MJD

My Feedback: (1)

Umm, because they know they will get smoked?

Weston says that speeds well in excess of 200 mph have been achieved with an 8-10 prop. I'd like to see that..

But is a fast airplane and cool looking.

slowmo777

Well, I assume that's part of good advertisement since the entire layout unfortunately does not allow these speeds:

too wide fuselage for a 8*10 prop
too large & thick tail feathers
"wrong" wing layout
and of course the non-concealed engine+pipe

The fastest runs of a Magnum/V1 combo with an 8*9 prop result in speeds of about 170 mph, which is nice for an ARF product. But 200 mph is a great dream!

That said here's a second picture of the aforementioned speed delta wing. Pic was taken during a Speed Cup in the 80s. Here it is powered by a .40 with open exhaust. Speeds of about 150 mph in the 200 m speed trap.

HaveBlue

Yes I do remember which thread , it's this one..the very first post

HaveBlue

Hey Slowmo thats actually a very cool looking delta!

bTW..I'll be talking with Rick , he's the ACM guy , they made the whip..I'm going to ring him on Tuesday or Wednesday..he tells me that his was clocked at 217MPH, and if a carbon fibre version would be made it could exceed 250MPH...cant wait for that chat..it'll be interesting!

MJD

My Feedback: (1)

I doubt it. Carbon fiber doesn't reduce the drag coefficient or increase horsepower. Sure, there would be a small reduction in induced drag if the weight was reduced, but 250 mph? I think not - that's 33% more drag from the same frontal profile, which I seriously doubt will be ovecome by the reduction in induced drag which is only part of the total drag equation. You'd need about 50% more horsepower to ovecome that if I'm not mistaken, IIRC drag squares and horsepower requirement cubes relative to the speed increase? To get that you need more engine, then you get more induced drag from the weight increase, more frontal area, and so on.

Another issue would be that the antenna would now have to be completely external adding a wee bit more drag.

A cleaned up whiplash would certainly be a cool thing though. I'd vote for rev. 2 if there ever was one to have a round nose and a fully cowled engine and pipe tunnel capable of holding up to 15cc engines with full "nitro" pipes. And airfoiled fins while he's at it..

MJD

slowmo777

MJD was faster than me but he hits the mark...


HaveBlue, that’s funny!

Does carbon fibre make a Whiplash faster?

Or does redesign make the Whip faster (featuring a fully concealed engine + pipe for instance)?

I thought we’re talking facts in this thread (physical background as well as practical experience) while dealing with speed deltas driven by props.

There’s NO way – believe me – to reach something like 250 mph with a prop driven Whiplash.

Let’s do some assumptions: Take your full carbon Whiplash and mount a hot .90 ducted fan engine turning a 8*10 carbon prop. Of course engine + pipe are fully concealed because we do own the newest version of the Whip for testing. [8D]

So what will happen? We all know that the delta layout unfortunately does not allow to use the needed 10” prop pitch effectively for the desired 250 mph. [:@]

On the other hand using same engine + even higher prop pitch 250 mph are very realistic, but only if using a conventional aircraft design. Here the 10” pitch can be used without problems. That has been done during the Speed Cups in Germany 15 years ago (and most likely this year again).

Fact is: Deltas make prop speed life too difficult. It is impossible to effectively use the needed prop pitch for your speed target.

However, if using something like a Whiplash XXL airframe, powered by a 60 to 100 cc two-stroke engine turning 20” or so pitch at 15000 rpm, then you should have the right combo for 250 mph (but still would be quite slow for that engine/prop). So that would be a different animal, basically in terms of $$. Also you would have to make use of a catapult to become that baby airborne and we wouldn’t be allowed to attend the German Speed Cup with engines larger than 15 cc and airframes (wet) heavier than 5 kilograms…

I would like to emphasise that all speed specifications should be based on a FAI 200 m trap to compensate the effects of down- and headwind. Makes for a realistic comparison of international speed results (see all the radar-gunned 200 mph Diamond Dusts and Whips) …

No offence – Just facts.[sm=frown.gif]

HaveBlue

Well guys , I'll make the call and get more detail on how this meant to be achieved...

personnal It doesnt worry me ..so I'm not offended slomo.. I am rather liking this topic

HighPlains

My Feedback: (1)

Really, the best feature of a delta platform is they drop out of the sky like a manhole cover. You can generate a bunch of drag with a high angle of attack as you set up for landing, and it makes them easy to land. A good clean conventional airframe is much much harder to land in a small field, since it is so close to being a good glider it will have a very flat approach.

HaveBlue

well while this might be amusing to you ..I would like to hear his reasoning.. this guy is not a novice as they make drones for the military..so I would think that there would be some validation in what he will have to say.. although his email is short without explanation.. I would imagine carbon fibre version is for strenght and weight factors..but since I dont have the capabilities to enter this conversion with facts ...please allow me to get a further explanation to how this should be achieved ..he did mention "the right powerplant"..I hope he doesnt mean turbine as this would nullify our topic

MJD

My Feedback: (1)

What he is likely getting at is that by making it lighter, you can reduce the induced drag which is always created as a result of generating lift. Reduce the lift needed, and you reduce the induced drag, therefore you fly a little cleaner - less reflex needed. A little cleaner, not gobs cleaner, though. There are practical limits to how light this thing can get, and there are fixed weights that don't go away, like engines, pipes, fuel, Rx, battery, servos etc. The airframe is already stiff as a board, so I can't imagine it is flexing and causing drag in that way. Beyond that, perhaps he is making some aerodynamic changes too.

But.. these things are already flying on some pretty snotty powerplants and not hitting 250 or even close to it. So.. I think what we're saying is 250 mph sounds good when you're bench racing, but to honestly achieve that in an aircraft of this size and planform is a far greater challenge than you might be imagining. Remember the drag and power relationships, 250 mph versus 217 mph is not 15% more power or 15% less drag. It is 33% less drag for the same power. And, again I have to check this, for the same drag it is either 250/217 cubed or to the fourth power for horsepower increase needed. Even if it is only cubed, that is 53% more horsepower delivered to the prop to push the same airplane to 250mph under the same conditions.

So, you may be optimistic about a small delta doing this, and that's cool. I'm very doubtful, and SlowMo is more so, and he's been involved in Euro extreme speed for a while and has seen the effort it takes - these guys ain't fooling around.

I'd guess, and I stress guess, that a cowled Whiplash on a hot 15cc powerplant with the best prop for the job, might up that ante to 225 or maybe a bit more out of a dive, IF it currently capable of 217 mph out of a dive on a hot engine.

The fun part will be proving that out!

HaveBlue

I oringinally asked Rick to check this thread out for his input...I think that neither you or slowmo are incorrect as I would imagine that if these speeds where possible out of a delta it would have been achieved after all there is no new technology here that we are dealing with..In all honesty I'm selling my whip because of the information provided...I do believe slowmo and der steuermann know what they are talking about, the explanations make lots of sense..
please dont think for a minute that I am trying to be contradictory..I just wanted to see if there was any reasoning to be had, to get a good debate with some technical input from both sides as I was rather dissapointed to hear that in pure piston powered speed applications deltas rate poorly after all the diamond dust is advertised as a 200mph plane...

I dont intend to challenge for an all out speed record..but I do want to crack 200mph ..thats my goal..and I'm finding that the choices I have made are poor and I need to address this challenge from a different angle

cyclops2

WAIT!!

The winning shape of guided missiles is Deltas. Single or 2 in tandem. Sub or super sonic.

cyclops2

WAIT!!

The winning shape of guided missiles is Deltas. Single or 2 in tandem. Sub or super sonic.

HighPlains

My Feedback: (1)

How long did it take you to get the word on the "flat earth"?

HaveBlue

well when I find a missile powered by a piston engine...I'll take note of it..

_King_Pin_

That would be funny! 2 or 4 stroke?

bob27s

My Feedback: (19)

A carbon fiber whiplash - the carbon won't make it fast , but it will make it strong enough for such a task and keep it from blowing apart when it approaches 250 mph. Thats the big key there. When you get to those speeds, dynamic pressure and aero loads really start to climb.

There are quite a few well documented flights with a Whiplash flying over 200 mph. But not much over. All I know of were out of a large dive, not sustained level flight, and used a radar gun for measurement. (correction, one used an on-board air data system - but I never did see the air data printout - but it was not an outlandish claim).

But 250 mph is a pipe dream with piston/prop power. Just not going to happen at these size models. Would require a small turbine mounted on a similar airframe to get to that sort of top end speed.

slowmo777

In the case of prop driven deltas – we should even call 200 mph a pipe dream. 250 mph with a conventional airframe up to 15cc – that is a tough but realistic goal.

Yes – speaking of turbine powered deltas. Taking a 1 m span delta and a 12 Kg turbine is no challenge at all to exceed even 300 mph. Quite “boring” because then we do not address sophisticated aerodynamic design associated with prop driven speed planes here. We just use pure power instead.

slowmo777

Again, I must repeat that all speed measurements being NOT recorded over a 150 or 200 m horizontal distance – cannot be compared on an objective basis. We have to use the averaged top speed over a certain horizontal distance, i.e. compensating down- and headwind to be able to extract the true speed capabilities of our speed planes.

For that reason speed trials all over the world should use such a “standardised” speed trap. No parabolic speed path allowed which would falsify the recording. Otherwise we never will be able


For instance, if somebody has measured his Whip or DD at 210 mph using the Stalker PRO radar gun, then nobody knows whether:

- this is the average speed considering head + downwind
- a parabolic flight path has been done (cosine angle error affects radar measurement)
- other effects we cannot evaluate



An adequate example for non-comparable speed results has been observed during the last two SpeedCups here in Germany:

[ul][*] 1. Measured by radar gun the “DAGORED INNOVATION” powered by the MB .40 has reached 230 mph in year 2004. Unfortunately the flight path wasn’t 200 m horizontal after a dive but parabolic after a dive. In addition there was strong downwind during that recording.
[*]2. Measured in a 150 m speed trap at an horizontal altitude of about 15 m, down- and headwind, the same F3D pylon plane/engine combo “only” achieves 210 mph after a dive. Yes - this is the true terminal speed of this airframe which objectively can be compared with purpose built speed planes for instance.
[/ul]


For that officially no radar gun measurements will be allowed during competition of the coming German Speed Cups. On-board speed measurement by GPS for instance only works if flying absolutely horizontally. Onboard units measuring pivot air pressure at a wing tip can only be installed in airframes delivering enough space – a big problem for purpose build speed planes.

Just trying to promote a more objective presentation of recorded speed and an encouragement to arrange a US Speed Cup in future. [sm=thumbup.gif]

Mike Connor

My Feedback: (5)

A parabolic flight path would show a speed slower then actual when radar is used. A small angle would not be significant unless it was a serious compitition event. If headwind and downwind passes are used for both radar and speed trap passes your example show the radar is not too far off for average local event. Another factor that hasn't been considered is the cross wind component that will show ground measured speed slower then true air speed.

I am not disputing the information given by those that know more then me on this subject. My attempts to hit 200 mph with a Jett powered Dust fell well short. It seems that after 150 mph drag becomes a serious issue

slowmo777

Yes that’s true,

the larger the angle of deviation from zero (= 150 meter horizontal flight path between gate 1 and 2) the slower the resulting speed from reality.

What I missed to write was the speed measurement by audio doppler effect which highly demands a non-parabolic flight path. The microphones must be placed exactly within the 150 m flight path. These audio shift detection has been carried out during the last two Speed Cups.

Sorry for leaving out this info.

As far as I know, the next Speed Cups will use an electronic speed measuring system that allows true time measurement – automatically activated by crossing gate 1 and automatically stopping by crossing gate 2. That is FAI conformous. The height of both gates determine the needed predefined horizontal flight path.

Yes – true 150 to 170 mph on a well powered Diamond Dust sound realistic for a measurement in such a speed trap.

ptulmer

My Feedback: (5)

Looks like you started a thread just to discourage delta flyers to me, Slowmo. You've consistantly ignored one factor in the deltas favor. What is more important to reduce than drag? Weight! None of the commercial delta kits that I've seen put a real emphasis on this with the exception of the diamond dust. They just don't have it right. Easy, yes. It could be made stronger, lighter and stiffer by sacrificing the easy construction.
Is the delta the best configuration for going around pylons? No, it's not. BUT, with the proper attention, it wouldn't get "smoked". The delta planform has many advantages over the conventional. Do you think the fuselage of the conventional airframe doesn't have any drag? Of any sort?
Since I'm sure you won't listen to a simple 1/2a flyer like myself, I'll suggest you take a close look at the delta below. This one isn't mine. Unfortunately, I didn't take any pics of mine before the maiden flight and I had a servo arm failure. Mine had a modified Cox Killer Bee and was getting along at about a 120mph clip. It wouldn't noticeably lose speed in a 180 degree turn either. I was running an almost square prop of 4.2x4 and wishing I could get my hands on something oversquare. Why did it have such great performance? Cuz it only weighed 7.5oz RTF. Coming back of the building board I've knocked another 1/2oz off. Now where do I get an oversquare 1/2a prop?!

At any rate, to anybody that will listen, don't write anything off. All the books ain't been wrote.

slowmo777

Yes weight is directly connected to induced drag. But while flying horizontally in a 200 m speed trap in both directions after a powerdive - which is THE method to measure speed objectively – weight is welcome. A heavier plane will turn its potential energy more effectively into kinetic energy. That has been proven during several German Speed Cups in the past when participants added some lead during competition to finally gain several additional mph. That implies that the 200 m horizontal distance is too short to suffer from slightly increased induced drag at these speeds we’re dealing with.

Since we’re not talking about pylon racing in general - where weight is most important – I will not focus on this type of speed. We all know that a delta will always lose a pylon race.


ptulmer, you’ll recognise that your speed delta will always be slower in a speed trap compared to an identically powered conventional 1/2A speed plane.

Just check it out: Make a direct comparison with a

[ul][*] conventional ½A speed plane powered by your hot Cox Killer Bee and the best suited prop and[*] your delta speed plane powered by the same Cox engine and the best suited prop
[/ul]

in a 150 or 200 m speed trap after a dive (not in the pylon course which would be unfair to the delta).


Let me give a significant example:

The speed delta pictured in my first post (with fully concealed engine/pipe and 6% thick airfoil) reaches an averaged speed over 200 m horizontal distance after a dive of 170 mph, powered by a .90 ducted fan engine/pipe and the best suited prop. A conventional speed plane with fully concealed engine/pipe, powered by exactly the same .90 ducted fan engine/pipe and the best suited prop achieves at least 200 mph!



No, but it works noticeably better (effective) with a rotating propeller compared to a prop driven delta airframe. The goal is finding the best COMBINATION of airframe shape/design and the type of propulsion.



ptulmer, so all delta fans should carry out such a direct and objective speed comparison, these will deliver just the facts this thread is exploring.

BTW, I am a delta fan as well, as long as I am not competing with a conventional speed plane.

ptulmer

My Feedback: (5)

Weight effects alot more than induced drag. You'll need more hp and thrust to move more mass.

An example of what I'm talking about is this. Look at the Killer Buzz on my website. www.ulmer-rc.com
You'll also see the Blink. (the previous delta)

With an entire club as witness, the 9oz Killer Buzz was no where near as fast as the 7.5oz Blink. Both were minimalist designs specifically for that engine. I'd say the Blink was fully 1/3 faster and didn't need a powerdive. Same engine, same size prop.
With such an extreme lack of weight, the delta would not only have competed doing pylons laps, it would have "smoked" the conventional design. Having learned alot from both attempts, the next KB will come in about 8oz and the delta at 7oz. It'll get closer, but beating the lightweight delta is going to be hard.

The tone of this thread has been to beat up deltas as an extreme speed prop plane. It's not a good attitude 'cause that's the reason deltas exist. The look and are fast, fun and furious airplanes. If that's not what this forum is about, I'm confused.

slowmo777

Right – that applies to all planes. Especially for pylon racing a very lightweight plane (within the regulations) does have advantages. Horizontal accelleration is important here.

But not for prop driven speed planes measured in a straight line speed trap. The setup of prop size, wing load, etc. is noticeable different here. I am comparing those purpose built straight line speed planes with speed deltas since these are always faster than equally powered pylon planes (F3D included).




ptulmer, sure deltas make much fun. Probably more than any other speed design.

The intention of this thread was to elaborate the reasons why deltas always are slower during straight line competition. So I was adressing the “pure speed” freaks rather than the “fun speed” fraction of this forum. No pylon racing addressed!

Accordingly I am not bashing deltas, I am just repeating/summarising experiences of competing speed deltas during Speed Cups and during serious speed measurement in general. That is based on about thirty years of objective and reliable straignt line speed measurement here in Germany.



Regarding your conventional speed plane construction several important features are missing:

- The eliptical or round fuse shape
- You can further reduce the fuse width
- Instead of flat bottom wing airfoil a symmetrical one [for straight line speed (that is the wanted speed in this thread), not for pylon racing]
- No flat tail feathers but symmetrically airfoiled
- fillets between wing & fuselage
- fillets between fuselage & tail feathers
- you may modify your wing and stab layout

I do like your ambitious ½A fleet, but I would like to point out that your conventional speed construction may need further design improvements.



Anyway – I am getting tired since right now in the US or elsewhere no equivalent does exist to the German Speed Cup. As long as nobody in the world will also attempt to measure speed in a FAI speed trap, we will have major difficulties to “understand” each other. We don’t speak the same “language” now. No objective comparison of speed numbers possible. Sorry.