Down Elevater to fly level?
 

Hi guys,
After flying my H9 Hellcat for the past few days, I noticed as the plane sat in the pits at the proper trims for level flight the Elevater is about a 1/2" down. What does this mean? The plane flys and lands great. Is this a CG issue? I did have to reattach the firewall a few times after some mishaps but had no problems lining things up.

Thanks

RE: Down Elevater to fly level?
 

It's most likely an incidence problem, wing or tail, although the wing would probably be easier to adjust.

Had a Waco like that, flew well all it's life until I sold it, didn't see a reason to fix it, plus it was harder to do on a bipe.

Check your wing seat, make sure the wing is sitting in it's intended angle.
The CofG will affect your elevators efficiency not it's level flight position, unless you have wide differences in elevator trim for different throttle settings.
Is this the case?

RE: Down Elevater to fly level?
 

I don't recall any wide differences in elevator trim at different throttle settings, but I will really check it out next time I fly it. I wll check the wing seating as well. It really does fly great, I'd almost hate to change anything. lol

Thanks

RE: Down Elevater to fly level?
 

Something you have to remember is the Hellcat was designed to climb. If the plans used to build the model were close to what Grumman designed, full size, it could account for some of it.

RE: Down Elevater to fly level?
 

CHecking the engine thrust angle against the stabaliser an then the wing ill tell ou which one is off. I would guess the stab needs more of a negative angle. It ma be the most difficult to change though.

RE: Down Elevater to fly level?
 

One more thing to check. You need to make sure the leading edge of the horizontal stab is not broke. They are very weak and it could be broke but not completely and be flexing.

RE: Down Elevater to fly level?
 

Or, even simpler, fly slower. Find a nice 'cruise speed' where you have a bit less 'down elevator' trim to maintain height. If you look at in-flight photos of 'Spitfires', guess what? There's a bit of down trim wound in...
Evan, WB #12.

RE: Down Elevater to fly level?
 

Thanks for your help guys. Next flight i'll pay more attention at slower speeds. My stab is not broken or flexing,I made it solid before I glassed and painted. I will check the thrust angle against the stab and wing.

RE: Down Elevater to fly level?
 

The engine thrust angle could be too high (pointing up too much). This will cause the plane to want to climb. So add some kind of shims or washers so the engine points down a bit and try flying it then - but be prepared to give it some up elevator to keep it away from the ground :D.

Ed

RE: Down Elevater to fly level?
 

My TF 1/7th scale mustang ARF climbs like crazy. It takes about half of the down trim to make it fly level. I added down thrust which helped some, but the stab to wing angle is the real culprit. I might have to change the wing in an effort to fix it. The problem really shows up when taking off and landing. With all of the down trim, it wants to nose over, but up elevator causes it to try to take off too soon, or lift off again when you are trying to plant the tail on landing. The stab needs to lose a degree or two of positive incidence.

RE: Down Elevater to fly level?
 

95% sure it'll be an incidence issue.
If it has the scale incidence built it 'll certainly climb dramatically due to the low weight/high power our models have compared to the full size.
Because its a carrier aircraft... max lift was needed in the shortest distance.
Having said that, it's a H9 sports scale so I'd have guessed they'd sorted that out and normalized it for RC use.
You can counter this with down thrust (not all but it'll help) or/and mix down evelator to throttle.
Don't know exactly which H9 H'cat you have but if you look at this clip, this model certainly seems to be flying tail low.
http://www.youtube.com/watch?v=3ozU6Pnq1Jg

RE: Down Elevater to fly level?
 

I don't have any nose over issues but It does sometimes want to take off again and it's hard to plant the tail wheel.
The plane flys pretty level in the air, not like the one in the vid. I bought it 2 years ago if that helps determin which version it is.

I think i'll try adding some shims like suggested.

RE: Down Elevater to fly level?
 

Regardless of the plans I am building to, I know how I like my aircraft rigged. That is why it is so important to have an incidence meter when building. Or whatever device you use.

This issue come up a lot with the Fokker designs. especially the triplane. All of that wing, highly cambered and then set at positive incidence really makes them climb.

I personally like my aircraft set up 0-0-0. I bet you have a bunch of positive incidence in the wing. If so, the easiest correction is to shim the leading edge of the wing down. I have found 1/8" equals around 1 degree, on most models.

An incidence meter is a very necessary investment IMO and I prefer the Robart offering. Not cheap really, but you will know exactly how your plane will fly before your maidens.

RE: Down Elevater to fly level?
 

If the model flies right in all respects, especially the 'sit' of it in the air, then the issue is simply tailplane incidence. Altering the wings incidence will alter the models sit in the air, in this instance it will make it sit tail high at the same speed. Altering the wing will also alter the actual thrustline inflight because of the different sit of the fuselage.

Ian.

RE: Down Elevater to fly level?
 

Actually .016 inch or 1/64 inch shim per inch of chord equals 1 degree.

A very inexpensive incidence meter can be quiclkley made from a $3.99 angle indicator from Harbor Freight. Or a few bucks more for a digital angle meter.

RE: Down Elevater to fly level?
 

It is important to realize that the incidence needs to be measured through the centerline of the airfoil and not simply by using a ruler or straight edge on the bottom of the wing. A common error. That is why I like a commercial incidence meter as they center themselves properly with the airfoil.

RE: Down Elevater to fly level?
 

OK, so it's a profile drawing and having done quite a few, there'll be a bit of artistic licience so not exactly NASA data. But the artist will have captured the aircrafts defined proporties.
You can see a pronounced engine down thrust plus a definate positive incidence on the stab.
Difficult to tell exactly how much positive incidence the wing is carrying but it''ll be more than plenty.
It's the pos incidence on the stab (similar/identical to down elevator trim) that's the give-a-way.
Plus the stonking load of down thrust.

As mentioned I'd have thought H9 would have designed those out for a sports scale rc model.
Could they have kept the wing scalish... then zero'd the stab and engine.
Hummm.http://www.rcuniverse.com/forum/js/f.../msn/50_50.gif

RE: Down Elevater to fly level?
 

Realizing the importance of that, I made a jig that centers the platform, on which the angle meter rests, on the leading and trailing edge centers. A simple V shape on the beam ends between the edges insures this. You do not need the expensive commercial meter unless you are incapable of constructing this simple jig that I made out of wooden paint sticks free from the big box hardware stores. Or unless you have excess money to spend.

RE: Down Elevater to fly level?
 

It can be difficult to assume the abilities of others.

RE: Down Elevater to fly level?
 

Thanks for all the info guys, it is kind of confusing though... A friend of mine has a incidence meter but is out of town at the moment. I plan to have him check it when he gets back.

RE: Down Elevater to fly level?
 

You will then know exactly what is going on and how to proceed. Good luck.

RE: Down Elevater to fly level?
 

My friend let me borrow his incidence meter but i'm having a hard time just leveling the plane. To me it looks like the engine mount needs to be shimmed for more down thrust. I put the meter on both the stab and wing then lifted the tail untill the bubble was centered ,both read 0 incidence. I know the plane needs to be level first but how do I level it when the engine thrust line is off.. What line do I go by?
It also doesn't help that the cowl is not on straight...

Thanks

RE: Down Elevater to fly level?
 

Just level the wing to zero, then check everything else relative to that. no need to know the datumn line. You need to establish the stab incidence relative to the wing first, then check the engine.

RE: Down Elevater to fly level?
 

Ok thanks, now both the wing and stab are leveled to 0. Plane is now angled nose down a bit. Now how do I check the engine?

RE: Down Elevater to fly level?
 

The 'plane angled nose down a bit' with the wing level is to be expected. This picture is a H9 that has the datum line of the fuselage levelled in the picture. Notice the wing shows positive incidence, while the stab shows none. If you look closely, you'll notice the up elevator trim.