RV 6 CG/speed enhancement.

Had a wonderfull conversation with Vans engineering at S & Fun on my 6 I am building....I am going for the lightest, fastest ever (look out Checkaway, hahahaha) and have issues with cowling drag and CG with my proposed Catto prop. Now, apparently, Vans says that if you put on the RV 7 engine mount, and cowl (drop in installation it appears), you can get the engine a full 2 inches further forward and an even lower drag cowling setup. Is this a unique idea? Or, is there other non shy builder out there that has tried/thought of this?

Glen RV 6, wings 25% and building up a 210+++ HP fire breathing Lycosaurous.

Did Van explain why moving the engine and cowl 2" farther forward would reduce cooling drag? Does this clean up the exit air path somehow?

Otherwise, color me puzzled...

Why would moving the engine two inches forward result in a lower drag cowling? Are there some differences between the RV-6 and RV-7 cowlings that affect drag?

If you really want to go fast, why wouldn't you go with a metal prop? Metal props have thinner blades than composite props, and that makes them more efficient. In other words, they produce more thrust, so the aircraft will go faster.

If speed is important, go with either a blended airfoil Hartzell, or a Sensenich.

Ok,...

Haha, well....I really did not want to start this conversation, as it is an open invitation for George to come in and patronize us all....but, since you ask,:
..

***CG benefits are intuitively obvious.
***My "OPINION" on the Catto, first, Craig is one smart SOB, and has great results with....Huge weight savings...No harmonics...Smoother operation... If an unfortunate prop strke occurs, a Catto prop will in most cases, eliminate a "required" teardown...Craig has some new ideas we/I are going to try....No corrosion...Can be moved farther ahead for a more blended (read custom nose) and inlet area. IMHO I will make up the 2 or 3 mph loss in drag reduction on inlets and exit drag enhancements, hence making the speed loss moot, yet saving many kilos. BTW, before anybody asks, look at the Lancair columbia nose, this is the direction I am going, with further and future consultation with Craig in this area.
***As far as the 7 cowl itself saving drag...remember, there is HUGE drag that can be reduced at the outlet of the cowl. Look at some Glasairs, read recent articles about this AND, remember that the less of an angle the air has to turn, the lower the drag. (remember that 2" farther forward engine, and the resulting lower angle the air will be turning?) According to Vans engineering, even minute decreases in angles make big differences. Ever wonder why apparently identical RV's have significant differences in speeds? Look here, trust me.
Vans also says that...ever notice that forward facing flange at the bottom of the firewall where bottom skin and firewall join? Yep, you guessed it H U G E drag there. ... Nosewheel weldmont? Huge drag.... Non aerodynamic, round engine mount tubes? Big drag... Virtually 90 angle the air has to turn on the way out? Huge drag...I have read/heard/imagined that order of magnitude, 50% of cooling drag is found as the air moves/accelerates out the bottom into free air. Remember...the P-51 has a net "0" increase in drag for that rather large belly scoop, hence proper cooling drag planning.
All my above ideas have been used on one plane or another, and given my building experience with fabric/metal/glass, IMHO will not add much if any to the total build time, and minimal weight gain vs. speed beneifits, or change Vans idea of how an RV should be built structurally or weight wise.
Glen
PS, soooo, has anybody tried this RV 7 mount/cowl thing yet/before?

Gee don't be be shy

glenmthompson said:

Haha, well....I really did not want to start this conversation, as it is an open invitation for George to come in and patronize us all....but, since you ask,: Glen PS, soooo, has anybody tried this RV 7 mount/cowl thing yet/before?

Click to expand...

Glen, I would never patronize you. Clearly you know things I never heard of? Can't we discuss this without the personal comments.

glenmthompson said:

......bottom of the firewall where bottom skin and firewall join? Yep, you guessed it H U G E drag there........."

Non aerodynamic, round engine mount tubes? BIG DRAG........"

Click to expand...

REALLY! That is fascinating. The lip at the firewall and round engine mount tubes are H U G E drag items. I am not saying they don't count, but it seems like these items, to me, are really minor, sorry no offense.

I do agree every little bit counts.

However back to the thread, First I did not know there was a big difference between the RV-6/7 cowl and engine mount. However if the RV-7 is longer I don't see that slight increase in cowl length helping that much as many have echoed. You say Van's Engineering (Richard VanGrunsven?) said this. I am just curious, no offense.

A longer nose is more aerodynamic, but a prop extension at the front gives that "pointy" effect better than just hanging the engine further off the firewall, which is what I gather from reading this thread? Some clever internal baffles would help "turn the air" better. All the 90 degree turning happens in the upper plenum. The lower cowl (plenum) is slower air and has lots of room to line back up with the free air steam. There are tubes and stuff in the way, but 2" will not make any differnce here. It's just my gut feeling, no offense.

A longer RV-7 engine mount/cowl would not hurt, but than with a RV-6 you could run into Fwd CG issues with a heavy engine. I agree a light wood prop, like the Catto would help offset this weight and balance issue. Less DRAG? I don't get it. No offense; I could be wrong. The longer you make the plane the more you also increase the "wetted area" drag.

Pops: Without patronizing either of us, teach me about Catto props. You brought it up. I want to hear more; From flight test (you probably don't want to hear this) Sensenich was the fastest along with the Hartzell BA c/s prop. It would be great to have a actual side by side fly off with a Catto vs a Sensenich.

I hear these "fastest claims" but when the side-by-side test comes around the claims don't match the reality. As far as cost, the Sensenich is about the same money as the Catto. On a RV-7 you need the weight on the nose. I am not putting your Catto down, but we need to talk without emotion. If you have some facts that the Catto is "fastest", that would be cool. People read this and need the facts to make their decision. I hear good things about Catto and only heard of one in flight failure.

Catto (fiberglass wrapped wood) has all the cool attributes over metal you stated: lighter weight and no harmonics. As far as "corrosion" you DO have have "erosion" and material breakdown, as with any bonded composite wood prop. However, like all props they can be refinished or overhauled, but nothing last for ever. Metal props are quite durable. With normal care metal corrosion is not an issue to achieve the props full and long service life.

I still say with out being patronizing, for the money you can't beat the Sensenich. For top overall performance and value you can't beat the Hartzell BA prop.

If you think that is patronizing, sorry it's just my opinion, there is a difference. You are entitled to yours. Obviously you are a big fan of Catto props, which is cool they are great I am sure. Good luck with that.

Cheers George

glenmthompson said:

snip..........I am going for the lightest, fastest ever.... with my proposed Catto prop............snip

Click to expand...

Glen,
Regarding propeller choices....I would refer you to the Fifth issue 2003 of the RVator. Facinating reading. In a nutshell, Van installed several different examples onto one test bed...a 180 HP RV-8 (N158RV). The results are as illustrated.

Rick Galati RV-6A "Darla" Sensenich equipped

Why Re-Ininvent?

If you like the Lancair cowl, buy a cowl from James (Sam/Will James) Aircraft. This will also require a 4" extension rather than 2.5" for fixed pitch. Buy the extension from Saber Mfg. This will give speed and you won't have to experiment. If you are changing the engine mount, tell them before you order, of course.
h

There is another option ...

hevansrv7a said:

If you like the Lancair cowl, buy a cowl from James (Sam/Will James) Aircraft. This will also require a 4" extension rather than 2.5" for fixed pitch. Buy the extension from Saber Mfg. This will give speed and you won't have to experiment. If you are changing the engine mount, tell them before you order, of course.
h

Click to expand...

If you get the newer "short" cowl from Will, you will **NOT** need the extension and the plane remains a "+6 g" plane.

That cowl is the same length as Van's and is made to fit an O-360 carbureted setup ... that is it has the air scoop at the bottom like Van's although it has a circular inlet.

Options, options, options ...

James
(no relation to Will or Sam)

Build clean

This was discussed in another area of the forum recently. Some of the conclusions were, 1) light doesn't, in itself, result in more speed. 2) More horsepower doesn't relate to more speed. 3) Cowl drag is probably the greatest detractor of speed, 4) building clean is probably one of the best methods to reducing drag and gaining speed.

I have incorporated many items to clean my plane as well as a couple of other mods. Basically, the airframe was built very clean. The mods, well you'll just have to look it over and see what the are!!!!

Oh yea..

Oh yea, it will be clean...More bullet posts...

**
****The cowling extension point I am making, is to make the engine further fwd. to make use of the Catto. Gonna use it, my plane, period.
****Another reason I want the engine fwd, is I am 6'2" and am not satisfied with the distance from my body to the panel. Hence Vans says (BTW I first spoke with Scott, and he refered me to a skinny guy with a beard, not Vans himself, but their engineering guru, sorry forgot his name) I can move easily the cross member behind the seats 4" aft for a more reclined seating position,headroom and face to panel room. I will only need to "box in with .032"" the crossmember, just like they do on the 10 cross member behind the aft seats. This will of course make the normal aft CG issue even MORE of a problem, especially with the Catto prop (14 lbs).
****Ok, erosion yes on the prop, but, planning to use the leading edge tape faired in with my custom paint (ie. paint at aft edge of tape built up PPG 2000) so as not to disturb the boundry layer on the prop that is going pertnear supersonic speeds at the tips.
****It appears that the Catto is an order of magnitude of 2 to 3 mph slower only, and Sammy James cowl-plenum/Lancair style nose, etc will easily make this up in the 200+ mph regime. Not theory guys, this happens in application.
****If anybody thinks the nose of a cowl of this design does not make an appreciable difference, well, then maybe they need to call "Knos 2 U" and have a discussion with them, as well as, Piper,Cirrus, Lancair, etc.
****Another fact of cooling drag is , the less drag at the outlet, the more airflow you will get, the smaller the inlet needs to be. Hence even less drag in the front of the cowling.
****Vans engineering (aboved mentioned bearded dude, really nice guy BTW) indicates that my previusly mentioned high drag cooling outlet areas ARE large drag areas, as well a a recent article in sport Aviation. He indicates that the big areas that deserve attention on a Vans acft are, interference drag at intersections, ie gear/fuselage and cooling drag. The latter is a very misunderstood and neglected area. So, I guess we will see the proof in the pudding in a year and a half or so when I get this puppy flying/racing.
**** I have seen many Sammy James products, as well as work with them. They are not quite, well a nighmare to get to fit/look right, BUT...they do make Vans fiberglass seem like child's play. I do already have the SJ plenum for example and it took a great deal of work to fit even half way decent.
****More HP DOES equal more speed! Ok, pretty small incrimentally, of course, but then, I have been spoiled by the neck wrenching acceleration of CS 180 HP set ups, and my FP Catto will appreciate the extra torque of my proposed FI fire breather.
**** Bingo on the fact that 30-40 lbs lighter planes do not really fly faster.....CG???..hhmmm.. Debatable. But to not try to build the lightest plane you are capable/able/willing to build, is well, irresponsible and lowers the amount of OSH camping gear as well!
Glen

It's good to read of your quest for speed.

Glenn you have two big things going for you right now desire and confidence that you will produce the fastest RV-6 around. I personally do not agree with some of your theories - like moving the CG forward makes the plane fly faster - but if you persist you will end up with a very fast RV-6. Maybe I will pick up on some of your successes.

Bob Axsom

Speed vs CG

At a given weight, the drag is decreased if the CG is moved aft. The effect is small, but definitely present.

It is not practical to build a plane with the CG so far that you cannot carry any baggage weight. But, if you are interested in max speed, try to arrange things so the empty CG is no further forward than necessary.

Note: I am not suggesting that you can reduce the drag by adding weight to the baggage compartment. The induced drag from the extra weight cancels out the drag reduction from moving the CG aft.

Is it soup yet

jclark said:

If you get the newer "short" cowl from Will, you will **NOT** need the extension and the plane remains a "+6 g" plane.

That cowl is the same length as Van's and is made to fit an O-360 carburetor setup ... that is it has the air scoop at the bottom like Van's although it has a circular inlet.

James
(no relation to Will or Sam)

Click to expand...

I see Sam James has the short cowl on his web site but heard it is not available yet? Do you know? G

PS glenmthompson, I agree with everything you said in your last post, and I am not patronizing you.

Yup ... it's available

gmcjetpilot said:

I see Sam James has the short cowl on his web site but heard it is not available yet? Do you know? G

PS glenmthompson, I agree with everything you said in your last post, and I am not patronizing you.

Click to expand...

It is in fact available.

I "worked with" Will to get the "short cowl" done and as a result, I got the first one out of the mold and provided additional feedback. I think the one I got is the one in the picture.

Currently, I have cut and fit to plane (RV6A with O-360 carbureted). The rings have been put in place and I have hinges horizontally and vertically on the bottom half. Screws on the top rear and bottom rear will hold it on.

I am now sorting out the "best" way to make the connection between the circular inlet and Van's filtered air box (FAB 360). Those that have done this can related to converting the air from the circular inlet "O" to the FAB "D" shapes.

I have promised some pictures to Will but have been working REALLY slowly (as usual on this project). With a few weeks, I should have a lot available for him.

But to the main question again ... ***YES*** it is available.

Now the BIG question in my mind is will it make my plane faster???

<<Note: I wanted it for looks ... something a bit different and hope that I get some speed as a bonus. But I was NOT willing to give up the 2 G penalty of the long cowl.>>


James

Is this a Retrofit.

jclark said:

It is in fact available.main question again ... ***YES*** it is available.

Now the BIG question in my mind is will it make my plane faster??? James

Click to expand...

I know it will add speed. My question is this a retrofit to an exisiting RV. I ask because it would be great to get the before and after. G

Extended RV6 Cowl

Glenmthompson,

If you want a longer cowl then just get an older long cowl version that Van's used to supply with the RV6! It is slightly better looking than the newer short cowls that were supplied in the later years. Also, you are making a BIG mistake to move your engine forward in the RV6, as it will result in a forward CG condition that will actually slow the plane down in flight since it will take more up elevator to raise the nose up and thus will create more drag. I assume the proposed 210 hp FI Lycoming you plan to build-up will be an IO-360 angle valve version, and you should know that they are about 30 lbs heavier than the O-360 parallel valve version. I can tell you here and now that the IO-360 angle valve version with a CS metal prop will push your CG too far forward with the stock RV6 engine mount, so it will be even WORSE with the RV7 engine mount. Van designed the RV6 to have a fairly rearward CG condition with a much lighter O-320 carb version Lycoming so that it would cruise at a fairly high speed with little or no up elevator required (obviously if the CG were such that zero up elevator were required, then that is where it will cruise the fastest), but in doing so it really limited the amount of baggage allowable. Most of us that have built RV6's quickly discovered that if a little heavier engine such as the O-360 parallel valve Lyc were to be used with a CS metal prop that it moved the CG forward just enough to allow the added flexibility for added baggage weight; but there is a limit to how much added forward weight you can add. I have found that using the counterweighted O-360 parallel valve Lyc with a McCauley CS prop & 1 5/8" prop spacer works perfect with the old long cowl and original RV6 engine mount, and seems to be virtually the ideal weight for this plane. So far at 8000' @ a max manifold pressure of 23" (I'm using an Ellison TBI injector) and 2300 RPM I am cruising at a GPS ground speed of 212 mph. That speed should increase if I turn the RPM up to 2500, but I haven't tried that yet. If you look closely at the chart that Rick6A posted, that the fastest CS combo that Van's tested in the 180 hp RV8 was 208.9 mph, and that was at 2500 RPM. My RV6 must be doing quite well since it is already faster at 2300 RPM with the same basic engine (well to be truthful I do have 9:1 pistons, electronic ignition, and the Ellison injector, and estimate that I'm making about 195 hp or so), and that is at Solo weight conditions. I have to trim with a small amount of up elevator, so with the added weight of some baggage would probably have little if any up elevator trim required and thus will probably see about a couple of mph increase in cruise speed. If I turn it up to 2500 be reducing the pitch of the prop slightly, I think I could come close to about a 216-218 mph criuse speed. I doubt that you will be able to get ANY RV6 to cruise all that much faster than that regardless of what you do to the RV6 during construction, but who knows for sure!! I do believe the McCauley prop I'm using (it's off a Mooney 201 & cut down 2" in dia to 72") is about as efficient as the best Hartzell blended airfoil blade CS prop, so that is certainly helping me out (the large paddle blades seem to work extremely well at altitude, and also give superior climb performance, though cruise down low is probably no better than a Hartzell...I am sure that it is more than a match for ANY Catto prop in any condition be it climb or cruise!!!) I have attached two photos to give you an idea what my RV6 looks like with the longer cowl and extended CS McCauley prop.

Clarification.

I never meant Bob, to imply that a fwd CG makes a plane fly faster, I think a few missplaced modifiers might have given you that idea. I am curious for this discussion, besides the missunderstood CG issue, what other ideas you disagree with? I have a parallel valve 0360-A1A to be modified with piston cooling jets, 10-1 pistons, and additional jets to spray oil on the disgustingly, hideously oil/cooling starved exhaust valves. I am modifying very similar to SI 1479. (This would be a great discussion in another thread, see http://precisionengine.home.mindspring.com/engine2.htm). This is the only info I am letting out about my engine build at this time, I have many ideas in mind, none new, just combinations of many already proven ideas) ( and I will let the dyno numbers at a later date speak for themselves..( I hope!!!!))
..
I want to move the engine fwd (basis for this thread) to allow....For the heavier "7" tail I have...Moving the seat back further aft ( endorsed already from Vans engineering)....Allow for my proposed ultra light EFIS panel and elec. ignition system and Catto prop...All this, so I can have a plane that I can carry baggage in without having to be paranoid about aft CG when loaded.
..
BTW thanks for the pics of the extended cowl, looks sleek like the 7 cowl, without the CG issues, especially with that heavier angle valved Lycosorous and prop. I hope my FW fwd install to be a full 60 lbs +++ lighter than yours (+/- 30# engine, 2 # mag vs. EI, and 30# +++ difference in props) so I feel I really do need the more fwd engine install to attempt to compensate for CG loading issues.
Thanks so much guys for all the info so far, and BTW I am looking for the 220mph regime for racing purposses only, and economy on a daily basis, very tough to get I know, but you know what they say about speed mods, ..."one, not noticable, but, as the plane gets faster, it all adds up and they compliment each other to some degree! Cool ! ! ! !
Glen

RV6 CG Issues

Glenmthompson,

You are imagining a rearward CG issue that does NOT exist in the RV6 with the stock engine mount. Let me repeat here, you do NOT need to extend the engine forward in the RV6 when using any of the O320 thru O360 series Lycoming engines!!!!!!!

As for your supposed 60lbs+++ lighter installation than mine, how do you plan to achieve that, in fantasyland? To start off with, every O360 parallel valve engine combination (non-counterweighted) weighs around 265-270 lbs or so (the O-320's only weigh about 10 lbs lighter), and the counterweighted versions like I have add about another 5 lbs to that weight. Since you are using an O-360 there in NO way you are going to be any lighter than that!!! Next, if you change out to electronic ignition (which I have in my installation) the weight of the ECU and components is virtually the same as the mag it replaces, so there is no weight savings to be found there!! Third, you will be using a HP fuel injection system which is about 3-4 lbs heavier than my Ellison TBI unit (which is lighter than a carb by about a lb or two), so no weight reduction there. Fourth, all the accessories and engine baffling you use will no doubt be virtually the same as what I have, so no weight reduction there!!! Fifth, the light weight Catto prop you plan to use that you claim is so light will in fact not be such an advantage. My McCauley CS prop is one of the lightest all metal CS props out there at 48 lbs total (the Hartzells weigh more at 55 lbs). If you want less weight it can always be upgraded to the Whirlwind composite blades (Whirlwind ues the lightweight one piece McCauley hub for their props) which will reduce the weight of the entire assembly 10 lbs so that it is only 38 lbs total in the end. All of the guys I know that are running a very light weight wooden FP prop have ended up adding a flywheel dampner to get the engine to run smoothly at lower RPM (due to the added flywheel mass) and that ends up making the entire assembly weighing close to 28 lbs. In otherwords, that is only about 10 lbs lighter than the composite blade McCauley setup, or 20 lbs lighter than an all metal McCauley prop, and then the FP setup doesn't even have the flexibility of operations that the CS prop has (I'll take the extra 10 lbs anyday, since I can allow it to rev up to 2900 RPM for phenominal takeoff climb performance, and then increase the pitch at max manifold pressure to reduce the cruise RPM to between 2200-2300 RPM for max economy at the same cruise speed as the FP prop gets at 2700-2800 RPM (which will get pathetic fuel economy!!).

I just don't see where you will get that 60 lb reduction in weight you claim you will be getting? Now, with the 48 lb prop (and admitedly I do have an additional 2.25 lb 1 5/8" long prop extension on mine...so call it all a 50 lb assembly), and the counterweighted O-360 parallel valve engine I find my CG to be virtually ideal in that I can carry up close to 80-90 lbs baggage solo (which is more capacity than I need), or up to about 60 lbs with a passenger. In all reality I am just a bit too forward in the CG envelope, and could always relocate my battery just behind the baggage compartment rear wall to reduce the forward CG to a virtually perfect CG combination when flying solo. I could also get about the same effect without moving the battery if I were to change out to the 10 lb lighter Whirlwind composite blades in my McCauley CS hub. As for the heavier RV7 tail weight you mentioned you were going to use, the only difference is a slightly taller & larger vertical stabilizer & rudder (the RV7 elevator is identical to what the RV6 has), but I should mention that I did upgrade both the elevator & rudder on my RV6 to the 0.020" thick skins with addition stub ribs to stiffen them up in order to prevent trailing edge cracking of the skins so my assembly is already slightly heavier. I also have electric trim tab control on the rudder itself that I added, so that adds a little extra weight at the rear. Overall I bet that an RV7 tail is not any heavier than my setup, and my CG is still OK with the stock RV6 engine mount. You are wasting your time and effort to move the CG forward by using an RV7 engine mount, and in my opinion will actually slow the plane down in the end because of that!!!

Just my 2 cents!!

Some confusion here..

"proposed 210 hp FI Lycoming you plan to build-up will be an IO-360 angle valve version, and you should know that they are about 30 lbs heavier than the O-360 parallel valve version."......Tloof, these are your words about the 30# I would gain if I had a parallel valve engine, I did not check your numbers, just repeating you.....I will stand by my 2 lbs mag saving since I am going with dual LSE's ( will already have standby battery for EFIS, so I am eating a few pounds here, yet it will be aft of firewall) and the LSE control boxes will be aft, with only coils mounted on firewall, ..further aft CG....I did not know you had the Ellison, FI is not that more that a normal carb........As far as the 7 tail, it is counterbalanced, unlike the old 6 tails. It also has .020 skins, read heavier, all this and it is 8 feet aft, pretty good moment arm!...As far as props, my Catto (2 blade) will weigh 14 lbs! If I use your numbers quoted today, I will have OVER 60 lbs savings. Well over 40 lbs if I use your "new" engine weight numbers....Lets just say I will easily have 40 lbs, easy and leave it at that.
Also, the 7 (most say) is a faster plane, yes, most due to airfoil changes, but I fail to see how anything I am doing will slow the plane down, ...no speed increase? Arguable...Slow down? Just cannot see it.
Van's engineer is 100% in agreement in the direction I am headed on ALL counts, and this is a pretty good recommendation and sourse I would say.
.
As a further note, I have flown 2 6's and a 10. They all at normal cruise actually have a slightly down elevator at cruise speeds, hence if I do, lets say have a more fwd CG, the down plane,as seen on on most 6's will only be helped.
.
regardless of how any of us thinks/believes,...this kind of interaction is only to benefit us all and I sincerely apprfeciate all input here. Somewhere in here is the truth and reality and we will all benefit. Keep it coming, ya all know I am not shy and we need to communicate!!!!
(Ps, just got in from a night in Copacabana in Rio, enjoying life and the RV comradare. I hope this, and all forums makes us all better RV'rs and better people...)
Glen.

Forward CG

Glenthompson,

You are not adding the weight reductions you claim correctly in comparison to what I have. First of all you are saying that you are planning to use a built-up 210 hp parrallel valve O-360 (granted I originally assumed you would be going with an angle valve IO-360 to get the 210 hp you were talking about, thus the reason for using an RV7 cowling since the angle valve version Lyc will fit into it without modification unlike the RV6 cowl...maybe the 60 lbs weight saving you mentioned is in comparison to an angle valve installation?). The parallel valve O-360 is the exact same engine I have in my RV6 (except it is only about 195-200 hp...it's tough to get much more than that without going with 10:1 pistons and somesort of aftermarket racing cam that has inceased lift & duration, which is very tough on the longevity of the Lycoming cylinders!!!) so the weight of your engine will be pound for pound the same as mine unless you use a non-counterweighted version which is 5 lbs lighter. Mags vs electronic ignition is really all a wash in the end and won't save a single pound of weight, and in fact will probably add a few when the backup battery system weight is added in due to using two electronic ignition systems (I personally think that's a bad idea since the 2nd elctronic system adds NO additional power over using a backup mag). I myself used a single Bendix 1200 series mag in place of the Dual-mag that was originally in my O-360-A1F6D engine, and a Lightspeed crank trip electronic system for my other ignition system (by doing this no backup electric system is required, and the Bendix 1200 series mag I used is the best mag on the market for the shear output spark power that it provides and it still has an impulse coupling to allow hand propping to start the engine up if the battery ever dies). By the way it is better and simpler to mount the coils directly on the top of the engine with short plug wires to each sparkplug than to mount the coils on the firewall, besides they hardly weigh anything to consider in the CG issue that will matter. My Ellison TBI unit is a few pounds lighter than a carb, which last time I looked is still a few pounds lighter than the Bendix FI system (don't forget the heavier HP fuel pump that the Bendix FI requires). So from an overall comparison of the engine, your proposed parallel valve O-360 will not be any lighter than what I have in my RV6 (I'll give you a 5 lb reduction for most likely using a non-counterweighted version since you will be using a FP prop that doesn't need counterweighting like the CS installations benefit from, but I also subtract that same 5 lbs for using the heavier Bendix FI system & having to install a back-up battery system due to the use of two electronic ignition systems...all other things like accessories & baffling should be identical in both ouir installations). So, the weight reduction in your engine installation is ZERO!!

This only leaves the propeller as any difference in weight reduction, and admittedly if you go with the 14 lb Catto prop (which doesn't include the spacer and longer prop bolts, etc...figure about 18-20 lbs for the total install weight, which is about the same for ALL wooden prop installations) it is much lighter than my McCauley CS metal prop. In reality I think you will find that the 18 lb weight of you FP installation to be too light for good flywheel effect to get smooth running charateristics out of your engine, which is what others have experienced thus they have added about another 10 lbs of additional flywheel weight up front to help out (this makes their total installed prop weight about 28 lbs) Now, my McCauley CS metal prop weighs about 50 lbs total installed weight so your setup will be about 30 lbs lighter, not the 40 like you conceded in your last email. Now I can always drop 10 lbs in a heartbeat off my prop weight by having the Whirlwind composite blades installed in my McCauley hub, which would then reduce your weight savings to only 20 lbs (or in reality more like 10 lbs when you realize that the additional 10 lb flywheel weight I mentioned earlier needs to be installed to smooth out your engine in flight). The thing is, I've found the current CG I get with the 50 lb CS prop to be just right in my RV6 since I do have the .020" skins on the elevators & rudder + the rudder electric trim motor in the rudder. No doubt that using the RV7 vert stabilizer & counterweighted rudder will add a few more lbs over my installation (I thought about changing out to the same myself, but decided it was too much added work & effort for only a small gain down at low speed to be worthwhile, but if buiding from scratch it would be worth it), but that will only make the heavier prop I have more desirable than a FP Catto prop setup like you are doing. As a side note the RV7 tail has to be mounted in the exact same location as the original RV6 tail, not farther aft like it is installed on the RV7, that is done because the RV7 is heavier up front than the RV6 in order to allow an angle valve IO-360 to be installed!! In my opinion you would be far better off to install the 3 bladed Whirlwind 151 series prop that only weighs 28 lbs total installed weight and that is also a full CS prop. It is just the right weight to smooth out your engine, and has the added flexibility of CS pitch control of the blades...far better than a Catto prop will EVER be (yes it will cost a bit more no doubt, but what do you expect for all the added flexibility?).

By the way, the only RV6's that I have seen that require down elevator trim in cruise flight are the lighter O-320's with wooden prop installations. All of the O-360 installations generally have from neutral to slight up elevator trim required depending on whether they have a FP prop or CS prop installed. The O-320 with FP prop installation weight seems to be what Van was after when he designed the RV6 for optimum cruise CG, but it did come with the penalty of reduced baggage & passenger weight.

Regards,

Tloof