N99JH

My Feedback: (66)

Has anyone tried dieseling the ST 4500? What size prop would you recommend? any experience shared will be most welcome. I have 2 of them and a Davis Diesel head.
Thanks
Joshua

Hobbsy

My Feedback: (102)

Josh, I was hoping that Dennis would check in here, I have a 4500 converted to Diesel but have not run it as a Diesel yet. I believe Dennis said he ran a 22x8 or 10 at 7,000 rpm, hopefully he'll see this or MR. Davis may make some suggestions.

N99JH

My Feedback: (66)

Are you planning to run yours anytime soon? I don't know who Dennis is - does he have much experience with Diesl conversion? I actually have 2 ST4500 engines, one brand new Davis Diesel head and about 15 gallons of diesel fuel I bought some 8 years ago, the only problem is that currently I am experimenting with giant scale electrics and therefore no incentive to try the diesel.
Joshua

ddd

Before you run this engine on diesel be sure to run it on glow for 1 1/2 hrs. to break it in. 22X8 or 20X10 are good places to start, the way the plane fly's will determine the best prop. There are issues with some of the carbs on these engines. Be sure this is not your first Davis Diesel.

Bob Davis
DDD

Hobbsy

My Feedback: (102)

Josh, I ordered a 20x10 MasterAirscrew Classic for the 4500 conversion, its the ;argest prop I could order on short notice. I should have it Wednesday, I'llll be baaack.

N99JH

My Feedback: (66)

If you need a 22-8 I may have one you can have for free. Let me know and I will look in my shop tomorrow.
Joshua

Hobbsy

My Feedback: (102)

Thanks, I may take you up on that offer, let us see how the 20x10 does and I'll get back to you here. Take care, Dave

N99JH

My Feedback: (66)

Well, here we are almost a year later. Have you run the ST 4500 ondiesel ye?

Joshua

N99JH

My Feedback: (66)

Well, here we are almost a year later. Have you run your ST 4500 on diesel yet?
Joshua

dennis

My Feedback: (90)

Funny how I just came accross this thread. To clarify my findings and they are years old and dealt with the 2nd prototype head from Bob. I ran it on a 24/8 prop and had about 6600 RPM on it. Bear in mind that this is a 4.2 C.I sized prop. Carb was from a st 60. Oh and at the same time I ren an old prototype engine from Bob. a Quadra 50 that he had converted to diesel but didn't get to run. While both of these engines wern't even near completely broken in they both turned the same 24 inch prop at about the same rpm. The Quadra 50 used the carb from a K&B 65 sportster. These engines were both extremly fuel efficient with these props idle was as low as 600 reliably with an almost clean acceleration. Diesels only get better as the cubic inches go up, or so these engines would make you believe. Oh and since they wern't completely broken in and I figured that it would take hours more of running to be completely set I used an electric starter to get both of them running. . Oh and with a 22/6/10 or 22'10 you could have a very nice war bird flying. Have you ever seen a ST6000 run with a 23/8 4 bladed prop. Note, the prop was homemade and not used for flying at the time.
Dennis

Edit, I just have to check my spelling before I hit post

N99JH

My Feedback: (66)

Dennis
Thanks for your reply. I have 2 ST 4500 and was wondering if after a good break-in and careful Diesel conversion (I have the head plus some 15 gallons of fuel) there is a chance that the 4500 will spin a 28-12 ar around 5000 rpm?
Thanks for your advice
Joshua

dennis

My Feedback: (90)

Josh,
I wouldn't consider using lumber that big. the engine is simply not capable of handleing it. The performance with a 24 inch prop was a suprise but it was reasonably expected that it would swing a larger prop then the 22 max recommended for glow
Remember that the engine is there to provide thrust for your model. depending on the type of model you could get the thrust you need at a relatively modest rpm. What I'm saying is don't be fixated simply on rpm as your only indicator for performance
Another point, I'd strongly recommend that you do not use the stock carb, it's simply too big and I don't like reducing the choke area by closing the carb down. I used a ST 60 carb wide open, the same carb that is used on the Tartan 1.3 CI single. Also I didn't do a lot of flying with the engine, most of the flying was done on a large airtrax model which was a great flyer with the ST4500. It was quite a few years ago and I don't have complete notes on most of the engines that I used anymore. But the summation is that it will swing serious lumber at suprising rpm for the displacement and give reasonable fuel econemy for it's size, I believe that it was around an oz a minute at full throttle. Bob Davis has better figures at his disposal and a much better memory then I do,so as always he is the definitive source for info
One other thing that I do remember is that the engine is cold blooded and takes awhile to warm up properly. I remember Bob chiding me for some pictures of the model with the tell tale sign of black exhaust residue of an over compressed state. Point is let it warm up before you fine tune it

One more thing, The rpm stated was the maximum that I got from it on the test stand, that is not a statement of fact that the engine will consistantly give you that rpm with that prop, it was a really great figure though.

N99JH

My Feedback: (66)

Dennis
I have full respect for your experience and knowledge. Not to be snide but I have an Engine Review for the ST 4500 done by Mike Billington way back when where he tested a Airflow 24-12 on a OS BGX-1 3500 and it turned around 4400 rpm. The ST 4500 is a full 10 cc more so why would it be too much to expect a 26-10 or 28-8 on diesel? I plan on building a 1/3 scale Fairchild 24 and would love to see a 28-8 flying it at scale speed. What do you and/or anyone else with experience think?
Best Regards
Joshua

dennis

My Feedback: (90)

Josh,
Generally dieseling an engine will be considered raising it up to the next displacement. When I said that I had a 24/8 on it I skipped the 3.6 disp and moved to 4.2 size props. But there is a limit to how much lumber you can put on an engine and have it run, or not break something or die from overheating because it has too much load for it to carry. Sorry but a 2.7 C.I engine dieselized is not going to give you meaningful performanceon that sized prop It cannot deliver a miracle. . If you do try it them how about letting us know how you made out. There is always something to be learned.

gkamysz

My Feedback: (19)

Simply put no. The engine does not output enough torque to turn a 28x12 at that kind of RPM. The best you could expect is 4000RPM, but you will probably see less in real life. It would take 50% more torque to turn the 28x12 at 5000 than the engine makes at 6600. That just isn't going to happen. You might see an equal amount of torque at 5000 RPM. If we assume that the engine can still make the same amount of torque at 4000 RPM, that's where my number comes from. In reality I think it will be less.

N99JH

My Feedback: (66)

Greg
Thanks for your analysis. My goal is to power a 1/3 scale Fairchild 24 with a scale dia. prop that will cruise at around 45 - 50 mph tops. I do want low rpm for realistic sound and speed. 28 in. is approx. scale dia. but the lowest pitch that I could find was 8.
I do plan on breaking in one of my ST4500 on methanol fuel this weekend, I intend to run approx. 2 gallons through it and than convert it to diesel and experiment. It may be some time before I will have solid results to report but right now my largest propeller is a Menz 24-12.
What kind of calculations are you using to analyse this kind of performance?
Thanks for your help
Joshua

gkamysz

My Feedback: (19)

I determine the torque for a given operating point, 6600 on the 24x8 quoted by Dennis. Then based on the torque curves I've seen I can guess what torque will be at some other RPM. That RPM is determined by the size of the prop and it's torque requirement. It's not going to be extremely accurate, but when I know a prop is going to take 50% more torque than a known operating point we can rule that out.

As a guess the 24x12 should run right around 5000 on glow, maybe a couple hundred RPM faster on diesel.

N99JH

My Feedback: (66)

Based on this analysis, would you estimate a 28X8 to require more, less, or, equal torque to a 24X12?

gkamysz

My Feedback: (19)

28x8 requires much more torque than the 24x12. Every inch in diameter increase requires 1.5" decrease of pitch to maintain the same torque requirement. So a 23x13.5, 25x10.5, or 26x9 would be the same load on the engine.

http://home.wanadoo.nl/pereivers/Goodies.html

The prop calculator on this page is pretty good. it has some other features as well. It's an Excel File. Please note that many props have manufacturing tolerances or other intentional or unintentional anomalies which might throw the calculated figures off quite a bit.

dennis

My Feedback: (90)

To reinforce what Glen has said about variences in props. Invest in a good prop pitch guage and you will see that most are not the pitch described on the front. Many are less then the stated pitch. This in many cases is what allows you to achieve some slightly higher results then you would expect. Also there is a world of difference in performance between props of the same pitch but from different manufacturers. It is always a challenge to match the best prop to the engine to get the performance you desire. Simply bolting on a prop and expecting it to do all that you want is in many cases totally unrealistic. But I will also state that if you use a 12 inch pitch on the 4500 your going to be very disappointed.
dennis

N99JH

My Feedback: (66)

Hi Fellas
I am going to revive this subject, please don't get mad
I finally ran my ST 4500 on diesel this morning and wanted to share the results. I broke the engine in as a glow on Super T fuel and 22-10 Zinger prop. At the end of the break in I ran it wide open (albeit slightly rich) and recorded 6000 rpm. Switched heads to DDD (brand new) and installed a ST 60 carb based on Dennis's experience. After three 6 oz. tanks, the best result I got was steady 5700 rpm with the Contra Piston open 2 1/8 turns from bottom, needle valve at 3 - 3 1/2 turns open. I also tried a Menz 24-12 and got 4000 rpm. To be honest - I am a little disappointed. Expected better than that.
What do you guys think?
Attached are a couple photos of the handsome beast.
Joshua

earlwb

I would suggest trying it with the same carb that you used for the glow fuel runs to see if the smaller carb affected the performance. The smaller carb has improved fuel draw but it restricts the intake more thus it won't quite rev up as high. But the smaller carb would allow it to turn larger props than the larger carb would.

Hobbsy

My Feedback: (102)

I agree with Earl, the .60 carb is too small. Get a SuperTigre 2300 carb, it has the same venturi dia. as the 4500 carb but with a fat spraybar. I haven't been able to do much since about Feb. 1st. I tore my left bicep from mu shoulder and 75% of my rotator cuff. One more week of wearing this huge thing called an Ultra Sling III and then therapy.

bogbeagle

I'd be very happy with that performance. You will be consuming a comparatively small volume of fuel, I expect.

Does the engine throttle reasonably well and idle reliably?

IMO a fan that keeps turning is worth any amount of brute force.

N99JH

My Feedback: (66)

bogbeagle

I could idle the engine down to 1000 rpm and hold it there all day long. Transition to wide open is instantanous every time. Not even a hint of hesitation. Fuel consumption at WOT is about 1 1/2 oz/min.

Earl, Dave

I do not have a ST 2300 carb but found a ST 3000 carb in my collection which is the same size as the 4500 carb. Lucky me though - it has a OEM restrictor in it so I assume that it is more or less similar to the 2300 one . Ran the engine again and recorded 6200 rpm.

Next test is going to be with the original 4500 carb. Same Zinger 22-10 kept with all carbs for proper reference and comparison.

Joshua