Dustflyer

My Feedback: (13)

Let's face it; our Diamond Dusts, Whiplashes and Patriots are not that fast!. Sure, we can hit 190 out of a dive, but straight and level I'm guessing 150-160 tops.

The problem is insufficient thrust. I've found through experience that a Diamond Dust really needs at least 8.5 to 9 inches of prop diameter. Right now the best our engines can turn is the 8.8 X 9.75 around 18.5 to 19,000 rpm. Even at that rpm it is just not enough pitch to generate the thrust necessary to move these airplanes all that fast in straight and level flight.

Pylon racers are faster because they have less drag and can turn an even smaller prop at ridiculous rpms, but that solution won't work with a Diamond Dust because it has too much drag.

Wouldn't it be great to turn an 8.8 X 20 at 15,000 rpm? Now you're talking some serious speed!

The question is: is it possible to build a small model airplane engine with the torque to do it?

combatpigg

My Feedback: (3)

Just like in drag racing, you can put a ton of time and money into adding horsepower, or you can work on stripping the car of all unneeded weight, and see bigger gains from the chassis work. If a DIAMOND DUST was built with a faired in engine, tank,etc., and a single fin, that would make a difference . The speed engines that are commercially sold to the public are conservatively setup so they aren't breaking parts every 10th run. The C/L speed guys have a forum over at DELPHI FORUMS, and they are happy to share their speed secrets. If you want to go really fast you need to own a lathe, or get to know someone who can crank out head buttons, lighten pistons, etc.

ChuckAuger

My Feedback: (12)

You just have to make your own props. The engines have the power (at least mine do..) but the commercially available prop selection is just lacking.

You got the wrong engine!

But the bottom line: (I have heard this so many times...)

Just buy a Jett and run commercial props.

combatpigg

My Feedback: (3)

You're right about the prop situation, but the APC Q40 prop, a NELSON 40, and a "poor man's" Q40 type airframe would be enough for me[X(]!

ChuckAuger

My Feedback: (12)

But they would be a poor choice for a Whiplash. Marginal on a Diamond Dust. There is a thread asking about an 8X8 vs a 10X8 and although I never voted, the guys who said the 10X8 would be faster (we weren't given the airframe) were ridiculed. Well, I say an 8" diameter prop won't give enough thrust on certain airframes to make speed, but on the other hand a 10" is a little large in the diameter department....and you need a LOT more HP to sling it.

So there is no simple answer (except the Jett line) other than to tailor your engine and prop to your airframe.

Dustflyer

My Feedback: (13)

Chuck,

You are right. I always felt the Jett 50 was a bit small. A great set up for a Dust would be a lightweight engine with about 50% more displacement and one of those 8.8 APC props at about 14 or 15 pitch.

Is Jett cranking out something now I don't know about?

ChuckAuger

My Feedback: (12)

No, but Rossi has been making them for years. Here is a pic of an APC 8.8X15:

MyWay

Best results for speed on a diamond dust and a 46 to 50 engine is a apc 8/10. The launch is slow and the torque difficult to overcome. however, after the plane gets moving and the engine unloads, max speeds can be obtained.

ChuckAuger

My Feedback: (12)

You must have missed Dustflyers post regarding the minimum diameter as 8.5~9" for speed.

FlooredCOBRA

I remember seeing that prop before. And again thumbs up for the work you did on it.

I do all my props and I know how much work is involved in making the prop work. It takes me a long time to get my props set up and the way I want them. I was looking at the Bolly site and remember they make custom props. That right there made me want to make a good selection of props and have sent out. Right now I have 2 different pitch props that are made up that work really good and run up on pipe with no problems.

I have 2 more to make then sending them out. After that I am hoping to just buy my props from them with my setup and never have to mess around for hours shaving and balancing over and over.

It would be nice to come home and have that Fed Ex package waiting. Especially perfectly made props from a company that specializes in that.

sydclement

My Feedback: (1)

Gene:
Dub Jett had his new BSE 76 in a 40 size case
at the Toledo Show. Hope someone gives that
a try soon. That 8.8 X 15 should be a good start.

Syd

Dustflyer

My Feedback: (13)

My Way,

Pitch and rpm don't mean a thing unless in combination they produce enough thrust to achieve the desired result.

You might be able to turn a 3 X 10 at 40,000 rpm but do you think you'd go any faster? Of course not, on a Diamond Dust I'd bet there wouldn't be enough thrust to even stay in the air.

I tried the 8X10 as well as the 9X10. Even though the 9X10 turned less rpm the airplane seemed faster to my eye, not to mention a lot easier to hand launch. For a Jett 50, I always seemed to get the best performance with around 9 inches of diameter. The best props for me were the 8.8X9.75, 9X8, 9X9 and 9X10.

Yes, you need pitch but along with that you need the right prop diameter to generate the thrust needed to do the job.



Syd,

More horsepower and more pitch. That's what I've been thinking all along. The BSE FIRE 60L was a good start but not quite enough. Something like that 76 married up with an 8.8 X 15 sounds like the ticket to get a Dust really moving.

I will have to contact APC. Maybe I can get them to crank out some higher pitch props. It must take a tremendous amount of time and effort to hand-carve one of those 11 X 12s into an 8.8 X 15.


Chuck,

Aren't those high performance Rossi's out of production? Not trying to steal any secrets from you but just curious what kind of rpm you've been able to turn your 8.8X15 and on what Rossi engine?

ChuckAuger

My Feedback: (12)

They are too heavy for your needs. I have accumulated a lifetime supply, so production isn't really a problem for me. I don't know what they turn, 15 pitch static is going to unload quite a bit, so I'm not sure any static RPM readings would mean anything.

Dustflyer

My Feedback: (13)

Chuck,

Yes, I vaguely recall that was one of the reasons I never really pursued the Rossi.

You bring up an excellent point. It always seemed the 9X10 unloaded a lot more than the other props. Makes perfect sense, it's like starting a car out in 4th gear.

About your 8.8X15. Did you have to actually recontour or twist the airfoil to get the 15 pitch or is it a result of cutting down the diameter which removes the lower pitch tips and raises the effective pitch of the blade?

banktoturn

Dustflyer,

You start by saying the problem is insufficient thrust, and then in the next paragraph you say that the Diamond Dust has too much drag. You can't pick one of these as "the problem". The real problem is that drag is equal to maximum thrust at a lower speed than you would prefer. You can increase thrust by using a bigger engine and the 9 inch prop, up to some reasonable weight limit, but you'll still be wasting power pulling a very draggy airframe through the air. If you really want to go faster, I would recommend that you work on both the thrust and drag issues. The drag of the Diamond Dust could be reduced quite a bit by fairing the engine, tank, & other draggy hardware. I'd be tempted to use a rear exhaust engine and run the pipe through a nice smooth hump. I'd probably also get rid of the twin fins, and replace them with a single fin on a short 'sting' extending behind the plane. It has always surprised me that the extreme speed crowd continues to fly these deltas with all the stuff sticking out into the airflow. I bet Dub Jett loves it though.

banktoturn

ChuckAuger

My Feedback: (12)

Yes, I re-worked the front and back and checked it regularly on a pitch gauge. If you just cut the tips off, the resulting tip is very thick. Moving the LE back will give more pitch quicker, moving the TE up will not change the pitch as much. Use a belt sander on the back of the prop to remove material and alter pitch. I just bolted a 9X8 to the 11X12, traced around it, and went to work. Takes about an hour/prop.

Here's a pic of one next to a 9X8

combatpigg

My Feedback: (3)

The DD also has the loose covering that sounds like a snare drum at speed, that has to cost something also. I built a 90% DD for a .32, and it is still too big. I think a 75% version with cowling and sheeting would be more like it, even for a lightweight .50. This combo should allow the use of a 7 to 7.5" prop. The apparent speed and actual speed of a model like this should be impressive. BTW, how to get more torque? 50 -60% nitro, and a remachined combustion chamber. Powermaster has custom hi-nitro blends. An upgrade to full compliment bearings, or ceramic bearings is a good thing. Throw away the carburetor and go with a fixed [oversized]venturi. Instead of a throttle, have inflight mixture control. The NELSON/GALBREATH plug is worth some extra Rs'. The intake closing for a bladder fed engine can be moved back to 60 degrees ATDC [or more]. The hole in the crank shaft should be as big as space permits, and some engines benefit from raising the liner, of course the head needs to be reworked to reestablish the squishband clearance[.010" or so].

bob27s

My Feedback: (19)

Hi Folks,

The best Jett can do for a Diamond Dust or Whiplash right now is the FIRE BSE-50 DF, which incorporates the higher timed ducted fan .50 sleeve and port timing. With the pipe tuned for using a 8x9 or 9x9 prop, it will absoultely scream. However, it is a bit less user friendly. I say that a bit tonge in cheek, because what dub considers "less user friendly" is what a lot of engines run like in the first place. This is about the limit of performance for a "40" size case engine... has to do with limits in crankcase and cranfshaft airflow.

For the question of what Jett has in the works, Dub is making the .76L which is the same size as the OS46fx and Jett50, but it is intended for lower rpm, and bigger props.... 3D stuff....using untuned mufflers. The 76L turns a 14x4W at 11.5K rpm, and a 14x6 at 10.5K rpm. Not bad from a "40" But not applicable for speed use. Same goes for the Jett 60L..... same type of animal. They can work in the "40" case at these RPMs since they dont require that huge massflow of air/fuel, such as requried by the 46 and 50 noted above. I guess with some creative prop selection at 13K rpm, they might be coaxed into going fast

I kinda liked the long-pipe setup Dub built for Gene a while back..... heavy prop.... lower RPM. Tends to be more efficient aerodynamically, but if I recall it was getting a bit outside of the envelope where the engine really wanted to run.

Gaining speed from HP is tough. It takes a huge increase in HP. upwards of 20%, to simply jump from 17K rpm to 18K rpm on a 10x6 (example). The resulting speed increase is more a function of the aircraft than the engine. When you start to get up into that 190 mph range, every crack, seam, gap, fuel tube, pushrod, pipe clamp, and servo arm hung out in the breeze, not to mention the engine and exhaust system iteself, contributes greatly to drag.

IF you look at an FAI racing plane, that exemplifies the extreams you have to go through to get the most speed out of an airframe and engine. Cowled engine, cowled pipe, high aspect ratio wing, low drag or retractable landing gear, and very low front cross sectional area. The price for going to the extreme is a tempermental engine, and a long, flat and fast landing (photo of a current example about to go to team trials)

Very nice prop Chuck..... I have a handful of old 11x11 thru 11x13 pattern props.... I will have to cut something up like that and try it. The higher pitch props will help things a bit. You can gain the speed, as long as the prop unloads in the air. If the plane is not moving at the velocity that the prop wants to 'move' at, you will actually degrade prop performance...engine rpm.... aircraft speed drops further..... its chasing its own tail from there.

One day Im going to have to draft up the 'ultimate" sport speed plane. Something user friendly, strong, and extremely stable...... and can slow down a bit for landing. Flying wings are quick, but from a speed standpoint, they are not the fastest configuration. You won't see any full scale speed airplanes flying tail-less. Without an empenage, the wing has to always fly at fairly high positive alpha, and the plane tends to be set up nose heavy. Drag due to lift combined with a stability issue. Those do more to slow the plane down that you might imagine.

A heavy airplane has a similar effect. It naturally has to fly at higher alpha to create enough lift, thus creates more drag.

On QM and Q-500 aircraft, the aircraft are built as close as possible to minimum weight, and I push the CG as far back as possible to unload the wing. Gets the center of pressure closer to the aircraft CG. You may have heard of NASCAR drivers refering to a 'loose' condition, where the car wants to turn a little too easily. This is the model racing equivelant. Loose is fast, but just on the edge of control. CG selection in this case depends on pilot preference, and aircraft flying qualities. On a Q-500 I've flown with the CG back as far as 34%....plane goes like heck, but is so pitch sensitive it is hard to fly a straight line.... so I tend to race them with the CG at 30% MAC. Its a trade of speed and stability.

Keep the parasitic drag to a minimum...... keep the plane light......... keep it properly trimmed...... and take what performance the engine can give you.

Bob Brassell

Rudeboy

I think Bob here just about sums it all up...
The bottom line is: you can have all the power you want, but it isn't going to do much when there's too much drag... aerodynamic drag increases with the square of the speed... going twice as fast means 4 times as much drag [X(]
We already talked about this engine in the MFG support forum... what do you think this thing will turn on a 8x9?

der_steuermann

My Feedback: (2)

I think this seems like an appropriate time to repeat one of my earlier posts belonging to the thread "Format for speed competition":

as we all know the key for serious speed is founded in the airframe/airfoil. That’s the key challenge, nothing else!

A highly competitive engine/pipe/prop combo to be perfectly matched to that specific airframe is obligatory.
Preferably a highly modified engine, but as said before that’s not the real challenge...

BOTTOM LINE: The contest MUST be defined by motor size classes in order to let the special revver brother win who realized the absolutely best aerodynamics.

Personally I don't accept compromises. In other words: Almost NO stock parts - consequently supercritical handling of the entire setup...

C roundy

[/quote]


It has always surprised me that the extreme speed crowd continues to fly these deltas with all the stuff sticking out into the airflow. I bet Dub Jett loves it though.

banktoturn
[/quote]

Well said, but just so you know, Dub Jett loves the optimized high aspect ratio wing, clean fuse. pylon planes... He scratches his head to some degree at the deltas flyers. I actually know better than most from time spent talking with him while doing business. As far as this "Extreme Speed" forum is concerned; the simple truth is that we try to get the most bang for the buck. I personally highly favor handling qualities as at least an equal part of a triangle with speed and cost as the other 2 cornerstones
I uussuuaaallly have less than $1,000 into each of these practice airplanes... And Simply put, no long winged thingy will ever roll in and out of a turn as instantaneously as a lightly built, steep swept delta. Nor will the high aspect ratio TRUE EXTREME SPEED planes allow the average bloke to approach and land without accidentally sailing into the next county before the model gets reasonably close to stall speed. I am speaking as a glider guider from waayyy back among other things.
So to reiterate I would bet you already know,.... These practice airplane are just that; they are for hardcore reflex building and tune-up.
If you want to streamline one I am pretty sure that it wouldn't hurt any feelings that matter... (you won't be the first. and you won't be the last) !!!
Best Regards Charles Roundy

banktoturn

Charles,

My comment about Mr. Jett was tongue-in-cheek, to imply that he benefits from the fact that many of the speed guys have a habit of buying more horsepower to go faster. I understand that he is an accomplished and knowledgeable pylon racer.

I agree that the simple deltas are great, practical practice planes. I think they are great for that, and also, potentially, great as very fast sport planes, and there is nothing about the delta layout that is really bad for speed. My only point was that if you really want to find a way to go faster, as many of the Diamond Dust fans do, it is silly to look for ways to squeeze a little more horsepower from the engine, while leaving all kinds of unnecessary protrusions sticking out, causing huge amounts of drag.

banktoturn

combatpigg

My Feedback: (3)

Hi CHARLES! I wonder how much demand there would be for a DIAMOND DUST upgrade that included a moulded cowl?

bob27s

My Feedback: (19)

One of the fastest things Ive seen in the past two years, was one customer who put a FIRE-50 into an old Formula 1. He built up an old Prather Toni kit, kept it fairly light weight (5 lbs). Had the engine cowled in as was normal for that design..... had to work the cheek cowl a bit to get the carb to fit... and modified the fuselage to tuck the pipe into the side. (wish I had a picture of it).

Plane was super fast (likely in the 190 range), and he actually got a bit of a laugh when he brought it in to land, and the engine was idling . He had a Q-500 prop on it..... a 8.8x9 if I recall.

Looked nice, flew great.

If you can get your hands on a retired F-1 plane, or some of the older QM40 aircraft.......you can own one fast sport ship !! And it will have wheels on it!