in each direction, and allowed them to develop 3 full rotations before applying the corrective rudder input. Recovery was immediate. I could have selected a compass heading to recover on.

Weight/balance: No real benefit from the slightly lighter rudder (it's really only a 1 lb difference). I've got other problems swelling my aircraft's empty weight, so I'll work on that later.

OK, Phase I complete, I'm done. Very happy with this change. Frankly, I just don't see what the problem was...my RV-7A flies perfectly fine with this rudder. I'm happy with the change, and feel more comfortable with its more-robust construction.

Good stuff! Thanks for posting!
 
Final results: Excellent performance on Sortie #3. Maneuvers and their results:

- Stalls, including clean stalls, half-flaps, and full-flaps: Zero change in performance. My stall speeds are unchanged. I had no trouble maintaining my heading.

- Aerobatic maneuvers, including Aileron Rolls, Aileron/Rudder rolls, Barrel Rolls, Horizontal 8s, Lazy 8s, Loops, Immelmanns, and Split-S: Zero change in performance, excellent results.

- Spins: This was the day's surprise. I executed two spins in each direction, and allowed them to develop 3 full rotations before applying the corrective rudder input. Recovery was immediate. I could have selected a compass heading to recover on.

Weight/balance: No real benefit from the slightly lighter rudder (it's really only a 1 lb difference). I've got other problems swelling my aircraft's empty weight, so I'll work on that later.

OK, Phase I complete, I'm done. Very happy with this change. Frankly, I just don't see what the problem was...my RV-7A flies perfectly fine with this rudder. I'm happy with the change, and feel more comfortable with its more-robust construction.


Excellent! Thank you for going through it and posting for us all to see!
 
Spins: This was the day's surprise. I executed two spins in each direction, and allowed them to develop 3 full rotations before applying the corrective rudder input. Recovery was immediate. I could have selected a compass heading to recover on.
Scroll -

What was your weight/CG for the spins? Only Van's knows the configurations they tested for the original -8/-9 rudder comparison but I'm guessing that the recovery characteristics that drove their choice were seen at more aft CGs.

Thank you for posting your results...that's some great info!

v/r

Dave
 
Scroll -

What was your weight/CG for the spins? Only Van's knows the configurations they tested for the original -8/-9 rudder comparison but I'm guessing that the recovery characteristics that drove their choice were seen at more aft CGs.

Thank you for posting your results...that's some great info!

v/r

Dave

Dave,
I had 15 gals fuel, and just me in the jet....um, I mean aircraft. I'm a heavy guy, so here are my numbers: 1555 lbs, 83.43" arm.
That's 2.59" aft of KELLI GIRL's empty CG.
That's 3.39" forward of her aft limit.
 
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