Thorp Air Command - T18.net

Hey Bruce,

We still love our 0-290GPU Thorp. It is a very fun airplane. We are know challenged to do more for old N6CM built in 1978 with no modifications since original build. My Brother, Partner Chris has some things we want to try to coax more speed out of her. Charlie Mike has 1,100 hours on her and we are thinking of an engine tear down and inspection and repair replacement of all out of tolerance parts. And then maybe some of engine mods discussed in the old newsletters.


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Brent Schultz

N327SB
N6CM

KAJO

Total newbie here but thought I'd throw in my 1 cent of thoughts.

1) first I would think you would want to do a BEFORE weight and balance. Aircraft are notorious to gain weight with age. (Much like its owners!- Opps, I resembal that remark!) Knowing the weight BEFORE you do anything I think is an important benchmark so that AFTER you do all your improvements, you will know what is what.

2) Engine mods are great so you may want to do some to hopefully get more power from it and hopefully also make it more reliable. I would caution you to never compromise reliability for max power. There is a balance point in there somewhere and everyone has to make their own decision where to stop the quest for power at the risk of reduced reliability/longevity.

3) I would think one possible large improvement in performance could be achieved by weight reduction. It sounds as if your plane has aged well. But one thing that could possibly save you weight would be in light weight starter. Another place that could save considerable weight would be in the panel itself. Transitioning from steam guages to light weight electronic displays may save several pounds (not to mention your wallet will be much lighter too!)

4) I think much of an aircraft drag comes from cooling drag. So possibly using a dedicated plenum for cooling air and reduced air inlets or other cooling and baffle work may result in measurable performance gains.

5) propeller- This is in my opinion all sort of black magic. But there is no denying that props have a huge effect on performance. The "magic" combination of pitch and length for a particular speed and even the material the prop is made from can all dramatically affect the performance. So I don't know the answer but if you are looking to optimize performance, I would think any changes you make, may end up affecting the prop and thus a change in yoour prop may be necessary or desired.

Like I said just my thoughts. Remember they are likely worth exactly what you paid for them!!

I believe John did the aviation community a great justice designing the thorp around the 290. there are faster rigs out there, there are some slower. The 290 offers a Big Bang for you buck and they are reliable. I have flown 2 t-18s that are 290 powered, can't say enough good about them. They will sip gas, car gas if you like and Cruz at about 140 knots at altitude. John hit the marker when he did the design work I think we will all agree. Fast is good, and faster yet is even better for some, but the 290 enabled a whole lot of folks to fly the Tiger. It would be good if the 290 was still plenty full, and at the low price they used to sell for, it is a real good fit for the Thorp airframe and maybe a whole lot more of the working class would have the opportunity that John offered many many years ago. I have always like the 290 powered Thorp, they are underestimated so to speak, and after all, they are still tigers just like the rest of em.....If John didn't create the perfect airplane, he was so close he made the rest of the designers cry, my opinion, within the parameters with which the Thorp was designed to be used and the purpose it was intended to be used, name one that does it better, and we already know there is not one better lookin that's just common knowledge........Dan

God Bless all those 0-290 Thorps still in the air. Please keep them goin. We love ours and agree it is an amazing airplane. John Thorp was a brillant designer. N6CM amazes me how fun it is to fly each time we take it out. And best yet its economical.

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Brent Schultz

N327SB
N6CM (0-290GPU)

KAJO

Good Morning to all. I to agree, I'm fortunate to be a proud owner of a o290 Thorp, I can't say enough about not only the fun factor but also the performance and economy, 7gph with 172 TAS at 2500 RPM can't complain, and having a Bad Ass looking plane to boot, not to mention all of the other Bad Ass Thorps i have seen, I've said it once and I'll say it again, "RVr's don't have a Damn thing on our Thorps," nothing personal RV guy's. ...Ira
Happy flying. C-ya all at Kvis west coast gathering.
N25801

Sorry about the Double Post, My Bad!!!

posted twice no troubles, some things sound so good it needs to be said more than once....oorah!! Dan

I too enjoy an O-290G in my T-18.
However, when (in about 1000 hours!) the engine requires an overhaul, I think I would review the newsletters and check out the air boaters about boring the case to accept O-320 cylinders. My engine already has the O-320 crankshaft, sump, carb & accessory case.
O-290 Cylinders assemblies are not available new, and those that can be found are expensive. I intend to try the upgrade to save a few $ while picking up 25-35 HP. I have an O-290G core engine for experiments, so I can fit a cylinder and do all the learning before I tear down my running T-18.
Part of my reasoning to stick with the O-290 is that John Thorp's engine mount for the O-290G is just fine, so changing it to accommodate a conical or dynafocal engine would add work, expense and down time.
I would end up with a solid tappet cam O-320E2 equivalent, (lesser type front main bearing) so a wood prop would be best.
I have upgraded one mag to a P-mag, and I have a ROTEC throttle body injector on hand to replace the Marvel carb. You could say it's a work in progress.

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Scott Emery
EAA Chapter 326
T-18 N18TE

That's why it's called an experimental, Scott. I love to hear about guys making improvements.
Cubes