C_Roundy

Mike, your doppler of my maiden flight nailed whichever pass you based it on at 196mph..... Now if you take the OTHER IMPORTANT RESULT from your own anylizer, I was turning very close to exactly 22,050 RPM (RIGHT THEN) ; and feed it into one of my favorite old online calculator standby's that I have used across many years to teach myself (pitch x diameter) prop loading relationships (given the 9.5 x 9.5W) that I ran on that run, and you get 198.36647727272728 mph...... So what I am saying really is that given a clean airframe your thoughts/ideas/concepts DO ring true using the casual benchmark of my own minds eye[sm=wink_smile.gif]
Here is a link, you have probably seen it before but I really like it for "ballparking initially" http://pages.sbcglobal.net/limeybob/

I especially have always held it as my favorite because given any "normal rpm x dia x pitch" you can feed in any known prop's actual rpm to get an HP, which without correction will tend to be very accurate when you feed it new props of the SAME type.
Actually though, in practice; the way it works out is that (for instance) once you have derived the HP for a given prop at a given rpm,............... Then you get to compare the three points of the triangle for ANY new combination of the above.

Mike Connor

My Feedback: (5)

This is another example of where radar and Doppler show the speed to be equal to the actual pitch x the unload rpm. At these speeds it took a much cleaner then average aircraft to do this. My way of looking at it is the theoretical pitch of 11.5, using the lift from pitch and the lift from the airfoil, would give you a theoretical speed of 240 mph. That would put slippage around 15% that is a little over the optimal 10%. My thought would be that maybe the perfect prop may put you at 216 with no other changes. Then minimizing drag at intersections and the wingtip vortices's could further increase speed.

I am a Delta nut and do wish you luck with your project. It would be neat for a delta to be capable of contending in something like the German Speed Cup. My little Delta would take some serious mods for serious speeds and the outcome of what a few are doing will be interesting. Of course yours is a purpose built speed delta and mine is lets have fun for under $100 with speed in mind.

C_Roundy

216mph? We will do a "Damn Sight Better Than That Missy"..... I have been fascinated by certain parts of HighPlains posts recently, And I am here to tell you that he has grasped with his powerful command of mathematics, fairly accurately; what I FEEEL bourne out through my gimbal sticks when I fly Slip Stream.

When you are far short of a given airframe's maximum EFFICIENT airspeed (have you ever heard the phrase "drag bucket"?), gravity figures in as a proportional amount of your total HP during an unloaded dive.
Our prototype airplane in all her 40" wingspan, 60 degree sweep, 800"sq. glory, is close to 9lbs of pure SLIPPERY-NESS at launch, go and run HighPlains formulas for an airframe like that.
When I finish MY work, I WILL have an airplane in my hands, and upon my thumbs that will in those brief magic moments be pushing martial art limits of human perception frame rate.
12" pitch unloaded at about 24,000 in the air being a simple obtainable goal.

The way my airplane's launch handle is positioned in relation to the C.G. right now, I cannot have any more pounds of thrust than the airplane weighs and still be able to guide her upon release.... which is a good thing anyway because it means that when we finish our work to mould the narrow chord 9 x 12/12.5 props and unload them in the air I won't have an unmanagable amount of pesky thrust!!!!... Put that into your way forward machine and tumble it!

Now, having said ALL that; why did Speedboy go 170?............... I truly believe that he built an exceptionally straight/strong/stiff airframe and then propped it correctly for his diving high speed passes.

Mike Connor

My Feedback: (5)

"Missy" [X(] I will take what is said in quotes as expressing your confidence and not that you are calling me a girl.
What is wrong with that "pesky thrust"? We learned in private ground school that when thrust equals drag you will go no faster. I will leave the complicated # crunching to the guys that work in rubber rooms and eat raw meat but I see high speed is equal to high drag so high thrust is needed. If your airframe is slippery enough for a 9" prop then I see potential for decent speed but the 15% slippage with a 9 1/2" prop makes me wonder it you will have enough thrust with 9".

As I stated before I am not an engineer but express my thoughts based on my knowledge and experiences. Also as I said before, "The proof is in the pudding" so time will tell the difference between theory and reality.


Speedboy, Any luck with the 9x10 prop?

SpeedBoy

Yesss !!!!!!

today arrived my props 9x10 apparently come some thin from the leading edge (compared with 10x8 )

maybe shave it is not good idea what you think ???

HighPlains

My Feedback: (1)

Don't knock it if you haven't tried it. Yukhoe is pretty tasty.

Speedboy, just clean up the mold lines on the leading and trailing edges. Light sanding or scraping with a single edge razor blade will do it.

Mike Connor

My Feedback: (5)

What highPlains said plus check the balance are my thoughts.
I find what you are doing very interesting. With level and diving speeds we can see the effects of pitch, thrust and terminal velocity. Pass the Yukhoe and then lets go fly.

SpeedBoy

HighPlans and Mike I follow your tips thank you so much both [sm=thumbs_up.gif]

It seems that the factory made the work by my shaving the leading edge and I like it

Is more thin even compared with 9x9 [X(]

Well I hope only a good weather for saturday and then lets go fly [sm=thumbup.gif]

Mike Connor

My Feedback: (5)

I was wondering if anyone would step forward.

SpeedBoy

Well , last saturday I flew my patriot and probe 9x10 and the result was 269 km/h in a dive , almost the same speed than the 10x8 but.... with more noise , I dont know exactly how much rpm turn the engine , I think that tach are crazy , for a while say 15,200 and then 19,000 [:'(]

I did not have time to tune the pipe to 9" prop so the length of the header was the same than before ,yes I know, maybe this do not help to gaing rpm , even that the engine listen more revolutionized but no more speed []

It seems that the wide of the blade (9" factory ) is very thin to haul the big tonnage of my patriot

I want to probe a 10x9 cut to 9x9 and 10x10 cut to 9x10 (shaved it and no squares tips) and see what happen with more wide blades

What you think guys ???

HighPlains

My Feedback: (1)

Pretty much as I predicted.

From post 14:
I suspect that you had pretty much the correct "sport" prop with the 10 x 8. Any gains from this point will be minor, and perhap more influenced by atmospheric conditions. Days with higher atmospheric pressure, temperatures in the 70's or less, and humidity in the 30 to 40% range will give the best power.

Mike Connor

My Feedback: (5)

Speedboy, Did you forget to raise the gear? [X(]
Many post about Patriots show the 9" and 10" diameter prop a good choice. It would seem that diving speed runs could take advantage of the smaller diameter prop. If the 10x8 prop is the best choice for this application then why was the speed almost the same with a very different prop? A 9x10 and 10x8 would be equivalent to changing gears in a car. Has the terminal velocity of the airframe been reached and the engine is not a factor? There are many variables to consider when calculating terminal velocity but my calculations did show 200 mph was possible without the engine.

To me this has raised as many questions as it has answered. My Yukhoe eating friend may be ahead but his prediction of 185 mph not being met keeps the answer at bay.

Edit - Speedboy, did you get any video for Doppler? I was able to calculate an unload rpm of 17,647 off the first video.

bob27s

My Feedback: (19)

A patriot is a big plane.... its only going to go so fast with given power.

The 10x8 probably is the best choice... better balance for that particular setup.

Usually something along a 10x8 to a 9x10 is about and even swap on static engine load. So keeping the pipe the same likely resulted in the same ground and flight rpms.

SpeedBoy

Yes , and of course I will show you , I hope in this week my brother can edit the video

I measured and compare 9x9 against 9x10 and the 9x9 comes 1 mm more wide that 9x10

I truely believe that if the prop 9x10 came at least 1.5 mm more wide, could mark the difference in speed , I dont know how much , but I think more than 170 mph .

We will see what it happens when I prove the other props but more wide .