der_steuermann

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The only plane with landing gear (retractable) was the winning plane, the Dago Red Innovation usually flown by many world class F3D competition pilots.

It can be purchased here: www.f3d.de

The rest of the competitors hand launched their speed planes not featuring wheels or skids. No catapult or other launch device is needed for these speed planes.

The engine of the winner is the Metkemeyer MB .40 featuring the trend-setting integral cylinder technology. It has been the predominant pylon FAI engine of the last years.

http://home.kabelfoon.nl/~fiorimet/Index.htm

All MB engines used for the contest have been modded to turn about 30500 statically. We think that in general it is quite hard to go any faster than 240 mph with a modern F3D plane.

But 240 mph is surpassable [8D]. In fact the 250 mph barrier has been exceeded in the past several times.

So let's take a look at another pilot flying the MB .40 engine - on a different airframe. I am talking about the third winner Achim hitting 'only' 210 mph. He flew an airframe similar to that I offered three months ago here at RCU optimized for straight in line speed. We all were quite surprised seeing Achim not approaching the 400 kph since he flew a prop with a bigger pitch and the hottest .40 engine on earth. The reason for the 'low' speed he admitted was the lack of time to accomplish enough test flights to adjust the best prop size and compression ratio. He finished his plane just before the contest.

Regarding the rules of that contest - there were only few rules. As a matter of course each participant must provide a valid insurance and radio license. Most important is the safety check prior to the first flight (heavy duty linkages + control horns, carbon fiber props, etc...)

Each pilot can make as many powerdives as he wants or as the fuel capacity allows. The speed measurements will be taken by radar gun and by Doppler simultaneously. Only horizontal speeds will be measured. The highest recorded speed will count for the final ranking. That's all

For the next German Speed Cup I suggested a classification based on cylinder capacity.

up to 2.0 ccm
2.1 ccm to 3.2 ccm
3.3 ccm to 5.5 ccm
5.6 ccm to 8.8 ccm
8.9 ccm to 13.5 ccm
13.6 ccm to 18.5 ccm
more than 18.6 ccm

The advantage of that system would be a tough competition within each class leading to an objective estimation of the performance. Who has the lowest drag airframe, the hottest engine/pipe and the best prop setting within that particular CC-class?

At the same time a classification would promote the development of new sophisticated speed plane designs being a very important factor IMHO. Speaking about speed plane diversity in future!

The disadvantage of a classification would be a possibly very limited number of participants within each class.

However, for the next Speed Cup it seems that again anyone with a prop driven speed plane will be admitted including the electric speed community. No classification system is planned so far.

der_steuermann

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The speed measurement devices...

bob27s

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Thanks....

Good information.... I appreciate it.
I was wondering if there were some rule prohibiting detaching a portion of the vehicle after launch (drop away wheels, etc).

Few rules are usually good for innovation.

That 250 mph mark is indeed tough to hit. Takes a lot of energy to get there.

You noted the planes may enter from a dive. How long was the horizontal flight timing distance? Or was the reading the instantanious max speed ?

Thanks
Bob

der_steuermann

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Of course for the take-off dollies or the like are allowed.

So, why powerdives from high altitude?

In general no horizontal turns should be flown, just smooth powerdives from high altitude to keep the push through the entire runtime of the engine.

The dives are useful supporting the engine to unload massively. For best in-flight rpms the speed engine should ‘jump‘ on the tuned pipe right after the first powerdive (short tuned pipe length required!). Alternatively you can pinch the fuel line manually at the ground right before the take-off to lean out the mixture a little. If set up correctly the engine will stay in resonance. For that R/C carbs are less practical. Once you throttle back a little during flight you may have a hard time getting the engine back in resonance. Let alone the R/C carb’s inferior efficiency.

So it is not surprising that almost all engines are equipped with a venturi speed carb (non-throttable). Accordingly each speed plane must feature a fuel shut-off device for safety reasons.

The speed planes should stay within the (imaginary) vertical plain determined by the microphone as a fixed point and the wind direction to achieve the most precise Doppler result. The altitude above the mic should not exceed about 100 feet for a strong audio-signal. The radar-gun guy shoots each plane right above the ‘Doppler’-microphone. Consequently both measuring methods happen to be more or less simultaneous. In case of the Speed-Cup in Germany fortunately almost identical speed numbers were obtained – very accurate.

The plane should fly horizontally for about 200 m through the section of measurements. Only few pilots had problems to meet this demand. They performed unfavorable parabolic flight paths out of the dives.

Ideally, the speed measurements should be carried out in both wind directions. For each heat only one wind direction should be considered for speed measurement. The maximum speed of a certain plane during the first heat (let’s say with headwind) has to be averaged with the maximum speed of the second heat (downwind) to maintain equal boundary conditions for all participants.

To facilitate a smooth progression of the contest program the microphone-man should announce the coming two pilots quite early. As soon pilot A finishes his flight pilot B should start his engine. In case of problems during the start procedure (defect glow plug...) the next pilot should be prepared to start immediately.

No fuel regulations do exist. The pilots run their home brews.

The sun should be located behind the pilot.

der_steuermann

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I forgot to mention that the Speed-Cup was a three days event. The first day allows the participants to fine-tune their speed machines and to become familiar with the flight site. Pilots experiencing serious problems with their engine (e.g. due to air humidity or site altitude) have enough time to even exchange their engine. One pilot for instance had four engines in his pit – each with a slightly different setup.

Also very important: The pilot and his/her assistant/thrower has to carry out the take-off far-off the crowd. The potential for injuries is reduced to a minimum then (propeller failure, radiointerference, failed or aborted take-off...)

HighPlains

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It would appear that some of the top end speed 230 mph (369 kph) is due to the dive. Were there any measured passes without extended diving?

170 mph with a 1/2 A? Perhaps. That would require 45,000 on your 4.2x4 prop. It would be interesting to try though.

combatpigg

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The GZ .061 puts out 42,000 static with 30% nitro and a stock APC prop. 42 K is a magic number because it represents 700 piston pops per second.

der_steuermann

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All measurements have been made with the diving.

But you are correct. The dive in fact makes a significant contribution to the final horizontal top speed. We keep in mind that the goal of this speed contest is the absolute highest possible horizontal speed.

For that the very low drag airframe must be combined with a prop featuring a high pitch. To be able to make use of the efficiency of such a high pitch two boundary conditions have to be met.
[ul][*] A very low drag airframe being the aerodynamic basis for a certain mph–target.
What do I want to achieve?
[*] The prop diameter and pitch has to be adjusted to the mph-target, the potential max rpm of your engine/pipe unit and to the aerodynamic limits of the airframe. You can start with the calculated/theoretical speed derived from the pitch at a certain max rpm number and continue with many tests flights applying the trial and error method.
[/ul]

If both conditions complement each another well, there will be a realistic chance to obtain the mph-target.



Generally the efficiency of such a high pitched prop really suffers at low flight speeds, i.e. the take-off process in particular and also the flight phase before the first powerdive. For instance 'regular bulky' airframes like most of our sport planes including most deltas would have a hard time to even take-off with such a big pitch small dia speed prop.

However, after the first extended dive the situation radically changes. Now the high prop pitch promotes the dynamic unloading of the engine effectively. The engine starts to scream like ........ Most important is to find the 'sweet spot' during the dive meaning the highest prop rpms coinciding with the 200 m distance of horizontal speed measurement.

In other words: Considering the setting of airframe and propeller we are talking about a very different approach compared to the pylon speed contests. And looking at the engine capacities, the top speeds observed during an ‘Extreme Speed Prop Competition’ are substantially higher.

Let’s take a foresight. A worthwhile objective certainly would be: Who designs the fastest plane with the smallest engine?

HighPlains

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Some years back on a windy day, I was diving a ST X-40 powered Formula One on long downwind passes from a pretty high altitude. Unfortunately, on the last pass, I skipped the airplane on the runway (concrete). Parts scattered for the next 600 feet down the runway. But the interesting thing was the scratch marks on the spinner cone. From the angle of the marks, diameter of the spinner and the airborne rpm, I calculated that it had hit at well over 230 mph. Now it was a windy day (20 or 30 mph), and this airplane/engine combination had been measured on radar at 170+ mph on a race course. So I would guess that the dive contributed at least 30 - 40 mph to the top speed.

However, I can’t consider a “diving” pass a true measure of top speed of any airplane. It is a testament to excellent design and construction of models since the structural loads during the pull-out could be rather high and flutter of the control surfaces a possibility. If you know the altitude dropped over what interval of time and the weight of the airplane, then you can calculate the input of energy from gravity. It may amount to as much as 50% of the engine’s output in those passes, perhaps more.

Good thing you are using radar to correlate audio Doppler shift. Someone might be tempted to just throttle down as they pass the mike to appear faster. ;-)

On the ½ A, 170mph is your “calculated” top speed if I have read your posts on the subject correctly. What actual speeds have you achieved? What span, wing area, airfoil, weight, and controls?

combatpigg

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The 1/2A plane has 32" of span and 160" of projected area. The airfoil is 7/16" thick and is flat bottom. The plane weighs 17 ozs [painted]. This plane covers 500 feet in 2 seconds, as measured by me with a little bit of trig and some fixed reference points. . I am using aileron/ elevator for control, 300 mah nimh cells, ELECTRON RX and HS 55 servos This GZ engine was flown at a FAI world championships by BILL HUGHES and turned in a 159 while dragging 84 feet worth of steel lines. Once I get some help with down range spotting, the speed figures will be verified, and the nitro and good props will be brought out.