[dan carley]

i've noticed when i trim for level flight, it need a slight down elevator trim. the elevator is in a slight down position. is this normal for the rv-4? or can this be fixed?

dan carley
RV4
N14ft

 

[Frank]

Yes and Yes. Adjust the angle of incidence of the horizontal stabilizer. Leading edge up a smidge. (Trial & error)

 

[mannanj]

Trim

i've noticed when i trim for level flight, it need a slight down elevator trim. the elevator is in a slight down position. is this normal for the rv-4? or can this be fixed?

dan carley
RV4
N14ft

Yes and Yes. My RV-8 shows slightly down elevator when trimmed for hands off in photos taken looking aft when the rear seat is occupied and with rear baggage. With me solo, it is fairly neutral. The tandem RV's show the need for more elev. trim when changing from one to two occupants than the side by side models.

This situation (down elevator) will give you slightly more speed than up elevator trim.

Check the situation out closely before changing the angle of incidence on the horizontal stabalizer. It may not be necessary, if it is, it is not hard to do.

 

[dan carley]

if you go through changing the angle of the elevator, will it pick up more speed? or just be happy with it

dan carley
RV4
N14FT

 

[pierre smith]

Hi Dan....

.....be careful if you decide to shim the stab up. Only a 1/16th of an inch is noticeable because you're moving a lot of area compared to just the tab.

Most of us just leave well enough alone... As Mannan pointed out...a slightly aft CG makes for a faster airplane....reason being that whatever the tail lifts, the wing is relieved of.

Regards,

 

[Steve Sampson]

.... is this normal for the rv-4?
dan carley
RV4
N14ft

Dan, when I was building mine I found quite a lot of discussion in this website about it. Smoky was a part of it so you might want to look through his posts starting 2 or so years ago. It was clear that what you are experiencing is standard on a -4.

As a result I did put the reccomended shim under the front of the stab (I cant remember how thick but it was in the various posts) during the build and I am glad I did because in the cruise the elevator is pretty much in trail....the way you want it. Obviously horns slightly up with a rear PAX but surprisingly little. You want it neutral because as you would expect that is the least drag situation.

There are a couple of posts below that, with respect, are confusing the decalage (not to be confused with even more interesting d?colletage) which you are asking about, with the CofG. They both affect stability, but in different ways. Rather than try to explain I will let you read the existing textbooks.

If you can face the rear fairing work you might want to - as Pierre said VERY CAREFULY - adjust the angle of incidence. Otherwise accept a small speed penalty

Have fun!

 

[smokyray]

Shim me up...

Hi Dan,

Steve is absolutely correct. My late great friend Arvil Porter built 11 RV4's over a 25 year period and we had several long discussions over this very subject. My RV4 had about 1/2" of down elevator in cruise flight. Arvil knew within a knot what changing the incidence would do. This was his discussion with me:

First, it doesn't add one knot of speed but does make it harder to slow down to land. I actually experimented fairly extensively changing it in both directions to aid in landing at my 900' strip. I found in the end that the stock incidence was perfect and that a properly trimmed RV4 will show a slightly nose down incidence on the elevator in cruise flight. Adding the shims will make it level in cruise flight but requires a large amount of aft trim for short field landings and a more abrupt stall.
As Steve stated, CG and stab incidence are separate subjects but intra-related. Arvil told me that the perfect CG for a -4 was 50 lb tail weight in level flight attitude empty. I have balanced many RV4's and my Rocket since and that magic 50lbs still makes for a great flying airplane. Steve operates his -4 out of a short strip as well as me with my Rocket which covers whether it would be a concern for STOL operations. Arvil liked landing VERY short. As mentioned above, why not put the shims in a bit at a time and experiment. That's the beauty of being experimental!

My Rocket has a perfectly level elevator inflight at 200 mph with the identical elevator and stab. When I asked Arvil about this he very quickly answered, longer fuselage, shimmed elevator. Sure miss him..

Hope that helps...

Smokey
HR2

BTW, Arvil's last RV4 project he was building is for sale by his widow. Contact me off line if you're interested.

 

[dan carley]

elevaror trim

hi rob,

that all makes good sence, i think i'll let it be. if there is no speed change and i'm not going out of short fields, no need to go through that work. if there was a quick fix without redoing the fairings i'd play with it.

thanks everyone

dan carley
RV-4
N14FT