What's new
Van's Air Force

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

new RV-4 owner questions

1

1flyingyogi

Well Known Member
Hi guys. So after looking for one since December, I finally got a good one! I just finished up my check-out with Mike Seager in Oregon two weeks ago, had another CFI fly with me in the back twice when I got back (just to be extra sure that everything would go smoothly), and had my second solo flight this morning. The plane is a blast to fly!!!

But I do have a few points of concern that maybe someone can chime in on. I'm finding that it requires a lot of up-trim just to fly level in cruise. (I should have taken a picture of the trim position after landing) And the difference b/t flaps and no flaps is a lot of trim (about 14 half turns!). In the RV-7 in Oregon, it was only 3 half-turns for trim b/t flaps and no flaps.

The plane to me, feels nose-heavy (CG too far forward). The two times I flew with someone in the back, the plane actually flies better (although heavier). Better meaning it does not require a huge amount of up-trim to stay level and the difference b/t flaps and no flaps is only about 4-6 half-turns (instead of 14). And overall it just felt more neutral and power changes don't affect level flight as much. Is this normal for RV-4s or does this indicate a too far forward CG or something else?

Also, I'm finding that it requires a huge amount of right rudder to stay coordinated. On climb-out, I would say it takes almost 70% deflection of right rudder to stay coordinated. And this is with already putting in a lot of rudder trim on the trim tab. And even level flight requires constant right rudder to stay coordinated. With power at idle, then it's neutral or slightly left rudder. Is this normal or could it be the engine thrust angle being off? (not enough right engine thrust). I don't know much about full-scale, but in RC the engine thrust angle is usually built into the firewall/ engine mount, but it can also be fine-tuned with washers (to angle the engine more right/ left/ up/ down). Am I just overly concerned? To me it doesn't feel quite right.

It's still a blast to fly though, and the landings are getting pretty decent. Most of the three-pointers are smooth and I've done about half a dozen wheel landings with my CFI in the back and 1 on my own this morning - it wasn't as scary as I anticipated. =)

Thanks in advance for your inputs. I have a lot to learn! This forum has been awesome so far. I couldn't have made it this far without you guys! Pilots are amazing people!

Brian
 
Congrats on your purchase.

The trim required changes greatly with a back seater vs solo as the cg changes quite a bit. Every airplane is different. Mine is very nose heavy due to a 360 and constant speed prop. However, with a more forward cg the aircraft is more stable. I find or a lot easier to land solo. There is quit a bit of trim difference between flaps up and flaps down. Again it depends on where your cg is, they are all over the map depending on equipment installed and weights.

As for rudder trim it does require more rudder than say a 172 but it should not need 70 percent. Mine has no trim tab and requires slight pressure straight and level to stay ball centered. Again every one is different.

My advice is to find a RV-4 guy in your area and let him fly it and see how it compares to other 4's.

Bob burns
Rv-4 n82rb
 
RV-4

Brian,

I'm with Chris, you should not need that much rudder if the airplane is set up right. You may need to look at the trim tab on the rudder again. Are you getting any fish tailing if you take your feet off the rudder? If the trim tab is in the wrong place/wrong size/wrong type you might not be getting the full benefit of it on the -4.

I flew my -4 without a trim tab and it makes a huge difference. Fish tailing, lots of rudder and always doing the rudder dance. With the trim tab on the rudder installed it was an instant fix- no more fish tailing and very little rudder input. Some even have two trim tabs, depends on your set up. Don't forget to squeeze the rudder trailing edge as called for in the plans- this is an EASY job but makes a profound difference as well.

For the elevator trim, Chris mentioned that we don't know your engine/prop combination or your empty weight/CG. Have you weighed your airplane to determine the CG? My -4 has an IO-360 and a C/S prop and it flies a lot differently than my buddy's FP prop on his IO-360 RV-4. My airplane is very easy to land but even easier with a back seater because it shifts the CG aft to counter the heavier nose with my engine/prop. Neither airplane has any trim issues. Most of the -4s I've seen have either the standard Van's elevator trim lever on the left side or electric trim. Lot easier than a trim knob and much quicker.

Oly
 
Set up

Hi

As the guys have said more inf on the set up is needed to give a difinative answer.

Right rudder in the climb is normal it will vary with power output, prop type fixed or CS.

The trim sounds odd though I am surprised you need to put that much in. Find out where the C of G really is then you can do some calculations
To see if relocating the battery would help.

The enGine offset is built into the engine mount, it should be spot on provided no one has put washers under the Lord mounts to alter it.
 
The empty weight is 1021lbs (but has not been weighed since it was built). Nothing has changed since original build. Sensinich metal FP prop, O-320 engine, manual flaps, trim, steam gauges. A very basic, but solid plane. Randy Thorne who did the inspection for me said it's rare to find a plane this well built and well taken care of.

It may not be 70% rudder deflection on take off as I posted above, but it sure feels like a lot (maybe closer to about 45%??). If I get off the right rudder the plane yaws pretty heavily to the left. And in general there's a lot of tail-wagging. Again, in level cruise, it's not as much, but I'm almost always on right rudder to stay coordinated. When power is at idle or low power (like coming in to land), then almost no right rudder is needed. This is about the only time it feels neutral.

I will weigh it again and see where the CG is and have another RV guy fly it by himself and see what he thinks. The forward CG and needing lots of trim compared to with someone in the back makes sense. But the excessive right rudder to stay coordinated doesn't feel right and quite annoying. Mike's RV-7 certainly didn't require as much right rudder. And the other RV-6 I've flown in also didn't require as much right rudder.
 
Trim Tab

Not too many -4s have adjustable rudder trim, most get by with fixed tabs or none at all. See if you can get a RV guy to check out the setup.

I find I will use wide travel for elevator trim throughout a flight, with the standard vans trim lever on the left (larger travel when you think of it). I can imagine if I had to crank that same amount of trim with a trim wheel my hand would cramp up. Come to think of it, I love my trim lever! :)
 
I bought a well built RV4 with a wooden FP on a 0360. Empty wt of 985 lbs and it's probably higher than that now.

Taking off and climb out it takes a substantial amount of right rudder to keep it coordinated. More so then with any of the factory built AC with the same size of motor. Even at full power 2650 RPM at 12,000 ft it would still take a small amount of R rudder to keep the ball centered. I put an Avery wedge on the rudder and now I'm at zero rudder input at altitude and reduced rudder on climb but it's still a boot full. For this AC, being short coupled, smaller rudder and tail with a high power to weight ratio I would consider this normal at least on my plane.

My elevator has a lever that I use to adjust the trim. Set to just over a 1/4 forward with me in it for takeoff and climb out. About 1/3+ forward with my 130 pd date in the back. Maybe almost 1/2 way when loaded to max with baggage to 1600 pds.

The only other RV time I have is with Mike in his 7. What I can remember is that the RV 4 seems to take more rudder then the RV7. As far as pitch the 4 was definitely more firm in elevator input where the 7 seemed too soft, almost mushy in comparison. In comparing trim it's more difficult as the 7 had a knob and I have a lever.

Tim
 
Similar

Hi

You have the same engine prop combination as me although 21lbs heavier. I would doubt that you have a forward C of G with that engine /prop.

I have a fixed tab giving right rudder and she flies hands and feet off straight and level at most speeds. Trim is usually midway in almost all aspects of flight, I get a slight nose pitch up at 10 degrees of flap but by the time I have 25 to 40 degrees of flap in the need for trim is almost gone.

If I put a someone in the back up to about 115 lbs she is just as pleasant to fly. When I hit max take off with 196lbs in the back she is much more pitch sensitive.

I would try to get someone with a similarly configured 4 to fly her so you can compare like for like, once you have done the W and B again.
 
I had an O-320 powered -4 with a metal fixed pitch Sensenich. Empty weight was 1046 with an empty CG of 70.98" (yes , quite heavy).

The first thing I did after buying it was to do a new weight and balance. There had been many changes made over the years with no change to weight and balance (I think the paperwork I got with the airplane showed an empty weight of 986).

The airplane was set up to be in trim at 160MPH. At that speed I could fly feet flat on the floor. Above or below that speed I had to hold some rudder. I needed a lot of right rudder for take off and climb, more than other Airplanes I had flown. In fact, once I got used to it I would use WAAAY too much right rudder in my Sportsman.

Pitch trim never needed more than the three half turns (manual trim). Of course, I only used flaps either up or down. On downwind I pulled the power off, dropped the flaps to full, gave three half turns on the trim and all was well. After landing three half turns the other way and I was ready to go again.
 
RV-4 Trim

Brian,

Sounds a lot like the rudder trailing edge has not been squeezed. It's a pretty simple process as noted in the plans, simply get some smal scraps of wood on either side of the rudder (protected by cloth) and squeeze the trailing edge (the wood) along the rear length. Specifics are in the plans but anyone near you that has built a -4 will know how to do it. It is literally a couple minute job and you can do it on a painted airplane without worries.

Do you have a small wedge shaped looking trim tab on the left side of the rudder? A combination of these two will definitely be an issue. As far as the CG goes it does sound like you might be nose heavy in CG for whatever reason. You should consider reweighing the airplane and recalculate the CG based on the weights noted at the three wheels. Someone mentioned relocating the battery farther aft if needed as well.

Keep us posted,
Oly
 
http://i816.photobucket.com/albums/zz87/qualityeyedoc/rudder trim.jpeg

Here is a photo of how much trim I'm having on the rudder trim tab. With this much, it feels better and not as annoying, but still requires moderate right rudder to stay coordinated on climb out. During level cruise, about zero to very slight right rudder required.

http://i816.photobucket.com/albums/zz87/qualityeyedoc/elevator trim.jpeg

And this is how much elevator up trim is required with full flaps and power at idle or just above idle (landing). This is about 12 half-turns of the knob (relative to level cruise with power and no flaps).
 
Last edited:
Just another data point - as I recall landing in my 1987 model -4, with full trim in landing configuration and speed I still need to apply a some back pressure on the stick. When flying straight an level is your elevator trim close to even with the elevator?

It would seem you have a pretty serious "out of rig" situation with your rudder. On my -4 I never had a trim tab and it flew coordinated when straight and level - of course it needed lots of right rudder on take off and climb, and left rudder on descent. Same with my Rocket now.
 
SMO said:
Just another data point - as I recall landing in my 1987 model -4, with full trim in landing configuration and speed I still need to apply a some back pressure on the stick.
Click to expand...

Same with my -4. I see nothing wrong with his elevator trim setting w/full flaps and at idle.

His rudder trim tab is excessive. My buddy's -4 rudder trim was also excessive to the point he installed an electric trim tab. The reason was his vertical stab was off centered. The OP should carefully check his.
 
AX-O said:
Wow! Will call you later.
Click to expand...

Thanks for the chat, Axel. I'll do those tests you recommended and post what I find. BTW, if you have a link to your post with the test for the landing gear fairings/ alignment, that would be helpful - your thread is like 40+ pages long and it would take forever for me to sift through it. Thanks!

Brian
 
springer said:
Same with my -4. I see nothing wrong with his elevator trim setting w/full flaps and at idle.

His rudder trim tab is excessive. My buddy's -4 rudder trim was also excessive to the point he installed an electric trim tab. The reason was his vertical stab was off centered. The OP should carefully check his.
Click to expand...


Id have to go back and check but im pretty sure the vert stab should not be centered. Also its hard to tell but that rudder trim tab might be in an area that gets disturbed airflow and bassically is doing nothing.



Cm
 
You must log in or register to reply here.
Back
Top