Bob Jones Memorial Air Show urges people to buy tickets
People are being urged to pay to enter a Powys air show instead of watching the displays from the surrounding hillsides.
The Bob Jones Memorial Air Show in Welshpool is being held on Sunday and attracts about 5,000 visitors a year.
The organisers said they might increase the £5 entrance fee next year to compensate for those refusing to pay.
The show was renamed last year in memory of the founder of Welshpool airport who died in an air crash.
Bob Jones was killed alongside Steven Carr from Denbighshire when their small plane crashed on Long Mountain near Welshpool in January 2012.
Years earlier Mr Jones, who was also a farmer, had turned his fields into a fully functioning airport with a runway and hangars.
This year's air show at Welshpool airport features a former RAF Vulcan bomber, the Battle of Britain Memorial Flight and an RAF Typhoon fighter jet.
But one of the organisers, Dr John Morgan, said people refusing to pay to enter the show were having an impact on its cash flow.
"It's a minority of people who watch from the hillsides," he said.
"They don't make a significant drain on the show, but they are draining it.
"It does start to have a real impact on the show.
"We need as much money as we can to help build the show."
"We can't stop people [watching from the hillsides] but perhaps we can make then understand that they need to come to the show and pay."
Dr Morgan said the entry fee was £5 for adults, £3 for children, while a family ticket was £15.
Last year staff from the show asked for contributions from those watching on the hills overlooking the event.
"People were not for giving much at all and it was noticeable how much copper was in the buckets we'd used and there were hardly any notes," Dr Morgan added.
"The impact of all this means that we might have to consider increasing the prices next year."