RPMs, KTAS, GPH, %BHP?

I'm trying out some new flight planning software called AirPlan. It's the cheapest I've found and talks to my Garmin 295, downloads routes and uploads tracks. Anyhow, it has planning, and there's a table I need to fill out to attempt to accurately forecast fuel use. Below follows the table supplied for a PA-18-135, I want to extrapolate for a PA-18-150.

Got a guess?

PA-18-135
RPM KTAS GPH %BHP
2000 76 4.3 45.0
2135 81 5.3 55.0
2255 85 6.2 65.0
2365 90 7.2 75.0
2600 99 10.6 100.0

PA-18-150
RPM KTAS GPH %BHP
???

I guess it depends on your prop. I have a climb prop and am lucky (very) to make much over 80 knots at 2450rpm with a 150. It's very slow, but I'm not complaining (much).

David

No disrespectr intended, but do you reaaly need a computer to fly a supercub? To me a big part of the allure of a SC is simplicity. If you must have numbers, try 2350 rpm, 90mph, and 7.5gph.
Ken

I agree with Ken. Also no disrespect but we stopped using computers when we started flying Cubs. They're so darn inaccurate. They can't predict the mileage you fly when you follow a river as it twists and turns. They can't predict the number of turns you need to do to count the points on an elk or to smell the new mown hay in a field you just couldn't pass up. Or how about the number of passes it takes to scare the hell out of coyote or identify the fish lying on the bottom of a pond. Besides does anyone who flys a Cub really takeoff with a Plan?
Tom and Steve

Perhaps the biggest issue regarding the suggestion of developing a program for your Cub is the notion that every Cub is so different that it would be virtually impossible to develop a program for any specific airplane, based on data from another.

For example, there are a half dozen different engines in these aircraft (I'm just talking basic engine models, guys, not dash numbers), there are a bunch of different lengths and pitches of props, there are a bunch of different ways to rig the wings, a bunch of different tire combinations, and so on, not to mention different wing tips, etc.

So, if you really want to develop a program for your airplane, you'll have to do it yourself. EAA has offered a series of articles in it's magazine (and I believe they are available on thier web site, but not sure) on doing just this for an experimental aircraft. You can use these techniques to derive the information that you want, specific to your airplane, and by the way, do some fun flying while developing those numbers.

It is in fact, an excellent idea to know as much as possible about your particular airplane, but with these airplanes, the best way to develop that information is to go fly your airplane, keep good notes, be specific, and then learn what it will do.

But learning what someone else's Super Cub will do may or may not be very helpful for use in your aircraft.
Mike Vivion

Come on.... somebody just throw the guy some numbers. I'm losing faith in the flying geek nature of this site. Sure, flying Super Cubs is more pure and less by the numbers, but some us of enjoy being scientific and playing with gadgetry. I might as well blast you no-numbers guys for even using a GPS receiver. Geek it up, give him some empirical data!

Yes I use digital machines!

I can navigate seat of the pants, and I'm sure I could have done that 150 mile flight I took this weekend (each way) without the GPS, it's all pretty familiar territory. None-the-less, by having a complete plan, and a simple machine that not only shows it to me, also updates my position, it takes care of one chore. I can spend more time seeing and avoiding because I'm not a) wondering where I am, and b) trying to figure out how to refold that chart to see where I am going. I do keep a current chart handy, I know how to read it, I use it all the time.

So, to answer your question directly, no, I don't need a computer to fly my plane.

The way I have my tables set up, my computer generated plan has more than enough fuel for all the diversions in throttle and route, and still get me where I'm going. It's just an estimate of how much gas I'm going to buy, the GPS has downloaded route information only.

My numbers: 2200 rpm, 85mph (74kts), and 7 gph, if I'm roughing it. I'm not in a hurry either.

But, again, that information is less than useful without the specifics of your airplane, particularly horsepower and prop specs (length and pitch).

Also, what method are you using for leaning?

This is what I meant in my earlier post. I think developing programs for your own plane is a great idea, but data of this sort is only useful if you know that you are comparing apples with apples.

Keep deriving data, it'll keep you flying and learning about your airplane, both of which are healthy, done intelligently.

Mike

Kts

kts. are for boats. Jerry.

or..... knots are for sailors and boy pilots. Thats how I heard it. Unfortunately I'm invariably referred to as a boy pilot being so young, but on the flipside I fly within the system alot so the use of knots is expected.

Rookie, Sounds like you have a cruise prop getting 85 mph on 2200 rpm. Like everyone has stated, the tables you use depend on your particular engine-prop combination and altitude.
The most fun you can have is to build your own tables for your airplane. Fly at different rpm settings and record your actual ground speed and fuel consumption. Think of the fun and experience you'll gain building tables.
Tom

I agree with Jerry, knots (kts) is for boats/ships so is NAUTICAL MILES (nm) stick with MPH and sm for distance

vb

Numbers numbers numbers

Hey, it's just an estimate! I am actually able to come within a half gallon of my actual use after a two and a half hour trip.

I put the KTS in for the bloke, it was just a courtesy.

Good to see you this weekend Jerry. Did you ever get to dance?

If you repitch the prop to take advantage of the increased horsepower, and if you are flying at the same total weight and density altitude before and after , then your cruise will increase with the cube root of the ratio of the two horsepowers.

V2 = V1 *(HP2/HP1)^(1/3)

All the best,
JimC

Rookie,
I have a chart of O-320 rpm/fuel/%hp that I borrowed off the net somewhere, send me an e-mail
klmartin@alaska.net
and I'll send you a copy.
You'll still have to figure the mph per rpm for your airplane (i.e. fly at 4 or 5 rpms and record airspeed)
and have an idea where you plan to operate (record manifold pressure while you're at it), but over the short range of speeds in my plane it seems to be pretty linear since the prop efficiency doesn't change too much.
Then you can use the nice formula JimC gave to take a known hp/rpm/mp combination and spread it to other rpms to estimate hp requirements.
KL

Hey, Tom -- isn't he getting about 95 to 96 mph (83 kts) at 2200 ?
JimC

Knot's?

It's best to travel Nautical miles' It's not as far!