Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Whiplash first fligh report

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Old 10-06-2002, 07:12 PM
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Glorfindel
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Default Whiplash first fligh report

Was a cold and very windy day, putted a 9x8 on my Jett Q500 to get more rpm and more trust at static for the first launch. At launch it goes straight to the sky i did a semi cicrle put the throttle back to 3/4 and engine quited I probably put the stick neer middle and the Jett dont wanna idle

I think i got to munch throw in the elerons and maybe to munch expo too. I lowered them and the second flight was better and longer but not that munch, engine quitted again when i pulled back the throttle. I will have to get used to the Jett throttle management I didnt do a 3th flight, it was very windy and that was enough for today In dive i was afraid of the 'lack of power' on my control surface(using hitech 605) due to the VERY stiff hinge line. I had to apply more up than i tough to exit dive, maybe too munch expo on elevator too...

I got a 560ko. video that i made of the launch, just email me if you wanna see it.

Sorry for my englsih, i'm french

Claude Perron
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Old 10-06-2002, 08:41 PM
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jlong34016
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Default jett q500

what kind of rpms do you think you have with the 9x8? My hinges were very stiff as well. The servos actually moved the entire center section of the plane up and down without the elevons moving. I broke the gel coat and composite surface over the hinge line. Also moved the rods in on the servo arms all the way. They work fine now. Had to cut out leading edge of fins to get rod not to hit.
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Old 10-06-2002, 10:09 PM
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Glorfindel
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Default Whiplash first fligh report

I didnt tach it. It was not sunny enough (cloud)and it's difficult to read when it's dark. I tried the new 8.8x9 prop from apc but it was a little bit too munch for the Jett Q500 (18500rpm) I have learn( on the pylon forum) that the Jett have shorter pipe than Nelson so you should use little less prop (8.8x8.75 for example). The Jett will unload more in the air than the Nelson but Nelson turn a little bit 'heavier' prop.

Also winter is comming so it's kind of cold now (5-15 deg.C) and the air is more dense so it's harder on the prop (even if the mixture is better with cold air) so i got little bit less rpm than i should. I called Jett he told me that my engine did 19500 on the 8.75x9W. so i ordered 4 new pylon prop : 8.8x8.5, 8.8x8.75, 8.75x9w and 8.8x8.9 i will do new engine rpm reading next week end
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Old 10-06-2002, 11:00 PM
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Default linkage

I must have missed the underslinging ball link post. I had to move my rods in that far to get the elevons to move. After I moved them and cut the fins is when i found the kevlar hinge post and cracked the hingeline. I probably didnt need to cut fins if i had known about cracking first. This is what i was refering to as an experimental model. I shouldnt have to be doing trial and error to get it to work.
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Old 10-07-2002, 12:23 AM
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Default Modified Fins

Although the fins look fine and worked today i'll take your advice and not trust their reliability. I'll retire this one and order another. I always have safety first.
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Old 10-07-2002, 01:51 AM
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Default 160 mph rossi

Are these speeds from radar? On a 7 inch pitch thats 24000 rpm theoretically. I only got up to 150 with an 8 inch pitch on my nelson. Perhaps i am lacking thrust with my 7.4 inch prop.
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Old 10-08-2002, 11:01 PM
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Default thrust

You are turning lots of RPMs but not going anywhere with that prop, the plane should do at least 180 with that engine combo, and I was thinking closer to 200, I'd use a bigger prop, perhaps a 8/9?
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Old 10-08-2002, 11:20 PM
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ChuckAuger
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Default Ah yes,,the speed....

200 on a 9X8...some folks say you can outrun your prop because of the airfoil on the front. Some folks say you can't achieve the theoretical speed because of efficiency. How much efficiency does the airfoil on the prop give?? Who knows?? But I'll bet that Jett 50 aint turning 26500, so there must be a great deal of efficiency from the airfoil on the prop...or he ain't doing 200.
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Old 10-08-2002, 11:54 PM
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Default Whiplash first fligh report

What baffles me is why no one consults the control line speed expertise out there on the performance of propellers. These guys KNOW how fast their planes fly (easy to calculate, circumference over time). A little research (I didn't do too much) will surprise you that full-scale props, with superior dynamics at best achieve efficiencies of about 90% of their nominal pitch. (what I found)

Since a prop is an airfoil, physics dictates that angle of attack (nominal pitch) is the lion's share contributor in an airfoil's ability to generate lift. Remember the symmetrical wing flies too - because of AOA.

Two good reads on airfoils I stumbled across look for an answer to this were:

http://www.aa.washington.edu/faculty/eberhardt/lift.htm

http://www.eskimo.com/~billb/wing/airfoil.html

Until I see evindence to the contrary (calibrated speed trap, calibrated radar under a controlled test), I find it doubtfull that any R/C plane flies level fight faster than it's prop's nominal pitch@RPM.
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Old 10-09-2002, 12:33 AM
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ChuckAuger
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Default Ah..the answer..

That's what I'm talkin' about, Bruce...and I have done some CL speed measurements...it is almost dead on accurate, increase variable X or variable Y and you can easily measure the time...I even had the little chart where if you flew X line length and it took you Y amount of time to complete 5 laps (or it might have been 7...) you would be going Z mph. I even put the pitch vs rpm equation into my HP-11C so I could quickly calculate the theoretical speed (it's still there! LOL)

And put me into the "very sceptical of any 200 MPH claims" category..I had a honkin' Dust, easily outpacing (by the numbers) many of the supposed 200 mph planes, and I always relied on the laws of physics to guide my speed estimations. But I was getting "outrun" by guys turning 5K rpm less with less pitch...so I named my Dust "Sky Pig" in defference to these breakers of the laws of physics, and right then and there quit guestimating how fast it went.

That's why I find this new round of speed claims amusing..man this stuff was hashed to death back when RCO worked! LOL but every day is a new day, and 200 mph guys still come out of the woodwork..and I set here with no Dust...I have a different plane as a replacement, but it won't balance with the 46VRDF, so that's going to have to be re-engined. Stay tuned...if we can ever get it off the ground, I'll post some RPM and pitch figures, and watch guys go faster with 5K less rpm and less pitch...full circle!
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Old 10-09-2002, 12:41 AM
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Default radar gun

All my speeds are radar gun timed. It is hard to pick up the whiplash but not the dust (i dont know why there is such a difference). But 148 on maiden flight of nelson qm 40. Im building second dust when i get a chance( for jetfire 50 and pipe) and second whiplash when it gets here for the nelson. Ys 45 dust 118 maiden flight. I will post data.
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Old 10-09-2002, 01:13 AM
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BruceDana
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Default Whiplash first fligh report

I just did some simple math, to estimate the RPM required* to go 200 MPH.

Assumptions:

1) The propellor is 90% efficient (see my post above about data I ran across about full scale props - used on racing aircraft) (but for a prop of less than 10" diameter - yeah right!)

2) No parasitic drag or other drag effects from the airframe (yeah right!)

3) 8" Nominal pitch propellor


200 miles/hour x 5280 feet/mile x 12 in/ft
----------------------------------------------------- x (1.10) = 29,040 RPM
60 min/hour x 8in

Not many engines yield these kind of RPM's are there??? And the RPM's would need to be even more if you factored in realistic numbers for 1) and 2).


In big racing (Reno) R/C planes, what RPM/Pitch/MPH are they doing? I read a fews years back in RCM that these beasts were getting up to 200 MPH? Big engines, big props, slippery airframes...
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Old 10-09-2002, 03:35 PM
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Default Whiplash first fligh report

The q40 guys launch at 22,000 to 23,000, so 29,040 in the air is believable, maybe? An 8" diameter prop has a tip speed of 689 mph at 29040 rpm. As tip speed approaches the speed of sound (758?) prop efficiency drops off drastically. The q40 planes average about 180 mph around a race course, I wonder what they do in a straight line?


I thought I read a few years ago they radared one of the lancairs at the 1/4 scale race at 240 mph.
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Old 10-09-2002, 05:35 PM
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Default Proof is in the puddin'

Let's take a look at the big picture here. RPM on the ground means absolutely nothing. When was the last time anyone clocked a plane on the ground? All the talk about CL is wonderful in theory, but since their airplanes are flying in a big circle, you can't compare what they're doing to what we're doing. As far as prop pitch goes, remember that when you apply force to any airfoil, especially a plastic propeller's airfoil , you get a lot of torsional forces going. It's easy to pick up a couple inches in pitch when you load one of these props. APC has taken all this into account when they design their props, so it's no wonder that when we fly a slick airframe with a given pitch prop, we can actually exceed the theoretical speed of the prop (tach'd on the ground) when we get it in the air. Let's face it, most things sound great on paper, but when plane and prop meet the air is where we really need to look for what we can or don't get out of our airframes. If someone says they're going 200+ with an airframe, you are right to dispute it, but don't rule anything out until you can prove it can't be done...Someone once said the sound barrier couldn't be broken..............
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Old 10-09-2002, 06:27 PM
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Default speed

ok lets see some accurate data.who has clocked their plane at 200 mph and what were you doing it with. i have seen the os 46fx on the web site with a 140+mph pass. I dont doubt it but the engine is going to be trashed in short time. Lets hear the nelsons, jetts, kb fans, os fans and whatever else you have speak up. BTW the first flight of my dust was estimated at 170 mph. The next week i had my gun and it was 116. It may have slowed down as i was having trouble with the jett fire 60 but not that much.
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Old 10-09-2002, 07:08 PM
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Default Whiplash first fligh report

Speed is one of those things that is impossible to judge accurately, like guessing some ones age or a distance. The other thing I find strange is when video taping a moving object, it always looks a lot slower when you view the tape.

BTW... The CL "D" speed record is 199.92 mph. Thats a 65 size engine on 60% fuel. They time them for 7 laps which equals 1/2 a mile. No guessing involved here.

NFZ, I have always heard that props flatten out (less pitch) at very high RPM's.
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Old 10-09-2002, 10:45 PM
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Default os durability

Really. Thats surprising. How many 5 minute flights and how many years? My understanding was that the os engines used a nickle plated piston that wore quickly at these rpm's, used a 15 mm crank, and thus smaller bearings that don't hold up to extreme use. I have a 46fx on my kids trainer and it runs great. This is the kind of data that I'm looking for. Why spend 500 for a nelson to go 148 when 100 for an os that goes 146?
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Old 10-09-2002, 11:08 PM
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Default Whiplash first fligh report

How are these speeds being validated? Is a speed trap with electrical timers being used?

What about radar guns (that have been calibrated)? How do you calibrate a "consumer grade" radar since you have no reference for comparison (what other 200 MPH objects can you measure)?

I'll guess I'll have to get my brother to flyby in his C-206 on a low VFR pass and see what the radar says - and have him call out his speed over ground from the GPS... But his plane (full scale) doesn't go 200 MPH either (only about 140 kts).

I'm just curious...

How about measuring the in-air RPM? In-air RPM can be measured by an observer on the ground with an O-scope... And there are some gadgets out there to do this onboard the model.

Has anyone determined reasonable "unloading" in the air? 22,000 RPM (ground) to 29,040 RPM (air) is a 32% increase, again these numbers seem suspect?

Also, propellers unload in the air because effective pitch generally decreases with RPM, not the other way around. Also, the materials the props are made of don't twist enough to make significant differences in geometric pitch. Then the propellor has a relatively narrow RPM band where it is most efficient.
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Old 10-10-2002, 01:09 AM
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Default radar guns

The radar gun i have uses an internal crystal for calibration. It reads to 294 mph _+0.1. It also has tuning fork for calibration. It does read slower than actual speed due to angle of pass but it usually reads very far out except on whiplash. I'm not willing to stand out on the field for a head on shot.
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Old 10-10-2002, 01:14 AM
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Default know it all

I have never claimed to know it all. I am learning daily. I read alot. I research subjects. Looking for input from everyone. Just putting out what information i have. I'm not sure why im getting so much grief from the LA clan.
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Old 10-10-2002, 02:16 AM
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Default Whiplash first fligh report

AtomicFrawg, I'm with ya man!!! lol
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Old 10-10-2002, 02:21 AM
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Default My attempt at 200 mph

I used a Diamond Dust and a Shrike 40 powered by Sport Jett engines for my speed runs. The max static rpm was 18,000+ with a 8" pitch and a possible unload rpm of 21,000.

Method #1 - Radar. The city police agreed to check the speed of my Dust with his radar gun. After several attempts, because of the profile of the aircraft, we never got a straight on reading. The best he could do was a hit the bottom at about 30* - 45* off being straight on. Since others have been able to get straight on radar readings on a Dust, my guy must need some practice.

It seemed a little rich on the above run so I checked the static rpm after the flight and it was about 16,000. The radar gun said 123 mph but because of the angle of the gun to the flight path we calculated 140+ mph. If the engine was in tune, maybe 160. Margin for error was too high to prove anything.

Method #2 - Stop watch. Using a car odometer you have one person 1/4 mile out in each direction from my position. Practice flying a pattern that gives you a 1/2 mile straight run. My average time in both directions was 10 seconds which would be 180 mph. Margin for error should not be too high.

Method #3 - Video. I would fly my planes over the Q-500 Pylons that were 660' apart. I would then use video editing software that had a 1/1000 sec timer to calculate speeds between 160 and 170 + mph. Parallax and low frames per sec were were my biggest concerns for not being totally accurate.

Despite my effort for accurate speeds, I would not bet my 401K on the above #'s. I do however feel they are probably not that far off. These #'s would indicate that a clean aircraft would allow a prop to exceed 100% efficiency. I understand a standard prop airfoil will generate a positive thrust starting at a negative 3* angle of attack.
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Old 10-10-2002, 02:21 AM
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Default imac

Well a shot from a new yorker. Thanks for your valuable input. Maybe you can get this tread locked too.
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Old 10-10-2002, 02:33 AM
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Default mike connor

Tremendous planes and website. Thanks for some useful information. Did you set that website up yourself? and is it difficult to do?
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Old 10-10-2002, 02:46 AM
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Default Re: mike connor

Originally posted by jlong34016
Tremendous planes and website. Thanks for some useful information. Did you set that website up yourself? and is it difficult to do?
Thanks for the kind words. I did set up the website myself. Everything is easy if you know how to do it. I work with computers for a living but a person that does not know HTML can use different software packages to create nice web pages.
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