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RE: Engine for SAE heavy lift Competition - 7/30/2008 10:54 PM   
CrateCruncher



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quote:

ORIGINAL: Sport_Pilot

quote:

However as you can see from the reports on the link the successful aircraft were usually ungeared.



Do you know if it was a performance issue (didn't climb as well, weighs too much), reliability issue (gear or belt breaks), or learning curve ( too much or too little prop, needs differant plug or fuel, etc). Knowing the issue could help the decision process.

I read everything in that link and couldn't find where anyone even attempted drive reduction. An SAE competition will draw many more entrants and a bit stiffer competition as a result. Both AeroDesign East and West 2008 attracted over 50 teams each from universities as far away as Brazil and Australia.

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RE: Engine for SAE heavy lift Competition - 7/31/2008 6:04 AM   
freakingfast


 

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Status: offline 		Ed Moorman’s post on a OS 55AX :

Quote:
“Temperature: low 80s
Humidity: medium
Fuel: Omega 10% nitro, castor blend
Props: All APC
Muffler: Jett-Stream

12-4: 15,000
12.25-3.75: 14,500
12-5: 14,600

The 12-4 looks a little small.
The Jett-Stream looks like a good thing for the 3D people who like the 12.25-3.75 wide blade.
I didn't have an APC 12-6, but I'll bet it would be good, too. Probably be the best sport prop.” End quote.



A Jett 60 turning an APC 14X4 @ 11000 RPM is not that impressive, it’s only 1.38 hp with 9.7 lbs thrust and 41.7 mph pitch speed.
An OS 55AX turning an APC 12X5 @ 14600 RPM is very impressive, that’s 2.05 hp with 11.3 lbs thrust and 68 mph pitch speed (with Jett-Stream muffler).

The Thrusthp program has problems with thrust. Change the pitch in the program and note that the thrust out put dose not change. I use the Excel based “Prop-power-calculator.”


For the project I would use a Jett 60 (L or LX????) a Webra 55 or an OS 55 AX, you just can’t beat a 2 stroke for power.

I would look into belt drive reduction for turning a larger diameter prop for greater efficiency. A belt drive would keep the prop shaft turning the original direction verses a gear drive. Even with the drive train losses it would still be way ahead of a four stroke.
You reduction ratio should be based on your needs like, thrust & airspeed needed, spin up time of a large prop, ground clearance and putting the engine near max hp at takeoff.

There are small Kevlar cored, timing belts and pulleys that fit the bill, but they need to maintain tension so you would need to have an outboard bearing on the crank shaft as to not put too much side load on the engine’s bearings. Should the belt try to “climb” a tooth because of low belt tension,…it would be very bad.

Have Fun and good luck!


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RE: Engine for SAE heavy lift Competition - 7/31/2008 6:49 AM   
submikester


 

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Status: offline 		It's my understanding that SAE contest has rules like this one:

Design and Fabrication
- Designed and built by the SAE student members (without direct involvement from professional engineers, radio control model experts, pilots, machinists, or related professionals)

Engine selection may fall under these criteria - I would be careful as you may be skirting the rules here and when doing a search for "SAE lifting competition" on google this is the first link that comes up.

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RE: Engine for SAE heavy lift Competition - 7/31/2008 6:51 AM   
XJet


 

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Status: offline 		I think the KISS principle is worth remembering whenever you're building something for a competition.

The less there is to go wrong, the less is likely to go wrong.

Reduction drives are nice in theory but the reality is that you *will* lose power through them, the do add weight (not a good thing when you're already struggling to lift a heavy payload) and they are a possible source of failure.

Remember that you are effectively changing your "gearing" when you simply select a different prop but it's much simpler to do.

A 14x4 will give a lot more static thrust than a 11x7 but it will not propel your vehicle to the same high speed so it has a similar effect to gearing the motor down to turn a larger coarser pitched prop (such as a 18x8). And although a 18x8 will be more efficient than a 14x4, the efficiency gains from the larger/slower-spinning prop may well be wiped out by the additional weight and losses.

If it were me, I'd first determine my optimum flying speed (you'll need to calculate this based on the l/d of your airfoil section, area and loading) and that will give you an idea of the propwash speed (with allowance for slip).

Once you have this figure you can work out the prop size/RPMs needed and thus the HP required. Try and match this info to the readily available engines and you may find you have a match somewhere.

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RE: Engine for SAE heavy lift Competition - 7/31/2008 2:08 PM   
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Status: offline 		Another option we have been researching is the possibility of a pusher/puller prop configuration (Using the Jett engines since these can be custom).
As far as previous discussion with the team goes, and my personal research shows great potential, as well I think it would give us some brownie points with the judges.

The configuration therefore, would entail having a higher displacement engine up font, such as 0.35, and have a pusher engine inline with i at say, 0.25. Since Jett and oher cstom engine producers would be able to optimize this configuration, I believe this to be a viable option.

And to answer the question about input from outside members, it is indeed in the rules of the compition that it is not allowed. But this pertains more to design and build of the aerdynamic properties of the aircraft, while motors, which are prebuilt and their performance data public knowledge, would not fall under such a catagory. To reiterate, this discussion is simply in the public realm of ideas.

Thanks again all!

< Message edited by Snare_TS -- 7/31/2008 2:16 PM >

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RE: Engine for SAE heavy lift Competition - 7/31/2008 2:24 PM   
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Status: offline 		Hey, what school are you in? Also, is that the Design, Build, Fly competition for Aerospace Engineers? If so, I'm dying to find out more about the club b/c I'll be at V Tech starting August 20.

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RE: Engine for SAE heavy lift Competition - 7/31/2008 10:46 PM   
XJet


 

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quote:

ORIGINAL: Snare_TS

Another option we have been researching is the possibility of a pusher/puller prop configuration (Using the Jett engines since these can be custom).

I wouldn't bother the inefficiencies of the push/pull configuration are higher than for a single-engine.

The problem is that the pusher engine's propellor is operating in what is effectively the turbulent propwash of the other engine so you'll get all sorts of aerodynamic losses as a result.

Push/Pull is only really a viable option when you have to keep the prop-diameters to a minimum but since that's probably not an issue for you, I'd stick with a single engine configuration.


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RE: Engine for SAE heavy lift Competition - 8/1/2008 1:10 AM   
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quote:

ORIGINAL: submikester

It's my understanding that SAE contest has rules like this one:

Design and Fabrication
- Designed and built by the SAE student members (without direct involvement from professional engineers, radio control model experts, pilots, machinists, or related professionals)

Engine selection may fall under these criteria - I would be careful as you may be skirting the rules here and when doing a search for "SAE lifting competition" on google this is the first link that comes up.



If doing a google search and getting advise here from some who may or may not be an expert is against the rules. Then using calculations from a textbook is also against the rules. I do not think that rule excludes research on google or here.

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RE: Engine for SAE heavy lift Competition - 8/1/2008 1:16 AM   
Sport_Pilot



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Status: offline 		Model engines are not the most reliable engines in the world. Though I think a skilled modeler can run a twin reliably your team is probably a mix of skilled and unskilled modelers. If you have a twin then there is twice the probability that one engine will quit. I doubt you have any better chance of winning on one engine that with no engines, though it may help you to get the plane back. Besides I suspect that one large engine will have better thrust, unless as with the Wankel you have two higher HP engines.

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RE: Engine for SAE heavy lift Competition - 8/1/2008 2:11 AM   
victorzamora


 

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Status: offline 		If you end up going with a twin, a Twin-Sync is the way to go. It's not too expensive but it's definitely worthwhile.

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RE: Engine for SAE heavy lift Competition - 8/1/2008 2:38 AM   
XJet


 

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ORIGINAL: victorzamora

If you end up going with a twin, a Twin-Sync is the way to go. It's not too expensive but it's definitely worthwhile.

Let me repeat the golden rule of competing in a competitive environment: Keep It Simple!

Forget twin engines.

A .60-sized engine turning a low-pitch (4") prop of 14" diameter has almost exactly the same prop-disc area as two .30-sized engines turning 10-inch props. But... the bigger prop will be noticeably more efficient.

And... the .60-sized engine will produce more horsepower than two .30-sized engines.

So more power, more efficiency means more thrust.

Plus... far less complexity and fewer points of failure.


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RE: Engine for SAE heavy lift Competition - 8/1/2008 2:41 AM   
victorzamora


 

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Status: offline 		I agree, single engine is the way to go...but if they absolutely HAD to for their design that's the way to go. That's what I meant. Sorry that it sounded like I was recommending a twin....it's DEFINITELY not what I meant.

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RE: Engine for SAE heavy lift Competition - 8/1/2008 2:23 PM   
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Status: offline 		Erico,

What you need is lots of horsepower..., lots!

This best way to get lots of power is with a two-stroke with a properly tuned pipe. Diesels, diesel conversions, crossflow scavenged engines with deflectors on their pistons and other curiosities are not going to cut it. A schneurle ported glow ignition two-stroke with a full length pipe is the best solution by far.

Find a good, high performance .60 or .61 that has actual bore and stroke dimensions (forget the ".60 or .61" number on the side) that calculate out at no greater than .60 ci. Downunder suggested a few engines that would be great choices. YS, OPS, Rossi, OS and many others made some great rear exhaust sport .61s back in the 80s. A Jett .60 is also a good choice and is lighter than the big block engines, but if you go this route, get a header and full length tuned pipe for it so you can fine tune the header length.

The key is to get a very fine pitch prop of the largest diameter you can spin at the engine's best horsepower output rpm. A good piped .61 will pull the readily available APC 12.25 x 3.75 prop at well over 15K, possibly 16K, which will produce craploads of static thrust. An even finer pitched, bigger diameter prop at the same rpm will produce even more thrust but might be harder to come by. A custom made prop might be the best solution.

The good thing about using a full length tuned pipe is that you can experiment with different props and tune the pipe for each one. For a good .61 sport engine, with proper pipe tuning, you have an effective rpm band from about 12k to 16k, depending on the length of your header pipe.

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RE: Engine for SAE heavy lift Competition - 8/2/2008 6:21 AM   
victorzamora


 

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Status: offline 		Try this engine, it's geared 2:1 so it's got MASSIVE torque. It may be the ticket for what you're looking to do.

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RE: Engine for SAE heavy lift Competition - 8/2/2008 3:00 PM   
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Status: offline 		I've crunched several sets of numbers for this. The best bet is going to be the .60 on a pipe. I would probably run something with a little more pitch than a 12.25x3.75 but that's just me. The gear reduction if allowed, would offer more thrust at the expense of weight, cost, complexity, and reliability.

I mentioned the RCV either here or in another forum. If it made the 0.9HP quoted it would be a great choice but on their prop selection page it list RPM figures for props and the engine only makes 0.6HP or so.

I know there must be brownie points for certain aspects of design and component selection. If these outweigh the issues of complexity and reliability it might be worth using an unorthodox approach for this competition. If you can exploit the rules to your advantage do so.

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RE: Heavy Lift Engine Optimisation - 8/8/2008 7:37 AM   
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Status: offline 		I was also involved in the heavy lift competition when I was in school so I no what you are looking for. Question. Must it be a 2 stroke running on conventional glow fuels?
I ask this because if your only limitation is engine displacement than I would sugest you try a Davis Deisel head conversion for whatever 60 size engine you choose. Your prop size goes up as does your thrust. Something to consider.
Hope this helps. Goo luck.

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RE: Engine for SAE heavy lift Competition - 8/8/2008 8:11 PM   
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Status: offline 		Greg,

Sorry for the delay... much travel and confusion since you commented on a post of mine 30July...

Agreed! If the GP car were not rebuilt thoroughly, it probably would survive to a hilltop much faster than a fat old fire engine. But, without that total rebuild, would it haul the same load as well? That's the point I'd hoped to address - similar demanded performance.

After finally getting back here, and reading further along, I get an impression that a close look at heli setups might simplify things for the contestants. They may be able to juggle gear pair, or cog- or friction- belt pulley ratios to get the needed RPM to the prop regardless of engine shaft RPM. Shaft RPM, of course, would then NEED to be at max HP. I'm not into RC helicopters, so only vaguely aware of their engine to rotor transmission systems. If there are no available .60 size setups, a pair in the .30 range might do it.

Thanks for catching the point on FD v GP!

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RE: Engine for SAE heavy lift Competition - 8/8/2008 8:40 PM   
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Status: offline 		What you don't want is a high reving racing engine like a Jett or any type of ducted fan motors.
You need TORQUE and more TORQUE to swing a large diameter/low pitch prop.
Back in the early 80s many manufactures where producing geared .60's. These where being used on the aerobatic comp' scene.
Aircraft up to 80inch span and then performing serious vertical manouvers. This is the thing you need!

Then you need the lightest air frame and a HUGE wing with a high lift airfoil set a well positive AofA.
When you're designing don't forget the body and the stab are both lifting bodies so design accordingly.
You're looking to get airborn, not win aerobatic prizes. But those 80's geared engines is exactly what you need.
eBay my friend!

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RE: Engine for SAE heavy lift Competition - 8/8/2008 9:08 PM   
TFF


 

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Status: offline 		Too many of these type contests are lost because what is on paper is harder to reproduce in real life without a NASA lab. A screaming 60 is only needed if you have already tested everything and it is not enough. Being able to start and tune, run without overheating every time will beat 95% every time. If I remember the story right, Beachcraft wanted a dynamic scale model of the Bonanza. I think it was built to about 1/5 scale, the plane weight was in the 20s, and the engine was an Enya .60 not geared. They flew it and it was featured in one of the mags. I think a geared 60 with a 4 meter sailplane type wing with structure would easly pick up 55# total with the open rules they have. If they were limited to something like a 10# airframe or 100 in wing the stakes would be much higher.

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RE: Engine for SAE heavy lift Competition - 8/8/2008 9:52 PM   
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quote:

ORIGINAL: David Bathe

What you don't want is a high reving racing engine like a Jett or any type of ducted fan motors.
You need TORQUE and more TORQUE to swing a large diameter/low pitch prop.



The Sport jett engines are not high-timed racing engines. Jett makes a variety of different sport engines.

For special applications, they can be tuned for what ever prop and rpm is appropriate.

What was discussed here is the SJ-60L or the FIRE-60L engine ..... its a .46 engine same physical size as an OS .36 or the Jett 46/50 engines very light weight at about 17oz flying weight (with muffler). Lots of toruqe and top end power, and it is very user friendly. Great midrange and transition.

With the long pipe on it, it can and does turns 12", 13" and 14" props. It would be set up more like the CL stunt Ro-jett (as was discussed earlier in the thread. Tuning to target 10,000 - 11,000 rpm mark with the 14x4 is pretty much a good bet. Dub has managed to get these to turn that prop very similar to what the BSE-76L is capable of.

Quite a few heavy life teams have used different Jett engines over the past 10 years. The FIRE-90 and FIRE-76L were quite popular, and Dub set them up quite well for the big prop/lower rpm applications. Many have in enjoyed the power.

A word of caution (advice?). Keep things simple. Focus on the powerplant as a system - engine - prop - exhaust and most importantly the fuel system. They function as a unit when combined with the airframe.

More than a few competitive SAE teams run into problems because of poorly set up fuel systems or trying to squeeze that last 1% out of the powerplant. Avoid that trap. You want reliablility. If that comes at the expense if running rich 200 rpm... it is worth it.

(besides, you static ground rpm is an important reference, but does not mean much once the plane is rolling... the engine will gain rpm and stage a bit more on the pipe once it unloads a bit)

Any questions..... I am always around here.... and both Dub and I are only an email away.

Bob Brassell


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RE: Engine for SAE heavy lift Competition - 8/9/2008 12:00 AM   
Broken Wings



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Status: offline 		It would be interesting to know how many SAE Heavy Lift Competitions have been won using Jett/RO-JETT engines.
I'd be willing to bet it's a bunch...


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RE: Engine for SAE heavy lift Competition - 8/9/2008 7:38 PM   
David Bathe



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Status: offline 		This was the type of thing I'm talking about.
Get Bob to build you one of these... he's keen.
I'd guess he'd supply it for free.
Be a good advert.

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RE: Engine for SAE heavy lift Competition - 8/9/2008 11:04 PM   
bob27s



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Status: offline 		I remember those never owned one but ive seen a couple run.

I am 90% sure the heavy lift rules do not permit gear reduction anyway.


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RE: Engine for SAE heavy lift Competition - 8/10/2008 12:33 AM   
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Status: offline 		SAE Aero Design 2008 engine rules for open class:

40.2.1 Engine Requirements (New for 2008)
Open Class aircraft must be powered by internal combustion, reciprocating engines. The total displacement of Open Class engines may not exceed .80 cubic inches. The common-use displacement will be used to determine displacement, i.e. the advertised displacement. Open Class aircraft are not limited to the number of engines. No changes to the internal displacement of the engine(s) will be allowed. There is, however, no restriction to the make and model of the engine(s).

40.2.2 Propeller and Gearbox Issues
Gearboxes are allowed in Open Class in which the propeller RPM differs from the engine RPM. Multiple engines, multiple propellers, propeller shrouds, and ducted fans are allowed in Open Class.

40.2.3 Competition Supplied Fuel
Open Class teams may provide their own fuel, but fuel for Open Class entries must be acceptable for use by the AMA and the competition organizer. No fuel systems with gaseous boosts in which gases other than air enter the internal combustion engine will be allowed; pressurized air is also not allowed. Engines utilizing extremely hazardous fuels such as those containing tetranitromethane or hydrazine are prohibited. Open Class teams are welcome to use the competition-supplied fuel used by the Regular Class.

I'm not sure why the contestants are so focused on .60 c.i., maybe rules changed for 2009? Also theres no wingspan limit in open class only a maximum weight limit with fuel of 55 pounds.

< Message edited by CrateCruncher -- 8/10/2008 12:39 AM >

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RE: Engine for SAE heavy lift Competition - 8/10/2008 1:38 AM   
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Status: offline 		That is open class.... a few folks are flying the lightweight jett 76L and the big block FIRE 76 engines for that event. Ive not seen anyone using gearing yet.

In the past there have been other classes with more limited aircraft and engine rules... likely remains the case. Ive not looked into much this season.


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