RVman

Hopefully this is the right forum, i'm trying to guess at what speed my GP RV-4/rocket will go. I cleaned up the plane a little bit, mostly around the cowling, the plane has always been fast when stock. I had a supertigre 45 in it previously, now I just put in my piped webra 50. I am using a 10-8 APC spinning about 14,000 static.
It is easily one of the quickest planes at our field which is mostly sport flyers, it definetely won't keep up with some of the stuff in this forum though.

combatpigg

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A cheap and accurate way is to measure off 1/16 of a mile, station 2 helpers at either end of the course [it helps if both helpers have a fixed object to reference, like a pylon pole]. All they need is a pair of cell phones and a stop watch. All you will need to do is fly through the timing zone level, turn around and repeat as many runs as you can while your helpers record the results. The rest is pretty simple math.

mintie

simple man.....average speed[velocity]=Total distance/Time.....set out a marked known distance and fly that /by the time and you have a good indication of the speed. kph or can convert to m/s... have fun....cheers

Clean

Record your model flying by and play it into your computer, then use one of the following programs to see how fast you go.

http://mywebpages.comcast.net/webmas...r/doppler.html

http://www.sprut.de/electronic/soft/scope.htm#download

The second one is easier but it's also in German. Not that it's impossible to figure out. After installing, click on the WAVos icon and pick one of the files that come up. That file will be analyzed and show you a graph with veritcal lines that shift from left to right as your model goes buy. Left click on the left vertical just before it shifts, then right click on the vertical just after the shift. Your speed is calculated and displayed in KmH.

RVman

Thanks guys

nitro junky

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IF your just looking to get a close speed ( RPM X Pitch X .000947 = speed) IT'S NOT perfect but it is pretty close. I have a radar gun that we have compared this to and it is usually with in 5 MPH of the radar gun on a flat level fly by.

RVman

That would be what the ThrustHp program does. So my speed would be about 105 mph. Does that seem about right for the plane? I will clock it over our 400 ft field next time I am out to get more accurate reading.

Cyclic Hardover

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I doubt it. Thats stuff does not take into consideration the plane. I'll pm you a simple time distance thing i use

nitro junky

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RVman you should take a look at
[link]http://www.rcuniverse.com/forum/m_173085/anchors_5175488/mpage_1/key_/anchor/tm.htm#5175488[/link]

Crazy4Flight

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After a dive at a 45 degree angle into the ground...
you multiply the depth of the hole, in inches times the length of the debris field


this formula does not work durring winter in Canada or the northern states because the ground is frozen [&o]

Warning! Do not attempt speed measurements with 3 miles of a worm ranch you may start a stampede!

combatpigg

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The problem with relying on mathematical theory is that slight errors get multiplied the faster you go, plus the airframe gets more critical to the final out come. Using the formulas, my deltas should go faster than what they really do.

vicman

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CP, I have read your coments several times with the stopwatch/cell phone technique. Does one timer simply call the trap for the other? Or is there more to it?

Cyclic Hardover

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I feel the simple math formulas are dead on bringing down the "tales" of 150mph planes to a more realistic speed of 100mph. This Ultra Sport with a Jett 90 flys anywhere between 100 & 110mph with a formula and a radar gun. However this is slow because of our altitude but shows me simple math works.

combatpigg

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VIC, we first set up a 315 foot long straight [1/16th mile]. Our hatch back cars are lined up with the tips of the raised tail gates even with the imaginary plane that the model has to cross. I am with helper #1 who is in charge of telling helper #2 when to start the stop watch. Then all helper #2 has to do is stop the watch when the plane flies past the finish line. If something was to go wrong with the plane, everyone has a car for protection. If both helpers have stop watches, then you don't need to do a complete lap to get another clocking, just do a U turn and let the helpers reverse roles.

CH, for what you're using the math for, the formulas work well. My point is that when you get into the 170 plus range the slightest wrong assumption in any formula is going to be amplified. I have a Diamond Dust that on paper should do 195 but it actually does 177. There's no substitute for knowing for sure and it is amazing how repeatable the clockings have been with my 2 helpers. No matter how hard I've tried, I can't get them to make my planes seem any faster.

vicman

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Thanks for the tutorial. It was like I thought. We have a guy out here that has a gun and wscope. Between the two lies the truth and so far I am satisfied with 4.9" looking like 8"[X(]

HighPlains

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ahmm....I used a variation of that technique one time. I was flying a Formula One some years back on a very windy day and started doing a series of long downwind dives. The last dive ended when the plane didn't pull out completely and it skipped into the concrete runway. About 600 feet from the impact was the engine.

By measuring the angle of the groove formed in the spinner where it first touched and knowing the RPM of the engine and diameter of the spinner, I was able to calculate the ground speed when it hit.

combatpigg

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My main point about using distance/time VS other methods is that it is practically free and very accurate. If I'm shooting for 200 mph, and radar or wave-o-scope data shows speeds in the 195-205 mph range, there is still a shadow of a doubt. I wouldn't feel good about the findings until they were validated with a stop watch...which brings us back to "square one".

vicman

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I have a problem getting two friends

combatpigg

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I'll be your friend if you give me an engine....

In addition to the CC races, it would make for another fun event to set up a timing zone to see who's got the fastest rig. This is where a radar gun would be just fine for comparative speed.

proptop

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You guys "crack" me "up"...[sm=bananahead.gif]

Chuck...next time we want to do some "speed trials" we should also measure off the 1/16 mi. like CP does and do the time/distance thing too...along w/ your radar gun.

Maybe make 2 of those barriers (to hide behind ) like you were talking about?

Guys...do you think 1" plywood would be sufficient to protect a person in case of impact with, let's say a Quickie 500?
Nitro Junkie and I were talking about a sheet of 1" ply, with a small "observation" hole to look thru while also aiming the radar gun.

combatpigg

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PT, I heard of a Pylon course official who was killed many years ago [by a F-1] even though he was inside a chain link cage. I can't see how a 5 pound plane going 200 mph could penetrate through even 3/4" plywood and have enough force left over to kill anybody, but I can't say I've ever tested out this theory.

HighPlains

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First off, it was not a F1 airplane that killed the guy. No one was ever killed by an Formula One airplane, partly due to the tight controls on airplanes that the rules imposed.

The guy was killed by a "Warbird" racing airplane, where in my opinion had few rules and very poor judgement in the event organization and race operation. The guy in question was leaning against the cage, so it offered no protection. This style of metal cage would stretch about 12-18" when impacted by an F1 airplane at speed, so the secret to surviving the impact was to be away from the walls by more than that amount.

RVman

Interesting discussion, I will get a couple helpers and clock the plane a bunch of times upwind and downwind over our 400ft field. Then average all the times and calculate my speed. That will be accurate enough for me. I'll let you guys know once i find out what speeds its going, who knows it may be one of the fastest RV-4's out there.

Cyclic Hardover

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Tell you what, this will be good. You get us the numbers and lets all put our estimates in the pot.--If not , we can always start another Super Tiger thread

nitro junky

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There is no doubt this is one of the cheapest way's to go. The accuracy is solely depended on how fast your fingers can move on that stop watch. If you are at the starting point there is a time delay by the time you get a signal the plane has past the ending point. Just a one second delay on the starting point on ending point at 200mph could give +/- 5mph. Witch would make this no more accurate than most radar guns out there. I think to most accurate way is to use a laser radar gun that most of us don't have access to. So until laser radar guns are cheep we will just all have to use the way we feel is the best.