William Robison

My Feedback: (3)

Tom:

Better than the old camera, wouldn't you say? Now I'm going to have to reshoot almost all of the old ones, keeping only what I took with the Nikon 35.

The carb shots were taken using the Nikon +4 lens on the Hewlett-Packard camera, focus point is right at 2" in front of the auxilliary lens.

Thanks again, Lee and Tom.

Bill.

William Robison

My Feedback: (3)

PL:

Your rpm sounds just a little lower than the engine might like. Keep an eye on it, if it doesn't run hot it should be fine.

I'd try the 15x6, if the plane flies as you like using it I'd leave it on.

Bill.

lrr

Like me, it is nice to see something old and considered outdated put back into service ...

HAW!

Lee

powerlines

Now another quickie question.. The 120. I am changing the ring and bearings. I got the front out with no problem. The rear. Is another story. I searched and found that you put the case in the oven @ 275 for 20 min. Tried no luck. Bumped to 300 5 more. No luck last 350 for 5 more minutes. Hit motor on wood and NOTTA!! Man. How do you get this fudgin thing out?? Any ideas..

LATER

William Robison

My Feedback: (3)

PL:

You have one of those instances that "Never happen," sad to say. But there is a light showing at the end of the tunnel, and it's not a train heading your way.

If you will look in the front end of the case with the front bearing out, you'll see the bore in the case is larger than the bore of the rear bearing.Find a rod or bar that fits snugly in the case and wont go through the bearing, reheat the case, and use your bar and a light hammer to tap it out.

Bill.

powerlines

From what I can tell. They are the same size. If it is larger it is only by a millimeter. I will see what I can find that will match up..

LATEr

William Robison

My Feedback: (3)

PL:

Right. It's about one tenth of an incfh, but it's enough.

Bill.

powerlines

1/10th is better than none. I will get it tomorrow. Thanks again for your help..


LATER

Thunderchild

For Bill or any other budding professor!

I fly an Saito 82a in my VMAR Arrow Tiger swinging a 12X8 APC prop. This combo appears to work reasonably well, however an identical Tiger being pulled around by a 46AX appears to have the wood on me in straight line speed.[:'(]

I have been experimenting with various pitch/diameter combinations, but can't quite seem to nail that extra few m.p.h. [>:]

Question:

To up my straight line speed (and keep within engine redline) what would you recommend in pitch/diameter for this motor without labouring it?

BTW I am running 10% nitro 15% synth, 5% castor.

Thanks again for all the other brilliant tips and information.

solafein

When he is not looking, give him three clicks rich on his HS needle. Then innocently challenge him to a race.

Horizon lists the benchmark prop as a 13X8. 12X10 seems reasonable. What have you tried? What is your RPM with the 12X8?

William Robison

My Feedback: (3)

TC:

I'm not familiar with your airplane, but if both are the same then it will be a matter of sheer effective power. Get an 11x10 prop, preferably wooden, and trim it a little at a time until you can peak it at 10K rpm. In theory this should put you about 80 mph, but the actual speed will depend on the drag of the plane.

Air speed at a given rpm is entirely dependent on the pitch of the prop, and how much slippage you get. More drag,more slip.

Bill.

solafein

Here are the RC Universe stats on the Vmar Arrow 40
[link]http://www.rcuniverse.com/product_guide/kitprofile.cfm?kit_id=1286[/link]

Jack211

Bill, I know you have a mathematical bent (sometimes just a serious curve), but you quote the rpm/prop/pitch figures so quickly, with such facility, I suspect you have a table which from which you read. Is there a place to find such a table on line? We won't know the drag co-efficients for our birds, but such a table would give us a point of beginning, an idea of speed.

One of our flyers here is a professor of geophysics (implies intelligence) and gave us a way to time our planes over a 1/10 mile course, too. With some help and a stop watch we can figure approximate speed, but we don't do that very often. That would help us figure our drag co-efficients, hm? I'll see if I can get him to share the formula with me and put it here, though.

Thanks,

Jack

jlkonn

My Feedback: (1)

Jack,
Interesting about the 1/10 mile timing.
I have heard of folks getting a friendly police officer to radar gun them.
Problem that can be introduced with that method is the "slant angle".
Something Bill had to consider when getting his ground speed off the VORTAC in his "57"!

JLK

Tom Jones

My Feedback: (4)

FFourU, Dubro makes exactly what you're talking aqbout. It's called a "Four stroke Throttle set-up" or something very similar. Very Handy. Ive usedit in a hog bipe with a Saito 100. Tom

William Robison

My Feedback: (3)

TC:

Looks like a pretty fat airfoil, 80 mph may not be possible without a large increase in power. You might have better results with a 9" pitch. Again, start at 11" and trim. In any case, if you don't get the rpm by the time you get down to a 10" diameter it will be getting to such a small prop disc area that it might not pull the plane well at all.
----------------------------------
Jack:

My mathematical bent, or curve, could also be construed as saying I'm warped. Haw.

Years ago when I was flying c/l speed any small advantage was something to strive for, I wrote a routine that not only gave tip speed at a given diameter and rpm, it could also TAS at a slip percentage you put in. Usually to start, I’ll use 30% slip, or 70% efficiency. And since it was a program to help me carve propellors, it calculated the blade angle at all points from the root to the tip. Needless to say you used a lot of pencil and paper stocks to make a run of it. Or a long time on your desk calculator.

When the TI-59 programmable calculator came along I was able to get it into six or seven program strips, much better speed, and that made the program much more useful to me.

Then guess what? Visi-Calc. The first spread sheet for home computers.

I converted the program to run in MicroSoft Multiplan, and it was off to the races. What had been 45 minutes to an hour for a run became two seconds. Heaven.

I later converted it for Lotus, the latest version runs in Excel. See screen shot attached.

Point of this dissertation is, if anyone would like a copy send me your email and I’ll send the model along with a text file of instructions.
---------------------------------
John:

Converting time/distance to speed is trivial. If it takes you six seconds to go the tenth mile, then obviously it takes sixty seconds to go a mile. Whatever number of seconds it takes to go your tenth mile, divide by six. This will give you a decimal fraction of a minute, divide that into 60 to get miles per hour. Example: five seconds, 0.8333 is you decimal, 60/.8333=72 mph. Proof of the method is left a an exercise for the student.

Precise timing is not trivial. You would need one person at each end of your measured distance, with some way to trigger the timing device from where they are standing. Even then one person might react more quickly than the other. Errors.

Much better is placing a cassette recorder on the runway, and doing a low pass over it. You will then have a recording of the engine both coming and going, the Doppler shift in the two frequencies is directly related to the air speed. Far more accurate than eyeballs and stop watches. I will NOT get into this method, but it works very well.

Finally, John, when I was driving B-57s in the far east TACAN sites were few and far between.

Bill.

loughbd

Simple ratio and proportion problem. 9th grade algebra

gjeffers

AHHHHH HAAAAA i knew i did it right
but notice Bill, in the second pic i did go to a more refined hammer--------HAW

William Robison

My Feedback: (3)

Gary:

All we self-respecting "Jacklegs" need is a shade tree, baling wire and pliers, a screwdriver that can also function as a chisel or punch, and a good hammer. We arethen ready for any repair of any sort, up to and including brain surgery.

Nicht wahr?

Haw.

Bill.

Thunderchild

Thanks Bill. I would not have thought of going down another inch in diameter to 11 inches.That's a lot of pictch with it. I have been experiemnting with 12X8, 13X7, 13X6, 13.5X6, 12X6 (scream) and have RPM ranging from 9,250 to 10,500. I was not comfortable at the latter. Is 10K the never exceed and will I do damage if I put the RPM up above that (10,500) routinely while chasiung the axtra MPH? BTW the picture is deceiving. The wing has a thick airfoil section at the root, but tapers and narrows significantly to the tip. My Arrow is a Tiger pictured in the forground (prior to my Saito upgrade) with my nemisis at rear. The "Tiger" version of the Arrow is an updated version of the one pictured at RCUniverse you were looking at:

Chuckar

My Feedback: (1)

Gary, will you be able to hammer that engine back together by Sunday, I am coming out to fly no matter what happens at work I will be MIA they will get over it I want to fly !!

Tom

gjeffers

true it is

gjeffers

yes tom, i have the parts ordered and shold be here by friday and i do have a bigger hammer if needed

the only thing is my granddaughters b-day party is at 200 sunday at the bowling alley so well be out at the strip at 900am-noon, hope for good weather!!(maybe even 800am)

jlkonn

My Feedback: (1)

At the beginning of my long career working for a major US tire company I worked shift in one of the chemical plants making synthetic rubber.
They issued all the production operators a pair of Channel Locks (sp?).
It was amazing what all you could do with them besides the obvious hammering and rounding nut and bolt heads.
I still have mine out in the tool box!
I think I even ground the tip of one handle into a screwdriver and tried to harden it by torch heating and quenching in oil at the central shop.
That was when I worked for a living before I became a finance type.
Ah...youth...
JLK

Jack211

Jkonn, the local cops, one of whom flies, says it's nearly impossible for the radar gun to "read" the forward profile of a model plane. Takes a special gun, I suspect. His gun has trouble reading motorbikes.

The perfessor (who loves all those decimal pts) sent this to me, for a measured 500 ft. course. The times are in seconds, 1 through 21 seconds; the speeds are to the right, so a one second time over a 500 foot course is equal to 340 miles per hour; at 21 seconds, 16 mph.

1 340.13605442
2 170.06802721
3 113.37868481
4 85.148053311
5 68.027210884
6 56.689342404
7 48.590864917
8 42.517006803
9 37.792894936
10 34.013605442
11 30.921459493
12 28.344671202
13 26.164311879
14 24.295432459
15 22.675736961
16 21.258503401
17 20.008003201
18 18.896447468
19 17.901897601
20 17.006802721
21 16.196954972

Jack