Thorp Air Command - T18.net

Is anyone flying a Thorp without a prop extension? Yes it would change the looks and the cowling but it seems like an obvious way to cut weight if aiming for the lightest possible build.

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

Why stop there?.... Why not eliminate the engine? And/or the wings?

Generally, Matt, if it's in the plans, it should be there.

The shape of the airplane came out of Mr. T's exhaustive aerodynamic studies. A shorter nose would change that. It would also change the W&B and the way the cowls fit. Do you really want to make fundamental design changes to a great airplane?

BTW - I have a prop extension for you when the time comes. (10 to 27 years?)

DW

Wow...sarcasm and actively discouraging a potential new builder all in the same post.

I absolutely respect the expertise of John Thorp and yes, I realize that removing the prop extension would require other changes to the aircraft.

Similarly, those who added a full cowling, canopy, 200+ hp, and a constant-speed prop to Thorp's original simple fun machine with exposed cylinders, open cockpit, 125 hp, and a fixed-pitch prop also had to make quite a few changes.

That's why it's called experimental, amateur-built aviation.

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

I just wonder if removing the prop extension to save weight, given multiple changes it may require would result in much net weight savings. And the goal of removing the weight is to increase performance. And the aerodnamic changes may actually REDUCE performace. Which negates the entire primary goal.

Typically any changes you make have a ripple effect of other changes and each change typically adds weight. Not to mention engineering time and trial and error efforts. So the net result may be a tremendous amount of work and little if any weight reduction or gain in performance.

I think sticking to easy to maintain O-320, and straight T-18 plans, no paint or even prime with minimal electrical instementation and little if any interior "finish" would result in the lightest and most reliable final product. I think you may in some area's be able to use thinner skin (0.25 instead of 0.32) on the fuselage sides that can save some weight over what most people are using. But you will have to look into that and that may only be OK if you use no larger than O-290.

One of the most overlooked weight savings is that of the pilot. You can spend thousand upon thousands of dollars and hudreds of hours to save 10 lbs. Or you could go on a diet as the pilot and save the same 10 lbs. The plane would perform the same and most likely the pilot will be more healthy. So it is a win-win. At least I know I could, and frankly should lose 10 lbs! And by the looks of what I see in the population, I'm not the only one.

All true, and I appreciate the thoughtful response. I hear you on the pilot weight reduction mod and on an overall KISS approach while sticking as closely as possible to the proven plans. On the potential performance gains or costs, that's certainly a valid point, but speed is not the only measure of performance. A lighter, lower powered, short-nose T-18 might make gains in climb or efficiency that would make up for the loss in top speed. Or it might not. That's what makes it fun to explore the options.

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

Not that I encourage anyone to disregard plans, but you may be interested in knowing that I have measured the top cowl on many Thorp's and found them from 31 to 36 inches long.
Cubes

A Thorp prop extension that I have in my garage has a weight of 4.2#, not a lot of weight loss for all the trouble to redesign the cowl. Plus not to mention without a prop extension the front of the cowl will need to be flatter to cover the fly wheel with a resulting increase in drag. I don't see much point in removing the prop extension myself, too many negatives, not enough positives. My $0.02.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

That occurred to me, but I wonder if airplanes without an electrical system can dispense with the flywheel? An O-200 doesn't have one there. I imagine you'd need an aluminum adapter plate to have the correct prop bolt pattern. The cowl would still be rather pigeon breasted, to clear the oil sump, etc. below the cylinders. The other choice would be to keep a spinner the size of the ring gear and shape the cowl around that, thick along the centerline but pinched down over the cylinders. Either way, be ready to spend quality time with sandbags forming the custom aluminum cowl.

Wood prop (instead of metal) , PC-680 battery (instead of a standard lead acid) , removing heavy vacuum powered instruments (replacing them with EFIS type instruments) , light weight SKY TEC starter are just a few of the weight saving items you can use instead of spending a LOT of time and effort redesigning the airframe to fit a few items (removing prop extension as an example) . BOOM !!

RB

All good points, thanks. As I said to DW offline, I certainly understand that any changes can have significant effects and should not be taken lightly. I like to explore the options, but in actual practice I would likely stick to the plans pretty closely. Still, it's worth keeping an open mind. If Thorp himself hadn't been open to modifying his original concept, would most of us even be interested in a T-18? Cheers, Matthew

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)

Cluttonfred,

What type of performance are you looking for exactly? What type of mission do you envision this aircraft to serve most of the time?

I understand about keeping things light etc. But as you point out the biggest gain in performance of being light is climb rate and perhaps take off and landing roll.

What type of airport are you going to be flying out of that makes the climbe rate and takeoff/landing roll so important?

The Thorp is an awesome airplane for sure. But there are a lot of awesome aircraft out there... Depending upon what the specific mission you have in mind. A thorp for example would not be my first choice for a sea plane. I'm wondering if what you are looking for in the type of flying that you plan to do if the Thorp is the best choice for that mission. Some of the things you suggest are great ideas but something like a Wittman Buttercup may be more in line with what your flight mission is. You still get respectable speed with the smaller engines and get shorter takeoff and landing performance even with the smaller motors. Granted it is not an all metal aircraft. But maybe a Zenair 750 Cruzer would fit the bill.

Your icon and your signature seems to all reflect a totally different type of flying mission than what niche the modern Thorp fills.

I think some of the biggest weight savings are; NOT painting, absolute minimalist interior & radio, with electronic instruments, LW starter and battery, wood prop. Keep the rest per plan. I personally would not skimp too much on engine (O-320) or on brakes. Sure the O290 could save a few pounds. But I'm not sure they are any less expensive and maybe even moer expensive for maintenance and parts. Every A&P will have ample ability to get O320 parts and you also gain several HP so I think the weight savings per the HP gain is offset as far as performance goes.

If the mission you see for your thorp, is to almost always fly from your home airport. You could eliminate a larger battery and just have a jump start battery. Some Aerobatic folks on their Pitts etc will remove the alternator. They can get multiple starts out of the battery and have a simple system to hook up a trickle charger after each flight from home.

I had an Aeronca Chief with no electical system and had to hand prop it. While hand propping can be done safely and has a nestalgia, it is a pain in the butt when away from home. Especially by yourself. Not too many people know how to safely hand prop a plane anymore. And tying it down etc to do it safely can be done, but it is a logistical pain in the butt.

The Thorp is a fast cross country airplane for the most part. As such I do not think it very practical to not have a battery and starter. Of course electric solid state instruments also need electrons and thus a battery of some sort.

Other weigh saving ideas may be the use of carbon fiber for the wing and tail tips and even the cowling. I do not know how much weight that would save or how much extra it would cost. Eliminating any provision for night flight would also save some weight. But with LED lights and the requirement to be on the ground by sunset and cannot fly until sunrise without nav lights is restrictive in the summer time. As it gets light visually and stays light visually for quite a long time the sun cracks the horizon. Again I know as my Aeronca had no nav lights and there were some awesome summer days for flying that time was not available legally to fly.

Also to save weight you could go down to say a 12 gallon fuel tank. this limits the amount of weight at full fuel and a smaller tank saves weight. But it is just as easy and only incremental weight savings than simply building the full size tank and leaving it with only 12 gallons in it. Not to mention it limits the capability of the aircraft with a 12 gallon tank for example.

I do not want to bust your chops here. I'm seriously thinking that you want to make sure that the aircraft you intend to pour countless hours and blood, sweat and tears, will provide the resulting aircraft that matches your mission.

Trust me. had been struggling with the mission idea for the last couple of years. The Aeronca was an absolute blast. But my wife didn't like flying in it because she could feel every bump and we couldn't travel in it. So the Aeronca to her was nothing but a very expensive motorcycle to her. One she didn't want to ride or travel in.

Now when the Thorp is done, we can get to the parents home town we grew up in in under 3 hours versus a 6 hour drive. And we can get to FL in a single not very long day (depending on weather of course) from WI. NOW she will see the value in the magic carpet. Now the plane becomes a tool, not soley an expensive play toy for her husband.

Mission accomplished!

No offense taken, my interests have long been in the low and slow range of the homebuilt world but now I am considering tackling something with more speed and range than the puddle jumpers that are my usual focus. I am serving overseas so my plans are quite changeable but the thought is to settle down in a couple of years either back in the USA or in Europe. If the USA, the Thorp would allow some real cross-country exploration and that appeals to me. If Europe, then I'll probably stick with microlights. For the Thorp, I would want to keel it light and simple but I would want a starter and electrical and night VFR capability for simple practicality. Thanks for your comments and I look forward to seeing your Thorp fly!

_________________
Matthew Long, Editor
cluttonfred.info
A site for builders, owners and fans of Eric Clutton's FRED

« Voici ce que j'ai fait...vous pouvez en faire autant! »
"This is what I have done...you can do the same!"
--Henri Mignet (1893-1965)