Can you share your RV-7 CG outcome ?

I have read a couple of times about managing the CG. There seems to be concern about getting it too far aft. I have the 360 finishing kit for vert induction but, have not purchased the engine.

Last months RVator talked about installing IO320 on the 360 mount. I like to have the option of this engine but, I am concerned about the lighter engine also being back a few inches.

What cautions can you share regarding CG management for an RV7 tip up?

Thanks, Dave Smith

RV7 CofG

I have just finished an RV7. We have a heavy front end; IOF-360 200hp with MT 3 blade CS Prop, inverted oil, twin alternators. About as heavy as you would want/or could get.

Our empty CofG is just aft of max fwd, which is absolutely perfect for us as with 2 (UK sized) passengers and fuel we fly at mid CofG. Don't forget that with the RV-7, all load moves the CofG progressively aft. I did a few calcs after our weigh in and found that with a light front end and max baggage etc you can shift the CofG out of range aft.

I would not believe all the scaremongering I have read about aft CofG on the 7, but is worthwhile being careful. To give yourself max flexibility keep the empty weight as far forward as you can to give yourself options when loading and flying.

Hope that helps.

Mark Castle-Smith
Flying RV7
Just started RV-3B!

No need to post those numbers here. Just check out Dan's W&B page.

My W&B worked out well (72KH on Dan's DB) - but it would have been even better if I had mounted the ELT and strobe power supply forward of the baggage wall.

I have a O-320 fp RV7- no vacuum pump, heavy starter, pretty clean firewall forward area, sensenich prop, light paint, seats are a few lbs, light interior.

I am mid range in the CG, I would go with a O-360 for the weight if I were to replace the engine. I would like to use the full baggage capacity and still have be good nose down attitude coming into the flare.

The tail dragger makes it a 'little' harder because you don't have that 3rd weight in the front.

begining and end of flight

One thing I noticed running some scenarios from Dans W&B table is that you can end up with the CG aft of the aft limit if you have full baggage and full tanks when you start but only minimum fuel at the end of a flight.
This seems particularly true with a -7 with 0-360 and FP prop (my configuration)
I am not a high time pilot but is this something that people take into account and what if anything should I consider (I have seen threads about heavy spacers ec)

As I am getting closer I am actualy starting to think about flying this project

Ballast?

uk_figs said:

One thing I noticed running some scenarios from Dans W&B table is that you can end up with the CG aft of the aft limit if you have full baggage and full tanks when you start but only minimum fuel at the end of a flight.

Click to expand...

If you look carefully you will end up way aft CG with a RV7(A) with full bags, if you have a light weight engine/prop. The most aft CG on Dan's W*B list is Cary Rhodes with an empty CG of 83.14" @ 1058 lbs. You'll noticed bags are limited to 60 lbs and there is no Acro limit. You can forget about the 84.5" Acro CG even solo, with fuel much less than full. Even limiting bags to 60 lb (vs std 100 lbs), you'll be aft the 86.82" CG limit w/ two 170 lb folks & full fuel by over 1/4". Yes, as you burn fuel, CG shifts further aft. With 14 gal you are 1" aft limit. This plane is begging for some ballast on the nose. (see below*)

Some workarounds when traveling, use soft bags on the floor (fwd of spar) with light stuff like clothes, secured so it does not interfere with the rudder.

>Use old fashion heavy starters and alternators.
>Fixed wood prop guys use the prop damper (about 20 lbs).
>Lead weight up from on the engine mount or on fwd engine area.
>Lead ballast could be remove ballast for local no baggage flights.
>If you don't want to do Acro or need to carry baggage, its not a problem.
>It would not take much weight in the starter/alternator area, like 20 lbs to move CG.*

Van made the RV7 for a 360/Hartzell. This is where the market was/is going. This combo on a RV4/6 is nose heavy, which was designed around the common combo back than, 320/wood prop.

Also priming and painting moves CG aft, since there is more surface aft of CG.

* Starting with 1058 lb / 83.14" CG, 20 lbs on the engine (big ol starter/alternator) moves wt/cg to 1078lbs/82.17", so 20 lbs moved CG almost 1" for this plane.. At least you could carry 40 lbs of bags with two people and 1 hr reserve fuel (10 gal). Forget dual Acro except with a 100 lb pass, 170 lb pilot, full fuel and no bags of course. Ballast can be good. 20 lbs of lead does not take much room.

PS - A 55 lb Hartzell BA prop would be the best solution. (I'm waiting for my commission check Mr. Hartzell.)

I've run all kinds of scenarios on Dan's WB page for my case (O-320). I've come up with a few areas where I would be aft CG, but the majority of the time, the numbers are green.

What I am curious about, is if the O-320 7/7A's out there have the O-320 mount (which moves the engine 2" forward), or if the 360 mount was/is used with a damper or some other ballast with a 320...

The engine dry weights are VERY close between O-320's and O-360's...

Lycoming O-320-D 160 253lbs
Lycoming O-360-A 180 265lbs

With the 2" forward mount, and a difference of 12 pounds in dry weight, it SEEMS like it wouldn't be too much of an issue.

The prop is a different story, as George said, the CS Hartzell will make the biggest difference.

My Experience

I have an earlier 7 kit and had absolutely no clue what I was doing when I started. I followed the ?generic? RV mantra, which was ?build it light?. Since my mission was going to be sport plane first, traveler second, that is what I did.

When the first FP 7?s where getting air borne the CGs were further aft then their other RV types. I was panicking since my prop was only 17 lbs. Here are a couple of things I did to help with CG:

1) Used the Saber prop spacer which is a few lbs heavier.
2) Used the 10lb (?) Saber crush plate. I still hate the idea of adding weight that has no other useful function but this will give you the most bang for the buck.
3) I installed everything I could under the boot cowl including the ELT (yeah I know it?s not the optimum place for the ELT but save it for another thread).

The strobe power supply and Dynon remote compass are mounted very close to CG but are the only items mounted outside of the boot cowl.


Before paint and wheel/leg/intersection fairing installation, my CG was exactly average for a RV-7 on Dan?s website. My weight was 1034.

After paint, wheel/leg/intersection fairing installation, my CG moved back just shy of .5? and my weight went up to 1055. I was surprised how far back the CG moved given the fairings are at/near the CG. I do consider my paint heavy due to the multiple coats the yellow took so I may be an extreme case in this regard.

I have to be careful about CG when doing acro with a passenger. Only skinny guys get to see the world upside down in my plane (not an issue thus far for women passengers).

I have not yet had any CG issues with passengers, baggage and fuel but I can?t get the full 100lbs in the baggage bay with low fuel. I am not advocating anything here, this is mealy a PIREP of my plane/experience. I should metion I love the way this thing flies. Good luck with your project.

Hugh

Hugh,

Is your 7 an O-320/Catto? Which mount if it's a 320?

Is your 7 an O-320/Catto? Which mount if it's a 320?

Click to expand...

O-360 with 3 blade Catto.

I fly a -7A with an O-360 and Sensenich (fixed pitch) prop and is, as yet, unpainted. At GTOW with 100# of bags, after a longish (3 - 4 hr.) flight that lightens the fuel tanks pretty well, be careful exiting off the wing onto the step. The plane will be in cg as it sits static on the ground.

But, the cg changes aft when you move aft off of the wing. I lightly crunched the rudder bottom after being the 1st to get out (about 220#). My wife didn't like the nose rearing up in front of her. Now, my wife gets out first and I lean forward as she does so it doesn't happen again.

I usually unscrew the tiedown rings when I fly. But from the geometry, it didn't look like the rear tiedown would have hit the pavement before the rudder bottom did.

Hard to tell

cjensen said:

The engine dry weights are VERY close between O-320's and O-360's...

Lycoming O-320-D 160 253lbs
Lycoming O-360-A 180 265lbs

With the 2" forward mount, and a difference of 12 pounds in dry weight, it SEEMS like it wouldn't be too much of an issue.

The prop is a different story, as George said, the CS Hartzell will make the biggest difference.

Click to expand...

Dry generic numbers are misleading. The O360A Lyc is the lightest 360 ever made and lighter than a Superior or ECI 360. Even later 360 Lycs are heavier than the Lyc "A" model. I doubt 265 lbs, even Lycs specs say 285 lbs for the lightest 180 hp 360.

As far as 320's weights, 268 to 299 lbs is the range. What about oil cooler? A 360 has bigger oil cooler than a 320's, with more oil (weight) in it. It adds up.

My estimate is about 20 lbs diff between the 320 v. 360 installed, fixed pitch prop, based on looking at RV empty weights. For some reason 320 v 360 w/ c/s props have a 45 lb difference. In general RV's with 360 tend to gain more than 20 lbs over the 320, possibly because builders who use 360's tend to add more 'other' stuff and goodies than 320 builders?

320 (150-160 hp) weights range from 268 to 299 lbs (according to Lyc)
http://www.lycoming.textron.com/engines/series/pdfs/320ci Engine Insert.pdf

360 (180 hp) weights range from 280 to 308 lbs (according to Lyc)
http://www.lycoming.textron.com/engines/series/pdfs/360ci Engine Insert.pdf

(what's dry weight? The pic shows starter & flywheel; I assume that's included.)

IO360's (200 hp) weigh 324-335! Has to be at least 35 lbs more than a 180 hp 360.

McFly said:

‘generic’ RV mantra, which was “build it light’.

1) Used the Saber prop spacer which is a few lbs heavier.
2) Used the 10lb (?) Saber crush plate. I still hate the idea of adding weight that has no other useful function but this will give you the most bang for the buck.
3) I installed everything I could under the boot cowl including the ELT (yeah I know it’s not the optimum place for the ELT but save it for another thread).

The strobe power supply and Dynon remote compass are mounted very close to CG but are the only items mounted outside of the boot cowl.

After paint, wheel/leg/intersection fairing installation, my CG moved back just shy of .5” and my weight went up to 1055. I was surprised how far back the CG moved given the fairings are at/near the CG. I do consider my paint heavy due to the multiple coats the yellow took so I may be an extreme case in this regard. Good luck with your project. Hugh

Click to expand...

Nice post McFly. Yea I'm moving my ELT near CG, avoiding any discretionary weight aft of 1/3 chord I can like the plague. If you're careful you can use a 320/wood prop, but it will be a challenge. Again the Mark Landoll Harmonic dampeners for wood props adds a good bit where its needed, out on the nose. These where use a lot when wood props where more popular, not just for weight but for better and smoother idle with low inertia props. Also don't forget about the Sensenich. Like I said 20 lbs in the starter/alternator station/datum is about 1" CG shift fwd.