[AndyRV7]

I was hoping to get some feedback. I'm sure, like everyone else, I could be easily led down a path of an expensive, complex, and heavy plane (generally speaking). Half of me wants to keep it super simple though like the plane I described above. I was just wondering what some other opinions might be. For all I know, I have misconceptions about the different aspects of the build, like weight and expense, or even how complex or difficult it might be to, for example, add an electronic ignition or CS prop.

But if I am making a fair assessment, does anyone that chose this route have any regrets or would you like to change anything a second time around?

For what it is worth, I would love to build an IFR plane with a glass panel, but even as such, keep that as simple as possible. I'm still trying to firm-up in my mind what I want my project to look like. I think not being able to get a clear picture in my mind is a large part of why I am dragging my feet still.

Thanks! Andy

 

[noelf]

I realized that you requested RV-7 specific, but I went through this with my -6A.

I came to the conclusion that I would not be satisfied if I kept it dirt simple. Sure, I could have finished much sooner (4,500+ build hours and getting real close to finishing) and would not have spent as much on "stuff". I really agonized over why I was building and not flying. But for me, it was personally a desire and challenge to implement my vision of what I wanted in MY creation.

That said, if I ever build another AC, it WILL BE VFR dirt simple. Van really does put a lot of thought (my opinion) into the creation of his airframe kits. And as long as I was following Van's instructions and drawings, I made steady progress. Once I decided to "personalize" the finishing stages of the AC, I slowed down to a crawl, and spent time learning (this is the education / recreation part of EXPERIMENTAL) what was appropriate for AC usage, and proper implementation.

I kept the engine / prop selection as you are indicating, but I put a lot of bells and whistles around it. Hope that helps...

 

[billnaz]

couldn't be happier

Mine's a 6A but I went with the 0360 and FP metal and I'm very satisfied. Also manual trim and flaps. A big consideration for me was cost, and I think I've got the most bang for the buck in aviation. An aditional benefit is the simplicity of the configuration. Easy maintanence and operation, less chance of systems failure. I'm saving for upgrades while I fly. Next annual I'll add auto pilot.
If you can afford going all out, by all means go for it. Most will agree that a more basic aircraft is in keeping with the RV spirit.

 

[Mel]

Just my $.02

And I'm sure that Larry Adamson will disagree.
I've had electronic ignitions and I've had C/S props. These are all nice. But for an RV, I now fly a 16 year old -6 with F/P 3-blade Catto and 2 mags and wouldn't have it any other way. Of course, I'm a "basic" sort of guy. I also have manual trim and flaps. I had an auto pilot for several years, but since Ann flies with me almost all the time, I took it out.

 

[AndyRV7]

That's what I am looking for. Thanks. I am thinking in terms of a 7, but I don't think the problem is any different for other models, so I probably shouldn't have specified the plane.

You make a good point that has been nagging me in the back of my mind. That is, build time and complexity. I have to admit that I have been seriously wooed by the RV12 because I think it takes all the guessing out of the project. Plus, the pulled rivets are a big plus (in terms of build simplicity). But as much as I think I might be able to "accept" a 12, I really want a 7, not an LSA. My buddy kind of shook his head and said "you only get one shot." Some of you proved that wrong, but I think it will be one shot for me.

Thanks for the feedback.

 

[L.Adamson]

That said, if I ever build another AC, it WILL BE VFR dirt simple. Van really does put a lot of thought (my opinion) into the creation of his airframe kits. And as long as I was following Van's instructions and drawings, I made steady progress. Once I decided to "personalize" the finishing stages of the AC, I slowed down to a crawl, and spent time learning (this is the education / recreation part of EXPERIMENTAL) what was appropriate for AC usage, and proper implementation.

I didn't deviate from the plans much, with my 6A; but I did want it to be a comfortable and equipped cross country machine. Personally, I wouldn't give up my CS prop for anything. Same goes for the electric pitch, aileron trim, and elec. flaps. Even threw in a heavier Garmin 696 to replace the 496.

As it turns out, it's fast. Faster than any 9's I fly with, and only slightly slower than a much less weighing 6A that I fly with. But then I don't have my main gear fairings yet.

I've flown with a 7 fixed pitch, as in the original question, but it was still in the break-in period and no fairings; so I have no comparison data.

Point is, I'm not into the total "keep it light" crowd. I can always fly a single seat Pitts for
the feel I suppose (used to fly Pitts S2B), or build a RV3 for local flying.

Someday I might even replace my heavy six pac panel for a light weight glass one. I've got the heavier starter motor too, and my painted plane naturally weighs more than an un-painted one. Yet it's very responsive on the controls, and just feels good!

L.Adamson -- RV6A/ 0360/ Hartzell C/S

 

[hecilopter]

Constant speed prop

Keep it as simple as you want, but I would not give up the Hartzell B/A constant speed prop for anything. It gives noticeable take off and climb performance (for those times when you are heavy, high, hot or all three). It gives the best speed and the most economy at the same time. Lower vibration levels at faster speeds, less fuel burn.

Just me, but I know several fellow RV-er's who have a fixed pitch and are wishing they had the constant speed. If they could change one thing, that is what it would be. It's more money, but very worth it in my opinion. I would give up panel toys for it if that made a difference in the decision.

I would do it again in a minute, and if I were buying a used RV, I would not get one without a C/S prop. If you haven't already, you really need to take a ride in a fixed pitch and then a constant speed plane. Max takeoff and then equivalent cruise speed. You have to "feel" it to believe the difference. A C/S literally throws you back in the seat!

Maintenance - it is about an $800 overhaul every 6 years or 2000 hrs, whichever first. Based on 6 yrs, that is about $150 a year for the performance increase. Barely a blip on the radar for an airplane IMO.

 

[L.Adamson]

And I'm sure that Larry Adamson will disagree.
I've had electronic ignitions and I've had C/S props. These are all nice. But for an RV, I now fly a 16 year old -6 with F/P 3-blade Catto and 2 mags and wouldn't have it any other way. Of course, I'm a "basic" sort of guy. I also have manual trim and flaps. I had an auto pilot for several years, but since Ann flies with me almost all the time, I took it out.

Of course I disagree! And I wrote my complete reply before seeing yours...

L.Adamson --- RV6A with heavier leather seats...too

 

[RV7AV8R]

Andy, I had a fixed pitch Sensenich on my RV7 and switched to a CS Hartzel. The differences that I have noticed are: CG is better with the CS in this airplane giving you more baggage weight allowed, the top speed and fuel consumption is so similar I would call it a wash, CS climbs better but with the Sensenich you will out climb almost anything else but an RV with a CS, the CS makes it easier to control speed if you are going to formation fly, and finally the CS makes it much easier to land. For me this last and unexpected difference has made me real happy with my choice.

 

[L.Adamson]

and finally the CS makes it much easier to land. For me this last and unexpected difference has made me real happy with my choice.

That's the benefit that really helped my decision. With a C/S it's much easier to fit into a crowded pattern. I have the choice of speeding up, or slowing down, as well as being high, or lower. Yet can easily decelerate and get on the runway where I want. It's especially useful when a "slug" Cessna does seems to be doing a turtle like touch & go in front of you.

L.Adamson

 

[s_tones]

cs prop

Since we're on the subject...kinda;
Would anyone like to summarize the operation of the cs prop.
I fly a fixed and would be interested in knowing how you manage the cs during take-off, cruise, landing and do's/don'ts.

Steve

 

[airguy]

Are you inquiring as to how the prop does what it does mechanically, or rather how it is used operationally by the pilot in flight?

 

[hecilopter]

Final C/S observation

I have yet to talk to anyone with a constant speed prop that wishes he had a fixed pitch. I know several that wish the other way.

 

[Ron Lee]

I have an O-360 and FP prop and would prefer a CS prop for the reasons already stated. Yes the plane does fine compared to a Cessna but is sluggish compared to CS RVs.

One electronic ignition plus one mag is a good way to go in my opinion.

 

[AndyRV7]

OK, some good feedback. Thanks!

How about this then. When would the project go awry? That is, if I went CS, or wanted an IFR panel, or wanted electronic trim and flaps, or if I wanted electronic ignition, when would I be deviating from simplicity and low cost? Or is it incremental? Are some of these things a no brainer when it comes to sticking to the plan? That is, are some of them simple and relatively inexpensive. Or do each have incremental costs? Is there any sweet spot in the build choices?

I think I would like to go with a CS prop maybe before some other indulgences, but it just seems so easy to keep rationalizing more and more amenities. Is there a logical compromise, or is it just a linear continuum between cheap-simple and expensive-complex? You pick how far toward either end you want to be and try to stick to the plan!?

If I let my mind go, I can imagine an IFR panel with a CS IO360, with horizontal induction (if that is even possible), with electric flaps. I like the idea of manual elevator trim. Obviously, the panel is going to add expense versus a night VFR panel, how about weight?

Thanks for helping me work through this. I guess I don't know as much as I hoped about the different choices yet.

 

[N941WR]

Andy,

You have received a lot of good advice in this thread but one thing no one mentioned is the ability to upgrade.

There are a good number of FP duel-mag RV's (in all verities) out there. You always have the option of upgrading your RV later, if you so desire.

Thus if your goal is to build an RV with a full IFR panel for long X-C trips, then do it. After you build up some experience in the plane, you can sell your FP prop and mag's, and replace them with whatever you want. As someone else said, a FP RV will out climb just about everything but a CS RV. You really have to experience this to believe it.

BTW, if you are not into acro, I suggest you take a serious look at the -9. You don't give up much speed and get a much more stable aircraft in return. In other words, it is a better instrument platform. (OK, LA, hit me.) It all comes down to what you want in your plane.

 

[Mel]

Andy,
Bottom line is do what YOU want. There are advantages and disadvantages to all sides. Everything is a compromise.
The RV was originally designed as a light weight sport plane.
If you want a constant speed prop, then by all means, get one. They are great. Personally, I prefer the simple, light weight, minimum maintenance, good performance of a fixed pitch. As I have said before, I have flown my -6 out of Leadville, CO (9926' msl) in the summer with a "tired" 150 hp engine and a wood prop. No Problem. Yes a C/S will out climb it. But a F/P on an RV is way more than adequate.
I'm based on a 1500' private strip in Texas and we have our share of density altitude.
And BTW, in spite of what has been said, there ARE people who have switched from C/S to F/P.

 

[JHines]

Electric flaps are already standard for the RV-7.

Electric elevator trim is supposedly about the same total weight as manual elevator trim.

For CS, in addition to the prop you need a governor, control cable, and a manifold pressure gauge (which might not be present on a FP ship). So that is an example of an upgrade that is "not linear" to use your terminology.

An IFR panel won't necessarily add a lot of weight depending on what you consider to be a "night VFR" panel and what level of redundancy you're comfortable with.

The more amenities you add the higher the empty weight and so the higher the operating wing and power loading and inertia. If you're in to aerobatics that might mean a lot to you, if you need a cross-country machine, not so much.

For me, I started my "mission analysis" by adding up the expected weights of pilot & passenger, baggage, and fuel to published empty weights and compared the resulting gross weight to Van's recommendations.

If you look at Dan Checkoway's site (link below), you can see the weight and CG implications of several engine/prop configurations.

Also, Mel makes a great point about performance - what is your personal desire and frame of reference? Example - for me a heavy IFR RV-9 will still blow the doors off my old spam can. Other folks aren't happy unless they are climbing at 2000 FPM and cruising at 180 knots.

http://www.rvproject.com/wab/

 

[RV6_flyer]

OK, some good feedback. Thanks!

How about this then. When would the project go awry? That is, if I went CS, or wanted an IFR panel, or wanted electronic trim and flaps, or if I wanted electronic ignition, when would I be deviating from simplicity and low cost? Or is it incremental? Are some of these things a no brainer when it comes to sticking to the plan? That is, are some of them simple and relatively inexpensive. Or do each have incremental costs? Is there any sweet spot in the build choices?

I think I would like to go with a CS prop maybe before some other indulgences, but it just seems so easy to keep rationalizing more and more amenities. Is there a logical compromise, or is it just a linear continuum between cheap-simple and expensive-complex? You pick how far toward either end you want to be and try to stick to the plan!?

If I let my mind go, I can imagine an IFR panel with a CS IO360, with horizontal induction (if that is even possible), with electric flaps. I like the idea of manual elevator trim. Obviously, the panel is going to add expense versus a night VFR panel, how about weight?

Thanks for helping me work through this. I guess I don't know as much as I hoped about the different choices yet.

It all boils down to personal preference. The difference in cost between simple and fancy is only a few percent of the total cost. Weight is another matter. The weight difference between simple and fancy could be 20%.

Some builders have more electrical skills than mechanical skills and can do the electrical stuff simply. Others have a hard time with electrics and stick with manual systems. I am an electrical engineer that know and understands electrics plus am also an A&P that understand the mechanical.
I have all manual elevator, aileron, and flaps. The electrical systems cost more and take longer to install.

There is no such thing as a free ride. It is going to cost you money and time. Each builder has different abilities, time, and budget. All these factors go int the decisions needed to be made the aircraft suit the individual builder.

 

[AndyRV7]

This is all good info. I never considered being able to upgrade. That is a comforting thought.

I DO want to be able to do loops and rolls and whatnot, but that is just going to be for fun. I don't plan to be pusuing an airshow career. So the 9 is nice but not going to fit the bill. I was actually introduced to the 9 first, but I like the 7 now. As far as IFR goes, I think I am like a lot of people. I want to be able to fly on days when the 2000'-3000' scattered might fill in en route, and not have to worry about it. Or on a day when it is already a little thicker but not going to get much lower. I hate to use the term soft IFR, but I guess you guys know what I mean. My main reason for wanting to do the build is to have a X-C platform. That means at least night VFR, and the speed of the RV will let me travel from NJ to Myrtle Beach or Orlando to visit my family without too much trouble. If I can do some rolls on the way, then that much better!

I appreciate all the patient responses. I'm sure I've read a ton of the similar discussions myself already, but I still seem to be sitting on the fence. I'm going to look at the site with the motor prop combo weights. And then I guess I am going to get out a pad and start organizing my thoughts a little better. Maybe I need a pros and cons kind of analysis to firm things up!

 

[s_tones]

What I meant was operationally

OK, I know it's hijacking a bit so I'll post it as a new thread (cs management)

 

[grjtucson]

I voted for C/S before I voted against it...

I've been pretty well set on a Hartzell B/A prop from early on, so much so I bought a PCU5000 governor in the last group buy. I ended up with an engine that's setup for a fixed pitch prop. It's got the hollow crank so I can change it, but...

...I decided not to a couple of weeks ago. Here's why:

- Cost (these are ballparked):
$6,300 Hartzell B/A
1,000 Governor
200 Oil Line
80 Control Cable & Bracket
25 New crank plugs
$7,605 Total

$1,650 Catto 2-Blade (no time to wait for 3-blade)
$ 500 Bolts/Crush Plate/Ext. from Saber
$2,150 Total

$5,455 Savings. That is, as they say, non-trivial. Shipping and swapping some spinner parts should be a wash or close.

- Convenience: If I didn't have to add a rear plug to the crank and fit the oil line, I might have stayed the course. Now I get one less cable and firewall penetration, less stuff on the back of the engine, lower maintenance costs, and an easier time fitting the spinner (by the look of it). Installing the FP is just flat-out easier from about any angle. As to flying it, one less knob and a handful fewer checklist items during several phases of flight.

- Flexibility: I can change my mind and upgrade with relatively little work or cost penalty. I'll still have lots of work to do and money to spend, but very little to redo and very little sunk costs. If this was a permanent choice I'd have stayed the course for sure.

- Minimum Sacrifice: The obvious downside is lower climb performance, more work for aerobatics and formation, and more work to slow down and land. If you don't like the term "more work" then read it as "diminished flexibility," which also applies nicely to flying in rain. These are factors, but for me my primary mission is cross-country travel in dry skies. According to Craig I won't be giving up anything at top speed or cruise, and efficiency should be close as well. Even if he's optimistic, I'm convinced we're still talking minimal loss. All told, though, I don't find $5,000+ worth of value delta here.


The weight difference on an RV-7 has concerned me and a recent call to Van's didn't help. I called to ask if they could get the 70amp Plane Power alternator at their pricing since it weighs 3 lbs more in a good location for added weight. I got a pretty condescending lecture about not building heavy, not reading the Internet or listening to other builders, and a description of this person's plane and how it was 160hp wood prop and how it wasn't nose heavy. I was further criticized for choosing a Sam James cowl, with him saying it couldn't possibly be less drag since there was no way Van would have left that many knots behind.

As you might guess, I was not impressed with this call. Reminds we of something I heard early in my build, "we don't buy from Van's because of the warm fuzzy customer service." So the single downside to my decision thus far is...

- Confusion: I have no idea whether to order a heavy extension or standard, or add a weighted crush plate, or try to get a reasonable price on the heavier PP alternator, all because I don't know how my RV-7 weight and balance will work out now that I'm putting on a light prop. I am also concerned that the starter will spin it too fast 'cuz its so light and I've read that starting can be difficult.

Maybe the guy at Van's was right, I shouldn't read the 'net.

Hope this is useful to someone. If anyone can "weigh" in on the nose-heavy issue, I'd appreciate it.

George

 

[Ron Lee]

There should be enough weight and balance info available to ease your mind on the prop.

When I had my Aymar Demuth two blade wood prop and PC 680 battery, I had problems starting because of not enough battery or prop inertia or something. The prop would not spin through in some starting positions. I had to stop, wait a bit then re-engage the starter. I changed to a PC925 battery and those problems went away.

Now with a 3 blade Catto I may go back to a PC 680 to see how it works and save about 10 pounds.

 

[N941WR]

George,

I seem to recall most of the fwd w&b issues had to do with -7A's, not -7's.

Check Dan's w&b page for more details. Also, Van's makes a longer engine mount for those who are going with lighter engines (O-320). You could always put that on your -7 and shift the W&B forward.

 

[n5lp]

One minute

I have a fixed pitch Sensenich on an O-360 and I find it a good combination. A constant speed does indeed push you back in the seat on the take-off roll but shortly after liftoff most CS drivers pull the RPM back to around 2,400. That is where I am already so no difference in climb performance from here on up, although there is additional performance available with the CS if the pilot chooses to run the RPM up. So the big performance difference is for about one minute normally, oh, and with the FP you can still takeoff shorter than you can land so it is hardly an important difference.

It is real nice to be able to cruise at a lower RPM, but for the money I can tolerate the slightly higher buzziness. There really isn't a level flight speed difference, in my experience. I'm sure they exist but I haven't seen a stock RV with the same horsepower that was noticeably faster than mine in cruise. They can descend faster however, as I have to reduce power to keep the RPM below redline.

Airplanes with the different style props do land differently. The constant speed airplane decelerates much faster which in my experience means you need a faster approach speed with the CS. If you use the correct approach speeds I think the actual landing difference would be very small without an obstacle. With an obstacle the CS should be quite a bit better because of the steeper possible approach but this is hairy edge stuff and I don't expect to ever use an airport where it would make a practical difference.

The fixed pitch prop is a royal pain for formation! If you are closing on someone from the rear you either have to do it very gradually or go to idle when you are getting close. You also have to keep on top of the speed more as deceleration happens so much slower. I don't live in hotbed of formation flying so it is a non-issue for me.

As others have said, there are compromises with every choice. I have thought seriously about changing to a CS but when it comes down to plunking down the money, it just hasn't seemed important enough.

By the way, the Sensenich for the O-360 is a very heavy prop, not much different than a CS.

edit: Oh yeah, I have dual mags and a carb also. Amazing the crude thing gets off the ground, isn't it?

 

[uk_figs]

Lonely out here

I built my -7 with the standard ECI 0-360 kit, dual mags and the Vans recommended Sensenich prop, I read this site and Vans and other white papers on the trade-off's while I was building. I am in the Phase 1 test period and have a total of 35 hours (actually 2 more today so 37). I am not a high time pilot (250 hours) so I cannot offer gobs of experience as the only constant speed planes I have flown were a Mooney, Arrow and Great Lakes. My reasoning was as follows:
Key Pros:
1. Keep the engine and prop combo as simple as possible, also allow the engine to run autogas if it becomes necessary
2. Keep the weight down (more on this in the cons section)
3. I am more comfortable with the FP (one less lever to deal with) as my Pacer is FP also.
4. Save some money and put it toward my glass panel which I love more every day.
Key cons:
1. The FP combo is lighter so the CG is further aft than with the CS setup, this does effect the baggage capacity limit at min fuel, as a result I have limited my max baggage to 80Lbs. You can fit a dynamic damper to the flywheel which adds 15Lbs and I could have used a heavier starter (went with skytech) which would have helped
2. Speed management in the pattern area has to be taken seriously, the first couple of times I came whistling into the downwind leg and needed speed brakes to slow down for the typical Cessnas in the pattern, I now enter the pattern at around 120 to make things manageable.
3. CS is also better for aerobatics particularly on the downline as you do not have to pull power to manage RPM

From what I have read the cruise is about a wash and as noted in elsewhere in this thread I dont think the rate of climb is really an issue, to keep CHT's down I rotate at 65 and let the speed build to about 140 as suggested by others on this site, if I pull the stick back I can easily see 3000 ft/min and my field elevation is 4600 ft.
The eci kit contained the constant speed governor etc which I have kept so I can change my mind in the future but at this point I have to say I am very happy with the setup. There is more on my site about the decision process but like many things on the RV there are numerous trade offs that can be made and it ends up being a function of personal preference, aircraft mission, time and of course money.
Whatever choice you make it is a great flying plane

 

[L.Adamson]

BTW, if you are not into acro, I suggest you take a serious look at the -9. You don't give up much speed and get a much more stable aircraft in return. In other words, it is a better instrument platform. (OK, LA, hit me.) It all comes down to what you want in your plane.

What's interesting, aside the fact that my 6A is faster and livelier ; is that it trims out so well. And this is with elec. elevator trim, and that little servo operated hinge trim out on the right aileron. I don't have have those trim speed controllers either.

But seriously.............I do know that the 9 is more stable as an instrument platform......
at least I think -----------because with 2 axis A/P's it just doesn't make much difference.

L.Adamson --- RV6A/ 0360/ Hartzell C/S

 

[roadrunner20]

I've been pretty well set on a Hartzell B/A prop from early on, so much so I bought a PCU5000 governor in the last group buy. I ended up with an engine that's setup for a fixed pitch prop. It's got the hollow crank so I can change it, but...

...I decided not to a couple of weeks ago. Here's why:

- Cost (these are ballparked):
$6,300 Hartzell B/A
1,000 Governor
200 Oil Line
80 Control Cable & Bracket
25 New crank plugs
$7,605 Total

$1,650 Catto 2-Blade (no time to wait for 3-blade)
$ 500 Bolts/Crush Plate/Ext. from Saber
$2,150 Total

$5,455 Savings. That is, as they say, non-trivial. Shipping and swapping some spinner parts should be a wash or close.

George

I did as you've addressed above. Hollow crank, FP-less maintenance & less $$$. The only downside with my FP is it limits my baggage due to CG issues especially with low fuel. It does impact my arrivals on cross country.
As far as performance, I still get ~1800+ on climb. It also sets me back into the seat on takeoff roll which is achieved in 4.5-5 seconds.
Someday I may go CS, but not now.

 

[mannanj]

What If?

This could go on and on, so I'll add my two cents. I have an RV-8 with an IO-360-A3B6D angle valve 200 hp with a constant speed prop. The engine weighs about 40lbs more than the 180hp and the prop probably adds 20lbs to the wood FP prop.

This scenario probably would be good for the W&B on an RV-7.

In my situation, I'm nose heavy in the -8 flying solo. It makes it not as sexy handling as say a -4, but, OMG does she climb and go fast. With my wife and baggage at full gross, 7500 ft, full throttle, 2330-2350 rpm, the Grand Rapids EFIS says that I'm at about 73 percent power and that my TAS is 190+ kts. This Grand Rapids TAS speed has been verified by the GPS on a 4 way average.

Originally I was going to equip it with an O-320 with a wood prop. I stumbled upon the engine from a Mooney 201 at a price I couldn't refuse. I wouldn't trade this combo for anything that I can think of.

I have a relatively simple panel with the GRT Sport, Tru-Trak autopilot, and a Garmin 396 with weather.

Yesterday I came back home to North Georgia from near Austin TX. in 5 hours and 10 minutes total time. This was 770 nautical miles with a potty break of about 45-50 min at Vicksburg. I can't beat this time on Delta.

TAS was about 190 kts and had a head wind starting at 15 kts and diminishing to 0 at about the Alabama/Georgia border.

These are amazing airplanes and no matter how you equip it, you will be awed at the performance when you fly it.

Strive to build it light. Watch for bargains as you build. Don't be afraid to add the 200hp engine with the constant speed prop, especially if you're going to do a lot of cross country flying. The plane will still do "gentlemen's aerobatics so that you can impress your neighbors and be a super hero to the Cessna Drivers at your local airport.

Just read David's post below and can't disagree.

I have to go back to my old flight instructor's quote. "You fly to go fast, if you don't want to go fast, drive.:

 

[David-aviator]

......If anyone can "weigh" in on the nose-heavy issue, I'd appreciate it.

George

George here are the numbers for a my RV-7A with the Barrett Lycoming IO360 parallel valve engine, 3 blade Catto and the Odyssey 680 on the firewall.

xxxxxxxxxxxxxxWeightxxArm xx Moment
Main wheel, right 417xx93.73xx39,085.41
Main wheel, left 412xx93.73xx38,616.76
Nose wheel 244xx37.13xx9,059.72
Totals 1,073xx86,761.89
Empty C.G. 80.86"

I have this data on a spread sheet and here are the numbers for a typical cross country flight.

xxxxxxWeight xxArm xxMoment
Aircraft 1,073xx80.86xx86,761.89
Fuel 252xx80.00xx20,160.00 (42.00 gal)
Pilot 210xx97.48xx20,470.80
Passenger 210xx97.48xx20,470.80
Baggage 55xx126.78xx6,972.90
Totals 1,800xx154,836.39
C.G. 86.02
CG envelopexxInWeightxxIn CG

The CG moves aft as fuel is burned but even with 10 gallons remaining the CG is forward of the aft limit.

I do not believe a light weight engine and prop are a cg problem and I much prefer this arrangement as to what I had with the H6 Subaru where the nose gear weighed in at 364 pounds (which is typical of many angle valve 200 hp cs Lycomings also).

It all comes down to personal preferences. If this were a time of war and power and speed were essential for survival it would be a different matter but for personal non-interventional flying, light weight suits me just fine at his stage of life.

By the way, the numbers above are for illustration only. My passenger (wife) does not weight 210 - its more like 115.

(Sorry about all the x's, but I don't know how to preserve the spread sheet format with its tabs and separations.)

 

[gasman]

BUT WHAT DOES IT COST TO MAINTAIN

Pricing Comparisons When Considering a Sensenich Fixed Pitch Aluminum Propeller to a Hartzell Constant Speed Propeller.

TBO:

* Sensenich: 2000 hours and no calendar! 20 cents an hour!
* Hartzell: 2000 hours or 6 years whichever comes first! That's 333 hours a year and if you fly that much it costs $1.00 per hour. If you fly 100 hours per year it will cost you $3.33 per hour.

Routine Overhaul At TBO:

* Sensenich: $400.00
* Hartzell: Prop and Governor $1850 to $2000 Minimum!


Taken from Sensenich web site.

 

[RV7AV8R]

Dave, A CG issue only shows up generally as you burn off fuel. If you punch in those cross country weights with 5 gal of fuel left in the tanks, will you still be with in the CG range?

 

[RV7AV8R]

Sorry Dave, I see you already answered this isn your post. I should read more carefully.

 

[Webb]

- Cost (these are ballparked):
$6,300 Hartzell B/A
1,000 Governor
200 Oil Line
80 Control Cable & Bracket
25 New crank plugs
$7,605 Total

$1,650 Catto 2-Blade (no time to wait for 3-blade)
$ 500 Bolts/Crush Plate/Ext. from Saber
$2,150 Total

$5,455 Savings. That is, as they say, non-trivial. Shipping and swapping some spinner parts should be a wash or close.

George

Solid math and makes sense. According to something I read (from Vans I think), the CS will save you about a gallon to a gallon and a half an hour. Based on fuel cost, it should pretty much be a wash over the time until TBO for your engine.

Pay up front or pay over time.

One thing I would definately take into consideration is whether you fly in instrument conditions. CS is definately a better choice for IMC.

 

[David-aviator]

Dave, A CG issue only shows up generally as you burn off fuel. If you punch in those cross country weights with 5 gal of fuel left in the tanks, will you still be with in the CG range?

Ten gallons leaves the cg just forward of the limit, 5 gallons and it is aft of the limit.

Again, all this is a matter of personal preference. Some guys prefer flying with a forward cg as the airplane is a bit more stable. But I found with the nose heavy Subaru install, I had to add ballast at the HS to have a decent airplane feel on final. I like it trimmed up and could not trim out all the nose down pressure. With the cg well aft as with the Lycoming and FP, this is not an issue. Also, an aft cg will give a bit more efficiency as there is slightly less airframe drag but don't ask me to prove that with an airplane this size. With transport airplanes it makes quite a difference and operators do load to within aft cg limits to save fuel and of course money.

 

[AndyRV7]

This has been very educational. Thank for all the feedback. Wait until I start asking about avionics and redundancy!!!

 

[penguin]

Andy,

Here's another couple of thoughts. If you can't afford a c/s prop & governor now then at least specify your engine as a c/s engine - that is make sure it has a governor pad and drive train, the governor adapter installed, the oil pipe from the gov adapter to the front of the crankcase and the bung at the back of the crank installed. If you decide to go FP then blank off the governor adapter (blanking plate is less than $10) and install a crankshaft plug, the external oil pipe will return the oil from the crank bore so you don't have to pierce the rear bung. If you decide to trade up to a c/s prop it will now be much more straight forward.

You will save gas and/or go faster at low level with a c/s prop, but as others have said, figure out what you want to do with the airplane and equip it accordingly.

Pete

 

[Brantel]

My engine has a hollow crank and the provisions for the rest of the gear but the plane will be FP, Carb'd and with two regular old mags.....

Reason = lowest cost to finish my plane and get it flying!

 

[dtw_rv6]

I have an RV6 with a Fuel Injected Superior IO-360, two mags, and fixed pitch Sensenich.

It was very inexpensive for me to have the engine built to take a constant speed prop, so I did this in case I ever wanted to sell the engine. I really have no desires for a constant speed prop after flying for 2 years now.

Slowing down is really not a big deal with the fixed pitch. In fact, I hardly noticed the difference after the first few flights. I did my transition flights in a -6 with a constant speed prop. The difference is noticeable, but easily adapted to. While the fuel savings is arguably higher with a constant speed prop, I'd recommend you look at total operating costs. Maintenance is simpler, and I've never had a problem climbing out of a 2200' grass strip at gross limit.

The mags are the only area I've considered changing, but I'm still on the fence. It appears that one Mag and one EI is what I might consider when my pair of slicks need rebuilding. The engines with EI run noticeably smoother than the mag powered machines. Dual EI is too complex for me since I would insist on dual batteries and redundant power.

I once overheard a saying that I repeated many times when building -- If you wonder if you need an {insert doodad name here -- constant speed prop, gyros, cameras, paint, turbocharger, IO540}, toss it in the air. If it comes back down, it's too heavy.

Don't get me wrong, there are a lot of RV's out there with the high end performance equipment, and the people who fly them are probably very happy, so this all boils down to your preference / tolerance for risk.

Don

 

[gasman]

Added weight, no matter what it is will change the way the aircraft feels. If you plan to travel a lot, then a c/s prop might work well for your w+b and save you some fuel.

But if most of your flying is a 45 minute flight in the evening after work and short trips of 400 miles or less, then the F/P prop will give you a more balanced aircraft.

My 6A is a 320 metal F/P, the a/c is lite and it flies it's BEST when I am solo with only about 7 gallons of fuel in each tank. I enjoy flying this aircraft for the feel of what Van designed. During my evening flights, I fly at about 2000 agl leaned 21 21 indicate 140 stat and enjoy the view through the tilt up and burning 4.8 gph. I can trim my manual trim for level flight and not change the trim for several days.

A friend changed to a C/S in his 6, and now needs full trim for landing. If you never fly a lite RV, then you will never know what your missing. Think about what you want the airplane for.

 

[airguy]

Agreed, it really depends on what kind of flying you intend to do.

In my case, I'll be doing lots of long XC trips, primarily for business travel - which means hard IFR, autopilot, and CS prop - but at high cruise altitude with the 9 wing, extra weight does not impose much penalty. For pure fun and aerobatic handling, I would probably go with a very light 7 and bone-simple panel, with a 3-blade Catto FP.

 

[Jconard]

Actually, for aerobatic work, you would be well advised to have a CS prop. I would recomend a composite counterweighted design.

In acro as in other regimes, the cs prop improves the dynamic behavior of the airplane....by reducing dramatically the rate by which it picks up speed when nosed over. In normal flight this also adds a bit of easy stability for turns and general flying as well.

I have flown both types, and lived with a fixed pitch acro airplane for years...you really have to be careful not to over speed the engine in fixed pitch acro work.

 

[rocketbob]

for all of you FP prop guys

I'll challenge you to do something. For a week, drive your cars in 3rd gear, and in 3rd gear only. Then tell me how much you like the simplicity of driving that way. No gears to shift, nothing to break, yada yada yada.

Now tell me why flying behind a FP prop is any different?

I cruise 2300/25" in my RV typically. Nice and quiet there. Nothing bugs me more than an engine screaming at max RPM when it doesn't have to.

Also consider the longevity of your engine and its parts. Think about how many fewer revolutions your engine will turn over its life and how much the wear and tear is reduced by simply reducing your cruise RPM's.

 

[David-aviator]

I'll challenge you to do something. For a week, drive your cars in 3rd gear, and in 3rd gear only. Then tell me how much you like the simplicity of driving that way. No gears to shift, nothing to break, yada yada yada.

Now tell me why flying behind a FP prop is any different?

I cruise 2300/25" in my RV typically. Nice and quiet there. Nothing bugs me more than an engine screaming at max RPM when it doesn't have to.

Also consider the longevity of your engine and its parts. Think about how many fewer revolutions your engine will turn over its life and how much the wear and tear is reduced by simply reducing your cruise RPM's.

Oh come on, Bob, it isn't all that bad.

Some years ago I bought a first run 0360A4M out of Cherokee. It had spent its entire life behind a fixed pitch metal prop and at over haul the crank was found to still be within new limits. In fact the overhaul guys said they could clean up the valves and cylinders, put it back together and it would run a long time yet as is. That seldom is the case with an IO360.

 

[Mel]

I'll challenge you to do something. For a week, drive your cars in 3rd gear, and in 3rd gear only. Then tell me how much you like the simplicity of driving that way. No gears to shift, nothing to break, yada yada yada.

Now tell me why flying behind a FP prop is any different?

OK, I'll tell you why flying behind a F/P prop is different.
This is an "apples/oranges" comparison.
If it were apples/apples, you would see single gear cars on the road. Fact is, you don't. And haven't in about 100 years. It simply doesn't work.
On the other hand, airplanes with F/P props have been flying very successfully for over 100 years and continue to do so.
This is a very good example that you can make statistics say anything you want if you present it a certain way.

 

[N941WR]

...Also consider the longevity of your engine and its parts. Think about how many fewer revolutions your engine will turn over its life and how much the wear and tear is reduced by simply reducing your cruise RPM's.

Bob,

It has to do with the power produced, not the RPM. This is why some small car engines can run for 200,000 miles while turning 4,000+ RPM's at highway speeds and V8's turn less than 2000 RPM's.

Since our engines TBO are determined at the continuous power RPM, there is nothing wrong with running an engine with a FP prop at redline when producing 75% power or less. Like WOT at 8,000? DA.

Granted, the noise may be an issue for you but it won't hurt the engine.

 

[rocketbob]

No matter how you want to cut it there's a significant performance disadvantage with a FP prop.

I've been on many trips with guys with FP props. Given the same engines, we always have to throttle back for those guys if we're flying formation, or we'll lose them climbing out. Some of the same guys have upgraded to Hartzells and in their words, there's no comparison.

The savings up front does not pay off in the long term.

One of the reasons why I like Rockets is the ability to loaf the engine at 2100/19" running the same speed as a RV. You simply cannot hurt the engine running at that power setting and its only possible running with a CS prop.

Another point of data. I have some friends with Super Cubs I fly regularly with. While they're running 2400rpm cruise I can pull up beside them, run 1700/17" and burn 3.5GPH while they're burning 9 or better. You simply can't do that with a FP prop.

 

[N941WR]

No matter how you want to cut it there's a significant performance disadvantage with a FP prop.

I've been on many trips with guys with FP props. Given the same engines, we always have to throttle back for those guys if we're flying formation, or we'll lose them climbing out. Some of the same guys have upgraded to Hartzells and in their words, there's no comparison.

The savings up front does not pay off in the long term.

Bob,

I agree with you that the mack daddy for performance is a CS prop, no question. Just like putting a bigger engine in your plane helps with all aspects, other than weight.

Getting back to the question, can a guy fly a FP, O-360, with duel magnetos? I think we have all answered "yes". For those who don't fly formation, could care less about being the first one to 10,500', and don't care if they are the first one to the local fly-in hamberger joint; then a FP prop will work just fine. Heck, even for acro it will work, you just have to remember to pull back on the throttle when the nose is pointed down.

As for me, the few times I have flown formation, they have to throttle way back because with only 135 HP on tap, I can't hang with them. Usually when we do a lunch run, I depart first, the rest of the RV's take off after me and pass me in flight and when I'm on downwind, I see the last of the RV-6, -7, & 8's rolling out on the runway.

Would I like to have a bigger engine with a CS prop? Yes & no. I like having the large useful load the light engine/prop combination gives me. Would I like to go faster? Yes, but I currently have a climb prop on my -9 and when I replace it (soon, I hope) I expect to jump from 165 MPH to around 180 MPH cruise. That is only slow when talking RV's.

The issue comes down to what kind of flying Greg wants to do and how much money he wants to spend on the initial build. As I said in an earlier post, he can upgrade to a CS prop later and sell his FP prop, if he elects to do so.

 

[Mel]

Bob,
I have no argument that C/S props have a definite advantage. That's a given. What I have a problem with is your original comparison making it sound like a F/P prop will not perform at all. i.e. A single gear car will not perform.
As I have said many times, if you want a constant speed prop, then by all means, get one. They are great. But don't make it sound like a F/P won't work. They do work, and very well.

 

[L.Adamson]

As I said in an earlier post, he can upgrade to a CS prop later and sell his FP prop, if he elects to do so.

True....

But then you have to change the panel for the blue prop knob and route the cable.

Then you have to build a new spinner and paint it.

Then do what you have to do with the engine plugs, and route the oil line up through the baffles.

The better option is to just do it now, and be done with it! Otherwise it's like flying a plane that's unpainted; and wishing it was. Painting later is just a big pain in the rear..............isn't it?

L.Adamson --- RV6A