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

OVERHAULIN' a DD

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Old 03-03-2007, 01:32 PM
  #1  
combatpigg
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Default OVERHAULIN' a DD

This plane had a K&B 6.5 RIRE on it last year. It was a good buy off the RCU auction for $65, talk about fast for cheap. I decided to get a Nelson .40 and use this plane to get aquainted with the engine out at the hay field. The Nelson is about 1/16" wider at the mount beams and the spinner is smaller than what I used on the K&B, so the whole front end of this plane needs to be reworked, new cowl, etc.
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Old 03-03-2007, 02:49 PM
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Ed Smith
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Default RE: OVERHAULIN' a DD

IF, IF that is a Nelson F3D moter with an APC carbon Q40 prop be carefull. According to a message on the APC website APC will not sell any more carbon Q40 props until certain issues have been resolved. The new Nelson Q40 engine has been throwing blades off the APC props.

Ed S
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Old 03-03-2007, 02:57 PM
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Default RE: OVERHAULIN' a DD

Thanks, ED. I read about that problem AFTER I bought the props. They were listed as FAI props, so I figured they were good to go. It is not easy to be 100% safe around these suckers. The F/F and C/L starter rigs look to be the safest, but what a contraption to have to lug around. I have dealt with Steve Wilks' Eliminator props in the past, it might pay to give him a call.
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Old 03-04-2007, 12:08 AM
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Default RE: OVERHAULIN' a DD

More progress on the body work. The needle valve stem is going to take some figuring to make it usable. All there is right now is a stem sticking out the side of the cowl. I think I have heard of silver soldering an Allen head to the needle. A long needle will beat itself to death, depends on how smooth this engine runs. The needle only has to be readily accessible, vibration proof, and not interfere with the aerodynamics, that's all.
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Old 03-04-2007, 08:37 AM
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Ed Smith
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Default RE: OVERHAULIN' a DD

If I may make a cowl suggestion.

On the cowls we made for F3D Pylon Racing using the piped Nelson engine the best cooling we found was with a pressure cowl. The only hole in the top of the cowl was for plug access. A piped engine can be sensative to heat variations. Our pressure cowls forced the cooling air through the cooling fins by means of tight fitting shrouds around the engine. We did not have air playing on the very front of the engine. The shrouds came around the rear of the case and were open at the back to allow the air to exit over the pipe which was also shrouded.

The pictures show what we did.

Ed S
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Old 03-04-2007, 12:28 PM
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Default RE: OVERHAULIN' a DD

Ed, are you saying that pressure cowling does a better job of uniform cooling? Judging from the scorched paint from running this thing last year, the bottom end was getting very hot. I think it would pay to bring fresh air into this area.
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Old 03-04-2007, 02:46 PM
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Ed Smith
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Default RE: OVERHAULIN' a DD

Combatpigg,

Yes, we had no problems with overheating engines, certainly not the bottom ends. The air entering the front openings is not allowed to just find its way to the engine. The pictures do not show it too well but the space from the front of the cowl to the shroud is blocked off. The incoming air is ducted right through to the engine.
As you can see from the pictures there is no paint scorching. There was not on the fuselage either. there is hardly any on the inner cowl shrouding. The shrouding actually was a tight fit on the engine. It was touching the outside of the fins. My early shrouds were made from the cardboard tubes from toilet rolls. I fitted them around the engine, slipped the outer cowl in place and glued it all in. I then removed the cowl with the tube in place and cut the required slots and added the duct work. I soaked the tubes in CA or resin. There is a fair bit of work actually. I think the C/L speed fliers do the same thing. I know the C/L team race fliers do it. Their diesel engines are realy heat sensitive. Even Volkswagen did it on the rear engine Beetle!

In writing this I remembered I had an old F1 Pylon Racer floating around. Cowl Pictures attached.

Ed S

Edited for minor corrections
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Old 03-04-2007, 02:50 PM
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Default RE: OVERHAULIN' a DD

Hi CP, What Ed is talkin about is very similar to that article on the supercool website I sent you a while back about making gains with low speed but high pressure cooling, albeit they achieved this with a further shroud built directly over the engineand then cowling the whole thing .One of the key aspects was to direct the air over the top of the engine and knowing where the ports are so thatair cooled the correct areas of the engine aswell
As a sub note it was also important to have cooling along the pipe especially the first 1/3rd of the pipe

this is how I built the cowling on my DD ..it doesn't have hole in the top as I decided to use a remote glow starter,
it just has two slots..one for the engine, one for the pipe

One other thing it that was found to be of benefit was to chamfer the slots with round edges. If you just cut slots and leave the edges sharp this apperently can cause turbulent air which might not flow correctly over the engine..being less effective
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Old 03-04-2007, 03:08 PM
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Default RE: OVERHAULIN' a DD

One of the key aspects was to direct the air over the top of the engine and knowing where the ports are so thatair cooled the correct areas of the engine aswell
As a sub note it was also important to have cooling along the pipe especially the first 1/3rd of the pipe
Exactly.

My red cowling has this. Easily seen is the horizontal inlet for the head cooling and the vertical inlet for the case. Both inlets were ducted seperately. The pipe was also shrouded down to its largest dia.

Ed S
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Old 03-04-2007, 03:55 PM
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Default RE: OVERHAULIN' a DD

.........and if this means that more aggressive needle settings are possible without using so much extra fuel as a coolant, then I'm beginning to catch on. Thanks for showing me examples of your work, Ed

HB, what was the end result of your efforts with your delta?.

Remember those old DD ads that said,"Clocked at over 200 mph"? It just hit me that they could have been cruising around in a private plane that was doing 200 mph while they held their radar gun on the 180 mph model, which technically is at least grammatically correct.
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Old 03-05-2007, 02:45 AM
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Default RE: OVERHAULIN' a DD


ORIGINAL: combatpigg

Remember those old DD ads that said,"Clocked at over 200 mph"? It just hit me that they could have been cruising around in a private plane that was doing 200 mph while they held their radar gun on the 180 mph model, which technically is at least grammatically correct.
or they forgot to mention they were down wind passes with 30mph tail winds. i have no cowling on mine and the bubble Jett tank sticks up a bit more then the average setup so i get allot of drag there but i don't think cleaning it up is going to gain me 40 mph, with the Jett 60LX turning an APC 8.8x9 Pylon prop at 21K i can only get a tad over 160mph out of it.

kc

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Old 03-05-2007, 04:44 AM
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Default RE: OVERHAULIN' a DD

I dont have hard figures to go with here but I am swapping the Irvine 40 re for a KB 7.5 DF engine...not that the delta will hit any real exciting speed but I would like to see if it can get into the high 180 mph low 190 mph range( conjecture on my part of course)

the Irvine 40 was turning a 7 X 10( didn't tach it leaned out)..but had to small of a prop... the instruction called for 7 x 11 or 11.5 ..which I couldn't find unless I went to a 12' prop and cut it down..I didn't feel like modifing the spinner to accommodate nor get a bushing made up to fit the prop hub to the prop stud

I have been told to tune the KB to about 18,000 ground rpm and it should really unload ..with a high nitro content( 30 to 40 %) might even see near 25,000( yeah I know I got high hopes here) but they say this engine can do it.. probably not with an 8.5 x 8.8 or something like that (still thinking the prop out)

the other factor now is making my own carbon fibre props .. I wouldn't mind trying some custom diameters and pitches and playing with different foil cross sections which means carving some blanks then making molds and lying down some CF.. I find few selections commercially available in CF, those that are seem a bit small in pitch..so there is a bit of work ahead

as soon as I get some free time I'll post some photos of the cowling with cooling chamber/diffuser
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Old 03-05-2007, 12:06 PM
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Default RE: OVERHAULIN' a DD


ORIGINAL: HaveBlue

I find few selections commercially available in CF

yeah and the carbon APC's are slinging blades left and right

kc
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Old 03-05-2007, 01:17 PM
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Ed Smith
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Default RE: OVERHAULIN' a DD

I think HaveBlue was refering to continous strand carbon props. The APC props are injection molded. Not the same structure at all.

Ed S
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Old 03-05-2007, 01:35 PM
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Default RE: OVERHAULIN' a DD

i belive the only blade issues had to do with the "new" apc 7.6" sizes ..... the 7.8" diameter props have been run for a while without issues that I know of.

Nice job on the DD overhaul.... good to see the major source of drag being addressed.
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Old 03-05-2007, 04:56 PM
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Default RE: OVERHAULIN' a DD

ORIGINAL: combatpigg

This plane had a K&B 6.5 RIRE on it last year. It was a good buy off the RCU auction for $65, talk about fast for cheap. I decided to get a Nelson .40 and use this plane to get aquainted with the engine out at the hay field. The Nelson is about 1/16" wider at the mount beams and the spinner is smaller than what I used on the K&B, so the whole front end of this plane needs to be reworked, new cowl, etc.
You don't do anything half-assed in the power department do you CP? Yikes!

Hope that covering is strong, those wings will take a worse pounding than the head on Buddy Rich's snare drum.

COOL!
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Old 03-05-2007, 04:59 PM
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Default RE: OVERHAULIN' a DD

Have you found a new flying field yet ,

Send some pic's of the DD,

Blew the wing of my VIPER500 in december and am now puting a LR-1 with a JETT BSE35 and pipe , this is a pretty little plane, I got the orange and red version,

Later Mate, Grant
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Old 03-08-2007, 01:26 AM
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Default RE: OVERHAULIN' a DD

Hey Grant,..no, no flying field yet.
she's primed and sanded but not painted yet..I having alot of trouble deciding on a colour scheme for it...probably going with green yellow for the aussie theme

I couldn't wait to see how it went before getting her all finished..but If I run the KB7.5DF engine, I'll have to make another cowl

I will have pic's as soon as I get my camera back in a coupe of weeks..I lent it to one of the guys at work for his holidays

The LR1 sounds wild..I have heard that those Jett 35's really scream..I'm still hoping to get a 60LX when things improve
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Old 08-01-2007, 10:18 PM
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Default RE: OVERHAULIN' a DD

I guess it has been awhile! Local club racing and getting ready for RC combat is my lame excuse, plus a couple of 1/2A projects. The plane is ready to fly, I just want to build a padded stand to hold it during start up. Another detail will be to come up with a starter cone for this needle nose spinner. Weather is supposed to be in the 60s and overcast this weekend......perfect.
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Old 08-01-2007, 10:38 PM
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Default RE: OVERHAULIN' a DD

I just flip the standard starting cone around as the rear hole is rather small (insert joke here), you could customize it---

GREAT thread!!
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Old 08-03-2007, 10:02 AM
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Default RE: OVERHAULIN' a DD

I cant wait for the flight report on this beast

should rip the sky a new one!
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Old 08-03-2007, 06:20 PM
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Default RE: OVERHAULIN' a DD

Bob, as soon as I can, there will be a clocking. With just a 4 oz tank, that's all there will be time for. It doesn't look like there will be any flying until some hurdles get cleared, though.
First problem is the tips came off the first APC FAI prop.......I think it was a 7.1x8.4. I think it was excess vibration that led to the prop failure, which leads to the second problem....indexing the spinner per the instructions. They tell you to center the crank port with the intake hole in the case, then allign the notch in the spinner backplate with the intake opening. Must be so the heavy part of the backplate cancels out the mass of the piston at TDC. I think my thinking is straight here, got to double check that. Right now it is a vibrating mess. Third hurdle, the engine came with a stack of head shims installed, to net about .060" squishband clearance....on 10% nitro the engine would not even start. I took out half the shims and got it to run. Now the challenge will be to find out where the head should be stationed and with what nitro %, instead of me finding out the hard way. I feel that I've already paid for that amount of R&D. Fourth detail will be to get some spare glow plugs [these aren't like the Nelson plugs you normally see] and of course some FAI props that actually are true C/F, continuous strand. I need to see about twice what I was getting last night before this plane is worth taking out to the field......stay tuned.
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Old 08-03-2007, 07:50 PM
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Default RE: OVERHAULIN' a DD


ORIGINAL: Razor-RCU

I just flip the standard starting cone around as the rear hole is rather small (insert joke here), you could customize it---

I ain't going to touch that !!!!! OH NO !!!!!
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Old 08-04-2007, 03:22 PM
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Default RE: OVERHAULIN' a DD

OK, much progress has been made. I was at fault for the vibration problem, I did not see a timing notch in the dust cover part of the spinner backplate, I was focused on the milled out portion of the backplate. In other words, I had the danged thing on there 180 out. Next item was setting the head clearance. The piston sits .230" below the deck at TDC. With all the head shims removed except for 1, the head only goes in .164", for a net of .070" clearance. I expected a zero nitro FAI engine to be designed much tighter. The head has what I would describe as an open chamber, as well. On 10% nitro and a 7.4x8.25 APC it began to resonate at 20,000, then amazingly kept on climbing up to 25,000 as I leaned it out. I didn't dare go any further, I'm going to read the plug and the top of the piston for signs of abuse.
Anyway, the performance is good enough now to go ahead and head on down to the field with the timing crew. The trick will be rounding them up.
As a side note, there must be much more power lurking here than what I've found in the first hour of snooping around. My question now is why would they ship this engine to me with 1/8" worth of extra head shims stacked inside the engine, to make the break in easier?
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Old 08-04-2007, 04:11 PM
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Default RE: OVERHAULIN' a DD

If the engine and airframe performs well my guess is 175 mph +/- 5 mph. Your timing method eliminates parallax so it is probably more accurate then some but a comparison to Doppler would be interesting.
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