The Great Ongoing General Aviation Thread

To be clear, the Camel had a rotary (you say rotary at one point and radial at another), but yeah, nothing like a Wankel rotary. It’s probably most correct to refer to the Camel’s engine as a radial rotary.

Yeah, I meant rotary. Efiting error.

What’s this on the wingtip of this U.S. Navy airplane?:

From here: Boeing E-6 Mercury - Wikipedia

The pointy forward facing probe-like things on the wingtips are almost certainly HF radio antennas. See also the top of the tail.

The original 707 airliners configured for international operations had the same antenna on the tail. It was for the HF long range radios. See Google Pix for many period examples. You’ll also notice some 707s don’t have the antenna. Those were configured for over-land use only.

The cigar-shaped tank-like things on the E-6 wingtips are almost certainly a combination of radio transmit/receive electronics and other antennas.

You didn’t ask, but if you look at the ass end tip of the fuselage there’s a little cone shaped thing you don’t find on other similar airplanes. That is a weight and drogue on the end of a long wire antenna stored on a reel in the tailcone. For some transmissions they enter a continuous turn while reeling out about a mile(!) of wire. Eventually most of the wire settles into a more or less vertical orientation hanging in the center of the turn circle. Once stable, that can be used to transmit messages via VLF to submarines.

My dad used that technique when one of two water skiers fell. Dad would start orbiting the downed skier, such that the handle on the rope was within his grasp. The other skier would lay out to the perimeter of the circle so that he had enough speed to remain on his ski. When the downed skier grabbed the handle and signalled, dad would straighten the course and the downed skier would be back on his ski.

Now I wonder if anyone has ever used a Wankel rotary engine in a a plane. IIRC their main advantages are small size and light weight compared to a traditional piston engine, which seems like it would make them ideal for aviation use.

Interesting! I had long noted that funny thing sticking out of the tail on the 707, and assumed they all had them (it’s clear from the pics that many did not). I had also assumed that it had some subtle aerodynamic purpose. Do you know why the DC-8 never had such an antenna?


But AFAIK (and as I remember from having seen them in quantity and ridden them occasionally when they were in mainline US service and I was young) DC-8s in operational service did not have the cool wingtip probes @Magiver cites. Clearly the first flight of the DC8 prototype did. But I’m going to bet that was test instrumentation. Here’s a Google image search in which we see lots of them painted in the colors of transoceanic airlines but all without wingtip probes / antennas.

Overwater DC8s certainly had HF radios. Heck, brand new 787s and A350s have them. Most likely overland-only DC8s did not have HF radios. So same as 707s in that regard.

On more modern airplanes the HF antenna is inside the vertical tail and is scarcely visible as a small dielectric patch. In the final livery it may or may not be painted so as to be invisible.

In this pic from Google you see a not-yet painted brand new 737 MAX. The leading edge of the vertical tail is in that weird slightly iridescent green primer color. Within that leading edge section of green from about 25% of the way up the tail to 50% is a gray section that obscures most of the green. That gray is the HF antenna.

Here’s another Google pic that shows a fully painted tail on an in-service 737 NG. At about 25% of the way up the leading edge you’ll see a small dark gray area just above the crossbars of the A’s of the company logo. That little gray area is the exposed part of the dielectric of the antenna. The rest of the antenna runs up the leading edge from there under the paint.

So why did the 707 have that cool probe and others not? Beats the heck outta me. Given how cool it looked and that nobody else did it, I suspect that was marketing or some unsung enginerd’s idea of Rule of Cool.

Or they had some real EMI problems and settled for that as the least bad way to solve them. HF radio is kinda flaky in airplanes; you’d like to have a reflective ground plane a few hundred feet in diameter below the antenna. That’s not gonna happen, so the RF wizards have to perform their magic incantations some other way.

the early days of HF radios were at the cutting edge of technology. the antenna was a shinny stick attached to the business end of the technology.

Similarly, the original navigation systems in DC-8’s were expensive and lacking in accuracy in the best of circumstances. when GPS became available pilots would bring their hand-held units into the cockpit In what I would describe as an aviation form of Rogaine. They’d still have to program the system in the plane but in reality it was the handheld that got them to their destination.

Thanks for the explanation!

the more I look at the liquid piston rotary engine the more I hope it goes into production. If it does what it claims then a twin rotor motorcycle would be really something. Air cooled at a fraction of the weight of engines on the market today. And it would be great in a twin engine aircraft with both engines inline.

The seals are in the block and not the rotor. Imagine seal ports that you could unscrew and swap the seals out while it’s mounted in the plane. you could have 500 hr TBO’s and nobody would care. It would be like changing spark plugs.

Talented guy: