T

tysonb

Member
This is pure speculation that is being fueled by the "panic" media. A what-if of sorts.

I've decided I want a 7 - it seems to be the best all around fit for my mission - fast, fun (yank 'n bank) w/some cross country mixed in.

With what appears to be the never ending rise in fuel costs, I have a nagging concern in the back of my mind that when I finish it the cost of avgas is gonna limit my flying. What if avgas shoots to 7~10$ a gallon? Will I be kicking myself for not building a 9 w/a 135hp? Or will I regret not building the 7 because of the limitations on the 9's airframe (no aero)? As my signature suggests, I've decided 7 - but every morning on the news there is the panic inducing "... fuel prices are on the rise, better top off the tanks..." I know most of it is blown WAY out of proportion and its the media making to stories more "gripping" but there is still that little voice in the back of my head "fuel prices are gonna kill you"

Comments and opinions greatly appreciated - this is probably along the lines of "tools sure are expensive"/"if you can't afford the tools you can't afford the plane" arguments. I can afford to operate it at todays costs, and I'm assuming I'll continue to move up at work and make more money, but I just don't know if my income is going to match my increased cost of flying.

Worst case I guess I could just sit in it making plane noises :eek:
 
disclaimer.......I M H O.......

........you will most likely not see THAT much difference in the two aircraft cost wise. Get the plane you want and don't look back! This is a sport/hobby. I gotta believe that most of us do this for fun - you should look at your plane choice the same way.

Planes are expensive. Fuel price increases drive up the costs of everything regardless. If the cost of fuel puts a hamper on the flying you do in a -7 it will do the same for the -9.

I M H O
 
If you're wanting to keep things at 135hp or so fuel burn rates, then put a breakable wire stop or detent on your throttle and go with any plane you want.
 
The detent on the throttle is a good idea...

I'm gonna go with the 7, I just needed reassurance that my conserns were unfounded... Seeing as this whole flying thing is totaly irrational anyway :)
 
The flying costs depend more on which motor you install than which model you pick- For the most part, except for hard acro, the two planes are so similiar that it does not matter. The longer wings on the 9 just make it a bit more efficient with smaller motors than the 7, but the differences are minimal- just compare the specs for the 160HP motors in each.

If you want to keep your future costs down, consider the alternative motors that can use mogas/ethanol if you desire.
 
Tyson,

I have a very accurate fuel flow gage....when I feel like conserving, I just throttle back until I see something that makes me feel better. My -7 will true out between 120-125kts on 4.5-5 gal/hr. Go with the -7.
 
Fuel is the cheapest thing I put into my RV-6. By the time I've paid insurance, hangar, etc, that is.
 
uncertainty

this is in the back of my head as well. what will avgas be next year? or next month? fortunately, the word "irrational" has already appeared, and those of us with enough disposable income to contemplate "hobby" aviation are better off than 98% of the rest of the world. to worry about the price of petrol at some indeterminate date is, indeed, irrational.
 
tobinbasford said:
Tyson,

I have a very accurate fuel flow gage....when I feel like conserving, I just throttle back until I see something that makes me feel better. My -7 will true out between 120-125kts on 4.5-5 gal/hr. Go with the -7.
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Tobin,

What is you engine and prop combo?

Thanks,

Paul
 
tobinbasford said:
Tyson,

I have a very accurate fuel flow gage....when I feel like conserving, I just throttle back until I see something that makes me feel better. My -7 will true out between 120-125kts on 4.5-5 gal/hr. Go with the -7.
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Thats more what I needed to hear. I like the 3k~4k$ first hour method of thinking - the first hour charge is the fixed cost for the year. After that its just fuel :D

I can putter around for 5gph and wind it up when I wanna go (which i'm sure will be most of the time)
 
Run yer IO 360 on mogas

Although many won't do this for perfectly understandable reasons I think there is enough evidence to belive your engine will make it to TBO if you run on super unleaded.

Yes its a a pain cus you have to haul your own fuel. But I did it for 7 years and its not that big of a deal.

This won't work for X country unless you go where your going on less than half a tank, but for around the patch it works very well.

You can't lean quite as agressively with 92 octane but GAMI suggests 100F ROP or 50 LOP up to 75% are conservative numbers.

Read John Deakinn's articles thoroughly and I think you will be convined your engine will be very happy (maybe even happier) on unleaded.

This does not apply to the break in period, even then I'm not sure i buy the "lead lubricates the valve seat" argument but I have no data to disprove it...So OK I'll go with 100LL until broken in and slosh a tank full of blue stuff in there on the odd cross country.

As others had indicated, the bigger engines only burn more fuel if you make them..Because you use full power on take off you will burn a little more than a small engine but in the grand scheme of things its a pretty small difference.

Frank

RV7a...Paperwork lost going to FSDO...Arrgh!
 
Buy a POS Dodge neon

Mine gets 38 to the gallon and can (does) pull a 1000lb trailer. (a 4*8 trailer will move one wing at a time to the airport..:).)

if everyone else has an SUV/Truck than your choosing to burn the same amount of fuel but "up there" rather than "down here"....:)

I think if fuel cost go really whacko then it will kill all GA, i.e it will make both an RV 9 AND an RV7 worthless no matter what engine you got under the hood.

Frank
Dodge Neon...Running...:)
 
tysonb said:
gonna limit my flying. What if avgas shoots to 7~10$ a gallon?
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AVGAS already has price tag like that here in Finland and at least it ain't gonna stop me building 7. In fact there should be about 25 % increase in beginning of next year in that price due some environmental taxes. I'm having mid income level but I do have priorities different compared to most (I think): wife&kid(s), food, decent living (house) and all aviation related. I would guess that for most W&K and food are the first but then they prefer their living in nice big house more important than I do -- I'm just fine when rain is not coming in and there is garage. With that difference, I'm going to pay my plane and flying in the future. It just your priorities -- what you think is important?

As said by others you don't have to fly full throttle... And there are engines which accept other than AVGAS if you wish to use. Typical combustion engines generally gives same amouth of HP with same fuel flow but in case you want to be precise you should find small differencies which may save some bucks.

of "tools sure are expensive"/"if you can't afford the tools you can't afford the plane" arguments. I can afford to operate it at todays costs, and I'm assuming I'll continue to move up at work and make more money, but I just don't know if my income is going to match my increased cost of flying.
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You said it, not us. :D I also count on that the income and flying costs will remain somewhat equal. However latest changes in past years and the future looks like flying costs are going high and fast. However that can't be everlasting and investing something more solid like MOGAS instead of AVGAS maybe wise. There are disadvantages on MOGAS but I'm sure there is cases were it is just sufficient. I will also brough up in salary discussions that my hobbies are becoming more expensive while salary will have only light increase and that will decrease my manner ja joy of living and therefore affecting also my labour input. We are just people -- what happens at your work will affect your personal life and vice versa in most cases.
 
The last time I checked, when the weather cooperates, we get almost the same miles/gal as automobiles, cover shorter distances between points, go 3-4 times faster, and arrive earlier refreshed. :D

Note concerning the alt engine choice: my Renesis rotary will weigh slightly less than an O320/360 w/CS prop firewall forward, provide 210+ glass-smooth HP on regular grade mogas (when needed), and still cruise 150 mph at 5gal/hr. Cost: around $8000 (w/new motor, redrive, and with electric inflight-adjustable propeller). Future costs <$1000 for complete rebuild, if ever needed- no one has worn one out yet.
 
Perspective

The events of the past couple of days has made airline travel a nightmare. This only makes RV ownership that much more valuable. Even for large distances, the RV really makes sense. Granted weather can be an issue but the thought of sitting in Terminals waiting for an airline is beyond comprehension.

My flight to Oshkosh took just over 9 hours door to door. This included just under 8 hours of actual stick time. (Phx area to Osh). I defy you to do this commercially. It cannot be done. Plus the view of the country experienced cannot be equaled.

In my opinion, RV ownership just became more valuable. Even if 100LL reaches $5 across the country and stays there, RV flying still makes sense.
 
Note concerning the alt engine choice: my Renesis rotary will weigh slightly less than an O320/360 w/CS prop firewall forward, provide 210+ glass-smooth HP on regular grade mogas (when needed), and still cruise 150 mph at 5gal/hr. Cost: around $8000 (w/new motor, redrive, and with electric inflight-adjustable propeller). Future costs <$1000 for complete rebuild, if ever needed- no one has worn one out yet.

Objection your honor..pure speculation...

Judge: you may be heard:

Well, your honor, this claim is made without any data to support it, in fact, the most recent test, conducted by Vans, sugests exactly the oposite conclusion on fuel burn. And, the experience of every single installation of this type has required more wieght and higher cost, without even one single exception.

Judge: Sustained...I find the comments unfounded, and frankly a self-serving, and of topic commentary within this thread, which was focused on the fuel burn of the rv series.

Seriously, I have tried to offer a little law and order entertainment, but let us not make claims until we are actually flying, especially claims which are unsupported by all the documented experience of all the other rotary installations.
 
Jconard-
I don't mind the humor nor the skepticism, but seriously, you need to do a bit more study my man before you start spewing biased nonfactual information around. Lots of working planes around do much better than the old-school Powersport numbers Vans reported on (variants of the 13B with non-adjustable mixture control). Did Van allow leaning to best mixture on the Lycs in the test comparison??? As I remember, the Rotaries outperformed the Lycs, with slightly higher fuel burns- an endorsement in itself imho.:rolleyes:

The Renesis motors are lighter, use an upgraded port engine used in the new RX-8 sports car; they produce more peak power at higher rpm, and get better "mileage" in the low and mid ranges than the older 13B engines. The induction system design is very important- They need to be tuned to sustain efficient higher "aircraft" engine speeds, with longer runners than auto designs.

Tracy Crook has kept and reported detailed measured records: he lists 6.0 gph at 172 mph @12.500' and 8.2 gph @ 202 mph at 14000' in his 13-B based Rotary RV4. His experimentation has discovered that the large rotor surfaces run very well with lean mixtures, w/o detonation- therefore, rotaries are ideal for turbocharging up to 300+ HP, and for leaning mixtures for cruise power.

Paul Lemar has Mazda "Lemans race car inspired" rotary engine dynographs published that detail miserly Rotary BSFC fuel burn numbers (example: 0.46 lb/HP-h @ 6000 rpm, 180HP output ((converted from 286g/kW-h)), lower than reported Lycoming burn rates under full power. This is a conservative engine speed for a rotary, but remember, the rotary has much more power available than the 0-360 Lyc, up to 234HP @ 9000 rpm. Bottom line, I do not see any big efficiency advantage either way. It's pretty difficult to find documented dynometer tests on Lyc products, but reported inflight burn rates over 20 gph at top speed (I assume 180 HP output) are common. Frankly, at the Renesis' peak power ratings, a power:weight comparison with the O-540 series seems more relevent.

Weight: Basic 13B weight is less than 200 lbs- add 44 lbs for redrive, another 100 for mounts, manifolds, fluids, ducting, radiator, etc, for a firewall forward wt of 345 lbs (tracy's measured numbers, btw). I dont know actual (measured) installed O-320/360 wet firewall-forward weight, but it is close.

Back to the original point though, the Rotary provides similiar power/weight as the more common Lycs, at significantly less cost, both initial and operational.
 
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Well,

I have raced in rotary powered cars, and against them...I think they are a neat little engine, and I follow the devlopmnent of an aircraft package with some curiosity.

When I see it, I will believe. I won't speak for Mr. Crook, but the numbers you quote are slightly slower/thirstier than an O-320 CS 6/7. his rv-4 numbers are fair, but nothing setting the world on fire.

He disagrees on the available power, suggesting that it should be limited to 170HP for continuous use. (See website).

As to the renesis, everyone who owns one has found them to be terribly thirsty is street application.

Maybe you will be the one to finally install one of these things, in a way that meets all the goals. But, you haven't and they haven't.

When you are flying your plane perhaps we will see. Frankly I hope such an outcome happens, then maybe my next RV will have one.

It is always possible to build a 12K engine package with a lyc, if you are willing to start with a used core, and do most work yourself, as I did. Not any harder than rebuilding a junkyard car motor.

Hope you do it...we can fly them off when you are done with the plane.
 
It is always possible to build a 12K engine package with a lyc, if you are willing to start with a used core, and do most work yourself

I just purchased a (nearly) new, 0-mile, Renesis 4-port engine, complete, for a little less than $2000 + $500 shipping...

Case closed, Your Honor! :D
 
future of aviation/ engines/mpg

Ok.... here goes :) I bought a 90 hp VW TDI for 13,700... Its Diesel and gets 51 mpg... it has ton -o- torque and can tow 1000 lbs. So I have a trailer to tow stuff with. I've save more money driving that thing.... not to mention no spark plugs//// no distributor.. no funky wiring..... oil change every 10k... and diesel engines will last at least 500K!!!! 51mpg hwy... 42 city. 53.002 mpg on a 222 mile stretch while drafting 18 wheelers... The same will be for our RV's soon... Somebody will come out with a 200 hp diesel... SMA has a 230 hp... and we will be flying so fast on so little.... 200 mph on 6 gal an hr. It's comming soon. Trust me.
Brian
 
I love to see a 180hp diesel if they can get the installed weight down to around 350 lbs and keep costs competetive... Diesel has higher btu/lb than gasoline and would be a natural with jet fuels.

FWIW, Mistral has been working on a diesel version of their wankel- it should be getting close to market, though my understanding is that it still uses spark plugs.
 
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