W

wingspan99

Active Member
Hi Everyone,
Last weekend I acquired a very pretty and nicely built RV-4 with an O-320 E2G engine 150hp and wood Warnke prop. I flew it two hours and noticed the elevator trim tab was very sensitive, it seemed 1/2" in either direction resulted in either a dive or a 1000fpm climb rate. I can't imagine putting someone in the rear, this is how a plane feels to me when it's on the rear of the CG envelope. The elevator's counterbalances were up about 1/2" above the LE of the stab, indicating it was trimming the elevator down slightly. This was with full fuel. A W&B is in order. I expected the elevator would be trimmed up a lot with just my 190lbs up front. The trim tab was so sensitive even 1/16" movements were a lot, and the full throw of the trim tab is maybe 45 deg each way and it just seems oversensitive. Has anyone lengthened the trim tab horn to cut down on throw? I'm thinking a harmonic balancer would be a good idea just for the CG improvement, and maybe a constant speed prop at 50lbs up there would really help the balance, but the E2G I don't think has a provision for a CS prop, can the crank be modified for a CS? -Tom
 
Speed controler

Hi

You can buy a speed controller I think Matronics supply them, I have them on my aeroplanes and they desensitise the trim.

WAM
 
RV-4 elevator trim

Tom,
Welcome to the grinning world of RV land and congratulations on your airplane. I have almost the exact set-up as you, and the sensitive manual elevator trim was one of the first things I noticed too whether solo or dual. I bought my RV-4 right after it had completed Phase 1 and the W&B calculations indicated I could have slightly over 200 lb. passenger. However, the first 200 pounder was a scarry experience with super sensitivity with pitch control and some induced pitch oscillations without input at slow speeds. On landing, I had full down elevator trim and still had to push the stick forward for the proper airspeed. Regardless of the W&B calculations, and I've reweighed the aircraft, my max in the rear is 185 lbs and I preset the trim forward.
I also thought about changing the trim sensitivity at first, but got use to it quickly and haven't thought about it since. My RV-4 doesn't fly very long straight and level regardless of how well I trim it hands off. Some of the fellows who have had them longer might have some suggestions.
Bill McLean
RV-4 Slider
Sky Dancing:)
 
Tom,

We did the same last Spring and are still grinning...

We have manual trim and a light-weight (Catto) prop on an O-320-D2J in our RV-4. I like the senistive trim response, but it does take some getting used to. I used to fly fighters (hence the need for an RV-4, the only suitable replacement in my price range!), and we always used to "blip" the trim switch to bias the stick force--if we wanted nose up trim, we'd pull the coolie cap (trim switch) aft in a series of short clicks...perhaps the same technique will work if you have electric trim in your plane? Definitely different from electric trim or trim wheel response in a typical certified light plane.

Good plan to reweigh your airplane and establish ground truth for CG. Van recommends this for a used RV purchase.

The RV-4 stick force gradient (pounds per G) is proportional to CG. As the CG moves aft, the gradient decreases along with static margin (stability). If stability becomes marginal, it's necessary to control pitch and angle of attack by putting the stick in WHATEVER position is required using WHATEVER force is required--i.e., flying an attitude and using power as required to control vertical velocity (it sure feels funny to be PUSHING the stick to control a nose-up pitch attitude). A light grip can help with PIO and once it starts, apply a small amount of consistent nose up force--the airplane will balloon or climb slightly while you get things stabilized.

Interestingly, pitch attitude also affects stability--your margin decreases (i.e., more sensitive stick) in nose up and nose down attitudes (e.g., during the flare, during a climb at Vx, during acro, etc.) for any given CG location. Not a big deal, but if stability is already marginal, it's just one more thing to be ready for. You may even feel the stick becoming lighter and notice some uncommanded nose rise as you slow in a pitch up.

We consider our RV-4 a "1.5" seat airplane. It depends who rides in the back. Fortunately, no one in my family is even close to FAA standard weight; but at a boarding weight of 155 and with a light nose, I have to be careful who I put in back. The handling characteristics change with CG and I find them pleasant throughout the envelope, but aft CG loading requires attention. We observe design limits for weight and CG (including acro limits). Any time computed CG is aft of the acro limit, it's a flag that handling characteristics will require more attention.

Depending on your airplane's empty weight and your mission requirements, one option to consider besides a CS prop is ballasting. A harmonic balancer bolted to the fly wheel (about 11 lbs) is one option. Another is a heavy weight crush plate. Different size plates are available from Sabre industries. After you weigh the airplane, you might consider building a spreadsheet that would allow you to "what if" things a bit. We swapped the heavier Concord battery in the cockpit for a light-weight battery on the front of the firewall--that helped our empty CG.

One other "RVism" we've learned is that the CG shifts aft as fuel is burned, it's slight; but when your looking at different load options, it's important to consider CG at minimum-fuel landing weight.

Forgive the disssertation...

Cheers,

Vac
 
Manual or electric?

I'm confused... is your elevator trim manual or electric? If manual; you can shorten the distance between the clevis pin hole and the pivot point on the pilot control lever. This would be a simple modification. If manual, is your control level set up exactly per the plans? Manual or electric?
 
wingspan99 said:
Hi Everyone,
Last weekend I acquired a very pretty and nicely built RV-4 with an O-320 E2G engine 150hp and wood Warnke prop. ... -Tom
Click to expand...

No intent to hijack the thread but.... Arrrgh! You bought that -4 out of Oklahoma I've been drooling over for over a month didn't you! Seriously, congratulations Tom, and I hope to follow in your foot steps with a -4 or -6 when the Cessna sells.
 
Manual Elev trim and Arrrgh

Thanks for all your replies, I am getting a W&B done before putting a pax in back for sure, I want to know where I'm at. I guarantee I will be an expert on W&B for N40MB. I had a Grumman Cheetah which was 4-seats with a huge baggage compartment and it all had to be managed very carefully, and sometimes I just couldn't fill the tanks more than half for certain flights. I have a friend who has the real deal aircraft scales. I figured it would not handle too much in the rear seat with the 0-320 and wood prop, but I figure 13lbs up front at the prop will allow 13lbs more in the rear seat. I will probably get a harmonic balancer for both the ballast and the smoothness, and maybe a weighted crush plate too, that's a great idea. The engine/prop combo is already very smooth as the engine is in great shape. My elevator trim is a manual setup, I think I will change the length of the control horn at the trim tab but make sure I can still get the same amount of down elevator trim, which will probably reduce the total up elevator trim, I doubt I'll ever need very much up. The workmanship and paint on the plane is just incredible, I can't believe how many people have been just hanging around my hanger staring at it. The red is a flip/flop Chromeillusion paint that goes from bronze to purple depending on the angle it's viewed from. Yes, sorry but this plane came from Alva, OK. After my friends at the airport saw it in my hangar I had to allow them to beat me up just so they felt better. I have this sly grin on my face that just won't quit even after the pummeling, nuggies, and purple nurples. I reclined the front seat 3" and what a world of a difference it made in comfort. Next I'll let the rudder pedals forward half an inch too. It had a loran, I'm so excited, I've always wanted one, I finally got one. It ought to make a great target at 100yds, I can already envision the parts exploding upwards with each subsequent shot. That's nothing though, compared to the thick loran manual, ought to stop a .22 at least, maybe useful as body armor. -Tom
Side.jpg


RV-4 N40MB 006.jpg
 
You must log in or register to reply here.