How can I carry a back seat passenger

Here is the deal. I have only had my RV-4 for a couple of months now. I carried a friend of mine who weighs 190 lbs in the back seat and it was scary. The pitch forces were so light that it took total concentration to keep from bobbing up and down. That tells me that my CG was way too far to the rear.
I have a 160 hp engine with a wood propeller, a lightweight starter, and a lightweight battery on the firewall. It seems like I need more weight on the nose to get the CG back in the envelope when I carry a passenger.
A friend of mine carries passengers all the time without any CG problem because he has a 180 hp engine and a constant speed prop which gives him a lot more weight on the nose than I have.
This must be a problem for everybody, has anyone got any suggestions. It sure would be nice to be able to add some weight way up front when I want to carry someone in back, then remove the weight when I am solo. I do not want to try and re-invent the wheel, someone must have a cure for this already.

Did you calculate where your CG actually was?

My experience is that Van's recommendations for fore and aft limits both normal and aerobatic are pretty close to the mark. I.e. you can go to the aft limit without much real problem, but beyond that it becomes too light and easy to overcontrol.

Many methods have been used to shift the CG forward: Landoll and inertia rings on the starter flywheel, heavier starters, lead strips glassed into the front of the top cowl...

Ideally you move the CG by removing or moving weight rather than adding weight, but there's limited scope for that: lighter tailwheel, ELT under front deck, removing strobe power pack and using LEDs.....

Of course the up-side is that it probably has great handling solo!

You probably need to borrow a set of scales and do a new weight and balance on the airplane so you're starting with a known CG. Then, calculate your CG limits (e.g a maximum passenger/minimum fuel limit) using Van's recommendations.

The airplanes fly just fine within Van's published envelope.

If you need to alter your CG, options have already been mentioned in the thread. Another option is the FP metal prop Dan Carley has for sale. That would probably move your empty CG 3/4 of an inch compared with your wood prop.

Put two batteries up front...

I weigh 190 and have ridden in the back seat of my friend's RV-4 many times (160hp, wood prop). He didn't seem to have any CG related handling issues but I can assure you it was not very comfortable back there, especially when it was cold outside and I was freezing my cajones off.

Just another post repeating Kyle's thoughts.

My RV-4 flies great 2 up within W&B (320 w/Aluminum Sensenich and ~985 lbs) even with a 200 lb passenger. The landing phase is much different 2 up than solo. During flight I have no problem w/stick forces or any sign of porpoising.

Stan

Yes, I realize every plane should be weighed now and then to calculate the CG but that will not fix the problem. There is nothing in the back of the airplane except the ELT, maybe it could be moved up front.
You got my attention with a metal prop that someone has for sale. I have been told that a metal prop has a RPM restriction, that says you cannot operate it in the 2300 - 2400 rpm range, is that true ? If so, it would not be practical. I have thought about replacing my lightweight starter with the old style, heavy type, that should help. What about this "balancing ring" behind the prop, anyone have any experience with it ?

The Sensenich for the O-320 has a vibration mode at about 2650 RPM, so has an RPM limit of 2600.

So that shouldn't be a problem except at WOT cruising with 160 KTAS or more.
It's quite happy at 2300-2500 settings.

But they tend not to be as smooth running as wooden props

Experimenting required...

Consider weighing to establish current weight and balance baseline...Vans recommends re weighing for any "new to you" RV. EAB weight and balance data can be problematic.

The starter is a good option. Likely you have a Saber extension on your wooden prop. Older cowls used a longer 4" type, newer cowls use a shorter 2 1/2" type. Regardless, a custom sized matching crush plate can be machined to add weight forward. Removing the spinner will allow you to measure the current plate. Older extensions were 6" diameter and newer versions are 7", also adding more mass. A fly wheel mounted weight is also practical. Some are solid, and the Landol design (no longer in production) provides viscous damping. They will occasionally pop up for sale on the classified page. A combination of starter, flywheel ring of some type and larger crush plate will help.

The -4 was engineered to carry 2 170 lb occupants. There is some good discussion on "light nose" (your configuration) and "heavy nose" on the forum if you search. If you observe the 1500 lb max gross recommendation, whatever you do will be a compromise. The maximum weight limit for the rear cockpit may or may not meet your requirements.

Part 3 of the Transition syllabus on the safety page has a fairly extensive stability and handling discussion that might provide some insight. You might also consider some additional flight test at aft CG to assist with establishing limits and explore handling characteristics. If you've got a copy of the builder's manual, there is also a good weight and balance discussion there.

Drop a PM or email, and I'll share a weight and balance spreadsheet with you that might help your analysis.

Cheers,

Vac

My -4 is set up similar to yours, O320 160 hp, Sterba wood prop, battery in the tunnel per plans. I also have a Smoking planes 3.5 gal oil tank in the baggage area. I have about 250 hrs in mine now, and since the 40.1 hr mark, I have had a backseater 99% of the time. Heaviest passenger I will take is 200 lbs, but only with no smoke oil and full full tanks. You will keep the CG fwd by having tanks full...so as you fly, obviously your CG goes AFT. I have long overcome the pitch sensitivity, and you will too...just be carefull on "hard pulls" with a PAX, as you can easily overstress the plane.Takes lots of FWD stick on take off roll to get the tail up also.

In my O-320, wood prop RV-4, I only carried passengers of 200# or less. And once you're familiar with the plane, you can tell if they lied about their weight!

I cured my problem by building a Rocket. No rear seat weight issues with that plane!

marv1121 said:

calculating the CG but that will not fix the problem.

Click to expand...

Well it's a good start to know whether the aft control surfaces have too much paint and filler added or if there's 5 lbs of mud dauber nests in the horizontal stabilizer.

If you're happy with your propeller performance I encourage you to keep it and use one of the other methods mentioned above to add weight up front.

Many thanks to all of you, this is some good info and just part of my learning curve on the RV-4. I think I am going to go with a heavy weight, old style starter and possibly a landoll ring and maybe a heavier prop crush plate. I really would like a metal prop but cost wise I am not able to do that right now.
Still looking for that easy way to add weight to the nose when I have a passenger then remove the weight and fly solo. It may be impossible but homebuilders come up with some pretty smart ideas.

I used the Landoll Balancer

Hi Marv,
When I went with a wood prop on my O-320 RV-4 I added the 11 pound Landoll Balancer on the nose. It made a huge difference in my ability to carry a larger rear seat passenger within CofG limits, and makes for an extremely smooth engine/prop combo too. You must remember though, whenever you carry someone in the back seat of a -4, any weight at all in the baggage compartment will compound your rear CG problems. I can easily get 30- 40+ pounds in the baggage area, but if I do, I fly solo or with a 110# girl... no Bubba's.

Ron
N8ZD

marv1121 said:

Many thanks to all of you, this is some good info and just part of my learning curve on the RV-4. I think I am going to go with a heavy weight, old style starter and possibly a landoll ring and maybe a heavier prop crush plate. I really would like a metal prop but cost wise I am not able to do that right now.
Still looking for that easy way to add weight to the nose when I have a passenger then remove the weight and fly solo. It may be impossible but homebuilders come up with some pretty smart ideas.

Click to expand...

Start with the steel ring or Landoll balancer. Then the crush plate. The old Prestolite starters really are problematic, which is why you find so many sitting on shelves in the dusty corners of hangars and shops at airports. You'll be happier keeping your modern starter.

Also, on my O-320, there is a machined pad on the underside of the engine, on the right side. It accepts 3 bolts. I've often considered bolting a chunk of lead or steel to that pad for ballast. I think most 4 cylinder Lycomings have that pad.

Mike, I would appreciate that spreadsheet to make my wt and balance calculations easier. I cannot seem to figure out how to send a private message or an email to you. Here is my email.
[email protected]

E-mail sent.

Cheers,

Vac

Pitchy

Just food for thought, sense your not a builder it might be a bit of a task for you but, when I changed my .016 elevator skins to .020 the plane got a lot more stable in pitch. I had an IO-320 and a C/S prop, had to move the battery to the baggage area to git into the CG. FYI

RT

marv1121 said:

Here is the deal. I have only had my RV-4 for a couple of months now. I carried a friend of mine who weighs 190 lbs in the back seat and it was scary. The pitch forces were so light that it took total concentration to keep from bobbing up and down. That tells me that my CG was way too far to the rear.

Click to expand...

First off, you need to know what the C/G is like has been suggested already. There may be an issue with it or there may not, no way to tell until the scales come out.

Second, you state you have only had the plane for a couple months--------RV's are known for light control stick forces, so I wonder if you are just needing more time to get used to things before making a lot of changes. This is of course assuming the C/G turns out to be where it belongs. What did you fly before getting the RV?

Have you considered having someone who is a long time -4 pilot take the plane up for a second opinion???

Good luck, let us know what the end result is.

I know that you are not able to purchase a metal prop just yet, so im not trying to pile on (i do also recommend the metal prop)..but i thought i'd submit my experience with my -4...

Its an early plans model from the 80's, completed in 89. O-320, wood prop, lightweight starter and alternator. The airplane performed well but was tail heavy with a passenger. Even when flown solo, it would easily run out of nose-down trim on long high speed descent from high altitude.

I changed the prop to the metal sensenich (this also includes a heavy 4" extension with long bolts, instead of the lighter "spool" shaped extension). This added 19 pounds total and the empty cg moved forward 1.34" which is a LOT! The light pitch problems with a passenger was fixed but still had limited trim authority.

Long story, but i experimented with adjusting the travel of the tab, and then added some fixed tabs on the right elevator trailing edge. I determined that the airplane just needed more trim authority. Increasing the tab deflection had limited results, even diminishing return as the deflection went past about 30-40 deg... The fixed tab on the other elevator worked great, even added some pitch stability and reduced the workload on the adjustable tab making it more effective.

I am guessing that Van designed the plane around a stock engine with the old style starter and generator, and a 900 lb empty weight. Most of our planes are lighter up front and heavier in the back (for multiple reasons!) .

At an annual i took the whole tail off to clean, inspect, lubricate, and replace a few hinges that had seized. I made a change to the aft turtle deck to make it more similar to a design change that Van did after mine was built. This involved removing the aft 4" or so of the turtle deck to allow better access to the horiz spar attach points. Then I added about 1/4 to 3/8" shim under the horiz spar to increase the incedence angle and reduce the aerodynamic downforce on the tail.
It was a lot of work, including modifying the tail fairing,,, but well worth it!

This worked very well! Much better trim authority and probably less trim drag , though i didnt notice any speed increase.

Marc

Another option

In the older -4s the location of the battery was between the rudder pedals resting on the inside skin of the aircraft. I moved the battery to in front of the firewall and then use this space as forward baggage. If you have a heavy pax, you can throw a bag of tools up there or something. It works pretty well, and then you don't have to haul all that weight around when you go solo. Also, the amount of gas you carry matters with a heavy PAX. Keep half tanks or better. And NO aerobatics.

Ditto Mike Starkey

I sure support his suggestions Marvin!
Best of luck to you.

hartzell provides the answer in exchange for a big check, its called a constant speed prop!

bob burns
RV-4 N82RB

The passenger seat on the RV-4 and RV-8 is well aft of the CG, so the CG moves a long ways aft when you fly with a passenger. This has a very significant effect on the stick forces, and the handling in general.

Rather than go from your normal solo CG to the aft CG all in one step, it is better to do some incremental testing using ballast. Move the CG aft a bit at a time, assessing aircraft handling, including stalls. The small increments in CG reduce the risk that you get it too far aft and have a significant problem, and it avoids having a passenger on board as you learn how the aircraft flys at the aft CG condition.

RV-4 CG

Our (My brother and I) RV-4 has an O-320 E2D with a Sensenich ground adjustable carbon propeller. We had to add the Landoll 12 pound ring to the starter gear and went back to the 18 pound Presolite starter. Now we have no problem flying a 200 pounder in back, but we don't let the fuel get too low while doing so.